Human Immunodeficiency Virus/simian Immunodeficiency Virus Research Articles

Simian Immunodeficiency Virus Infection Modulates CD94+ (KLRD1+) NK Cells in Rhesus Macaques.

Recently, we and others have shown that natural killer (NK) cells exhibit memory-like recall responses against cytomegalovirus (CMV) and human immunodeficiency/virus simian immunodeficiency virus (HIV/SIV) infections. Although the mechanism(s) have not been fully delineated, several groups have shown that the activating receptor NKG2C is elevated on NK cells in the context of rhesus CMV (rhCMV) or human CMV (hCMV) infections. CD94, which heterodimerizes with NKG2C is also linked to adaptive NK cell responses. Because nonhuman primates (NHP) play a crucial role in modeling HIV (SIV) infections, it is crucial to be able to assess and characterize the NKG2 family in NHP. Unfortunately, it is not possible to detect CD94 using commercially available antibodies in NHP. Our work, a first for NHP, has focused on developing RNA flow cytometry using mRNA transcripts as proxies distinguishing NKG2C from NKG2A. We have expanded the application of this technology and here we show the first characterization of CD94+ (KLRD1+) NK cells in NHP using multiparametric RNA flow cytometry. Peripheral blood mononuclear cells from naive and matched acutely (n = 4) or chronically (n = 12) SIV-infected rhesus macaques were analyzed by flow cytometry using commercially available antibodies, determining expression of transcripts for NKG2A, NKG2C, and CD94 (KLRC1, KLRC2, and KLRD1, respectively) on NK cells using RNA flow cytometry. Our data show that KLRC1+/- KLRC2+ KLRD1+ NK cells decrease following chronic, but not acute, infection with SIV. This approach will allow us to investigate the kinetics of infection and NK memory formation and will further improve our understanding of basic NK cell biology, especially in the context of SIV infection.IMPORTANCE Nonhuman primates play a crucial role in approximating human biology and many diseases that are difficult, if not impossible, to achieve in other animal models, notably HIV. Current advances in adaptive NK cell research positions us to address fundamental deficiencies in our fight against infection and disease at the earliest moments after infection or substantially earlier in disease progression. We show here that we can identify specific NK cell subpopulations that are modulated following chronic, but not acute, SIV infection. The ability to identify these subsets more precisely will inform therapeutic and vaccine strategies targeting an optimized NK cell response.

Longitudinal Examination of the Intestinal Lamina Propria Cellular Compartment of Simian Immunodeficiency Virus-Infected Rhesus Macaques Provides Broader and Deeper Insights into the Link between Aberrant MicroRNA Expression and Persistent Immune Activation.

