CD8+ lymphocytes can control HIV infection in vitro by suppressing virus replication

Viral Persistence in the Gut-Associated Lymphoid Tissue and Barriers to HIV Cure

More than 40 years after the first reported cases of what then became known as acquired immunodeficiency syndrome (AIDS), tremendous progress has been achieved in transforming the disease from almost universally fatal to a chronic manageable condition. Nonetheless, the efforts to find a preventative vaccine or a cure for the underlying infection with Human Immunodeficiency Virus (HIV) remain largely unsuccessful. Many challenges intrinsic to the virus characteristics and host response need to be overcome for either goal to be achieved. This article will review the obstacles to an effective HIV cure, specifically the steps involved in the generation of HIV latency, focusing on the role of the gut-associated lymphoid tissue, which has received less attention compared with the peripheral blood, despite being the largest repository of lymphoid tissue in the human body, and a large site for HIV persistence.

HIV-1 protective epitope-specific CD8+ T cells in HIV-1-exposed seronegative individuals

Although previous studies have reported HIV-1-specific T cell responses in HIV-1-exposed seronegative (HESN) individuals, there has been no detailed analysis of these T cells against HIV-1 infection. We investigated HIV-1-specific CD8+ T cell responses in 200 Japanese HESN men who have sex with men (MSM). T cell responses to 143 well-characterized HIV-1 epitope peptides were analyzed by intracellular cytokine staining assay consisting of 3-week cultures of PBMCs stimulated with peptides. HLA-B∗51:01-restricted Pol TI8-specific and HLA-A∗02:06-restricted Pol SV9-specific CD8+ T cells were identified in two and one individuals, respectively, whereas CD8+ T cells specific for other HLA-A∗02:06-restricted or HLA-B∗51:01 epitopes were not present in these individuals. These epitope-specific T cells recognized HIV-1-infected cells. Because these two epitopes were previously reported to be protective in HIV-1-infected individuals, these protective epitope-specific T cells might suppress HIV-1 replication in HESN-MSM individuals. The present study suggests the contribution of protective epitope-specific T cells to protection against HIV-1 infection.

CD8+ T cells control SIV infection using both cytolytic effects and non-cytolytic suppression of virus production

Whether CD8+ T lymphocytes control human immunodeficiency virus infection by cytopathic or non-cytopathic mechanisms is not fully understood. Multiple studies highlighted non-cytopathic effects, but one hypothesis is that cytopathic effects of CD8+ T cells occur before viral production. Here, to examine the role of CD8+ T cells prior to virus production, we treated SIVmac251-infected macaques with an integrase inhibitor combined with a CD8-depleting antibody, or with either reagent alone. We analyzed the ensuing viral dynamics using a mathematical model that included infected cells pre- and post- viral DNA integration to compare different immune effector mechanisms. Macaques receiving the integrase inhibitor alone experienced greater viral load decays, reaching lower nadirs on treatment, than those treated also with the CD8-depleting antibody. Models including CD8+ cell-mediated reduction of viral production (non-cytolytic) were found to best explain the viral profiles across all macaques, in addition an effect in killing infected cells pre-integration (cytolytic) was supported in some of the best models. Our results suggest that CD8+ T cells have both a cytolytic effect on infected cells before viral integration, and a direct, non-cytolytic effect by suppressing viral production.

CD8+ Lymphocytes from Healthy Blood Donors Secrete Antiviral Levels of Interferon-Alpha

The adaptive immune response to viral infections features the antigen-driven expansion of CD8+ T cells. These cells are widely recognized for their cytolytic activity that is mediated through the secretion of cytokines such as perforin and granzymes. Less appreciated is their ability to secrete soluble factors that restrict virus replication without killing the infected cells. In this study we measured the ability of primary anti-CD3/28-stimulated CD8+ T cells from healthy blood donors to secrete interferon-alpha. Supernatants collected from CD8+ T cell cultures were screened for their ability to suppress HIV-1 replication in vitro and their interferon-alpha concentrations were measured by ELISA. Interferon-alpha concentrations in the CD8+ T cell culture supernatants ranged from undetectable to 28.6 pg/mL. The anti-HIV-1 activity of the cell culture supernatants was observed to be dependent on the presence of interferon-alpha. Appreciable increases in the expression levels of type 1 interferon transcripts were observed following T cell receptor stimulation, suggesting that the secretion of interferon-alpha by CD8+ T cells is an antigen-driven response. In 42-plex cytokine assays, the cultures containing interferon-alpha were also found to contain elevated levels of GM-CSF, IL-10, IL-13, and TNF-alpha. Together, these results demonstrate that the secretion of anti-viral levels of interferon-alpha is a common function of CD8+ T cells. Furthermore, this CD8+ T cell function likely plays broader roles in health and disease.

Role of CXCR5+ CD8+ T cells in human immunodeficiency virus-1 infection

Human immunodeficiency virus (HIV) infection can be effectively suppressed by life-long administration of combination antiretroviral therapy (cART). However, the viral rebound can occur upon cART cessation due to the long-term presence of HIV reservoirs, posing a considerable barrier to drug-free viral remission. Memory CD4⁺ T cell subsets, especially T follicular helper (T _FH ) cells that reside in B-cell follicles within lymphoid tissues, are regarded as the predominant cellular compartment of the HIV reservoir. Substantial evidence indicates that HIV-specific CD8⁺ T cell-mediated cellular immunity can sustain long-term disease-free and transmission-free HIV control in elite controllers. However, most HIV cure strategies that rely on expanded HIV-specific CD8⁺ T cells for virus control are likely to fail due to cellular exhaustion and T _FH reservoir-specialized anatomical structures that isolate HIV-specific CD8⁺ T cell entry into B-cell follicles. Loss of stem-like memory properties is a key feature of exhaustion. Recent studies have found that CXC chemokine receptor type 5 (CXCR5)-expressing HIV-specific CD8⁺ T cells are memory-like CD8⁺ T cells that can migrate into B-cell follicles to execute inhibition of viral replication. Furthermore, these unique CD8⁺ T cells can respond to immune checkpoint blockade (ICB) therapy. In this review, we discuss the functions of these CD8⁺ T cells as well as the translation of findings into viable HIV treatment and cure strategies.

Non-cytotoxic functions of CD8 T cells: “repentance of a serial killer”

Cytotoxic CD8 T cells (CTLs) are classically described as the “serial killers” of the immune system, where they play a pivotal role in protective immunity against a wide spectrum of pathogens and tumors. Ironically, they are critical drivers of transplant rejection and autoimmune diseases, a scenario very similar to the famous novel “The strange case of Dr. Jekyll and Mr. Hyde”. Until recently, it has not been well-appreciated whether CTLs can also acquire non-cytotoxic functions in health and disease. Several investigations into this question revealed their non-cytotoxic functions through interactions with various immune and non-immune cells. In this review, we will establish a new classification for CD8 T cell functions including cytotoxic and non-cytotoxic. Further, we will discuss this novel concept and speculate on how these functions could contribute to homeostasis of the immune system as well as immunological responses in transplantation, cancer, and autoimmune diseases.

PD-1 blockade following ART interruption enhances control of pathogenic SIV in rhesus macaques

Programmed death-1 (PD-1) blockade during chronic Simian immunodeficiency virus (SIV) infection results in restoration of CD8 T-cell function and enhances viral control. Here, we tested the therapeutic benefits of PD-1 blockade administered soon after anti-retrovial therapy (ART) interruption (ATI) by treating SIV-infected and ART-suppressed macaques with either an anti-PD-1 antibody (n = 7) or saline (n = 4) at 4 wk after ATI. Following ATI, the plasma viremia increased rapidly in all animals, and the frequency of SIV-specific CD8 T cells also increased in some animals. PD-1 blockade post ATI resulted in higher proliferation of total memory CD8 and CD4 T cells and natural killer cells. PD-1 blockade also resulted in higher proliferation of SIV-specific CD8 T cells and promoted their differentiation toward better functional quality. Importantly, four out of the seven anti-PD-1 antibody-treated animals showed a rapid decline in plasma viremia by 100- to 2300-fold and this was observed only in animals that showed measurable SIV-specific CD8 T cells post PD-1 blockade. These results demonstrate that PD-1 blockade following ATI can significantly improve the function of anti-viral CD8 T cells and enhance viral control and strongly suggests its potential synergy with other immunotherapies that induce functional CD8 T-cell response under ART. These results have important implications for HIV cure research.

