Passive transfer studies to elucidate the role of antibody-mediated protection against HIV-1

In order to understand immune correlates of protection and to develop effective immunization strategies, it is important to know if antibodies can confer protection against HIV-1 infection or disease. The recent development of the pathogenic simian/human immunodeficiency virus (SHIV)-macaque model based on env genes from primary HIV-1 isolates permits the in vivo evaluation of anti-HIV-1 envelope glycoprotein immune responses. Using this model, we and others initially showed that passively infused antibody can protect against an intravenous SHIV-challenge. However, HIV-1 is most often transmitted across mucosal surfaces and the intravenous challenge model may not accurately predict the role of antibody in protection against mucosal exposure. We, therefore, adapted the SHIV89.6PD model to allow evaluation of anti-HIV-1 antibodies against vaginal challenge. In order to make comparisons to our prior intravenous challenge study, we used the same SHIV89.6PD stock and antibodies. Our data show that antibodies can confer protection against vaginal exposure to a pathogenic SHIV; if virus transmission occurs, their presence can ameliorate the subsequent pathogenic manifestations of virus infection. Compared to our previous intravenous challenge study, greater protection was achieved after vaginal challenge. Because the highest level of protection occurred when the most potent combinations of antibodies were used, the data confirm that in vitro neutralization assays on peripheral blood mononuclear cells (PBMC) targets cells are a relevant measure of protective antibody activity.