Potent autologous and heterologous neutralizing antibody responses occur in HIV-2 infection across a broad range of infection outcomes

Abstract

Few studies have explored the role of neutralizing antibody (NAb) responses in controlling HIV-2 viremia and disease progression. Using a TZM-bl neutralization assay, we assessed heterologous and autologous NAb responses from a community cohort of HIV-2-infected individuals with a broad range of disease outcomes in rural Guinea-Bissau. All subjects (n = 40) displayed exceptionally high heterologous NAb titers (50% inhibitory plasma dilution or 50% inhibitory concentration [IC(50)], 1:7,000 to 1:1,000,000) against 5 novel primary HIV-2 envelopes and HIV-2 7312A, whereas ROD A and 3 primary envelopes were relatively resistant to neutralization. Most individuals also showed high autologous NAb against contemporaneous envelopes (78% of plasma-envelope combinations in 69 envelopes from 21 subjects), with IC(50)s above 1:10,000. No association between heterologous or autologous NAb titer and greater control of HIV-2 was found. A subset of envelopes was found to be more resistant to neutralization (by plasma and HIV-2 monoclonal antibodies). These envelopes were isolated from individuals with greater intrapatient sequence diversity and were associated with changes in potential N-linked glycosylation sites but not CD4 independence or CXCR4 use. Plasma collected from up to 15 years previously was able to potently neutralize recent autologous envelopes, suggesting a lack of escape from NAb and the persistence of neutralization-sensitive variants over time, despite significant NAb pressure. We conclude that despite the presence of broad and potent NAb responses in HIV-2-infected individuals, these are not the primary forces behind the dichotomous outcomes observed but reveal a limited capacity for adaptive selection and escape from host immunity in HIV-2 infection.

Fig 1

Heat map depicting heterologous neutralization titers of 40 HIV-2-infected individuals against 10 HIV-2 envelopes. Values given are reciprocal IC₅₀s. The panel clearly separates into envelopes with divergent neutralization phenotypes. Plasma-envelope combinations that were resistant to neutralization (based on a titer below a cutoff 3 times the VSV IC₅₀) are additionally marked with a closed diamond.

Fig 2

Relationship between plasma viral load and median reciprocal IC₅₀ of heterologous neutralization titers against a panel of 10 HIV-2 envelopes from HIV-2-infected individuals (n = 40). A significant positive correlation between viremia and the magnitude of the heterologous neutralizing antibody response is found (Spearman's rho = 0.359, P = 0.02).

Fig 3

Contemporaneous autologous neutralization of HIV-2 envelopes stratified by plasma viral load. Of the 69 primary HIV-2 envelopes (from 21 subjects) used, 64 represented gp140 cloned into 7312A-SNAG. Values are means of two or three independent experiments. No significant difference in median IC₅₀ is seen between viral load categories (P = 0.09).

Fig 4

Comparison of neutralization of 239T-grown and PBMC-passaged virus with the same plasma sample. Shown are autologous neutralization of CA4153.9, CA4145.8, CA381.4, CA4137.19, CA4013.5, and CA4182.4 and heterologous neutralization of 7312A and NL4.3. Plotted values are means (and SDs) from three separate experiments. Virus infectivity (percent) is compared to a virus-only condition.

Fig 5

Association between greater intrapatient diversity and the presence of neutralization-resistant HIV-2 envelopes. Plotted values are mean pairwise genetic distances (substitutions/site) between env variants from each patient.

Fig 6

Alignments from two subjects (a and b) demonstrating amino acid changes specific to resistant envelopes (R). Either additional or shifted potential N-linked glycosylation sites are highlighted in bold red, and other changes are in black. Only regions with differences between resistant and sensitive envelopes are displayed for each subject.

Fig 7

Assessment of neutralization escape in HIV-2. (a) Neutralization of HIV-2 envelopes by autologous plasma from older time points in 10 subjects. The legend depicts the year of plasma sampling. HIV-2 envelopes were isolated from the most recent time point of plasma collection depicted for each clone (either 2003 or 2006). (b to d) Neutralization of envelopes from either 2003 or 2006 by contemporaneous plasma for subjects TD11 (b), TD16 (c), and TD19 (d), from whom variants were isolated at both time points. All values represent means (and SDs) of three independent experiments. Virus infectivity (percent) is compared to a virus-only condition.

Fig 8

Comparison of the ratio of nonsynonymous (dN) to synonymous (dS) changes in HIV-2 (n = 75) and HIV-1 (n = 56) partial C2 to gp41 ectodomain fragments. Plotted values are those obtained under the SLAC algorithm with values normalized to alignment length. Positions found to be under significant positive selection (red) and negative selection (blue) under all three algorithms (SLAC, FEL and REL) are highlighted.