Increased loss of CCR5+ CD45RA- CD4+ T cells in CD8+ lymphocyte-depleted Simian immunodeficiency virus-infected rhesus monkeys

Making a Monkey out of Human Immunodeficiency Virus/Simian Immunodeficiency Virus Pathogenesis: Immune Cell Depletion Experiments as a Tool to Understand the Immune Correlates of Protection and Pathogenicity in HIV Infection

Understanding the underlying mechanisms of HIV pathogenesis is critical for designing successful HIV vaccines and cure strategies. However, achieving this goal is complicated by the virus's direct interactions with immune cells, the induction of persistent reservoirs in the immune system cells, and multiple strategies developed by the virus for immune evasion. Meanwhile, HIV and SIV infections induce a pandysfunction of the immune cell populations, making it difficult to untangle the various concurrent mechanisms of HIV pathogenesis. Over the years, one of the most successful approaches for dissecting the immune correlates of protection in HIV/SIV infection has been the in vivo depletion of various immune cell populations and assessment of the impact of these depletions on the outcome of infection in non-human primate models. Here, we present a detailed analysis of the strategies and results of manipulating SIV pathogenesis through in vivo depletions of key immune cells populations. Although each of these methods has its limitations, they have all contributed to our understanding of key pathogenic pathways in HIV/SIV infection.

Antibody-mediated depletion of select leukocyte subsets in blood and tissue of nonhuman primates

Understanding the immunological control of pathogens requires a detailed evaluation of the mechanistic contributions of individual cell types within the immune system. While knockout mouse models that lack certain cell types have been used to help define the role of those cells, the biological and physiological characteristics of mice do not necessarily recapitulate that of a human. To overcome some of these differences, studies often look towards nonhuman primates (NHPs) due to their close phylogenetic relationship to humans. To evaluate the immunological role of select cell types, the NHP model provides distinct advantages since NHP more closely mirror the disease manifestations and immunological characteristics of humans. However, many of the experimental manipulations routinely used in mice (e.g., gene knock-out) cannot be used with the NHP model. As an alternative, the in vivo infusion of monoclonal antibodies that target surface proteins on specific cells to either functionally inhibit or deplete cells can be a useful tool. Such depleting antibodies have been used in NHP studies to address immunological mechanisms of action. In these studies, the extent of depletion has generally been reported for blood, but not thoroughly assessed in tissues. Here, we evaluated four depleting regimens that primarily target T cells in NHP: anti-CD4, anti-CD8α, anti-CD8β, and immunotoxin-conjugated anti-CD3. We evaluated these treatments in healthy unvaccinated and IV BCG-vaccinated NHP to measure the extent that vaccine-elicited T cells - which may be activated, increased in number, or resident in specific tissues - are depleted compared to resting populations in unvaccinated NHPs. We report quantitative measurements of in vivo depletion at multiple tissue sites providing insight into the range of cell types depleted by a given mAb. While we found substantial depletion of target cell types in blood and tissue of many animals, residual cells remained, often residing within tissue. Notably, we find that animal-to-animal variation is substantial and consequently studies that use these reagents should be powered accordingly.

HPV and the Risk of HIV Acquisition in Women

The risk of HIV acquisition is low on a per-contact basis but increased by transmission co-factors such as other sexually transmitted infections (STIs). Human papillomavirus (HPV) is a prevalent STI that most individuals will acquire HPV in their lifetime. Current HPV vaccines can prevent newly acquired infections, but are largely ineffective against established HPV, complicating worldwide eradication efforts. In addition to being the causative agent of cervical cancer, accumulating evidence suggests that HPV infection and/or accompanying cervical inflammation increase the risk of HIV infection in men and women. The fact that immunological features observed during HPV infection overlap with cellular and molecular pathways known to enhance HIV susceptibility underscore the potential interplay between these two viral infections that fuel their mutual spread. Here we review current insights into how HPV infection and the generation of anti-HPV immunity contribute to higher HIV transmission rates, and the impact of HPV on mucosal inflammation, immune cell trafficking, and epithelial barrier function.

Distinct Immune Profiles of Exhausted Effector and Memory CD8+ T Cells in Individuals With Filarial Lymphedema

CD8⁺ T cells are crucial for the clearance of viral infections, and current research begins to highlight their importance in parasitic diseases too. In-depth research about characteristics of CD8⁺ T-cell subsets and exhaustion remains uncertain, especially during filariasis, a chronic helminth infection. Lymphatic filariasis, elicited by Wuchereria bancrofti, remains a serious health problem in endemic areas in Ghana, especially in those suffering from morbidity due to lymphedema (LE). In this observational study, the characteristics and profiles of CD8⁺ T cells were compared between asymptomatic Wuchereria bancrofti-infected individuals, uninfected endemic normals, and those with LE (grades 2–6). Focusing on exhausted memory (CD8⁺ex_mem: CD8⁺ T-bet^dimEomes^hi) and effector (CD8⁺ex_eff: CD8⁺T-bet^hiEomes^dim) CD8⁺ T-cell subsets, advanced flow cytometry revealed that LE individuals presented reduced frequencies of IFN-γ⁺CD8⁺ex_mem T cells expressing Tim-3 or LAG-3 which negatively correlated to the presence of LE. Moreover, the LE cohort further showed significantly higher frequencies of IL-10⁺CD8⁺ex_eff T cells expressing either Tim-3, LAG-3, CD39, KLRG-1, or PD-1, all associated markers of exhaustion, and that these frequencies positively correlated with the presence of LE. In summary, this study shows that distinct exhausted CD8⁺ T-cell subsets are prominent in individuals suffering from LE, suggesting that enhanced inflammation and constant immune activation might drive exhaustion of CD8⁺ T cells. Since T-cell exhaustion is known to be associated with insufficient control of persisting antigen, the data presented here reveals that these CD8⁺ T-cell exhaustion patterns in filarial LE should be taken into consideration for prevention and control management of LE.

