The quest for a prophylactic AIDS vaccine is ongoing and it is probable that the successful vaccine must elicit protective antibody responses. Regardless of the mechanism of antibody-mediated protection, antibody persistence and appropriate T cell help are emerging as significant problems in AIDS vaccine development. The problem of antibody persistence is seen clearly in the RV144 trial. Protection was as highest in the first year but waned rapidly to background in parallel with anti-V2 antibodies that were associated with reduced risk of infection. Poor antibody persistence is not unique to RV144. It occurred in the VAX003/VAX004 efficacy trials, also using gp120 immunogens, and it has been observed repeatedly in gp120 vaccine trials in humans and non-human primates. Poor antibody persistence to gp120 is entwined with a second major problem. How to elicit necessary CD4+ T cell help without establishing fertile fields for increased HIV replication at sites of exposure, blunting protection, or increasing acquisition. It appears that vaccine-elicited CD4+ T cell and innate immune responses are associated with increased acquisition in the Step/Phambili trials that used an Ad5Hu- HIV T-cell vaccine as the immunogen. There are reports of vaccine-associated increased acquisition in non- human primate (NHP) models using other vectors and immunogens in addition to AdHu5. Taken together, the conjoint problems of antibody persistence and T cell balance must be solved for any antibody-based HIV vaccine to be effective. This requirement introduces a new concept for HIV vaccine development based on achieving balanced T cell and humoral responses, contrasting sharply with current approaches that focus on one arm or the other, or that seek to maximize both arms in parallel. Exploration of this concept forms the foundation of the proposed program that will test the central hypothesis that an HIV vaccine candidate can elicit durable antibody responses supported by a balanced CD4+ T cell profile that favors protection. This hypothesis is based on published work from the investigators and on solid preliminary data in RM models. This hypothesis will be tested via three highly interactive projects. Dr. Robert C. Gallo (IHV) will lead the program. Dr. Anthony L. DeVico (IHV) will lead Project 1 that exploits DNA/Protein co-immunization protocols to test hypotheses regarding the disposition of plasma cell subsets and how they determine the unusually poor durability of anti-gp120 antibody responses. Dr. George K. Lewis (IHV) will lead Project 2 to determine how vaccine elicited CD4+ T cells attenuate antibody-mediated protection. Dr. Guido Silvestri (Emory) will lead Project 3 to determine the phenotypes of vaccine-elicited CD4+ T cells and innate immune signatures that favor durable protection. In terms of major outcomes, this work is expected to fully identify the mechanism of poor anti-Env antibody persistence and to overcome this problem while maintaining safe levels of CD4+ T cells that don't blunt protection. These results are expected to fundamentally advance AIDS vaccine development for which broad durable protection is the Holy Grail.
The proposed research is key to public health because there is a lingering need for an effective AIDS vaccine, which is complicated by the fact that the AIDS virus grows in a key population of cells that are required to make a vaccine work. The proposed research focuses on how to overcome this problem ultimately resulting in an effective AIDS vaccine. As such, it is relevant to the NIH mission of developing a safe and effective AIDS vaccine. Project 1: Mechanism of Anti-Gp120 Antibody Persistence Project Leader: DeVico, A DESCRIPTION (as provided by applicant): Recent clinical trials and a host of nonhuman primate studies have pushed the HIV vaccine field further toward the development of concepts based on humoral anti-HIV envelope immunity. However, such efforts face a major hurdle in that the routinely short-lived humoral responses to HIV envelope antigens will severely compromise HIV vaccine efficacy. An additional caveat is that any solution to the humoral persistence problem must include balanced immune responses that do not engender forms of CD4+ T cell activation that might increase HIV infection risk. The recent RV144 clinical trial of a poxvirus/ envelope protein regimen underscores the issue in humans. In this trial, anti-gp120 antibody responses, including those linked with partial efficacy, decayed to undetectable levels within 12 months. Based on the available literature, we hypothesize that anti-gp120 titers rapidly fade in this manner because 1) HIV gp120-specific plasma cells are extensively killed during the germinal center reaction or 2) HIV gp120-specific plasma cells survive the germinal center reaction but cannot move into the bone marrow to become long-lived cells. Theoretically, these questions can be addressed by comparative analyses of vaccine regimens that yield persistent antibody titers versus ones that do not. This strategy has been hampered by a paucity of regimens that reliably yield persistent anti-gp120 humoral responses. Our group has tested the same gp120-based antigen in a wide variety of adjuvant formulations and vaccination regimens in macaques. Recently we determined that one of these regimens, which involves coimmunizing with envelope protein in adjuvant along with electroporation of DNA encoding IL-12 (herein termed DNA/protein coimmunization), generates significantly more persistent antibody titers compared to any other approach we tested. These findings now provide the necessary means to conduct comparative studies that elucidate the determinants for persistent anti-gp120 antibody responses. Accordingly, this Project will juxtapose the DNA/protein coimmunization regimen with a matched protein/adjuvant regimen that yields non-persistent responses. Our proposed comparative analyses will be driven by the two hypotheses listed above. In two specific aims, we will address whether persistent anti-HIV antibody responses are distinguished by 1) the preservation of short-term anti-gp120 plasmablasts without the enhancement of long-lived plasma cells in the bone marrow or 2) the establishment of long-lived anti-gp120 plasma cells in the bone marrow. We will also exploit the multifaceted nature of DNA/protein coimmunization to Identify vaccine components and associated immunological pathways that afford persistent humoral anti-gp120 responses, desirable CD4+ T cell profiles and protective efficacy against heterologous SHIV challenge. Information from this project should have significant impact, providing broadly applicable, immune-based underpinnings for the development of vaccine regimens that provide persistent anti-envelope antibody responses.
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| Lewis, George K; Pazgier, Marzena; DeVico, Anthony L (2017) Survivors Remorse: antibody-mediated protection against HIV-1. Immunol Rev 275:271-284 |
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| Tolbert, William D; Gohain, Neelakshi; Veillette, Maxime et al. (2016) Paring Down HIV Env: Design and Crystal Structure of a Stabilized Inner Domain of HIV-1 gp120 Displaying a Major ADCC Target of the A32 Region. Structure 24:697-709 |
