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

Previously we have shown that CD8(+) T cells are critical for containment of simian immunodeficiency virus (SIV) viremia and that rapid and profound depletion of CD4(+) T cells occurs in the intestinal tract of acutely infected macaques. To determine the impact of SIV-specific CD8(+) T-cell responses on the magnitude of the CD4(+) T-cell depletion, we investigated the effect of CD8(+) lymphocyte depletion during primary SIV infection on CD4(+) T-cell subsets and function in peripheral blood, lymph nodes, and intestinal tissues. In peripheral blood, CD8(+) lymphocyte-depletion changed the dynamics of CD4(+) T-cell loss, resulting in a more pronounced loss 2 weeks after infection, followed by a temporal rebound approximately 2 months after infection, when absolute numbers of CD4(+) T cells were restored to baseline levels. These CD4(+) T cells showed a markedly skewed phenotype, however, as there were decreased levels of memory cells in CD8(+) lymphocyte-depleted macaques compared to controls. In intestinal tissues and lymph nodes, we observed a significantly higher loss of CCR5(+) CD45RA(-) CD4(+) T cells in CD8(+) lymphocyte-depleted macaques than in controls, suggesting that these SIV-targeted CD4(+) T cells were eliminated more efficiently in CD8(+) lymphocyte-depleted animals. Also, CD8(+) lymphocyte depletion significantly affected the ability to generate SIV Gag-specific CD4(+) T-cell responses and neutralizing antibodies. These results reemphasize that SIV-specific CD8(+) T-cell responses are absolutely critical to initiate at least partial control of SIV infection.     

Human immunodeficiency virus viremia induces plasmacytoid dendritic cell activation in vivo and diminished alpha interferon production in vitro

Human immunodeficiency virus type 1 (HIV-1) infection has been associated with perturbations of plasmacytoid dendritic cells (PDC), including diminished frequencies in the peripheral blood and reduced production of type I interferons (IFNs) in response to in vitro stimulation. However, recent data suggest a paradoxical increase in production of type 1 interferons in vivo in HIV-infected patients compared to uninfected controls. Using a flow cytometric assay to detect IFN-alpha-producing cells within unseparated peripheral blood mononuclear cells, we observed that short-term interruptions of antiretroviral therapy are sufficient to result in significantly reduced IFN-alpha production by PDC in vitro in response to CpG A ligands or inactivated HIV particles. The primary cause of diminished IFN-alpha production was reduced responsiveness of PDC to de novo stimulation, not diminished per cell IFN-alpha production or migration of cells to lymphoid organs. Real-time PCR analysis of purified PDC from patients prior to and during treatment interruptions revealed that active HIV-1 replication is associated with upregulation of type I IFN-stimulated gene expression. Treatment of hepatitis C virus-infected patients with IFN-alpha2b and ribavirin for hepatitis C virus infection resulted in a profound suppression of de novo IFN-alpha production in response to CpG A or inactivated HIV particles, similar to the response observed in HIV-infected patients. Together, these results suggest that diminished production of type I interferons in vitro by PDC from HIV-1-infected patients may not represent diminished interferon production in vivo. Rather, diminished function in vitro is likely a consequence of prior activation via type I interferons or HIV virions in vivo.     

Protection Afforded by an HIV Vaccine Candidate in Macaques Depends on the Dose of SIVmac251 at Challenge Exposure

We used the simian immunodeficiency virus mac251 (SIV_mac251) macaque model to study the effect of the dose of mucosal exposure on vaccine efficacy. We immunized macaques with a DNA prime followed by SIV gp120 protein immunization with ALVAC-SIV and gp120 in alum, and we challenged them with SIV_mac251 at either a single high dose or at two repeated low-dose exposures to a 10-fold-lower dose. Infection was neither prevented nor modified following a single high-dose challenge of the immunized macaques. However, two exposures to a 10-fold-lower dose resulted in protection from SIV_mac251 acquisition in 3 out of 12 macaques. The remaining animals that were infected had a modulated pathogenesis, significant downregulation of interferon responsive genes, and upregulation of genes involved in B- and T-cell responses. Thus, the choice of the experimental model greatly influences the vaccine efficacy of vaccines for human immunodeficiency virus (HIV).     

Simian immunodeficiency virus infection in neonatal macaques

Children with human immunodeficiency virus infection often have higher viral loads and progress to AIDS more rapidly than adults. Since the intestinal tract is a major site of early viral replication and CD4(+) T-cell depletion in adults, we examined the effects of simian immunodeficiency virus (SIV) on both peripheral and intestinal lymphocytes from 13 neonatal macaques infected with SIVmac239. Normal neonates had more CD4(+) T cells and fewer CD8(+) T cells in all tissues than adults. Surprisingly, neonates had substantial percentages of CD4(+) T cells with an activated, memory phenotype (effector CD4(+) T cells) in the lamina propria of the intestine compared to peripheral lymphoid tissues, even when examined on the day of birth. Moreover, profound and selective depletion of jejunum lamina propria CD4(+) T cells occurred in neonatal macaques within 21 days of infection, which was preceded by large numbers of SIV-infected cells in this compartment. Furthermore, neonates with less CD4(+) T-cell depletion in tissues tended to have higher viral loads. The persistence of intestinal lamina propria CD4(+) T cells in some neonates with high viral loads suggests that increased turnover and/or resistance to CD4(+) T-cell loss may contribute to the higher viral loads and increased severity of disease in neonatal hosts.     