IL-7 induces sCD127 release and mCD127 downregulation in human CD8+ T cells by distinct yet overlapping mechanisms, both of which are impaired in HIV infection

The IL‐7 receptor specific α chain, CD127, can be expressed both as a membrane‐associated (mCD127) and a soluble form (sCD127), however, the mechanisms involved in their regulation remain to be defined. We first demonstrated in primary human CD8⁺ T cells that IL‐7‐induced downregulation of mCD127 expression is dependent on JAK and PI3K signaling, whereas IL‐7‐induced sCD127 release is also mediated by STAT5. Following stimulation with IL‐7, expression of alternatively spliced variants of the CD127 gene, sCD127 mRNA, is reduced, but to a lesser degree than the full‐length gene. Evaluation of the role of proteases revealed that MMP‐9 was involved in sCD127 release, without affecting the expression of mCD127, suggesting it does not induce direct shedding from the cell surface. Since defects in the IL‐7/CD127 pathway occur in various diseases, including HIV, we evaluated CD8⁺ T cells derived from HAART‐treated HIV‐infected individuals and found that IL‐7‐induced (1) downregulation of mCD127, (2) release of sCD127, and (3) expression of the sCD127 mRNA were all impaired. Expression of mCD127 and sCD127 is, therefore, regulated by distinct, but overlapping, mechanisms and their impairment in HIV infection contributes to our understanding of the CD8⁺ T cell dysfunction that persists despite effective antiretroviral therapy.

HPV infection and the genital cytokine milieu in women at high risk of HIV acquisition

Human papillomavirus (HPV) infection correlates with higher rates of HIV acquisition, but the underlying biological mechanisms are unclear. Here we study associations between HPV and HIV acquisition and relate these to vaginal cytokine profiles in an observational cohort of women at high risk of HIV infection (CAPRISA 004, n = 779) and with 74% HPV prevalence. We report here that HPV infection associates with a 2.5-fold increase in HIV acquisition risk in this population (95% CI: 1.2-5.3). Among 48 vaginal cytokines profiled, cytokines associated with HPV infection overlap substantially with cytokines associated with HIV risk, but are distinct from those observed in HPV negative women. Although our data do not establish a causative link between HPV status and the risk of HIV, we suggest that increasing HPV vaccination coverage may carry an additional benefit of reducing the risk of contracting HIV infection, particularly in regions with high HPV prevalence.

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.

Acute Infection and Subsequent Subclinical Reactivation of Herpes Simplex Virus 2 after Vaginal Inoculation of Rhesus Macaques

Herpes simplex virus 2 (HSV-2) is a common sexually transmitted infection with a highly variable clinical course. Many infections quickly become subclinical, with episodes of spontaneous virus reactivation. To study host-HSV-2 interactions, an animal model of subclinical HSV-2 infection is needed. In an effort to develop a relevant model, rhesus macaques (RM) were inoculated intravaginally with two or three HSV-2 strains (186, 333, and/or G) at a total dose of 1 × 10⁷ PFU of HSV-2 per animal. Infectious HSV-2 and HSV-2 DNA were consistently shed in vaginal swabs for the first 7 to 14 days after each inoculation. Proteins associated with wound healing, innate immunity, and inflammation were significantly increased in cervical secretions immediately after HSV-2 inoculation. There was histologic evidence of acute herpesvirus pathology, including acantholysis in the squamous epithelium and ballooning degeneration of and intranuclear inclusion bodies in epithelial cells, with HSV antigen in mucosal epithelial cells and keratinocytes. Further, an intense inflammatory infiltrate was found in the cervix and vulva. Evidence of latent infection and reactivation was demonstrated by the detection of spontaneous HSV-2 shedding post-acute inoculation (10² to 10³ DNA copies/swab) in 80% of RM. Further, HSV-2 DNA was detected in ganglia in most necropsied animals. HSV-2-specifc T-cell responses were detected in all animals, although antibodies to HSV-2 were detected in only 30% of the animals. Thus, HSV-2 infection of RM recapitulates many of the key features of subclinical HSV-2 infection in women but seems to be more limited, as virus shedding was undetectable more than 40 days after the last virus inoculation.IMPORTANCE Herpes simplex virus 2 (HSV-2) infects nearly 500 million persons globally, with an estimated 21 million incident cases each year, making it one of the most common sexually transmitted infections (STIs). HSV-2 is associated with increased human immunodeficiency virus type 1 (HIV-1) acquisition, and this risk does not decline with the use of antiherpes drugs. As initial acquisition of both HIV and HSV-2 infections is subclinical, study of the initial molecular interactions of the two agents requires an animal model. We found that HSV-2 can infect RM after vaginal inoculation, establish latency in the nervous system, and spontaneously reactivate; these features mimic some of the key features of HSV-2 infection in women. RM may provide an animal model to develop strategies to prevent HSV-2 acquisition and reactivation.

