Evolution of cross-neutralizing antibodies and mapping epitope specificity in plasma of chronic HIV-1-infected antiretroviral therapy-naïve children from India

Abstract

Delineating the factors leading to the development of broadly neutralizing antibodies (bnAbs) during natural HIV-1 infection and dissecting their epitope specificities generates useful information for vaccine design. This is the first longitudinal study to assess the plasma-neutralizing antibody response and neutralizing determinants in HIV-1-infected children from India. We enrolled 26 and followed up 20 antiretroviral therapy (ART)-naïve, asymptomatic, chronic HIV-1-infected children. Five (19.2 %) baseline and 10 (50 %) follow-up plasma samples neutralized ≥50 % of subtypes A, B and C tier 2 viruses at an ID50 titre ≥150. A modest improvement in neutralization breadth and potency was observed with time. At baseline, subtype C-specific neutralization predominated (P=0.026); interestingly, follow-up samples exhibited cross-neutralizing activity. Epitope mapping revealed V3C reactive antibodies with significantly increased Max50 binding titres in follow-up samples from five infected children; patient #4's plasma antibodies exhibited V3-directed neutralization. A salient observation was the presence of CD4 binding site (CD4bs)-specific NAbs in patient #18 that improved with time (1.76-fold). The RSC3 wild-type (RSC3WT) protein-depleted plasma eluate of patient #18 demonstrated a more than 50% ID50 decrease in neutralization capacity against five HIV-1 pseudoviruses. Further, the presence of CD4bs-neutralizing determinants in patient #18's plasma was confirmed by the neutralizing activity demonstrated by the CD4bs-directed IgG fraction purified from this plasma, and competition with sCD4 against JRFLgp120, identifying this paediatric donor as a potential candidate for the isolation of CD4bs-directed bnAbs. Overall, we observed a relative increase in plasma-neutralizing activity with time in HIV-1-infected children, which suggests that the bnAbs evolve.

Broadly neutralizing plasma antibodies effective against diverse autologous circulating viruses in infants with multivariant HIV-1 infection

“…A cut-off of 0.7 defined the 90th-percentile boundary and was used to define ENs (neutralizing ≥90% pseudoviruses), whereas a cut-off of 0.35 (75th-percentile) was used to define BNs (neutralizing ≥60% pseudoviruses) ( Table 1 ). The neutralization scores for known ENs and BNs from previously reported pediatric 9 and adult 10 cohorts were calculated based on the above criteria, confirming the validity of the panel and the scoring system defined herein to decipher pediatric broad and elite neutralizers ( Figure 1E ).…”

Viral characteristics associated with sustenance of elite neutralizing activity in chronically HIV-1C infected monozygotic pediatric twins

“…HIV-1 infected children have been shown to mount potent plasma broadly neutralizing antibodies (bnAbs) earlier than adults and more frequently with multiple bnAb specificities. than adults (4–6). The bnAb BF520.1 was recently isolated from an infant one-year post-infection (p.i) (4,7).…”

A rare mutation in an infant derived HIV-1 envelope glycoprotein alters interprotomer stability and susceptibility to broadly neutralizing antibodies targeting the trimer apex

“…Destabilization of the trimer apex has been shown to alter the neutralization susceptibility of HIV-1 Env to antibodies present in the plasma of infected individuals. As L184F mutation resulted in a more open trimer configuration, we next evaluated the sensitivity of L184F mutant to a panel of HIV-1 clade C infected pediatric patient plasma with varied neutralization potency (weak versus strong neutralizers) against the global panel of representative HIV-1 isolates (35–37). Patient plasma antibodies neutralizing more than half the global panel were considered strong neutralizers while those neutralizing less than half the panel were considered weak to moderate neutralizers depending on their breadth and potency.…”

“…Of note, none of the non-nAbs could achieve 50% neutralization (17b, which binds preferentially to the CD4-induced, CCR5 co-receptor binding site epitope on Env achieved a maximum percent neutralization of 32%) (34), suggesting that the L184F mutation did not substantially alter the conformation of the Env. In addition, the L184F mutant virus showed high susceptibility to neutralization by polyclonal antibodies present in the plasma of weak neutralizers (HIV-1 infected patients that do not generate a potent response to HIV-1 Env) (35–37). HIV-1 Envs are categorized into tiers based on neutralization susceptibility to plasma antibodies (44, 45).…”

“…Viral infectivity was determined after normalizing pseudoviruses to an RLU value of 150,000 followed by titration curve generation to calculate relative infectivity. Neutralization studies included heat-inactivated plasmas from AIIMS731 and previously characterized thirty plasmas of chronically infected children (35–37), 25 bnAbs (PG9, PG16, PGT145, PGDM1400, CAP256.25, CH01, 10-1074, BG18, AIIMS-P01, PGT121, PGT128, PGT135, VRC01, VRC03, VRC07-523LS, N6, 3BNC117, NIH45-46 G54W, PG05, PGT151, 35O22, N123.VRC34.01, 10E8, 4E10 and 2F5) and 6 non-nAbs (447-52D, 19b, 17b, A32, 48d, b6). Briefly, envelope pseudoviruses were incubated in presence of serially diluted heat inactivated plasmas, bnAbs or non-nAbs for one hour.…”