Abstract
CD4+ cytotoxic T lymphocytes (CD4-CTLs) have been reported to play a protective role in several viral infections. However, little is known in humans about the biology of CD4-CTL generation, their functional properties, and heterogeneity, especially in relation to other well-described CD4+ memory T cell subsets. We performed single-cell RNA sequencing in more than 9000 cells to unravel CD4-CTL heterogeneity, transcriptional profile, and clonality in humans. Single-cell differential gene expression analysis revealed a spectrum of known transcripts, including several linked to cytotoxic and costimulatory function that are expressed at higher levels in the TEMRA (effector memory T cells expressing CD45RA) subset, which is highly enriched for CD4-CTLs, compared with CD4+ T cells in the central memory (TCM) and effector memory (TEM) subsets. Simultaneous T cell antigen receptor (TCR) analysis in single cells and bulk subsets revealed that CD4-TEMRA cells show marked clonal expansion compared with TCM and TEM cells and that most of CD4-TEMRA were dengue virus (DENV)–specific in donors with previous DENV infection. The profile of CD4-TEMRA was highly heterogeneous across donors, with four distinct clusters identified by the single-cell analysis. We identified distinct clusters of CD4-CTL effector and precursor cells in the TEMRA subset; the precursor cells shared TCR clonotypes with CD4-CTL effectors and were distinguished by high expression of the interleukin-7 receptor. Our identification of a CD4-CTL precursor population may allow further investigation of how CD4-CTLs arise in humans and, thus, could provide insights into the mechanisms that may be used to generate durable and effective CD4-CTL immunity.
INTRODUCTION
After exposure to pathogens, naive CD4+ T helper (TH) lymphocytes differentiate into memory and effector TH cell subsets: tissue-resident memory cells, which are mainly retained in the tissues, and central memory (TCM) and effector memory (TEM) cells, which recirculate between the blood and lymphoid organs or tissues, respectively (1, 2). In addition, TH cell subsets have been classified on the basis of their cytokine profile and functional properties into TH1, TH2, TH17, TH* (TH1/TH17), regulatory T cell, and follicular helper (TFH) T cell subsets (3, 4). Although T lymphocytes with cytotoxic function (CTLs) are predominantly restricted to conventional major histocompatibility complex (MHC) class I–restricted CD8+ T lymphocytes, the existence of MHC class II–restricted TH cells with cytotoxic potential (CD4-CTLs) in humans, nonhuman primates, and mice has been reported for many decades (5, 6). However, compared with the other TH subsets, the molecular and epigenetic mechanisms that drive the differentiation, maintenance, and function of human CD4-CTLs are poorly understood, mainly because of the lack of precise definition of the nature of this subset in humans.
CD4-CTLs were initially reported in humans with chronic viral infections such as human cytomegalovirus (hCMV), HIV, dengue virus (DENV), and hepatitis C virus (5, 7–15). CD4-CTLs have also been detected in mouse lungs as early as 1 week after acute influenza viral infection (16, 17). The magnitude of the CD4-CTL response has been associated with better clinical outcomes in both acute and chronic viral infections, implying that CD4-CTLs are an important component of the protective immune responses to viral infections (6). Furthermore, expansion of CD4-CTLs has been observed in donors carrying human leukocyte antigen (HLA) alleles associated with protection from severe dengue disease (7). Thus, eliciting a strong CD4-CTL response is considered an important goal of vaccination against certain viral infections (16, 18–20). The highly effective yellow fever vaccine has been shown to elicit a strong CD4-CTL response, which is required for protection against fatal infection in mouse models (18). CD4-CTLs have also been linked to protective antitumor immune responses, especially in virally induced tumors (18).
Given the importance of CD4-CTLs in acquired cellular immunity, we present here the single-cell transcriptomic and T cell antigen receptor (TCR) analysis of circulating human CD4-CTLs. CD4-CTLs were highly enriched in the effector memory T cells expressing CD45RA (CD4-TEMRA) subset and displayed notable intra- and interdonor heterogeneity. We show that the magnitude of CD4-TEMRA response is linked to the degree of clonal expansion and cytotoxicity profile of CD4-CTLs. Besides a comprehensive definition of the transcriptional program of conventional CD4-CTL effectors, we identified precursor cells sharing TCR clonotypes with CD4-CTL effectors that were distinguished by higher expression of the interleukin-7 receptor (IL-7R).
RESULTS
Cytotoxicity-related genes are enriched in the CD4-TEMRA subset
Human CD4-CTLs are enriched in the CD4-TEMRA subset (defined as CD3+CD4+CD45RA+CCR7− cells) (Fig. 1A), most notably in donors with previous DENV and CMV infection (5, 7–10). To capture the extent of cellular heterogeneity among human CD4-CTLs, we performed single-cell RNA sequencing (RNA-seq) in more than 9000 cells isolated ex vivo from the TEMRA subset and, as a control, in TH subsets that contain relatively fewer CD4-CTLs, such as TEM (CD3+CD4+CD45RA−CCR7− cells) and TCM (CD3+CD4+CD45RA−CCR7+ cells) subsets (Fig. 1A and table S1) (21). Using complementary methods of single-cell differential gene expression analysis [SCDE and MAST analysis, see Supplementary Materials and Methods and in (22, 23)], we compared the full-length transcriptome of CD4+ T lymphocytes present in TEMRA, TEM, and TCM subsets from three donors with previous DENV infection, carrying the HLA allele (DRB1*0401) previously reported to be protective against severe dengue disease (Fig. 1B and table S1) (7, 24).
We found 111 “TEMRA-enriched” transcripts with significantly higher mean expression in single cells from the TEMRA subset compared with the TEM and TCM subsets (see Supplementary Materials and Methods, Fig. 1B, and table S2). These included several transcripts linked to the cytotoxic function of CD8+ T lymphocytes and natural killer (NK) cells such as GZMB, PRF1, GZMH, GNLY, CCL4, CTSW, FCRL6, SPON2, CX3CR1, S1PR5, NKG7, and CD244 (Fig. 1, B and C) (6, 25); we confirmed the expression of some of these transcripts (CX3CR1, GPR56, CD244, CD314, KLRG1, GZMB, and PRF1) at the protein level (Fig. 1D). Gene set enrichment analysis (GSEA) (26) and ingenuity pathway analysis (IPA) of TEMRA-enriched transcripts also revealed significant overrepresentation of cytotoxicity signature genes in the TEMRA subset (Fig. 1, E and F). Transcripts encoding transcription factors (TFs) related to CTL function such as ZNF683 (Hobit), and Eomes and T-bet (encoded by TBX21) were also expressed at higher levels in single cells from the TEMRA subset (Fig. 1, B and C). ZNF683 has recently been shown to identify human CD4-CTLs (24), and Eomes and T-bet appear to be important in the development of CD4-CTLs (27, 28). These results confirm that human CD4-CTLs are highly enriched in the TEMRA subset. Coexpression analysis of TEMRA-enriched transcripts also revealed a number of genes (PFN1, PFN1P1, EFHD2, VCL, DIP2A, SYNE1, and PLEK) (29–32) whose expression was highly correlated with cytotoxicity signature genes, suggesting that the products of these genes may also play important roles in the development or function of CD4-CTLs (Fig. 1G).