The dynamics of simian immunodeficiency virus after depletion of CD8+ cells

Human immunodeficiency virus infection is still one of the most important causes of morbidity and mortality in the world, with a disproportionate human and economic burden especially in poorer countries. Despite many years of intense research, an aspect that still is not well understood is what (immune) mechanisms control the viral load during the prolonged asymptomatic stage of infection. Because CD8+ T cells have been implicated in this control by multiple lines of evidence, there has been a focus on understanding the potential mechanisms of action of this immune effector population. One type of experiment used to this end has been depleting these cells with monoclonal antibodies in the simian immunodeficiency virus-macaque model and then studying the effect of that depletion on the viral dynamics. Here we review what these experiments have told us. We emphasize modeling studies to interpret the changes in viral load observed in these experiments, including discussion of alternative models, assumptions and interpretations, as well as potential future experiments.

EcoHIV infection of mice establishes latent viral reservoirs in T cells and active viral reservoirs in macrophages that are sufficient for induction of neurocognitive impairment

Suppression of HIV replication by antiretroviral therapy (ART) or host immunity can prevent AIDS but not other HIV-associated conditions including neurocognitive impairment (HIV-NCI). Pathogenesis in HIV-suppressed individuals has been attributed to reservoirs of latent-inducible virus in resting CD4+ T cells. Macrophages are persistently infected with HIV but their role as HIV reservoirs in vivo has not been fully explored. Here we show that infection of conventional mice with chimeric HIV, EcoHIV, reproduces physiological conditions for development of disease in people on ART including immunocompetence, stable suppression of HIV replication, persistence of integrated, replication-competent HIV in T cells and macrophages, and manifestation of learning and memory deficits in behavioral tests, termed here murine HIV-NCI. EcoHIV established latent reservoirs in CD4+ T lymphocytes in chronically-infected mice but could be induced by epigenetic modulators ex vivo and in mice. In contrast, macrophages expressed EcoHIV constitutively in mice for up to 16 months; murine leukemia virus (MLV), the donor of gp80 envelope in EcoHIV, did not infect macrophages. Both EcoHIV and MLV were found in brain tissue of infected mice but only EcoHIV induced NCI. Murine HIV-NCI was prevented by antiretroviral prophylaxis but once established neither persistent EcoHIV infection in mice nor NCI could be reversed by long-acting antiretroviral therapy. EcoHIV-infected, athymic mice were more permissive to virus replication in macrophages than were wild-type mice, suffered cognitive dysfunction, as well as increased numbers of monocytes and macrophages infiltrating the brain. Our results suggest an important role of HIV expressing macrophages in HIV neuropathogenesis in hosts with suppressed HIV replication.

Lymph Node Cellular and Viral Dynamics in Natural Hosts and Impact for HIV Cure Strategies

Combined antiretroviral therapies (cARTs) efficiently control HIV replication leading to undetectable viremia and drastic increases in lifespan of people living with HIV. However, cART does not cure HIV infection as virus persists in cellular and anatomical reservoirs, from which the virus generally rebounds soon after cART cessation. One major anatomical reservoir are lymph node (LN) follicles, where HIV persists through replication in follicular helper T cells and is also trapped by follicular dendritic cells. Natural hosts of SIV, such as African green monkeys and sooty mangabeys, generally do not progress to disease although displaying persistently high viremia. Strikingly, these hosts mount a strong control of viral replication in LN follicles shortly after peak viremia that lasts throughout infection. Herein, we discuss the potential interplay between viral control in LNs and the resolution of inflammation, which is characteristic for natural hosts. We furthermore detail the differences that exist between non-pathogenic SIV infection in natural hosts and pathogenic HIV/SIV infection in humans and macaques regarding virus target cells and replication dynamics in LNs. Several mechanisms have been proposed to be implicated in the strong control of viral replication in natural host's LNs, such as NK cell-mediated control, that will be reviewed here, together with lessons and limitations of in vivo cell depletion studies that have been performed in natural hosts. Finally, we discuss the impact that these insights on viral dynamics and host responses in LNs of natural hosts have for the development of strategies toward HIV cure.

Differential Impact of In Vivo CD8+ T Lymphocyte Depletion in Controller versus Progressor Simian Immunodeficiency Virus-Infected Macaques

Numerous studies have demonstrated that CD8(+) T lymphocytes suppress virus replication during human immunodeficiency virus (HIV)/simian immunodeficiency virus (SIV) infection. However, the mechanisms underlying this activity of T cells remain incompletely understood. Here, we conducted CD8(+) T lymphocyte depletion in 15 rhesus macaques (RMs) infected intravenously (i.v.) with SIVmac239. At day 70 postinfection, the animals (10 progressors with high viremia and 5 controllers with low viremia) were CD8 depleted by i.v. administration of the antibody M-T807R1. As expected, CD8 depletion resulted in increased virus replication, more prominently in controllers than progressors, which correlated inversely with predepletion viremia. Of note, the feature of CD8(+) T lymphocyte predepletion that correlated best with the increase in viremia postdepletion was the level of CD8(+) T-bet(+) lymphocytes. We next found that CD8 depletion resulted in a homogenous increase of SIV RNA in superficial and mesenteric lymph nodes, spleen, and the gastrointestinal tract of both controllers and progressors. Interestingly, the level of SIV DNA increased postdepletion in both CD4(+) central memory T lymphocytes (TCM) and CD4(+) effector memory T lymphocytes (TEM) in progressor RMs but decreased in the CD4(+) TCM of 4 out of 5 controllers. Finally, we found that CD8 depletion is associated with a greater increase in CD4(+) T lymphocyte activation (measured by Ki-67 expression) in controllers than in progressors. Overall, these data reveal a differential impact of CD8(+) T lymphocyte depletion between controller and progressor SIV-infected RMs, emphasizing the complexity of the in vivo antiviral role of CD8(+) T lymphocytes.

