Comparison of the antibody repertoire generated in healthy volunteers following immunization with a monomeric recombinant gp120 construct derived from a CCR5/CXCR4-using human immunodeficiency virus type 1 isolate with sera from naturally infected individuals

Abstract

We have characterized sera from healthy volunteers immunized with a monomeric recombinant gp120 (rgp120) derived from a CCR5/CXCR4 (R5X4)-using subtype B isolate of human immunodeficiency virus type (HIV-1), HIV-1W61D, in comparison to sera from long-term HIV-1-infected individuals, using homologous reagents. Sera from vaccinees and HIV-1 positive subjects had similar binding titers to native monomeric rgp120W61D and showed a similar titer of antibodies inhibiting the binding of soluble CD4 (sCD4) to rgp120W61D. However, extensive peptide binding studies showed that the overall pattern of recognition of vaccinee and HIV-1-positive sera is different, with vaccinee sera displaying a wider and more potent recognition of linear V1/V2 and V3 domain epitopes. Neutralization of homologous HIV-1W61D or heterologous HIV-1M2424/4 peripheral blood mononuclear cell (PBMC)-derived virus lines by vaccinee sera could be achieved, but only after adaptation of the viruses to T-cell lines and was quickly lost on readaptation to growth in PBMC. Sera from HIV-positive individuals were able to neutralize both PBMC-grown and T-cell line-adapted viruses. Interestingly, rgp120W61D was recognized by monoclonal antibodies previously shown to neutralize primary HIV-1 isolates. The use of very potent adjuvants and R5X4 rgp120 led to an antibody response equivalent in binding activity and inhibition of binding of sCD4 to gp120 to that of HIV-positive individuals but did not lead to the induction of antibodies capable of neutralizing PBMC-grown virus.

FIG. 1

Amino acid sequences for a series of approximately 20-mer overlapping peptides spanning the C1 to C5 domains of gp120 derived from the isolate HIV-1_W61D. The V1/V2 and V3 domains are located within peptides p9 to p18 and p25 to p29, respectively. Note that there was no available overlapping peptide to link the contiguous sequences represented by peptides p18-p19 and p21-p22.

FIG. 2

Proportion and level of antibody binding to a series of overlapping peptides spanning the C1 to C5 domains of gp120 derived from the primary isolate HIV-1_W61D. The percentage of sera samples which gave a positive reactivity (above the assay cutoff [CO] defined as the mean + 3 SD of a panel of HIV-1-negative serum controls) to each peptide is shown for vaccinee sera (a), W61D-nonneutralizing sera (b), or W61D-neutralizing sera (c). The level of antibody bound (expressed as the mean optical density [OD]/CO ± [SD for positively reactive sera) is shown for vaccinee sera (d), W61D-nonneutralizing sera (e), and W61D-neutralizing sera (f). Approximate positions of the conserved (C1 to C5) and variable (V1 to V5) domains are shown for clarity.

FIG. 3

Binding of human MAbs to immobilized monomeric rgp120 derived from the isolate HIV-1_W61D. 447-52D (■), 257-D (▴), and 268-D (•) are directed to the V3 domain, while IgG1b12 (▵), 2G12 (□), and 2F5 (○) are directed to the CD4-binding domain, a discontinuous epitope on gp120 and a linear epitope in gp41, respectively.