Chronic immune activation/inflammation driven by factors like microbial translocation is a key determinant of human immunodeficiency virus/simian immunodeficiency virus (HIV/SIV) disease progression. Although extensive research on inflammation has focused on studying protein regulators, increasing evidence suggests a critical role for microRNAs (miRNAs) in regulating several aspects of the immune/inflammatory response and immune cell proliferation, differentiation, and activation. To understand their immunoregulatory role, we profiled miRNA expression sequentially in intestinal lamina propria leukocytes (LPLs) of eight macaques before and at 21, 90, and 180 days postinfection (dpi). At 21 dpi, ∼20 and 9 miRNAs were up- and downregulated, respectively. However, at 90 dpi (n = 60) and 180 dpi (n = 44), ≥75% of miRNAs showed decreased expression. Notably, the T-cell activation-associated miR-15b, miR-142-3p, miR-142-5p, and miR-150 expression was significantly downregulated at 90 and 180 dpi. Out of ∼10 downregulated miRNAs predicted to regulate CD69, we confirmed miR-92a to directly target CD69. Interestingly, the SIV-induced miR-190b expression was elevated at all time points. Additionally, elevated lipopolysaccharide (LPS)-responsive miR-146b-5p expression at 180 dpi was confirmed in primary intestinal macrophages following LPS treatment in vitro Further, reporter and overexpression assays validated IRAK1 (interleukin-1 receptor 1 kinase) as a direct miR-150 target. Furthermore, IRAK1 protein levels were markedly elevated in intestinal LPLs and epithelium. Finally, blockade of CD8(+) T-cell activation/proliferation with delta-9 tetrahydrocannabinol (Δ(9)-THC) significantly prevented miR-150 downregulation and IRAK1 upregulation. Our findings suggest that miR-150 downregulation during T-cell activation disrupts the translational control of IRAK1, facilitating persistent gastrointestinal (GI) inflammation. Finally, the ability of Δ(9)-THC to block the miR-150-IRAK1 regulatory cascade highlights the potential of cannabinoids to inhibit persistent inflammation/immune activation in HIV/SIV infection. Persistent GI tract disease/inflammation is a cardinal feature of HIV/SIV infection. Increasing evidence points to a critical role for miRNAs in controlling several aspects of the immune/inflammatory response. Here, we show significant dysregulation of miRNA expression exclusively in the intestinal lamina propria cellular compartment through the course of SIV infection. Specifically, the study identified miRNA signatures associated with key pathogenic events, such as viral replication, T-cell activation, and microbial translocation. The T-cell-enriched miR-150 showed significant downregulation throughout SIV infection and was confirmed to target IRAK1, a critical signal-transducing component of the IL-1 receptor and TLR signaling pathways. Reduced miR-150 expression was associated with markedly elevated IRAK1 expression in the intestines of chronically SIV-infected macaques. Finally, Δ(9)-THC-mediated blockade of CD8(+) T-cell activation in vitro significantly inhibited miR-150 downregulation and IRAK1 upregulation, suggesting its potential for targeted immune modulation in HIV infection.

In VivoSelection of CD4+T Cells Transduced with a Gamma-Retroviral Vector Expressing a Single-Chain Intrabody Targeting HIV-1 Tat

We evaluated the potential of an anti-human immunodeficiency virus (HIV) Tat intrabody (intracellular antibody) to promote the survival of CD4(+) cells after chimeric simian immunodeficiency virus (SIV)/HIV (SHIV) infection in rhesus macaques. Following optimization of stimulation and transduction conditions, purified CD4(+) T cells were transduced with GaLV-pseudotyped retroviral vectors expressing either an anti-HIV-1 Tat or a control single-chain intrabody. Ex vivo intrabody-gene marking was highly efficient, averaging four copies per CD4(+) cell. Upon reinfusion of engineered autologous CD4(+) cells into two macaques, high levels of gene marking (peak of 0.6% and 6.8% of peripheral blood mononuclear cells (PBMCs) and 0.3% or 2.2% of the lymph node cells) were detected in vivo. One week post cell infusion, animals were challenged with SHIV 89.6p and the ability of the anti-HIV Tat intrabody to promote cell survival was evaluated. The frequency of genetically modified CD4(+) T cells progressively decreased, concurrent with loss of CD4(+) cells and elevated viral loads in both animals. However, CD4(+) T cells expressing the therapeutic anti-Tat intrabody exhibited a relative survival advantage over an 8- and 21-week period compared with CD4(+) cells expressing a control intrabody. In one animal, this survival benefit of anti-Tat transduced cells was associated with a reduction in viral load. Overall, these results indicate that a retrovirus-mediated anti-Tat intrabody provided significant levels of gene marking in PBMCs and peripheral tissues and increased relative survival of transduced cells in vivo.

Plasma IP-10 Is Associated with Rapid Disease Progression in Early HIV-1 Infection

Cytokines play key roles in modulating disease progression in simian immunodeficiency virus/human immunodeficiency virus (SIV/HIV) infection. There are a few studies on the relationship between early cytokines and HIV disease prognosis. In this study, we first report the relationship based on two groups with clearly different disease progression. We found that IP-10 was the only cytokine among the 26 cytokines tested that was always positively correlated with disease progression, and was associated with the time for CD4 counts to fall below 200 cells/μL during Fiebig stages III-V in HIV-1 infection. This suggests that high IP-10 levels in the blood are associated with rapid disease progression during Fiebig stages III-V in HIV-1 infection.

