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Journal of Virology logoLink to Journal of Virology
. 2010 Oct 27;85(1):644–648. doi: 10.1128/JVI.01851-10

R5 HIV env and Vesicular Stomatitis Virus G Protein Cooperate To Mediate Fusion to Naïve CD4+ T Cells

Matthew J Pace 1, Luis Agosto 1,, Una O'Doherty 1,*
PMCID: PMC3014180  PMID: 20980513

Abstract

Naïve CD44 T cells are resistant to both HIV R5 env and vesicular stomatitis virus G protein (VSV-G)-mediated fusion. However, viral particles carrying both HIV R5 env and VSV-G infect naïve cells by an unexplained mechanism. We show that VSV-G-pseudotyped virus cannot fuse to unstimulated cells because the viral particles cannot be endocytosed. However, virions carrying both HIV R5 env and VSV-G can fuse because CD4 binding allows viral uptake. Our findings reveal a unique mechanism by which R5 HIV env and VSV-G cooperate to allow entry to naïve CD4+ T cells, providing a tool to target naïve CD4+ T cells with R5 HIV to study HIV coreceptor signaling and latency.


Scientists commonly utilize pseudotyped virions, viruses surrounded with foreign envelope glycoproteins (17). Vesicular stomatitis virus G protein (VSV-G) is a commonly used envelope for pseudotyping particles in order to study HIV infection (9, 30, 32). The use of these particles created confusion in the field of resting CD4+ T cell infection. Studies utilizing VSV-G-pseudotyped particles indicated that resting CD4+ T cells could not be infected without prior activation (9, 12, 30). However, studies that used HIV env showed resting CD4+ T cells were susceptible (1, 29, 31). This discrepancy was resolved when we showed that VSV-G could not mediate fusion to these cells (2).

The inability of VSV-G to mediate fusion seemed to contradict our prior results. We previously showed that R5 HIV could not fuse to naïve CD4+ T cells; however, viral particles created by transfecting R5 HIV and VSV-G together could (7). Since neither R5 HIV env (7) nor VSV-G (2) can mediate fusion to naïve CD4+ T cells, we wanted to determine how viral particles created by transfecting R5 HIV and VSV-G plasmids were able to fuse to these cells.

Here, we demonstrate that double-pseudotyped (DP) particles expressing both R5 HIV env and VSV-G can exist and fuse to naïve CD4+ T cells. We then showed that these particles require CD4 binding and low pH to fuse but do not require HIV env-mediated fusion. Our findings suggest that R5 HIV env and VSV-G cooperate to allow fusion. R5 HIV env mediates internalization through CD4 binding, while VSV-G mediates fusion. We found that VSV-G alone could not mediate internalization.

We first determined whether DP particles or a mixture of R5 HIV and VSV-G singly pseudotyped particles fused to naïve cells. While many viral envelopes can colocalize to the same virion (6), some cannot (6, 22). Thus, we wanted to verify that DP particles exist in our system. To test this, we inoculated unstimulated CD4+ T cells with R5 HIV particles, particles singly pseudotyped with VSV-G, a mixture of these two viruses, and DP particles and measured fusion to memory and naïve CD4+ T cells by using the BlamVpr fusion assay as previously described (2). If only DP particles could mediate entry to naïve cells, then the mixture of singly pseudotyped particles would not fuse. All viruses were generated by calcium precipitation in 293T cells as previously described (2).

As expected, R5 HIV fused to memory CD4+ T cells but not naïve CD4+ T cells (Fig. 1). Additionally, VSV-G-pseudotyped particles were unable to fuse to either unstimulated memory CD4+ T cells or naïve CD4+ T cells, consistent with results previously reported in the literature (Fig. 1) (2, 12, 34). The mixture of singly pseudotyped particles did not fuse to naïve CD4+ T cells (Fig. 1). However, virus made by simultaneously transfecting cells with R5 HIV and VSV-G plasmids could fuse to naïve cells (Fig. 1). Together, these results show that particles expressing both HIV env and VSV-G were generated and that only these DP particles fused to naïve CD4+ T cells.

FIG. 1.

FIG. 1.

