Characterization of anti-HIV-1 neutralizing and binding antibodies in chronic HIV-1 subtype C infection

Abstract

Neutralizing (nAbs) and high affinity binding antibodies may be critical for an efficacious HIV-1 vaccine. We characterized virus-specific nAbs and binding antibody responses over 21 months in eight HIV-1 subtype C chronically infected individuals with heterogeneous rates of disease progression. Autologous nAb titers of study exit plasma against study entry viruses were significantly higher than contemporaneous responses at study entry (p=0.002) and exit (p=0.01). NAb breadth and potencies against subtype C viruses were significantly higher than for subtype A (p=0.03 and p=0.01) or B viruses (p=0.03; p=0.05) respectively. Gp41-IgG binding affinity was higher than gp120-IgG (p=0.0002). IgG-FcγR1 affinity was significantly higher than FcγRIIIa (p<0.005) at study entry and FcγRIIb (p<0.05) or FcγRIIIa (p<0.005) at study exit. Evolving IgG binding suggests alteration of immune function mediated by binding antibodies. Evolution of nAbs was a potential marker of HIV-1 disease progression.

Figure 1

(A). Schematic illustrating the autologous neutralizing antibody challenge assays in all participants over a median of 21 months from study entry to study exit. The average nAb IC₅₀ titers for study entry and exit Envs used in the assays are shown. The study entry Envs were tested against nAbs from the study entry (contemporaneous) and study exit plasma samples. Likewise the study exit Envs were tested against nAbs from the study entry and study exit (contemporaneous) plasma samples. Figure 1(B) depicts the autologous nAb IC₅₀ titers in study participant entry and exit plasma samples for all participants. Figure 1(C) and 1(D) shows the CD4 T-cell decline rate and the log viral load changes over time respectively. P-values <0.05 were considered significant. P value was calculated using the two-tailed Mann-Whitney non-parametric test overall. All the p values (p<0.0125) remained statistically significant after Bonferroni adjustment for multiple comparisons.

Figure 1

(A). Schematic illustrating the autologous neutralizing antibody challenge assays in all participants over a median of 21 months from study entry to study exit. The average nAb IC₅₀ titers for study entry and exit Envs used in the assays are shown. The study entry Envs were tested against nAbs from the study entry (contemporaneous) and study exit plasma samples. Likewise the study exit Envs were tested against nAbs from the study entry and study exit (contemporaneous) plasma samples. Figure 1(B) depicts the autologous nAb IC₅₀ titers in study participant entry and exit plasma samples for all participants. Figure 1(C) and 1(D) shows the CD4 T-cell decline rate and the log viral load changes over time respectively. P-values <0.05 were considered significant. P value was calculated using the two-tailed Mann-Whitney non-parametric test overall. All the p values (p<0.0125) remained statistically significant after Bonferroni adjustment for multiple comparisons.

Figure 1

(A). Schematic illustrating the autologous neutralizing antibody challenge assays in all participants over a median of 21 months from study entry to study exit. The average nAb IC₅₀ titers for study entry and exit Envs used in the assays are shown. The study entry Envs were tested against nAbs from the study entry (contemporaneous) and study exit plasma samples. Likewise the study exit Envs were tested against nAbs from the study entry and study exit (contemporaneous) plasma samples. Figure 1(B) depicts the autologous nAb IC₅₀ titers in study participant entry and exit plasma samples for all participants. Figure 1(C) and 1(D) shows the CD4 T-cell decline rate and the log viral load changes over time respectively. P-values <0.05 were considered significant. P value was calculated using the two-tailed Mann-Whitney non-parametric test overall. All the p values (p<0.0125) remained statistically significant after Bonferroni adjustment for multiple comparisons.

Figure 2

Correlation between the amino acid length of (A) V1-V5, (B) V1-V2 and (C) C2-V5 of Env and autologous neutralization titers (nAb IC₅₀ titer) when study entry viruses were tested against study exit plasma samples. The Spearman r-coefficient and p-values are shown and a correlation was considered significant when p<0.05.

Figure 3

Heterologous responses of participant plasma tested at study entry and study exit against 20 Env pseudoviruses from a standard reference panel including subtypes C, B and A of tier 1A, 1B, tier 2 and 3 categories over a median of 21 months. The neutralization titer is shown as reciprocal plasma dilution required to inhibit 50% of virus infectivity when the virus is challenged with the participant's plasma. The highest titer (>1,000) is shown in red, and the lowest in light orange, yellow depicts a titer of <1:45 that is below detection as shown above.

Figure 4

(A). IgG EC₅₀ binding titers for gp41, gp120 and p24-specific antibodies at study entry and exit time points. Panels for Figure 4(B) and (C) show the correlation of EC₅₀ binding titers for gp41, gp120 and p24-specific antibodies with CD4-T cell counts at study entry and study exit respectively. None of the correlations were statistically significant (p< 0.05).

Figure 4

(A). IgG EC₅₀ binding titers for gp41, gp120 and p24-specific antibodies at study entry and exit time points. Panels for Figure 4(B) and (C) show the correlation of EC₅₀ binding titers for gp41, gp120 and p24-specific antibodies with CD4-T cell counts at study entry and study exit respectively. None of the correlations were statistically significant (p< 0.05).

Figure 5

(A). EC₅₀ binding titers of IgGs for FcγRI, FcγRIIa, FcγRIIb and FcγRIIIa at study entry and exit time points. Intra- or inter-group comparisons were statistically different i.e. p< 0.05. Figure 5(B) and (C). Correlation of CD4 T-cell counts at study entry and study exit with FcγRI, FcγRIIa, FcγRIIb and FcγRIIIa (EC₅₀) are shown. Only p-values <0.05 are shown.

Figure 5

(A). EC₅₀ binding titers of IgGs for FcγRI, FcγRIIa, FcγRIIb and FcγRIIIa at study entry and exit time points. Intra- or inter-group comparisons were statistically different i.e. p< 0.05. Figure 5(B) and (C). Correlation of CD4 T-cell counts at study entry and study exit with FcγRI, FcγRIIa, FcγRIIb and FcγRIIIa (EC₅₀) are shown. Only p-values <0.05 are shown.