Schmitz/Santra: Second Generation rBCG Immunogens

OVERVIEW

An effective AIDS vaccine must elicit robust cellular and humoral immune responses to HIV-1, and these responses must be active in mucosal tissues. These complementing arms of the immune system have important anti-HIV-1 activity and should synergize to block the establishment of an infection upon mucosal exposure to the virus.

CD4+ T lymphocytes play a central and important role in HIV-1 control, by providing critical help for the induction and maintenance of both virus-specific CD8+ T lymphocyte and antibody responses. Previous work accomplished by the consortium led by Dr. Letvin, resulted in the development of a novel recombinant BCG prime/recombinant NYVAC boost strategy that induces CD8+ T lymphocyte responses as well as mucosal CD4+ T lymphocyte responses to the SIV Gag transgene. These 2nd generation rBCG immunogens generated robust CD4+ T cell responses with properties that should make them better priming immunogens than some of the other currently available vaccine modalities. This grant will extend that work and add in a protein boosting component in an effort to optimize antibody responses.

Vaccine candidates developed in this grant may be tested in future phase I clinical trials, with the goal of eventually advancing them to larger trials. As immune correlates data from the RV144 trial is further described and understood, this information will be used to evaluate and optimize the rBCG/protein prime- boost regimen to the greatest extent possible.

​RESEARCH OBJECTIVES

1. Create, optimize and evaluate QC-produced rBCG and rBCG auxotrophic vaccine strains in mice and support SHIV stocks generation for challenge studies in primates

2. Choose formulation and route of vaccine administration to optimize CD8+ and CD4+ T cell responses and antibody induction

3. Explore impact of pre-existing anti-vector immunity on efficacy of rBCG vectors

4. Evaluate final versions of mycobacterial vaccine constructs as priming immunogens in primates​

5. Evaluate frequencies of B cell responses to BCG vector in BCG-gag immunized macaques to determine the relative frequency of vector-targeted (BCG) abs vs. insert (SIV Gag) antibodies.

PROGRESS

Objectives 1-4 were met in previous years of this grant. The goals of the fi nal studies in this grant were twofold: to determine if BCG immunized macaques induce HLA E CD8 T cell responses and to defi ne the SIV Gag vs vector-directed responses. HLA-E restricted CD8 splenic T cells were isolated in collaboration with Dr. Louis Picker. SIV Gag and BCG (vector)-specifi c plasma levels and memory B cell frequencies were measured in collaboration with Drs. Barton Haynes and Mattia Bonsignori. To measure vector-directed plasma antibody levels, the Bonsignori laboratory developed a new fl ow-based technology to measure BCG surface-specifi c serum antibody using Danish strain BCG engineered to express the tomato red protein (courtesy of Dr. Bill Jacobs). The same technology was also used to measure binding to BCG by monoclonal antibodies. SIV Gag-specifi c vector-directed monoclonal antibodies are being recovered from sorted memory B cells and these monoclonal antibodies will be made available for future use among consortium members and will have applications in HIV, TB, and other infectious disease research.