DP particles with R5 HIV env and VSV-G overcome a fusion restriction in naïve CD4+ T cells. A total of 5 × 105 unstimulated CD4+ T cells were spinoculated with 8 μg/ml Polybrene with viruses containing BlamVpr. R5 HIV was generated by transfecting pNLAD8 (13), and VSV-G-pseudotyped particles were generated by transfecting pNL4-3Δenv and pHIT as previously described (2). Double-pseudotyped (DP) particles were generated by transfecting pNLAD8 and pHIT. After spinoculation, cells were incubated for 1 h at 37°C to allow fusion. Cells were stained with anti-CD45RO Texas Red (Beckman Coulter) and anti-CCR7 PECy7 (BD Bioscience) to distinguish memory from naïve T cells. An uninfected control was used to set the gates in the infected samples. The numbers represent the percentages of cells in which fusion has occurred. All flow plots use a logarithmic scale. Representative fusion levels in one experiment are seen in panel A. The fusion levels of three separate experiments using three different donors are shown in panel B. The error bars represent the standard deviations of the measurements. The amount of virus added was based on late reverse transcripts found in CD3/CD28-activated CD4+ T cells after 24 h. FSC, forward scatter.

We next tested the mechanism by which DP particles fused to naïve CD4+ T cells. Because these cells express low levels of CCR5 (14, 21, 26), we questioned whether fusion of DP particles was CCR5 independent by inoculating CD4+ T cells from a Δ32 donor, whose cells lack CCR5 because of a 32-bp deletion within the CCR5 gene. DP particles fused to these cells (Fig. 2), indicating that fusion to naïve CD4+ T cells is CCR5 independent.

FIG. 2.

FIG. 2.

DP particles can fuse in a coreceptor-independent manner. A total of 5 × 105 CD4+ T cells from a Δ32 donor, whose cells do not express CCR5, were infected, and a fusion assay was performed as described for Fig. 1. CD4+ T cells were labeled with anti-CD3 allophycocyanin (APC) and anti-CD4 PerCpCy5.5 (BD Bioscience) to identify CD4+ T cells. Data were analyzed as described for Fig. 1. Representative fusion levels in one experiment are shown in panel A. The fusion levels of three separate experiments are shown in panel B. The error bars represent the standard deviations of the measurements. FSC, forward scatter.

We then wanted to determine which properties of R5 HIV env and VSV-G were required for fusion. Therefore, we tested the necessity of CD4 binding, HIV env-mediated fusion, and low endosomal pH. We first tested if CD4 binding was required by inoculating CD4+ T cells in the presence or absence of a CD4-blocking antibody. The antibody blocked fusion of both DP particles and the X4 HIV control (Fig. 3). This indicates that fusion of DP particles requires CD4 binding. We next tested if an HIV fusion inhibitor, T20, could block fusion of DP particles to naïve CD4+ T cells. Untreated infected cells and T20-treated X4 HIV were used as controls. While T20 was able to inhibit X4 HIV fusion, it did not inhibit fusion of DP particles (Fig. 3). Because T20 blocks HIV env-mediated fusion, these results indicate that DP particles do not require HIV env-mediated fusion to enter naïve cells and so rely on VSV-G to fuse. To confirm that VSV-G mediates fusion, we tested if low endosomal pH was required, since VSV-G is pH dependent (15, 16), while HIV env is pH independent (8, 24). After neutralizing endosomal pH by using 10 mM NH4Cl, we found that X4 HIV fusion was uninhibited, while DP particle fusion was blocked (Fig. 3). Thus, low pH is required for fusion of DP particles, confirming that VSV-G mediates fusion. These experiments were repeated in cells from a Δ32 donor and produced the same results (data not shown).

FIG. 3.

FIG. 3.

DP particles require CD4 binding and low pH but not HIV env-mediated fusion to fuse to naïve CD4+ T cells. A total of 5 × 105 unstimulated CD4+ T cells were left untreated, preincubated with 10 mM NH4Cl for 1 h at room temperature, preincubated with 25 μg/ml anti-CD4 clone 19 (Ron Collman) for 1 h at 4°C, or treated with 10 μg/ml T20 (AIDS Research and Reference Reagent Program) immediately before spinoculation. All cells were then spinoculated with 8 μg/ml Polybrene by using NL4-3, an X4-tropic HIV strain, or DP particles, and a BlamVpr fusion assay was performed as described for Fig. 1. X4 HIV was generated by transfecting pNL4-3 as previously described (2). Only fusion to naïve cells is shown. Numbers represent the mean fusion percentages relative to the values for untreated controls for three separate experiments using three different donors. Error bars represent the standard deviations of the measurements.

