Stoichiometry of monoclonal antibody neutralization of T-cell line-adaptedhuman immunodeficiency virus type 1

In order to study the stoichiometry of monoclonal antibody (MAb) neutraliza tion of T-cell line-adapted human immunodeficiency virus type 1 (HIV-1) in antibody excess and under equilibrium conditions, we exploited the ability of HIV-I to generate mixed oligomers when different env genes are coexpress ed, By the coexpression of Env glycoproteins that either can or cannot bind a neutralizing MAb in an env transcomplementation assay, virions were gene rated in which the proportion of MAb binding sites could be regulated. As t he proportion of MAb binding sites in Env chimeric virus increased, MAb neu tralization gradually increased. Virus neutralization by virion aggregation was minimal, as MAb binding to HIV-1 Env did not interfere with an AMLV En v-mediated infection by HN-I(AMLV/HIV-1) pseudotypes of CD4(-) NEK293 cells . MAb neutralization of chimeric virions could be described as a third-orde r function of the proportion of Env antigen refractory to MAb binding. This scenario is consistent with the Env oligomer Constituting the minimal func tional unit and neutralization occurring incrementally as each Env oligomer binds MAb. Alternatively, the data could be fit to a sigmoid function. Thu s, these data could not exclude the existence of a threshold for neutraliza tion. However, results from MAb neutralization of chimeric virus containing wild-type Env and Env defective in CD4 binding aas readily explained by a model of incremental MAb neutralization. In summary, the data indicate that MAb neutralization of T-cell line-adapted HIV-1 is incremental rather than all or none and that each MAb binding an Env oligomer reduces the likeliho od of infection.