Global transcriptomic characterization of T cells in individuals with chronic HIV-1 infection

To obtain a comprehensive scenario of T cell profiles and synergistic immune responses, we performed single-cell RNA sequencing (scRNA-seq) on the peripheral T cells of 14 individuals with chronic human immunodeficiency virus 1 (HIV-1) infection, including nine treatment-naive (TP) and eight antiretroviral therapy (ART) participants (of whom three were paired with TP cases), and compared the results with four healthy donors (HD). Through analyzing the transcriptional profiles of CD4⁺ and CD8⁺ T cells, coupled with assembled T cell receptor sequences, we observed the significant loss of naive T cells, prolonged inflammation, and increased response to interferon-α in TP individuals, which could be partially restored by ART. Interestingly, we revealed that CD4⁺ and CD8⁺ Effector-GNLY clusters were expanded in TP cases, and persistently increased in ART individuals where they were typically correlated with poor immune restoration. This transcriptional dataset enables a deeper understanding of the pathogenesis of HIV-1 infection and is also a rich resource for developing novel immune targeted therapeutic strategies.

Collaboration of a Detrimental HLA-B*35:01 Allele with HLA-A*24:02 in Coevolution of HIV-1 with T Cells Leading to Poorer Clinical Outcomes

Although mutant-specific T cells are elicited in some individuals infected with HIV-1 mutant viruses, the detailed characteristics of these T cells remain unknown. A recent study showed that the accumulation of strains expressing Nef135F, which were selected by HLA-A*24:02-restricted T cells, was associated with poor outcomes in individuals with the detrimental HLA-B*35:01 allele and that HLA-B*35:01-restricted NefYF9 (Nef135-143)-specific T cells failed to recognize target cells infected with Nef135F mutant viruses. Here, we investigated HLA-B*35:01-restricted T cells specific for the NefFF9 epitope incorporating the Nef135F mutation. Longitudinal T-cell receptor (TCR) clonotype analysis demonstrated that 3 types of HLA-B*35:01-restricted T cells (wild-type [WT] specific, mutant specific, and cross-reactive) with different T cell repertoires were elicited during the clinical course. HLA-B*35:01⁺ individuals possessing wild-type-specific T cells had a significantly lower plasma viral load (pVL) than those with mutant-specific and/or cross-reactive T cells, even though the latter T cells effectively recognized the mutant virus-infected cells. These results suggest that mutant-specific and cross-reactive T cells could only partially suppress HIV-1 replication in vivo. An ex vivo analysis of the T cells showed higher expression of PD-1 on cross-reactive T cells and lower expression of CD160/2B4 on the mutant-specific T cells than other T cells, implying that these inhibitory and stimulatory molecules are key to the reduced function of these T cells. In the present study, we demonstrate that mutant-specific and cross-reactive T cells do not contribute to the suppression of HIV-1 replication in HIV-1-infected individuals, even though they have the capacity to recognize mutant virus-infected cells. Thus, the collaboration of HLA-A*24:02 with the detrimental allele HLA-B*35:01 resulted in the coevolution of HIV-1 alongside virus-specific T cells, leading to poorer clinical outcomes.

IMPORTANCE HIV-1 escape mutations are selected under pressure from HIV-1-specific CD8⁺ T cells. Accumulation of these mutations in circulating viruses impairs the control of HIV-1 by HIV-1-specific T cells. Although it is known that HIV-1-specific T cells recognizing mutant virus were elicited in some individuals infected with a mutant virus, the role of these T cells remains unclear. Accumulation of phenylalanine at HIV-1 Nef135 (Nef135F), which is selected by HLA-A*24:02-restricted T cells, led to poor clinical outcome in individuals carrying the detrimental HLA-B*35:01 allele. In the present study, we found that HLA-B*35:01-restricted mutant-specific and cross-reactive T cells were elicited in HLA-B*35:01⁺ individuals infected with the Nef135F mutant virus. These T cells could not effectively suppress HIV-1 replication in vivo even though they could recognize mutant virus-infected cells in vitro. Mutant-specific and cross-reactive T cells expressed lower levels of stimulatory molecules and higher levels of inhibitory molecules, respectively, suggesting a potential mechanism whereby these T cells fail to suppress HIV-1 replication in HIV-1-infected individuals.

The CD8+ T Cell Noncytotoxic Antiviral Responses

The CD8+ T cell noncytotoxic antiviral response (CNAR) was discovered during studies of asymptomatic HIV-infected subjects more than 30 years ago. In contrast to CD8+ T cell cytotoxic lymphocyte (CTL) activity, CNAR suppresses HIV replication without target cell killing. This activity has characteristics of innate immunity: it acts on all retroviruses and thus is neither epitope specific nor HLA restricted. The HIV-associated CNAR does not affect other virus families. It is mediated, at least in part, by a CD8+ T cell antiviral factor (CAF) that blocks HIV transcription. A variety of assays used to measure CNAR/CAF and the effects on other retrovirus infections are described. Notably, CD8+ T cell noncytotoxic antiviral responses have now been observed with other virus families but are mediated by different cytokines. Characterizing the protein structure of CAF has been challenging despite many biologic, immunologic, and molecular studies. It represents a low-abundance protein that may be identified by future next-generation sequencing approaches. Since CNAR/CAF is a natural noncytotoxic activity, it could provide promising strategies for HIV/AIDS therapy, cure, and prevention.

Latency Reversal 2.0: Giving the Immune System a Seat at the Table

PURPOSE OF REVIEW

For most people living with HIV (PLWH), treatment with effective antiretroviral therapy (ART) results in suppression of viremia below the limit of detection of clinical assays, immune reconstitution, reduced immune activation, avoidance of opportunistic infections, and progression to AIDS. However, ART alone is not curative, and HIV persists in a non-replicating, latent form. In this review, we provide a historical perspective on non-specific latency reversal approaches (LRA 1.0) and summarize recent advances in latency reversal strategies that target specific signaling pathways within CD4+ T cells or other immune cells to induce expression of latent HIV (immune-based latency reversal, or LRA 2.0).

RECENT FINDINGS

The HIV reservoir is primarily composed of latently infected CD4+ T cells carrying integrated, replication-competent provirus that can give rise to rebound viremia if ART is stopped. Myeloid lineage cells also contribute to HIV latency in certain tissues; we focus here on CD4+ T cells as a sufficient body of evidence regarding latency reversal in myeloid cells is lacking. The immunomodulatory LRA 2.0 approaches we describe include pattern recognition receptor agonists, immune checkpoint inhibitors, non-canonical NF-kB stimulation, and transient CD8+ lymphocyte depletion, along with promising combination strategies. We highlight recent studies demonstrating robust latency reversal in nonhuman primate models. While significant strides have been made in terms of virus reactivation from latency, initial hopes for latency reversal alone to result in a reduction of infected cells, through viral cytopathic effect or an unboosted immune system, have not been realized and it seems clear that even effective latency reversal strategies will need to be paired with an approach that facilitates immune recognition and clearance of cells containing reactivated virus.

The importance of advanced cytometry in defining new immune cell types and functions relevant for the immunopathogenesis of HIV infection

: In the last years, novel, exciting immunological findings of interest for HIV research and treatment were identified thanks to different cytometric approaches. The analysis of the phenotypes and functionality of cells belonging to the immune system could clarify their role in the immunopathogenesis of HIV infection, and to elaborate key concepts, relevant in the treatment of this disease. Important discoveries have been made concerning cells that are important for protective immunity like lymphocytes that display polyfunctionality, resident memory T cells, innate lymphoid cells, to mention a few. The complex phenotype of myeloid-derived suppressor cells has been investigated, and relevant changes have been reported during chronic and primary HIV infection, in correlation with changes in CD4 T-cell number, T-cell activation, and with advanced disease stage. The search for markers of HIV persistence present in latently infected cells, namely those molecules that are important for a functional or sterilizing cure, evidenced the role of follicular helper T cells, and opened a discussion on the meaning and use of different surface molecules not only in identifying such cells, but also in designing new strategies. Finally, advanced technologies based upon the simultaneous detection of HIV-RNA and proteins at the single cell level, as well as those based upon spectral cytometry or mass cytometry are now finding new actors and depicting a new scenario in the immunopathogenesis of the infection, that will allow to better design innovative therapies based upon novel drugs and vaccines.

