In pathogenic HIV and SIV infections of humans and rhesus macaques (RMs), preferential depletion of CD4+ Th17 cells correlates with mucosal immune dysfunction and disease progression. Interleukin (IL)-21 promotes differentiation of Th17 cells, long-term maintenance of functional CD8+ T cells, and differentiation of memory B cells and antibody-secreting plasma cells. We hypothesized that administration of IL-21 will improve mucosal function in the context of pathogenic HIV/SIV infections. To test this hypothesis, we infected 12 RMs with SIVmac239 and at day 14 post-infection treated six of them with rhesus rIL-21-IgFc. IL-21-treatment was safe and did not increase plasma viral load or systemic immune activation. Compared to untreated animals, IL-21-treated RMs showed (i) higher expression of perforin and granzyme B in total and SIV-specific CD8+ T cells and (ii) higher levels of intestinal Th17 cells. Remarkably, increased levels of Th17 cells were associated with reduced levels of intestinal T cell proliferation, microbial translocation and systemic activation/inflammation in the chronic infection. In conclusion, IL-21-treatment in SIV-infected RMs improved mucosal immune function through enhanced preservation of Th17 cells. Further preclinical studies of IL-21 may be warranted to test its potential use during chronic infection in conjunction with antiretroviral therapy.

Background Infection of nonhuman primates with simian immunodeficiency virus (SIV) or chimeric simian-human immunodeficiency virus (SHIV) strains is widely used to study lentiviral pathogenesis, antiviral immunity and the efficacy of AIDS vaccine candidates. SHIV challenges allow assessment of anti-HIV-1 envelope responses in primates. As such, SHIVs should mimic natural HIV-1 infection in humans and, to address the pandemic, encode HIV-1 Env components representing major viral subtypes worldwide. Results We have developed a panel of clade C R5-tropic SHIVs based upon env of a Zambian pediatric isolate of HIV-1 clade C, the world's most prevalent HIV-1 subtype. The parental infectious proviral clone, SHIV-1157i, was rapidly passaged through five rhesus monkeys. After AIDS developed in the first animal at week 123 post-inoculation, infected blood was infused into a sixth monkey. Virus reisolated at this late stage was still exclusively R5 tropic and mucosally transmissible. Here we describe the long-term follow-up of this initial cohort of six monkeys. Two have remained non-progressors, whereas the other four gradually progressed to AIDS within 123–270 weeks post-exposure. Two progressors succumbed to opportunistic infections, including a case of SV40 encephalitis. Conclusion These data document the disease progression induced by the first mucosally transmissible, pathogenic R5 non-clade B SHIV and suggest that SHIV-1157i-derived viruses, including the late-stage, highly replication-competent SHIV-1157ipd3N4 previously described (Song et al., 2006), display biological characteristics that mirror those of HIV-1 clade C and support their expanded use for AIDS vaccine studies in nonhuman primates.

Heart disease is common in both humans and chimpanzees, manifesting typically as sudden cardiac arrest or progressive heart failure. Surprisingly, although chimpanzees are our closest evolutionary relatives, the major cause of heart disease is different in the two species. Histopathology data of affected chimpanzee hearts from two primate centers, and analysis of literature indicate that sudden death in chimpanzees (and in gorillas and orangutans) is commonly associated with diffuse interstitial myocardial fibrosis of unknown cause. In contrast, most human heart disease results from coronary artery atherosclerosis, which occludes myocardial blood supply, causing ischemic damage. The typical myocardial infarction of humans due to coronary artery thrombosis is rare in these apes, despite their human-like coronary-risk-prone blood lipid profiles. Instead, chimpanzee 'heart attacks' are likely due to arrythmias triggered by myocardial fibrosis. Why do humans not often suffer from the fibrotic heart disease so common in our closest evolutionary cousins? Conversely, why do chimpanzees not have the kind of heart disease so common in humans? The answers could be of value to medical care, as well as to understanding human evolution. A preliminary attempt is made to explore possibilities at the histological level, with a focus on glycosylation changes.

