Novel monoclonal antibodies with neutralizing breadth from HIV-1-infected individuals

Researchers:

Davide Corti, Scientist
Blanca Maria Fernandez Rodriguez, Technician
David Jarrossay, Scientist, Responsible for the flow cytometry Facility
Debora Pinna, Scientist
Federica Sallusto,
Chiara Silacci Fregni, Technician

Status: Finished

The isolation of human monoclonal antibodies (mAbs) that neutralize a broad spectrum of primary HIV-1 isolates and the characterization of the human neutralizing antibody B cell response to HIV‑1 infection are important goals that are central to the design of an effective antibody-based vaccine. We immortalized IgG⁺ memory B cells from individuals infected with diverse clades of HIV-1 and selected on the basis of plasma neutralization profiles that were cross-clade and relatively potent. Culture supernatants were screened using various recombinant forms of the envelope glycoproteins (Env) in multiple parallel assays. We isolated 58 mAbs that were mapped to different Env surfaces, most of which showed neutralizing activity. One mAb in particular (HJ16) specific for a novel epitope proximal to the CD4 binding site on gp120, selectively neutralized a multi-clade panel of Tier-2 HIV-1 pseudoviruses, and demonstrated reactivity that was comparable in breadth, but distinct in neutralization specificity, to that of the other CD4 binding site-specific neutralizing mAb b12. HJ16 was used to define a conserved region of the CD4 binding site, which has been defined as “core epitope” formed by an immunodominant triad of conserved amino acids (D474, M475, R476) at the outer domain/inner domain junction of gp120 that could not be mutated without loss of viral fitness. A second mAb (HGN194) bound a conserved epitope in the V3 crown and neutralized all Tier-1 and a proportion of Tier-2 pseudoviruses tested, irrespective of clade. HGN194 was able to provide sterilizing immunity to macaques challenged mucosally with a clade C SHIV isolate while inducing gag-specific CD4⁺ and CD8⁺ T cells. A third mAb (HK20) with broad neutralizing activity, particularly as a Fab fragment, recognized a highly conserved epitope in the HR-1 region of gp41, but showed striking assay-dependent selectivity in its activity. This study reveals that by using appropriate screening methods, a large proportion of memory B cells can be isolated that produce mAbs with HIV-1 neutralizing activity. Three of these mAbs show unusual breadth of neutralization and therefore add to the current panel of HIV-1 neutralizing antibodies with potential for passive protection and template-based vaccine design.

This work was done in collaboration with the Bill and Melinda Gates Foundation VDC consortium led by Robin Weiss, University College London, London, UK and Quentin Sattenteau, Dunn School of Pathology, University of Oxford, Oxford, UK; Fabrizia Vanzetta and Gloria Agatic, Humabs BioMed, Bellinzona, CH; Michel Nussenzweig, Rockefeller University, New York, NY, USA; and Ruth Ruprecht, Dana Farber, Boston, MA, USA.

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