Rosemarie D. Mason

Control of Viremia and Prevention of AIDS following Immunotherapy of SIV-Infected Macaques with Peptide-Pulsed Blood

Effective immunotherapies for HIV are needed. Drug therapies are life-long with significant toxicities. Dendritic-cell based immunotherapy approaches are promising but impractical for widespread use. A simple immunotherapy, reinfusing fresh autologous blood cells exposed to overlapping SIV peptides for 1 hour ex vivo, was assessed for the control of SIVmac251 replication in 36 pigtail macaques. An initial set of four immunizations was administered under antiretroviral cover and a booster set of three immunizations administered 6 months later. Vaccinated animals were randomized to receive Gag peptides alone or peptides spanning all nine SIV proteins. High-level, SIV-specific CD4 and CD8 T-cell immunity was induced following immunization, both during antiretroviral cover and without. Virus levels were durably ∼10-fold lower for 1 year in immunized animals compared to controls, and a significant delay in AIDS-related mortality resulted. Broader immunity resulted following immunizations with peptides spanning all nine SIV proteins, but the responses to Gag were weaker in comparison to animals only immunized with Gag. No difference in viral outcome occurred in animals immunized with all SIV proteins compared to animals immunized against Gag alone. Peptide-pulsed blood cells are an immunogenic and effective immunotherapy in SIV-infected macaques. Our results suggest Gag alone is an effective antigen for T-cell immunotherapy. Fresh blood cells pulsed with overlapping Gag peptides is proceeding into trials in HIV-infected humans.

Evaluation of recombinant Kunjin replicon SIV vaccines for protective efficacy in macaques

Persistent gag-specific T cell immunity would be a useful component of an effective HIV vaccine. The Flavivirus Kunjin replicon was previously engineered to persistently express HIV gag and was shown to induce protective responses in mice. We evaluated Kunjin replicon virus-like-particles expressing SIVgag-pol in pigtail macaques. Kunjin-specific antibodies were induced, but no SIV-specific T cell immunity were detected. Following SIVmac251 challenge, there was no difference in SIV viremia or retention of CD4 T cells between Kunjin-SIVgag-pol vaccine immunized animals and controls. An amnestic SIV gag-specific CD8 T cell response associated with control of viremia was observed in 1 of 6 immunized animals. Refinements of this vector system and optimization of the immunization doses, routes, and schedules are required prior to clinical trials.

Inactivated Simian Immunodeficiency Virus-Pulsed Autologous Fresh Blood Cells as an Immunotherapy Strategy

ABSTRACT Practical immunotherapies for human immunodeficiency virus infection are needed. We evaluated inactivated simian immunodeficiency virus (SIV) pulsed onto fresh peripheral blood mononuclear cells in 12 pigtail macaques with chronic SIVmac251 infection for T-cell immunogenicity in a randomized cross-over design study. The immunotherapy was safe and convincingly induced high levels of SIV-specific CD4+ T-cell responses (mean, 5.9% ± 1.3% of all CD4+ T cells) and to a lesser extent SIV-specific CD8+ T-cell responses (mean, 0.7% ± 0.4%). Responses were primarily directed toward Gag and less frequently toward Env but not Pol or regulatory/accessory SIV proteins. T-cell responses against Gag were generally broad and polyfunctional, with a mean of 2.7 CD4+ T-cell epitopes mapped per animal and more than half of the SIV Gag-specific CD4+ T cells expressing three or more effector molecules. The immunogenicity was comparable to that found in previous studies of peptide-pulsed blood cells. Despite the high-level immunogenicity, no reduction in viral load was observed in the chronically viremic macaques. This contrasts with our studies of immunization with peptide-pulsed blood cells during early SIV infection in macaques. Future studies of inactivated virus-pulsed blood cell immunotherapy during early infection of patients receiving antiretroviral therapy are warranted.

Low pre-infection levels and loss of central memory CD4+ T cells may predict rapid progression in SIV-infected pigtail macaques

CD4+ T lymphocyte subsets are targeted to different degrees by SIV infection. We studied central memory, effector memory, naïve, and regulatory T cell levels longitudinally in 11 SIV(mac251)-infected pigtail macaques. Depletion of CD28+CD95+ central memory CD4+ T cells, but not other populations, correlated with both SIV viral load and disease progression. A low pre-infection level of central memory CD4+ T cells was also predictive of rapid disease progression. If confirmed in larger studies, our results suggest stratifying macaques for baseline central memory CD4+ T cells would be useful in defining both the pathogenesis of SIV disease and SIV vaccine efficacy.

Safety, immunogenicity and efficacy of peptide-pulsed cellular immunotherapy in macaques

Background  Simple and effective delivery methods for cellular immunotherapies are needed. We recently published on the effectiveness of using ex vivo pulsing of overlapping SIV Gag 15mer peptides onto fresh peripheral blood cells in 32 SIVmac251‐infected pigtail macaques.

Differential patterns of immune escape at Tat-specific cytotoxic T cell epitopes in pigtail macaques.

Cytotoxic T lymphocyte responses to conserved proteins such as Gag within HIV- or SIV-infected hosts can facilitate partial control of viremia. However, the utility of targeting variable viral proteins by CTL responses is unclear. We studied CTL responses to regulatory and accessory proteins of SIV in pigtail macaques. The regulatory and accessory proteins were the most commonly targeted proteins by CTL responses from pigtail macaques. We identified 2 novel Tat-specific CTL responses that were both restricted by the Mane-A10 allele. Viral escape at one of the Tat epitopes, KSA10, was slower in comparison to another Tat epitope KVA10. The kinetics of escape of the KSA10 Tat epitope were more similar to an immunodominant KP9 Gag epitope also restricted by Mane-A10. Our results suggest that some regulatory or accessory CTL epitopes may be useful targets for vaccination against HIV.

Delivery of immunotherapy with peptide-pulsed blood in macaques

Simple and effective delivery methods for cellular immunotherapies are needed. We assessed ex vivo pulsing of overlapping SIV Gag 15mer peptides onto either whole blood or PBMC in 15 randomly assigned SIV-infected macaques. Both delivery methods were safe and immunogenic, stimulating high levels of broad and polyfunctional Gag-specific CD4 and CD8 T cells. Delivery of overlapping Gag peptides via either whole blood or PBMC is suitable for clinical evaluation.

CD4+ T-cell subsets: what really counts in preventing HIV disease?

Despite the urgent need, no HIV vaccine currently exists. While binding antibody responses to HIV are readily generated in vivo, eliciting broadly neutralizing antibody responses to HIV has proven extraordinarily difficult [1]. Studies demonstrating the importance of HIVand SIV-specific CD8 T cells (cytotoxic T lymphocytes [CTLs]) in the initial control of viremia during acute infection led to a glut of vaccines designed to induce specific CTL responses [2]. The recent failure of adenovirus-vector HIV vaccines (which typically induce robust HIV-specific CTL responses) in proof-ofefficacy Phase IIb trials, highlights the enormity of the challenge [3].

Protection afforded by live attenuated SIV is associated with rapid killing kinetics of CTLs

Background  Live attenuated SIV vaccines are highly efficacious, but how they mediate protection is poorly understood. A feature of the effectiveness of live attenuated vaccines is their ability to control high dose challenge viruses early, without a large peak of acute viraemia. We hypothesized that long‐lived antigen exposure from live attenuated SIV may result in CD8+ cytotoxic T lymphocytes persistently capable of rapidly cytolytic potential.