Species-specific differences in the expression and regulation of α4ß7 integrin in various nonhuman primates.

Among nonhuman primates, SIV-infected Asian pigtailed macaques (PM) are relatively more susceptible to infection and disease progression than SIV-infected rhesus macaques (RM). In addition, SIV-infected African natural hosts such as the sooty mangabeys (SM) are resistant to disease. The mechanisms associated with such species-related variable clinical outcomes remain ill-defined but hold the potential to provide insights into the underlying mechanisms surrounding HIV pathogenesis. Recent findings indicate that the expression of the heterodimeric gut homing integrin α4ß7 can influence both susceptibility and disease progression in RM. It was reasoned that differences in the frequencies/surface densities of α4ß7-expressing lymphocytes might contribute to the differences in the clinical outcome of SIV infection among NHPs. In this article, we report that CD4(+) T cells from PM constitutively express significantly higher levels of α4ß7 than RM or SM. Retinoic acid, a key regulator of α4ß7 expression, was paradoxically found at higher levels in the plasma of SM versus RM or PM. We also observed pairing of ß7 with αE (αEß7) on CD4(+) T cells in the peripheral blood of SM, but not PM or RM. Finally, the differential mean density of expression of α4ß7 in RM versus SM versus PM was predominantly dictated by species-specific sequence differences at the level of the ß7 promoters, as determined by in vitro reporter/promoter construct transfection studies. We propose that differences in the regulation and expression of α4ß7 may explain, in part, the differences in susceptibility and SIV disease progression in these NHP models.

In vivo administration of a JAK3 inhibitor during acute SIV infection leads to significant increases in viral load during chronic infection.

The studies reported herein are the first to document the effect of the in vivo administration of a JAK3 inhibitor for defining the potential role of NK cells during acute SIV infection of a group of 15 rhesus macaques (RM). An additional group of 16 MHC/KIR typed RM was included as controls. The previously optimized in vivo dose regimen (20 mg/kg daily for 35 days) led to a marked depletion of each of the major NK cell subsets both in the blood and gastro-intestinal tissues (GIT) during acute infection. While such depletion had no detectable effects on plasma viral loads during acute infection, there was a significant sustained increase in plasma viral loads during chronic infection. While the potential mechanisms that lead to such increased plasma viral loads during chronic infection remain unclear, several correlates were documented. Thus, during acute infection, the administration of the JAK3 inhibitor besides depleting all NK cell subsets also decreased some CD8⁺ T cells and inhibited the mobilization of the plasmacytoid dendritic cells in the blood and their localization to the GIT. Of interest is the finding that the administration of the JAK3 inhibitor during acute infection also resulted in the sustained maintenance during chronic infection of a high number of naïve and central memory CD4⁺ T cells, increases in B cells in the blood, but decreases in the frequencies and function of NKG2a⁺ NK cells within the GIT and blood, respectively. These data identify a unique role for JAK3 inhibitor sensitive cells, that includes NK cells during acute infection that in concert lead to high viral loads in SIV infected RM during chronic infection without affecting detectable changes in antiviral humoral/cellular responses. Identifying the precise mechanisms by which JAK3 sensitive cells exert their influence is critical with important implications for vaccine design against lentiviruses.

Blocking of α4ß7 gut-homing integrin during acute infection leads to decreased plasma and gastrointestinal tissue viral loads in simian immunodeficiency virus-infected rhesus macaques.

Intravenous administration of a novel recombinant rhesus mAb against the α4ß7 gut-homing integrin (mAb) into rhesus macaques just prior to and during acute SIV infection resulted in significant decrease in plasma and gastrointestinal (GI) tissue viral load and a marked reduction in GI tissue proviral DNA load as compared with control SIV-infected rhesus macaques. This mAb administration was associated with increases in peripheral blood naive and central memory CD4(+) T cells and maintenance of a high frequency of CCR5(+)CD4(+) T cells. Additionally, such mAb administration inhibited the mobilization of NK cells and plasmacytoid dendritic cells characteristically seen in the control animals during acute infection accompanied by the inhibition of the synthesis of MIP-3α by the gut tissues. These data in concert suggest that blocking of GI trafficking CD4(+) T cells and inhibiting the mobilization of cell lineages of the innate immune system may be a powerful new tool to protect GI tissues and modulate acute lentiviral infection.

Incorporation of innate immune effector mechanisms in the formulation of a vaccine against HIV-1.