IMPORTANCE

In this study, we further dissect the impact of CD8(+) T lymphocytes on HIV/SIV replication during SIV infection. CD8(+) T lymphocyte depletion leads to a relatively homogenous increase in viral replication in peripheral blood and tissues. CD8(+) T lymphocyte depletion resulted in a more prominent increase in viral loads and CD4(+) T lymphocyte activation in controllers than in progressors. Interestingly, we found T-bet expression on CD8(+) T lymphocytes to be the best predictor of viral load increase following depletion. The levels of SIV DNA increase postdepletion in both CD4(+) TCM and TEM in progressor RMs but decrease in the CD4(+) TCM of controllers. The findings described in this study provide key insights into the differential functions of CD8(+) T lymphocytes in controller and progressor RMs.

Humanized mouse models for HIV-1 infection of the CNS

Since the onset of the HIV epidemic, there has been a shift from a deadly diagnosis to the management of a chronic disease. This shift is the result of the development of highly effective drugs that are able to suppress viral replication for years. The availability of these regimens has also shifted the neurocognitive pathology associated with infection from potentially devastating to a much milder phenotype. As the disease outcome has changed significantly with the availability of antiretroviral therapy, there is an opportunity to re-evaluate the currently available models to address the neurocognitive pathology seen in suppressed patients. In the following, we seek to summarize the current literature on humanized mouse models and their utility in understanding how HIV infection leads to changes in the central nervous system (CNS). Also, we identify some of the unanswered questions regarding HIV infection of the CNS as well as the opportunities and limitations of currently existing models to address those questions. Finally, our conclusions indicate that the earlier humanized models used to study HIV infection in the CNS provided an excellent foundation for the type of work currently being performed using novel humanized mouse models. We also indicate the potential of some humanized mouse models that have not been used as of this time for the analysis of HIV infection in the brain.

HIV-1-induced AIDS in monkeys

Primate lentiviruses exhibit narrow host tropism, reducing the occurrence of zoonoses but also impairing the development of optimal animal models of AIDS. To delineate the factors limiting cross-species HIV-1 transmission, we passaged a modified HIV-1 in pigtailed macaques that were transiently depleted of CD8(+) cells during acute infection. During adaptation over four passages in macaques, HIV-1 acquired the ability to antagonize the macaque restriction factor tetherin, replicated at progressively higher levels, and ultimately caused marked CD4(+) T cell depletion and AIDS-defining conditions. Transient treatment with an antibody to CD8 during acute HIV-1 infection caused rapid progression to AIDS, whereas untreated animals exhibited an elite controller phenotype. Thus, an adapted HIV-1 can cause AIDS in macaques, and stark differences in outcome can be determined by immunological perturbations during early infection.

Rhesus macaques vaccinated with consensus envelopes elicit partially protective immune responses against SHIV SF162p4 challenge

The development of a preventative HIV/AIDS vaccine is challenging due to the diversity of viral genome sequences, especially in the viral envelope (Env₁₆₀). Since it is not possible to directly match the vaccine strain to the vast number of circulating HIV-1 strains, it is necessary to develop an HIV-1 vaccine that can protect against a heterologous viral challenge. Previous studies from our group demonstrated that a mixture of wild type clade B Env(gp160s) were able to protect against a heterologous clade B challenge more effectively than a consensus clade B Envg(p160) vaccine. In order to broaden the immune response to other clades of HIV, in this study rhesus macaques were vaccinated with a polyvalent mixture of purified HIV-1 trimerized consensus Envg(p140) proteins representing clades A, B, C, and E. The elicited immune responses were compared to a single consensus Env(gp140) representing all isolates in group M (Con M). Both vaccines elicited anti- Env(gp140) IgG antibodies that bound an equal number of HIV-1 Env(gp160) proteins representing clades A, B and C. In addition, both vaccines elicited antibodies that neutralized the HIV-1(SF162) isolate. However, the vaccinated monkeys were not protected against SHIV(SF162p4) challenge. These results indicate that consensus Env(gp160) vaccines, administered as purified Env(gp140) trimers, elicit antibodies that bind to Env(gp160s) from strains representing multiple clades of HIV-1, but these vaccines did not protect against heterologous SHIV challenge.

Transcriptional profiling of experimental CD8(+) lymphocyte depletion in rhesus macaques infected with simian immunodeficiency virus SIVmac239

CD8(+) T cells inhibit virus replication in SIV-infected rhesus macaques. However, it is unclear to what extent the viral suppression mediated by CD8(+) T cells reflects direct killing of infected cells as opposed to indirect, noncytolytic mechanisms. In this study, we used functional genomics to investigate noncytolytic mechanisms of in vivo viral suppression mediated by CD8(+) lymphocytes. Eight chronically SIVmac239-infected rhesus macaques underwent CD8(+) lymphocyte depletion, and RNA from whole blood was obtained prior to depletion, during the nadir of CD8(+) cell depletion, and after CD8(+) lymphocyte numbers had rebounded. We observed significant downregulation of the expression of genes encoding factors that can suppress SIV replication, including the CCR5-binding chemokine CCL5/RANTES and CCL4 and several members of the tripartite motif-containing (TRIM) family. Surprisingly, we also noted a strong, widespread downregulation of α- and θ-defensins with anti-HIV activity, which are not expressed by CD8(+) T cells. After cessation of depleting antibody treatment, we observed induction of a transcriptional signature indicative of B lymphocyte activation. Validation experiments demonstrated that animals during this period had elevated levels of B cells coupled with higher expression of the proliferative marker Ki67, indicating that CD8(+) depletion triggered a potent expansion of B cell numbers. Collectively, these data identify antiviral pathways perturbed by in vivo CD8(+) T cell depletion that may contribute to noncytolytic control of SIV replication.

