Analysis of viral inhibitory activity of cytotoxic T. Lymphocytes targeting identical epitopes restricted by different class 1 HLA alleles from the same HLA supertype.

Abstract

Master of Medical Sciences in Immunology. University of KwaZulu-Natal, Medical School 2015.Human leukocyte antigen (HLA) polymorphism and the genetic diversity of human immunodeficiency virus (HIV) are the major obstacles for designing an effective HIV Cytotoxic T Lymphocytes (CTLs) based vaccine. Interestingly, recent studies have demonstrated that multiple class I alleles can recognize common epitopes “supertopes” due to the homology of amino acids within the major binding pockets of the peptide binding cleft. The implications of this for vaccine design is that a vaccine containing a small number of highly promiscuous supertopes can confer protection against a wide range of HIV variants. This notion makes supertopes immunogen design an attractive option. However, it is not clear whether supertopes presented in the context of different class I HLA alleles would induce functional equivalent CTL responses. In this study, we investigated the inhibitory activity of CTLs targeting identical epitopes presented by class I HLA alleles from the same superfamily. The viral inhibitory activity was measured using a newly developed CEM-GFP reporter T-cell line (GXR-cell) as target cell. We first compared the inhibitory activity of CTLs from 8 subjects targeting TPQDLNTML (Gag p24 residue 180-188-TL9) epitope presented by HLA-B*81:01 or B*42:01 alleles. We then assessed the inhibitory activity of the 8 subjects’ CTLs when presented with in-vivo occurring mutant (Q182S)-TL9 epitope by HLA-B*81:01 or B*42:01 alleles. Furthermore, we compared the inhibitory activity of CTLs from 4 subjects targeting ISPRTLNAW (Gag p24 residue 147-155-IW9) epitope presented by HLA-B*57:03 or B*58:01 alleles. Comparative analysis of the inhibitory activity of the 8 subjects’ CTLs showed no statistical significant difference when TL9 epitope was presented by HLA-B*81:01 or B*42:01 alleles (1:1; p-value = 0.8785, paired t test), even at low target to effector ratio (1:8; p-value = 0.4418). No statistical significant difference was observed in the inhibitory activity of the 8 subjects’ CTLs when mutant (Q182S)-TL9 epitope was presented by HLA-B*81:01 or B*42:01 alleles (1:1; p-value = 0.8042), same result was observed at low target to effector ratio (1:8; p-value = 0.9396). Comparative analysis of the inhibitory activity of the 4 subjects’ CTLs targeting identical IW9 epitopes presented by HLA-B*57:03 or B*58:01 alleles showed a trend towards significance at target to effector ratio 1:1 (1:1; p-value = 0.0924), but at low target to effector ratio, no significance difference was observed (1:8; p-value = 0.1496). In conclusion, we have demonstrated that there is no observable significant difference in the inhibitory activity of CTLs targeting wildtype TL9 or mutant (Q182S)-TL9 epitopes presented in the context of HLA-B*81:01 or B*42:01 alleles. Thus, TL9 epitope could be immunogenic for individuals expressing HLA-B*81:01 or B*42:01 alleles. We have also shown that the inhibitory activity of CTLs targeting identical IW9 epitopes presented by HLAB* 57:03 or B*58:01 alleles is comparable. Indicating that IW9 epitope could be included in immunogen design for individuals expressing HLA-B*57:03 or B*58:01 alleles. These findings are relevant for HIV vaccine approach that seeks to identify immunogenic supertopes that can be cross-presented in a broadly cross-reactive T cell based vaccine design