Neutralizing antibody responses in acute human immunodeficiency virus type 1 subtype C infection

Abstract

The study of the evolution and specificities of neutralizing antibodies during the course of human immunodeficiency virus type 1 (HIV-1) infection may be important in the discovery of possible targets for vaccine design. In this study, we assessed the autologous and heterologous neutralization responses of 14 HIV-1 subtype C-infected individuals, using envelope clones obtained within the first 2 months postinfection. Our data show that potent but relatively strain-specific neutralizing antibodies develop within 3 to 12 months of HIV-1 infection. The magnitude of this response was associated with shorter V1-to-V5 envelope lengths and fewer glycosylation sites, particularly in the V1-V2 region. Anti-MPER antibodies were detected in 4 of 14 individuals within a year of infection, while antibodies to CD4-induced (CD4i) epitopes developed to high titers in 12 participants, in most cases before the development of autologous neutralizing antibodies. However, neither anti-MPER nor anti-CD4i antibody specificity conferred neutralization breadth. These data provide insights into the kinetics, potency, breadth, and epitope specificity of neutralizing antibody responses in acute HIV-1 subtype C infection.

FIG. 1.

Comparison of autologous neutralization sensitivities of multiple envelope clones from individual patients. One to three functional envelope clones at a single time point (as indicated in Table 1) for each of 14 acutely infected patients were tested against autologous serum in an Env-pseudotyped virus neutralization assay. Results are shown as IC₅₀ values (neutralization titers) over time among participants defined as controllers (A), rapid progressors (B), or normal progressors (C) according to criteria listed in Table 1. The clones marked with a pound sign were used in all subsequent experiments.

FIG. 2.

Correlation between number of N-linked glycosylation sites, variable loop length, and autologous neutralization titer. The autologous neutralization titer at 12 months of infection for each of the 14 study subjects was plotted against the numbers of PNGS in the V1-to-V5 (a), V1-V2 (b), and C3-to-V5 (c) regions or the lengths of the V1-to-V5 (d), V1-V2 (e), and C3-to-V5 (f) regions of the matched viral clone. The Spearman r coefficient and the P value are shown when the correlation is significant (P < 0.05).

FIG. 3.

Heterologous neutralization of enrollment viruses by sera obtained at 6 and 12 months postinfection. Sera obtained at 6 and 12 months postinfection from all 14 patients were tested for neutralization against a representative Env-pseudotyped virus clone from each patient. The reciprocal ID₅₀ values are shown, and those in bold show where neutralization was observed. The highlighted (boxed) cells represent autologous neutralization.

FIG. 4.

Neutralization of SF162, a neutralization-sensitive subtype B virus. Sequential serum samples from 14 HIV-1 subtype C-infected patients were tested for neutralizing activity against SF162. Results are shown as the ID₅₀ values (neutralization titers) over time.

FIG. 5.

Neutralization sensitivities of early envelope clones from HIV-1 subtype C-infected patients. The neutralization sensitivities of 14 Env-pseudotyped viruses are represented as the GMTs for neutralization by six HIV-1-positive plasma samples (BB8, BB12, BB28, BB55, BB70, and BB106). The bars indicate the clinical status of the patients from whom the clones were derived.

FIG. 6.

Correlation between neutralization sensitivity and genetic characteristics of the envelope. The length of the V1-V2 region of each envelope clone tested for heterologous neutralization was plotted against the number of cross-neutralizing sera (derived from Fig. 3) or the GMT of six HIV-1-positive plasma samples (Fig. 5). The Spearman r coefficient and the P value are depicted for each correlation.

FIG. 7.

CD4i NAb responses in acute HIV-1 subtype C infection. Sera were assayed using an HIV-2 (7312A) envelope in the presence of 9 nM sCD4. Titers are shown as ID₅₀ values over time. No neutralization was observed in the absence of sCD4 (data not shown).

FIG. 8.

MPER NAb responses in acute HIV-1 subtype C infection. Serum samples from 14 acutely infected individuals were tested against an HIV-2 envelope containing an HIV-1 MPER optimized for HIV-1 subtype C sequences (7312A CIC). Results are shown as ID₅₀ values over time.

FIG. 9.

Mapping of anti-MPER neutralizing activity in two patients. Serum samples from patients CAP85 (A) and CAP206 (B) were tested against eight HIV-2 chimeric viruses containing HIV-1 MPER fragments (C) plus the 7312A control virus. Results are shown as percentages of inhibition. The inserted fragments or mutated residues are shaded for each construct. The amino acids involved in the 2F5 and 4E10 epitopes are represented in bold. The common regions among the constructs where activity was found are boxed.