Conformational epitope analysis of week 24 serum responses. (A) Cross-competition ELISA of sera against a panel of gp140-specific human MAbs. (B) D368R sensitivity ELISA shows amount of CD4bs antibodies. Pos, panel of CD4bs MAbs; Neg, panel of non-CD4bs MAbs. (C) Endpoint titers against an engineered outer domain of ENV. (D) Binding of sera to the CD4 binding site probe RSC3 in the presence of an excess of competing RSC3 Δ371I/P363N CD4bs knockout protein. A one-way ANOVA with Bonferroni's posttest (A), Student's t test (B), and Student's t test of log-transformed data (C and D) were used for statistical analysis. *, P < 0.05; **, P < 0.01; ***, P < 0.001.