CD4-CTLs show marked clonal expansion
Given that memory CD4-CTLs are mainly generated after exposure to certain viruses such as DENV or CMV (5, 7–10), we expected to see a more restricted TCR repertoire, that is, greater clonal expansion in the CD4-TEMRA subset compared with CD4+ T lymphocytes in the TEM or TCM subsets, which harbor a more common memory pool. We performed parallel analysis of the TCR repertoire in single cells by decoding the full-length transcriptome profiles generated by the Smart-seq2 assay (33, 34). Using the TraCeR software (35), we reconstructed the TCRβ chains in 41 to 89% of single cells, the TCRα chain in 31 to 81%, and both chains in 22 to 70% of cells across all memory subsets (table S3). As expected, a greater clonal expansion was observed in the TEMRA subset compared with other subsets, as shown by highly interconnected clonotype network graphs for single cells from donor #6 (Fig. 2A). Furthermore, the analysis of single cells that shared TCRα or TCRβ chain clonotypes showed that more than 50% of cells in the TEMRA subset were clonally expanded (Fig. 2B, left and middle). To address the rare possibility of independent cells sharing one of the TCR chains, we also analyzed single cells that shared both TCRα and TCRβ chain clonotypes and found that ~46% of cells in the TEMRA subset (CD4-CTL–enriched) were clonally expanded compared with only ~5% and none of the cells in TEM and TCM subsets, respectively (Fig. 2B, right, and table S4). Together, these results suggested a highly restricted TCR repertoire in the TEMRA subset (Fig. 2, A and B). The clonally expanded cells had a higher mean expression of cytotoxic signature genes (TEMRA-enriched gene set) (Fig. 2, C and D), suggestive of greater effector potential (6, 25, 36).
To probe the pathogen specificity of clonally expanded CD4-TEMRA cells (CD4-CTL–enriched), we first determined the TCR clonotype of single cells in the CD4-TEMRA subset that responded ex vivo to a pool of DENV-specific peptides (7, 37) from four donors with previous DENV infection (Fig. 2, E and F, fig. S1, and table S4). Next, we asked what fraction of these DENV-specific TCR clonotypes was present in the general pool of cells present in the TEMRA subset from the same donor. On an average, 64% (n = 4) of the clonally expanded cells in the general TEMRA population carried the DENV-specific TCR clonotypes, and in all donors, one or both of the top two clonally expanded clonotypes in the TEMRA population were always DENV-specific (Fig. 2, E and F, fig. S1, and table S4), which suggested that most of the clonally expanded cells in the TEMRA population in these individuals were specific for DENV.
CD4-CTLs (CD4-TEMRA cells) are heterogeneous across donors
We next asked whether the clonality and transcriptome of CD4-CTLs differed between donors with and without previous DENV infection or among donors across different geographical locations [Sri Lanka (Asia) and the Americas (Nicaragua and San Diego, California)]. We observed a wide range in the proportion (0 to 88%; median, 44%) of clonally expanded cells across the 12 donors with no major differences in their proportion when classifying donors based on previous DENV infection status or geographical location [Sri Lanka (Asia) versus the Americas; table S1]. When we compared the percentage of clonally expanded cells between donors with higher versus lower proportion of CD4+ T lymphocytes in the TEMRA subset (classified as TEMRAhigh or TEMRAlow donors), we observed greater clonal expansion in TEMRAhigh donors (Fig. 3A). Consistent with this finding, there was a positive correlation between the proportion of CD4+ T lymphocytes in the TEMRA subset and the percentage of clonally expanded cells, suggesting that donors with a larger TEMRA pool have a greater degree of clonal expansion (Fig. 3B).
In most donors, we observed sharing of a single unique TCRα and TCRβ chain clonotype in a large fraction of CD4-TEMRA cells, as exampled in donor #4 [58% (11 of 19)], donor #1 [50% (21 of 42)], donor #2 [41% (24 of 58)], donor #5 [37% (11 of 30)], donor #8 [22% (6 of 27)], donor #3 [16% (4 of 25)], and donor #6 [10% (7 of 67)] of cells (Fig. 3C). Considering some of these donors were previously infected with DENV (DENV+ donors) raised the hypothesis that selection and expansion of such TCR clonotypes may be linked to the DENV infection. Even in donors without previous DENV infection (DENV− donors), we observed very high levels of clonal expansion (Fig. 3C), suggesting that other infections—perhaps CMV, which is common in the general population—may also contribute to the preferential expansion of some CD4-CTL clones.
Besides the heterogeneity in clonality, we also observed marked variability in the expression of TEMRA-enriched transcripts in CD4-TEMRA cells across the study donors (Fig. 3, D and E). For several cytotoxicity-related transcripts, the expression pattern was highly variable across the 12 donors (Fig. 3, D and E). CD4-TEMRA cells from donors with a larger preexisting TEMRA pool and greater clonal expansion displayed more cytotoxic features (Fig. 3D). In other words, cytotoxicity-related transcripts were expressed in a greater fraction of single cells or at higher mean levels; other TEMRA-enriched transcripts such as ZNF683, PRSS23, FCRL6, and IFIT2 also showed a similar pattern (Fig. 3, D and E). We confirmed at the protein level that greater proportion of CD4-TEMRA cells expressed cytotoxicity-related molecules CD244, GPR56, GZMB, and PRF1 in donors with larger preexisting TEMRA pool (Fig. 3F). Therefore, our combined transcriptomic, protein, and TCR analysis suggests that the CD4-TEMRA subset exhibits quantitative and qualitative differences across different donors irrespective of their DENV infection status or geographical location and, in many instances, related to the CD4-CTL function.
CD4-CTL effector cells revealed by single-cell analysis
We next asked whether the heterogeneity observed in the single-cell transcriptomes of CD4-TEMRA was due to the presence of multiple distinct subsets. Four clusters were revealed by unbiased clustering of CD4-TEMRA cells from the 12 study donors (917 cells) using the Seurat software (Fig. 4A) (38); other methods of clustering also revealed a similar pattern, and no major changes were introduced by technical and batch effects (see figs. S2 and S3, table S1, and Supplementary Materials and Methods) (39). The proportion of cells in each cluster varied greatly among donors, with marked differences observed between donors from Sri Lanka and the Americas (Fig. 4B, left), suggesting that the nature and type of infections may shape the molecular profiles of CD4-CTLs. Clonal expansion was observed more frequently in cells from clusters 1 and 2 (Fig. 4B, right, and table S4).
Single-cell differential gene expression analysis among the four clusters revealed notable differences in their molecular profiles (Fig. 4C, fig. S4, A to D, and table S5). IPA and differential expression analysis of the transcripts enriched in clusters 1 and 2 compared with clusters 3 and 4 showed significant overrepresentation of genes encoding products related to cytotoxicity, such as GZMB, GZMH, PRF1, GNLY, NKG7, ZNF683, and FGFBP2 (figs. S4, C and D, and S5 and table S5). Among these two clusters (1, 2), cluster 2 shows further enrichment for the cytotoxicity-related genes (figs. S4A and S5A), which suggested that cells in cluster 2 had a higher cytotoxic potential. Pairwise comparison of the clusters (fig. S4D and table S5) showed differences in the enrichment of cytotoxicity-related genes among clusters 1 and 2; although several of them were expressed by both the clusters (GZMB, GZMH, GNLY, NKG7, FASLG, and CASP10), many were expressed in a cluster-specific manner (Fig. 4, D and E, fig. S4D, and table S5). On the basis of the differential expression pattern of cytotoxicity-related transcripts in cluster 1 (FADD, IFNG, TNF, IFIT2, LMNA, CD69, FOS, JUN, DUSP1, and DUSP2) and cluster 2 (FGFBP2, SPON2, CX3CR1, GPR56, and PRF1), we hypothesize that their cytotoxic function is preferentially mediated by the FAS/death receptor and perforin pathways, respectively, which requires further functional verification (Fig. 4, D and E, fig. S4, A and D, and table S5).