The realization of a major role for events that occur during acute viremia that dictate the course of disease both in HIV-1 infected humans and susceptible SIV infected non-human primates has prompted an intense interest in studies of the contribution of innate immune effector mechanisms. It is reasoned that findings from such studies may be important and need to be incorporated into the design and formulation of potential candidate vaccines against HIV-1. This review serves to outline the various non-human primate models that can best serve to address this issue, a summary of our knowledge on the various subsets of NK cells (one of the major innate immune cell lineage) that have an impact on the course of disease, the potential pathways that regulate their function and the potential role of the KIRs on SIV-induced disease course. Finally, the major points from this report and the data presented on similar subjects by other investigators is utilized to provide a summary of the potential future directions that we need to take in efforts to move this field forward.

Distinct host cell proteins incorporated by SIV replicating in CD4+ T cells from natural disease resistant versus non-natural disease susceptible hosts.

BACKGROUND: Enveloped viruses including the simian immunodeficiency virus (SIV) replicating within host cells acquire host proteins upon egress from the host cells. A number of studies have catalogued such host proteins, and a few have documented the potential positive and negative biological functions of such host proteins. The studies conducted herein utilized proteomic analysis to identify differences in the spectrum of host proteins acquired by a single source of SIV replicating within CD4+ T cells from disease resistant sooty mangabeys and disease susceptible rhesus macaques. RESULTS: While a total of 202 host derived proteins were present in viral preparations from CD4+ T cells from both species, there were 4 host-derived proteins that consistently and uniquely associated with SIV replicating within CD4+ T cells from rhesus macaques but not sooty mangabeys; and, similarly, 28 host-derived proteins that uniquely associated with SIV replicating within CD4+ T cells from sooty mangabeys, but not rhesus macaques. Of interest was the finding that of the 4 proteins uniquely present in SIV preparations from rhesus macaques was a 26 S protease subunit 7 (MSS1) that was shown to enhance HIV-1 'tat' mediated transactivation. Among the 28 proteins found in SIV preparations from sooty mangabeys included several molecules associated with immune function such as CD2, CD3ε, TLR4, TLR9 and TNFR and a bioactive form of IL-13. CONCLUSIONS: The finding of 4 host proteins that are uniquely associated with SIV replicating within CD4+ T cells from disease susceptible rhesus macaques and 28 host proteins that are uniquely associated with SIV replicating within CD4+ T cells from disease resistant sooty mangabeys provide the foundation for determining the potential role of each of these unique host-derived proteins in contributing to the polarized clinical outcome in these 2 species of nonhuman primates.

Soluble PD-1 rescues the proliferative response of simian immunodeficiency virus-specific CD4 and CD8 T cells during chronic infection.

Phenotypic and functional studies of the programmed death-1 (PD-1) molecule on CD4(+) and CD8(+) T cells were performed on peripheral blood mononuclear cells from uninfected and simian immunodeficiency virus (SIV)-infected rhesus macaques. These data demonstrated a rapid upregulation of PD-1 expression on tetramer-positive CD8(+) T cells from MamuA.01(+) SIV-infected macaques upon infection. Upregulation of PD-1 on total CD8(+) T cells was not detectable. In contrast, CD4(+) T-cell PD-1 expression was markedly higher in total CD4(+) T cells during chronic, but not acute, infection and there was a correlation between the level of PD-1 expression on naive and central memory CD4(+) T cells and the levels of viral loads. Such association was emphasized further by a marked decrease of PD-1 expression on tetramer-positive CD8 T cells as well as on CD4(+) T cells on longitudinal samples collected before and after the initiation of antiretroviral therapy and downregulation of viral replication in vivo. Cloning of PD-1 and its two ligands from several non-human primate species demonstrated > 95% conservation for PD-1 and PD-L2 and only about 91% homology for PD-L1. Functional studies using soluble recombinant PD-1 protein or PD-1-immunoglobulin G fusion proteins induced marked increases in the SIV-specific proliferative responses of both CD4(+) and CD8(+) T cells from rhesus macaques. The results of these studies serve as a foundation for future in vivo trials of the use of rMamu-PD-1 to potentially enhance and/or restore antiviral immune responses in vivo.

Delipidated retroviruses as potential autologous therapeutic vaccines--a pilot experiment.

