Heterogeneity of the simian immunodeficiency virus (SIV) specific CD8(+) T-cell response in mucosal tissues during SIV primary infection

Acute HIV infection: it takes more than guts

PURPOSE OF REVIEW

To understand the cellular and molecular mechanisms of acute HIV pathogenesis.

RECENT FINDINGS

Recent studies have given us new insights into the mechanisms of acute HIV pathogenesis by demonstrating the 'systemic' destruction of the CD4 memory T cell compartment. This destruction occurs well before the emergence of a strong and broad immune response, highlighting the failure of the immune response to contain early viral infection and destruction. However, recent data also suggest that very few founder populations of cells are infected early, at the portal of entry, making them ideal targets for vaccine-induced immune responses that may aid in the effective control of early infection and transmission.

SUMMARY

HIV causes a massive destruction of memory CD4 T cells during the early acute phase of infection. This destruction proceeds largely in the absence of emerging antiviral immune responses, and severely disables the ability of the immune system to generate secondary immune responses. Early preservation of the memory CD4 compartment by shifting emphasis of antiretroviral therapeutic strategies to early treatment, and development of vaccines that can induce strong and broad immune responses, will be critical to prevent the destructive effects of early HIV infection.

Antiretroviral therapy initiation during primary HIV infection enhances both CD127 expression and the proliferative capacity of HIV-specific CD8+ T cells

OBJECTIVES

HIV-specific CD8+ T cells from patients with primary HIV infection (PHI) and after antiretroviral therapy initiation were evaluated for CD127 expression and proliferative capacity and were compared with cells from chronically-infected patients, including long-term nonprogressors and HIV controllers.

METHODS

We studied 30 patients with PHI (from the Agence Nationale de Recherche sur le SIDA Primo-infection Cohort) and 33 patients with chronic HIV infection (including nonprogressor patients from the Agence Nationale de Recherche sur le SIDA ALT Cohort and the Agence Nationale de Recherche sur le SIDA HIV Controllers Study Group). HIV-specific CD8+ T cells were identified by costaining with HIV human leukocyte antigen class I pentamers. CD127 expression was assessed by flow cytometry and cell proliferation by carboxyfluorescein succinimidyl ester labeling.

RESULTS

During PHI, most HIV-specific CD8+ T cells coexpressed CD27 and CD45RO, were highly activated, and showed weak Bcl-2 expression. Their CD127 expression was very low and correlated negatively both with HIV RNA and DNA levels and with expression of the activation marker CD38. CD127 expression correlated positively with CD4 cell count, Bcl-2 expression and proliferative capacity. Strong CD127 expression was observed in the two groups of chronically-infected nonprogressors. CD127 expression on HIV-specific CD8+ T cells increased in early-treated PHI patients, reaching levels similar to those observed in nonprogressors. In parallel, these cells acquired strong proliferative capacity. No change in CD127 expression or proliferative potential was observed in untreated patients.

CONCLUSION

Early antiretroviral therapy initiation enhances CD127 expression on HIV-specific CD8+ T cells, reaching levels similar to those observed in aviremic nonprogressors, and restores their proliferative capacity.

Identification of a particular HIV-specific CD8+ T-cell subset with a CD27+ CD45RO-/RA+ phenotype and memory characteristics after initiation of HAART during acute primary HIV infection

CD8(+) T cells play an important role in controlling viral infections. Defective CD8(+) T-cell responses during HIV infection could contribute to viral persistence. Early initiation of highly active antiretroviral therapy during acute primary HIV infection helps to preserve HIV-specific immune responses. Here, we describe a particular CD27(+) CD45RO(-)/RA(+) HIV-specific CD8(+) T cell in participants treated early during the primary infection. These cells, which were present at a very low frequency during primary HIV infection, increased markedly after early treatment, whereas their frequency remained unchanged in untreated participants and in participants treated later. These nonnaive antigen-experienced cells are in a resting state and have characteristics of long-lived memory cells. They also possess direct effector capabilities, such as cytokine production, and are able to proliferate and to acquire cytotoxic functions on reactivation. Our results suggest that these HIV-specific CD27(+) CD45RO(-)/RA(+) CD8(+) T cells, observed when early viral replication is inhibited, form a pool of resting cells with memory characteristics.

