IgG and IgA antibodies against HIV-1 envelope protein in the absence of infection is well documented in highly exposed seronegative individuals. The origin of these immune responses may be due to cross reactivity with intestinal commensal bacteria or result from ongoing exposure to viral particles. Pre-HIV-1 infection immune responses against envelope glycoproteins may influence the future trajectory of disease. This project aimed to describe anti-HIV-1 gp140 envelope antibody responses in exposed seronegative individuals and track their development before and after HIV-1 infection. I screened sera from a cohort of highly exposed seronegative men who have sex with men with a yeast displayed HIV-1 gp140 envelope antigen fragment library to map discrete epitopes responsible for anti-HIV-1 humoral responses.
Using batched seronegative serum aliquots, I found humoral immune responses against V1/V2 and C2 gp120 epitopes, and the C helical region, membrane proximal external region, transmembrane domain and endodomain of gp41. Stratification of cohort according to risk region of acquisition of HIV-1 infection revealed no significant changes in the distribution of envelope epitope detected. Immune response to gp41 envelope epitopes were significantly greater in high risk compared with low risk individuals. Antibody response to HIV-1 gp140 envelope protein were assessed longitudinally in five individuals before and after HIV-1 infection. I showed the same HIV-1 gp140 epitopes were recognized in pre and post seroconversion samples suggesting previous antigen exposure lays a template for future humoral responses. In addition, certain pre-exposure gp140 epitopes had amino sequence similarity to intestinal bacterial antigens.
I then used gp140 envelope fragments expressed by yeast cells to isolate single antigen-specific B cells, followed by expression cloning to generate monoclonal envelope antibodies. Antibody dependent cytotoxic function of a single pre-infection monoclonal envelope antibody was assessed. This technology may help increase understanding of humoral immunity to HIV-1.