A polyvalent Clade B virus-like particle HIV vaccine combined with partially protective oral preexposure prophylaxis prevents simian-human immunodeficiency virus Infection in macaques and primes for virus-amplified immunity

Efficacy of Oral Tenofovir Alafenamide/Emtricitabine Combination or Single-Agent Tenofovir Alafenamide Against Vaginal Simian Human Immunodeficiency Virus Infection in Macaques

BACKGROUND

Tenofovir alafenamide (TAF)-based regimens are being evaluated for pre-exposure prophylaxis (PrEP). We used a macaque model of repeated exposures to simian human immunodeficiency virus (SHIV) to investigate whether TAF alone or the combination of TAF and emtricitabine (FTC) can prevent vaginal infection.

METHODS

Pigtail macaques were exposed vaginally to SHIV162p3 once a week for up to 15 weeks. Animals received clinical doses of FTC/TAF (n = 6) or TAF (n = 9) orally 24 hours before and 2 hours after each weekly virus exposure. Infection was compared with 21 untreated controls.

RESULTS

Five of the 6 animals in the FTC/TAF and 4 of the 9 animals in the TAF alone group were protected against infection (P = .001 and P = .049, respectively). The calculated efficacy of FTC/TAF and TAF was 91% (95% confidence interval [CI], 34.9%-98.8%) and 57.8% (95% CI, -8.7% to 83.6%), respectively. Infection in FTC/TAF but not TAF-treated macaques was delayed relative to controls (P = .005 and P = .114). Median tenofovir diphosphate (TFV-DP) levels in peripheral blood mononuclear cells (PBMCs) were similar among infected and uninfected macaques receiving TAF PrEP (351 and 143 fmols/106 cells, respectively; P = .921).

CONCLUSIONS

Emtricitabine/TAF provided a level of protection against vaginal challenge similar to FTC/TFV disoproxil fumarate combination in the macaque model. Our results support the clinical evaluation of FTC/TAF for PrEP in women.

Combining biomedical preventions for HIV: Vaccines with pre-exposure prophylaxis, microbicides or other HIV preventions

Biomedical preventions for HIV, such as vaccines, microbicides or pre-exposure prophylaxis (PrEP) with antiretroviral drugs, can each only partially prevent HIV-1 infection in most human trials. Oral PrEP is now FDA approved for HIV-prevention in high risk groups, but partial adherence reduces efficacy. If combined as biomedical preventions (CBP) an HIV vaccine could provide protection when PrEP adherence is low and PrEP could prevent vaccine breakthroughs. Other types of PrEP or microbicides may also be partially protective. When licensed, first generation HIV vaccines are likely to be partially effective. Individuals at risk for HIV may receive an HIV vaccine combined with other biomedical preventions, in series or in parallel, in clinical trials or as part of standard of care, with the goal of maximally increasing HIV prevention. In human studies, it is challenging to determine which preventions are best combined, how they interact and how effective they are.

Animal models can determine CBP efficacy, whether additive or synergistic, the efficacy of different products and combinations, dose, timing and mechanisms. CBP studies in macaques have shown that partially or minimally effective candidate HIV vaccines combined with partially effective oral PrEP, vaginal PrEP or microbicide generally provided greater protection than either prevention alone against SIV or SHIV challenges. Since human CBP trials will be complex, animal models can guide their design, sample size, endpoints, correlates and surrogates of protection. This review focuses on animal studies and human models of CBP and discusses implications for HIV prevention.

A multiplex assay for detection of SHIV plasma and mucosal IgG and IgA

Evaluating antibody maturation provides valuable data to characterize immune responses to HIV infection and can provide insight into biomedical intervention efficacy. It is important to develop assays that evaluate antibody maturation in both plasma and mucosal compartments. The nonhuman primate model provides a controlled system to collect temporal data that are integral to assessing intervention strategies. We report the development of a novel multiplex assay, based on the Bio-Plex platform, to evaluate plasma and mucosal IgG and IgA avidity and maturation against simian/human immunodeficiency virus (SHIV) in this controlled system. Vaginal mucosa and plasma samples were collected from a prior study evaluating the efficacy of a tenofovir disoproxil fumarate (TDF) intravaginal ring (IVR) against SHIVSF162P3 challenge in female pigtailed macaques. For validation of the multiplex assay, specimens from six SHIV-infected placebo animals and one TDF breakthrough animal were evaluated. For SHIV and HIV envelope analytes, antibody levels and avidity in both compartments continued to mature post-infection. Maturation of IgG and IgA levels was similar in each compartment, however, mucosal antibody levels tended to be more variable. This SHIV assay elucidates IgG/IgA antibody kinetics in the plasma and vaginal mucosa and will be a valuable tool in vaccine and other biomedical intervention studies in the nonhuman primate model.

Understanding HIV infection for the design of a therapeutic vaccine. Part II: Vaccination strategies for HIV

HIV infection leads to a gradual loss CD4(+) T lymphocytes comprising immune competence and progression to AIDS. Effective treatment with combined antiretroviral drugs (cART) decreases viral load below detectable levels but is not able to eliminate the virus from the body. The success of cART is frustrated by the requirement of expensive lifelong adherence, accumulating drug toxicities and chronic immune activation resulting in increased risk of several non-AIDS disorders, even when viral replication is suppressed. Therefore, there is a strong need for therapeutic strategies as an alternative to cART. Immunotherapy, or therapeutic vaccination, aims to increase existing immune responses against HIV or induce de novo immune responses. These immune responses should provide a functional cure by controlling viral replication and preventing disease progression in the absence of cART. The key difficulty in the development of an HIV vaccine is our ignorance of the immune responses that control of viral replication, and thus how these responses can be elicited and how they can be monitored. Part one of this review provides an extensive overview of the (patho-) physiology of HIV infection. It describes the structure and replication cycle of HIV, the epidemiology and pathogenesis of HIV infection and the innate and adaptive immune responses against HIV. Part two of this review discusses therapeutic options for HIV. Prevention modalities and antiretroviral therapy are briefly touched upon, after which an extensive overview on vaccination strategies for HIV is provided, including the choice of immunogens and delivery strategies.