P37.08
Background: HIV-1 Nef plays a major role in enhancing the pathogenicity of the virus through various mechanisms such as down-regulation of CD4 and HLA class I surface expression and interfering with cell signaling pathways. Identifying and characterizing CD8+ T cell epitopes in Nef that are under host immune selection can help in selecting targets for an effective vaccine.
Methods: 326 subtype A Nef sequences from treatment naïve patients of a Kenyan sex-worker cohort were generated using 454 pyrosequencing. Positively selected (PS) mutations were determined using a bioinformatics approach, quasi analysis. Peptides were designed with mutation placed in anchor position 2, 5, 8, 9 of epitopes of HLA class I alleles for validation with ELISpot assay using patient PBMCs.
Results: E70D, I109V and I176M were associated with rapid CD4 decline (p=0.010, 0.015, 0.025 respectively). H124N and K190M were associated with slow CD4 decline (p=0.001 and 0.029). The five PS mutations were significantly associated with HLA class I alleles including A*23:01 (E70D, p=0.002; I176M, p=0.003), A*02:01 (I109V, p=0.028; H124N, p=0.021), B*58:01 (I109V, p=0.048), A*3002, B*57:03 and C*02:01 (H124N, p=0.026, 0.0004, and 0.011 respectively) and C*06:02 (K190M, p=0.037). ELISpot analysis identified 27 novel epitopes containing either the consensus or the PS mutations. Six new epitopes contained E70D, five epitopes contained K190M, and I109V and H124N were each contained by eight new epitopes. No epitopes containing I176M was confirmed by ELISpot. It is possible that I176M represents compensatory mutations due to functional requirements under host immune selective pressure.
Conclusions: Identification and characterization of epitopes containing beneficial and detrimental PS mutations can provide important insight for selecting immunogens for an effective HIV vaccine. More detailed investigation of T-cell responses, such as poly-functionality and proliferation to these mutations will be conducted to further characterize these Nef epitopes.
