Skip to main content
NCBI home page
NIHPA Author Manuscripts logoLink to NIHPA Author Manuscripts
. Author manuscript; available in PMC: 2020 May 1.
Published in final edited form as: Cancer Immunol Res. 2019 Mar 6;7(5):773–783. doi: 10.1158/2326-6066.CIR-18-0636

Cancer immunotherapy with T cells carrying bispecific receptors that mimic antibodies

Sarah Ahn 1,2, Jingjing Li 3,4, Chuang Sun 1,2, Keliang Gao 3,4, Koichi Hirabayashi 2, Hongxia Li 2,6, Barbara Savoldo 1,2,5, Rihe Liu 2,3,4,*, Gianpietro Dotti 1,2,*
PMCID: PMC6760241  NIHMSID: NIHMS1523393  PMID: 30842091

Abstract

Tumors are inherently heterogeneous in antigen expression and escape from immune surveillance due to antigen loss remains one of the limitations of targeted immunotherapy. Despite the clinical use of adoptive therapy with chimeric antigen receptor (CAR)–redirected T cells in lymphoblastic leukemia, treatment failure due to epitope loss occurs. Targeting multiple tumor-associated antigens (TAA) may thus improve the outcome of CAR-T cell therapies. CARs developed to simultaneously target multiple targets are limited by the large size of each single-chain variable fragment and compromised protein folding when several single chains are linearly assembled. Here we describe single-domain antibody mimics that function within CAR parameters but form a very compact structure. We show that antibody mimics targeting EGFR and HER2 of the ErbB receptor tyrosine kinase family can be assembled into receptor molecules, which we call antibody mimic receptors (amR). These amR can redirect T cells to recognize two different epitopes of the same antigen or two different TAAs in vitro and in vivo.

Introduction

Chimeric antigen receptors (CARs) are synthetic receptors. Their specificity is determined by the single chain variable fragment (scFv) obtained from a monoclonal antibody, with their activation controlled by the ζ-chain signaling domain from the T cell receptor complex and costimulatory endodomains [1, 2]. Gene transfer of CARs into T cells redirects T cell antigen specificity through the scFv. T cell activation and proliferation is amplified through costimulatory signals[3]. The infusion of CAR-T cells in patients with lymphoid malignancies has led to durable complete remission in more than 40% of patients [4, 5]. However, up to 20% of patients with acute lymphoblastic leukemia receiving CD19-specific CAR-T cells relapse due to the emergence of leukemic clones that have lost the targeted epitope[4, 6]. Furthermore, the heterogeneity of tumor-associated antigen (TAA) expression in solid tumors leads to CAR-T treatment failure when a single TAA is targeted[7].

The generation of multi-redirected CAR-T cells, namely by recognition of two non-overlapping epitopes of a TAA or two different TAAs, may be necessary to effectively eradicate tumor cells. Several approaches have been proposed to achieve this goal including: pooling CAR-T products targeting different TAAs, generating vectors encoding two different CARs that can be expressed simultaneously by each T cell, and engineering cassettes in which two scFvs are assembled into a single CAR moiety[2, 8, 9]. Although these approaches are feasible, a challenge in using an scFv-based antigen receptor is the need for multiple VH and VL domains to appropriately pair and stabilize in complex structures. In addition to the complexity and costs of manufacturing multiple T cell products, reduced expression of simultaneously expressed CARs, and compromised protein folding when several scFvs are linearly assembled in one single CAR, remain challenges to current methods of generating multi-redirected CAR-T cells.

Achieving multiple tumor targeting features using scFv-based CAR-T cells is difficult. We hypothesized that extracellular antigen receptors with simple structure, high stability, and small size could address the challenge. Various small protein domains that are not structurally equivalent to the immunoglobulin domains have been developed using various display technologies[10–14]. Tumor-homing ligands based on a small protein domain possess advantages over those on a multi-domain, complex structure in terms of engineering higher modularity. Ideally, the scaffold should be a monomeric small protein domain with high solubility and stability that is not inclined to aggregation, that tolerates sequence variations, and that is amenable to directed molecular evolution to create antigen-binding ligands with multiple functions[13].

Among numerous scaffolds that have been examined, three single-domain antibody mimics are of interest for developing CARs with multiple tumor-targeting features: 1) monobody, based on the type III domain of fibronectin (FN3); 2) affibody, based on a three-helix bundle Z domain; 3) DARPin, based on the designed ankyrin repeat protein[11, 12, 15, 16]. These engineered proteins can have high specificity and affinity, despite their simple structures and relatively small size. The FN3 domain is a stable protein with a MW around 10 kDa. Structurally, it has a β-sandwich scaffold similar to that of the immunoglobulin VH domain, with putative ligand-binding sites composed of three solvent accessible surface loops that are structurally analogous to the CDR H1, H2, and H3 of the VH domain[11]. The advantage of the FN3 domain is in their lack of disulfide bonds and post-translational modifications for biological functions. Affibodies (AFF) are based on the three-helix bundle Z domain derived from Staphylococcal protein A[17, 18]. As with the FN3 domain, AFF domains are resistant to proteolysis and heat-induced denaturation and lack disulfide bonds. Finally, DARPins contain consecutive copies of small structural repeats, which stack together to form a contiguous interacting surface[14]. DARPin-based targeting ligands that bind to various targets including CD4, EGFR, and HER2 have been generated[19].

Taking into consideration the simplicity, stability and smaller size of these targeting ligands, as well as their current applications in therapeutics and diagnostics[20], we explored the use of these molecules in generating antigen-specific receptors for T cells. In particular, we investigated if a combination of these single domain antibody mimics allows the generation of a T cell surface antigen receptor that recognizes two different epitopes of the same tumor antigen or two different antigens, aiming to develop T cells with bispecific redirection targeting two epitopes of the same antigen or two different antigens. As proof-of-principle, we have adapted high affinity antibody mimics specific for ErbB1 (EGFR) and ErbB2 (HER2), to generate receptor molecules called antibody mimic receptors (amRs).

Materials and Methods

Construction of bispecific CAR vectors.

