DNAVAC 001: A Phase 1 Open-labelled Trial to Optimise DNA Vaccination for Antibody Induction

It is generally accepted that globally effective HIV-1 vaccine will likely need to induce bnAbs against HIV-1. The proposed study is based on the recognition of the potential strategic importance of performing iterative small human studies to accelerate HIV-1 immunogen discovery, where DNA vaccines offer the fastest and most cost effective approach for rapid screening of multiple immunogens. This study aims to leverage DNA immunization as a platform to accelerate the discovery of HIV-1 immunogens capable of inducing bnAbs in humans.

To meet this aim this study seeks to apply recent state of the art technological advances in DNA vaccination and immune monitoring, both at the single cell and molecular level, to enable detailed probing of developing vaccine induced antibody responses. In this respect it represents the first attempt in humans to use a DNA vaccine approach to investigate the development and focusing of B cell responses to vaccination. Should this approach be successful it will provide an important new strategy for rapidly conducting systematic clinical research studies in humans aimed at moving the HIV-1 vaccine field closer to achieving the key objective of identification of immunogens and vaccine strategies required for induction of bnAbs in humans.

At the end of 2012, an estimated 35.3 million people were living with HIV worldwide, up 17% from 2001. This reflects the continued large number of new HIV infections and a significant expansion of access to antiretroviral therapy, which has helped reduce AIDS-related deaths, especially in more recent years (UNAIDS Report on the global AIDS epidemic 2013. Geneva 2013). The majority of new HIV infections continue to occur in sub-Saharan Africa. There is an urgent need to strengthen and scale-up existing and new prevention methods such as HIV testing and counselling, behavioural interventions, condom use, treatment of sexually transmitted diseases, harm reduction, male circumcision (Wamai, Morris et al. 2011) and antiretroviral drugs for prevention (Granich, Gupta et al. 2011). New prevention strategies to control the epidemic and prevent new infections, including pre-exposure prophylaxis (Kim, Becker et al. 2010), antiviral treatment for prevention (Granich, Lo et al. 2011), topical microbicides (Krakower and Mayer 2011), and HIV preventive vaccines must be explored and their access ensured. However the development of an efficacious preventive vaccine against HIV-1 remains among the best hopes for controlling the HIV/AIDS pandemic (Kim, Rerks-Ngarm et al. 2010, Koff 2010).

Data from a recent community-based efficacy trial in Thailand (RV144) testing a vaccination regimen consisting of priming with the canarypox vector ALVAC-HIV, expressing HIV gag, pro, and env genes, and boosting with recombinant AIDSVAX B/E HIV Env protein demonstrated modest vaccine protection against HIV acquisition. The vaccine efficacy decreased over the first year after vaccination from 60% at one year to 31.2 % at 3.5 years post first vaccination, suggesting that protection may be related to HIV-specific antibodies waning over time (Rerks-Ngarm, Pitisuttithum et al. 2009). The regimen did not decrease HIV viral load in vaccine recipients who acquired HIV. CD8 T-cell responses were in few vaccine recipients, while binding antibodies were detected in a majority of them, with very limited detectable neutralizing antibody responses to HIV. These results suggest that more potent vaccines are needed for providing significant and sustained protection against HIV acquisition as well as for controlling viral replication.

Neutralizing antibodies against circulating isolates are induced principally by HIV Env and could potentially confer sterilizing immunity against HIV, as suggested by non-human primate SHIV challenge studies (Mascola, Stiegler et al. 2000, Pantophlet and Burton 2006, Hessell, Poignard et al. 2009). Moreover, a recent Non Human Primates (NHP) study demonstrates that SIV (Simian Immunodeficiency Virus) Env antigen was essential to confer protection against SIV challenge and that SIV Env-specific binding non-neutralizing antibodies played a role in this protection (Barouch, Liu et al. 2012). Previous trials using monomeric AIDSVAX gp120 showed no efficacy in a phase III trials (Flynn, Forthal et al. 2005, Pitisuttithum, Gilbert et al. 2006). This failure has been a major drawback for Env-based HIV vaccines, since current immunogens afford only very narrow protection against HIV strains that are closely related to the vaccine antigen (Zhang and Dimitrov 2007, Montero, van Houten et al. 2008). In RV144, an analysis of the correlates of risk showed that IgG3 binding antibodies to scaffolded-V1V2 recombinant protein correlated inversely with infection rate while Env binding plasma IgA correlated directly with infection rate (Haynes, Gilbert et al. 2012). Several lines of evidence suggest that vaccine induced antibodies recognize conformational epitopes in the scaffolded V1V2 reagent, which has been shown to detect conformational V1V2 antibodies (Pinter, Honnen et al. 1998, Zolla-Pazner, deCamp et al. 2013). The results of an analysis of breakthrough viruses from patients in the RV144 trial were consistent with immune pressure focused on amino acid patterns in and flanking the V1V2 region of HIV-1 Env (Edlefsen, Gilbert et al. 2013). This region serves critical functions, such as participating in CD4-receptor and chemokine-receptor binding, binding to α4β7 integrin (Nawaz, Cicala et al. 2011) and serving as the binding site of neutralizing antibodies (Gorny, Stamatatos et al. 2005, Walker, Phogat et al. 2009, Changela, Wu et al. 2011, McLellan, Pancera et al. 2011). However, the search for an immunogen able to induce broad cross-protective and long-lasting neutralizing/functional antibodies remains difficult and critical (Burton, Desrosiers et al. 2004, Montefiori, Sattentau et al. 2007).