Alcohol and HIV Infection

Alcohol abuse and human immunodeficiency virus (HIV) infection are major public health problems and frequently coexist in the same individual. Although several studies have shown a significant association between alcohol consumption and the risk of being infected with HIV, it is unclear whether this association is due to behavioral and/or biomedical mechanisms. Studies of HIV-infected patients are inherently limited in their ability to control for variables such as timing and dose of HIV exposure, nutrition, concurrent use of drugs of abuse, use of anti-retroviral therapy, and the frequency of alcohol consumption and amount of alcohol consumed. In order to study the impact of alcohol on HIV infection, we developed a model of chronic alcohol consumption in rhesus macaques monkeys (Macaca mulatta) infected with simian immunodeficiency virus (SIV), a lentivirus closely related to HIV that infects and destroys CD4+ cells and produces a progressive immunodeficiency representative of HIV disease. Using this model, our studies have shown that plasma viral loads are significantly higher in alcohol-consuming macaques at 60-120 days after SIV infection (viral set point) than in control animals. The viral set point has been shown to be predictive of disease progression, and in our studies, alcohol consumption was associated with accelerated disease progression to end-stage disease. The rhesus macaque SIV model should be useful in identifying the mechanisms by which alcohol increases the viral load of HIV, affects HIV-associated comorbidities, and influences the efficacy of anti-retroviral therapy.

Links between progressive HIV-1 infection of humanized mice and viral neuropathogenesis

Few rodent models of human immunodeficiency virus type one (HIV-1) infection can reflect the course of viral infection in humans. To this end, we investigated the relationships between progressive HIV-1 infection, immune compromise, and neuroinflammatory responses in NOD/scid-IL-2Rγ(c)(null) mice reconstituted with human hematopoietic CD34(+) stem cells. Human blood-borne macrophages repopulated the meninges and perivascular spaces of chimeric animals. Viral infection in lymphoid tissue led to the accelerated entry of human cells into the brain, marked neuroinflammation, and HIV-1 replication in human mononuclear phagocytes. A meningitis and less commonly an encephalitis followed cM-T807 antibody-mediated CD8(+) cell depletion. We conclude that HIV-1-infected NOD/scid-IL-2Rγ(c)(null) humanized mice can, at least in part, recapitulate lentiviral neuropathobiology. This model of neuroAIDS reflects the virological, immunological, and early disease-associated neuropathological components of human disease.

Emergence of simian immunodeficiency virus-specific cytotoxic CD4+ T cells and increased humoral responses correlate with control of rebounding viremia in CD8-depleted macaques infected with Rev-independent live-attenuated simian immunodeficiency virus

Indian rhesus macaques infected with the Rev-independent live-attenuated SIVmac239 strains control viremia to undetectable levels, have persistent but low cellular and humoral anti-SIV responses, and show no signs of immune deficiency. To analyze the immune mechanisms responsible for viral control, five macaques infected at day 1 after birth were subjected to CD8(+) cell depletion at 6.7 y postinfection. This resulted in viremia increases to 3.7-5.5 log(10) RNA copies, supporting a role of CD8-mediated responses in the control of viral replication. The rebounding viremia was rapidly controlled to levels below the threshold of detection, and occurred in the absence of SIV-specific CD8(+) T cells and significant CD8(+) T cell recovery in four of the five animals, suggesting that other mechanisms are involved in the immunological control of viremia. Monitoring immune responses at the time of viral control demonstrated a burst of circulating SIV-specific CD4(+) T cells characterized as CD45RA(-)CD28(+)CD95(+)CCR7(-) and also granzyme B(+), suggesting cytotoxic ability. Control of viremia was also concomitant with increases in humoral responses to Gag and Env, including a transient increase in neutralizing Abs against the neutralization-resistant SIVmac239 in four of five animals. These data demonstrate that a combination of cellular responses mediated by CD4(+) T cells and humoral responses was associated with the rapid control of the rebounding viremia in macaques infected by the Rev-independent live-attenuated SIV, even in the absence of measurable SIV-specific CD8(+) T cells in the blood, emphasizing the importance of different components of the immune response for full control of SIV infection.

CD8+ cell depletion accelerates HIV-1 immunopathology in humanized mice

Stable engraftment of human lymphoid tissue in NOD/scid-IL-2Rgammacnull mice after CD34+ hematopoietic stem cell reconstitution permits the evaluation of ongoing HIV-1 infection for weeks to months. We demonstrate that HIV-1-infected rodents develop virus-specific cellular immune responses. CD8+ cell depletion, 2 or 5-7 wk after viral infection, resulted in a significant increase of HIV-1 load, robust immune cell activation, and cytopathology in lymphoid tissues but preserved CD4/CD8 double-positive thymic T cell pools. Human CD8+ cells reappeared in circulation as early as 2-3 wk. These data support a role of CD8+ cells in viral surveillance and the relevance of this humanized mouse model for the studies of HIV-1 pathobiology and virus-specific immunity.

