HIV, asymptomatic STI, and the rectal mucosal immune environment among young men who have sex with men.

Young men who have sex with men (YMSM) are disproportionately affected by HIV and bacterial sexually transmitted infections (STI) including gonorrhea, chlamydia, and syphilis; yet research into the immunologic effects of these infections is typically pursued in siloes. Here, we employed a syndemic approach to understand potential interactions of these infections on the rectal mucosal immune environment among YMSM. We enrolled YMSM aged 18-29 years with and without HIV and/or asymptomatic bacterial STI and collected blood, rectal secretions, and rectal tissue biopsies. YMSM with HIV were on suppressive antiretroviral therapy (ART) with preserved blood CD4 cell counts. We defined 7 innate and 19 adaptive immune cell subsets by flow cytometry, the rectal mucosal transcriptome by RNAseq, and the rectal mucosal microbiome by 16S rRNA sequencing and examined the effects of HIV and STI and their interactions. We measured tissue HIV RNA viral loads among YMSM with HIV and HIV replication in rectal explant challenge experiments among YMSM without HIV. HIV, but not asymptomatic STI, was associated with profound alterations in the cellular composition of the rectal mucosa. We did not detect a difference in the microbiome composition associated with HIV, but asymptomatic bacterial STI was associated with a higher probability of presence of potentially pathogenic taxa. When examining the rectal mucosal transcriptome, there was evidence of statistical interaction; asymptomatic bacterial STI was associated with upregulation of numerous inflammatory genes and enrichment for immune response pathways among YMSM with HIV, but not YMSM without HIV. Asymptomatic bacterial STI was not associated with differences in tissue HIV RNA viral loads or in HIV replication in explant challenge experiments. Our results suggest that asymptomatic bacterial STI may contribute to inflammation particularly among YMSM with HIV, and that future research should examine potential harms and interventions to reduce the health impact of these syndemic infections.

The rectal mucosal immune environment and HIV susceptibility among young men who have sex with men.

Young men who have sex with men (YMSM) represent a particularly high-risk group for HIV acquisition in the US, despite similarly reported rates of sexual activity as older, adult MSM (AMSM). Increased rates of HIV infection among YMSM compared to AMSM could be partially attributable to differences within the rectal mucosal (RM) immune environment associated with earlier sexual debut and less lifetime exposure to receptive anal intercourse. Using an ex vivo explant HIV challenge model, we found that rectal tissues from YMSM supported higher levels of p24 at peak viral replication timepoints compared to AMSM. Among YMSM, the RM was characterized by increased CD4+ T cell proliferation, as well as lower frequencies of tissue resident CD8+ T cells and pro-inflammatory cytokine producing CD4+ and CD8+ T cells. In addition, the microbiome composition of YMSM was enriched for anaerobic taxa that have previously been associated with HIV acquisition risk, including Prevotella, Peptostreptococcus, and Peptoniphilus. These distinct immunologic and microbiome characteristics were found to be associated with higher HIV replication following ex vivo challenge of rectal explants, suggesting the RM microenvironment of YMSM may be uniquely conducive to HIV infection.

T-cell activation and B-cell interaction signatures in rectal tissues are associated with HIV replication in ex-vivo model of infection.

OBJECTIVE: The rectal mucosa is a critical site of HIV vulnerability. We sought to identify transcriptomic features of rectal mucosal tissue prior to exposure associated with support or restriction of HIV replication. DESIGN: Rectal tissue from HIV-negative cis gender men ( n  = 57) underwent concurrent RNAseq transcriptomic analyses (two biopsies/participant) and challenge with HIV in the ex-vivo explant model of infection (three biopsies challenged/participant) as part of a larger cohort study to understand the rectal mucosal immune environment among MSM. METHODS: P24 was quantified in the explant supernatants over a culture period of 18 days via ELISA. Participant median p24 log area under the curve was correlated with bulk transcriptomic data (Illumina HiSeq3000) to identify associations between gene expression and p24 production. Significant differentially expressed genes (DEGs) were identified via DESeq2 analysis and analyzed with Reactome to identify pathways of interest. RESULTS: In total, 183 DEG (181 upregulated, two downregulated) were associated with higher p24 accumulation in the ex-vivo challenge model, including T-cell activation, B-cell function, and chemokine DEG. Reactome analysis of the upregulated genes identified 'Adaptive Immune System', 'Cytokine Signaling in Immune System', and 'Innate Immune System' as significantly upregulated pathways. CONCLUSION: For the first time, we identified rectal tissue transcriptomic signatures associated with increased p24 production utilizing an ex-vivo model. Our findings are highly relevant to HIV transmission and the early establishment of HIV reservoirs in humans, and future studies should examine the identified pathways as targets for new or improved biomedical prevention or treatment interventions.