Cells in clusters 1 and 2 expressed higher levels of KLRG1 (40–42) and CX3CR1 (7, 43) transcripts, which are linked to effector status of memory cells, and lower levels of CD27 and CD28 transcripts, which encode costimulation molecules (Figs. 4E and 5, A and B) (44, 45). These results indicate that cells in clusters 1 and 2 have a terminal effector state and hence are CD4-CTL effectors with high cytotoxic potential. Genes linked to cell survival and CD4-CTL function such as PRSS23, SPON2, TCF7 (encodes for TCF1), CRTAM, and ZNF683 (encodes for Hobit) (24, 46–51) were also highly expressed in single cells from clusters 1 and 2 (Fig. 4E). The role of ZNF683 (Hobit) (24, 46, 49) and other transcripts (PRSS23, SPON2, and TCF7) (47, 48) in the survival and long-term persistence of these high cytotoxic terminal effector cells deserves further investigation (45).
The TEMRA subset includes CD4-CTL precursor cells
We next examined the transcriptional profiles of cells in clusters 3 and 4 to evaluate their clonal origin and functional relationship to the other cell populations. Compared with cells in clusters 1 and 2 (referred as CD4-CTL effectors), those in clusters 3 and 4 expressed lower levels of KLRG1 transcripts and higher levels of transcripts encoding IL-7R (IL7R or CD127), which is known to play an important role in mediating the long-term homeostatic survival of naive and memory T lymphocytes (Fig. 5A) (52–55). The mean expression of IL7R transcripts in cluster 4 cells was even higher than that in TCM cells (Fig. 5, A and B). The opposing expression pattern of KLRG1 and IL7R transcripts in clusters 3 and 4 is similar to that observed in memory precursor effector cells (IL-7Rhigh and KLRG1−) described in murine models of resolving acute infections (52, 56). Transcripts encoding CD27 and CD28 costimulation molecules, lymphotoxin β (LTB), and JUNB TF were also expressed at higher levels in clusters 3 and 4, similar to the pattern observed in TCM cells (Fig. 5, B and C). However, cells in both clusters 3 and 4 were still markedly different from TCM cells in that they expressed several transcripts that are specifically enriched in TEMRA cells (KLRG1, TBX21, S1PR5, FGFBP2, CCL4, PRF1, GZMH, GNLY, NKG7, ZEB2, and GPR56), albeit at lower levels compared with CD4-CTL effectors (cells in clusters 1 and 2) (Figs. 4E and 5C). On the basis of these results, we hypothesize that cells in clusters 3 and 4 likely represent memory precursor cells for the cells present in cluster 1 and 2 that have a terminal CD4-CTL effector phenotype.
Given that surface expression of IL-7R (CD127) can be readily determined by flow cytometry, we looked for the presence of potential CD4-CTL precursors within the CD4-TEMRA subset from an independent cohort of healthy donors. For these studies, we capitalized on the La Jolla Institute cohort of 89 healthy donors, of which 15 donors had longitudinal samples (two time points) (104 samples in total). As expected, there was a large variation (0.12 to 15.2%) in the proportion of the CD4-TEMRA subset across the study donors (Fig. 5D). On the basis of the surface expression pattern of IL-7R, cells in the CD4-TEMRA subset were classified into IL-7Rhigh and IL-7R− (Fig. 5E). The expression level of IL-7R on IL-7Rhigh TEMRA cells was similar to that observed in TCM and TN (naive T cell) CD4+ T lymphocytes (Fig. 5E and fig. S5B). These cells (IL-7Rhigh TEMRA cells) may represent the CD4-CTL precursors defined by our single-cell transcriptome analysis. In longitudinal samples obtained at 3- to 6-month intervals, the proportion of cells in the CD4-TEMRA subset was quite stable (Fig. 5F); however, in one donor, we noted a marked (>8-fold) expansion of the CD4-TEMRA subset; this expansion was mainly confined to the IL-7R− TEMRA cells (CD4-CTL effectors), and not the IL-7Rhigh TEMRA (CD4-CTL precursors), perhaps reflecting an expansion of effectors in response to an infection that occurred during the interval period (Fig. 5, F and G).
To further confirm that the IL-7Rhigh TEMRA subset (CD4-CTL precursors) shared the molecular profile of both TCM (long-term memory cells) and cytotoxic cells, we isolated IL-7Rhigh TEMRA and IL-7R− TEMRA (CD4-CTL effectors) along with TCM and TEM subsets and performed RNA-seq in two longitudinal samples from five donors (Fig. 5H). Consistent with our single-cell cluster analysis (Fig. 5C), the IL-7Rhigh TEMRA subset shared molecular features of both TCM (memory precursor cells) and cytotoxic cells (IL-7R− TEMRA, CD4-CTL effectors) that were stable over two longitudinal visits (Fig. 5H and table S6). The IL-7Rhigh TEMRA subset (CD4-CTL precursors) expressed both cytotoxicity-related molecules (GPR56 and CD244) and a co-stimulatory molecule (CD28, TCM-enriched) at the protein level (Fig. 5I). Together, these results show that cells in the IL-7Rhigh TEMRA subset have properties of memory precursor cells and cytotoxic cells.
CD4-CTL precursors share TCRs with CD4-CTL effectors
To verify our hypothesis, we analyzed the overlap in the TCR clonotypes of CD4-CTL effectors (clusters 1 and 2) with those from CD4-CTL precursors (clusters 3 and 4). In a total of 5 of 12 donors, TCR clonotypes were shared between CD4-CTL precursors and effectors (Figs. 2A and 6A, fig. S6A, and table S4). As examples, in donor #1, 23 of 80 TEMRA cells had the same TCRα chain clonotype (fig. S6A) as a single cell from precursor cluster (cluster 3); in donor #12, four TCRβ chain clonotypes were shared between CD4-CTL precursors and effectors (Fig. 6A, clones highlighted in dashed lines with the precursor cells indicated with red arrows). A similar pattern was observed in donors #3, #5, and #6 (Figs. 2A and 6A and table S4). To further support our inference, we constructed cell-state hierarchy maps using the Sincell software (39) for cells in the TCM, TEM, and TEMRA subsets and observed that CD4-CTL effectors clustered closest to the CD4-CTL precursors (Fig. 6B and fig. S6B). Together, these data lend support to the hypothesis that CD4-CTL effectors were mainly generated in vivo from distinct CD4-CTL precursor cells, although the possibility of arising from memory TEM or TCM cells cannot be excluded.
To support our hypothesis that CD4-CTL effectors are mainly derived from the precursor population, we performed a unique molecular identifier (UMI)–based TCR sequencing (TCR-seq) assays (57) in TCM, TEM, IL-7Rhigh TEMRA (CD4-CTL precursors), and IL-7R− TEMRA (CD4-CTL effectors) subsets from 14 donors (table S7). Consistent with single-cell TCR analysis (Fig. 2, A and B), the CD4-CTL precursor and effector cells in the TEMRA subset had highly restricted TCR repertoire, compared with cells in the TCM and TEM subsets, as shown by lower Shannon-Wiener diversity index (Fig. 6C) (58), and contained higher percentage of expanded clonotypes (Fig. 6, D, E and F, left, and fig. S7, left). A larger fraction of the clonotypes in the CD4-CTL precursor cells relative to TEM and TCM was composed of the expanded clonotypes (frequency, ≥3) present in the CD4-CTL effector cells (Fig. 6E, middle, and fig. S7, middle). Further, the most expanded clonotype in the CD4-CTL effector cells was observed more often and at higher frequency in CD4-CTL precursor cells relative to TEM and TCM (Fig. 6E, right graphs, and fig. S7, right graphs).