To construct bispecific CAR vectors, the codon-optimized (for expression in human cells) coding regions for a monomeric or heterodimeric EGFR- or/and HER2-binding ligand were fused through an optimized flexible linker. The final coding region was cloned into the SFG vector, resulting in a fusion protein that is composed of the signaling peptide from human IgG heavy chain, EGFR- or HER2-binding domain(s), a FLAG tag, a 45-residue hinge region from human CD8α extracellular domain, the transmembrane domain of human CD8α, the CD28-costimulatory endodomain, and the ζ chain of the TCR/CD3 complex[21]. The CD8α hinge and transmembrane domains contain the native cysteine residues. Single domain antibody mimics (AFF, DARPin and FN3) were PCR amplified and cloned into the SFG vector. The scFv derived from the Cetuximab mAb was PCR amplified and cloned into the SFG vector. EGFR WT (Addgene plasmid #110110) and pBABE-puro-ErbB2 (Addgene plasmid #40978) were gifts from Matthew Meyerson. Full-length EGFR and HER2 were amplified by PCR and cloned into the SFG retroviral vector. A truncated form of HER2 lacking an intracellular domain was amplified by PCR and also cloned into the SFG retroviral vector. All retroviral supernatants were prepared as previously described[22].

Expression and purification of recombinant EGFR and HER2 binding protein domains.

Coding sequences codon-optimized for expression in E. coli with a C-terminal His tag were cloned into the pET28b vector. To express the ligands, vectors were transformed into E. coli BL21 (DE3) Rosetta cells and positive clones were selected on lysogeny broth (LB) plates containing 50 μg/mL kanamycin and 34 μg/mL chloramphenicol. Single colonies were picked and grown overnight at 37°C. Overnight cell cultures were added to 1 L of LB media and grown at 37°C. When the OD 600 was between 0.6–0.8, 1 mM IPTG was added to induce expression for 4h at 37°C. To purify the binding ligands, the cell pellet was resuspended in buffer A (25 mM HEPES pH 7.4 and 300 mM NaCl) supplemented with 1 mM phenylmethylsulfonyl fluoride (PMSF) and sonicated on ice for 10 min on a Sonifier 450 sonicator (Branson). After cell lysis, the soluble fraction was recovered by centrifugation at 4°C. The resulting soluble fraction was loaded onto an IMAC Ni-charged affinity column (Bio-Rad) pre-equilibrated with buffer A. The column was washed with Buffer A containing 20 mM imidazole (Buffer B) and then 50 mM imidazole (Buffer C) and the proteins were eluted with buffer D (buffer A and 200 mM imidazole). Following dialysis against 1×PBS, the quality of the purified proteins was verified by SDS-PAGE.

Characterization of target-binding features.

BLI analyses of the monomeric and heterodimeric EGFR and HER2-binding domains were performed on a Octet QK system (FortéBio LLC., Menlo Park, CA) against recombinant EGFR-Fc and HER2-Fc (AcroBiosystems, Newark, NJ) [17, 23] using 96-well microplates (Greiner Bio-One) at 30°C. Streptavidin biosensors (FortéBio) were used to immobilize concentrations of biotinylated ErbB-binding domains and samples resuspended in an assay buffer (1× PBS, 1% BSA, 0.05% Tween 20, pH 7.4) were applied to the 96-well microplate. Assays run in triplicate were acquired and analyzed on the FortéBio Data Acquisition 6.4 software. Savitzky-Golay filtering was applied to the averaged reference biosensors and then globally fitted at a 1:1 model.

Cell lines.

Tumor cell lines Panc-1, BxPC-3, HPAF-II and AsPC-1 (pancreatic cancer), MCF-7 (breast cancer), BV173 (B cell lymphoma) were purchased from American Type Culture Collection (ATCC). BxPC-3 and BV173 were cultured in RPMI1640 (Gibco). AsPC-1 was cultured in RPMI1640 supplemented with 1 mM sodium pyruvate (Gibco). HPAF-II and MCF-7 were cultured in MEM (Gibco). Panc-1 was cultured in DMEM (Gibco). All media were supplemented with 10% FBS (Sigma), 2 mM GlutaMax (Gibco) and penicillin (100 units/mL) and streptomycin (100mg/mL) (Gibco). All cells were maintained at 37°C with 5% CO2. All cell lines are regularly tested for mycoplasma and the identity of the cell lines is validated by flow cytometry for relevant cell surface markers and are also monitored for morphological drift in culture. Cell lines are maintained in culture no longer than 30 days and then replaced with cells from stored vials. The number of previous passages of these cell lines are unknown. Panc-1 cells were transduced with a retroviral vector encoding the eGFP-Firefly-Luciferase (eGFP-FFluc) gene[21]. BV173 cells were transduced with a retroviral construct encoding full-length human EGFR to generate BV173-EGFR cells or a truncated form of HER2 to generate BV173-HER2 cells. Panc-1 cells were transduced with a retroviral vector encoding HER2 to make Panc-1-HER2.

Generation of redirected T cells.

T cells expressing CAR and amRs were generated in accordance to standard operating procedures currently used to manufacture CAR-T cells for clinical use at our institution[24, 25]. Peripheral blood mononuclear cells (PBMCs) were isolated from discharged buffy coats (Gulf Coast Regional Blood Center, Houston, TX) using Lymphoprep medium (Accurate Chemical and Scientific Corporation) and activated on plates coated with 1 μg/mL CD3 (Miltenyi Biotec, Bergisch Gladback, Germany) and CD28 (BD Biosciences, San Jose, CA) mAbs. Activated T cells were transduced with retroviral supernatants on retronectin-coated 24-well plates (Takara Bio Inc., Shiga, Japan) 2–3 days post-activation. Transduced T cells were expanded in 50% Click’s Medium (Irvine Scientific, Santa Ana, CA) and 50% RPMI-1640 supplemented with 10% Hyclone FBS (GE Healthcare, Chicago, IL), 2 mM GlutaMax (Gibco) and penicillin (100 units/mL) and streptomycin (100mg/mL) (Gibco) with 10 ng/mL IL-7 and 5 ng/mL of IL-15 (Peprotech, Rocky Tech, NJ) for 10–14 days of culture before being used for functional assays[24–26].

Flow cytometry.

We used mAbs specific for human CD3 (APC-H7; SK7; 560176), CD45 (BV510; HI30; 563204), CD4 (BV711; SK3; 563028), CD8 (APC; SK1; 340584), CD19 (FITC; SJ25C1; 340409), CD45RA (PE; HI100; 555489), CD45RO (BV786; UCHL1; 564290), CD69 (FITC; L78; 347823), HER2 (PE; Neu24.7; 340879) from BD Biosciences (San Jose, CA), CCR7 (FITC; 150503; FAB197F-100) from R&D (Minneapolis, MN) and EGFR (PE; AY13; 352904) from BioLegend (San Diego, CA). We detected the expression of the EGFR.CAR or amRs using anti-FLAG mAb (APC; L5; 637308). An anti-idiotype mAb was used to detect the expression of the CD19.CAR as previously described[21]. All samples were acquired on a BD LSRFortessa and a minimum of 10,000 events was acquired per sample. Samples were analyzed on FlowJo 9 (FlowJo LLC, Ashland, OR).

