Replication of simian immunodeficiency virus (SIV) in ex vivo lymph nodes as a means to assess susceptibility of macaques in vivo

Baboon CD8 T cells suppress SIVmac infection in CD4 T cells through contact-dependent production of MIP-1α, MIP-1β, and RANTES

Simian immunodeficiency virus (SIV) infection in rhesus macaques is often characterized by high viremia and CD4 T cell depletion. By contrast, SIV infection in African nonhuman primate natural hosts is typically nonpathogenic despite active viral replication. Baboons are abundant in Africa and have a geographical distribution that overlaps with natural hosts, but they do not harbor SIVs. Previous work has demonstrated baboons are resistant to chronic SIV infection and/or disease in vivo but the underlying mechanisms remain unknown. Using in vitro SIVmac infections, we sought to identify SIV restriction factors in baboons by comparing observations to the pathogenic rhesus macaque model. SIVmac replicated in baboon PBMC but had delayed kinetics compared to rhesus PBMC. However, SIVmac replication in baboon and rhesus isolated CD4 cells were similar to the kinetics seen for rhesus PBMC, demonstrating intracellular restriction factors do not play a strong role in baboon inhibition of SIVmac replication. Here, we show CD8 T cells contribute to the innate SIV-suppressive activity seen in naïve baboon PBMC. As one mechanism of restriction, we identified higher production of MIP-1α, MIP-1β, and RANTES by baboon PBMC. Contact between CD4 and CD8 T cells resulted in maximum production of these chemokines and suppression of viral replication, whereas neutralization of CCR5-binding chemokines in baboon PBMC increased viral loads. Our studies indicate baboon natural restriction of SIVmac replication is largely dependent on CD4-extrinsinc mechanisms mediated, in part, by CD8 T cells.

Preclinical AIDS vaccine research: survey of SIV, SHIV, and HIV challenge studies in vaccinated nonhuman primates

This current supplementary and systematic survey of 237 preclinical AIDS vaccine challenge/protection studies in nonhuman primates enumerates and broadly describes the recent status of different vaccine strategies in macaque and chimpanzee experimental models. Published studies since the previous survey were compiled and categorized by their vaccine types, challenge parameters, and challenge results. These models have supportively verified that some prophylactic vaccine approaches, though rarely preventing infection (which is observed in these models with some passively administered antibody-based vaccines), can control to some degree primate lentivirus replication and disease development, and this is encouraging because it places more potentially effective immunogens on the precipice for early clinical studies. Many of these promising approaches may benefit from more testing in mucosal challenge models, and resources will be needed to follow more of these partially protected vaccinees for longer periods.

Rhesus macaque resistance to mucosal simian immunodeficiency virus infection is associated with a postentry block in viral replication

Elucidation of the host factors which influence susceptibility to human immunodeficiency virus or simian immunodeficiency virus (SIV) infection and disease progression has important theoretical and practical implications. Rhesus macaque 359, a vaccine control animal, resisted two successive intravaginal challenges with SIV(mac251) and failed to seroconvert. Here, after an additional intrarectal SIVmac32H challenge, macaque 359 remained highly resistant to infection. Viral RNA (10(6) copies/ml) was observed in plasma only at week 2 postchallenge. Virus isolation and proviral DNA were positive only once at week eight postchallenge. The animal remained seronegative and cleared SIV in vivo. Its blood and lymph node cells obtained at 49 weeks after intrarectal challenge did not transmit SIV to a naive macaque. We found that the resistance of macaque 359 to SIV infection was not due to a high level of CD8(+) suppressor activity but to an inherent resistance of its CD4(+) T cells. To elucidate the basis for the unusually strong resistance of macaque 359 to SIV infection in vivo and in vitro, we investigated early events of viral infection and replication in CD4(+) cells of macaque 359, including expression and mutation screening of SIV coreceptors and analysis of viral entry and reverse transcription. Mutation screening revealed no genetic alteration in SIV coreceptors. PCR analysis revealed a significant delay in production of early in vitro reverse transcription intermediates in macaque 359 cells compared to susceptible controls, but cell fusion assays showed that SIV entered the CD4(+) CCR5(+) cells of macaque 359 as readily as cells of macaques susceptible to SIV infection. Our results suggest that the resistance of macaque 359 to SIV infection is due to a postentry block in viral replication and implicate a cellular inhibitory mechanism in its CD4(+) T cells. Identification of this host mechanism will help further elucidate the biochemistry of reverse transcription and may suggest therapeutic strategies. Determining the prevalence of this host resistance mechanism among macaques may lead to better design of SIV pathogenesis and vaccine studies.