We also performed TCR-seq in CD4+ T cell memory subsets from five donors who provided longitudinal samples obtained at 3- to 6-month intervals to assess the kinetics of precursor-effector relation. To better assess the relationship between effectors and putative precursors for each donor, we determined the proportion of expanded CD4-CTL effectors clonotypes from second visit (V2) that were present in the different CD4+ T cell memory subsets at the first visit (V1) (table S8). In four of the five donors analyzed, a greater fraction of the TCR clonotypes detected in CD4-CTL effectors at V2 was shared with cells in the precursor population (IL-7Rhigh TEMRA subset) relative to the TEM or TCM subset at V1 (Fig. 6F, middle, fig. S7, and table S8). A total of 12 of the CD4-CTL effector clonotypes from V2 were only found in CD4-CTL precursors at V1 but not in the TEM, TCM, or CD4-CTL effectors (table S8). Together, the kinetic data from the longitudinal samples provided stronger evidence to support the precursor-effector relationship and suggested that the IL-7Rhigh TEMRA subset is the predominant precursor/progenitor for the CD4-CTL effector cells.
Variable number of CD4-CTL precursors across donors
The proportion of CD4-CTL precursors varied greatly among donors, ranging from 3 to 92% of cells in the TEMRA subset (fig. S8A). To determine whether additional CD4-CTL subsets exist and to definitively assess the presence of CD4-CTL precursors, we analyzed single-cell transcriptomes of 10 times as many cells (>6000 cells) from two donors using the high-throughput 10× genomics platform. The sensitivity of the 10× genomics platform, which uses beads to capture transcripts and also sequences only their 3′ ends (59), is twofold lower than the Smart-seq2 protocol used to study full-length transcriptomes of the same donors (fig. S8, B and C). In donor #2, where 24 of 87 cells (28%) (fig. S8A) were previously assessed as CD4-CTL precursors, unbiased clustering of more than 3000 single-cell transcriptomes revealed two dominant clusters of ~2000 and ~1000 cells each, implying that sequencing more cells does not necessarily reveal additional clusters (Fig. 7A, left). These two clusters differentially expressed transcripts characteristic of CD4-CTL effectors (GZMB and NKG7) and precursors (IL7R, JUNB, and LTB), respectively (Fig. 7B, left, and table S9). Even in donor #1, where only 3 of 87 cells (3.4%) (fig. S8A) were previously found to be CD4-CTL precursors by full-length transcriptome analysis, we observed a similar proportion of CD4-CTL precursors [116 of 3664 cells (3.2%)] when analyzing more cells by the 10× genomics platform (Fig. 7, A and B, right, and table S9). At the single-cell level, CD4-CTL precursors in the CD4-TEMRA subset were distinguished by the high expression levels of IL7R transcripts. The expression pattern of molecules in CD4-CTL precursor and effector cells was further confirmed by single-cell RNA-seq analysis of purified population of IL-7Rhigh and IL-7R− TEMRA cells (Fig. 7C and table S1).
DISCUSSION
CD4-CTLs have long been considered to be terminal effector cells derived from TEM cells after persistent or repeated (long-term) antigen stimulation in the context of certain viral infections, particularly CMV and DENV (7, 8, 14). Consistent with the notion, our single-cell transcriptome studies of the TEMRA subset did identify cells that have features of terminal CD4-CTL effector cells (KLRG1high and IL-7Rlow; clusters 1 and 2). However, we observed another population of cells in the TEMRA subset that displayed a molecular program (KLRG1low and IL-7Rhigh; clusters 3 and 4) indicative of memory precursor cells, intermixed with several features of CD4-CTLs (KLRG1, TBX21, S1PR5, FGFBP2, CCL4, PRF1, GZMH, GNLY, NKG7, ZEB2, and GPR56), albeit less prominently expressed than in the CD4-CTL effectors. Bulk and single-cell transcriptome analysis of the purified IL-7Rhigh and IL-7R− TEMRA subset further confirmed our observation from single-cell transcriptome analysis of total TEMRA subset. In several donors, we found cells in the CD4-CTL effector subset that shared their TCR clonotypes with cells in the precursor subset. TCR-seq analysis in longitudinal samples further confirmed this finding and provided more evidence for the relation between CD4-CTL precursors and effectors. Although the kinetic studies support the development of effectors from precursor cells, the nature of our studies in humans limits the definitive assessment of directionality; hence, we cannot completely exclude the possibility that the progenitor cell generated immediately after infection is the cytotoxic effector cell that eventually reverts. By defining the single-cell transcriptional program of CD4-CTL precursor cells, we have identified a number of previously unknown molecules potentially important for their differentiation and function and represent attractive targets for further validation studies.
We showed that surface expression of the IL-7R (CD127) in TEMRA cells defines a subset of cells with the expression of IL-7R as high as that observed in the TCM subset. Given the established role of the IL-7R signaling pathway in homeostatic T cell proliferation and survival, such IL-7Rhigh TEMRA cells are likely to represent the precursors of CD4-TEMRA. The isolation of a CD4-CTL precursor subset based on the surface expression of IL-7R would enable detailed epigenetic studies to define the nature and extent of CD4-CTL reprogramming in such precursor cells. These future studies are likely to provide insights into the molecular mechanisms that govern the early development, differentiation, and function of CD4-CTLs in humans as they transit from naive to memory precursor and effector cells.
The CD4-CTL effector cells displayed a number of known cytotoxicity molecules and previously unknown players (PFN1, PFN1P1, EFHD2, VCL, DIP2A, PLEK, and SYNE1) whose single-cell coexpression pattern suggests an important biological role for these molecules in CD4-CTL function. Further, their transcriptional program suggests that CD4-CTL effectors are terminally differentiated and likely short-lived because they express low levels of the costimulatory molecules CD27 and CD28 and high levels of KLRG1 transcripts (41, 52, 60–62). However, we observed marked clonal expansion of CD4-CTL effectors in several donors, suggesting that, compared with other conventional TH effector cells, different molecular mechanisms may operate in CD4-CTL effectors to promote their long-term survival. IL-7R− TEMRA CD4-CTL effectors highly expressed several molecules that are linked to cell survival such as CRTAM, ZNF683 (Hobit), PRSS23, SPON2, and TCF7 (encodes TCF1) (24, 46–51). Therefore, we hypothesize that these candidate molecules are likely to confer long-term survival properties to CD4-CTL effectors, which warrants further functional investigation in model organisms.
Overall, our single-cell transcriptomic studies in the human CD4-TEMRA population have uncovered an unprecedented level of heterogeneity, presumably created by the diverse nature of infections and the timing of exposures coupled with genetic diversity among our study donors. We identified a TEMRA subset of precursor CD4-CTLs, whose isolation and further characterization may open avenues for investigating the mechanisms that govern the generation of CD4-CTLs in humans. The stem-like virus-specific long-lived human memory T cell subset originating from TN cells has been described for CD8 compartment, where these cells share the molecular profiles of TN and TCM subsets (63). Considering the expansion of TEMRA in response to viral infections such as DENV and CMV, it is possible that IL-7Rhigh TEMRA subset (CD4-CTL precursors) may develop from such compartment. Understanding the origins and biology of potentially long-lived CD4-CTL precursors may pave the way for developing strategies to boost durable CD4-CTL immune responses after vaccination against viral infections and cancer. A comprehensive assessment of heterogeneity in pathogen- or vaccine epitope–specific CD4-CTLs by single-cell approaches is likely to yield insights into the nature of protective CD4-CTL response generated against specific pathogens or vaccines.