Experimental depletion of CD8+ cells in acutely SIVagm-infected African Green Monkeys results in increased viral replication

Background

In vivo CD8⁺ cell depletions in pathogenic SIV infections identified a key role for cellular immunity in controlling viral load (VL) and disease progression. However, similar studies gave discordant results in chronically-infected SMs, leading some authors to propose that in natural hosts, SIV replication is independent of cellular immunity. To assess the role of cellular immune responses in the control of SIV replication in natural hosts, we investigated the impact of CD8⁺ cell depletion during acute SIV infection in AGMs.

Results

Nine AGMs were infected with SIVagm.sab and were followed up to day 225 p.i. Four were intravenously infused with the cM-T807 antibody on days 0 (50 mg/kg), 6, and 13 (10 mg/kg, respectively) post infection (p.i.). CD8⁺ cells were depleted for up to 28 days p.i. in peripheral blood and LNs in all treated AGMs. Partial CD8⁺ T cell depletion occurred in the intestine. SIVagm VLs peaked at similar levels in both groups (10⁷-10⁸ RNA copies/ml). However, while VLs were controlled in undepleted AGMs, reaching set-point levels (10⁴-10⁵ RNA copies/ml) by day 28 p.i., high VLs (>10⁶ RNA copies/ml) were maintained by day 21 p.i. in CD8-depleted AGMs. By day 42 p.i., VLs were comparable between the two groups. The levels of immune activation and proliferation remained elevated up to day 72 p.i. in CD8-depleted AGMs and returned to preinfection levels in controls by day 28 p.i. None of the CD8-depleted animals progressed to AIDS.

Conclusion

CD8⁺ cells are responsible for a partial control of postacute viral replication in SIVagm.sab-infected AGMs. In contrast to macaques, the SIVagm-infected AGMs are able to control viral replication after recovery of the CD8⁺ T cells and avoid disease progression.

Suppression of adaptive immune responses during primary SIV infection of sabaeus African green monkeys delays partial containment of viremia but does not induce disease

One of the most puzzling observations in HIV research is the lack of pathogenicity in most nonhuman primate species that are natural hosts of simian immunodeficiency virus (SIV) infection. Despite this, natural hosts experience a level of viremia similar to humans infected with HIV or macaques infected with SIV. To determine the role of adaptive immune responses in viral containment and lack of disease, we delayed the generation of cellular and humoral immune responses by administering anti-CD8- and anti-CD20 lymphocyte-depleting antibodies to sabaeus African green monkeys (Chlorocebus sabaeus) before challenge with SIV(sab9315BR). In vivo lymphocyte depletion during primary infection resulted in a brief elevation of viremia but not in disease. Based on the magnitude and timing of SIV-specific CD8(+) T-cell responses in the lymphocyte-depleted animals, CD8(+) T-cell responses appear to contribute to viral containment in natural hosts. We found no evidence for a contribution of humoral immune responses in viral containment. These studies indicate that natural hosts have developed mechanisms in addition to classic adaptive immune responses to cope with this lentiviral infection. Thus, adaptive immune responses in natural hosts appear to be less critical for viral containment than in HIV infection.

Alcohol's role in HIV transmission and disease progression

Alcohol use has negative effects on HIV disease progression through several mechanisms, including transmission, viral replication, host immunity, and treatment efficacy. Research with animal models has explored the effect of alcohol intake on several aspects of simian immunodeficiency virus (SIV) disease progression. Data suggest that the increased SIV levels observed in alcohol-consuming animals may represent an increase in virus production as opposed to a decrease in host defense. Results also suggest that changes in nutritional balance and metabolism, as a possible consequence of a proinflammatory state, together with increased virus production in animals consuming alcohol, accelerate SIV and possibly HIV disease progression. Further studies using the animal model are necessary.

Inhibition of adaptive immune responses leads to a fatal clinical outcome in SIV-infected pigtailed macaques but not vervet African green monkeys

African green monkeys (AGM) and other natural hosts for simian immunodeficiency virus (SIV) do not develop an AIDS-like disease following SIV infection. To evaluate differences in the role of SIV-specific adaptive immune responses between natural and nonnatural hosts, we used SIV_agmVer90 to infect vervet AGM and pigtailed macaques (PTM). This infection results in robust viral replication in both vervet AGM and pigtailed macaques (PTM) but only induces AIDS in the latter species. We delayed the development of adaptive immune responses through combined administration of anti-CD8 and anti-CD20 lymphocyte-depleting antibodies during primary infection of PTM (n = 4) and AGM (n = 4), and compared these animals to historical controls infected with the same virus. Lymphocyte depletion resulted in a 1-log increase in primary viremia and a 4-log increase in post-acute viremia in PTM. Three of the four PTM had to be euthanized within 6 weeks of inoculation due to massive CMV reactivation and disease. In contrast, all four lymphocyte-depleted AGM remained healthy. The lymphocyte-depleted AGM showed only a trend toward a prolongation in peak viremia but the groups were indistinguishable during chronic infection. These data show that adaptive immune responses are critical for controlling disease progression in pathogenic SIV infection in PTM. However, the maintenance of a disease-free course of SIV infection in AGM likely depends on a number of mechanisms including non-adaptive immune mechanisms.