Did The World Pour Gas On The HIV Fire?Tinderbox: How The West Sparked The AIDS Epidemic And How The World Can Finally Overcome It By Timberg Craig Halperin Daniel New York (NY) : Penguin Press , 2012 421 pp.; $29.95

Did The World Pour Gas On The HIV Fire?Tinderbox: How The West Sparked The AIDS Epidemic And How The World Can Finally Overcome It By Timberg Craig Halperin Daniel New York (NY) : Penguin Press , 2012 421 pp.; $29.95

SIV Infection Induces Accumulation of Plasmacytoid Dendritic Cells in the Gut Mucosa

Multiple studies suggest that plasmacytoid dendritic cells (pDCs) are depleted and dysfunctional during human immunodeficiency virus/simian immunodeficiency virus (HIV/SIV) infection, but little is known about pDCs in the gut-the primary site of virus replication. Here, we show that during SIV infection, pDCs were reduced 3--fold in the circulation and significantly upregulated the gut-homing marker α4β7, but were increased 4-fold in rectal biopsies of infected compared to naive macaques. These data revise the understanding of pDC immunobiology during SIV infection, indicating that pDCs are not necessarily depleted, but instead may traffic to and accumulate in the gut mucosa.

Replicating Adenovirus-Simian Immunodeficiency Virus (SIV) Recombinant Priming and Envelope Protein Boosting Elicits Localized, Mucosal IgA Immunity in Rhesus Macaques Correlated with Delayed Acquisition following a Repeated Low-Dose Rectal SIV mac251 Challenge

We have shown that sequential replicating adenovirus type 5 host range mutant human immunodeficiency virus/simian immunodeficiency virus (HIV/SIV) recombinant priming delivered first intranasally (i.n.) plus orally and then intratracheally (i.t.), followed by envelope protein boosting, elicits broad cellular immunity and functional, envelope-specific serum and mucosal antibodies that correlate with protection from high-dose SIV and simian/human immunodeficiency virus (SHIV) challenges in rhesus macaques. Here we extended these studies to compare the standard i.n./i.t. regimen with additional mucosal administration routes, including sublingual, rectal, and vaginal routes. Similar systemic cellular and humoral immunity was elicited by all immunization routes. Central and effector memory T cell responses were also elicited by the four immunization routes in bronchoalveolar lavage fluid and jejunal, rectal, and vaginal tissue samples. Cellular responses in vaginal tissue were more compartmentalized, being induced primarily by intravaginal administration. In contrast, all immunization routes elicited secretory IgA (sIgA) responses at multiple mucosal sites. Following a repeated low-dose intrarectal (i.r.) challenge with SIV(mac251) at a dose transmitting one or two variants, protection against acquisition was not achieved except in one macaque in the i.r. immunized group. All immunized macaques exhibited reduced peak viremia compared to that of controls, correlated inversely with prechallenge serum antienvelope avidity, antibody-dependent cellular cytotoxicity (ADCC) titers, and percent antibody-dependent cell-mediated viral inhibition. Both antibody avidity and ADCC titers were correlated with the number of exposures required for infection. Notably, we show for the first time a significant correlation of vaccine-induced sIgA titers in rectal secretions with delayed acquisition. Further investigation of the characteristics and properties of the sIgA should elucidate the mechanism leading to this protective effect.

Experimental infection of Cynomolgus Macaques (Macaca fascicularis) with human varicella-zoster virus.