Western Blot analysis.

T cell lysates were resuspended in 2× Laemelli Buffer (Bio-Rad) in reducing or non-reducing conditions. To assess signaling through the CAR or amR, T cells on ice were incubated with 1 μg of anti-FLAG Ab (clone M2) for 15 minutes and then 1 μg of goat anti-mouse secondary Ab (BD Biosciences, San Jose, CA) for an additional 15 minutes. Cells were then transferred to a 37° C water bath for the indicated time points and lysed with 4× Laemelli buffer. All lysates were separated in 4–15% sodium dodecyl sulfate polyacrylamide (SDS-PAGE) gels and transferred to polyvinylidene diflouride membranes (all Bio-Rad). Blots were probed for human CD3ζ (Santa Cruz Biotechnology, Dallas, TX), p-Y142 CD3ζ (Abcam, Cambridge, MA), pan-ERK (BD Biosciences) and pan-Akt, p-S473 Akt and p-T202/Y204 MAPK (all Cell Signaling, Danvers, MA) diluted 1:1000 in TBS-Tween/5% skim milk. Membranes were then incubated with HRP-conjugated goat anti-mouse or goat anti-rabbit IgG (both Santa Cruz) at a dilution of 1:3000 and imaged using the ECL Substrate Kit on a ChemiDoc MP System (both Bio-Rad) according to manufacturer’s instructions.

In vitro activation.

Biotinylated recombinant EGFR and EGFRvIII protein (AcroBiosystems) were added to 96-well plates coated with 1 μg of avidin (Thermo Fisher Scientific) at a 3:1 ratio. Recombinant EGFR-Fc and HER2-Fc (R&D Systems) were coated on 96-well plates overnight at a concentration of 1 μg/well. T cells were seeded in duplicate or triplicate for 6 hours and supernatant was collected for IFNγ and T cells were assessed for CD69 by flow cytometry.

Proliferation assay.

T cells were labeled with 1.5 mM carboxyfluorescein diacetate succinimidyl ester (CFSE) (Invitrogen) and plated with irradiated AsPC-1 at 4:1 E:T in the absence of exogenous cytokines. CFSE dilution of CAR-T cells or amR-T cells was analyzed on day 5 using flow cytometry[21]. The proliferation index was quantified using FlowJo 9.

Long-term in vitro cytotoxicity.

Tumor cells were seeded at 2.5 × 105 per well in 24-well plates. Donor-matched T cells normalized for transduction efficiency were added at 1:5 effector to target (E:T) ratio. On day 5 of co-culture, cells were collected and the frequency of T cells and residual tumors cells was measured by flow cytometry. Tumor cells were identified as CD19+ for BV173 tumor cells or CD4– CD8– in the case of all adherent tumor cell lines[27].

Repetitive co-culture assay.

For multiple rounds of co-culture, tumor cells were seeded at 5 × 105 per well in 24-well plates. Donor-matched T cells normalized for transduction efficiency were added at 1:2 effector to target (E:T) ratio. On day 3 of co-culture, a fraction of the cells was collected and the frequency of T cells and residual tumors cells were measured by flow cytometry. Between co-cultures, T cells were washed and resuspended in fresh medium, without the addition of exogenous cytokines, and left to rest for 3 days[27].

Cytokine analysis.

Supernatant was collected from 5 × 104 CAR-T cells or amR-T cells plated in in vitro cytotoxicity assays at 1:5 E:T ratio after 24 hours. IFN-γ and IL-2 were measured by ELISA per manufacturer’s instructions (R&D) in duplicate.

Xenograft murine models.

Six to eight-week-old male or female non-obese diabetic severe combined immunodeficiency/γc−/- (NSG) mice were injected intravenously by tail vein (iv.) with the Panc-1 tumor cell line (1 × 106 cells/mouse) transduced with the GFP-FFLuc reporter intravenously by tail vein (iv.) injection[28]. In other experiments, HPAF-II GFP-FFLuc tagged cells were suspended in Matrigel and inoculated intraperitoneally (ip.) (1 × 106 cells/mouse)[29]. In re-challenge experiments, Panc-1 GFP-FFLuc cells (1 × 106 cells/mouse) were injected 10 days prior to T cell injection. Upon clearance of the Panc-1 tumor cells, mice were then infused with BV173-HER2 cells (2 × 106 cells/mouse). Mice were matched based on the bioluminescence intensity and injected with 5 × 106 or 1 × 107 T cells iv 12 – 14 days post tumor cell engraftment. The IVIS-Kinetic Optical System (Perkin Elmer, Waltham, MA) was used to monitor tumor burden. Mice were monitored and euthanized according to UNC-IACUC Standards.

Statistical Analysis.

Data are reported as the mean and standard deviation, unless otherwise reported. To compare significant differences between 2 samples, a two-tailed Student’s t-test was applied. An ANOVA with Bonferroni’s post-hoc analysis was applied when a comparison between multiple groups was required. A p value of less than 0.05 was considered statistically significant. All figures were generated using GraphPad Prism (GraphPad Software, La Jolla, CA).

Results

A soluble single domain antibody targets EGFR in a bispecific manner.

To develop a single domain-based tumor antigen binding moiety that targets two different epitopes of EGFR, we assembled the previously identified Z domain-based EGFR-binding affibody ZEGFR:1907 and an FN3-based EGFR-binding monobody [17]. The length and flexibility of the linker between the two EGFR-binding domains were optimized to retain the target-binding affinity, specificity, and independent folding of each EGFR-binding domain. We observed that when the linker is too short, both domains failed to bind targets. An overly long linker resulted in the loss of the bivalent effect as well as instability of the ligands. Since the linker length appeared to be antigen and binder dependent, we only used the linker length that worked well in this proof-of-concept work. In this study, the two antigen-binding moieties were separated by a 25-residue flexible linker. The resulting bispecific affinity molecule, from now on referred as Bi-EGFR, binds to the extracellular domain of human EGFR at two non-overlapping epitopes with an affinity (Kd) around 0.38 ± 0.07 nM (Fig. 1A), which is approximately 10-times higher than that of the monomeric EGFR-binding FN3 domain (FN3.EGFR: 3.1 ± 0.9 nM, Fig. 1B) or Z domain (AFF.EGFR: 3.2 ± 0.3 nM, Fig. 1C).

