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Masters Degrees (Immunology)

Permanent URI for this collectionhttps://hdl.handle.net/10413/12324

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Browsing Masters Degrees (Immunology) by Author "Ndhlovu, Zaza Mtine."

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    Analysis of viral inhibitory activity of cytotoxic T. Lymphocytes targeting identical epitopes restricted by different class 1 HLA alleles from the same HLA supertype.
    (2015) Ogunshola, Funsho Japhet.; Ndhlovu, Zaza Mtine.; Ndung'u, Peter Thumbi.
    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.
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    Mapping immunodominant patterns and HLA class II restriction characteristics of HIV-specific CD4+ T cell responses in acute and chronic HIV-1 subtype C infection.
    (2014) Laher, Faatima.; Ndhlovu, Zaza Mtine.; Ndung'u, Peter Thumbi.
    Increasing evidence suggests that virus-specific CD4+ T cells contribute to immune-mediated control of HIV-1 infection. However, precise details of CD4+ T cell contribution to immune protection against HIV have not been adequately defined and most of the existing data was predominantly generated in clade B HIV-1 infection. Understanding the contribution of CD4+ T cell responses in clade C infection is important for developing vaccines that would be efficacious in sub-Saharan Africa which carries the highest burden of the HIV epidemic in the world. Therefore this study focused on the role of CD4+ T helper cells in the immune response to clade C HIV-1 infection. We tested the hypothesis that HIV-1-specific CD4+ T cell responses and protective class II HLA alleles are important determinants of effective immunological control of HIV-1 infection. Firstly, CD8 depleted PBMCs were used in an IFN-γ ELISPOT assay to conduct a comprehensive analysis of virus-specific CD4+ T cell responses in acute and chronic HIV-1 clade C infection. Thereafter the host genetic effects of class II HLA-DRB1 alleles on HIV viremia were assessed using the HLA-DRB1 restriction assay, where HLA class II-restriction characteristics of detectable responses were defined. Lastly, functional differences of HIV-specific CD4+ T cells were further characterized using flow cytometric analysis. In our study, Gag and Pol regions of the HIV proteome were found to be the most frequently targeted in acute HIV-1 infection (69% of total responses), with CD4+ T cell targeting across the proteome remaining relatively stable over time. In chronic HIV-1 clade C infection, dominant HIV-1-specific CD4+ T cell responses were detectable against a limited number of epitopes. Epitopes in the Gag region were the most targeted by CD4+ T cells (30/40 peptides), with OLP 41 in the Gag p24 region being the most dominant epitope targeted (15% of responses). There were no significant differences observed between total or Gag-specific CD4+ T cell responses and contemporaneous viral load. Interestingly, responses rarely targeted the envelope region in clade C infection, in contrast to multiple epitopes targeted in this protein in previous clade B studies. Functional analysis demonstrated that IFN-γ, IL-2 and TNFα were the most secreted cytokines by HIV-specific CD4+ T cells in 18/25 individuals, with IFN-γ being the most dominant response in individual subjects. The HLA class II DRB1 restriction in clade C HIV infected individuals showed epitope promiscuity, consistent with previous studies in clade B infection. The HLA-DRB1*13:01 allele variant was associated with the highest frequency of responders (22%) in our cohort and restricted the highest number of HIV-specific peptides (9/15). Together, our data identify immunodominant regions of HIV-specific CD4+ T cell responses and their association with viral control during clade C infection. Furthermore, our findings will inform studies aimed at elucidating the underlying mechanism by which CD4+ T cells modulate effective CD8+ T cell and B cell responses. Additionally, these data suggest that epitope promiscuity among class II HLA molecules should be taken into account for vaccines designed to induce CD4+ T cell responses. This information will be critical to vaccine efforts designed to induce these responses, as well as potential therapeutic manipulation of immunity in persons with acute and chronic HIV-1 infection.