A retroviral late-domain promotes cell-surface expression, extracellular vesicle formation, and immunogenicity of a trimeric HIV-1 Env antigen

Abstract The immunogenicity of membrane-associated antigens can be enhanced by addition of cytoplasmic-tail elements that promote release of extracellular vesicles (EVs). Here we explore whether these elements enhance humoral responses to SOSIP-TM, a stabilized form of the HIV-1 envelope glycoprotein (Env). We compared modifications designed to promote EV release by engaging the cellular Endosomal Sorting Complex Required for Transport (ESCRT). These modifications include viral late domains and the previously described EPM-EABR, which combines an endocytosis prevention motif (EPM) with the ESCRT- and ALG-2-interacting protein X-binding region (EABR) of the cellular protein CEP55. We observed that p2, an 18 amino-acid ESCRT-associated feline immunodeficiency virus (FIV) late domain, promoted higher SOSIP-TM expression and a stronger total antibody response than other EV-enhancing modifications. p2 also elicited significantly higher neutralizing responses to a quaternary Env epitope than did EPM-EABR. FIV p2 thus promotes humoral responses to Env-based transmembrane antigens more effectively than other ESCRT-engaging elements.