Anti-Immune Complex Antibodies are Elicited During Repeated Immunization with HIV Env Immunogens

Vaccination strategies against HIV-1 aim to elicit broadly neutralizing antibodies (bnAbs) using prime-boost regimens with HIV envelope (Env) immunogens. Early antibody responses to easily accessible epitopes on these antigens are directed to non-neutralizing epitopes instead of bnAb epitopes. Autologous neutralizing antibody responses appear upon boosting once immunodominant epitopes are saturated. Here we report another type of antibody response that arises after repeated immunizations with HIV Env immunogens and present the structures of six anti-immune complexes discovered using polyclonal epitope mapping. The anti-immune complex antibodies target idiotopes composed of framework regions of antibodies bound to Env. This work sheds light on current vaccine development efforts for HIV, as well as for other pathogens, in which repeated exposure to antigen is required. One Sentence Summary Polyclonal epitope mapping reveals anti-immune complex antibodies which target idiotopes on antibodies bound to HIV Env. ### Competing Interest Statement The authors have declared no competing interest.