This pilot experiment in a simian immunodeficiency virus (SIV) chronic infection model aimed at extending our previous findings that vaccination with delipidated SIV resulted in more potent and diversified antiviral responses (1). Macaques chronically infected with SIVmac239 treated with antiretroviral therapy (ART) were vaccinated with autologous delipidated virus via consecutive lymph node targeted immunizations-1, 1 and 10 mug of virus spaced monthly. Results showed all animals had lasting viral load reduction approaching 1 log compared to set-point, and disease delay. Delipidation may enhance processing/ presentation of viral antigen eliciting potent antiviral control even at such late infection stage.

Central memory CD4 T cells are the predominant cell subset resistant to anergy in SIV disease resistant sooty mangabeys.

OBJECTIVE: HIV infection in humans and experimental SIV infection in rhesus macaques leads to the loss of recall antigen responses, immunological anergy in CD4 T cells and AIDS. In contrast, natural infection in sooty mangabeys with SIV does not lead to disease despite high viral loads accompanied by resistance of their CD4 T cells to undergo immunological anergy. The objective of the study was to further elucidate the mechanisms that contribute to anergy resistance in CD4 T cells from sooty mangabeys and identify whether the anergy resistance is a function of a specific subset or the entire cell population. MATERIALS AND METHODS: Susceptibility or resistance to anergy was analyzed in antigen specific and defined CD4 T cell subsets from peripheral blood of sooty mangabeys and rhesus macaques by using an in vitro anergy inducing protocol; expression of the anergy associated gene GRAIL was measured. RESULTS: Antigen specific CD4 T cells from SIV disease resistant sooty mangabey are relatively resistant to the development of anergy. This resistance is associated with a lack of an upregulation of GRAIL. Conversely, rhesus macaque CD4 T cells are sensitive to anergy induction associated with upregulation of GRAIL. Furthermore the anergy resistant phenotype of sooty mangabey CD4 T cells predominantly resides in central memory cells defined either as CD4+CD45RA-CD62L+ or CD4+CD28+CD95+CCR7+. CONCLUSIONS: The maintenance of recall responses in sooty mangabeys is associated with the resistance of central memory CD4 T cells to the induction of anergy which may represent an important mechanism underlying SIV disease resistance in this species.

Sustained virologic control in SIV+ macaques after antiretroviral and α4ß7 antibody therapy.

Antiretroviral drug therapy (ART) effectively suppresses replication of both the immunodeficiency viruses, human (HIV) and simian (SIV); however, virus rebounds soon after ART is withdrawn. SIV-infected monkeys were treated with a 90-day course of ART initiated at 5 weeks post infection followed at 9 weeks post infection by infusions of a primatized monoclonal antibody against the α4ß7 integrin administered every 3 weeks until week 32. These animals subsequently maintained low to undetectable viral loads and normal CD4+ T cell counts in plasma and gastrointestinal tissues for more than 9 months, even after all treatment was withdrawn. This combination therapy allows macaques to effectively control viremia and reconstitute their immune systems without a need for further therapy.

Phenotypic and Functional Characterization of Monoclonal Antibodies with Specificity for Rhesus Macaque CD200, CD200R and Mincle.

Lectin-like molecules and their receptors are cell surface molecules that have been shown to play a role in either facilitating infection or serving as transporters of HIV/SIV in vivo. The role of these lectin-like molecules in the pathogenesis of HIV/SIV infection continues to be defined. In efforts to gain further insight on the potential role of these lectin-like molecules, our laboratory generated monoclonal antibodies (mAb) against the human analogs of rhesus macaque CD200, CD200R and Mincle, since the rhesus macaques are accepted as the most reliable animal model to study human HIV infection. The characterization of the cell lineages from the blood and various tissues of rhesus macaques that express these lectin-like molecules are described herein. Among the mononuclear cells, the cells of the myeloid lineage of rhesus macaques are the predominant cell lineages that express readily detectable levels of CD200, CD200R and Mincle that is similar to the expression of Siglec-1 and Siglec-3 reported by our laboratory earlier. Subset analysis revealed that a higher frequency of the CD14+/CD16- subset from normal rhesus macaques express CD200, CD200R and Mincle. Differences in the frequencies and density of expression of these molecules by the gated population of CD14+ cells from various tissues are noted with PBMC and bone marrow expressing the highest and the mononuclear cells isolated from the colon and ileum expressing the lowest levels. While a significant frequency of pDCs and mDCs express Siglec-1/Siglec-3, a much lower frequency expresses CD200, CD200R and Mincle in PBMCs from rhesus macaques. The mAb against CD200 and CD200R but not Mincle appear to inhibit the infection of macrophage tropic SIV/SHIV in vitro. We conclude that these mAbs may have potential to be used as adjunctive therapeutic agents to control/inhibit SIV/HIV infection.

