In an effort to more precisely define Nab targets and escape pathways in 205F, B cell hybridomas were generated from viably frozen PBMC samples collected at 49 months after infection, which were the earliest available sample of this type. A 0-month Env (clone PB1.1) was used to screen for neutralizing activity in the hybridoma supernatants, and two hybridomas produced monoclonal antibodies (Mabs; 6.4C and 13.6A) that neutralized this and other 0-month Envs ( Fig. 5A and B, respectively) . Surprisingly, the 0-month Envs were not equally sensitive to neutralization by the two Mabs, despite being very homogeneous in sequence and potently neutralized by patient plasma (Fig. 1B) . For Mab 6.4C, 0-month EnvPL6.3 was moderately more sensitive to neutralization than the other two 0-month Envs (Fig. 5A ). In contrast, neutralizing activity for 13.6A was not detectable against EnvPL6.3, but the other two 0-month Envs were neutralized at levels similar to those observed with Mab 6.4C (Fig. 5B ). The 2month EnvPB2.3 was neutralized by both Mabs (Fig. 5A and B). Neutralizing activity against Envs cloned at 8-months or beyond, however, was undetectable for both Mabs ( Fig. 5A and B), providing strong evidence that these Mabs could be representative of those elicited during early infection and that the later Env variants had developed resistance mutations that protected against both specificities. An identical pattern was observed for the purified 6.4C and 13.6A Mabs, with a mean IC50 against the sensitive 0-months Envs of 39 and 156 ng/ml, respectively (data not shown). Envs from 8-months and beyond were not neutralized at 10 mg/ml of either purified Mab (data not shown).