Figure 1. Bi-EGFR.amR-T cells and conventional EGFR.CAR-T cells show comparable activity.

Figure 1.

Open in a new tab

(A-C) Bio-layer Interferometry (BLI) was used to measure the affinity of the monomeric or heterodimeric single domain antibody mimics binding to recombinant Fc-EGFR on the FortéBio Octet system. 100 nM biotinylated antibody mimics were immobilized onto a streptavidin biosensor. Binding kinetics were measured against various concentrations of EGFR (0, 25, 50, 100 nM). The Kd was calculated based on kinetic fitting. (D) Representative expression of the Bi-EGFR.amR, EGFR.CAR or CD19.CAR in T cells as assessed by flow cytometry. Activated T cells were transduced with retroviral vectors encoding the Bi-EGFR.amR, EGFR.CAR or CD19.CAR. With the exception of the CD19.CAR, all constructs were detected using an anti-FLAG Ab. The CD19.CAR was detected using an anti-idiotype Ab. Shaded and unshaded histograms indicate non-transduced and specific mAb, respectively. (E) Summary of amR or CAR expression (n=4). (F) Expansion kinetics of Bi-EGFR.amR-T cells, EGFR.CAR-T cells or CD19.CAR-T cells NT (n=4); error bars denote SD (G) Phenotypic composition of Bi-EGFR.amR-T cells, EGFR.CAR-T cells or CD19.CAR-T cells 10 days post-transduction (n=4); error bars denote SD (H) Reducing immunoblots of Bi-EGFR.amR-T cell and EGFR.CAR-T cell lysates. Immunoblots were probed with anti-CD3ζ. Upper panel and lower panels represent detection of the receptors and endogenous ζ-chain, respectively. (I) EGFR.CAR-T cells and Bi-EGFR.amR-T cells were incubated at the indicated time points with the anti-FLAG Ab and cross-linked with a secondary Ab to induce the aggregation of the receptors. Cell lysates were immunoblotted to detect proximal (CD3ζ p-Y142) and distal (Akt p-S473 and ERK p-T202/204) phosphorylation events following receptor cross-linking. Total CAR.CD3ζ or amR.CD3ζ and endogenous CD3ζ were used as loading controls. Data are representative of 4 experiments.

Bi-EGFR.amR T cells resemble those expressing conventional EGFR-specific CAR.

To construct the CAR vector, the sequence of biochemically optimized Bi-EGFR was fused to the CD28 and CD3ζ-chain signaling domains via the CD8α hinge and transmembrane domains[21]. To detect the expression of the Bi-EGFR.amR in T cells (Bi-EGFR.amR-T cells) following transduction, we included a FLAG-tag into the Bi-EGFR.amR cassette (Supplementary Fig. S1). A conventional EGFR-specific CAR (EGFR.CAR) generated using the scFv derived from Cetuximab (Supplementary Fig. S1), and the CD19-specific CAR (CD19.CAR)[21] were used as controls. AmRs composed of either the EGFR-A binding moiety (FN3.EGFR.amR) or the EGFR-B binding moiety (AFF.EGFR.amR) alone were also constructed (Supplementary Fig. S1). Upon retroviral gene transfer, T cells stably expressed the Bi-EGFR.amR (Fig. 1D,E), expanded in vitro in response to exogenous cytokines (Fig. 1F), and maintained T cell composition comparable to EGFR.CAR-T cells and CD19.CAR-T cells (Fig. 1G). Western blot (WB) analysis of lysates from Bi-EGFR.amR-T cells detecting the CD3ζ chain under reducing conditions showed the native ζ-chain (17 kDa) and a band at the expected size of 55 kDa, indicating the integrity of the assembled Bi-EGFR.amR (Fig. 1H). We then analyzed proximal and distal signaling in EGFR.CAR-T cells and Bi-EGFR.amR-T cells upon receptor cross-linking. As shown in Fig. 1I, receptor cross-linking in both Bi-EGFR.amR-T cells and EGFR.CAR-T cells triggered similar phosphorylation of proximal (CD3ζ) and distal (Akt and ERK) signaling molecules.

Bi-EGFR.amR T cells demonstrate activity against tumor cells expressing EGFR.

To demonstrate that Bi-EGFR.amR-T cells specifically target EGFR, we used the EGFR– tumor cell line BV173 (BV173-WT) and transduced it to express EGFR (BV173-EGFR) with a retroviral vector encoding the full-length human EGFR (Supplementary Fig. S2A). We then co-cultured BV173-WT or BV173-EGFR cells with control non-transduced T cells (NTs), CD19.CAR-T cells, EGFR.CAR-T cells and Bi-EGFR.amR-T cells. NTs did not eliminate either BV173-WT or BV173-EGFR cells, CD19.CAR-T cells eliminated both cell types (Supplementary Fig. S2B, C), and Bi-EGFR.amR-T cells and EGFR.CAR-T cells only eliminated BV173-EGFR cells (Supplementary Fig. S2B, C), indicating the antigen specificity of the redirected T cells. Anti-tumor activity was then tested against tumor cell lines that physiologically express EGFR (Supplementary Fig. S2D). In co-culture experiments, Bi-EGFR.amR-T cells and EGFR.CAR-T cells demonstrated similar anti-tumor activity in vitro (Fig. 2A) and released comparable amounts of IFNγ (Fig. 2B) and IL-2 (Fig. 2C). Using a CFSE dilution assay, we demonstrated the proliferation of Bi-EGFR.amR-T cells in response to EGFR-expressing targets (Fig. 2D, E). Finally, we evaluated the anti-tumor activity of Bi-EGFR.amR-T cells in a metastatic model of EGFR-expressing pancreatic cancer in NSG mice (Fig. 2F). Bi-EGFR.amR-T cells and EGFR.CAR-T cells equally controlled human Panc-1 tumor cell growth as assessed by measurement of tumor bioluminescence intensity (Fig. 2G, H).

Figure 2. Bi-EGFR.amR-T cells show activity against EGFR-expressing tumor cells in vitro and in vivo.

Figure 2.

