Characterizing the role of CD4+ T cell immunoregulatory networks in peripheral blood and lymphoid tissue during HIV-1 clade C infection.
Year: 2018
Type: dissertation
Study design: Observational Study
Abstract: HIV eradication efforts have been unsuccessful due to virus persistence in cellular and \ntissue reservoirs. Recent evidence suggests that germinal centers (GCs) within lymph \nnodes (LN) contain a novel subset of regulatory T cells (TREGs), termed follicular \nregulatory T (TFR) cells. These cells control the magnitude and specificity of the GC \nresponse and like TREGs are essential for the maintenance of self-tolerance and immune \nhomeostasis. However, the exact role of TFR cells in HIV infection and their contribution \nto viral control is not completely understood, possibly due to their low frequency, \nheterogeneity and more so, the difficulty in accessing human lymphoid tissue samples to \nfully study them. \nThus, we set out to comprehensively investigate TFR cells in LN and peripheral blood \n(PB) samples, using a multifaceted approach including flow cytometry, MHC class II \ntetramers, immunofluorescence microscopy (IF), ELISA, digital droplet PCR and singlecell \nRNA sequencing (SeqWell), in HIV-1 clade C infection. Furthermore, we aimed to \ndetermine the effect of very early treatment on the frequency and function of this cell \nsubset. \nOverall, our studies contributed various notable findings to the field. Firstly, we were able \nto develop MHC class II tetramers, specific in our HIV-1 clade C setting, as a more \nsensitive method of identifying very low cell frequency antigen-specific CD4+ T cells \nwithout relying on function. Tetramers eliminate the bias associated with in vitro \nstimulation required for functional assays and the limitation associated with only \ndetecting subsets of cells capable of secreting a cytokine. Notably, we used class II tetramers to demonstrate that HIV-specific CD4+ T cell responses restricted to \nDRB1*11-Gag41 are associated with immune control of HIV-1 infection. \nWe next focused on understanding the role of CD4+ regulatory cells during HIV-1 \ninfection. Firstly, we showed that TFR cell frequencies were significantly higher in LN \ncompared to PB samples. Secondly, TFR are a phenotypically and transcriptionally \ndistinct subset compared to regulatory T cells (TREGs) and T Follicular Helper cells \n(TFH). Thirdly, we were able to detect HIV-specific TFR using our newly synthesized \nMHC class II tetramers, and showed higher frequencies observed in LNs during untreated \nHIV infection. Fourthly, as measured by both flow cytometry and IF, most of TFR \nlocalized outside of the GC, with very early ART initiators displaying larger proportions \nof TFR within the GC. Lastly, TFR cells exhibited a potential suppressive functional \ncapacity as they produced IL-10, which is a canonical suppressive cytokine and they were \nalso positively associated with gp41 IgG antibodies titers. \nOverall, the data presented in this thesis highlights the advantage of MHC class II \ntetramers in evaluating HIV-specific CD4 + T cell responses in natural infections. More \nso, the results give important insights into regulatory cells within lymph nodes; their \nbiology, function and their role in the setting of very ART initiation.
Author: Faatima Laher
Language: English
Topic: HIV Research and Treatment
Subfield: Virology
Field: Immunology and Microbiology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W3014296722