Detection and activation of HIV broadly neutralizing antibody precursor B cells using anti-idiotypes

Bancroft, Tara; DeBuysscher, Blair L.; Weidle, Connor; Schwartz, Allison; Wall, Abigail; Gray, Matthew D.; Feng, Junli; Steach, Holly R.; Fitzpatrick, Kristin S.; Gewe, Mesfin M.; Skog, Patrick D.; Doyle-Cooper, Colleen; Ota, Takayuki; Strong, Roland K.; Nemazee, David; Pancera, Marie; Stamatatos, Leonidas; McGuire, Andrew T.; Taylor, Justin J.

Among the four anti-iglb12 idiotypes identified by our screen, we focused upon IB2 and IB3 because we solved their crystal structures in complex with iglb12 at a resolution of 2.6Å and 3.0Å, respectively. The crystal structures revealed that IB2 and IB3 displayed distinct modes of interaction with iglb12 ( Fig. 2 ). IB3 interacted with both the heavy and light chains of iglb12 (Fig. 2 , A-C), consistent with biolayer interferometry (BLI) data ( Fig. 1 C) . Most interactions occurred within the heavy chain of iglb12 (Fig. 2 , B and C), which contributed 76% of the buried surface area (BSA) and six of the eight hydrogen bonds. One hydrogen bond occurred in each of the CDRH3 and CDRL3 regions of iglb12, with the remaining six hydrogen bonds and BSA occurring in the CDR1, CDR2, and framework regions of iglb12, encoded by V H 1-3 or V K 3-20 (Fig. 2 , D and E). In contrast, IB2 approached iglb12 at a 45°angle relative to IB3 and bound exclusively to the iglb12 heavy chain (Fig. 2, A and F) . The CDRH3 region of iglb12 contributed nearly half of the BSA and two of the six hydrogen bonds, with the remaining BSA and hydrogen bonds largely focused upon CDRH1 and CDRH2, which are encoded by V H 1-3 (Fig. 2 , G-J). The extensive interactions with the iglb12 heavy chain CDRH3 likely explain why IB2 and IB3 do not bind other antibodies using V H 1-3 ( Fig. 1 C) .