Open in a new tab

(A) Control T cells (NTs or CD19.CAR-T cells), Bi-EGFR.amR-T cells and EGFR.CAR-T cells were co-cultured with MCF-7 cells (EGFR negative) or EGFR-expressing pancreatic adenocarcinoma cell lines (AsPC-1, BxPC-3, HPAF-II and Panc-1) at 1:5 E:T. Cells were collected and quantified by flow cytometry on day 5. The frequency of residual tumor cells was identified as CD4−CD8− live cells (n=3–4), p<0.01 when Bi-EGFR.amR-T cells or EGFR.CAR-T cells are compared with control T cells; two-way ANOVA with Tukey correction (B) IFN-γ and (C) IL-2 released in the co-culture supernatant by Bi-EGFR.amR-T cells, EGFR.CAR-T cells and control T cells after 24 hours of co-culture with tumor cells as assessed by ELISA (n=3–4), p<0.01 when Bi-EGFR.amR-T cells or EGFR.CAR-T cells are compared with control T cells; two-way ANOVA with Tukey correction (D) Bi-EGFR.amR-T cells, EGFR.CAR-T cells or control T cells were labeled with CFSE and stimulated with irradiated EGFR-expressing AsPC-1 cells at 4:1 E:T. Representative CFSE dilution on day 5. (E) Proliferation index as assessed by CFSE dilution (n=4), p<0.01 when Bi-EGFR.amR-T cells or EGFR.CAR-T cells are compared with control T cells; two-way ANOVA with Tukey correction (F) Schematic representation of a metastatic pancreatic cancer model in NSG mice using the FFLuc-labeled human Panc-1 cell line. Representative images of tumor bioluminescence (BLI) (G) and kinetics (H) of tumor growth as assessed by BLI measurements. Data are representative of two independent experiments with 5 mice per group; p<0.01 when Bi-EGFR.amR-T cells or EGFR.CAR-T cells are compared with control T cells; two-way ANOVA with Tukey correction

Bi-EGFR.amR-T cells recognize two non-overlapping epitopes of EGFR.

AmRs composed of either the FN3.EGFR.amR or the AFF.EGFR.amR alone were transduced in T cells (Supplementary Fig. S3A). Both AFF.EGFR.amR-T cells and FN3.EGFR.amR-T cells showed comparable activity in vitro against tumor cells expressing the full length EGFR (Supplementary Fig. S3B–F) and proliferated in response to EGFR-expressing targets (Supplementary Fig. S3G, H). To demonstrate the bispecific feature of the Bi-EGFR, we analyzed the binding of Bi-EGFR and each of its monomeric domains using the recombinant extracellular domain of the wild-type EGFR (wtEGFR) and the EGFRvIII (EGFRvIII) mutant, a constitutively active and ligand-independent variant of EGFR with deletions in exons 2–7. We found that Bi-EGFR and Z domain-based AFF.EGFR bound both wtEGFR and EGFRvIII. However, FN3 domain-based FN3.EGFR bound to wtEGFR but not EGFRvIII (Supplementary Fig. S4A), suggesting that it recognizes an antigen encoded in the 267 AA that are absent in EGFRvIII. To assess recognition of the two different EGFR epitopes, we used the extracellular domain of wtEGFR and EGFRvIII mutant recombinant proteins. Control, AFF.EGFR.amR-T cells, FN3.EGFR.amR-T cells and Bi-EGFR.amR-T cells were seeded in tissue culture plates coated with either wtEGFR or EGFRvIII, and the CD69 expression and IFN-γ release by T cells were measured. Both wtEGFR and EGFRvIII recombinant proteins activated AFF.EGFR.amR-T cells and BiEGFR.amR-T cells, whereas only the wtEGFR protein activated FN3.EGFR.amR-T cells (Fig. 3A–C), indicating that the epitope recognized by the FN3.EGFR binding moiety is either located in the 267 AA region deleted in EGFRvIII, or the mutation has altered the epitope accessibility due to the deletion-induced conformational changes. In contrast, the AFF.EGFR binding moiety recognizes an epitope that is conserved between EGFR and EGFRvIII (Fig. 3A–C). To ensure that both AFF.EGFR and FN3.EGFR binding moieties can induce the activation of T cells when assembled into the Bi-EGFR.amR, we generated an AFF.EGFR.amR mutant-binding moiety (mAFF.EGFR.amR) in which critical residues at the EGFR-binding alpha helices were mutated to alanine to reduce binding to EGFR. As shown in Supplementary Fig. S4B, mAFF.EGFR.amR was expressed in T cells, but mAFF.EGFR.amR-T cells did not eliminate BV173-EGFR cells (Supplementary Fig. S4C,D), indicating that the mutations had abrogated binding to EGFR. However, T cells expressing a Bi-EGFR.amR constructed with the FN3.EGFR and mAFF.EGFR binding moieties (mBi-EGFR.amR) upregulated CD69 and released IFN-γ when seeded in wells coated with wtEGFR recombinant protein, but not in response to EGFRvIII protein, indicating that the FN3.EGFR binding moiety alone can induce T cell activation when the function of the other EGFR-binding moiety (AFF.EGFR) is abolished in the mBi-EGFR.amR (Fig. 3D–F).

Figure 3. Bi-EGFR.amR-T cells are activated by recognition of two non-overlapping epitopes on EGFR.

Figure 3.

Open in a new tab

Control (NTs), AFF.EGFR.amR-T cells, FN3.EGFR.amR-T cells and Bi-EGFR.amR-T cells were seeded in tissue culture plates coated with either recombinant human EGFR WT protein (rEGFR) or the truncated mutant EGFRvIII recombinant protein (rEGFRvIII). (A) Representative expression of CD69 on NTs, AFF.EGFR.amR-T cells, FN3.EGFR.amR-T cells and Bi-EGFR.amR-T cells 6 hours post-stimulation with plate-bound rEGFR or rEGFRvIII protein as assessed by flow cytometry. Shaded and dashed histograms indicate media and PMA/Iono controls, respectively. Solid and dashed lines indicate rEGFR and rEGFRvIII protein stimulation, respectively. (B) Summary of CD69 expression on total live T cells (n=4), p<0.01 when comparing FN3.EGFR.amR-T cells seeded in rEGFR and rEGFRvIII-coated wells; two-way ANOVA with Tukey correction. (C) IFN-γ released in the supernatant by AFF.EGFR.amR-T cells, FN3.EGFR.amR-T cells and Bi-EGFR.amR-T cells as assessed by ELISA (n=3), p<0.01 when comparing FN3.EGFR.amR-T cells seeded in rEGFR and rEGFRvIII-coated wells; two-way ANOVA with Tukey correction. (D) mAFF.EGFR.amR-T cells or mBi-EGFR.amR-T cells were co-cultured with BV173-WT or BV173-EGFR cells at 1:5 E:T for 3 days. CD19.CAR-T cells were used as a positive control. Cells were collected and T cells (CD3+) and tumor cells (CD19+) were quantified by flow cytometry. Representative flow plots are illustrated. (E) Quantification of BV173-WT or BV173-EGFR cells remaining after 3 days of co-culture. (F) IFN-γ released in the supernatant by NT, CD19.CAR-T, mAFF.EGFR.amR-T and mBi-EGFR.amR-T cells as assessed by ELISA (n=2–4), p<0.01 when comparing the percentage of residual BV173-WT and BV173-EGFR cells remaining in the mBi-EGFR.amR-T wells; two-way ANOVA with Tukey correction

Bispecific amR against HER2 demonstrates anti-tumor activity.