Since VSV-G mediates fusion of DP particles to naïve cells but cannot fuse to unstimulated CD4+ T cells (2), we wanted to determine if endocytosis of VSV-G pseudotyped particles was restricted in unstimulated CD4+ T cells. We therefore inoculated unstimulated CD4+ T cells with R5 HIV, VSV-G-pseudotyped particles, DP particles, and particles without any envelope (Δenv) to control for non-envelope-mediated internalization. Inoculations were performed at 4°C to prevent viral uptake, and the number of bound virions per cell was measured. Then, samples were either kept cold, which prevents viral uptake, or incubated at 37°C for 2 h, to allow uptake. Noninternalized particles in both samples were removed with a 4-h treatment with 10 mg/ml pronase at 4°C. In the cold sample, in which endocytosis had not occurred, the only cell-associated virions were external virions uncleaved by the pronase treatment. Therefore, the cold sample served as a control for background p24 levels associated with noninternalized particles. Viral uptake was quantified by subtracting the amount of p24 associated with the cold fraction from the amount associated with the warm fraction. Only R5 HIV and DP particles were endocytosed (Fig. 4). Neither the nonenveloped control nor the VSV-G-pseudotyped virus was internalized: the levels of cell-associated p24 were the same in the warm and cold fractions (Fig. 4 and data not shown). This VSV-G-mediated internalization restriction cannot be explained by binding differences, since the amounts of binding among the viruses were comparable (Fig. 4). This indicates that endocytosis is a major entry restriction for VSV-G in unstimulated CD4+ T cells, but double pseudotyping with HIV env can overcome this restriction.

FIG. 4.

FIG. 4.

There is a VSV-G-mediated endocytosis restriction in unstimulated CD4+ T cells. A total of 4 × 106 unstimulated CD4+ T cells were spinoculated with R5 HIV, DP particles, VSV-G-pseudotyped particles (VSV-G), and particles with no envelope (generated by transfecting with pNL4-3Δenv) at 4°C. After unbound virions were washed away, samples were collected as follows. Half of the remaining cells were placed on ice and treated with 10 mg/ml pronase (Roche) to remove noninternalized virions (referred to as the cold sample). The other half of the cells were incubated at 37°C for 2 h to allow viral uptake (referred to as the warm sample). After the warm sample was incubated for 2 h, the cells were treated with pronase. Virions still associated with the cells after pronase treatments in both cold and warm samples were measured via a p24 enzyme-linked immunosorbent assay (ELISA). The amount of internalized virions was then calculated by subtracting the amount of p24 associated with the cold fraction from the amount of p24 associated with the warm fraction. The amount of p24 was then converted to virions/cell as previously described (27). The graph reflects three different inoculations with different donors. The error bars represent the standard deviations of the measurements.

In this study, we clarify apparent discrepancies in the literature (2, 7) by revealing a unique mechanism by which R5 HIV env and VSV-G cooperate to allow fusion to naïve CD4+ T cells, while neither envelope alone can (Fig. 1). Fusion of DP particles was dependent on CD4 binding and low endosomal pH but not on HIV env-mediated fusion (Fig. 3). These results indicate a mechanism by which CD4 binding leads to endocytosis of DP particles into a low-pH compartment where VSV-G mediates fusion. This entry mechanism is similar to that of a modified Sindbis virus envelope recently described (23). CD4-mediated endocytosis mediated by R5 HIV env binding is also consistent with recent literature showing the importance of endocytosis for HIV entry (25). Our results differ from those describing another mechanism showing that a fusion-defective VSV-G stem along with HIV env could mediate fusion in an HIV coreceptor-independent manner while still relying on HIV env-mediated fusion (15).

The DP particle fusion mechanism led us to test the restriction of VSV-G entry in unstimulated CD4+ T cells. Our prior work showed that VSV-G-pseudotyped particles could not fuse to unstimulated CD4+ T cells (2). Because VSV-G can mediate fusion in DP particles, endocytosis of VSV-G seemed a likely restriction. We therefore tested the ability of CD4+ T cells to internalize VSV-G-pseudotyped particles. VSV-G-pseudotyped particles were not internalized into unstimulated CD4+ T cells, while both R5 HIV and DP particles were internalized (Fig. 4). There were similar levels of uptake of R5 HIV and DP particles, since both can enter all CD4+ T cells via CD4-mediated endocytosis. The endocytosis restriction of VSV-G-pseudotyped particles could not be explained by lack of binding or detection limits (data not shown). Our results differ from those of a recent report showing similar levels of uptake of HIV and VSV-G-pseudotyped virus in resting CD4+ T cells (34). These differences could be explained by external virions contributing to the endocytosis levels seen by Yu et al. due to inefficiently cleaved, external virus (34). We found that a longer and more concentrated enzyme treatment with several enzymes was needed to remove external virions. We also found that it was critically important to include a cold control to compensate for external, uncleaved virions. Our results suggest important differences in the cell biology and endocytosis properties of resting and activated CD4+ T cells consistent with previous literature (11).

