Overlayed LCDR2 ED motif regions of CH58 and CH59 show striking similarity between the two LC-Env binding regions (Figures S6G, H). perfect and a combination of clades B and E gp120 (AIDSVAX gp120 B/E) proteins as a boost (Rerks-Ngarm et al., 2009). This trial provided hope that a vaccine could induce protective immune responses to HIV-1 (Rerks-Ngarm et al., 2009). In 2012 an immune correlates study of the RV144 trial revealed that antibodies against the Env gp120 V1V2 L-655708 region were associated with lower risk of contamination (Haynes et al., 2012a). Epitope mapping of plasma V1V2 antibody responses showed that within V2, vaccine-induced antibodies targeted a region of HIV-1 Env, amino acid (aa) residues at positions163178 (Karasavvas et al., 2012;Zolla-Pazner et al., 2011). There is considerable sequence variability in V1V2, ~75% of the residues are conserved or demonstrated to be only conservative changes (Zolla-Pazner and Cardozo, 2010). Whereas the demonstration that V1V2 antibody responses directly correlated with decreased contamination risk was suggestive of their protective role in the trial, this association was not sufficient for proving causation of protection (Plotkin and Gilbert, 2012). Indeed further studies are needed to evaluate the ability of such responses to mediate immune pressure on HIV-1. Viral genetic (sieve) analyses, isolation of V1V2 antibodies and understanding their effector functionin vitroandin vivo, as well as validation of correlates of contamination risk in future vaccine trials are needed. By comparing sequences of breakthrough infections that occur in vaccinees versus placebo recipients, genetic or sieve analysis of sequences of viruses that caused breakthrough infections in a vaccine trial can demonstrate sites of immune pressure (Rolland et al., 2011). A recent genetic analysis of breakthrough HIV-1 infections in the RV144 trial exhibited 48% (CI: 18 to 68%, p=0.0036) vaccine efficacy against viruses matching the CRF_01AE vaccine immunogens with a lysine (K) at position 169 (Rolland et al., 2012). Thus, it is critical L-655708 to determine the binding site and effector functions of RV144-induced V1V2 antibodies. Antibody effector function candidates for mediation of protection from HIV-1 transmission include the ability of V1V2 antibodies to neutralize those computer virus strains involved in HIV-1 transmission (i.e. transmitted-founder viruses) (Keele et al., 2008), or to mediate other effector functions such as antibody-dependent cellular cytotoxicity (ADCC) (Haynes et al., 2012a). Herein, we have probed the specificities and effector functions of four V2 monoclonal antibodies (mAbs) isolated from RV144 ALVAC-AIDSVAX vaccine recipients, and decided the crystal structures of two of these mAbs with V2 peptides made up of position 169. We show that V2 residue 169 was in a structurally polymorphic region of HIV-1, thus exposing the structural heterogeneity of the V2 region to which Env immune responses correlated with decreased transmission. We go on to show that this V2 antibodies isolated from RV144 vaccinees mediated ADCC against RV144 trial breakthrough Env-target cells, and this ADCC activity was dependent on position 169 in breakthrough Envs. These data directly demonstrate the plausibility of these forms of V2 antibodies to mediate immune pressure targeted at position169 of Env V2. == RESULTS == == Vaccine-Induced Antibodies == Using clonal memory B cell cultures and high throughput antigen-specific screening assays (Bonsignori et al., 2011), two mAbs, CH58 and CH59, were L-655708 in the beginning isolated and found to bind the RV144 vaccine immunogen AE.A244 gp120 and to a V2 peptide (residues 169182, KKKVHALFYKLDIV) (Table S1;Physique S1A). RP11-175B12.2 Epitope mapping of mAbs CH58 and CH59 using alanine-scanning peptides L-655708 with the sequence of AE.A244 Env from positions 165 to186 (LRDKKQKVHALFYKLDIVPIED) showed that this footprint for binding of mAb CH58 involved 10 residues (K168, K169, K171, V172, H173, F176, Y177, K178, D180, P183), while that of mAb CH59 involved 4 residues (K169, H173, F176, L-655708 Y177) (Figure 1A). HIV-1 Env V1V2 broadly neutralizing antibodies (bnAbs) have been explained that bind both glycans as well as bind V1V2 aa residues around and including position 169 (Bonsignori et al., 2011;Doria-Rose et al., 2012;McLellan et al., 2011;Walker et al., 2009). The epitope mapping results suggested that mAbs CH58 and CH59 (while themselves not bnAbs) bind at or near the site in V2 to which the HIV-1 V1V2 bnAbs (e.g. PG9, CH01) bind (Doria-Rose et al., 2012;McLellan et al., 2011) ==.