We also constructed an amR receptor against another member of the ErbB family of receptor tyrosine kinase, HER2, to demonstrate the applicability of this technology to other TAAs. Using a similar approach to the construction of Bi-EGFR, a tumor antigen binding moiety that targets two different epitopes of HER2 (Bi-HER2) was generated, which showed a HER2-binding affinity (Kd) around 0.25 ± 0.04 nM (Fig. 4A), compared to 1.8 ± 0.6 nM (Fig. 4B) of a HER2-binding DARPin[15] and 1.3 ± 0.4 nM of a HER2-binding Z domain[18] (Fig. 4C), respectively. Based on this HER2-binding ligand, a bispecific Bi-HER2.amR was constructed (Supplementary Fig. S5A). T cells stably expressed the Bi-HER2.amR (Bi-HER2.amR-T cells) upon retroviral transfer, expanded in vitro in response to exogenous cytokines (Supplementary Fig. S5B) and maintained T cell composition comparable to control T cells (Supplementary Fig. S5C). Bi-HER2.amR-T cells demonstrated targeting of HER2-expressing cells (Supplementary Fig. S5D–F). Furthermore, Bi-HER2.amR-T cells exhibited anti-tumor activity (Fig. 4D) and released IFNγ (Fig. 4E) and IL-2 (Fig. 4F) in a HER2-dependent manner when co-cultured with tumor cell lines expressing HER2, but not with HER2-negative cell lines (Supplementary Fig. S5D). We also evaluated the efficacy of Bi-HER2.amR-T cells in a metastatic tumor model of HER2-expressing human HPAF-II pancreatic cancer in NSG mice (Fig. 4G). Bi-HER2.amR-T cells and EGFR.CAR-T cells equally controlled tumor cell growth as assessed by measurement of tumor bioluminescence intensity (Fig. 4H,I).

Figure 4. Bi-HER2.amR-T cells have anti-tumor activity against HER2-expressing primary cells in vitro and in vivo.

Figure 4.

Open in a new tab

(A-C) Bio-layer Interferometry (BLI) was used to measure the affinity of the monomeric or heterodimeric single domain antibody mimics binding to recombinant Fc-HER2 using the FortéBio Octet system. 100 nM biotinylated antibody mimics were immobilized onto a streptavidin biosensor. Binding kinetics was measured against various concentrations of HER2 (0, 25, 50, 100 nM). The Kd was calculated based on kinetic fitting. (D) Control T (NT), Bi-HER2.amR-T cells and EGFR.CAR-T cells were co-cultured with Panc-1 cells (HER negative) or HER2-expressing pancreatic adenocarcinoma cell lines (AsPC-1 and HPAF-II) at 1:5 E:T. Cells were collected and quantified by flow cytometry on day 5. The frequency of residual tumor cells was identified as CD4− CD8− live cells (n=3–6), p<0.01 when comparing Bi-HER2.amR-T cells or EGFR.CAR-T cells with NTs; two-way ANOVA with Tukey correction (E) IFN-γ and (F) IL-2 released in the co-culture supernatant by NTs, Bi-HER2.amR-T cells or EGFR.CAR-T cells after 24 hours of co-culture with tumor cells as assessed by ELISA (n=3–6), p<0.01 when comparing Bi-HER2.amR-T cells or EGFR.CAR-T cells with NTs; two-way ANOVA with Tukey correction (G) Schematic representation of a metastatic pancreatic cancer model in NSG mice using the using the FFLuc-labeled human HPAF-II cell line. Representative images of tumor bioluminescence (BLI) (H) and kinetics (I) of tumor growth as assessed by BLI measurements. Data are representative of two independent experiments with 5 mice per group; p<0.01 when Bi-HER2.amR-T cells or EGFR.CAR-T cells are compared with NTs; two-way ANOVA with Tukey correction

Bispecific EGFR-HER2.amR-T cells target tumor cells expressing EGFR and HER2.

To generate amRs targeting two different TAAs, we integrated the EGFR specific FN3 binding moiety and the HER2 specific DARPin binding moiety and created the EGFR-HER2.amR with a 27-residue flexible linker between the two antigen-binding moieties (Supplementary Fig. S6A). T cells stably expressed the EGFR-HER2.amR (Supplementary Fig. S6B,C), expanded in vitro in response to exogenous cytokines (Supplementary Fig. S6D) and maintained T cell composition comparable to monospecific FN3.EGFR.amR-T cells and DARPin.HER2.amR-T cells (Supplementary Fig. S6E). To establish the bispecificity of EGFR-HER2.amR-T cells, we seeded control, FN3.EGFR.amR-T cells, DARPin.HER2.amR-T cells and EGFR-HER2.amR-T cells in tissue cultures plates coated with either the extracellular domain of rhEGFR or rhHER2 recombinant proteins and assessed CD69 expression and IFN-γ release by T cells. EGFR-HER2.amR-T cells expressed CD69 (Supplementary Fig. S6F) and secreted IFN-γ (Supplementary Fig. S6G) when seeded in wells coated with either rhEGFR or rhHER2 proteins, whereas FN3.EGFR.amR-T cells and DARPin.HER2.amR-T cells were only activated by rhEGFR and rhHER2, respectively. Next, we evaluated the functionality of EGFR-HER2.amR-T cells against BV173-WT, BV173-EGFR and BV173-HER2 cells (Supplementary Fig. S6H). We performed a series of co-cultures in which T cells were plated with respective BV173 target cells, and 3 days later T cells were collected and re-plated with the same BV173 tumor cell line or BV173 cells expressing a non-specific target (Fig 5A). As shown in Fig. 5B–D, FN3.EGFR.amR-T cells and DARPin.HER2.amR continued to eliminate only BV173-EGFR and BV173-HER2, respectively, whereas EGFR-HER2.amR-T cells eliminated both BV173-EGFR and BV173-HER2 targets in both the primary and secondary co-cultures. In order to demonstrate the bispecificity of the EGFR-HER2.amR-T cells in vivo, mice were engrafted with the EGFR+HER2− human Panc-1 cell line labeled with FF-Luc, and infused either with EGFR.amR-T cells or EGFR-HER2.amR-T cells. Tumor growth was equally controlled by both EGFR.amR-T cells and EGFR-HER2.amR-T cells (Fig. 5E–G). However, when these mice were re-challenged with the EGFR−HER2+ BV173 tumor cell line, EGFR.amR-T treated mice developed limb paresis due to growth of the BV173 tumor within the spinal cord, whereas EGFR-HER2.amR-T cell treated mice remained healthy (Fig. 5H).