Viremia controls Env-specific antibody-secreting cell responses in simian immunodeficiency virus infected macaques pre and post-antiretroviral therapy.

OBJECTIVE: The aim of this study was to investigate the kinetics of Env (gp140)-specific antibody-secreting cells (ASCs) during acute and early chronic simian immunodeficiency virus (SIV) infection, and prior to and postantiretroviral therapy (ART) in rhesus macaques. DESIGN AND METHODS: At week 0, rhesus macaques were inoculated intravenously with SIVmac239 and the viral loads were allowed to develop. Daily ART was initiated at week 5 post infection until week 18, though the animals were monitored until week 28 for the following parameters: enumeration of SIV gp140-specific ASCs by ELISPOT; quantification of viremia and SIV gp140-specific IgG titres through qRT-PCR and ELISA, respectively; estimation of monocytes, follicular helper T cells (Tfh) and memory B cell frequencies using polychromatic flow cytometry. RESULTS: Direct correlations were consistently found between blood SIV gp140-specific ASC responses and viremia or SIV Env-specific IgG titres. In contrast, SIV gp140-specific ASC responses showed inverse correlations with the percentage of total memory B cells in the blood. In lymph nodes, the magnitude of the SIV gp140-specific ASC responses also followed the viral load kinetics. In contrast, the number of SIV gp140-specific ASCs presented did not correlate with frequencies of circulating activated monocyte (CD14+CD16+) or Tfh cells. CONCLUSION: Blood and/or lymph node viral loads may regulate the onset and magnitude of SIV gp140-specific ASCs during SIV infection and following ART in rhesus macaques.

Ex vivo rectal explant model reveals potential opposing roles of Natural Killer cells and Marginal Zone-like B cells in HIV-1 infection.

Our understanding of innate immune responses in human rectal mucosal tissues (RM) and their contributions to promoting or restricting HIV transmission is limited. We defined the RM composition of innate and innate-like cell subsets, including plasmacytoid dendritic cells; CD1c + myeloid DCs; neutrophils; macrophages; natural killer cells (NK); Marginal Zone-like B cells (MZB); γδ T cells; and mucosal-associated invariant T cells in RM from 69 HIV-negative men by flow cytometry. Associations between these cell subsets and HIV-1 replication in ex vivo RM explant challenge experiments revealed an inverse correlation between RM-NK and p24 production, in contrast to a positive association between RM-MZB and HIV replication. Comparison of RM and blood-derived MZB and NK illustrated qualitative and quantitative differences between tissue compartments. Additionally, 22 soluble molecules were measured in a subset of explant cultures (n = 26). Higher production of IL-17A, IFN-γ, IL-10, IP-10, GM-CSF, sFasL, Granzyme A, Granzyme B, Granulysin, and Perforin following infection positively correlated with HIV replication. These data show novel associations between MZB and NK cells and p24 production in RM and underscore the importance of inflammatory cytokines in mucosal HIV infection, demonstrating the likely critical role these innate immune responses play in early mucosal HIV replication in humans.

Short Communication:Transgender Women on Feminizing Hormone Therapy Demonstrate a Distinct Rectal Mucosal Transcriptome from Cisgender Men.