Canonical Wnts Mediate CD8+ T Cell Noncytolytic Anti-HIV-1 Activity and Correlate with HIV-1 Clinical Status

CD8⁺ T cells do not rely solely on cytotoxic functions for significant HIV control. Moreover, the noncytotoxic CD8⁺ T cell antiviral response is a primary mediator of natural HIV control such as that seen in HIV elite controllers and long-term nonprogressors that does not require combined antiretroviral therapy. In this study, we investigated the biological factors contributing to the noncytotoxic control of HIV replication mediated by primary human CD8⁺ T cells. We report that canonical Wnt signaling inhibits HIV transcription in an MHC-independent, noncytotoxic manner and that mediators of this pathway correlate with HIV controller clinical status. We show that CD8⁺ T cells express all 19 Wnts and CD8⁺ T cell-conditioned medium (CM) induced canonical Wnt signaling in infected recipient cells while simultaneously inhibiting HIV transcription. Antagonizing canonical Wnt activity in CD8⁺ T cell CM resulted in increased HIV transcription in infected cells. Further, Wnt2b expression was upregulated in HIV controllers versus viremic patients, and in vitro depletion of Wnt2b and/or Wnt9b from CD8⁺ CM reversed HIV inhibitory activity. Finally, plasma concentration of Dkk-1, an antagonist of canonical Wnt signaling, was higher in viremic patients with lower CD4 counts. This study demonstrates that canonical Wnt signaling inhibits HIV and significantly correlates with HIV controller status.

Jigsaw falling into place: A review and perspective of lymphoid tissue CD8+ T cells and control of HIV

CD8+ T cells are crucial for immunity against viral infections, including HIV. Several characteristics of CD8+ T cells, such as polyfunctionality and cytotoxicity, have been correlated with effective control of HIV. However, most of these correlates have been established in the peripheral blood. Meanwhile, HIV primarily replicates in lymphoid tissues. Therefore, it is unclear which aspects of CD8+ T cell biology are shared and which are different between blood and lymphoid tissues in the context of HIV infection. In this review, we will recapitulate the latest advancements of our knowledge on lymphoid tissue CD8+ T cells during HIV infection and discuss the insights these advancements might provide for the development of a HIV cure.

The inhibitor of apoptosis proteins antagonist Debio 1143 promotes the PD-1 blockade-mediated HIV load reduction in blood and tissues of humanized mice

The immune checkpoint programmed cell death protein 1 (PD-1) plays a major role in T cell exhaustion in cancer and chronic HIV infection. The inhibitor of apoptosis protein antagonist Debio 1143 (D1143) enhances tumor cell death and synergizes with anti-PD-1 agents to promote tumor immunity and displayed HIV latency reversal activity in vitro. We asked in this study whether D1143 would stimulate the potency of an anti-human PD-1 monoclonal antibody (mAb) to reduce HIV loads in humanized mice. Anti-PD-1 mAb treatment decreased PD-1+ CD8+ cell population by 32.3% after interruption of four weeks treatment, and D1143 co-treatment further reduced it from 32.3 to 73%. Anti-PD-1 mAb administration reduced HIV load in blood by 94%, and addition of D1143 further enhanced this reduction from 94 to 97%. D1143 also more profoundly promoted with the anti-PD-1-mediated reduction of HIV loads in all tissues analyzed including spleen (71 to 96.4%), lymph nodes (64.3 to 80%), liver (64.2 to 94.4), lung (64.3 to 80.1%) and thymic organoid (78.2 to 98.2%), achieving a >5 log reduction of HIV loads in CD4+ cells isolated from tissues 2 weeks after drug treatment interruption. Ex vivo anti-CD3/CD28 stimulation increased the ability to activate exhausted CD8+ T cells in infected mice having received in vivo anti-PD-1 treatment by 7.9-fold (5 to 39.6%), and an additional increase by 1.7-fold upon D1143 co-treatment (39.6 to 67.3%). These findings demonstrate for the first time that an inhibitor of apoptosis protein antagonist enhances in a statistically manner the effects of an immune check point inhibitor on antiviral immunity and on HIV load reduction in tissues of humanized mice, suggesting that the combination of two distinct classes of immunomodulatory agents constitutes a promising anti-HIV immunotherapeutic approach.

Elite control of HIV is associated with distinct functional and transcriptional signatures in lymphoid tissue CD8+ T cells

The functional properties of circulating CD8+ T cells have been associated with immune control of HIV. However, viral replication occurs predominantly in secondary lymphoid tissues, such as lymph nodes (LNs). We used an integrated single-cell approach to characterize effective HIV-specific CD8+ T cell responses in the LNs of elite controllers (ECs), defined as individuals who suppress viral replication in the absence of antiretroviral therapy (ART). Higher frequencies of total memory and follicle-homing HIV-specific CD8+ T cells were detected in the LNs of ECs compared with the LNs of chronic progressors (CPs) who were not receiving ART. Moreover, HIV-specific CD8+ T cells potently suppressed viral replication without demonstrable cytolytic activity in the LNs of ECs, which harbored substantially lower amounts of CD4+ T cell-associated HIV DNA and RNA compared with the LNs of CPs. Single-cell RNA sequencing analyses further revealed a distinct transcriptional signature among HIV-specific CD8+ T cells from the LNs of ECs, typified by the down-regulation of inhibitory receptors and cytolytic molecules and the up-regulation of multiple cytokines, predicted secreted factors, and components of the protein translation machinery. Collectively, these results provide a mechanistic framework to expedite the identification of novel antiviral factors, highlighting a potential role for the localized deployment of noncytolytic functions as a determinant of immune efficacy against HIV.

CD8β Depletion Does Not Prevent Control of Viral Replication or Protection from Challenge in Macaques Chronically Infected with a Live Attenuated Simian Immunodeficiency Virus

We evaluated the contribution of CD8αβ+ T cells to control of live-attenuated simian immunodeficiency virus (LASIV) replication during chronic infection and subsequent protection from pathogenic SIV challenge. Unlike previous reports with a CD8α-specific depleting monoclonal antibody (mAb), the CD8β-specific mAb CD8β255R1 selectively depleted CD8αβ+ T cells without also depleting non-CD8+ T cell populations that express CD8α, such as natural killer (NK) cells and γδ T cells. Following infusion with CD8β255R1, plasma viremia transiently increased coincident with declining peripheral CD8αβ+ T cells. Interestingly, plasma viremia returned to predepletion levels even when peripheral CD8αβ+ T cells did not. Although depletion of CD8αβ+ T cells in the lymph node (LN) was incomplete, frequencies of these cells were 3-fold lower (P = 0.006) in animals that received CD8β255R1 than in those that received control IgG. It is possible that these residual SIV-specific CD8αβ+ T cells may have contributed to suppression of viremia during chronic infection. We also determined whether infusion of CD8β255R1 in the LASIV-vaccinated animals increased their susceptibility to infection following intravenous challenge with pathogenic SIVmac239. We found that 7/8 animals infused with CD8β255R1, and 3/4 animals infused with the control IgG, were resistant to SIVmac239 infection. These results suggest that infusion with CD8β255R1 did not eliminate the protection afforded to LASIV vaccination. This provides a comprehensive description of the impact of CD8β255R1 infusion on the immunological composition in cynomolgus macaques, compared to an isotype-matched control IgG, while showing that the control of LASIV viremia and protection from challenge can occur even after CD8β255R1 administration.IMPORTANCE Studies of SIV-infected macaques that deplete CD8+ T cells in vivo with monoclonal antibodies have provided compelling evidence for their direct antiviral role. These studies utilized CD8α-specific mAbs that target both the major (CD8αβ+) and minor (CD8αα+) populations of CD8+ T cells but additionally deplete non-CD8+ T cell populations that express CD8α, such as NK cells and γδ T cells. In the current study, we administered the CD8β-specific depleting mAb CD8β255R1 to cynomolgus macaques chronically infected with a LASIV to selectively deplete CD8αβ+ T cells without removing CD8αα+ lymphocytes. We evaluated the impact on control of virus replication and protection from pathogenic SIVmac239 challenge. These results underscore the utility of CD8β255R1 for studying the direct contribution of CD8αβ+ T cells in various disease states.

Confirmed marijuana use and lymphocyte count in black people living with HIV

BACKGROUND

Marijuana is a commonly used recreational substance with purported analgesic and mood enhancing properties. Many people living with HIV identify marijuana as a palliative substance. However, through its main psychoactive component, tetrahydrocannabinol (THC), is known to influence the immune system. The effects of marijuana use in people with HIV are still controversial, with very scant literature in Black adults.