MATERIALS AND METHODS
Study design
The goal of this study was to use single-cell RNA-seq assay to capture the transcriptome of individual cells in CD4+ T cell memory subsets in human peripheral blood mononuclear cells (PBMCs). Details on the sample collection and processing are described in Supplementary Materials and Methods.
Flow cytometry
Human PBMCs were isolated and stained as described in Supplementary Materials and Methods.
Single-cell RNA-seq
Single-cell RNA-seq was performed as described previously (33, 34), with some modifications that are described in Supplementary Materials and Methods.
Single-cell RNA-seq and statistical analysis
Data processing and analysis were performed using R, Qlucore Omics, and GraphPad Prism, as described in Supplementary Materials and Methods.
TCR-seq and analysis
TCR-seq was performed and analyzed as described previously (57, 58). Details are described in Supplementary Materials and Methods.
Supplementary Material
Acknowledgments
We thank the members of the Vijayanand laboratory for the critical reading of the manuscript and discussions and the Human Immune Profiling Consortium team at the La Jolla Institute (LJI) for the valuable discussions. We thank S. Rosales, S. Liang, and D. Singh from Vijayanand’s group for the help with sequencing runs. We thank C. Kim, L. Boggeman, D. Hinz, and R. Simmons at the LJI Flow Cytometry Core for assisting with cell sorting. We thank C. Cerpas and A. Balmaseda for the preparation of PBMCs in Nicaragua. We thank D. M. Chudakov for sharing the detailed protocol for TCR-seq.
Funding: This work was supported by NIH grants [U19AI118626 and U19AI118610 (to P.V. and A.S.); R01HL114093 and R24AI108564 (to P.V.)], the William K. Bowes Jr. Foundation (to P.V.), and NIH contract nos. HHSN272200900042C and HHSN27220140045C (to A.S.).
Footnotes
Author contributions: V.S.P., G.S., A.S., B.P., and P.V. conceived the work. V.S.P. and P.V. designed the study and wrote the manuscript. V.S.P. designed and performed the experiments and analyzed the data under the supervision of P.V. A.M. assisted V.S.P. in the RNA-seq analysis and performed all R-based programming. J.C. assisted V.S.P. in the single-cell RNA-seq experiments. P.O. assisted V.S.P. and D.W. in the DENV peptide stimulation experiments. B.J.S. performed the IL-7R fluorescence-activated cell sorting experiments shown in Fig. 5 (D to G). E.H. and A.D.d.S. collected the blood samples in Nicaragua and Sri Lanka and determined the DENV serostatus, respectively.
Competing interests: All authors declare that they have no competing interests.
Data and materials availability: The sequence data sets reported in this paper have been deposited in the Gene Expression Omnibus with accession no. GSE106544.
SUPPLEMENTARY MATERIALS
immunology.sciencemag.org/cgi/content/full/3/19/eaan8664/DC1
Materials and Methods
References (64–73)
REFERENCES AND NOTES
- 1.Rosenblum MD, Way SS, Abbas AK. Regulatory T cell memory. Nat Rev Immunol. 2016;16:90–101. doi: 10.1038/nri.2015.1. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Swain SL, McKinstry KK, Strutt TM. Expanding roles for CD4+ T cells in immunity to viruses. Nat Rev Immunol. 2012;12:136–148. doi: 10.1038/nri3152. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.O’Shea JJ, Paul WE. Mechanisms underlying lineage commitment and plasticity of helper CD4+ T cells. Science. 2010;327:1098–1102. doi: 10.1126/science.1178334. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Arlehamn CL, Seumois G, Gerasimova A, Huang C, Fu Z, Yue X, Sette A, Vijayanand P, Peters B. Transcriptional profile of tuberculosis antigen–specific T cells reveals novel multifunctional features. J Immunol. 2014;193:2931–2940. doi: 10.4049/jimmunol.1401151. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 5.Cheroutre H, Husain MM. CD4 CTL: Living up to the challenge. Semin Immunol. 2013;25:273–281. doi: 10.1016/j.smim.2013.10.022. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6.Juno JA, van Bockel D, Kent SJ, Kelleher AD, Zaunders JJ, Munier CML. Cytotoxic CD4 T cells—Friend or foe during viral infection? Front Immunol. 2017;8:19. doi: 10.3389/fimmu.2017.00019. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Weiskopf D, Bangs DJ, Sidney J, Kolla RV, De Silva AD, de Silva AM, Crotty S, Peters B, Sette A. Dengue virus infection elicits highly polarized CX3CR1+ cytotoxic CD4+ T cells associated with protective immunity. Proc Natl Acad Sci USA. 2015;112:E4256–E4263. doi: 10.1073/pnas.1505956112. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 8.Derhovanessian E, Maier AB, Hähnel K, Beck R, de Craen AJM, Slagboom EP, Westendorp RGJ, Pawelec G. Infection with cytomegalovirus but not herpes simplex virus induces the accumulation of late-differentiated CD4+ and CD8+ T-cells in humans. J Gen Virol. 2011;92:2746–2756. doi: 10.1099/vir.0.036004-0. [DOI] [PubMed] [Google Scholar]
- 9.Intlekofer AM, Takemoto N, Wherry EJ, Longworth SA, Northrup JT, Palanivel VR, Mullen AC, Gasink CR, Kaech SM, Miller JD, Gapin L, Ryan K, Russ AP, Lindsten T, Orange JS, Goldrath AW, Ahmed R, Reiner SL. Effector and memory CD8+ T cell fate coupled by T-bet and eomesodermin. Nat Immunol. 2005;6:1236–1244. doi: 10.1038/ni1268. [DOI] [PubMed] [Google Scholar]
- 10.Takemoto N, Intlekofer AM, Northrup JT, Wherry EJ, Reiner SL. Cutting edge: IL-12 inversely regulates T-bet and eomesodermin expression during pathogen-induced CD8+ T cell differentiation. J Immunol. 2006;177:7515–7519. doi: 10.4049/jimmunol.177.11.7515. [DOI] [PubMed] [Google Scholar]
- 11.Appay V, Zaunders JJ, Papagno L, Sutton J, Jaramillo A, Waters A, Easterbrook P, Grey P, Smith D, McMichael AJ, Cooper DA, Rowland-Jones SL, Kelleher AD. Characterization of CD4+ CTLs ex vivo. J Immunol. 2002;168:5954–5958. doi: 10.4049/jimmunol.168.11.5954. [DOI] [PubMed] [Google Scholar]
- 12.Zaunders JJ, Dyer WB, Wang B, Munier ML, Miranda-Saksena M, Newton R, Moore J, Mackay CR, Cooper DA, Saksena NK, Kelleher AD. Identification of circulating antigen-specific CD4+ T lymphocytes with a CCR5+, cytotoxic phenotype in an HIV-1 long-term nonprogressor and in CMV infection. Blood. 2004;103:2238–2247. doi: 10.1182/blood-2003-08-2765. [DOI] [PubMed] [Google Scholar]