Among transgender women (TGW), the effects of feminizing hormone therapy use on rectal mucosal (RM) HIV transmission are largely unknown. In this small pilot study, we compared the RM transcriptome in TGW utilizing feminizing hormone therapy with a group of cisgender men who have sex with men (MSM) engaging in condomless receptive anal intercourse (AI) and to a group of cisgender men who had never engaged in AI. There were 498 differentially expressed genes (DEGs) in TGW compared with men who had never engaged in AI, and 154 DEGs compared with the MSM. Among TGW, a unique RM transcriptome was identified that implicated pathways critical for mucosal immune responses, including upregulation of genes that mediate immune cell activation and the production of cytokines and other immune signaling molecules. Furthermore, gene set enrichment analyses identified immune signatures that implicated enrichment of proinflammatory immunological pathways in TGW, specifically involving interferon-α, interleukin-6, and tumor necrosis factor-α signaling, whereas metabolic pathways were shown to be enriched among the cisgender male groups. These findings suggest that TGW have a distinct RM immune environment influenced by the use of feminizing hormones, and consequently, there is an urgent need for further investigation into the immunological effects of gender-affirming hormone therapy and its potential impact on HIV mucosal transmission risk for transgender individuals.

Author Correction: Distribution of Functional CD4 and CD8 T cell Subsets in Blood and Rectal Mucosal Tissues.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Distribution of Functional CD4 and CD8 T cell Subsets in Blood and Rectal Mucosal Tissues.

A better understanding of the distribution and functional capacity of CD4 T helper (Th) and CD8 T cytotoxic (Tc) cell subsets in the rectal mucosa (RM), a major site for HIV acquisition and replication, in adults is needed. In this study, we compared the distribution of Th and Tc cell subsets between blood and RM compartments in 62 HIV negative men, focusing primarily on IL-17-producing CD4 and CD8 T cells due to their importance in establishing and maintaining mucosal defenses, and examined associations between the frequencies of Th17 and Tc17 cell subsets and the availability of highly HIV-susceptible target cells in the RM. The RM exhibited a distinct immune cell composition comprised of higher frequencies of Th2, Th17, and Tc17 cells compared to the peripheral blood. The majority of Tc17 cells in RM were quadruple-cytokine producers (IL-17A+, IFN-γ+, TNF-α+, and IL4+), whereas most Th17 cells in blood and RM were single IL-17A producers or dual-cytokine producers (IL-17A+TNF-α+). In a separate cohort of 21 HIV positive men, we observed similar tissue distributions of Th and Tc cell subsets, although Tc17 cell frequencies in both blood and tissues were very low. Higher frequencies of multi-cytokine-producing Th17 and Tc17 cells in RM of HIV negative men positively correlated with increased mucosal HIV target cells, suggesting a need to further characterize the effector functions of these cells and their role in HIV acquisition and pathogenesis.

In vivo characterization of macrophage-tropic simian immunodeficiency virus molecular clones in rhesus macaques.

Macrophages are a major target of HIV/SIV infection and play an important role in pathogenesis by serving as viral reservoirs in the central nervous system. Previously, a unique early SIVmac251 envelope (Env) variant, deSIV147 was cloned from blood of a rhesus macaque with rapid disease progression and SIV-associated encephalitis. Here, we show that infectious molecular clone deSIV147 caused systemic infection in rhesus macaques following intravenous or intrarectal exposure. Next, we inoculated deSIV147 into macaques depleted of CD4+ T cells and found that animals were SIV-positive, with high plasma and CSF viral loads. These macaques also showed SIVp17-positive macrophages in brain, lymph nodes, colon, lung, and liver. Furthermore, accumulation of perivascular macrophages, multinucleated giant cells, and microgliosis was detected. These findings suggest that the neurotropic deSIV147 clone will be useful to study macrophage infection in HIV/SIV-associated neurocognitive disorders, gain insights into myeloid cell reservoirs in brain and other anatomical sites, as well as test strategies for eradication.

Immune Cell Dynamics in Rhesus Macaques Infected with a Brazilian Strain of Zika Virus.