METHODS

The current study determined the differences in the lymphocyte count, specifically the number cluster differentiation 4 and 8 (CD4+ and CD8+), among patients who urine drug tested negative for THC (n = 70) and those who tested positive for THC (n = 25). The sample included 95 Black people living with HIV, 51% female, with a mean age of 46 ± 11 years. Participants provided a urine sample for substance use testing and a trained researcher extracted clinical data from clinical charts on the day of appointment.

RESULTS

After adjusting for demographic and HIV-related covariates, THC-positive patients had significantly higher CD4+ and CD8+ counts than their THC-negative counterparts.

CONCLUSION

These results extend previous HIV-related immunity findings in an underrepresented group, and suggest that THC use does not reduce immune function as measured by CD count. Further research is warranted on the overall effects of THC on immune function in HIV positive patients.

Effective Suppression of HIV-1 Replication by Cytotoxic T Lymphocytes Specific for Pol Epitopes in Conserved Mosaic Vaccine Immunogens

It is likely necessary for an effective AIDS vaccine to elicit CD8⁺ T cells with the ability to recognize circulating HIV-1 and suppress its replication. We recently developed novel bivalent mosaic T-cell vaccine immunogens composed of conserved regions of the Gag and Pol proteins matched to at least 80% globally circulating HIV-1 isolates. Nevertheless, it remains to be proven if vaccination with these immunogens can elicit T cells with the ability to suppress HIV-1 replication. It is well known that Gag-specific T cells can suppress HIV-1 replication more effectively than T cells specific for epitopes in other proteins. We recently identified 5 protective Gag epitopes in the vaccine immunogens. In this study, we identified T cells specific for 6 Pol epitopes present in the immunogens with strong abilities to suppress HIV-1 in vivo and in vitro. This study further encourages clinical testing of the conserved mosaic T-cell vaccine in HIV-1 prevention and cure.

Cytotoxic T lymphocytes (CTLs) with strong abilities to suppress HIV-1 replication and recognize circulating HIV-1 could be key for both HIV-1 cure and prophylaxis. We recently designed conserved mosaic T-cell vaccine immunogens (tHIVconsvX) composed of 6 Gag and Pol regions. Since the tHIVconsvX vaccine targets conserved regions common to most global HIV-1 variants and employs a bivalent mosaic design, it is expected that it could be universal if the vaccine works. Although we recently demonstrated that CTLs specific for 5 Gag epitopes in the vaccine immunogens had strong ability to suppress HIV-1 replication in vitro and in vivo, it remains unknown whether the Pol region-specific CTLs are equally efficient. In this study, we investigated CTLs specific for Pol epitopes in the immunogens in treatment-naive Japanese patients infected with HIV-1 clade B. Overall, we mapped 20 reported and 5 novel Pol conserved epitopes in tHIVconsvX. Responses to 6 Pol epitopes were significantly associated with good clinical outcome, suggesting that CTLs specific for these 6 Pol epitopes had a strong ability to suppress HIV-1 replication in HIV-1-infected individuals. In vitro T-cell analyses further confirmed that the Pol-specific CTLs could effectively suppress HIV-1 replication. The present study thus demonstrated that the Pol regions of the vaccine contained protective epitopes. T-cell responses to the previous 5 Gag and present 6 Pol protective epitopes together also showed a strong correlation with better clinical outcome. These findings support the testing of the conserved mosaic vaccine in HIV-1 cure and prevention in humans.

IMPORTANCE It is likely necessary for an effective AIDS vaccine to elicit CD8⁺ T cells with the ability to recognize circulating HIV-1 and suppress its replication. We recently developed novel bivalent mosaic T-cell vaccine immunogens composed of conserved regions of the Gag and Pol proteins matched to at least 80% globally circulating HIV-1 isolates. Nevertheless, it remains to be proven if vaccination with these immunogens can elicit T cells with the ability to suppress HIV-1 replication. It is well known that Gag-specific T cells can suppress HIV-1 replication more effectively than T cells specific for epitopes in other proteins. We recently identified 5 protective Gag epitopes in the vaccine immunogens. In this study, we identified T cells specific for 6 Pol epitopes present in the immunogens with strong abilities to suppress HIV-1 in vivo and in vitro. This study further encourages clinical testing of the conserved mosaic T-cell vaccine in HIV-1 prevention and cure.

Novel advances on tissue immune dynamics in HIV/simian immunodeficiency virus: lessons from imaging studies

PURPOSE OF REVIEW

To describe recent findings on the effect of HIV/SIV infection on lymph node viral and T-cell dynamics using imaging-based methodologies.

RECENT FINDINGS

Chronic infection, particularly HIV/SIV, alters dramatically the microenvironment, immune cell frequency, distribution, function and tissue organization of secondary lymphoid tissues. These changes are not always reversible. Over the past few years, the implementation of advanced imaging protocols on human lymph node biopsies as well as on longitudinal lymphoid tissues samples from nonhuman primates (NHP) have provided a wealth of information on how local immune responses evolve over time in response to a persisting retroviral pathogen. Most of the information concerns cytotoxic and helper T cells and viral dynamics. In this review, we detail this information focusing on HIV/SIV infection. We also comment on the gaps that imaging technologies have bridged in our understanding and discuss the translational value of these new findings in the light of emerging therapeutic agendas.

SUMMARY

Novel imaging platforms allow for dissecting the spatiotemporal dynamics of immune interactions further improving our understanding of the interplay between virus and host and providing important information for designing successful preventive and curative strategies.

CD8+ lymphocyte control of SIV infection during antiretroviral therapy

CD8⁺ lymphocytes play an important role in suppressing in vivo viral replication in HIV infection. However, both the extent to which and the mechanisms by which CD8⁺ lymphocytes contribute to viral control are not completely understood. A recent experiment depleted CD8⁺ lymphocytes in simian immunodeficiency virus (SIV)-infected rhesus macaques (RMs) on antiretroviral treatment (ART) to study the role of CD8⁺ lymphocytes. CD8⁺ lymphocytes depletion resulted in temporary plasma viremia in all studied RMs. Viral control was restored when CD8⁺ lymphocytes repopulated. We developed a viral dynamic model to fit the viral load (VL) data from the CD8 depletion experiment. We explicitly modeled the dynamics of the latent reservoir and the SIV-specific effector cell population including their exhaustion and their potential cytolytic and noncytolytic functions. We found that the latent reservoir significantly contributes to the size of the peak VL after CD8 depletion, while drug efficacy plays a lesser role. Our model suggests that the overall CD8⁺ lymphocyte cytolytic killing rate is dynamically changing depending on the levels of antigen-induced effector cell activation and exhaustion. Based on estimated parameters, our model suggests that before ART or without ART the overall CD8 cytolytic killing rate is small due to exhaustion. However, after the start of ART, the overall CD8 cytolytic killing rate increases due to an expansion of SIV-specific CD8 effector cells. Further, we estimate that the cytolytic killing rate can be significantly larger than the cytopathic death rate in some animals during the second phase of ART-induced viral decay. Lastly, our model provides a new explanation for the puzzling findings by Klatt et al. and Wong et al. that CD8 depletion done immediately before ART has no noticeable effect on the first phase viral decay slope seen after ART initiation Overall, by incorporating effector cells and their exhaustion, our model can explain the effects of CD8 depletion on VL during ART, reveals a detailed dynamic role of CD8⁺ lymphocytes in controlling viral infection, and provides a unified explanation for CD8 depletion experimental data.

CD8⁺ lymphocytes play an important role in suppressing in vivo viral replication in HIV infection. However, both the extent to which and the mechanisms by which CD8⁺ lymphocytes contribute to viral control are not completely understood. By mathematically modeling data from a recent CD8 depletion experiment done in antiretroviral (ART) treated animals, our results suggest that the overall CD8⁺ lymphocyte cytolytic killing rate is dynamically changing depending on the levels of antigen-induced effector cell activation and exhaustion, i.e. before ART or without ART the overall CD8 cytolytic killing rate is small due to exhaustion. However, after the start of ART, the overall CD8 cytolytic killing rate increases due to an expansion of SIV-specific CD8 effector cells. By incorporating effector cells and their exhaustion, our model explains the effects on viral load of CD8 depletion done before ART or during ART, reveals a detailed dynamic role of CD8⁺ lymphocytes in controlling viral infection, and provides a unified explanation for CD8 depletion experimental data.

