ADA.CM neutralization activities in sera 5393 and 5396 target V1 and the gp120-gp41 interface. (A) Serum 5393 from bleed 3, following immunization with ADA.CM, was tested for neutralization of ADA.CM, parental ADA, and an ADA mutant containing an N139/I140 deletion and N142S substitution in V1 of gp120. (B) Four rabbit sera from bleed 4 that neutralized ADA.CM with an IC50 of >10 were tested in neutralization assays against ADA.CM with glycan knockout mutations (N88A, N241S, N611D, and N637K) or glycan hole-filling mutations (D230N/K232T and K289N) near the gp120-gp41 interface.