- 13.Norris PJ, Moffett HF, Yang OO, Kaufmann DE, Clark MJ, Addo MM, Rosenberg ES. Beyond help: Direct effector functions of human immunodeficiency virus type 1-specific CD4+ T cells. J Virol. 2004;78:8844–8851. doi: 10.1128/JVI.78.16.8844-8851.2004. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 14.van Leeuwen EMM, Remmerswaal EBM, Vossen MTM, Rowshani AT, Wertheim-van Dillen PME, van Lier RAW, ten Berge IJM. Emergence of a CD4+CD28-granzyme B+, cytomegalovirus-specific T cell subset after recovery of primary cytomegalovirus infection. J Immunol. 2004;173:1834–1841. doi: 10.4049/jimmunol.173.3.1834. [DOI] [PubMed] [Google Scholar]
- 15.Aslan N, Yurdaydin C, Wiegand J, Greten T, Ciner A, Meyer MF, Heiken H, Kuhlmann B, Kaiser T, Bozkaya H, Tillmann HL, Bozdayi AM, Manns MP, Wedemeyer H. Cytotoxic CD4+ T cells in viral hepatitis. J Viral Hepat. 2006;13:505–514. doi: 10.1111/j.1365-2893.2006.00723.x. [DOI] [PubMed] [Google Scholar]
- 16.Brown DM, Lee S, de la Luz Garcia-Hernandez M, Swain SL. Multifunctional CD4 cells expressing gamma interferon and perforin mediate protection against lethal influenza virus infection. J Virol. 2012;86:6792–6803. doi: 10.1128/JVI.07172-11. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 17.McKinstry KK, Strutt TM, Kuang Y, Brown DM, Sell S, Dutton RW, Swain SL. Memory CD4+ T cells protect against influenza through multiple synergizing mechanisms. J Clin Invest. 2012;122:2847–2856. doi: 10.1172/JCI63689. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 18.Watson AM, Lam LK, Klimstra WB, Ryman KD. The 17D-204 vaccine strain-induced protection against virulent yellow fever virus is mediated by humoral immunity and CD4+ but not CD8+ T cells. PLOS Pathog. 2016;12:e1005786. doi: 10.1371/journal.ppat.1005786. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 19.Vogel AJ, Brown DM. Single-dose CpG immunization protects against a heterosubtypic challenge and generates antigen-specific memory T cells. Front Immunol. 2015;6:327. doi: 10.3389/fimmu.2015.00327. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 20.Terahara K, Ishii H, Nomura T, Takahashi N, Takeda A, Shiino T, Tsunetsugu-Yokota Y, Matano T. Vaccine-induced CD107a+ CD4+ T cells are resistant to depletion following AIDS virus infection. J Virol. 2014;88:14232–14240. doi: 10.1128/JVI.02032-14. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 21.Mahnke YD, Brodie TM, Sallusto F, Roederer M, Lugli E. The who’s who of T-cell differentiation: Human memory T-cell subsets. Eur J Immunol. 2013;43:2797–2809. doi: 10.1002/eji.201343751. [DOI] [PubMed] [Google Scholar]
- 22.Finak G, McDavid A, Yajima M, Deng J, Gersuk V, Shalek AK, Slichter CK, Miller HW, McElrath MJ, Prlic M, Linsley PS, Gottardo R. MAST: A flexible statistical framework for assessing transcriptional changes and characterizing heterogeneity in single-cell RNA sequencing data. Genome Biol. 2015;16:278. doi: 10.1186/s13059-015-0844-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 23.Kharchenko PV, Silberstein L, Scadden DT. Bayesian approach to single-cell differential expression analysis. Nat Methods. 2014;11:740–742. doi: 10.1038/nmeth.2967. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 24.Oja AE, Vieira Braga FA, Remmerswaal EBM, Kragten NAM, Hertoghs KML, Zuo J, Moss PA, van Lier RAW, van Gisbergen KPJM, Hombrink P. The transcription factor hobit identifies human cytotoxic CD4+ T cells. Front Immunol. 2017;8:325. doi: 10.3389/fimmu.2017.00325. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 25.Hidalgo LG, Einecke G, Allanach K, Halloran PF. The transcriptome of human cytotoxic T cells: Similarities and disparities among allostimulated CD4+ CTL, CD8+ CTL and NK cells. Am J Transplant. 2008;8:627–636. doi: 10.1111/j.1600-6143.2007.02128.x. [DOI] [PubMed] [Google Scholar]
- 26.Subramanian A, Tamayo P, Mootha VK, Mukherjee S, Ebert BL, Gillette MA, Paulovich A, Pomeroy SL, Golub TR, Lander ES, Mesirov JP. Gene set enrichment analysis: A knowledge-based approach for interpreting genome-wide expression profiles. Proc Natl Acad Sci USA. 2005;102:15545–15550. doi: 10.1073/pnas.0506580102. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 27.Pearce EL, Mullen AC, Martins GA, Krawczyk CM, Hutchins AS, Zediak VP, Banica M, DiCioccio CB, Gross DA, Mao C-a, Shen H, Cereb N, Yang SY, Lindsten T, Rossant J, Hunter CA, Reiner SL. Control of effector CD8+ T cell function by the transcription factor eomesodermin. Science. 2003;302:1041–1043. doi: 10.1126/science.1090148. [DOI] [PubMed] [Google Scholar]
- 28.Eshima K, Chiba S, Suzuki H, Kokubo K, Kobayashi H, Iizuka M, Iwabuchi K, Shinohara N. Ectopic expression of a T-box transcription factor, eomesodermin, renders CD4+ Th cells cytotoxic by activating both perforin- and FasL-pathways. Immunol Lett. 2012;144:7–15. doi: 10.1016/j.imlet.2012.02.013. [DOI] [PubMed] [Google Scholar]
- 29.Witke W. The role of profilin complexes in cell motility and other cellular processes. Trends Cell Biol. 2004;14:461–469. doi: 10.1016/j.tcb.2004.07.003. [DOI] [PubMed] [Google Scholar]
- 30.Chen H, Choudhury DM, Craig SW. Coincidence of actin filaments and talin is required to activate vinculin. J Biol Chem. 2006;281:40389–40398. doi: 10.1074/jbc.M607324200. [DOI] [PubMed] [Google Scholar]
- 31.Cohen DM, Kutscher B, Chen H, Murphy DB, Craig SW. A conformational switch in vinculin drives formation and dynamics of a talin-vinculin complex at focal adhesions. J Biol Chem. 2006;281:16006–16015. doi: 10.1074/jbc.M600738200. [DOI] [PubMed] [Google Scholar]
- 32.Hoppmann N, Graetz C, Paterka M, Poisa-Beiro L, Larochelle C, Hasan M, Lill CM, Zipp F, Siffrin V. New candidates for CD4 T cell pathogenicity in experimental neuroinflammation and multiple sclerosis. Brain. 2015;138:902–917. doi: 10.1093/brain/awu408. [DOI] [PubMed] [Google Scholar]
- 33.Picelli S, Faridani OR, Björklund ÅK, Winberg G, Sagasser S, Sandberg R. Full-length RNA-seq from single cells using Smart-seq2. Nat Protoc. 2014;9:171–181. doi: 10.1038/nprot.2014.006. [DOI] [PubMed] [Google Scholar]