Varicella-zoster virus (VZV) is a member of the alphaherpesvirus family and the causative agent of chickenpox and shingles. To determine the utility of cynomolgus macaques (Macaca fascicularis) as a nonhuman primate model to evaluate VZV-based simian immunodeficiency virus/human immunodeficiency virus (SIV/HIV) vaccines, we experimentally inoculated 10 animals with the parental Oka (Oka-P) strain of VZV derived from MeWo or Telo-RF cells. VZV DNA could be detected in the lungs as late as 4 days postinfection, with replicating virus detected by shell vial culture assay in one case. Infection did not result in any overt clinical symptoms but was characterized by humoral and cell-mediated immunity in a time frame and at a magnitude similar to those observed following VZV vaccination in humans. The cell line source of VZV inoculum influenced both the magnitude and polyfunctionality of cell-mediated immunity. Animals mounted a vigorous anamnestic antibody response following a second inoculation 12 weeks later. Inoculations resulted in transient increases in CD4(+) T-cell activation and proliferation, as well as a sustained increase in CD4(+) T cells coexpressing CCR5 and α4β7 integrin. In contrast to previous failed attempts to successfully utilize attenuated VZV-Oka as an SIV vaccine vector in rhesus macaques due to suboptimal infectivity and cellular immunogenicity, the ability to infect cynomolgus macaques with Oka-P VZV should provide a valuable tool for evaluating VZV-vectored SIV/HIV vaccines.

α4+β7hiCD4+ memory T cells harbor most Th-17 cells and are preferentially infected during acute SIV infection

Human immunodeficiency virus/simian immunodeficiency virus (HIV/SIV) infections are believed to infect minimally activated CD4+ T cells after viral entry. Not much is known about why SIV selectively targets these cells. Here we show that CD4+ T cells that express high levels of the α4β7 heterodimer are preferentially infected very early during the course of SIV infection. At days 2–4 post infection, α4+β7hiCD4+ T cells had ∼5× more SIV-gag DNA than β7−CD4+ T cells. α4+β7hiCD4+ T cells displayed a predominantly central memory (CD45RA−CD28+CCR7+) and a resting (CD25−CD69−HLA-DR−Ki-67−) phenotype. Although the expression of detectable CCR5 was variable on α4+β7hi and β7−CD4+ T cells, both CCR5+ and CCR5− subsets of α4+β7hi and β7−CD4+ T cells were found to express sufficient levels of CCR5 mRNA, suggesting that both these subsets could be efficiently infected by SIV. In line with this, we found similar levels of SIV infection in β7−CD4+CCR5+ and β7−CD4+CCR5− T cells. α4β7hiCD4+ T cells were found to harbor most T helper (Th)-17 cells that were significantly depleted during acute SIV infection. Taken together, our results show that resting memory α4+β7hiCD4+ T cells in the blood are preferentially infected and depleted during acute SIV infection, and the loss of these cells alters the balance between Th-17 and Th-1 responses, thereby contributing to disease pathogenesis.

Correlation of Vaccine-Elicited Systemic and Mucosal Nonneutralizing Antibody Activities with Reduced Acute Viremia following Intrarectal Simian Immunodeficiency Virus SIV mac251 Challenge of Rhesus Macaques

Cell-mediated immunity and neutralizing antibodies contribute to control of human immunodeficiency virus/simian immunodeficiency virus (HIV/SIV) infection, but the role of nonneutralizing antibodies is not defined. Previously, we reported that sequential oral/oral or intranasal/oral (I/O) priming with replication-competent adenovirus type 5 host range mutant (Ad5hr)-SIV recombinants, followed by intramuscular envelope protein boosting, elicited systemic and mucosal cellular immunity and exhibited equivalent, significant reductions of chronic viremia after rectal SIV(mac251) challenge. However, I/O priming gave significantly better control of acute viremia. Here, systemic and mucosal humoral immunity were investigated for potential correlates with the acute challenge outcome. Strong serum binding but nonneutralizing antibody responses against SIV(mac251) were induced in both groups. Antibody responses appeared earlier and overall were higher in the I/O group. Reduced acute viremia was significantly correlated with higher serum binding titer, stronger antibody-dependent cellular cytotoxicity activity, and peak prechallenge and 2-week-postchallenge antibody-dependent cell-mediated viral inhibition (ADCVI). The I/O group consistently displayed greater anti-envelope immunoglobulin A (IgA) antibody responses in bronchoalveolar lavage and a stronger rectal anti-envelope IgA anamnestic response 2 weeks postchallenge. Pre- and postchallenge rectal secretions inhibited SIV transcytosis across epithelial cells. The inhibition was significantly higher in the I/O group, although a significant correlation with reduced acute viremia was not reached. Overall, the replicating Ad5hr-SIV priming/envelope boosting approach elicited strong systemic and mucosal antibodies with multiple functional activities. The pattern of elevated immune responses in the I/O group is consistent with its better control of acute viremia mediated, at least in part, by ADCVI activity and transcytosis inhibition.