Simian immunodeficiency virus (SIV) is a naturally occurring infection in a wide range of African nonhuman primates, including African green monkeys (AGM), which generally results in a clinically inapparent infection. In contrast, SIV infection of Asian nonhuman primates such as macaques can result in an AIDS-like disease similar to that observed in humans infected with human immunodeficiency virus (HIV). This different pathogenic outcome occurs despite similar levels of viremia. In order to evaluate the contribution of adaptive immune responses to these different outcomes, we transiently inhibited the generation of CD8+ and CD20+ lymphocyte-mediated immune responses in vervet AGM and pigtailed macaques (PTM) during primary SIV infection. PTM experienced higher viremia and accelerated progression to disease, whereas AGM showed only a short prolongation of peak viremia but exhibited no signs of illness. These results demonstrate that protection against development of disease in AGM does not solely rely on adaptive immune responses. Future efforts should aim to determine the underlying mechanisms that enable natural hosts to cope with SIV infection and to apply these findings to develop new treatment modalities for humans infected with HIV.

HIV vaccination: turning the spotlight on effector memory T cells as mucosal gatekeepers

The accumulating failures in HIV vaccine development demonstrate that the immunization approaches used so far are insufficient to reproduce the naturally occurring immunity that controls the virus in long-term non-progressors, HIV controllers, and continuously exposed sex workers. They also underscore the desperate need for new approaches in the design of more effective vaccination protocols. Recent findings might have brought us closer to that goal by providing proof of concept for a novel preventative HIV vaccine by establishing CD8 effector memory T cells within the mucosal sites of transmission.

CD8+ cell depletion of SHIV89.6P-infected macaques induces CD4+ T cell proliferation that contributes to increased viral loads

Previous studies have shown that depletion of CD8(+) cells during acute and chronic simian immunodeficiency virus (SIV) infection leads to increased viral replication, morbidity, and mortality, which have been attributed to loss of CD8(+) T cell-mediated control of SIV. However, these studies did not exclude that CD8(+) cell depletion increased homeostatic proliferation of CD4(+) T cells, resulting in increased viral targets and, therefore, viral rebound. Chronically SHIV89.6P-infected cynomolgus macaques were CD8(+) cell-depleted, and the frequency, cell number, and phenotype of CD4(+) T cells and viral infection were examined using flow cytometry and quantitative real-time PCR. The frequency and number of Ki-67-expressing CD4(+) T cells were increased with CD8(+) cell depletion. This proliferation of CD4(+) T cells occurred even in animals with no rebound of viral loads. Most of the proliferating cells were effector memory CD4(+) T cells. Plasma simian HIV (SHIV) RNA copies positively correlated with proliferating CD4(+) T cells and SHIV DNA copies in Ki-67(+) CD4(+) T cells. Although this study does not exclude an important role for virus-specific CD8(+) T cells in SIV and SHIV infection, our data suggest that homeostatic proliferation is an important contributor to increases in plasma viremia that follow CD8(+) cell depletion.

Pathogenic infection of Macaca nemestrina with a CCR5-tropic subtype-C simian-human immunodeficiency virus

Background

Although pig-tailed macaques (Macaca nemestrina) have been used in AIDS research for years, less is known about the early immunopathogenic events in this species, as compared to rhesus macaques (Macaca mulatta). Similarly, the events in early infection are well-characterized for simian immunodeficiency viruses (SIV), but less so for chimeric simian-human immunodeficiency viruses (SHIV), although the latter have been widely used in HIV vaccine studies. Here, we report the consequences of intrarectal infection with a CCR5-tropic clade C SHIV-1157ipd3N4 in pig-tailed macaques.

Results

Plasma and cell-associated virus was detectable in peripheral blood and intestinal tissues of all four pig-tailed macaques following intrarectal inoculation with SHIV-1157ipd3N4. We also observed a rapid and irreversible loss of CD4⁺ T cells at multiple mucosal sites, resulting in a marked decrease of CD4:CD8 T cell ratios 0.5–4 weeks after inoculation. This depletion targeted subsets of CD4⁺ T cells expressing the CCR5 coreceptor and having a CD28^-CD95⁺ effector memory phenotype, consistent with the R5-tropism of SHIV-1157ipd3N4. All three animals that were studied beyond the acute phase seroconverted as early as week 4, with two developing cross-clade neutralizing antibody responses by week 24. These two animals also demonstrated persistent plasma viremia for >48 weeks. One of these animals developed AIDS, as shown by peripheral blood CD4⁺ T-cell depletion starting at 20 weeks post inoculation.

Conclusion

These findings indicate that SHIV-1157ipd3N4-induced pathogenesis in pig-tailed macaques followed a similar course as SIV-infected rhesus macaques. Thus, R5 SHIV-C-infection of pig-tailed macaques could provide a useful and relevant model for AIDS vaccine and pathogenesis research.

Profound CD4+/CCR5+ T cell expansion is induced by CD8+ lymphocyte depletion but does not account for accelerated SIV pathogenesis

Depletion of CD8⁺ lymphocytes during acute simian immunodeficiency virus (SIV) infection of rhesus macaques (RMs) results in irreversible prolongation of peak-level viral replication and rapid disease progression, consistent with a major role for CD8⁺ lymphocytes in determining postacute-phase viral replication set points. However, we report that CD8⁺ lymphocyte depletion is also associated with a dramatic induction of proliferation among CD4⁺ effector memory T (T_EM) cells and, to a lesser extent, transitional memory T (T_TrM) cells, raising the question of whether an increased availability of optimal (activated/proliferating), CD4⁺/CCR5⁺ SIV “target” cells contributes to this accelerated pathogenesis. In keeping with this, depletion of CD8⁺ lymphocytes in SIV⁻ RMs led to a sustained increase in the number of potential CD4⁺ SIV targets, whereas such depletion in acute SIV infection led to increased target cell consumption. However, we found that the excess CD4⁺ T_EM cell proliferation of CD8⁺ lymphocyte–depleted, acutely SIV-infected RMs was completely inhibited by interleukin (IL)-15 neutralization, and that this inhibition did not abrogate the rapidly progressive infection in these RMs. Moreover, although administration of IL-15 during acute infection induced robust CD4⁺ T_EM and T_TrM cell proliferation, it did not recapitulate the viral dynamics of CD8⁺ lymphocyte depletion. These data suggest that CD8⁺ lymphocyte function has a larger impact on the outcome of acute SIV infection than the number and/or activation status of target cells available for infection and viral production.