Use of recombinant cytokines for optimized induction of antiviral immunity against SIV in the nonhuman primate model of human AIDS.

Outbreaks of infectious diseases such as HIV and the much televised and attention-getting outbreaks of diseases such as Ebola, Hantaviruses, and the most recent outbreak of SARS have induced a significant new interest in the formulations and more importantly the science of vaccinology, which has previously to a large extent been conducted empirically. Our laboratory has focused on the use of recombinant nonhuman primate cytokines as adjunctive therapies for inducing antigen-specific immune responses in monkeys because most recombinant human cytokines appear to be immunogenic. This article provides a summary of our work with such cytokines, which includes attempts to define optimum dosing schedules that lead to optimal primary and lasting memory antigen-specific immune responses.

Lessons learnt from studies of the immune characterization of naturally SIV infected sooty mangabeys.

The vast number of African non-human primates species that are naturally infected with the simian immunodeficiency viruses ( SIV) but have not shown any signs of lentivirus associated disease as compared to the Asian non-human primate species that do not demonstrate any detectable signs of lentiviral infection but who upon experimental infection with select SIV isolates from the African species develop clinical signs and laboratory based findings similar to human HIV-1 infection provide a powerful model to define virus-host relationships. It is our belief that unraveling those differences which are specifically associated with disease resistance and/or disease susceptibility culled out from those that are species specific differences unrelated to disease outcome may provide some important insights which maybe fruitful for the formulation of vaccine strategies. The purpose of this chapter is to provide the reader with a summary of the findings from our laboratory from the past decade using the naturally SIV infected sooty mangabey model aimed at ferreting out some of these differences. Some very important paradoxes exist with this naturally infected lentivirus model. Thus, it is difficult to determine why these species demonstrate highly effective immune responses but yet maintain very high viral loads. Why do these naturally SIV infected species not demonstrate the plethora of clinical symptoms ascribed to select proteins of the SIV such as 'tat', 'nef', and other viral proteins as do the rhesus macaques and humans to HIV? Most of the targets of such proteins are highly conserved and yet no detectable pathology? We submit that the naturally infected species has evolved over time with a highly regulated immune system (a perfect host/parasite relationship) that is sufficient to prevent pathology and not in the order to exhaust the immune system. In addition, the quality of the anti-viral immune response is of interest. Thus, the mangabeys demonstrate a clear skew in their cytokine based immune response towards a predominantly TH2 bias which we believe is the reason why this species of mangabeys among the many studied, is perhaps is the only species that is susceptible to M. leprae infection (see Dr. B. Gormus's chapter). Some of our working hypotheses that are aimed to provide explanations for some of these paradoxes are provided herein.

Autoimmune mechanisms as the basis for human peripartum cardiomyopathy.

The etiology and mechanisms of pathogenesis of human peripartum cardiomyopathy (PPCM) remain unknown. The incidence and prevalence of this disease is rare in some parts of the world and more common in others. The purpose of this review is to summarize our current knowledge of the factors that have been entertained which may contribute to the pathogenesis of PPCM with special emphasis on more recent data from our laboratory that provide support to the view that this disease is an autoimmune disease with multiple contributing factors and effector mechanisms. This is supported by the fact that sera from PPCM patients contain high titers of auto-antibodies against normal human cardiac tissue proteins of 37, 33, and 25 kD that was not present in the sera of patients with idiopathic cardiomyopathy (IDCM), indicating for the first time that PPCM is distinct from IDCM. In addition to the autoantibodies, the PBMC's from PPCM patients demonstrate a heightened level of fetal microchimerism, an abnormal cytokine profile, decreased levels of CD4+ CD25lo regulatory T cells, and a significant reduction in the plasma levels of progesterone, estradiol and relaxin in PPCM patients as compared with other normal pregnant non-PPCM patients. A potential role for reduced plasma levels of selenium in the pathogenesis of select PPCM patients was also noted. These findings for the first time suggest that such abnormalities may in concert lead to the initiation and perpetuation of an autoimmune process, which leads to cardiac failure and disease. Identification of the precise nature of the cardiac tissue autoantigens (currently in progress) will pave the way for the delineation of mechanism of this autoimmune disease. A working model for the pathogenesis of this disease is also described herein.