Reduced Protection from Simian Immunodeficiency Virus SIV mac251 Infection Afforded by Memory CD8 + T Cells Induced by Vaccination during CD4 + T-Cell Deficiency

Adaptive CD4(+) and CD8(+) T-cell responses have been associated with control of human immunodeficiency virus/simian immunodeficiency virus (HIV/SIV) replication. Here, we have designed a study with Indian rhesus macaques to more directly assess the role of CD8 SIV-specific responses in control of viral replication. Macaques were immunized with a DNA prime-modified vaccinia virus Ankara (MVA)-SIV boost regimen under normal conditions or under conditions of antibody-induced CD4(+) T-cell deficiency. Depletion of CD4(+) cells was performed in the immunized macaques at the peak of SIV-specific CD4(+) T-cell responses following the DNA prime dose. A group of naïve macaques was also treated with the anti-CD4 depleting antibody as a control, and an additional group of macaques immunized under normal conditions was depleted of CD8(+) T cells prior to challenge exposure to SIV(mac251). Analysis of the quality and quantity of vaccine-induced CD8(+) T cells demonstrated that SIV-specific CD8(+) T cells generated under conditions of CD4(+) T-cell deficiency expressed low levels of Bcl-2 and interleukin-2 (IL-2), and plasma virus levels increased over time. Depletion of CD8(+) T cells prior to challenge exposure abrogated vaccine-induced protection as previously shown. These data support the notion that adaptive CD4(+) T cells are critical for the generation of effective CD8(+) T-cell responses to SIV that, in turn, contribute to protection from AIDS. Importantly, they also suggest that long-term protection from disease will be afforded only by T-cell vaccines for HIV that provide a balanced induction of CD4(+) and CD8(+) T-cell responses and protect against early depletion of CD4(+) T cells postinfection.

SIV‐induced activation of the blood‐brain barrier requires cell‐associated virus and is not restricted to endothelial cell activation

It has never been determined if activation of the blood-brain barrier (BBB) during simian immunodeficiency virus/human immunodeficiency virus (SIV/HIV) infection is a function of high levels of circulating virus or if the virus has to be within a cell capable of crossing the BBB to activate it. In vitro models of the BBB are becoming recognized as an acceptable method for determining the cellular events associated with HIV neuroinvasion. Cell free virus (when added in the physiologically relevant lumen) although capable of activating the endothelial cells of our in vitro BBB did not activate astrocytes beneath. SIVmac251-infected CEMx174 cells, however, were capable of activating both components of the BBB model. Here we demonstrate that an in vitro model of the BBB can be activated in a physiologically relevant manner, that SIV requires to be cell-associated and that endothelial cells of the BBB are not the only components that are activated during SIV neuroinvasion.

Highly effective control of an AIDS virus challenge in macaques by using vesicular stomatitis virus and modified vaccinia virus Ankara vaccine vectors in a single-boost protocol.

Previous studies have shown that vaccination and boosting of rhesus macaques with attenuated vesicular stomatitis virus (VSV) vectors encoding Env and Gag proteins of simian immunodeficiency virus-human immunodeficiency virus (SHIV) hybrid viruses protect rhesus macaques from AIDS after challenge with the highly pathogenic SHIV 89.6P (23). In the present study, we compared the effectiveness of a single prime-boost protocol consisting of VSV vectors expressing SHIV Env, Gag, and Pol proteins to that of a protocol consisting of a VSV vector prime followed with a single boost with modified vaccinia virus Ankara (MVA) expressing the same SHIV proteins. After challenge with SHIV 89.6P, MVA-boosted animals controlled peak challenge viral loads to less than 2 x 10(6) copies/ml (a level significantly lower than that seen with VSV-boosted animals and lower than those reported for other vaccine studies employing the same challenge). MVA-boosted animals have shown excellent preservation of CD4(+) T cells, while two of four VSV-boosted animals have shown significant loss of CD4(+) T cells. The improved protection in MVA-boosted animals correlates with trends toward stronger prechallenge CD8(+)-T-cell responses to SHIV antigens and stronger postchallenge SHIV-neutralizing antibody production.