Mucosal priming of simian immunodeficiency virus-specific cytotoxic T-lymphocyte responses in rhesus macaques by the Salmonella type III secretion antigen delivery system

Nearly all human immunodeficiency virus (HIV) infections are acquired mucosally, and the gut-associated lymphoid tissues are important sites for early virus replication. Thus, vaccine strategies designed to prime virus-specific cytotoxic T lymphocyte (CTL) responses that home to mucosal compartments may be particularly effective at preventing or containing HIV infection. The Salmonella type III secretion system has been shown to be an effective approach for stimulating mucosal CTL responses in mice. We therefore tested DeltaphoP-phoQ attenuated strains of Salmonella enterica serovar Typhimurium and S. enterica serovar Typhi expressing fragments of the simian immunodeficiency virus (SIV) Gag protein fused to the type III-secreted SopE protein for the ability to prime virus-specific CTL responses in rhesus macaques. Mamu-A*01(+) macaques were inoculated with three oral doses of recombinant Salmonella, followed by a peripheral boost with modified vaccinia virus Ankara expressing SIV Gag (MVA Gag). Transient low-level CTL responses to the Mamu-A*01 Gag(181-189) epitope were detected following each dose of SALMONELLA: After boosting with MVA Gag, strong Gag-specific CTL responses were consistently detected, and tetramer staining revealed the expansion of Gag(181-189)-specific CD8(+) T-cell responses in peripheral blood. A significant percentage of the Gag(181-189)-specific T-cell population in each animal also expressed the intestinal homing receptor alpha4beta7. Additionally, Gag(181-189)-specific CD8(+) T cells were detected in lymphocytes isolated from the colon. Yet, despite these responses, Salmonella-primed/MVA-boosted animals did not exhibit improved control of virus replication following a rectal challenge with SIVmac239. Nevertheless, this study demonstrates the potential of mucosal priming by the Salmonella type III secretion system to direct SIV-specific cellular immune responses to the gastrointestinal mucosa in a primate model.     

Control of viremia and prevention of simian-human immunodeficiency virus-induced disease in rhesus macaques immunized with recombinant vaccinia viruses plus inactivated simian immunodeficiency virus and human immunodeficiency virus type 1 particles

An effective vaccine against the human immunodeficiency virus type 1 (HIV-1) will very likely have to elicit both cellular and humoral immune responses to control HIV-1 strains of diverse geographic and genetic origins. We have utilized a pathogenic chimeric simian-human immunodeficiency virus (SHIV) rhesus macaque animal model system to evaluate the protective efficacy of a vaccine regimen that uses recombinant vaccinia viruses expressing simian immunodeficiency virus (SIV) and HIV-1 structural proteins in combination with intact inactivated SIV and HIV-1 particles. Following virus challenge, control animals experienced a rapid and complete loss of CD4(+) T cells, sustained high viral loads, and developed clinical disease by 17 to 21 weeks. Although all of the vaccinated monkeys became infected, they displayed reduced postpeak viremia, had no significant loss of CD4(+) T cells, and have remained healthy for more than 15 months postinfection. CD8(+) T-cell and neutralizing antibody responses in vaccinated animals following challenge were demonstrable. Despite the control of disease, virus was readily isolated from the circulating peripheral blood mononuclear cells of all vaccinees at 22 weeks postchallenge, indicating that immunologic control was incomplete. Virus recovered from the animal with the lowest postchallenge viremia generated high virus loads and an irreversible loss of CD4(+) T-cell loss following its inoculation into a na?ve animal. These results indicate that despite the protection from SHIV-induced disease, the vaccinated animals still harbored replication-competent and pathogenic virus.     

Human immunodeficiency virus type 1 activates plasmacytoid dendritic cells and concomitantly induces the bystander maturation of myeloid dendritic cells

In this study, we analyzed the phenotypic and physiological consequences of the interaction of plasmacytoid dendritic cells (pDCs) with human immunodeficiency virus type 1 (HIV-1). pDCs are one cellular target of HIV-1 and respond to the virus by producing alpha/beta interferon (IFN-alpha/beta) and chemokines. The outcome of this interaction, notably on the function of bystander myeloid DC (CD11c+ DCs), remains unclear. We therefore evaluated the effects of HIV-1 exposure on these two DC subsets under various conditions. Blood-purified pDCs and CD11c+ DCs were exposed in vitro to HIV-1, after which maturation markers, cytokine production, migratory capacity, and CD4 T-cell stimulatory capacity were analyzed. pDCs exposed to different strains of infectious or even chemically inactivated, nonreplicating HIV-1 strongly upregulated the expression of maturation markers, such as CD83 and functional CCR7, analogous to exposure to R-848, a synthetic agonist of toll-like receptor-7 and -8. In addition, HIV-1-activated pDCs produced cytokines (IFN-alpha and tumor necrosis factor alpha), migrated in response to CCL19 and, in coculture, matured CD11c+ DCs, which are not directly activated by HIV. pDCs also acquired the ability to stimulate na?ve CD4+ T cells, albeit less efficiently than CD11c+ DCs. This HIV-1-induced maturation of both DC subsets may explain their disappearance from the blood of patients with high viral loads and may have important consequences on HIV-1 cellular transmission and HIV-1-specific T-cell responses.