Haynes: B-Cell Lineage Envelope Design

OVERVIEW

The RV144 Thai vaccine trial had 31% estimated vaccine effi cacy. The protective effect was short-lived, and anti-HIV-1 CD8+ T cell responses were not induced by the vaccine. Thus, is it critical to improve on the RV144 trial by making an immunogen that induces higher levels and longer duration of protective anti-HIV-1 immune responses. One hypothesis for a correlate of protective immunity in the RV144 trial is that a short- lived antibody prevented HIV-1 acquisition at mucosal sites by one or more mechanisms.

Dr. Barton Haynes and colleagues at the Duke Human Vaccine Institute seek to develop HIV-1 envelope immunogens that improve on the results of the RV144 trial (ALVAC/AIDSVAX® vaccine) by using B cell lineage-based vaccine design based on two principles. First, inferring the reverted unmutated ancestor of a mutated antibody gives an approximation of the naïve B cell receptor (BCR) from which the antibody origi- nated. Second, the optimal antigens for triggering naïve B cells bind naïve BCRs with the highest affi nity. B cell lineage-based vaccine design is, therefore, the design of vaccine immunogens based on optimal binding to reverted unmutated ancestors (putative mimics of B cell receptors of naïve B cells) of the desired mutated antibody to be elicited. The research team will focus on evaluation of antibodies as candidates for correlates of protection in RV144 and studies that build upon RV144 (RV305, RV305 extended boost, RV306, and RV328 trials).

RESEARCH OBJECTIVES

1.) Isolate antibodies from RV144, RV305, RV305 extended boost, RV306, and RV328 trials that are candi- dates for correlates of protective immunity.

2.) Determine the neutralizing capacity and Fc-mediated effector functions of the long HCDR3, V2-specifi c and CD4 binding site-specifi c (bs) antibodies that were induced with the ALVAC/AIDSVAX® vaccine.

3.) Perform a longitudinal analysis of the antibody repertoire after subsequent boosts in RV305, and RV305 extended trial vaccines to determine the effects of delayed and repetitive boosting on antibody development.

​4.) Determine whether the timing of the AIDSVAX® vaccine boost in RV306 (the repeat of RV144 with the 6-month boost) affects the antibody repertoire and determine whether the ALVAC prime, missing from RV328, is necessary in the regimen to induce these types of antibodies.

PROGRESS

One of the major goals of this work was to determine whether additional protein boosting could induce a better quality of antibodies, i.e., neutralizing antibodies with breadth for tier 2 challenge virus strains. Thus, we have analyzed the repertoires of RV144 vaccinees and those vaccinees who also received a boost with ALVAC + AIDSVAX B/E 6-8 years after the fi nal RV144 boost (RV305 trial). We found that with the 6-8-year boost, the Env-specifi c B cell repertoire contained an increased number of long HCDR3 antibodies. Broadly neutralizing antibodies (bNAbs) have a number of unusual traits including several bNAb types having long HCDR3 regions. Long HCDR3 region-antibodies are culled in the bone marrow due to their propensity to be polyreactive (Meffre E. et al. JCI 108: 879, 2001); thus, to induce bNAbs with long HCDR3s, one is starting with a pool of B cells that is only ~ 2% of the B cell pool (Briney, B et al. PLoS One 7:36750, 2012). We found that the long HCDR3 antibodies induced by the RV305 boost regimen are either CD4bs antibodies or constant region 1 and 2 (C1/C2), and of these, ~2% have characteristics of early members of CD4 binding site HCDR3-binder bNAbs and neutralize two primary isolates, AE.CNE8 and C.6644 (Easterhoff D. et al. PLoS Path 24;13(2), 2017).

This year, we evaluated the ontogeny and Fc-mediated effector functions of V2-specifi c and C1/C2-specifi c antibodies isolated from RV305 vaccinees. After boosting, we identifi ed V2 linear peptide binding, conformational V2-dependent and N156-glycan dependent antibodies. Compared to the RV144 antibodies CH58 and CH59, collectively, these new V2-specifi c antibodies had increased ADCC breadth. In addition, the linear V2-specifi c antibodies were potent inhibitors of α4β7 binding. Boosting also increased the breadth and potency of C1/C2-specifi c ADCC responses, including continued boosting of a clonal lineage started 6-8 years previously in the RV144 vaccine trial. From these data, we conclude that continued boosting of RV144 vaccinees increases the breadth and potency of vaccine-induced Fc-mediated effector functions, which could potentially contribute to increased vaccine-effi cacy simply by repetitively boosting with the same immunogens.

After profi ling the repertoire of vaccinees from the RV305, RV305 extended boost, RV306, RV328 vaccine trials, no difference was noted in the Env-reactive antibody HCDR3 distribution.

By using clonal memory B cell cultures couple with antigen-specifi c B cell sorting, we have developed a strategy for probing the Env-specifi c memory B cell repertoire to a depth of 2 logs deeper than prior techniques, from 1/30,000 memory B cells to 1/2,500,000 memory B cells. The total number of unbiased memory B cells interrogated at the end of this study will be ~40,000,000 memory B cells, thus providing the deepest evaluation of B cell responses of any vaccine trial to date. Using this technology, we identifi ed antibodies with immunogenetics similar to VRC01 in the RV305, RV306 and RV328 HIV-1 vaccine trials, indicating that these responses were subdominant and that an ALVAC prime was not necessary for their induction.