Figure 5. EGFR-HER2.amR-T cells show dual specificity.

Figure 5.

Open in a new tab

Co-culture experiment in which T cells were plated with its respective BV173 target cells, and 3 days later T cells were collected and re-plated with the same BV173 tumor cell line or BV173 cells expressing the non-specific target. (A) Schema of the repetitive co-culture experiments with control (CD19.CAR-T cells), monospecific FN3.EGFR.amR-T cells, DARPin.HER2.amR-T cells and bispecific EGFR-HER2.amR-T cells all plated at 1:2 E:T. (B) Representative flow plots of the repetitive co-culture experiments on the second round. Cells were collected and quantified by flow cytometry on day 3. The frequency of residual tumor cells was identified as CD3−CD19+ live cells. (C) Quantification of tumor cells remaining after the second co-culture (n=2–3), p<0.01 when comparing FN3.EGFR.amR-T cells and DARPin.HER2.amR-T cells and their respective targets against WT tumor cells; two-way ANOVA with Tukey correction (D) IFN-γ released in the co-culture supernatant by CD19.CAR-T cells, FN3.EGFR.amR-T cells, DARPin.HER2-amR-T cells or EGFR-HER2.CAR-T cells after 24 hours of co-culture with tumor cells as assessed by ELISA (n=2–3), p<0.01 when comparing FN3.EGFR.amR-T cells and DARPin.HER2.amR-T cells and their respective targets against WT cells; two-way ANOVA with Tukey correction (E) Schematic representation of the re-challenge tumor model in NSG mice using the EGFR+HER2− human Panc-1 cell line labeled with the FF-Luc and the EGFR−HER2 human BV173-HER2 cell line. Representative images of the Pan-1 tumor BLI (F) and BLI kinetics (G) of tumor growth of one experiment 3 – 7 mice per group. (H) Kaplan-Meier survival curve of NSG mice after re-challenge with the BV173-HER2 cell line; p<0.01 when mice treated with EGFR.amR-T cells are compared with mice treated with EGFR-HER2.amR-T cells.

Discussion

The generation of multi-redirected CAR-T cells may be necessary to effectively eradicate tumors in which TAAs of interest can be lost or are heterogeneously expressed in tumor cells. Here we demonstrated that modular single domain antibody mimics are a practical alternative to the conventional scFvs to generate T cells with engineered multiple antigen-targeting features. We constructed antibody mimics that can be assembled with signaling molecules of the T cell receptor and costimulatory endodomains. We further demonstrated the functionality in vitro and in vivo of T cells expressing antibody mimics showing their ability to recognize simultaneously two epitopes of the same antigens or two distinct antigens.

In this proof-of-principle study, we have assessed whether single domain antibody mimics can be used to redirect the specificity of human T lymphocytes[30, 31]. We integrated single domain antibody mimics binding to the non-overlapping regions of EGFR to create a EGFR-binding ligand with bispecificity. We showed that T cells expressing the single domain AFF.EGFR.amR or FN3.EGFR.amR have comparable activity in vitro and in vivo to the conventional scFv-based Cetuximab EGFR.CAR. To further demonstrate the applicability of redirecting T cell specificity by using antibody mimics, we also validated the approach by targeting HER2 expressing tumors using a Bi-HER2 targeting ligand.

Targeting two epitopes of the same molecule may help prevent tumor escape when the targeted antigen can be expressed by alternative mRNA splicing, which may cause loss of a targeted epitope[6]. When the AFF.EGFR and FN3.EGFR were combined in one single amR cassette, we demonstrated that two epitopes of EGFR can be targeted without causing detrimental effects in T cells. Targeting two distinct antigens expressed by tumor cells remains challenging. We demonstrated that single domain antibody mimics can be assembled in one single cassette to efficiently target two different antigens. As a proof of principle, we showed that both EGFR and HER2 can be effectively targeted by dual-specific amRs neither with impairing targeting of each single antigen nor with detrimental effects of engineered T cells.

In summary, we provided proof of concept that antibody mimics can be used to generate combinatorial targeting of engineered T cells. Taking in consideration that antibody mimics are generated synthetically, our proposed approach can be adapted to a systematic screening of combinatorial antigens to be tested in human malignancies.

Supplementary Material

1

Acknowledgments

This work was partially supported by the R01CA157738 from NCI to RL, University Cancer Research Fund (UCRF) to GD, R01-CA193140–03 from NCI to GD, and innovation grants from the Eshelman Institute for Innovation RX03612118 and RX03712112 to RL. The UNC Imaging Core is supported in part by an NCI core grant (P30-CA016086–40). The UNC Flow Cytometry Core is supported in part by the North Carolina Biotech Center Institutional Support grant (2012-IDG-1006). We thank Dr. Ashutosh Tripathy for assistance in the biophysical analyses of the bispecific antigen receptors.

Footnotes

Conflict of Interest Statement: The authors have declared that no conflict of interest exists.