Our data also provide a useful, practical tool for studying HIV infection. In vitro models of HIV latency would be improved if R5 viruses were utilized, particularly since these viruses are responsible for transmission (19). Many protocols studying HIV latency in memory cells include an activation step, which lowers levels of CCR5 (5), preventing efficient infection using R5 HIV. However, DP particles could deliver R5 HIV to cells with low CCR5 levels, including naïve cells, so that latency models could be generated using R5 HIV.

Additionally, our data shed light on coreceptor signaling in HIV. While coreceptor signaling is not needed for infection of activated T cells (3, 4, 10), some studies suggest it is important (20), particularly in resting cells (33). DP particles provide the perfect tool to study coreceptor signaling, since they can fuse in a coreceptor-independent manner while still signaling through CD4. Our current data suggest that coreceptor signaling is not required for resting CD4+ T cell infection, since DP particles result in similar levels of infection in memory and naïve cells (7) and thus in the presence and absence of coreceptor signaling.

Our results appear to disagree with data from Yoder et al. (33) that suggest that CXCR4 signaling is required for resting CD4+ T cell infection. One possibility is that although CXCR4 signaling enhances infection, it is not required. Another possibility is that the use of VSV-G and endocytosis by DP particles bypasses the CXCR4 signaling requirement. Finally, we use an CCR5-tropic HIV, which may have different signaling requirements than the X4 virus used by Yoder et al. (33).

Overall, our data emphasize how the fusion capabilities of viral envelopes as well as the biological properties of the target cell affect viral entry. In the case of HIV, not understanding the fusion properties of viral envelopes led to contradictory results in the study of resting CD4+ T cell infection (18, 28-31). Our studies also identify an important difference between the biologies of resting and activated CD4+ T cells which impacts viral infection.

Acknowledgments

We acknowledge Drew Weissman, Paul Bates, Stuart Isaacs, and Robert Doms for consultation, experimental suggestions, and reviewing the manuscript. We also thank Gabi Plesa, Erin Graf, and Angela Mexas for reading the manuscript. We thank the University of Pennsylvania Immunology Core for providing unstimulated CD4+ T cells as well as Farida Shaheen and the Penn-CFAR Immunology and Molecular Cores for p24 testing.

This work was supported by the NIH grants R21 AI081215-02, KO2AIO78766-03, and T32 AI00762.

Footnotes

Published ahead of print on 27 October 2010.