Mother-to-infant transmission of SIV via breast-feeding in rhesus macaques.

To decipher the mechanisms involved in oral transmission of human immunodeficiency virus/simian immunodeficiency virus (HIV/SIV) through breast-feeding, we have developed an animal model using SIV-infected lactating rhesus macaques (Macaca mulatta) and their infants. Five of eight macaque infants became infected during a 10-month study course after SIV inoculation of lactating dams. In a second study, three of four chronically infected female macaques transmitted virus to their infants through breast-feeding within 4 months of birth. Transmission of virus to infants did not correlate with viral loads in either milk or plasma. Infants were infected with homogeneous virus populations, while milk samples near the time of transmission were more diverse. These studies suggest that specific viral phenotypes are selectively transmitted through breast-feeding.

Intra- and interspecific variation of the CCR5 gene in higher primates.

We have evaluated the molecular evolution of the chemokine receptor CCR5 in primates. The chemokine receptor CCR5 serves as a major co-receptor for human immunodeficiency virus/simian immunodeficiency virus (HIV/SIV) infection. Knowledge of evolution of the CCR5 molecule and selection on the CCR5 gene may shed light on its functional role. The comparison of differences between intraspecific polymorphisms and interspecific fixed substitutions provides useful information regarding modes of selection during the course of evolution. There is marked polymorphism in the CCR5 gene sequence within different primate species, whereas sequence divergence between different species is small. By using contingency tests, we compared synonymous (SS) and nonsynonymous (NS) CCR5 mutations occurring within and between a broad range of primates. Our results demonstrate that CCR5 evolution did not follow expectations of strict neutrality at the level of the whole gene. The proportion of NS to SS at the intraspecific level was significantly higher than that observed at the interspecific level. These results suggest that most CCR5 NS polymorphisms are slightly deleterious. However, at domains more closely correlated with its known biological functions, there was no obvious evidence to support deviation from neutrality.

ALVAC-SIV-gag-pol-env-based vaccination and macaque major histocompatibility complex class I (A*01) delay simian immunodeficiency virus SIVmac-induced immunodeficiency.

T-cell-mediated immune effector mechanisms play an important role in the containment of human immunodeficiency virus/simian immunodeficiency virus (HIV/SIV) replication after infection. Both vaccination- and infection-induced T-cell responses are dependent on the host major histocompatibility complex classes I and II (MHC-I and MHC-II) antigens. Here we report that both inherent, host-dependent immune responses to SIVmac251 infection and vaccination-induced immune responses to viral antigens were able to reduce virus replication and/or CD4+ T-cell loss. Both the presence of the MHC-I Mamu-A*01 genotype and vaccination of rhesus macaques with ALVAC-SIV-gag-pol-env (ALVAC-SIV-gpe) contributed to the restriction of SIVmac251 replication during primary infection, preservation of CD4+ T cells, and delayed disease progression following intrarectal challenge exposure of the animals to SIV(mac251 (561)). ALVAC-SIV-gpe immunization induced cytotoxic T-lymphocyte (CTL) responses cumulatively in 67% of the immunized animals. Following viral challenge, a significant secondary virus-specific CD8+ T-cell response was observed in the vaccinated macaques. In the same immunized macaques, a decrease in virus load during primary infection (P = 0.0078) and protection from CD4 loss during both acute and chronic phases of infection (P = 0.0099 and P = 0.03, respectively) were observed. A trend for enhanced survival of the vaccinated macaques was also observed. Neither boosting the ALVAC-SIV-gpe with gp120 immunizations nor administering the vaccine by the combination of mucosal and systemic immunization routes increased significantly the protective effect of the ALVAC-SIV-gpe vaccine. While assessing the role of MHC-I Mamu-A*01 alone in the restriction of viremia following challenge of nonvaccinated animals with other SIV isolates, we observed that the virus load was not significantly lower in Mamu-A*01-positive macaques following intravenous challenge with either SIV(mac251 (561)) or SIV(SME660). However, a significant delay in CD4+ T-cell loss was observed in Mamu-A*01-positive macaques in each group. Of interest, in the case of intravenous or intrarectal challenge with the chimeric SIV/HIV strains SHIV(89.6P) or SHIV(KU2), respectively, MHC-I Mamu-A*01-positive macaques did not significantly restrict primary viremia. The finding of the protective effect of the Mamu-A*01 molecule parallels the protective effect of the B*5701 HLA allele in HIV-1-infected humans and needs to be accounted for in the evaluation of vaccine efficacy against SIV challenge models.