Targeting α4ß7 integrin reduces mucosal transmission of simian immunodeficiency virus and protects gut-associated lymphoid tissue from infection.

α4ß7 integrin-expressing CD4(+) T cells preferentially traffic to gut-associated lymphoid tissue (GALT) and have a key role in HIV and simian immunodeficiency virus (SIV) pathogenesis. We show here that the administration of an anti-α4ß7 monoclonal antibody just prior to and during acute infection protects rhesus macaques from transmission following repeated low-dose intravaginal challenges with SIVmac251. In treated animals that became infected, the GALT was significantly protected from infection and CD4(+) T cell numbers were maintained in both the blood and the GALT. Thus, targeting α4ß7 reduces mucosal transmission of SIV in macaques.

Relationships between IL-17(+) subsets, Tregs and pDCs that distinguish among SIV infected elite controllers, low, medium and high viral load rhesus macaques.

Comprehensive studies of the frequencies and absolute numbers of the various cell lineages that synthesize IL-17 in the blood and corresponding gastrointestinal (GI) tissues, their correlation with CD4(+) Tregs, CD8(+) Tregs, total and IFN-α synthesizing plasmacytoid dendritic cells (pDC) relative to plasma viral load in SIV infection has been lacking. The unique availability of SIV infected rhesus macaques (RM) classified as Elite Controllers (EC), and those with Low, Intermediate and High Viral Loads (HVL) provided a unique opportunity to address this issue. Results of these studies showed that EC demonstrated a remarkable ability to reverse changes that are induced acutely by SIV in the various cell lineages. Highlights of the differences between EC and HVL RM within Gastro-intestinal tissues (GIT) was the maintenance and/or increases in the levels of IL-17 synthesizing CD4, CD8, and NK cells and pDCs associated with slight decreases in the levels of CD4(+) Tregs and IFN-α synthesizing pDCs in EC as compared with decreases in the levels of IL-17 synthesizing CD4, CD8 and NK cells associated with increases in pDCs and IFN-α synthesizing pDCs in HVL monkeys. A previously underappreciated role for CD8(+) Tregs was also noted with a moderate increase in ECs but further increases of CD8(+) Tregs with increasing VL in viremic monkeys. Positive correlations between plasma VL and decreases in the levels of Th17, Tc17, NK-17, CD4(+) Tregs and increases in the levels of CD8(+) Tregs, total and IFN-α synthesizing pDCs were also noted. This study also identified 2 additional IL-17(+) subsets in GIT as CD3(-/)CD8(+)/NKG2a(-) and CD3(+)/CD8(+)/NKG2a(+) subsets. Studies also suggest a limited role for IFN-α synthesizing pDCs in chronic immune activation despite persistent up-regulation of ISGs. Finally, elevated persistent innate immune responses appear associated with poor prognosis. These findings provide an initial foundation for markers important to follow for vaccine design.

In vivo administration of a JAK3 inhibitor to chronically siv infected rhesus macaques leads to NK cell depletion associated with transient modest increase in viral loads.

Innate immune responses are reasoned to play an important role during both acute and chronic SIV infection and play a deterministic role during the acute stages on the rate of infection and disease progression. NK cells are an integral part of the innate immune system but their role in influencing the course of SIV infection has been a subject of debate. As a means to delineate the effect of NK cells on SIV infection, use was made of a Janus kinase 3 (JAK3) inhibitor that has previously been shown to be effective in the depletion of NK cells in vivo in nonhuman primates (NHP). Extensive safety and in vitro/in vivo PK studies were conducted and an optimal dose that depletes NK cells and NK cell function in vivo identified. Six chronically SIV infected rhesus macaques, 3 with undetectable/low plasma viral loads and 3 with high plasma viral loads were administered a daily oral dose of 10 mg/kg for 35 days. Data obtained showed that, at the dose tested, the major cell lineage affected both in the blood and the GI tissues were the NK cells. Such depletion appeared to be associated with a transient increase in plasma and GI tissue viral loads. Whereas the number of NK cells returned to baseline values in the blood, the GI tissues remained depleted of NK cells for a prolonged period of time. Recent findings show that the JAK3 inhibitor utilized in the studies reported herein has a broader activity than previously reported with dose dependent effects on both JAK2 and JAK1 suggests that it is likely that multiple pathways are affected with the administration of this drug that needs to be taken into account. The findings reported herein are the first studies on the use of a JAK3 inhibitor in lentivirus infected NHP.

