Having found that changes in the V1V2 and b23 regions drove early escape from Nab in 205F, we investigated whether this pattern was maintained over time. Env chimeras were created for 205F using Nab resistant Envs from five time points over a 26month follow-up period (Fig. 1B) and evaluated using the same approach as for 185F. V1V2 was the major determinant of Nab resistance at all time points analyzed (see Fig. S5 ). By contrast, the V3V5 region alone had little effect on resistance, although in combination with V1V2 it clearly contributed to escape.