REFERENCES

  • 1.Agosto, L. M., J. J. Yu, J. Dai, R. Kaletsky, D. Monie, and U. O'Doherty. 2007. HIV-1 integrates into resting CD4+ T cells even at low inoculums as demonstrated with an improved assay for HIV-1 integration. Virology 368:60-72. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 2.Agosto, L. M., J. J. Yu, M. K. Liszewski, C. Baytop, N. Korokhov, L. M. Humeau, and U. O'Doherty. 2009. The CXCR4-tropic human immunodeficiency virus envelope promotes more-efficient gene delivery to resting CD4+ T cells than the vesicular stomatitis virus glycoprotein G envelope. J. Virol. 83:8153-8162. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 3.Amara, A., A. Vidy, G. Boulla, K. Mollier, J. Garcia-Perez, J. Alcami, C. Blanpain, M. Parmentier, J. L. Virelizier, P. Charneau, and F. Arenzana-Seisdedos. 2003. G protein-dependent CCR5 signaling is not required for efficient infection of primary T lymphocytes and macrophages by R5 human immunodeficiency virus type 1 isolates. J. Virol. 77:2550-2558. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 4.Atchison, R. E., J. Gosling, F. S. Monteclaro, C. Franci, L. Digilio, I. F. Charo, and M. A. Goldsmith. 1996. Multiple extracellular elements of CCR5 and HIV-1 entry: dissociation from response to chemokines. Science 274:1924-1926. [DOI] [PubMed] [Google Scholar]
  • 5.Bosque, A., and V. Planelles. 2009. Induction of HIV-1 latency and reactivation in primary memory CD4+ T cells. Blood 113:58-65. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 6.Briggs, J. A., T. Wilk, and S. D. Fuller. 2003. Do lipid rafts mediate virus assembly and pseudotyping? J. Gen. Virol. 84:757-768. [DOI] [PubMed] [Google Scholar]
  • 7.Dai, J., L. M. Agosto, C. Baytop, J. J. Yu, M. J. Pace, M. K. Liszewski, and U. O'Doherty. 2009. Human immunodeficiency virus integrates directly into naive resting CD4+ T cells but enters naive cells less efficiently than memory cells. J. Virol. 83:4528-4537. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 8.Doms, R. W., and J. P. Moore. 2000. HIV-1 membrane fusion: targets of opportunity. J. Cell Biol. 151:F9-F14. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 9.Ducrey-Rundquist, O., M. Guyader, and D. Trono. 2002. Modalities of interleukin-7-induced human immunodeficiency virus permissiveness in quiescent T lymphocytes. J. Virol. 76:9103-9111. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 10.Farzan, M., H. Choe, K. A. Martin, Y. Sun, M. Sidelko, C. R. Mackay, N. P. Gerard, J. Sodroski, and C. Gerard. 1997. HIV-1 entry and macrophage inflammatory protein-1beta-mediated signaling are independent functions of the chemokine receptor CCR5. J. Biol. Chem. 272:6854-6857. [DOI] [PubMed] [Google Scholar]
  • 11.Fomina, A. F., T. J. Deerinck, M. H. Ellisman, and M. D. Cahalan. 2003. Regulation of membrane trafficking and subcellular organization of endocytic compartments revealed with FM1-43 in resting and activated human T cells. Exp. Cell Res. 291:150-166. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 12.Frecha, C., C. Costa, D. Negre, E. Gauthier, S. J. Russell, F. L. Cosset, and E. Verhoeyen. 2008. Stable transduction of quiescent T-cells without induction of cycle progression by a novel lentiviral vector pseudotyped with measles virus glycoproteins. Blood 112:4843-4852. [DOI] [PubMed] [Google Scholar]
  • 13.Freed, E. O., G. Englund, and M. A. Martin. 1995. Role of the basic domain of human immunodeficiency virus type 1 matrix in macrophage infection. J. Virol. 69:3949-3954. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 14.Groot, F., T. M. van Capel, J. Schuitemaker, B. Berkhout, and E. C. de Jong. 2006. Differential susceptibility of naive, central memory and effector memory T cells to dendritic cell-mediated HIV-1 transmission. Retrovirology 3:52. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 15.Jeetendra, E., C. S. Robison, L. M. Albritton, and M. A. Whitt. 2002. The membrane-proximal domain of vesicular stomatitis virus G protein functions as a membrane fusion potentiator and can induce hemifusion. J. Virol. 76:12300-12311. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 16.Johannsdottir, H. K., R. Mancini, J. Kartenbeck, L. Amato, and A. Helenius. 2009. Host cell factors and functions involved in vesicular stomatitis virus entry. J. Virol. 83:440-453. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 17.Jorgenson, R. L., V. M. Vogt, and M. C. Johnson. 2009. Foreign glycoproteins can be actively recruited to virus assembly sites during pseudotyping. J. Virol. 83:4060-4067. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 18.Kamata, M., Y. Nagaoka, and I. S. Chen. 2009. Reassessing the role of APOBEC3G in human immunodeficiency virus type 1 infection of quiescent CD4+ T-cells. PLoS Pathog. 5:e1000342. