Impaired mitogen-driven proliferation and cytokine transcription of lymphocytes from macaques early after simian immunodeficiency virus (SIV) infection

Changes in soluble factor-mediated CD8+ cell-derived antiviral activity in cynomolgus macaques infected with simian immunodeficiency virus SIVmac251: relationship to biological markers of progression

Cross-sectional studies have shown that the capacity of CD8+ cells from human immunodeficiency virus (HIV)-infected patients and simian immunodeficiency virus (SIV) SIVmac-infected macaques to suppress the replication of human and simian immunodeficiency viruses in vitro depends on the clinical stage of disease, but little is known about changes in this antiviral activity over time in individual HIV-infected patients or SIV-infected macaques. We assessed changes in the soluble factor-mediated noncytolytic antiviral activity of CD8+ cells over time in eight cynomolgus macaques infected with SIVmac251 to determine the pathophysiological role of this activity. CD8+ cell-associated antiviral activity increased rapidly in the first week after viral inoculation and remained detectable during the early phase of infection. The net increase in antiviral activity of CD8+ cells was correlated with plasma viral load throughout the 15 months of follow-up. CD8+ cells gradually lost their antiviral activity over time and acquired virus replication-enhancing capacity. Levels of antiviral activity correlated with CD4+ T-cell counts after viral set point. Concentrations of beta-chemokines and interleukin-16 in CD8+ cell supernatants were not correlated with this antiviral activity, and alpha-defensins were not detected. The soluble factor-mediated antiviral activity of CD8+ cells was neither cytolytic nor restricted to major histocompatibility complex. This longitudinal study strongly suggests that the increase in noncytolytic antiviral activity from baseline and the maintenance of this increase over time in cynomolgus macaques depend on both viral replication and CD4+ T cells.

MHC class I alleles influence set-point viral load and survival time in simian immunodeficiency virus-infected rhesus monkeys

In HIV-infected humans and SIV-infected rhesus macaques, host genes influence viral containment and hence the duration of the disease-free latency period. Our knowledge of the rhesus monkey immunogenetics, however, is limited. In this study, we describe partial cDNA sequences of five newly discovered rhesus macaque (Mamu) class I alleles and PCR-based typing techniques for the novel and previously published Mhc class I alleles. Using 15 primer pairs for PCR-based typing and DNA sequence analysis, we identified at least 21 Mhc class I alleles in a cohort of 91 SIV-infected macaques. The results confirm the presence of multiple class I genes in rhesus macaques. Of these alleles, Mamu-A*01 was significantly associated with lower set-point viral load and prolonged survival time. Mamu-A*1303 was associated with longer survival and a "novel" Mhc class I allele with lower set-point viral load. The alleles are frequent in rhesus macaques of Indian origin (12-22%). In addition, survival probability of individual SIV-infected rhesus monkeys increased with their number of alleles considered to be associated with longer survival. The results contribute to improve the interpretation and quality of preclinical studies in rhesus monkeys.

Mechanisms of protection induced by attenuated simian immunodeficiency virus

To determine whether attenuated simian immunodeficiency virus (SIV) vaccines confer protection against superinfection via secondary cellular immune responses, we searched for markers of immune activation following rechallenge. Productive infection with either attenuated SIVmacC8 or wild-type SIVmacJ5 resulted in a transient increase in T-lymphocyte CD25 and Mafa-DR expression. A pronounced increase in the frequency of FAS+ CD8+ lymphocytes was observed following SIVmacJ5 infection only. A transient increase in lymphocytes positive for intracellular IFN-gamma and IL-4 was observed following primary infection with either virus. In contrast, lymphocytes positive for intracellular IL-2 were reduced. Following SIVmacJ5 challenge of SIVmacC8-infected vaccinees, no evidence of detectable superinfection was obtained. Rechallenge of vaccinees did not alter the frequency of activated peripheral T-lymphocytes, perturb cytokine profiles, or generate an anamnestic antibody response. These data do not support the hypothesis that protection conferred by live attenuated SIV is mediated by the induction of vigorous T-cell responses upon rechallenge.

Kinetics of lymphocyte apoptosis in macaques infected with different simian immunodeficiency viruses or simian/human immunodeficiency hybrid viruses

Increased rates of T-cell apoptosis have been detected in human immunodeficiency virus (HIV)-infected individuals and in the simian immunodeficiency model (SIV) for AIDS research. We have infected macaques with virulent SIV or SIV/HIV hybrid viruses (SHIV) of different pathogenic potentials to study the early kinetics of apoptosis in this model. Animals infected with SIV showed an increased degree of apoptosis in their peripheral blood mononuclear cells as early as 8 weeks after virus inoculation. Apoptotic cells were detected in the CD4 and CD8 cell populations of infected animals. In contrast, apathogenic SHIV did not lead to increased lymphocyte apoptosis and moderately pathogenic SHIV induced only transient apoptosis. T-cell death was temporally linked to viral replication in vivo. Furthermore, lymphocyte apoptosis in infected macaques was associated with impaired proliferative responses of helper T-cells and with CD4 cell depletion. The monkey model described here provides the opportunity for testing early therapeutic interventions to prevent virus-induced programmed cell death and the subsequent onset of AIDS.