Potent simian immunodeficiency virus-specific cellular immune responses in the breast milk of simian immunodeficiency virus-infected, lactating rhesus monkeys

Breast milk transmission of HIV is a leading cause of infant HIV/AIDS in the developing world. Remarkably, only a small minority of breastfeeding infants born to HIV-infected mothers contract HIV via breast milk exposure, raising the possibility that immune factors in the breast milk confer protection to the infants who remain uninfected. To model HIV-specific immunity in breast milk, lactation was pharmacologically induced in Mamu-A*01(+) female rhesus monkeys. The composition of lymphocyte subsets in hormone-induced lactation breast milk was found to be similar to that in natural lactation breast milk. Hormone-induced lactating monkeys were inoculated i.v. with SIVmac251 and CD8(+) T lymphocytes specific for two immunodominant SIV epitopes, Gag p11C and Tat TL8, and SIV viral load were monitored in peripheral blood and breast milk during acute infection. The breast milk viral load was 1-2 logs lower than plasma viral load through peak and set point of viremia. Surprisingly, whereas the kinetics of the SIV-specific cellular immunity in breast milk mirrored that of the blood, the peak magnitude of the SIV-specific CD8(+) T lymphocyte response in breast milk was more than twice as high as the cellular immune response in the blood. Furthermore, the appearance of the SIV-specific CD8(+) T lymphocyte response in breast milk was associated with a reduction in breast milk viral load, and this response remained higher than that in the blood after viral set point. This robust viral-specific cellular immune response in breast milk may contribute to control of breast milk virus replication.

Improved protection against simian immunodeficiency virus mucosal challenge in macaques primed with a DNA vaccine and boosted with the recombinant modified vaccinia virus Ankara and recombinant Semliki Forest virus

Using the experimental infection of cynomolgus macaques with simian immunodeficiency virus (SIV) as a model of human immunodeficiency virus infection in humans, we studied the immunogenicity and protective efficacy of a vaccine strategy combining DNA, the modified recombinant vaccinia virus strain Ankara (MVA) and Semliki Forest virus (SFV) expressing gag, pol, env, tat, rev and nef from SIV. Although this immunization strategy induced moderate immune responses, the control of pathogenic SIVmac251 infection following mucosal challenge was clearly improved by vaccination. The viral load in vaccinated animals was reduced by 2 logs during the acute phase of infection and, in five of the six macaques, viral load fell below the detection limit at set point. No correlates of immune protection were identified, but SIV-specific T-cell responses were detected earlier in vaccinated animals than in controls. These results highlight the power of live attenuated virus vectors for vaccination strategies.

In HIV-1 pathogenesis the die is cast during primary infection

The chronic stage of HIV-1 infection has been extensively described as a slowly evolving phase, in which the virus induces T-cell death slightly faster than the human body is able to recover. In contrast, T-cell and viral replication dynamics during primary infection have been less well studied. Recent studies in the SIV-macaque model and in HIV-positive patients during the acute infection period have highlighted the massive and irreversible depletion of CD4 memory T cells in the mucosa, particularly in the gut. Hence, gut-associated lymphoid tissue (GALT) plays a central role in the early stages of HIV-1 pathogenesis. Due to its particular cytokine expression pattern, GALT may favour the differential replication of certain HIV-1 subtypes during primary infection, particularly of subtype C. This could enhance the chance of a successful transmission. Moreover, these early events taking place in GALT during primary infection have major implications for therapy and vaccine design.

Gene expression profiling of gut mucosa and mesenteric lymph nodes in simian immunodeficiency virus-infected macaques with divergent disease course

BACKGROUND

Although the majority of drug-naïve HIV-infected patients develop acquired immunodeficiency syndrome (AIDS), a small percentage remains asymptomatic without therapeutic intervention.

METHODS

We have utilized the simian immunodeficiency virus (SIV)-infected rhesus macaque model to gain insights into the molecular mechanisms of long-term protection against simian AIDS.

RESULTS

Chronically SIV-infected macaques with disease progression had high viral loads and CD4(+) T-cell depletion in mucosal tissue and peripheral blood. These animals displayed pathologic changes in gut-associated lymphoid tissue (GALT) and mesenteric lymph node that coincided with increased expression of genes associated with interferon induction, inflammation and immune activation. In contrast, the animal with long-term asymptomatic infection suppressed viral replication and maintained CD4(+) T cells in both GALT and peripheral blood while decreasing expression of genes involved in inflammation and immune activation.

CONCLUSIONS

Our findings suggest that reduced immune activation and effective repair and regeneration of mucosal tissues correlate with long-term survival in SIV-infected macaques.

A DNA prime-oral Listeria boost vaccine in rhesus macaques induces a SIV-specific CD8 T cell mucosal response characterized by high levels of alpha4beta7 integrin and an effector memory phenotype

In this study in Rhesus macaques, we tested whether IL-12 or IL-15 in a DNA prime-oral Listeria boost amplifies the SIV-Gag-specific CD8 mucosal response. SIV-specific CD8 T cells were demonstrated in the peripheral blood (PB) in all test vaccine groups, but not the control group. SIV-Gag-specific CD8 T cells in the PB expressed alpha4beta7 integrin, the gut-homing receptor; a minor subset co-express alphaEbeta7 integrin. SIV-Gag-specific CD8 T cells were also detected in the gut tissue, intraepithelial (IEL) and lamina propria lymphocytes (LPL) of the duodenum and ileum. These cells were characterized by high levels of beta7 integrin expression and a predominance of the effector memory phenotype. Neither Il-12 nor IL-15 amplified the frequency of SIV-specific CD8 T cells in the gut. Thus, the DNA prime-oral Listeria boost strategy induced a mucosal SIV-Gag-specific CD8 T cell response characterized by expression of the alpha4beta7 integrin gut-homing receptor.