Dynamics of Simian Immunodeficiency Virus Two-Long-Terminal-Repeat Circles in the Presence and Absence of CD8+ Cells

CD8⁺ cells play a key role in human immunodeficiency virus (HIV)/simian immunodeficiency virus (SIV) infection, but their specific mechanism(s) of action in controlling the virus is unclear. Two-long-terminal-repeat (2-LTR) circles are extrachromosomal products generated upon failed integration of HIV/SIV. To understand the specific effects of CD8⁺ cells on infected cells, we analyzed the dynamics of 2-LTR circles in SIVmac251-infected rhesus macaques (RMs) treated with an integrase inhibitor (INT). Twenty RMs underwent CD8⁺ cell depletion and received raltegravir (RAL) monotherapy or a combination of both. Blood, lymph nodes (LNs), and gut biopsy specimens were routinely sampled. Plasma viral loads (pVLs) and 2-LTR circles from peripheral blood mononuclear cells (PBMCs) and LN lymphocytes were measured with quantitative reverse transcription-PCR (qRT-PCR). In the CD8 depletion group, an ∼1-log increase in pVLs and a slow increase in PBMC 2-LTRs occurred following depletion. In the INT group, a strong decline in pVLs upon treatment initiation and no change in 2-LTR levels were observed. In the INT and CD8⁺ cell depletion group, an increase in pVLs following CD8 depletion similar to that in the CD8 depletion group was observed, with a modest decline following INT initiation, and 2-LTR circles significantly increased in PBMCs and LNs. Analyzing the 2-LTR data across all treatment groups with a mathematical model indicates that the data best support an effect of CD8⁺ cells in killing cells prior to viral integration. Sensitivity analyses of these results confirm that effect but also allow for additional effects, which the data do not discriminate well. Overall, we show that INT does not significantly increase the levels of 2-LTR circles. However, CD8⁺ cell depletion increases the 2-LTR levels, which are enhanced in the presence of an INT.IMPORTANCE CD8⁺ T cells play an essential role in controlling HIV and SIV infection, but the specific mechanisms involved remain poorly understood. Due to failed viral infection, HIV and SIV can form 2-LTR extrachromosomal circles that can be quantified. We present novel data on the dynamics of these 2-LTR forms in a SIV-infected macaque model under three different treatment conditions: depletion of CD8⁺ cells, administration of the integrase inhibitor in a monotherapy, which favors the formation of 2-LTR circles, and a combination of the two treatments. We used a new mathematical model to help interpret the data, and the results suggest that CD8⁺ cells exert a killing effect on infected cells prior to virus integration. These results provide new insights into the mechanisms of action of CD8⁺ cells in SIV infection. Confirmation of our results would be an important step in understanding immune control of HIV.

Differentiation and Function of Follicular CD8 T Cells During Human Immunodeficiency Virus Infection

The combination antiretroviral therapeutic (cART) regime effectively suppresses human immunodeficiency virus (HIV) replication and prevents progression to acquired immunodeficiency diseases. However, cART is not a cure, and viral rebound will occur immediately after treatment is interrupted largely due to the long-term presence of an HIV reservoir that is composed of latently infected target cells that maintain a quiescent state or persistently produce infectious viruses. CD4 T cells that reside in B-cell follicles within lymphoid tissues, called follicular helper T cells (TFH), have been identified as a major HIV reservoir. Due to their specialized anatomical structure, HIV-specific CD8 T cells are largely insulated from this TFH reservoir. It is increasingly clear that the elimination of TFH reservoirs is a key step toward a functional cure for HIV infection. Recently, several studies have suggested that a fraction of HIV-specific CD8 T cells can differentiate into a CXCR5-expressing subset, which are able to migrate into B-cell follicles and inhibit viral replication. In this review, we discuss the differentiation and functions of this newly identified CD8 T-cell subset and propose potential strategies for purging TFH HIV reservoirs by utilizing this unique population.

Treatment Intensification in HIV-Infected Patients Is Associated With Reduced Frequencies of Regulatory T Cells

In untreated HIV infection, the efficacy of T cell responses decreases over the disease course, resulting in disease progression. The reasons for this development are not completely understood. However, immunosuppressive cells are supposedly crucially involved. Treatment strategies to avoid the induction of these cells preserve immune functions and are therefore the object of intense research efforts. In this study, we assessed the effect of treatment intensification [=5-drug antiretroviral therapy (ART)] on the development of suppressive cell subsets. The New Era (NE) study recruited patients with primary HIV infection (PHI) or chronically HIV-infected patients with conventional ART (CHI) and applied an intensified 5-drug regimen containing maraviroc and raltegravir for several years. We compared the frequencies of the immune suppressive cells, namely, the myeloid-derived suppressor cells (MDSCs), regulatory B cells (Bregs), and regulatory T cells (Tregs), of the treatment intensification patients to the control groups, especially to the patients with conventional 3-drug ART, and analyzed the Gag/Nef-specific CD8 T cell responses. There were no differences between PHI and CHI in the NE population (p > 0.11) for any of the studied cell types. Polymorphonuclear myeloid-derived suppressor cell (PMN-MDSC), monocytic myeloid-derived suppressor cell (M-MDSC), and the Breg frequencies were comparable to those of patients with a 3-drug ART. However, the Treg levels were significantly lower in the NE patients than those in 3ART-treated individuals and other control groups (p ≤ 0.0033). The Gag/Nef-specific CD8 T cell response was broader (p = 0.0134) with a higher magnitude (p = 0.026) in the NE population than that in the patients with conventional ART. However, we did not find a correlation between the frequency of the immune suppressive cells and the interferon-gamma⁺ CD8 T cell response. In the treatment intensification subjects, the frequencies of the immune suppressive cells were comparable or lower than those of the conventional ART-treated subjects, with surprisingly broad HIV-specific CD8 T cell responses, suggesting a preservation of immune function with the applied treatment regimen. Interestingly, these effects were seen in both treatment intensification subpopulations and were not attributed to the start of treatment in primary infection.

Mechanisms of CD8+ T cell-mediated suppression of HIV/SIV replication

In this article, we summarize the role of CD8⁺ T cells during natural and antiretroviral therapy (ART)-treated HIV and SIV infections, discuss the mechanisms responsible for their suppressive activity, and review the rationale for CD8⁺ T cell-based HIV cure strategies. Evidence suggests that CD8⁺ T cells are involved in the control of virus replication during HIV and SIV infections. During early HIV infection, the cytolytic activity of CD8⁺ T cells is responsible for control of viremia. However, it has been proposed that CD8⁺ T cells also use non-cytolytic mechanisms to control SIV infection. More recently, CD8⁺ T cells were shown to be required to fully suppress virus production in ART-treated SIV-infected macaques, suggesting that CD8⁺ T cells are involved in the control of virus transcription in latently infected cells that persist under ART. A better understanding of the complex antiviral activities of CD8⁺ T cells during HIV/SIV infection will pave the way for immune interventions aimed at harnessing these functions to target the HIV reservoir.

Confirmed marijuana use and lymphocyte count in black people living with HIV

BACKGROUND

Marijuana is a commonly used recreational substance with purported analgesic and mood enhancing properties. Many people living with HIV identify marijuana as a palliative substance. However, through its main psychoactive component, tetrahydrocannabinol (THC), is known to influence the immune system. The effects of marijuana use in people with HIV are still controversial, with very scant literature in Black adults.

METHODS

The current study determined the differences in the lymphocyte count, specifically the number cluster differentiation 4 and 8 (CD4+ and CD8+), among patients who urine drug tested negative for THC (n=70) and those who tested positive for THC (n=25). The sample included 95 Black people living with HIV, 51% female, with a mean age of 46±11years. Participants provided a urine sample for substance use testing and a trained researcher extracted clinical data from clinical charts on the day of appointment.

RESULTS

After adjusting for demographic and HIV-related covariates, THC-positive patients had significantly higher CD4+ and CD8+ counts than their THC-negative counterparts.

CONCLUSION

These results extend previous HIV-related immunity findings in an underrepresented group, and suggest that THC use does not reduce immune function as measured by CD count. Further research is warranted on the overall effects of THC on immune function in HIV positive patients.