Human immunodeficiency virus clade C (HIV-C) accounts for >56% of all HIV infections worldwide. To investigate vaccine safety and efficacy in nonhuman primates, a pathogenic, R5-tropic, neutralization-sensitive simian-human immunodeficiency virus (SHIV) carrying HIV-C env would be desirable. We have constructed SHIV-2873Ni, an R5-tropic SHIV carrying a primary pediatric HIV-C env gene isolated from a 2-month-old Zambian infant, who died within 1 year of birth. SHIV-2873Ni was constructed using SHIV-1157ipd3N4 (R. J. Song, A. L. Chenine, R. A. Rasmussen, C. R. Ruprecht, S. Mirshahidi, R. D. Grisson, W. Xu, J. B. Whitney, L. M. Goins, H. Ong, P. L. Li, E. Shai-Kobiler, T. Wang, C. M. McCann, H. Zhang, C. Wood, C. Kankasa, W. E. Secor, H. M. McClure, E. Strobert, J. G. Else, and R. M. Ruprecht. J. Virol. 80:8729-8738, 2006) as the backbone, since the latter contains additional NF-κB sites in the long terminal repeats to enhance viral replicative capacity. The parental virus, SHIV-2873Ni, was serially passaged through five rhesus monkeys (RMs); SHIV-2873Nip, the resulting passaged virus, was reisolated from the fourth recipient about 1 year postinoculation. SHIV-2873Nip was replication competent in RM peripheral blood mononuclear cells of all random donors tested and was exclusively R5 tropic, and its env gene clustered with HIV-C by phylogenetic analysis; its high sensitivity to neutralization led to classification as a tier 1 virus. Indian-origin RMs were inoculated by different mucosal routes, resulting in high peak viral RNA loads. Signs of virus-induced disease include depletion of gut CD4+ T lymphocytes, loss of memory T cells in blood, and thrombocytopenia that resulted in fatal cerebral hemorrhage. SHIV-2873Nip is a highly replication-competent, mucosally transmissible, pathogenic R5-tropic virus that will be useful to study viral pathogenesis and to assess the efficacy of immunogens targeting HIV-C Env.

Mother-to-infant transmission (MTIT) of HIV is a serious global health concern, with over 300,000 children newly infected in 2011. SIV infection of rhesus macaques (RMs) results in similar rates of MTIT to that of HIV in humans. In contrast, SIV infection of sooty mangabeys (SMs) rarely results in MTIT. The mechanisms underlying protection from MTIT in SMs are unknown. In this study we tested the hypotheses that breast milk factors and/or target cell availability dictate the rate of MTIT in RMs (transmitters) and SMs (non-transmitters). We measured viral loads (cell-free and cell-associated), levels of immune mediators, and the ability to inhibit SIV infection in vitro in milk obtained from lactating RMs and SMs. In addition, we assessed the levels of target cells (CD4+CCR5+ T cells) in gastrointestinal and lymphoid tissues, including those relevant to breastfeeding transmission, as well as peripheral blood from uninfected RM and SM infants. We found that frequently-transmitting RMs did not have higher levels of cell-free or cell-associated viral loads in milk compared to rarely-transmitting SMs. Milk from both RMs and SMs moderately inhibited in vitro SIV infection, and presence of the examined immune mediators in these two species did not readily explain the differential rates of transmission. Importantly, we found that the percentage of CD4+CCR5+ T cells was significantly lower in all tissues in infant SMs as compared to infant RMs despite robust levels of CD4+ T cell proliferation in both species. The difference between the frequently-transmitting RMs and rarely-transmitting SMs was most pronounced in CD4+ memory T cells in the spleen, jejunum, and colon as well as in central and effector memory CD4+ T cells in the peripheral blood. We propose that limited availability of SIV target cells in infant SMs represents a key evolutionary adaptation to reduce the risk of MTIT in SIV-infected SMs.

Recent studies suggest that closely related species can accumulate substantial genetic and phenotypic differences despite ongoing gene flow, thus challenging traditional ideas regarding the genetics of speciation. Baboons (genus Papio) are Old World monkeys consisting of six readily distinguishable species. Baboon species hybridize in the wild, and prior data imply a complex history of differentiation and introgression. We produced a reference genome assembly for the olive baboon (Papio anubis) and whole-genome sequence data for all six extant species. We document multiple episodes of admixture and introgression during the radiation of Papio baboons, thus demonstrating their value as a model of complex evolutionary divergence, hybridization, and reticulation. These results help inform our understanding of similar cases, including modern humans, Neanderthals, Denisovans, and other ancient hominins.