- 34.Engel I, Seumois G, Chavez L, Samaniego-Castruita D, White B, Chawla A, Mock D, Vijayanand P, Kronenberg M. Innate-like functions of natural killer T cell subsets result from highly divergent gene programs. Nat Immunol. 2016;17:728–739. doi: 10.1038/ni.3437. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 35.Stubbington MJT, Lönnberg T, Proserpio V, Clare S, Speak AO, Dougan G, Teichmann SA. T cell fate and clonality inference from single-cell transcriptomes. Nat Methods. 2016;13:329–332. doi: 10.1038/nmeth.3800. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 36.Takeuchi A, Badr MESG, Miyauchi K, Ishihara C, Onishi R, Guo Z, Sasaki Y, Ike H, Takumi A, Tsuji NM, Murakami Y, Katakai T, Kubo M, Saito T. CRTAM determines the CD4+ cytotoxic T lymphocyte lineage. J Exp Med. 2016;213:123–138. doi: 10.1084/jem.20150519. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 37.Weiskopf D, Angelo MA, Grifoni A, O’Rourke PH, Sidney J, Paul S, Silva AD De, Phillips E, Mallal S, Premawansa S, Premawansa G, Wijewickrama A, Peters B, Sette A. HLA-DRB1 alleles are associated with different magnitudes of dengue virus–specific CD4+ T-cell responses. J Infect Dis. 2016;214:1117–1124. doi: 10.1093/infdis/jiw309. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 38.Satija R, Farrell JA, Gennert D, Schier AF, Regev A. Spatial reconstruction of single-cell gene expression data. Nat Biotechnol. 2015;33:495–502. doi: 10.1038/nbt.3192. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 39.Juliá M, Telenti A, Rausell A. Sincell: An R/Bioconductor package for statistical assessment of cell-state hierarchies from single-cell RNA-seq. Bioinformatics. 2015;31:3380–3382. doi: 10.1093/bioinformatics/btv368. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 40.Hanke T, Corral L, Vance RE, Raulet DH. 2F1 antigen, the mouse homolog of the rat “mast cell function-associated antigen”, is a lectin-like type II transmembrane receptor expressed by natural killer cells. Eur J Immunol. 1998;28:4409–4417. doi: 10.1002/(SICI)1521-4141(199812)28:12<4409::AID-IMMU4409>3.0.CO;2-3. [DOI] [PubMed] [Google Scholar]
- 41.Voehringer D, Koschella M, Pircher H. Lack of proliferative capacity of human effector and memory T cells expressing killer cell lectinlike receptor G1 (KLRG1) Blood. 2002;100:3698–3702. doi: 10.1182/blood-2002-02-0657. [DOI] [PubMed] [Google Scholar]
- 42.Blaser C, Kaufmann M, Pircher H. Virus-activated CD8 T cells and lymphokine-activated NK cells express the mast cell function-associated antigen, an inhibitory C-type lectin. J Immunol. 1998;161:6451–6454. [PubMed] [Google Scholar]
- 43.Böttcher JP, Beyer M, Meissner F, Abdullah Z, Sander J, Höchst B, Eickhoff S, Rieckmann JC, Russo C, Bauer T, Flecken T, Giesen D, Engel D, Jung S, Busch DH, Protzer U, Thimme R, Mann M, Kurts C, Schultze JL, Kastenmüller W, Knolle PA. Functional classification of memory CD8+ T cells by CX3CR1 expression. Nat Commun. 2015;6:8306. doi: 10.1038/ncomms9306. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 44.Appay V, Dunbar PR, Callan M, Klenerman P, Gillespie GMA, Papagno L, Ogg GS, King A, Lechner F, Spina CA, Little S, Havlir DV, Richman DD, Gruener N, Pape G, Waters A, Easterbrook P, Salio M, Cerundolo V, McMichael AJ, Rowland-Jones SL. Memory CD8+ T cells vary in differentiation phenotype in different persistent virus infections. Nat Med. 2002;8:379–385. doi: 10.1038/nm0402-379. [DOI] [PubMed] [Google Scholar]
- 45.Appay V, Rowland-Jones SL. Lessons from the study of T-cell differentiation in persistent human virus infection. Semin Immunol. 2004;16:205–212. doi: 10.1016/j.smim.2004.02.007. [DOI] [PubMed] [Google Scholar]
- 46.Braun J, Frentsch M, Thiel A. Hobit and human effector T-cell differentiation: The beginning of a long journey. Eur J Immunol. 2015;45:2762–2765. doi: 10.1002/eji.201545959. [DOI] [PubMed] [Google Scholar]
- 47.Chan HS, Chang SJ, Wang TY, Ko HJ, Lin YC, Lin KT, Chang KM, Chuang YJ. Serine protease PRSS23 is upregulated by estrogen receptor alpha and associated with proliferation of breast cancer cells. PLOS ONE. 2012;7:e30397. doi: 10.1371/journal.pone.0030397. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 48.Schmid F, Wang Q, Huska MR, Andrade-Navarro MA, Lemm M, Fichtner I, Dahlmann M, Kobelt D, Walther W, Smith J, Schlag PM, Stein U. SPON2, a newly identified target gene of MACC1, drives colorectal cancer metastasis in mice and is prognostic for colorectal cancer patient survival. Oncogene. 2016;35:5942–5952. doi: 10.1038/onc.2015.451. [DOI] [PubMed] [Google Scholar]
- 49.Vieira Braga FA, Hertoghs KML, Kragten NAM, Doody GM, Barnes NA, Remmerswaal EBM, Hsiao C-C, Moerland PD, Wouters D, Derks IAM, vanS tijn A, Demkes M, Hamann J, Eldering E, Nolte MA, Tooze RM, ten Berge IJM, van Gisbergen KPJM, van Lier RAW. Blimp-1 homolog Hobit identifies effector-type lymphocytes in humans. Eur J Immunol. 2015;45:2945–2958. doi: 10.1002/eji.201545650. [DOI] [PubMed] [Google Scholar]
- 50.Jeannet G, Boudousquié C, Gardiol N, Kang J, Huelsken J, Held W. Essential role of the Wnt pathway effector Tcf-1 for the establishment of functional CD8 T cell memory. Proc Natl Acad Sci USA. 2010;107:9777–9782. doi: 10.1073/pnas.0914127107. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 51.Zhou X, Yu S, Zhao DM, Harty JT, Badovinac VP, Xue HH. Differentiation and persistence of memory CD8+ T cells depend on T cell factor 1. Immunity. 2010;33:229–240. doi: 10.1016/j.immuni.2010.08.002. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 52.Kaech SM, Tan JT, Wherry EJ, Konieczny BT, Surh CD, Ahmed R. Selective expression of the interleukin 7 receptor identifies effector CD8 T cells that give rise to long-lived memory cells. Nat Immunol. 2003;4:1191–1198. doi: 10.1038/ni1009. [DOI] [PubMed] [Google Scholar]
- 53.Ibegbu CC, Xu YX, Harris W, Maggio D, Miller JD, Kourtis AP. Expression of killer cell lectin-like receptor G1 on antigen-specific human CD8+ T lymphocytes during active, latent, and resolved infection and its relation with CD57. J Immunol. 2005;174:6088–6094. doi: 10.4049/jimmunol.174.10.6088. [DOI] [PubMed] [Google Scholar]
- 54.Bengsch B, Spangenberg HC, Kersting N, Neumann-Haefelin C, Panther E, von Weizsäcker F, Blum HE, Pircher H, Thimme R. Analysis of CD127 and KLRG1 expression on hepatitis C virus-specific CD8+ T cells reveals the existence of different memory T-cell subsets in the peripheral blood and liver. J Virol. 2007;81:945–953. doi: 10.1128/JVI.01354-06. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 55.Robbins SH, Terrizzi SC, Sydora BC, Mikayama T, Brossay L. Differential regulation of killer cell lectin-like receptor G1 expression on T cells. J Immunol. 2003;170:5876–5885. doi: 10.4049/jimmunol.170.12.5876. [DOI] [PubMed] [Google Scholar]
