Browsing by Subject "T cell receptor"

Now showing 1 - 3 of 3
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    Analysis of the pre-immune T cell repertoire.
    (2009-12) Chu, Hon Man Hamlet
    Cell-mediated immune responses are initiated when a population of pre-immune (or naïve) T cells recognize their cognate ligands in the form of a specific peptide bound to a self major histocompatibility complex molecule (pMHC). This recognition is made possible by highly specific T-cell receptors (TCR) on individual T cell clones specific for a given pMHC complex. The pre-immune T cell repertoire is comprised of populations specific for at least 100,000 different pMHC, each containing multiple clones. It is important to understand the composition of this repertoire because it is the repository of all the host's potential for future cell-mediated immune responses to microbes and tumors, and in some cases its own tissues. . However, the study of pre-immune tumor antigen-specific, or any other pathogen-specific T cell populations within such a diverse T cell repertoire have been extremely difficult due to their low frequency in the body. A novel soluble pMHC magnetic enrichment technique was therefore developed to analyze naive T cell populations in mice and humans,. Using this procedure, different pMHCII-specific naive CD4+ T cell populations could be identified and enumerated. The size of these populations was found to vary depending on pMHC specificity. Additionally, these differences were directly proportional to the magnitude and TCR gene usage diversity of the primary CD4+ T cell response after immunization with relevant peptide. Thus, variation in naive T cell frequencies can explain why some peptides give rise to greater T cell responses than others. We explored this issue by enumerating pMHCII-specific CD4+ T cell populations that normally number 20 or 200 cells per mouse. Thymic positive or negative selection was required for optimizing the absolute size pf each population but did not alter the 10-fold ratio between the two populations. Large naïve population size was related to the presence of certain amino acids at T cell receptor contact sites within the peptide. These results suggest that certain MHCII-bound peptides are immunodominant because they contain amino acids with chemical properties that foster binding to many TCRs.
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    Analysis of the pre-immune T cell repertoire.
    (2009-11) Chu, Hon Man Hamlet
    Cell-mediated immune responses are initiated when a population of pre-immune (or naïve) T cells recognizes their cognate ligands in the form of a specific peptide bound to a self-major histocompatibility complex molecule (pMHC). This recognition is made possible by highly specific Tcell receptors (TCR) on individual T cell clones specific for a given pMHC complex. The pre-immune T cell repertoire is comprised of populations specific for at least 100,000 different pMHC, each containing multiple clones. It is important to understand the composition of this repertoire because it is the repository of the host’s potential for future cell-mediated immune responses to microbes and tumors, and in some cases its own tissues. However, the study of individual pre-immune pMHC-specific T cell populations within such a diverse repertoire has been extremely difficult because of their small size. A novel soluble pMHC-based magnetic enrichment technique was therefore developed to analyze naive T cell populations in mice and humans. Using this procedure, different pMHCII-specific naive CD4+ T cell populations were identified and enumerated. The size of these populations was found to vary depending on pMHC specificity. Additionally, these differences were directly proportional to the magnitude of the primary CD4+ T cell response after immunization with the relevant peptide.Thus, variation in naive T cell frequencies can explain why some peptides give rise to greater T cell responses than others. We explored this issue by enumerating pMHCII-specific CD4+ T cell populations that normally number 20 or 200 cells per mouse. Thymic positive or negative selection was required for optimizing the absolute size of each population but did not alter the 10-fold ratio between the two populations. Large naïve population size was related to the presence of certain amino acids at TCR contact sites within the peptide. These results suggest that certain MHCII-bound peptides are immunodominant because they contain amino acids with chemical properties that foster binding to many TCRs.
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    The role of T cell receptor affinity in CD4+ T cell differentiation
    (2019-02) Kotov, Dmitri
    Naïve helper T cells become activated when their T cell receptor (TCR) recognizes a microbial peptide presented on MHCII (p:MHCII) by dendritic cells (DCs). During this interaction, DCs provide polarizing cues to guide T cell differentiation towards specific fates, like T follicular helper cells which help B cells. The affinity of TCR for its cognate p:MHCII is known to influence the fate adopted by CD4+ T cells, but the mechanisms responsible for this effect are not completely understood. The mechanism could be T cell extrinsic, by affecting the DC subset a T cell contacts thereby influencing the polarizing factors received, or T cell intrinsic, by modulating TCR signal strength thus regulating genes involved in T cell differentiation. The T cell extrinsic hypothesis was tested with a quantitative, imaging approach called histo-cytometry to analyze the T cell-DC interactions. This technique involves time-consuming manual image analysis. Therefore, we wrote software to automate histo-cytometry analysis, reducing hands-on analysis time by up to 90%. With histo-cytometry, we determined that TCR affinity did not affect the DC subset contacted by CD4+ T cells, rendering the cell extrinsic hypothesis unlikely. We therefore focused on the T cell intrinsic hypothesis by performing a CRISPR/Cas9 screen to identify TCR regulated genes that influence T cell differentiation. This screen revealed two novel regulators of helper T cell differentiation, Eef1e1 and Gbp2, which are expressed at a higher level in high affinity than low affinity T cells. These results suggest that TCR affinity influences helper T cell differentiation intrinsically by regulating genes that control the differentiation process. We next explored the relationship between CD4+ T cell differentiation and cytotoxic activity. This study determined that cytotoxic function of helper T cells was dependent on the Fas pathway and Fas was upregulated on target cells proportional to the TCR affinity of the responding T cells. Additionally, we identified that many different helper T cell subsets express FasL and have cytotoxic potential. Thus, my work could benefit future vaccines by providing greater understanding of how helper T cell fate decisions occur and how these decisions influence cytotoxic function.