(P519) Characterization of HIV epitopes restricted by the Amerindian B*39

Aim: HLA loci are considered a major driver of HIV evolution, since they select mutations within the circulating virus, which allow it to elude cytotoxic T lymphocyte immune responses. These escape mutations are selected in predictable molecular patterns, imposing an HLA subtype-specific “footprint” (i.e. HLA-associated polymorphisms or HAPs) on the circulating virus. In previous research, we have identified in Mexican HIV+ cohorts, the B*39:02 subtype (frequent in Mestizo and Amerindian populations) linked to both protective HIV disease outcome (i.e. associated to HIV clinical parameters) and by imposing a footprint on HIV Gag and Pol at the population level in Mexico. Here, we aimed to characterize B*39:02 HIV epitopes using IFNg ELISpot assays using as stimuli Gag and Pol peptides that encompass described B*39:02-associated polymorphisms.

Method: Overlapping 9-mer peptides, were synthetized for each viral region where B*39:02-associated polymorphisms (HAP) have been described (i.e. 45 peptides for 5 HAPs in HIV Gag/Pol). Peptides were tested individually in IFNg ELISpot plates using PBMCs of recently HIV-diagnosed B*39:02+ individuals. Spot-forming units (SFU) were counted using plate reader CTL S6 Micro M2, and positive responses were recognized with the non-parametric distribution-free resampling method.

Results: A total of ten B*39:02+ individuals were recruited for sample donation. Briefly, we have found an HIV epitope in Gag (p24/capsid) encompassing the 315N and 319E B*39:02-associated escape mutations, which we named B*39:02-VL9 epitope (VKNWMTETL, median of 567 SFU/10^6 PBMC, Kruskal-Wallis p-value = 1.23e-08 difference among peptides tested). In Pol, we have found that peptides 2 & 3 of 178E-HAP have the higher magnitude of response (medians: 175 and 190 SFU/10^6, respectively), meanwhile peptides 7 & 8 represent have the higher response in the 70K-HAP (medians: 200 and 193 SFU/10^6, respectively).

Conclusion: In summary, epitopes found here are coherent with the unstudied binding motif described for B*39:02(X[KQ]XXXXXX[LFM]; X denotes any residue & preferred residues in anchor pockets are shown in brackets) and confirm that HAPs can be used to map HIV epitopes of frequent HLA subtypes in the Latin America region. These findings may improve future research regarding global of geographical tailored HIV vaccine constructs.