Natural Killer (NK) Cell Education Differentially Influences HIV Antibody-Dependent NK Cell Activation and Antibody-Dependent Cellular Cytotoxicity

Immunotherapy using broadly neutralizing antibodies (bNAbs) endowed with Fc-mediated effector functions has been shown to be critical for protecting or controlling viral replication in animal models. In human, the RV144 Thai trial was the first trial to demonstrate a significant protection against HIV infection following vaccination. Analysis of the correlates of immune protection in this trial identified an association between the presence of antibody-dependent cellular cytotoxicity (ADCC) mediated by immunoglobulin G (IgG) antibodies (Abs) to HIV envelope (Env) V1/V2 loop structures and protection from infection, provided IgA Abs with competing specificity were not present. Systems serology analyses implicated a broader range of Ab-dependent functions in protection from HIV infection, including but not limited to ADCC and Ab-dependent NK cell activation (ADNKA) for secretion of IFN-γ and CCL4 and expression of the degranulation marker CD107a. The existence of such correlations in the absence of bNAbs in the RV144 trial suggest that NK cells could be instrumental in protecting against HIV infection by limiting viral spread through Fc-mediated functions such as ADCC and the production of antiviral cytokines/chemokines. Beside the engagement of FcγRIIIa or CD16 by the Fc portion of anti-Env IgG1 and IgG3 Abs, natural killer (NK) cells are also able to directly kill infected cells and produce cytokines/chemokines in an Ab-independent manner. Responsiveness of NK cells depends on the integration of activating and inhibitory signals through NK receptors, which is determined by a process during their development known as education. NK cell education requires the engagement of inhibitory NK receptors by their human leukocyte antigen ligands to establish tolerance to self while allowing NK cells to respond to self cells altered by virus infection, transformation, stress, and to allogeneic cells. Here, we review recent findings regarding the impact of inter-individual differences in NK cell education on Ab-dependent functions such as ADCC and ADNKA, including what is known about the HIV Env epitope specificity of ADCC competent Abs and the conformation of HIV Env on target cells used for ADCC assays.

Analysis of the CD8+ T cell anti-HIV activity in heterologous cell co-cultures reveals the benefit of multiple HLA class I matches

CD8⁺ T lymphocytes can reduce the production of human immunodeficiency virus 1 (HIV-1) by CD4⁺ T cells by cytotoxic and non-cytotoxic mechanisms. To investigate the involvement of human leukocyte antigen (HLA) class I compatibility in anti-HIV responses, we co-cultured primary CD8⁺ T cells, isolated from the peripheral blood of HIV-1-infected individuals, with panels of autologous and heterologous acutely HIV-1-infected primary CD4⁺ T cells. Altogether, CD8⁺ T cell anti-HIV activity was evaluated in more than 200 co-cultures. Marked heterogeneity in HIV-1 replication levels was observed among the co-cultures sharing a common CD8⁺ T cell source. The co-cultures that exhibited greater than 50% reduction in HIV production were found to have significantly increased numbers of matching HLA class I alleles (Yates chi-square = 54.21; p < 0.001). With CD8⁺ T cells from HIV controllers and asymptomatic viremic individuals, matching HLA-B and/or HLA-C alleles were more predictive of strong anti-HIV activity than matching HLA-A alleles. Overall, HLA class I genotype matches were more closely associated with CD8⁺ T cell anti-HIV activity than supertype pairings. Antibodies against HLA class I and CD3 reduced the CD8⁺ T cell anti-HIV activity. Stimulated CD8⁺ T cells exhibited increased anti-HIV activity and reduced dependency on HLA compatibility. These findings provide evidence that the maximal suppression of HIV replication by CD8⁺ T cells requires the recognition of multiple epitopes. These studies provide insight for HIV vaccine development, and the analytic approach can be useful for the functional characterization of HLA class I alleles and tentative HLA class I supertypes.

Fighting Viral Infections and Virus-Driven Tumors with Cytotoxic CD4+ T Cells

CD4+ T cells have been and are still largely regarded as the orchestrators of immune responses, being able to differentiate into distinct T helper cell populations based on differentiation signals, transcription factor expression, cytokine secretion, and specific functions. Nonetheless, a growing body of evidence indicates that CD4+ T cells can also exert a direct effector activity, which depends on intrinsic cytotoxic properties acquired and carried out along with the evolution of several pathogenic infections. The relevant role of CD4+ T cell lytic features in the control of such infectious conditions also leads to their exploitation as a new immunotherapeutic approach. This review aims at summarizing currently available data about functional and therapeutic relevance of cytotoxic CD4+ T cells in the context of viral infections and virus-driven tumors.

Thymosin alpha 1 and HIV-1: recent advances and future perspectives

In spite of the consistent benefits for HIV-1 infected patients undergoing antiretroviral therapy, a complete immune reconstitution is usually not achieved. Actually, antiretroviral therapy may be frequently accompanied by immunological unresponsiveness, persistent inflammatory conditions and inefficient cytotoxic T-cell response. Thymosin alpha 1 is a thymic peptide that demonstrates a peculiar ability to restore immune system homeostasis in different physiological and pathological conditions (i.e., infections, cancer, immunodeficiency, vaccination and aging) acting as multitasking protein depending on the host state of inflammation or immune dysfunction. This review reports the present knowledge on the in vitro and in vivo studies concerning the use of thymosin alpha 1 in HIV-1 infection. Recent findings and future perspectives of therapeutic intervention are discussed.

Simian Immunodeficiency Virus-Producing Cells in Follicles Are Partially Suppressed by CD8+ Cells In Vivo

Human immunodeficiency virus (HIV)- and simian immunodeficiency virus (SIV)-specific CD8+ T cells are typically largely excluded from lymphoid B cell follicles, where HIV- and SIV-producing cells are most highly concentrated, indicating that B cell follicles are somewhat of an immunoprivileged site. To gain insights into virus-specific follicular CD8+ T cells, we determined the location and phenotype of follicular SIV-specific CD8+ T cells in situ, the local relationship of these cells to Foxp3+ cells, and the effects of CD8 depletion on levels of follicular SIV-producing cells in chronically SIV-infected rhesus macaques. We found that follicular SIV-specific CD8+ T cells were able to migrate throughout follicular areas, including germinal centers. Many expressed PD-1, indicating that they may have been exhausted. A small subset was in direct contact with and likely inhibited by Foxp3+ cells, and a few were themselves Foxp3+ In addition, subsets of follicular SIV-specific CD8+ T cells expressed low to medium levels of perforin, and subsets were activated and proliferating. Importantly, after CD8 depletion, the number of SIV-producing cells increased in B cell follicles and extrafollicular areas, suggesting that follicular and extrafollicular CD8+ T cells have a suppressive effect on SIV replication. Taken together, these results suggest that during chronic SIV infection, despite high levels of exhaustion and likely inhibition by Foxp3+ cells, a subset of follicular SIV-specific CD8+ T cells are functional and suppress viral replication in vivo These findings support HIV cure strategies that augment functional follicular virus-specific CD8+ T cells to enhance viral control.

IMPORTANCE

HIV- and SIV-specific CD8+ T cells are typically largely excluded from lymphoid B cell follicles, where virus-producing cells are most highly concentrated, suggesting that B cell follicles are somewhat of an immunoprivileged site where virus-specific CD8+ T cells are not able to clear all follicular HIV- and SIV-producing cells. To gain insights into follicular CD8+ T cell function, we characterized follicular virus-specific CD8+ T cells in situ by using an SIV-infected rhesus macaque model of HIV. We found that subsets of follicular SIV-specific CD8+ T cells are able to migrate throughout the follicle, are likely inhibited by Foxp3+ cells, and are likely exhausted but that, nonetheless, subsets are likely functional, as they express markers consistent with effector function and show signs of suppressing viral replication in vivo These findings support HIV cure strategies that increase the frequency of functional follicular virus-specific CD8+ T cells.

Collapse of Cytolytic Potential in SIV-Specific CD8+ T Cells Following Acute SIV Infection in Rhesus Macaques

Poor maintenance of cytotoxic factor expression among HIV-specific CD8+ T cells, in part caused by dysregulated expression of the transcription factor T-bet, is associated with HIV disease progression. However, the precise evolution and context in which CD8+ T cell cytotoxic functions become dysregulated in HIV infection remain unclear. Using the rhesus macaque (RM) SIV infection model, we evaluated the kinetics of SIV-specific CD8+ T cell cytolytic factor expression in peripheral blood, lymph node, spleen, and gut mucosa from early acute infection through chronic infection. We identified rapid acquisition of perforin and granzyme B expression in SIV-specific CD8+ T cells in blood, secondary lymphoid tissues and gut mucosa that collapsed rapidly during the transition to chronic infection. The evolution of this expression profile was linked to low expression of T-bet and occurred independent of epitope specificity, viral escape patterns and tissue origin. Importantly, during acute infection SIV-specific CD8+ T cells that maintained T-bet expression retained the ability to express granzyme B after stimulation, but this relationship was lost in chronic infection. Together, these data demonstrate the loss of cytolytic machinery in SIV-specific CD8+ T cells in blood and at tissue sites of viral reservoir and active replication during the transition from acute to chronic infection. This phenomenon occurs despite persistent high levels of viremia suggesting that an inability to maintain properly regulated cytotoxic T cell responses in all tissue sites enables HIV/SIV to avoid immune clearance, establish persistent viral reservoirs in lymphoid tissues and gut mucosa, and lead ultimately to immunopathogenesis and death.

