Introduction and Objective: In NOD mice, impaired T cell development and negative selection are implicated in disease development. However, in T1D patients, it remains unknown whether abnormalities in thymic selection contribute to disease development. Our knowledge of human T Cell Receptor (TCR) repertoire formation is limited by lack of access to human thymi. Thus, humanized mice provide a unique opportunity to investigate formation of the human TCR repertoire.Methods: We utilized the Personalized Immune (PI) Mouse model, in which partially HLA-matched fetal thymic tissue and adult T1D or Healthy Control (HC) bone marrow CD34+ Hematopoietic Stem Cells are engrafted in immunodeficient mice. Following human T cell reconstitution, whole thymocytes are used for scRNA/TCR sequencing and DNA isolated from FACS-sorted thymocytes is used for high throughput TCRbeta CDR3 sequencing.Results: Published studies show that hydrophobicity of the TCR midCDR3 (mCDR3) region correlates with autoreactivity. In HC-derived mice, mCDR3 hydrophobicity increased during positive selection and then decreased in mature CD4 single positive (SP) cells compared to CD69+ CD4/8 double positive thymocytes, indicating effective selection processes. In T1D-derived mice, hydrophobicity increased during positive selection, albeit to a lesser extent at certain lengths of the mCDR3 region and failed to decrease as the cells matured into CD4SP cells, indicating defective negative selection. Using scRNA sequencing, Clusters 2 and 10 were significantly enriched in HC mice and correspondingly depleted in T1D mice. Using Chopp et al., 2020 as a reference, these two clusters were associated with hsDP3 and Sig4 maturation stages which precede positive selection and demonstrate features related to negatively selected subsets respectively.Conclusion: We provide in-vivo evidence both at the physio-chemical and transcriptional level, for abnormalities in thymocyte selection in human T1D-derived human immune systems.
V. Agashe: None. B. Vermette: None. R. Winchester: None. M. Sykes: None.
4R01AI1778721UG3DK142184U01DK123559
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