Mosaic HIV-1 vaccination induces anti-viral CD8+ T cell functionality in the phase 1/2a clinical trial APPROACH.

IMPORTANCE: The functionality of CD8+ T cells against human immunodeficiency virus-1 (HIV-1) antigens is indicative of HIV-progression in both animal models and people living with HIV. It is, therefore, of interest to assess CD8+ T cell responses in a prophylactic vaccination setting, as this may be an important component of the immune system that inhibits HIV-1 replication. T cell responses induced by the adenovirus serotype 26 (Ad26) mosaic vaccine regimen were assessed previously by IFN-γ ELISpot and flow cytometric assays, yet these assays only measure cytokine production but not the capacity of CD8+ T cells to inhibit replication of HIV-1. In this study, we demonstrate direct anti-viral function of the clinical Ad26 mosaic vaccine regimen through ex vivo inhibition of replication of diverse clades of HIV-1 isolates in the participant's own CD4+ T cells.

Viral Inhibitory Activity of CD8+ T Cells in HIV Infection.

Cytotoxic T lymphocytes, or CD8+ T cells, play an important role in the control of replication of HIV. Inducing effective and durable HIV-specific CD8+ T cell responses are, therefore, a major objective in prophylactic and curative strategies for HIV infection. To evaluate such strategies, reliable immunological assays are needed that measure the capacity of CD8+ T cells to exert their effector functions and control viremia. Classical immunological assays such as interferon-γ (IFN-γ) enzyme-linked immunospot or intracellular cytokine staining measure the production of one or several effector molecules but do not actually show suppression of viral replication. Perhaps unsurprisingly, these assays do not correlate with either prevention of infection or lower viral set-points after infection. Therefore, more relevant assays are needed which directly measure the viral inhibitory activity (VIA) of CD8+ T cells and are more likely to predict success or failure of different immune interventions. The present review discusses the methodology of the VIA in detail as well as the practical implications of the several variations that have been described. We then go onto discuss existent literature on the relationship between VIA and HIV control, give an overview of examples where VIA has been induced or boosted in vivo or in vitro, and finally discuss observed associations between VIA and other immunological parameters. We conclude that while VIA is complex and laborious, it provides functional information about CD8+ T cells that no other assay can deliver.

Evaluation of the immunogenicity and impact on the latent HIV-1 reservoir of a conserved region vaccine, MVA.HIVconsv, in antiretroviral therapy-treated subjects.

INTRODUCTION: Vaccines may be key components of a curative strategy for HIV-1. We investigated whether a novel immunogen, HIVconsv, designed to re-direct T cell responses to conserved viral epitopes, could impact the HIV-1 reservoir in chronic antiretroviral therapy (ART)-treated subjects when delivered by modified vaccinia virus Ankara (MVA). METHODS: Nineteen virologically suppressed individuals were randomized to receive vaccinations with MVA.HIVconsv (5.5 × 107 plaque-forming units, pfu, n = 8; 2.2 × 108 pfu, n = 7) or placebo (n = 4) at 0, 4 and 12 weeks. Magnitude, breadth and antiviral function of vaccine-induced T cells, cell-associated HIV-1 DNA in circulating CD4+ T cells and residual viremia in plasma were measured before and after vaccination. RESULTS: 90% of subjects completed the vaccine regimen; there were no serious vaccine-related adverse events. The magnitude of HIVconsv-specific IFN-γ-secreting T cells was not significantly boosted in vaccinees when compared with placebos in ex vivo Elispot assays, due to greater than expected variation in HIV-specific T cell responses in the latter during the observation period. Ex vivo CD8+ T cell viral inhibitory capacity was modest but significantly increased post-vaccination with MVA.HIVconsv at the higher dose (p = 0.004) and was positively correlated with the frequency of HIVconsv-specific CD8+ CD107+ IFN-α± T cells (r = 0.57, p = 0.01). Total HIV-1 DNA and residual viral load did not change significantly from baseline in any group. CONCLUSIONS: Homologous prime-boost vaccination with MVA.HIVconsv was safe in HIV-positive ART-treated subjects but showed modest immunogenicity and did not significantly change the size of the viral reservoir. MVA.HIVconsv may be more effective when used in a heterologous prime-boost vaccination regimen and when combined with a latency-reversing agent. CLINICAL TRIALS REGISTRATION: NCT01024842.

Aviremia 10 Years Postdiscontinuation of Antiretroviral Therapy Initiated During Primary Human Immunodeficiency Virus-1 Infection and Association With Gag-Specific T-Cell Responses.

Combination antiretroviral therapy during primary human immunodeficiency virus-1 infection may enable long-term drug-free virological control in rare individuals. We describe a female who maintained aviremia and a normal CD4(+)/CD8(+) T cell ratio for 10 years after stopping therapy, despite a persistent viral reservoir. Cellular immune responses may have contributed to this outcome.

Development of a luciferase based viral inhibition assay to evaluate vaccine induced CD8 T-cell responses.

Emergence of SIV and HIV specific CD8 T cells has been shown to correlate with control of in vivo replication. Poor correlation between IFN-γ ELISPOT responses and in vivo control of the virus has triggered the development of more relevant assays to assess functional HIV-1 specific CD8 T-cell responses for the evaluation and prioritization of new HIV-1 vaccine candidates. We previously established a viral inhibition assay (VIA) that measures the ability of vaccine-induced CD8 T-cell responses to inhibit viral replication in autologous CD4 T cells. In this assay, viral replication is determined by measuring p24 in the culture supernatant. Here we describe the development of a novel VIA, referred to as IMC LucR VIA that exploits replication-competent HIV-1 infectious molecular clones (IMCs) in which the complete proviral genome is strain-specific and which express the Renilla luciferase (LucR) gene to determine viral growth and inhibition. The introduction of the luciferase readout does provide significant improvement of the read out time. In addition to switching to the LucR read out, changes made to the overall protocol resulted in the miniaturization of the assay from a 48 to a 96-well plate format, which preserved sample and allowed for the introduction of replicates. The overall assay time was reduced from 13 to 8 days. The assay has a high degree of specificity, and the previously observed non-specific background inhibition in cells from HIV-1 negative volunteers has been reduced dramatically. Importantly, we observed an increase in positive responses, indicating an improvement in sensitivity compared to the original VIA. Currently, only a limited number of "whole-genome" IMC-LucR viruses are available and our efforts will focus on expanding the panel to better evaluate anti-viral breadth. Overall, we believe the IMC LucR VIA provides a platform to assess functional CD8 T-cell responses in large-scale clinical trial testing, which will enhance the ability to select the most promising HIV-1 vaccine candidates capable of controlling HIV-1 replication in vivo.