Immune control of an SIV challenge by a T-cell-based vaccine in rhesus monkeys

A recombinant adenovirus serotype 5 (rAd5) vector-based vaccine for HIV-1 has recently failed in a phase 2b efficacy study in humans. Consistent with these results, preclinical studies have demonstrated that rAd5 vectors expressing simian immunodeficiency virus (SIV) Gag failed to reduce peak or setpoint viral loads after SIV challenge of rhesus monkeys (Macaca mulatta) that lacked the protective MHC class I allele Mamu-A*01 (ref. 3). Here we show that an improved T-cell-based vaccine regimen using two serologically distinct adenovirus vectors afforded substantially improved protective efficacy in this challenge model. In particular, a heterologous rAd26 prime/rAd5 boost vaccine regimen expressing SIV Gag elicited cellular immune responses with augmented magnitude, breadth and polyfunctionality as compared with the homologous rAd5 regimen. After SIV(MAC251) challenge, monkeys vaccinated with the rAd26/rAd5 regimen showed a 1.4 log reduction of peak and a 2.4 log reduction of setpoint viral loads as well as decreased AIDS-related mortality as compared with control animals. These data demonstrate that durable partial immune control of a pathogenic SIV challenge for more than 500 days can be achieved by a T-cell-based vaccine in Mamu-A*01-negative rhesus monkeys in the absence of a homologous Env antigen. These findings have important implications for the development of next-generation T-cell-based vaccine candidates for HIV-1.

Initial B-cell responses to transmitted human immunodeficiency virus type 1: virion-binding immunoglobulin M (IgM) and IgG antibodies followed by plasma anti-gp41 antibodies with ineffective control of initial viremia

A window of opportunity for immune responses to extinguish human immunodeficiency virus type 1 (HIV-1) exists from the moment of transmission through establishment of the latent pool of HIV-1-infected cells. A critical time to study the initial immune responses to the transmitted/founder virus is the eclipse phase of HIV-1 infection (time from transmission to the first appearance of plasma virus), but, to date, this period has been logistically difficult to analyze. To probe B-cell responses immediately following HIV-1 transmission, we have determined envelope-specific antibody responses to autologous and consensus Envs in plasma donors from the United States for whom frequent plasma samples were available at time points immediately before, during, and after HIV-1 plasma viral load (VL) ramp-up in acute infection, and we have modeled the antibody effect on the kinetics of plasma viremia. The first detectable B-cell response was in the form of immune complexes 8 days after plasma virus detection, whereas the first free plasma anti-HIV-1 antibody was to gp41 and appeared 13 days after the appearance of plasma virus. In contrast, envelope gp120-specific antibodies were delayed an additional 14 days. Mathematical modeling of the earliest viral dynamics was performed to determine the impact of antibody on HIV replication in vivo as assessed by plasma VL. Including the initial anti-gp41 immunoglobulin G (IgG), IgM, or both responses in the model did not significantly impact the early dynamics of plasma VL. These results demonstrate that the first IgM and IgG antibodies induced by transmitted HIV-1 are capable of binding virions but have little impact on acute-phase viremia at the timing and magnitude that they occur in natural infection.

With minimal systemic T-cell expansion, CD8+ T Cells mediate protection of rhesus macaques immunized with attenuated simian-human immunodeficiency virus SHIV89.6 from vaginal challenge with simian immunodeficiency virus

The presence, at the time of challenge, of antiviral effector T cells in the vaginal mucosa of female rhesus macaques immunized with live-attenuated simian-human immunodeficiency virus 89.6 (SHIV89.6) is associated with consistent and reproducible protection from pathogenic simian immunodeficiency virus (SIV) vaginal challenge (18). Here, we definitively demonstrate the protective role of the SIV-specific CD8(+) T-cell response in SHIV-immunized monkeys by CD8(+) lymphocyte depletion, an intervention that abrogated SHIV-mediated control of challenge virus replication and largely eliminated the SIV-specific T-cell responses in blood, lymph nodes, and genital mucosa. While in the T-cell-intact SHIV-immunized animals, polyfunctional and degranulating SIV-specific CD8(+) T cells were present in the genital tract and lymphoid tissues from the day of challenge until day 14 postchallenge, strikingly, expansion of SIV-specific CD8(+) T cells in the immunized monkeys was minimal and limited to the vagina. Thus, protection from uncontrolled SIV replication in animals immunized with attenuated SHIV89.6 is primarily mediated by CD8(+) T cells that do not undergo dramatic systemic expansion after SIV challenge. These findings demonstrate that despite, and perhaps because of, minimal systemic expansion of T cells at the time of challenge, a stable population of effector-cytotoxic CD8(+) T cells can provide significant protection from vaginal SIV challenge.