Together, these findings indicate that the combined V5 mutations facilitated neutralization resistance at 5 months, while the changes in the a2 helix and the V2 loop did not contribute to a detectable level, at least within the context of the 0-month Env. A different scenario was observed for early escape in 205F. For the 2-month escape variant EnvPB2.3, the V1V5 region contained determinants for Nab resistance (Fig 3D) , and this entire region differed from 0-month EnvPL6.3 by only 3 amino acids (Fig. 3E ). Two changes were located within V1 (an N134S substitution that introduced a potential N-linked glycosylation site near the Nterminal V1V2 stem and a Y140P substitution; numbered according to Fig. S2 ). In contrast to 185F, introduction of the two changes in V1 decreased Nab sensitivity by more than 10-fold in the context of the 0-month Env (Fig. 3D) . A third change, A453T, was located within the b23 region and has the potential to impact CD4 binding (Fig. 3E ). This residue by itself reduced Nab sensitivity by about 3-fold ( Fig. 3D ). Thus, for 205F, complete Nab resistance at 2-months could be achieved by sequence changes in V1, including addition of a potential N-linked glycan, and a change in a region involved in CD4 contact [39] .