HUMORAL RESPONSES TO LINEAR EPITOPES ON THE HIV-1 ENVELOPE IN SEROPOSITIVE VOLUNTEERS AFTER VACCINE THERAPY WITH RGP160

Humoral responses to the HIV-1 envelope were investigated in 30 human volunteers enrolled in a phase I vaccine therapy trial of rgp160 (LAI/ LAV) using two techniques that emphasize detection of antibody respons e against linear (continuous) epitopes: immunoblotting and PEPSCAN. Se ven fusion proteins containing large portions from constant regions 1, 2, 3, and 5, and variable region 3 of gp120 and two regions in the tr ansmembrane protein, gp41, were employed in immunoblots to quantitativ ely measure immune response as a function of immunization. In addition , the entire gp160 (LAI/LAV) envelope protein was constructed in dupli cate sets of 211 overlapping 12-mer peptides to fine-map the changes. Immunoblotting defined significant changes in reactivity to epitopes i n constant regions; of 28 volunteers completing the trial, the percent age with reactivity against C1 changed from 62 to 100%; for C2, from 0 to 46%; for C3, from 0 to 82%; and for a constant region in gp41, fro m 25 to 68%. PEPSCAN on a subset (n = 8) of these volunteers identifie d new reactivity to epitopes throughout the envelope, concentrated in V1, C3, and C5 in gp120 and several peptides in gp41. Completely immun ized patients responded to double the number of linear epitopes compar ed with two patients receiving alum alone. The results verify that the response to rgpl60 is significantly broadened after immunization, pro viding additional evidence that HIV-1-infected volunteers can expand t heir antibody repertoire against a protein from a pathogen during chro nic infection with that same pathogen. These results expand those prev iously obtained in this patient cohort, by defining explicitly the imm unogenic regions recognized postvaccination and by providing methodolo gy for quantitating those changes.