Reference List

  • [1].Eshhar Z, Waks T, Gross G, Schindler DG. Specific activation and targeting of cytotoxic lymphocytes through chimeric single chains consisting of antibody-binding domains and the gamma or zeta subunits of the immunoglobulin and T-cell receptors. Proc Natl Acad Sci U S A 1993;90:720–4. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [2].Dotti G, Gottschalk S, Savoldo B, Brenner MK. Design and development of therapies using chimeric antigen receptor-expressing T cells. Immunol Rev 2014;257:107–26. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [3].Sadelain M, Brentjens R, Riviere I. The basic principles of chimeric antigen receptor design. Cancer Discov 2013;3:388–98. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [4].Maude SL, Frey N, Shaw PA, et al. Chimeric antigen receptor T cells for sustained remissions in leukemia. N Engl J Med 2014;371:1507–17. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [5].Kochenderfer JN, Dudley ME, Kassim SH, et al. Chemotherapy-Refractory Diffuse Large B-Cell Lymphoma and Indolent B-Cell Malignancies Can Be Effectively Treated With Autologous T Cells Expressing an Anti-CD19 Chimeric Antigen Receptor. J Clin Oncol 2015;33:540–9. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [6].Sotillo E, Barrett DM, Black KL, et al. Convergence of Acquired Mutations and Alternative Splicing of CD19 Enables Resistance to CART-19 Immunotherapy. Cancer Discov 2015;5:1282–95. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [7].O’Rourke DM, Nasrallah MP, Desai A, et al. A single dose of peripherally infused EGFRvIII-directed CAR T cells mediates antigen loss and induces adaptive resistance in patients with recurrent glioblastoma. Sci Transl Med 2017;9. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [8].Grada Z, Hegde M, Byrd T, et al. TanCAR: A Novel Bispecific Chimeric Antigen Receptor for Cancer Immunotherapy. Mol Ther Nucleic Acids 2013;2:e105. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [9].Hegde M, Mukherjee M, Grada Z, et al. Tandem CAR T cells targeting HER2 and IL13Ralpha2 mitigate tumor antigen escape. J Clin Invest 2016;126:3036–52. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [10].Cotten SW, Zou J, Valencia CA, Liu R. Selection of proteins with desired properties from natural proteome libraries using mRNA display. Nat Protoc 2011;6:1163–82. [DOI] [PubMed] [Google Scholar]
  • [11].Koide A, Bailey CW, Huang X, Koide S. The fibronectin type III domain as a scaffold for novel binding proteins. J Mol Biol 1998;284:1141–51. [DOI] [PubMed] [Google Scholar]
  • [12].Nygren PA. Alternative binding proteins: affibody binding proteins developed from a small three-helix bundle scaffold. FEBS J 2008;275:2668–76. [DOI] [PubMed] [Google Scholar]
  • [13].Binz HK, Amstutz P, Pluckthun A. Engineering novel binding proteins from nonimmunoglobulin domains. Nat Biotechnol 2005;23:1257–68. [DOI] [PubMed] [Google Scholar]
  • [14].Binz HK, Pluckthun A. Engineered proteins as specific binding reagents. Curr Opin Biotechnol 2005;16:459–69. [DOI] [PubMed] [Google Scholar]
  • [15].Zahnd C, Pecorari F, Straumann N, Wyler E, Pluckthun A. Selection and characterization of Her2 binding-designed ankyrin repeat proteins. J Biol Chem 2006;281:35167–75. [DOI] [PubMed] [Google Scholar]
  • [16].Fellouse FA, Esaki K, Birtalan S, et al. High-throughput generation of synthetic antibodies from highly functional minimalist phage-displayed libraries. J Mol Biol 2007;373:924–40. [DOI] [PubMed] [Google Scholar]
  • [17].Friedman M, Orlova A, Johansson E, et al. Directed evolution to low nanomolar affinity of a tumor-targeting epidermal growth factor receptor-binding affibody molecule. J Mol Biol 2008;376:1388–402. [DOI] [PubMed] [Google Scholar]
  • [18].Orlova A, Magnusson M, Eriksson TL, et al. Tumor imaging using a picomolar affinity HER2 binding affibody molecule. Cancer Res 2006;66:4339–48. [DOI] [PubMed] [Google Scholar]
  • [19].Steiner D, Forrer P, Pluckthun A. Efficient selection of DARPins with sub-nanomolar affinities using SRP phage display. J Mol Biol 2008;382:1211–27. [DOI] [PubMed] [Google Scholar]
  • [20].Vazquez-Lombardi R, Phan TG, Zimmermann C, Lowe D, Jermutus L, Christ D. Challenges and opportunities for non-antibody scaffold drugs. Drug Discov Today 2015;20:1271–83. [DOI] [PubMed] [Google Scholar]
  • [21].Diaconu I, Ballard B, Zhang M, et al. Inducible Caspase-9 Selectively Modulates the Toxicities of CD19-Specific Chimeric Antigen Receptor-Modified T Cells. Mol Ther 2017;25:580–92. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [22].Dotti G, Savoldo B, Pule M, et al. Human cytotoxic T lymphocytes with reduced sensitivity to Fas-induced apoptosis. Blood 2005;105:4677–84. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [23].Kim D, Friedman AD, Liu R. Tetraspecific ligand for tumor-targeted delivery of nanomaterials. Biomaterials 2014;35:6026–36. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [24].Ramos CA, Ballard B, Zhang H, et al. Clinical and immunological responses after CD30-specific chimeric antigen receptor-redirected lymphocytes. J Clin Invest 2017;127:3462–71. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [25].Ramos CA, Savoldo B, Torrano V, et al. Clinical responses with T lymphocytes targeting malignancy-associated kappa light chains. J Clin Invest 2016;126:2588–96. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [26].Xu Y, Zhang M, Ramos CA, et al. Closely related T-memory stem cells correlate with in vivo expansion of CAR.CD19-T cells and are preserved by IL-7 and IL-15. Blood 2014;123:3750–9. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [27].Hoyos V, Savoldo B, Quintarelli C, et al. Engineering CD19-specific T lymphocytes with interleukin-15 and a suicide gene to enhance their anti-lymphoma/leukemia effects and safety. Leukemia 2010;24:1160–70. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [28].Vera JF, Hoyos V, Savoldo B, et al. Genetic manipulation of tumor-specific cytotoxic T lymphocytes to restore responsiveness to IL-7. Mol Ther 2009;17:880–8. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [29].Caruana I, Savoldo B, Hoyos V, et al. Heparanase promotes tumor infiltration and antitumor activity of CAR-redirected T lymphocytes. Nat Med 2015;21:524–9. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [30].Han X, Cinay GE, Zhao Y, Guo Y, Zhang X, Wang P. Adnectin-Based Design of Chimeric Antigen Receptor for T Cell Engineering. Mol Ther 2017;25:2466–76. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [31].Siegler E, Li S, Kim YJ, Wang P. Designed Ankyrin Repeat Proteins as Her2 Targeting Domains in Chimeric Antigen Receptor-Engineered T Cells. Hum Gene Ther 2017;28:726–36. [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.

Supplementary Materials

1
NIHMS1523393-supplement-1.pptx (1.1MB, pptx)

RESOURCES