Zika virus (ZIKV) is a mosquito-borne and sexually transmitted flavivirus that is associated with fetal CNS-damaging malformations during pregnancy in humans. This study documents the viral kinetics and immune responses in rhesus macaques infected with a clinical ZIKV Brazilian isolate. We evaluated the viral kinetics and immune responses induced after an i.v. infection with a Brazilian ZIKV clinical isolate (HS-2015-BA-01) in rhesus macaques for up to 142 d. ZIKV-specific Ab-secreting cells, germinal center reactions, and monocyte, dendritic cell, NK, and T cell frequencies were monitored. ZIKV loads were readily detected in plasma (until day 5 or 7), semen and urine (until days 7 and 14), and saliva (until day 42), but the viremia was rapidly controlled. No detectable clinical manifestations were observed. However, lymph node hyperplasia was clearly visible postviremia but was associated with low frequencies of ZIKV-specific Ab-secreting cells in lymph nodes and bone marrow, correlating with low Ab titers. CD14+/CD16- monocytes and myeloid CD11chi dendritic cells decreased in blood, whereas NK and T cell numbers were only marginally altered during the course of the study. ZIKV infection caused a significant lymphoid tissue activation but limited induction of ZIKV-specific B cells, suggesting that these parameters need to be considered for ZIKV vaccine design.

Early initiation of antiretroviral treatment postSIV infection does not resolve lymphoid tissue activation.

OBJECTIVE: Germinal center resident follicular helper T (TFH) cells in lymphoid follicles are a potential sanctuary for HIV/simian immunodeficiency virus (SIV) replication. But the dynamics of germinal centers upon early initiation of antiretroviral therapy (ART) and their potential role in the formation of viral sanctuaries post-SIV infection are not fully understood. DESIGN: Sequential lymph node biopsies (n = 10) were collected from SIVmac239-infected rhesus macaques before infection, at 5 weeks postinfection/pre-ART, 6 and 12 weeks following ART initiation. These tissues and cells were analyzed for frequencies of TFH cells and assignment of germinal center scores. RESULTS: Modest but significant increases in TFH cells and hyperplastic follicles with large germinal centers were noted during the acute phase of SIV infection (week 5/pre-ART). However, 6 weeks after ART initiation, substantial increases in germinal center TFH cells, germinal center B cells, hyperplastic follicles with large germinal centers, and abundant local IL-21 production were observed, whereas levels of SIV RNA and DNA of lymph nodes had decreased to barely detectable values along with barely detectable levels of SIV antibody-producing cells. An additional 6 weeks of ART did not appreciably decrease germinal center TFH or germinal center scores. CONCLUSION: Thus, although early ART rapidly controls SIV replication, it does not regulate early lymphoid activation, which may contribute to the seeding and magnitude of viral reservoirs.

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.

Experimental transfusion-induced Babesia microti infection: dynamics of parasitemia and immune responses in a rhesus macaque model.

BACKGROUND: Babesiosis is an emerging tick-borne infection in humans. The increasing numbers of reported cases of transfusion-associated babesiosis (TAB), primarily caused by Babesia microti, represents a concern for the safety of the US blood supply. STUDY DESIGN AND METHODS: This study investigated kinetics of parasitemia and innate immune responses and dynamics of antibody responses during B. microti infection in rhesus macaques (RMs) using blood smears, quantitative polymerase chain reaction (qPCR), flow cytometry, and indirect fluorescent antibody testing. A total of six monkeys were transfused with either hamster or monkey-passaged B. microti-infected red blood cells (two and four monkeys, respectively) simulating TAB. RESULTS: The prepatent period in monkeys inoculated with hamster-passaged B. microti was 35 days compared with 4 days in monkeys transfused with monkey-passaged B. microti; the latter monkeys also had markedly higher parasitemia levels. The duration of the window period from the first detected parasitemia by qPCR analysis to the first detected antibody response ranged from 10 to 17 days. Antibody responses fluctuated during the course of the infection. Innate responses assessed by the frequencies of monocytes and activated B cells correlated with the kinetics and magnitude of parasitemia. On Day 14, additional activation peaks were noted for CD14+CD16+ and CD14-CD16+ monocytes and for CD11c+ myeloid dendritic cells, but only in animals transfused with monkey-passaged B. microti. Parasitemia persisted in these immunocompetent animals, similar to human infection. CONCLUSION: The results suggest that transfusion-associated transmission of B. microti leads to rapid onset of parasitemia (Day 4) in RMs, detectable antibody response 14 days later, and persistent parasitemia.

Whole-body immunoPET reveals active SIV dynamics in viremic and antiretroviral therapy-treated macaques.