Pre-infection transcript levels of FAM26F in peripheral blood mononuclear cells inform about overall plasma viral load in acute and post-acute phase after simian immunodeficiency virus infection

CD8⁺ cells from simian immunodeficiency virus (SIV)-infected long-term non-progressors and some uninfected macaques can suppress viral replication in vitro without killing the infected cells. The aim of this study was to identify factors responsible for non-cytolytic viral suppression by transcriptional profiling and to investigate their potential impact on SIV replication. Results of microarray experiments and further validation with cells from infected and uninfected macaques revealed that FAM26F RNA levels distinguished CD8⁺ cells of controllers and non-controllers (P=0.001). However, FAM26F was also expressed in CD4⁺ T-cells and B-cells. FAM26F expression increased in lymphocytes after in vitro IFN-γ treatment on average 40-fold, and ex vivo FAM26F RNA levels in peripheral blood mononuclear cells correlated with plasma IFN-γ but not with IFN-α. Baseline FAM26F expression appeared to be stable for months, albeit the individual expression levels varied up to tenfold. Investigating its role in SIV-infection revealed that FAM26F was upregulated after infection (P<0.0008), but did not directly correlate with viral load in contrast to MX1 and CXCL10. However, pre-infection levels of FAM26F correlated inversely with overall plasma viral load (AUC) during the acute and post-acute phases of infection (e.g. AUC weeks post infection 0–8; no AIDS vaccine: P<0.0001, Spearman rank correlation coefficient (rs)=−0.89, n=16; immunized with an AIDS vaccine: P=0.033, rs=−0.43; n=25). FAM26F transcript levels prior to infection can provide information about the pace and strength of the antiviral immune response during the early stage of infection. FAM26F expression represented, in our experiments, one of the earliest prognostic markers, and could supplement major histocompatibility complex (MHC)-typing to predict disease progression before SIV-infection.

Innate and Adaptive Mucosal Immunity in Protection against HIV Infection

The appalling toll on the populations of developing countries as a result of the HIV epidemic shows no signs of abatement. While costly drug therapies are effective in developed nations, the sheer scale of the epidemic elsewhere makes the need for a vaccine an ever more urgent goal. The prevalent DNA prime-viral boost strategy aims to elicit cytotoxic lymphocytes (CTL) against HIV, but this approach is undermined by the rapid mutation of HIV, which thereby escapes CTL control. Alloimmunity has been found to be protective in vertical transmission from infected mothers to their babies, in alloimmunization of women with their partners’ mononuclear cells, and in monkeys immunized with SIV grown in human T-cells. Vaginal mucosal immunization, as a result of unprotected sex with a regular partner, induced in vitro protection against HIV infection, and this was confirmed in macaques. The second type of natural protection is found in persons with the homozygous Δ32 CCR5 mutation, a 32-base-pair deletion of the CCR5 gene, which results in a lack of cell-surface expression of CCR5, which is associated with an increase in CC chemokines and the development of CCR5 antibodies. These two ‘experiments of nature’ have been used to develop vaccine strategies—first, in vaginal immunization of macaques with CCR5 peptides, in addition to HIV envelope (env) and SIV core (gag) antigens, all of which were linked to the 70-kD heat-shock protein (HSP70); and second, in mucosal allo-immunization of macaques, which also gave rise to in vitro protection from infection. Immunization with this vaccine elicited serum and vaginal IgG and IgA antibodies, IFNγ- and IL-12-producing cells, and increased concentrations of CCL-3 and CCL-4. Vaginal challenge with a simian immunodeficiency virus engineered to carry a human envelope protein (SHIV 89.6) showed significant clearance of SHIV in the immunized macaques. This platform strategy will now be developed to activate the co-stimulatory pathways with the aim of enhancing the primary allogeneic and CCR5-directed responses which are involved in natural protection against HIV infection. Abbreviations: IFN-γ, gamma interferon; IL-12, interleukin 12; MIP-1 α,β, Macrophage inflammatory protein-1; RANTES, Regulated on activation normal T-cell expressed and secreted; SDF-1, stromal-derived factor 1; SIV, simian immunodeficiency virus; and SHIV, engineered SIV carrying a human envelope protein.

CD8(+) Lymphocytes Are Required for Maintaining Viral Suppression in SIV-Infected Macaques Treated with Short-Term Antiretroviral Therapy

Infection with HIV persists despite suppressive antiretroviral therapy (ART), and treatment interruption results in rapid viral rebound. Antibody-mediated CD8(+) lymphocyte depletion in simian immunodeficiency virus (SIV)-infected rhesus macaques (RMs) shows that these cells contribute to viral control in untreated animals. However, the contribution of CD8(+) lymphocytes to maintaining viral suppression under ART remains unknown. Here, we have shown that in SIV-infected RMs treated with short-term (i.e., 8-32 week) ART, depletion of CD8(+) lymphocytes resulted in increased plasma viremia in all animals and that repopulation of CD8(+) T cells was associated with prompt reestablishment of virus control. Although the number of SIV-DNA-positive cells remained unchanged after CD8 depletion and reconstitution, the frequency of SIV-infected CD4(+) T cells before depletion positively correlated with both the peak and area under the curve of viremia after depletion. These results suggest a role for CD8(+) T cells in controlling viral production during ART, thus providing a rationale for exploring immunotherapeutic approaches in ART-treated HIV-infected individuals.

Elite controller CD8+ T cells exhibit comparable viral inhibition capacity, but better sustained effector properties compared to chronic progressors

Mechanisms modulating HIV-specific CD8+ T cell-mediated viral inhibition are not well defined. To delineate features of effective control, we compared the ability of CD8⁺ T cells from HIV ECs and CPs to inhibit HIV ex vivo. ECs showed superior inhibition compared to HAART-treated or untreated CPs in a typical VIA in which CD8+ T cells are rested 3 d before use (P = 0.025). In contrast, comparable antiviral activity was observed in freshly thawed cells. Rested CD8⁺ T cells underwent apoptosis with preferential loss of HIV-specific cells. EC CD8⁺ T cells showed greater capacity to sustain polyfunctionality ex vivo compared with those of CPs, and incubation of CD8⁺ T cells with IL-15 augmented inhibition. These results indicate that superior ex vivo inhibition of viral replication by CD8⁺ T cells from ECs is associated with enhanced retention of functional qualities and that in vitro antiviral function is enhanced by IL-15.

Noncytolytic CD8+ Cell Mediated Antiviral Response Represents a Strong Element in the Immune Response of Simian Immunodeficiency Virus-Infected Long-Term Non-Progressing Rhesus Macaques

The ability of long term non progressors to maintain very low levels of HIV/SIV and a healthy state, involves various host genetic and immunological factors. CD8+ non-cytolytic antiviral response (CNAR) most likely plays an important role in this regard. In order to gain a deeper insight into this unique phenomenon, the ability of CD8+ T cells to suppress viral replication in vitro was investigated in 16 uninfected, longitudinally in 23 SIV-infected long-term non-progressing (LTNPs), and 10 SIV-infected rhesus macaques with progressing disease. An acute infection assay utilizing CD4⁺ cells from MHC-mismatched monkeys to avoid cytolytic responses was employed. The study has identified CNAR as a long-term stable activity that inversely correlated with plasma viral load. The activity was also detected in CD8⁺ cells of uninfected macaques, which indicates that CNAR is not necessarily a virus specific response but increases after SIV-infection. Physical contact between CD4⁺ and CD8⁺ cells was mainly involved in mediating viral inhibition. Loss of this activity appeared to be due to a loss of CNAR-expressing CD8+ cells as well as a reduction of CNAR-responsive CD4+ cells. In contrast, in vitro viral replication did not differ in CD4+ cells from un-infected macaques, CNAR(+) and CNAR(-) LTNPs. A role for transitional memory cells in supporting CNAR in the macaque model of AIDS was questionable. CNAR appears to represent an important part of the immune response displayed by CD8+ T cells which might be underestimated up to now.

