Simian immunodeficiency virus (SIV)-specific CD8+ cytotoxic T lymphocyte responses of naive and vaccinated cynomolgus macaques infected with SIVmac32H(J5): quantitative analysis by in vitro antigenic stimulation

Cell-mediated immunity to low doses of SIVsm in cynomolgus macaques did not confer protection against mucosal rechallenge

Simian immunodeficiency virus (SIV) infection of macaques is a useful model for studies of the roles of different immune responses against viruses that cause (AIDS). In this study, six cynomolgus macaques were inoculated intrarectally with subinfectious or infectious doses of SIVsm to assess the SIV specific immunity, in particular protective immunity against subsequent challenge with a higher dose of SIVsm. Following the first inoculation with SIVsm, the two monkeys given the highest doses of cell-free SIVsm stock and one monkey given the intermediate dose became infected. In the three remaining animals, one animal inoculated with an intermediate dose and two animals given low doses of SIVsm, no overt infection occurred. Nevertheless, SIV specific cytotoxic T-cells against Gag/Pol and Nef proteins and T-cell proliferative responses against HIV-2 whole viral lysate, native HIV-2 gp125, recombinant SIV gp140 and SIV Env synthetic peptides were detected. After intrarectal rechallenge of the uninfected macaques with a higher dose of SIVsm all the animals became infected. These results demonstrate that cell mediated immunity can occur in the absence of detectable infection in monkeys inoculated with a low dose of SIVsm. Despite the presence of cellular immune responses, the animals were not protected when challenged with a higher dose of virus later.

Detection of simian immunodeficiency virus (SIV)-specific T-cell-mediated cytotoxicity in the peripheral blood from infected cynomolgus monkeys

We have previously demonstrated that peptide immunization restimulates the memory CD4 T-cell response, but fails to induce cytotoxic T lymphocyte (CTL) in cynomolgus macaques. To examine the nature of protective immunity to simian immunodeficiency virus (SIV) in this study, freshly isolated peripheral blood mononuclear cells (PBMC) from four infected juvenile cynomolgus macaques and from three uninfected control macaques were assessed for CTL activity monthly for 9 consecutive months, beginning 1 month after detection of infection. Target cells consisted of major histocompatibility (MHC) haploidentical parental PBMC which were stimulated with mitogen and then pulsed with heat-killed SIVcyn. CTL activity was demonstrated in PBMCs from all four infected animals. The effector cells are T cells which mediate cytotoxicity against SIVcyn-pulsed target cells in an MHC-restricted manner. Furthermore, the cytotoxicity is virus specific and predominantly, if not exclusively, mediated by CD8+ T cells; it is also MHC class I restricted. Incubation of target cells with pepstatin A during antigen pulsing prior to the cytotoxic assay inhibited target cell generation, suggesting that viral antigens are processed via an endocytic pathway.

Simian immunodeficiency virus as a model of human HIV disease

Because of strong clinical, pathological, virological and immunological analogies with HIV infection of humans, infection of macaques with SIV provides a valuable model for exploring crucial issues related to both the pathogenesis and prevention of HIV infection. The model has offered a unique setting for the preclinical evaluation of drugs, vaccines and gene-therapies against HIV, and has helped to identify many virus and host determinants of lentiviral disease. For instance, the importance of an intact nef gene for efficient lentivirus replication and disease induction, and the protective ability of live attenuated, nef-deleted viruses have been first demonstrated in macaques using molecular clones of SIV. More recently, the development of chimeric HIV-SIV vectors able to establish infection and induce disease in macaques has provided new opportunities for the evaluation of vaccination strategies based upon HIV antigens. The aim of this review is to describe the natural course of SIV infection in macaques and to outline how this model has contributed to our understanding of the complex interaction between lentiviruses and host immune system.

Presence of circulating CTL induced by infection with wild-type or attenuated SIV and their correlation with protection from pathogenic SHIV challenge

The aim of this study was to evaluate the role of CTLs in the protection from challenge with pathogenic SHIV in macaques vaccinated with attenuated virus. More specifically, we have analyzed the CTL response in cynomolgus macaques vaccinated/infected with the attenuated SIVmacC8 or the wild-type SIVmacJ5 and correlated these responses to the protection from SHIV89.6P challenge. SIVmacC8-vaccinated monkeys demonstrated a broader CTL response than the SIVmacJ5-infected animals. Nevertheless, CTL against some proteins in SIVmacC8-vaccinated monkeys became progressively more difficult to detect through the day of challenge. In regards to protection from superinfection with SHIV89.6P, neither the presence of circulating CTL nor the CTL precursor frequency against any of the tested proteins correlated with the outcome of the challenge when SIVmacJ5- and SIVmacC8-infected animals were analyzed together. By analyzing the SIVmacC8-vaccinated animals separately, only the protected animal had detectable CTL precursors with moderate frequencies against all three tested proteins at the day of challenge.