INACTIVATION OF A COMMON EPITOPE RESPONSIBLE FOR THE INDUCTION OF ANTIBODY-DEPENDENT ENHANCEMENT OF HIV

Background: The primary antigenic domain responsible for complement-me diated antibody-dependent enhancement (C'-ADE) of HIV and simian immun odeficiency virus resides in the principal immunodominant sequence of the transmembrane protein. Objective: To identify whether there are am ino-acid residues common to the epitopes of the known enhancing human monoclonal antibodies (MAb), and to provide a structural model for thi s functional region present on the HIV envelope. Since our model predi cts that this region is involved in the association of gp120 with gp41 , this association was monitored for each mutant. Design: The binding of enhancing human MAb to point and deletion mutations within the enha ncing domain was analyzed by two methods. The first analyzed binding t o mutants expressed in COS cells: the second quantified the binding of four enhancing human MAb to each mutant gp160 versus wild-type contro l by enzyme-linked immunosorbent assay (ELISA). Methods: Site-directed mutagenesis was used to produce specific deletions and point mutants, which were expressed in COS cells. Binding of MAb 50-69 and V3-loop M Ab 5F7 were visualized in the wild-type and each of the mutant constru cts by immunohistochemistry. Quantitative evaluation of enhancing huma n MAb binding to each mutant versus wild-type was performed by ELISA. A model for the enhancing domain and its relationship to gp120 associa tion with gp41 was provided by molecular dynamics and ligand docking m ethods. Results: All available enhancing human MAb known to bind to th e principal immunodominant region of gp41 were unable to bind to delet ions involving the disulfide loop, which in our molecular model provid ed the primary association site between gp120 and gp41. Point mutation s in the loop blocked this association, but had a quantitatively small er effect on the binding of the enhancing human MAb. A conservative W- 596 Y mutation completely blocked the binding of all human MAb, but ha d no effect on gp120-gp41 association. Conclusions: A variety of mutat ions within the primary C'-ADE domain inhibit binding of enhancing hum an MAb as well as blocking the association of gp120 and gp41. A conser vative W 596 Y mutation blocks binding of all enhancing human MAb with retention of gp120-gp41 association. These data are important to the design of vaccines in which the primary enhancing epitope is disarmed to prevent the subsequent induction of an amnestic response that could lead to viral enhancement of infection. The retention of the gp120-gp 41 association is postulated to yield an immunogen similar to natural infection for both subunit and genetic vaccines.