Innate immune natural killer cells and their role in HIV and SIV infection.

The findings that early events during HIV-1 and SIV infection of Asian rhesus macaques dictate the levels of viremia and rate of disease progression prior to the establishment of mature and effective adaptive immune responses strongly suggest an important role for innate immune mechanisms. In addition, the fact that the major target of HIV and SIV during this period of acute infection is the gastrointestinal tissue suggests that whatever role the innate immune system plays must either directly and/or indirectly focus on the GI tract. The object of this article is to provide a general overview of the innate immune system with a focus on natural killer (NK) cells and their role in the pathogenesis of lentivirus infection. The studies summarized include our current understanding of the phenotypic heterogeneity, the putative functions ascribed to the subsets, the maturation/differentiation of NK cells, the mechanisms by which their function is mediated and regulated, the studies of these NK-cell subsets, with a focus on killer cell immunoglobulin-like receptors (KIRs) in nonhuman primates and humans, and finally, how HIV and SIV infection affects these NK cells in vivo. Clearly much has yet to be learnt on how the innate immune system influences the interaction between lentiviruses and the host within the GI tract, knowledge of which is reasoned to be critical for the formulation of effective vaccines against HIV-1.

The role of disease stage, plasma viral load and regulatory T cells (Tregs) on autoantibody production in SIV-infected non-human primates.

Autoantibodies appear in the sera of rhesus macaques following SIV infection. The present study was conducted to examine the role of viral load, antiviral chemotherapy and stage of disease on the titers of such autoantibodies and the spectrum of autoantigens that become the target of such autoimmune responses. In addition, the role of regulatory T cells (Tregs) was also examined. Results of these studies showed that the highest autoantibody titers were noted in animals with lower relative plasma viral loads with a wider spectrum of autoantigens that are the target of such responses as compared with lower autoantibody titers in animals with relatively higher plasma viral loads and a narrower spectrum of autoantigens. Short-term antiviral chemotherapy did not influence the titers of autoantibodies. While there was a gradual decrease in the frequency and absolute number of Tregs, the levels of Tregs was inversely correlated with viral load and lower autoantibody titers. The mechanisms for these differences remain unknown and suggest complex relationships exist between levels of immunosuppression, autoimmune response, homeostatic proliferation and the spectrum of autoantigens that become the target of such autoimmune responses.

Anti-CD3/28 mediated expansion of macaque CD4+ T cells is polyclonal and provides extended survival after adoptive transfer.

BACKGROUND: Our lab has previously shown that adoptive transfer of in vitro expanded autologous purified polyclonal CD4(+) T cells using anti-CD3/CD28 coated beads induced antiviral responses capable of controlling simian immunodeficiency virus (SIV) replication in vivo. RESULTS: Expansion on anti-CD3/28 coated beads was found to induce a true polyclonal expansion as CFSE labeled cells uniformly showed dilution of the dye over several days of culture, in contrast to aliquots of the same cells subjected to mitogen stimulation. Of interest was the finding that CD4(+) T cells collected before and during early chronic SIV infection or AIDS stage did not show any or only modest differences in proliferative response or expansion kinetics. The reason for such excellent expansion properties was analyzed by the quantitation of telomerase activity in aliquots of expanding CD4(+) T cells from sample collected at various times post-infection. First, anti-CD3/28 expanded CD4(+) T cells exhibited telomerase levels 2- to 20-fold higher than the starting population of CD4(+) T cells. Moreover, while telomerase activity in ex vivo tested CD4(+) T cells was found to decrease following SIV infection and disease progression, anti-CD3/28 expansion appeared to restore significant levels of telomerase activity as no difference was noted in telomerase expression between CD4(+) T cells expanded from samples collected before or during the chronic SIV infection. When such expanded and CFSE labeled T cells were autologously transferred to monkeys, evidence for extended survival in vivo was provided as CFSE labeled cells were detected to relatively high levels in blood and spleen at 1 week post-infection. CONCLUSION: In summary, the data suggest that anti-CD3/28 mediated expansion of CD4(+) T cells retains its immunotherapeutic potential not only during the early stages of lentiviral infection but also at more advanced stages of disease.