The detection of viral dynamics and localization in the context of controlled HIV infection remains a challenge and is limited to blood and biopsies. We developed a method to capture total-body simian immunodeficiency virus (SIV) replication using immunoPET (antibody-targeted positron emission tomography). The administration of a poly(ethylene glycol)-modified, (64)Cu-labeled SIV Gp120-specific antibody led to readily detectable signals in the gastrointestinal and respiratory tract, lymphoid tissues and reproductive organs of viremic monkeys. Viral signals were reduced in aviremic antiretroviral-treated monkeys but detectable in colon, select lymph nodes, small bowel, nasal turbinates, the genital tract and lung. In elite controllers, virus was detected primarily in foci in the small bowel, select lymphoid areas and the male reproductive tract, as confirmed by quantitative reverse-transcription PCR (qRT-PCR) and immunohistochemistry. This real-time, in vivo viral imaging method has broad applications to the study of immunodeficiency virus pathogenesis, drug and vaccine development, and the potential for clinical translation.

Up-regulation of Tim-3 on T cells during acute simian immunodeficiency virus infection and on antigen specific responders.

OBJECTIVE: Understanding the role of T-cell immunoglobulin and mucin domain-containing molecule 3 (Tim-3) on T cells and dendritic cells during the course of simian immunodeficiency virus (SIV) infection. DESIGN: Sequentially collected PBMCs from uninfected and SIVmac239-infected rhesus macaques were evaluated for Tim-3 expression by flow cytometry and antigen-specific responses. RESULTS: Blood innate immune cells (dendritic cells) and B cells showed high constitutive expression of Tim-3, whereas, compared to humans, only a minority of macaque T cells did. However, TIM-3 expression was transiently up-regulated on both CD4 and CD8 T cells during acute SIV infection, correlating with plasma viral loads, CD4 cell counts, and Ki67 expression up to 6 weeks postinfection and returned to baseline values by 8 weeks postinfection. Upon antigen-specific stimulation, most Tim-3 T cells produced various cytokines, suggesting that this marker is up-regulated on effector antigen-specific T cells and not associated with T-cell exhaustion. Among myeloid dendritic cells (mDCs), a clear separation was seen between blood mDCs expressing Tim-3 and those expressing PD-L2 - a ligand for inhibitory receptor programmed death 1. CONCLUSION: Rhesus macaques show constitutive expression of Tim-3 primarily on innate immune cells, but markedly lower levels on T cells compared to humans. Nevertheless, Tim-3 expression on T cells is transiently up-regulated during acute, but not chronic, SIV infection, and appears to be a marker of antigen-specific effector cells. The exact role and contribution of Tim-3 to the modulation of antiviral responses in vivo will require additional investigation.

Association of Cytokines With Exosomes in the Plasma of HIV-1-Seropositive Individuals.

Human immunodeficiency virus (HIV)-infected and viremic individuals exhibit elevated levels of plasma cytokines. Here we show that most cytokines are not in free form but appear associated with exosomes that are distinct from virions. Purified exosomes were analyzed to determine the levels of 21 cytokines and chemokines and compared with exosome-depleted plasma. Most cytokines were markedly enriched in exosomes from HIV-positive individuals relative to negative controls and to plasma. Moreover, exposure of naive peripheral blood mononuclear cells to exosomes purified from HIV-positive patients induced CD38 expression on naive and central memory CD4(+) and CD8(+) T cells, probably contributing to inflammation and viral propagation via bystander cell activation.

Early lymphoid responses and germinal center formation correlate with lower viral load set points and better prognosis of simian immunodeficiency virus infection.

We have investigated the dynamics of germinal center (GC) formation in lymphoid tissues following acute SIV infection. SIV induces a marked follicular hyperplasia, associated with an aberrant accumulation of nonproliferating T follicular helper cells within GCs, but with an abundance of cells producing IL-21, demonstrating that the mechanisms involved for these two events appear independent. IL-21-stimulated T follicular helper cells are considered a critical element for GC formation, a physiological process that seems dysregulated and excessive during HIV/SIV infection, contributing to lymphoid pathogenesis. However, the data suggest that the kinetics by which such GCs are formed may be an important predictor of the host-pathogen equilibrium, as early GC hyperplasia was associated with better control of viral replication. In contrast, monkeys undergoing fast disease progression upon infection exhibited an involution of GCs without local IL-21 production in GCs. These results provide important clues regarding GC-related hyperimmune responses in the context of disease progression within various individuals during HIV/SIV infection and may open novel therapeutic avenues to limit lymphoid dysfunction, postinfection.