Rhesus macaque dendritic cells efficiently transmit primate lentiviruses independently of DC-SIGN

Here, we describe the isolation and characterization of the rhesus macaque homolog for human DC-SIGN, a dendritic cell-specific C-type lectin. mac-DC-SIGN is 92% identical to hu-DC-SIGN. mac-DC-SIGN preserves the virus transmission function of hu-DC-SIGN, capturing and efficiently transducing simian and human immunodeficiency virus to target CD4(+) T cells. Surprisingly, however, mac-DC-SIGN plays no discernable role in the ability of rhesus macaque dendritic cells to capture and transmit primate lentiviruses. Expression and neutralization analyses suggest that this process is DC-SIGN independent in macaque, although the participation of other lectin molecules cannot be ruled out. The ability of primate lentiviruses to effectively use human and rhesus dendritic cells in virus transmission without the cells becoming directly infected suggests that these viruses have taken advantage of a conserved dendritic cell mechanism in which DC-SIGN family molecules are significant contributors but not the only participants.

Cervicovaginal lamina propria lymphocytes: phenotypic characterization and their importance in cytotoxic T-lymphocyte responses to simian immunodeficiency virus SIVmac251

Most human immunodeficiency virus (HIV) type 1 infections occur by the mucosal route. Thus, it is important to assess the immune responses to HIV in the vaginal, cervical, and rectal compartments. Here we quantitated the virus-specific CD8+ T-cell response and characterized the phenotype of lymphocytes in the genital tracts of naive macaques, macaques acutely or chronically infected with simian immunodeficiency virus SIVmac251, and macaques chronically infected with chimeric simian/human immunodeficiency virus SHIV(KU2.) Vaginal biopsy samples or samples obtained at the time of euthanasia were used in this analysis. The percentage of Gag-specific, tetramer-positive T cells was as high as 13 to 14% of the CD3+ CD8+ T-cell population in the vaginal and cervical laminae propriae of both SIVmac251 and SHIV(KU2) chronically infected macaques. In most cases, the frequency of this response in the cervicovaginal compartment far exceeded the frequency in the blood or the draining iliac lymph node. Vaginal laminae propriae of naive macaques contained 55 to 65% CD3+ CD8+ cells and 28 to 34% CD3+ CD4+ cells, while the majority of intraepithelial cells were CD8+ T cells (75 to 85%). For the same cells, the surface expression of CD62L was low whereas that of alphaEbeta7 was high. No difference in the expression of CD45RA on CD8+ T cells was observed in the chronic stage of SIVmac251 infection. Although no decrease in the percentage of CD4+ cells in the genital tract was observed within the first 12 days of infection, by 6 weeks from SIVmac251 infection and thereafter the percentage of CD4+ T cells was decreased in the laminae propriae of the vagina and cervix. Expression of CD45RA did not differ in naive and acutely SIVmac251 infected macaques. Information on the quality and quantity of local immune responses may help in the design of vaccine strategies aimed at containing viral replication at the site of viral encounter.

Apoptosis induced by in vitro infection with simian-human immunodeficiency chimeric virus in macaque and human peripheral blood mononuclear cells

We investigated apoptosis induced by in vitro infection with the chimeric virus of simian immunodeficiency virus and human immunodeficiency virus (SHIV). Macaque and human peripheral blood mononuclear cells (PBMCs) were infected with pathogenic SHIV-89.6p (89.6p) or nonpathogenic SHIV-NM-3rN (NM-3rN). In macaque PBMCs, the extent of virus production and apoptosis induction in CD4(+) cells was much greater in 89.6p infection than in NM-3rN infection. The result was consistent with our previous study of in vivo SHIV infection. In human PBMCs, 89.6p replicated and induced apoptosis more extensively than did NM-3rN, when the cells were infected with the same infectious doses of the viruses. However, in cells infected with a high dose of NM-3rN, the levels of virus production and apoptosis induction were comparable to those in 89.6p infection. There was no significant difference in the extent of apoptosis induction between 89.6p and NM-3rN infection when growth curves of the two viruses matched. Thus, apoptosis induction by SHIV might depend quantitatively on the amount of virus production rather than on the strains of the virus. Moreover, the correlation between the extent of apoptosis induction and virus pathogenicity in macaque PBMCs has also been found in SHIV-infected macaques. This suggests that the profiles of SHIV infection in vitro reflect the in vivo phenomena. Therefore, the in vitro evaluation of apoptosis induction by SHIV could be useful as a safety test for the development of live-attenuated vaccines.