- 56.Kaech SM, Cui W. Transcriptional control of effector and memory CD8+ T cell differentiation. Nat Rev Immunol. 2012;12:749–761. doi: 10.1038/nri3307. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 57.Shugay M, Britanova OV, Merzlyak EM, Turchaninova MA, Mamedov IZ, Tuganbaev TR, Bolotin DA, Staroverov DB, Putintseva EV, Plevova K, Linnemann C, Shagin D, Pospisilova S, Lukyanov S, Schumacher TN, Chudakov DM. Towards error-free profiling of immune repertoires. Nat Methods. 2014;11:653–655. doi: 10.1038/nmeth.2960. [DOI] [PubMed] [Google Scholar]
- 58.Shugay M, Bagaev DV, Turchaninova MA, Bolotin DA, Britanova OV, Putintseva EV, Pogorelyy MV, Nazarov VI, Zvyagin IV, Kirgizova VI, Kirgizov KI, Skorobogatova EV, Chudakov DM. VDJtools: Unifying post-analysis of T Cell receptor repertoires. PLOS Comput Biol. 2015;11:e1004503. doi: 10.1371/journal.pcbi.1004503. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 59.Zheng GXY, Terry JM, Belgrader P, Ryvkin P, Bent ZW, Wilson R, Ziraldo SB, Wheeler TD, McDermott GP, Zhu J, Gregory MT, Shuga J, Montesclaros L, Underwood JG, Masquelier DA, Nishimura SY, Schnall-Levin M, Wyatt PW, Hindson CM, Bharadwaj R, Wong A, Ness KD, Beppu LW, Deeg HJ, McFarland C, Loeb KR, Valente WJ, Ericson NG, Stevens EA, Radich JP, Mikkelsen TS, Hindson BJ, Bielas JH. Massively parallel digital transcriptional profiling of single cells. Nat Commun. 2017;8:14049. doi: 10.1038/ncomms14049. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 60.Boettler T, Panther E, Bengsch B, Nazarova N, Spangenberg HC, Blum HE, Thimme R. Expression of the interleukin-7 receptor alpha chain (CD127) on virus-specific CD8+ T cells identifies functionally and phenotypically defined memory T cells during acute resolving hepatitis B virus infection. J Virol. 2006;80:3532–3540. doi: 10.1128/JVI.80.7.3532-3540.2006. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 61.Fuller MJ, Hildeman DA, Sabbaj S, Gaddis DE, Tebo AE, Shang L, Goepfert PA, Zajac AJ. Cutting edge: Emergence of CD127high functionally competent memory T cells is compromised by high viral loads and inadequate T cell help. J Immunol. 2005;174:5926–5930. doi: 10.4049/jimmunol.174.10.5926. [DOI] [PubMed] [Google Scholar]
- 62.Lang KS, Recher M, Navarini AA, Harris NL, Löhning M, Junt T, Probst HC, Hengartner H, Zinkernagel RM. Inverse correlation between IL-7 receptor expression and CD8 T cell exhaustion during persistent antigen stimulation. Eur J Immunol. 2005;35:738–745. doi: 10.1002/eji.200425828. [DOI] [PubMed] [Google Scholar]
- 63.Gattinoni L, Lugli E, Ji Y, Pos Z, Paulos CM, Quigley MF, Almeida JR, Gostick E, Yu Z, Carpenito C, Wang E, Douek DC, Price DA, June CH, Marincola FM, Roederer M, Restifo NP. A human memory T cell subset with stem cell-like properties. Nat Med. 2011;17:1290–1297. doi: 10.1038/nm.2446. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 64.Weiskopf D, Angelo MA, de Azeredo EL, Sidney J, Greenbaum JA, Fernando AN, Broadwater A, Kolla RV, De Silva AD, de Silva AM, Mattia KA, Doranz BJ, Grey HM, Shresta S, Peters B, Sette A. Comprehensive analysis of dengue virus-specific responses supports an HLA-linked protective role for CD8+ T cells. Proc Natl Acad Sci USA. 2013;110:E2046–E2053. doi: 10.1073/pnas.1305227110. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 65.Kanakaratne N, Wahala WMPB, Messer WB, Tissera HA, Shahani A, Abeysinghe N, de Silva AM, Gunasekera M. Severe dengue epidemics in Sri Lanka, 2003–2006. Emerg Infect Dis. 2009;15:192–199. doi: 10.3201/eid1502.080926. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 66.Fernandez RJ, Vazquez S. Serological diagnosis of dengue by an ELISA inhibition method (EIM) Mem Inst Oswaldo Cruz. 1990;85:347–351. doi: 10.1590/s0074-02761990000300012. [DOI] [PubMed] [Google Scholar]
- 67.Kraus AA, Messer W, Haymore LB, de Silva AM. Comparison of plaque- and flow cytometry-based methods for measuring dengue virus neutralization. J Clin Microbiol. 2007;45:3777–3780. doi: 10.1128/JCM.00827-07. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 68.Swanstrom JA, Plante JA, Plante KS, Young EF, McGowan E, Gallichotte EN, Widman DG, Heise MT, de Silva AM, Baric RS. Dengue virus envelope dimer epitope monoclonal antibodies isolated from dengue patients are protective against Zika virus. mBio. 2016;7:e01123–e16. doi: 10.1128/mBio.01123-16. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 69.Gaublomme JT, Yosef N, Lee Y, Gertner RS, Yang LV, Wu C, Pandolfi PP, Mak T, Satija R, Shalek AK, Kuchroo VK, Park H, Regev A. Single-cell genomics unveils critical regulators of Th17 cell pathogenicity. Cell. 2015;163:1400–1412. doi: 10.1016/j.cell.2015.11.009. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 70.Zheng C, Zheng L, Yoo JK, Guo H, Zhang Y, Guo X, Kang B, Hu R, Huang JY, Zhang Q, Liu Z, Dong M, Hu X, Ouyang W, Peng J, Zhang Z. Landscape of infiltrating T cells in liver cancer revealed by single-cell sequencing. Cell. 2017;169:1342–1356. doi: 10.1016/j.cell.2017.05.035. [DOI] [PubMed] [Google Scholar]
- 71.Seumois G, Zapardiel-Gonzalo J, White B, Singh D, Schulten V, Dillon M, Hinz D, Broide DH, Sette A, Peters B, Vijayanand P. Transcriptional profiling of Th2 cells identifies pathogenic features associated with asthma. J Immunol. 2016;197:655–664. doi: 10.4049/jimmunol.1600397. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 72.Ganesan AP, Clarke J, Wood O, Garrido-Martin EM, Chee SJ, Mellows T, Samaniego-Castruita D, Singh D, Seumois G, Alzetani A, Woo E, Friedmann PS, King EV, Thomas GJ, Sanchez-Elsner T, Vijayanand P, Ottensmeier CH. Tissue-resident memory features are linked to the magnitude of cytotoxic T cell responses in human lung cancer. Nat Immunol. 2017;18:940–950. doi: 10.1038/ni.3775. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 73.Love MI, Huber W, Anders S. Moderated estimation of fold change and dispersion for RNA-seq data with DESeq2. Genome Biol. 2014;15:550. doi: 10.1186/s13059-014-0550-8. [DOI] [PMC free article] [PubMed] [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.