Human immunodeficiency virus type 1 (HIV-1) infection is characterized by persistent viral replication in the context of CD4 + T cell depletion and elevated immune activation associated with disease progression. In contrast, simian immunodeficiency virus (SIV) infection of African-origin sooty mangabeys (SM) generally does not result in simian AIDS despite high viral loads and therefore affords a unique model in which to study the immunologic contributions to a nonpathogenic lentiviral disease outcome. A key feature of these natural SIV infections is the maintenance of low levels of immune activation during chronic infection. Our goal was to delineate the contribution of monocytes to maintaining low levels of immune activation in SIV-infected SM. Utilizing an ex vivo whole-blood assay, proinflammatory cytokine production was quantified in monocytes in response to multiple Toll-like receptor (TLR) ligands and a specific, significant reduction in the tumor necrosis factor alpha (TNF-α) response to lipopolysaccharide (LPS) was observed in SIV-infected SM. In contrast, monocytes from hosts of pathogenic infections (HIV-infected humans and SIV-infected Asian macaques) maintained a robust TNF-α response. In SIV-infected SM, monocyte TNF-α responses to low levels of LPS could be augmented by the presence of plasma from uninfected control animals. The impact of LPS-induced TNF-α production on immune activation was demonstrated in vitro, as TNF-α blocking antibodies inhibited downstream CD8 + T cell activation in a dose-dependent manner. These data demonstrate an association between nonpathogenic SIV infection of SM and a reduced monocyte TNF-α response to LPS, and they identify a role for monocytes in contributing to the suppressed chronic immune activation observed in these natural hosts. © 2012, American Society for Microbiology.

Chronic immune activation is a key determinant of AIDS progression in HIV-infected humans and simian immunodeficiency virus (SIV)-infected macaques but is singularly absent in SIV-infected natural hosts. To investigate whether natural killer T (NKT) lymphocytes contribute to the differential modulation of immune activation in AIDS-susceptible and AIDS-resistant hosts, we compared NKT function in macaques and sooty mangabeys in the absence and presence of SIV infection. Cynomolgus macaques had significantly higher frequencies of circulating invariant NKT lymphocytes compared to both rhesus macaques and AIDS-resistant sooty mangabeys. Despite this difference, mangabey NKT lymphocytes were functionally distinct from both macaque species in their ability to secrete significantly more IFN-γ, IL-13, and IL-17 in response to CD1d/α-galactosylceramide stimulation. While NKT number and function remained intact in SIV-infected mangabeys, there was a profound reduction in NKT activation-induced, but not mitogen-induced, secretion of IFN-γ, IL-2, IL -10, and TGF-β in SIV-infected macaques. SIV-infected macaques also showed a selective decline in CD4 + NKT lymphocytes which correlated significantly with an increase in circulating activated memory CD4 + T lymphocytes. Macaques with lower pre-infection NKT frequencies showed a significantly greater CD4 + T lymphocyte decline post SIV infection. The disparate effect of SIV infection on NKT function in mangabeys and macaques could be a manifestation of their differential susceptibility to AIDS. Alternately, these data also raise the possibility that loss of anti-inflammatory NKT function promotes chronic immune activation in pathogenic SIV infection, while intact NKT function helps to protect natural hosts from developing immunodeficiency and aberrant immune activation.

Background CCR5 is a main co-receptor for HIV, but also homes lymphocytes to sites of inflammation. We hypothesized that inhibition of CCR5 signaling would reduce HIV-associated chronic immune activation. Methods To test this hypothesis, we administered an antagonistic anti-CCR5 monoclonal antibody (HGS101) to five uninfected rhesus macaques (RMs) and monitored lymphocyte dynamics in blood and tissue. Results CCR5 blockade resulted in decreased levels of CCR5+ T-cells in blood and, at later timepoints, in lymph nodes. Additionally, the levels of CD25+ T-cells increased in lymph nodes, but decreased in blood, bone marrow, and rectal mucosa. Finally, a profile of gene expression from HGS101-treated RMs revealed a subtle, but consistent, in vivo signature of CCR5 blockade that suggests a mild immune modulatory effect. Conclusions Treatment with anti-CCR5 antibody induces changes in the tissue distribution of CCR5+ and CD25+ T-cells that may impact on the overall levels of immune activation during HIV and SIV infection.

CD4+ T cells play a central role in the immunopathogenesis of HIV/AIDS, and their depletion during chronic HIV infection is a hallmark of disease progression. However, the relative contribution of CD4+ T cells as mediators of antiviral immune responses and targets for virus replication is still unclear. Here, we have generated data in SIV-infected rhesus macaques (RMs) that suggest that CD4+ T cells are essential in establishing control of virus replication during acute infection. To directly assess the role of CD4+ T cells during primary SIV infection, we in vivo depleted these cells from RMs prior to infecting the primates with a pathogenic strain of SIV. Compared with undepleted animals, CD4+ lymphocyte–depleted RMs showed a similar peak of viremia, but did not manifest any post-peak decline of virus replication despite CD8+ T cell– and B cell–mediated SIV-specific immune responses comparable to those observed in control animals. Interestingly, depleted animals displayed rapid disease progression, which was associated with increased virus replication in non-T cells as well as the emergence of CD4-independent SIV-envelopes. Our results suggest that the antiviral CD4+ T cell response may play an important role in limiting SIV replication, which has implications for the design of HIV vaccines.