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A binary neutralizing determinant of gp120 defined by nucleophilic monoclonal antibodies
Presented by Yasuhiro Nishiyama, United States.
Nishiyama Y.1, Planque S.1, Mitsuda Y.1, Taguchi H.1, Jin L.1, Boivin S.1, Salas M.2, Hanson C.2, Paul S.1
1University of Texas-Houston Medical School, Chemical Immunology Research Center, Department of Pathology and Laboratory Medicine, Houston, Texas, United States, 2California Department of Health Services, Viral and Rickettsial Disease Lab, Richmond, California, United States
Objectives: Monoclonal antibodies (MAbs) raised to HIV gp120 containing electrophilic phosphonates within its antigenic epitopes (E-gp120) display two types of chemical reactivities as a consequence of their enhanced nucleophilic reactivity, gp120-specific proteolysis and pseudo-covalent binding [1,2]. However, the nucleophilic strength of the MAbs did not predict their ability to neutralize primary HIV strains. Consequently, we studied the importance of MAb epitope specificity as a factor in viral neutralization.
Methods: MAbs were raised by immunizations of mice with E-gp120 (30-46 phosphonates/gp120; oligomer proportions 50-80%). HIV neutralization was assayed using purified MAbs in PBMC cultures. The epitope reactivity was studied by competition ELISAs using 15-mer gp120 fragments and electrophoresis assays using phosphonate analogs of gp120-related peptides as probes for specific MAb binding activity [1,2].
Results: Ten of 18 anti-E-gp120 IgGs neutralized the primary R5/clade C strain 97ZA009. Two IgGs (proteolytic YZ18 and pseudo-covalent YZ23) neutralized the clade C strains 97ZA009, 98BR004, and the clade B strain SF162 with potency superior to the reference MAb, clone b12. Further characterization of MAb YZ23 indicated that it neutralized the majority of 8 additional clade B/C/D strains. Both cross-clade neutralizing IgGs recognized two spatially distinct gp120 regions, residues 301-311 and 421-433. These regions are known to contribute to viral binding to host receptors. Residues 421-433 constitute the gp120 B cell superantigenic site recognized by antibodies from uninfected humans and dual recognition of the two regions appears to be gained by adaptive immune processes induced by immunization. Both regions are comparatively conserved. Of 8 dual binding anti-E-gp120 MAbs studied, the majority (6) neutralized HIV strain 97ZA009.
Conclusions: The dual epitope recognition property frequently results in the neutralization of HIV. The unique binary determinant defined by the MAbs is a promising target for induction of broadly neutralizing Abs. References: [1] J Biol Chem 2003;278:20429; [2] J Mol Recognit 2006;19:423.
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