Pathogenic simian/human immunodeficiency virus SHIV(KU) inoculated into immunized macaques caused infection, but virus burdens progressively declined with time.

Using the simian immunodeficiency virus/human immunodeficiency virus (SHIV)-macaque model of AIDS, we had shown in a previous report that a live, nonpathogenic strain of SHIV, further attenuated by deletion of the vpu gene and inoculated orally into adult macaques, had effectively prevented AIDS following vaginal inoculation with pathogenic SHIV(KU). Examination of lymph nodes from the animals at 18 weeks postchallenge had shown that all six animals were persistently infected with challenge virus. We report here on a 2-year follow-up study on the nature of the persistent infections in these animals. DNA of the vaccine virus was present in the lymph nodes at all time points tested, as far as 135 weeks postchallenge. In contrast, the DNA of SHIV(KU) became undetectable in one animal by week 55 and in three others by week 63. These four macaques have remained negative for SHIV(KU) DNA as far as the last time point examined at week 135. Quantification of the total viral DNA concentration in lymph nodes during the observation period showed a steady decline. All animals developed neutralizing antibody and cytotoxic-T-lymphocyte responses to SHIV(KU) that persisted throughout the observation period. Vaccine-like viruses were isolated from two animals, and a SHIV(KU)-like virus was isolated from one of the two macaques that remained positive for SHIV(KU) DNA. There was no evidence of recombination between the vaccine and the challenge viruses. Thus, immunization with the live vaccine not only prevented disease but also contributed to the steady decline in the virus burdens in the animals.

In vivo distribution of the human immunodeficiency virus/simian immunodeficiency virus coreceptors: CXCR4, CCR3, and CCR5.

We have evaluated the in vivo distribution of the major human immunodeficiency virus/simian immunodeficiency virus (HIV/SIV) coreceptors, CXCR4, CCR3, and CCR5, in both rhesus macaques and humans. T lymphocytes and macrophages in both lymphoid and nonlymphoid tissues are the major cell populations expressing HIV/SIV coreceptors, reaffirming that these cells are the major targets of HIV/SIV infection in vivo. In lymphoid tissues such as the lymph node and the thymus, approximately 1 to 10% of the T lymphocytes and macrophages are coreceptor positive. However, coreceptor expression was not detected on follicular dendritic cells (FDC) in lymph nodes, suggesting that the ability of FDC to trap extracellular virions is unlikely to be mediated by a coreceptor-specific mechanism. In the thymus, a large number of immature and mature T lymphocytes express CXCR4, which may render these cells susceptible to infection by syncytium-inducing viral variants that use this coreceptor for entry. In addition, various degrees of coreceptor expression are found among different tissues and also among different cells within the same tissues. Coreceptor-positive cells are more frequently identified in the colon than in the rectum and more frequently identified in the cervix than in the vagina, suggesting that the expression levels of coreceptors are differentially regulated at different anatomic sites. Furthermore, extremely high levels of CXCR4 and CCR3 expression are found on the neurons from both the central and peripheral nervous systems. These findings may be helpful in understanding certain aspects of HIV and SIV pathogenesis and transmission.