Regulation of CD8+ T-cell cytotoxicity in HIV-1 infection

Understanding the mechanisms involved in cellular immune responses against control of human immunodeficiency virus (HIV) infection is key to development of effective immunotherapeutic strategies against viral proliferation. Clear insights into the regulation of cytotoxic CD8+ T cells is crucial to development of effective immunotherapeutic strategies due to their unique ability to eliminate virus-infected cells during the course of infection. Here, we reviewed the roles of transcription factors, co-inhibitory molecules and regulatory cytokines following HIV infection and their potential significance in regulating the cytotoxic potentials of CD8+ T cells.

The CD8+ cell non-cytotoxic antiviral response affects RNA polymerase II-mediated human immunodeficiency virus transcription in infected CD4+ cells

A CD8+ cell non-cytotoxic antiviral response (CNAR), mediated by a CD8+ cell antiviral factor (CAF), is associated with a long-term healthy state in human immunodeficiency virus (HIV) infection. CNAR/CAF reduces viral transcription without a known effect on specific viral sequences in the HIV genome. In studies to define the mechanism involved in the block in viral transcription, we now report that transcription from the HIV-LTR reporter is reduced in infected CD4+ cells upon treatment with CAF. In agreement with this observation, the amount of RNA polymerase II (RNAPII) on the HIV promoter and other viral regions was strongly diminished in HIV-infected CD4+ cells co-cultivated with CNAR-expressing CD8+ cells. These results demonstrate further that CNAR/CAF has a specific role in regulating HIV transcription and a step during the preinitiation complex assembly appears to be sensitive to CNAR/CAF.

Large granular lymphocytes are universally increased in human, macaque, and feline lentiviral infection

Large granular lymphocytes (LGLs) have only been anecdotally reported in HIV infection. We previously reported an LGL lymphocytosis in FIV-infected cats associated with a rise in FIV proviral loads and a marked neutropenia that persisted during chronic infection. Extensive immunophenotyping of peripheral blood mononuclear cells in cats chronically infected with FIV were identified LGLs as CD8lo(+)FAS(+); this cell population expanded commensurate with viral load. CD8lo(+)FAS(+) cells expressed similar levels of interferon-γ compared to CD8lo(+)FAS(+) cells from FIV-naive control animals, yet CD3ɛ expression, which was increased on total CD8(+) T cells in FIV-infected cats, was decreased on CD8lo(+)FAS(+) cells. Down-modulation of CD3 expression was reversed after culturing PBMC for 3 days in culture with ConA/IL-2. We identified CD8lo(+)FAS(+) LGLs to be polyclonal T cells lacking CD56 expression. Blood smears from HIV-infected individuals and SIVmac239-infected rhesus macaques revealed increased LGLs compared to HIV/SIV negative counterparts. In humans, there was no correlation with viral load or treatment and in macaques the LGLs arose in acute SIV infection with increases in viremia. This is the first report describing and partially characterizing LGL lymphocytosis in association with lentiviral infections in three different species.

TOE1 is an inhibitor of HIV-1 replication with cell-penetrating capability

Target of Egr1 (TOE1) is a nuclear protein localized primarily in nucleoli and Cajal bodies that was identified as a downstream target of the immediate early gene Egr1. TOE1 displays a functional deadenylation domain and has been shown to participate in spliceosome assembly. We report here that TOE1 can function as an inhibitor of HIV-1 replication and show evidence that supports a direct interaction of TOE1 with the viral specific transactivator response element as part of the inhibitory mechanism. In addition, we show that TOE1 can be secreted by activated CD8(+) T lymphocytes and can be cleaved by the serine protease granzyme B, one of the main components of cytotoxic granules. Both full-length and cleaved TOE1 can spontaneously cross the plasma membrane and penetrate cells in culture, retaining HIV-1 inhibitory activity. Antiviral potency of TOE1 and its cell-penetrating capability have been identified to lie within a 35-amino-acid region containing the nuclear localization sequence.

Dispelling myths and focusing on notable concepts in HIV pathogenesis

Since the discovery of HIV over three decades ago, major efforts have been made to control and perhaps eliminate HIV infection worldwide. During these studies, certain myths or misconceptions about this infectious disease have been emphasized and other potentially beneficial concepts have received less attention. A true long-term solution to HIV infection merits an appreciation of alternative ideas and findings that could be beneficial in the ultimate control of HIV/AIDS. Here, I discuss six issues and call for more attention to the science of HIV and well-designed clinical trials.

Coinhibitory receptors and CD8 T cell exhaustion in chronic infections

PURPOSE OF REVIEW

To describe the recent data on the role of coinhibitory receptors, such as PD-1, Tim-3, CD160, as mediators of the 'exhaustion' of virus-specific CD8 T cells in chronic infections and particularly in HIV.

RECENT FINDINGS

Exhaustion of chronic virus-specific CD8 T cells is a dynamic process characterized by altered differentiation, impaired function, and compromised proliferation/survival profile of these cells. This process is mediated by coinhibitory receptors expressed on the surface of virus-specific CD8 T cells and an orchestrated function of centrally connected pathways. Coexpression of several coinhibitory receptors characterizes severely exhausted virus-specific CD8 T cells. Several studies suggest a synergistic action, instead of a redundant role, of the different receptors. In-vivo manipulation of the coinhibitory network can rejuvenate exhausted virus-specific CD8 T cell responses and constrain replication of chronic viruses, including HIV.

SUMMARY

Revealing the molecular basis of virus-specific CD8 T cell exhaustion in chronic infections is critical for the understanding of the disease pathogenesis and the designing of novel vaccines aiming to enhance the cytolytic arm of the immune system. This is of particular interest for the development of immunotherapies in the context of a functional cure for HIV.

The upregulation of LAG-3 on T cells defines a subpopulation with functional exhaustion and correlates with disease progression in HIV-infected subjects

T cells develop functional defects during HIV-1 infection, partially due to the upregulation of inhibitory receptors such as programmed death-1 (PD-1) and CTLA-4. However, the role of lymphocyte activation gene-3 (LAG-3; CD223), also known as an inhibitory receptor, in HIV infection remains to be determined. In this study, we revealed that LAG-3 on T cells delivers an inhibitory signal to downregulate T cell functionality, thereby playing an immunoregulatory role during persistent HIV-1 infection. We observed that HIV-1 infection results in a significant increase in LAG-3 expression in both the peripheral blood and the lymph nodes. The upregulation of LAG-3 is dramatically manifested on both CD4(+) and CD8(+) T cells and is correlated with disease progression. As expected, prolonged antiretroviral therapy reduces the expression of LAG-3 on both CD4(+) and CD8(+) T cells. The ex vivo blockade of LAG-3 significantly augments HIV-specific CD4(+) and CD8(+) T cell responses, whereas the overexpression of LAG-3 in T cells or the stimulation of LAG-3 on T cells leads to the reduction of T cell responses. Furthermore, most LAG-3 and PD-1 are expressed in different T cell subsets. Taken together, these data demonstrate that the LAG-3/MHC class II pathway plays an immunoregulatory role, thereby providing an important target for enhancing immune reconstitution in HIV-infected patients. Additionally, the LAG-3/MHC class II pathway may synergize with PD-1/PD ligand to enhance T cell-mediated immune responses.

CD8 T cell response maturation defined by anentropic specificity and repertoire depth correlates with SIVΔnef-induced protection

The live attenuated simian immunodeficiency virus (LASIV) vaccine SIVΔnef is one of the most effective vaccines in inducing protection against wild-type lentiviral challenge, yet little is known about the mechanisms underlying its remarkable protective efficacy. Here, we exploit deep sequencing technology and comprehensive CD8 T cell epitope mapping to deconstruct the CD8 T cell response, to identify the regions of immune pressure and viral escape, and to delineate the effect of epitope escape on the evolution of the CD8 T cell response in SIVΔnef-vaccinated animals. We demonstrate that the initial CD8 T cell response in the acute phase of SIVΔnef infection is mounted predominantly against more variable epitopes, followed by widespread sequence evolution and viral escape. Furthermore, we show that epitope escape expands the CD8 T cell repertoire that targets highly conserved epitopes, defined as anentropic specificity, and generates de novo responses to the escaped epitope variants during the vaccination period. These results correlate SIVΔnef-induced protection with expanded anentropic specificity and increased response depth. Importantly, these findings render SIVΔnef, long the gold standard in HIV/SIV vaccine research, as a proof-of-concept vaccine that highlights the significance of the twin principles of anentropic specificity and repertoire depth in successful vaccine design.