Early antiretroviral therapy for simian immunodeficiency virus infection leads to mucosal CD4+ T-cell restoration and enhanced gene expression regulating mucosal repair and regeneration

Simian immunodeficiency virus (SIV) and human immunodeficiency virus (HIV) infections lead to rapid depletion of CD4(+) T cells from gut-associated lymphoid tissue (GALT). Although the administration of antiretroviral therapy (ART) has been shown to increase CD4(+) T-cell levels in the peripheral blood in both SIV and HIV infections, its efficacy in restoring intestinal mucosal CD4(+) T cells has not been well investigated. To gain insights into the molecular mechanisms of virally induced disruptions in the mucosal immune system, we have evaluated longitudinal changes in viral burden, T-cell subsets, and mucosal gene expression profiles in SIV-infected rhesus macaques in the absence or presence of ART. Our results demonstrate a dramatic suppression of mucosal viral loads and rapid reconstitution of CD4(+) T cells in GALT in animals receiving ART that were not observed in untreated SIV-infected animals. DNA microarray-based gene expression profiling indicated that CD4(+) T-cell restoration in GALT was associated with up regulation of growth factors and genes involved in repair and regeneration of the mucosal epithelium. In contrast, untreated SIV-infected animals increased expression of lymphocyte activation and inflammatory response-associated genes and did not up regulate mucosal growth and repair associated transcription. In conclusion, these data indicate that initiating ART in primary SIV infection may lead to the restoration of the mucosal immune system through reduction of inflammation and promotion of epithelial repair in the intestinal mucosa.

Low autocrine interferon beta production as a gene therapy approach for AIDS: Infusion of interferon beta-engineered lymphocytes in macaques chronically infected with SIVmac251

Background

The aim of this study was to evaluate gene therapy for AIDS based on the transduction of circulating lymphocytes with a retroviral vector giving low levels of constitutive macaque interferon β production in macaques chronically infected with a pathogenic isolate of SIVmac251.

Results

Two groups of three animals infected for more than one year with a pathogenic primary isolate of SIVmac251 were included in this study. The macaques received three infusions of their own lymphocytes transduced ex vivo with the construct encoding macaque IFN-β (MaIFN-β or with a vector carrying a version of the MaIFN-β gene with a deletion preventing translation of the mRNA. Cellular or plasma viremia increased transiently following injection in most cases, regardless of the retroviral construct used. Transduced cells were detected only transiently after each infusion, among the peripheral blood mononuclear cells of all the animals, with copy numbers of 10 to 1000 per 10⁶ peripheral mononuclear cells.

Conclusion

Long-term follow-up indicated that the transitory presence of such a small number of cells producing such small amounts of MaIFN-β did not prevent animals from the progressive decrease in CD4⁺ cell count typical of infection with simian immunodeficiency virus. These results reveal potential pitfalls for future developments of gene therapy strategies of HIV infection.

CD4+ T cell depletion during all stages of HIV disease occurs predominantly in the gastrointestinal tract

The mechanisms underlying CD4⁺ T cell depletion in human immunodeficiency virus (HIV) infection are not well understood. Comparative studies of lymphoid tissues, where the vast majority of T cells reside, and peripheral blood can potentially illuminate the pathogenesis of HIV-associated disease. Here, we studied the effect of HIV infection on the activation and depletion of defined subsets of CD4⁺ and CD8⁺ T cells in the blood, gastrointestinal (GI) tract, and lymph node (LN). We also measured HIV-specific T cell frequencies in LNs and blood, and LN collagen deposition to define architectural changes associated with chronic inflammation. The major findings to emerge are the following: the GI tract has the most substantial CD4⁺ T cell depletion at all stages of HIV disease; this depletion occurs preferentially within CCR5⁺ CD4⁺ T cells; HIV-associated immune activation results in abnormal accumulation of effector-type T cells within LNs; HIV-specific T cells in LNs do not account for all effector T cells; and T cell activation in LNs is associated with abnormal collagen deposition. Taken together, these findings define the nature and extent of CD4⁺ T cell depletion in lymphoid tissue and point to mechanisms of profound depletion of specific T cell subsets related to elimination of CCR5⁺ CD4⁺ T cell targets and disruption of T cell homeostasis that accompanies chronic immune activation.