TIM-3, a Possible Target for Immunotherapy in Cancer and Chronic Viral Infections.

Effector T-cell responses are controlled by complex mechanisms involving various soluble factors and co-stimulatory and co-inhibitory molecules. These inhibitory receptors act as immune checkpoints and are extensively investigated as possible therapeutic targets, such as PD-1 and CTLA-4. Recently TIM-3 is also gaining prominence in tumor and chronic viral infection models as a candidate for immunotherapy in conjunction with other inhibitory receptors. This review discusses the recent findings on the expression of TIM-3 and its ligand in tumor and chronic viral infection.

Expression of functional folate receptors by human parathyroid cells.

BACKGROUND: Human pituitary adenomas express folate receptors (FR); therefore, we hypothesized that parathyroid (PT) tumors also might express FR, whereas normal human thyroids might not. The purpose of our study was to characterize the functionality of FRs on human PT tumors, with the goal of developing an imaging tool that would concentrate in PT more than in the thyroid. METHODS: Human PTs and thyroids were evaluated for FR expression by immunohistochemistry. Expression of genes for FRα and FRß was measured with the Illumina Human HT-12 Expression Bead Chips and verified by quantitative reverse-transcription polymerase chain reaction. Folate incorporation by PT cells versus normal thyroid cells was determined by incubation with (99m)Technetium ((99m)Tc)(CO)3-folate and (99m)Tc-Etarfolatide, and uptake was determined by gamma counting. Specific targeting of FRs was demonstrated by blocking with cold folate. A549 cells and Jurkat cells served as FR-negative controls, and KB cells and HeLa cells were FR-positive controls. RESULTS: On immunohistochemistry and Western blotting, human PT cells expressed FRs, whereas human thyroid cells did not. The FRα gene was expressed in all PTs analyzed, and the FRß gene was expressed by most. Uptake of (99m)Tc(CO)3-folate was increased in PT cells versus thyroid cells. There was dose-dependent uptake of (99m)Tc-etarfolatide, and uptake was inhibited by preincubation with cold folate, confirming FR-mediated binding. CONCLUSION: This is the first report of the expression and functionality of FRs on human PT cells. These findings suggest that (99m)Tc-folate holds potential for localization of PT tumors preoperatively and their treatment.

In vivo blockade of the programmed cell death-1 pathway using soluble recombinant PD-1-Fc enhances CD4+ and CD8+ T cell responses but has limited clinical benefit.

The programmed cell death-1 (PD-1)/programmed cell death ligand-1 pathway has been shown to limit cell-mediated effector functions during chronic viral infections impeding clearance of pathogens. As a strategy to reverse this exhaustion and increase T cell polyfunctionality, PD-1 ligands were blocked in vivo using a recombinant macaque PD-1 fused to a macaque Ig-Fc (rPD-1-Fc) in SIVmac239-infected rhesus macaques during the early chronic phase of infection, either alone or in combination with antiretroviral therapy. In vitro blockade showed improvement of Ag-specific CD4(+) and CD8(+) T cells from monkeys chronically infected with SIV. Of note, a prolonged 5-d blockade in culture was beneficial for both gag-specific CD4(+) and CD8(+) T cells based on proliferation and dual cytokine production. Although the in vivo administration of rPD-1-Fc induced enhanced SIV-specific CD4 and CD8 T cell proliferation both in the blood and gut, it failed to alter plasma viremia. However, rPD-1-Fc administration in the context of antiretroviral therapy interruption induced a significant delay of viral load rebound. In addition, rPD-1-Fc administration in MamuA*001(+) monkeys led to both an increase in the frequencies and Ki67 expression of GagCM9(+) CD8(+) T cells in the blood and rectal mucosa and polyfunctionality of GagCM9(+) CD8(+) T cells in blood. In conclusion, however, our data suggest that PD-1/programmed cell death ligand-1 blockade using soluble rPD-1-Fc instead of anti-PD-1 mAb, although effective in rescuing the effector function of SIV-specific CD4(+) and CD8(+) T cells during the early chronic phase of infection, has limited clinical benefit.