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 19.Keele, B. F., E. E. Giorgi, J. F. Salazar-Gonzalez, J. M. Decker, K. T. Pham, M. G. Salazar, C. Sun, T. Grayson, S. Wang, H. Li, X. Wei, C. Jiang, J. L. Kirchherr, F. Gao, J. A. Anderson, L. H. Ping, R. Swanstrom, G. D. Tomaras, W. A. Blattner, P. A. Goepfert, J. M. Kilby, M. S. Saag, E. L. Delwart, M. P. Busch, M. S. Cohen, D. C. Montefiori, B. F. Haynes, B. Gaschen, G. S. Athreya, H. Y. Lee, N. Wood, C. Seoighe, A. S. Perelson, T. Bhattacharya, B. T. Korber, B. H. Hahn, and G. M. Shaw. 2008. Identification and characterization of transmitted and early founder virus envelopes in primary HIV-1 infection. Proc. Natl. Acad. Sci. U. S. A. 105:7552-7557. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 20.Kinter, A., A. Catanzaro, J. Monaco, M. Ruiz, J. Justement, S. Moir, J. Arthos, A. Oliva, L. Ehler, S. Mizell, R. Jackson, M. Ostrowski, J. Hoxie, R. Offord, and A. S. Fauci. 1998. CC-chemokines enhance the replication of T-tropic strains of HIV-1 in CD4(+) T cells: role of signal transduction. Proc. Natl. Acad. Sci. U. S. A. 95:11880-11885. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 21.Lee, B., M. Sharron, L. J. Montaner, D. Weissman, and R. W. Doms. 1999. Quantification of CD4, CCR5, and CXCR4 levels on lymphocyte subsets, dendritic cells, and differentially conditioned monocyte-derived macrophages. Proc. Natl. Acad. Sci. U. S. A. 96:5215-5220. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 22.Leung, K., J. O. Kim, L. Ganesh, J. Kabat, O. Schwartz, and G. J. Nabel. 2008. HIV-1 assembly: viral glycoproteins segregate quantally to lipid rafts that associate individually with HIV-1 capsids and virions. Cell Host Microbe 3:285-292. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 23.Liang, M., K. Morizono, N. Pariente, M. Kamata, B. Lee, and I. S. Chen. 2009. Targeted transduction via CD4 by a lentiviral vector uses a clathrin-mediated entry pathway. J. Virol. 83:13026-13031. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 24.Marsh, M., and A. Helenius. 2006. Virus entry: open sesame. Cell 124:729-740. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 25.Miyauchi, K., Y. Kim, O. Latinovic, V. Morozov, and G. B. Melikyan. 2009. HIV enters cells via endocytosis and dynamin-dependent fusion with endosomes. Cell 137:433-444. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 26.Mo, H., S. Monard, H. Pollack, J. Ip, G. Rochford, L. Wu, J. Hoxie, W. Borkowsky, D. D. Ho, and J. P. Moore. 1998. Expression patterns of the HIV type 1 coreceptors CCR5 and CXCR4 on CD4+ T cells and monocytes from cord and adult blood. AIDS Res. Hum. Retroviruses 14:607-617. [DOI] [PubMed] [Google Scholar]
  • 27.O'Doherty, U., W. J. Swiggard, and M. H. Malim. 2000. Human immunodeficiency virus type 1 spinoculation enhances infection through virus binding. J. Virol. 74:10074-10080. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 28.Spina, C. A., J. C. Guatelli, and D. D. Richman. 1995. Establishment of a stable, inducible form of human immunodeficiency virus type 1 DNA in quiescent CD4 lymphocytes in vitro. J. Virol. 69:2877-2988. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 29.Swiggard, W. J., C. Baytop, J. J. Yu, J. Dai, C. Li, R. Schretzenmair, T. Theodosopoulos, and U. O'Doherty. 2005. Human immunodeficiency virus type 1 can establish latent infection in resting CD4+ T cells in the absence of activating stimuli. J. Virol. 79:14179-14188. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 30.Unutmaz, D., V. N. KewalRamani, S. Marmon, and D. R. Littman. 1999. Cytokine signals are sufficient for HIV-1 infection of resting human T lymphocytes. J. Exp. Med. 189:1735-1746. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 31.Vatakis, D. N., G. Bristol, T. A. Wilkinson, S. A. Chow, and J. A. Zack. 2007. Immediate activation fails to rescue efficient human immunodeficiency virus replication in quiescent CD4+ T cells. J. Virol. 81:3574-3582. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 32.Verhoeyen, E., V. Dardalhon, O. Ducrey-Rundquist, D. Trono, N. Taylor, and F. L. Cosset. 2003. IL-7 surface-engineered lentiviral vectors promote survival and efficient gene transfer in resting primary T lymphocytes. Blood 101:2167-2174. [DOI] [PubMed] [Google Scholar]
  • 33.Yoder, A., D. Yu, L. Dong, S. R. Iyer, X. Xu, J. Kelly, J. Liu, W. Wang, P. J. Vorster, L. Agulto, D. A. Stephany, J. N. Cooper, J. W. Marsh, and Y. Wu. 2008. HIV envelope-CXCR4 signaling activates cofilin to overcome cortical actin restriction in resting CD4 T cells. Cell 134:782-792. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 34.Yu, D., W. Wang, A. Yoder, M. Spear, and Y. Wu. 2009. The HIV envelope but not VSV glycoprotein is capable of mediating HIV latent infection of resting CD4 T cells. PLoS Pathog. 5:e1000633. [DOI] [PMC free article] [PubMed] [Google Scholar]

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