Characterizing the Functional Autoreactivity and Polyspecificity of the MPER-Specific bNAb 4E10 and an Ensemble of Its Germline-Encoded Precursors

Publication Type:

Journal Article

Source:

AIDS Research and Human Retroviruses, Volume 29, Number 11, p.A48-A48 (2013)

ISBN:

0889-2229

Keywords:

2013, Basic Sciences Division, Center-Authored Paper, Clinical Research Division, December 2013, Immunology, Infectious Diseases, Vaccine and Infectious Disease Division, Virology

Abstract:

Background: The bNAb 4E10 recognizes an epitope in the HIV gp41 MPER. Previous attempts at eliciting 4E10, by vaccination with envelope-derived or reverse-engineered immunogens, have failed, but have yielded tight-binding, computationally-designed 4E10 ‘epitope-scaffolds’ that can elicit epitope-specific responses. The ontogeny of functional 4E10-equivalent responses has been presumed to be blocked by inherent autoreactivity. Previously identified candidate 4E10 autoantigens include the mitochondrial lipid cardiolipin and a nuclear splicing factor, 3B3. Methods: Heavy-chain knock-in mice were generated to confirm functional autoreactivity. A large-scale peptide library was used to identify candidate protein autoantigens. Carefully-controlled SPR binding assays were performed to characterize 4E10, substructure and germline precursor recognition of candidate autoantigens and epitope-scaffolds. Immunohistochemistry was used to validate autoantigens. Crystal structures of a panel of 4E10 germline precursors were determined, alone and in complexes. Results: 4E10 knock-in mice displayed significant B cell compartment dysregulation, consistent with autorecognition. However, 4E10 bound only weakly and non-specifically to cardiolipincontaining liposomes, through interactions dominated by electrostatic rather than hydrophobic interactions. Based on peptide library binding patterns, 4E10 displays limited, focused polyspecificity and recognizes a novel epitope shared by three inositol trisphosphate receptors (ITPRs). Tissue staining demonstrated reactivity consistent with ITPR1 as the likeliest candidate autoantigen and precluded nuclear antigens, such as 3B3. Conclusion: These results argue that 4E10 recognition of lipids in general, or cardiolipin specifically, is unlikely to affect selection or neutralization mechanisms and that 4E10 MPER and ITPR1 recognition are distinct enough to permit eliciting 4E10-like responses while evading autoimmunity. Functional, structural and binding studies of an ensemble of the twelve likeliest 4E10 germline-encoded precursors show no neutralizing potency, extremely weak binding to Env, but strong affinities for epitopescaffolds, and remarkable conservation of recognition mechanisms. These results, in combination with the observed variation in the human 4E10 precursor repertoire, suggest pathways to achieve 4E10-equivalent responses by vaccination.

Notes:

PT: J; CT: Conference on AIDS Vaccine; CY: OCT 07-10, 2013; CL: Barcelona, SPAIN; NR: 0; TC: 0; J9: AIDS RES HUM RETROV; SI: SI; PG: 1; GA: 239PI