αßT cell receptors expressed by CD4(-)CD8αß(-) intraepithelial T cells drive their fate into a unique lineage with unusual MHC reactivities.

Coreceptor CD4 and CD8αß double-negative (DN) TCRαß(+) intraepithelial T cells, although numerous, have been greatly overlooked and their contribution to the immune response is not known. Here we used T cell receptor (TCR) sequencing of single cells combined with retrogenic expression of TCRs to study the fate and the major histocompatibility complex (MHC) restriction of DN TCRαß(+) intraepithelial T cells. The data show that commitment of thymic precursors to the DN TCRαß(+) lineage is imprinted by their TCR specificity. Moreover, the TCRs they express display a diverse and unusual pattern of MHC restriction that is nonoverlapping with that of CD4(+) or CD8αß(+) T cells, indicating that they sense antigens that are not recognized by the conventional T cell subsets. The new insights indicate that DN TCRαß(+) T cells form a third lineage of TCRαß T lymphocytes expressing a variable TCR repertoire, which serve nonredundant immune functions.

Antigen-specificity of clonally-enriched CD8+ T cells in multiple sclerosis.

CD8+ T cells are the dominant lymphocyte population in multiple sclerosis (MS) lesions where they are highly clonally expanded. The clonal identity, function, and antigen specificity of CD8+ T cells in MS are not well understood. Here we report a comprehensive single-cell RNA-seq and T cell receptor (TCR)-seq analysis of the cerebrospinal fluid (CSF) and blood from a cohort of treatment-naïve MS patients and control participants. A small subset of highly expanded and activated CSF-enriched CD8+ T cells were abundant in people with MS and displayed high cytotoxicity and tissue-homing transcriptional profiles. Using a combination of unbiased and targeted antigen discovery approaches, several MS-derived CD8+ T cell clonotypes recognizing Epstein-Barr virus (EBV) antigens and novel mimotopes were identified. These findings shed insight into the functions of CD8+ T cells in MS and may serve as potential disease biomarkers and therapeutic targets.

High-Yield Purification, Preservation, and Serial Transplantation of Human Satellite Cells.

Investigation of human muscle regeneration requires robust methods to purify and transplant muscle stem and progenitor cells that collectively constitute the human satellite cell (HuSC) pool. Existing approaches have yet to make HuSCs widely accessible for researchers, and as a result human muscle stem cell research has advanced slowly. Here, we describe a robust and predictable HuSC purification process that is effective for each human skeletal muscle tested and the development of storage protocols and transplantation models in dystrophin-deficient and wild-type recipients. Enzymatic digestion, magnetic column depletion, and 6-marker flow-cytometric purification enable separation of 104 highly enriched HuSCs per gram of muscle. Cryostorage of HuSCs preserves viability, phenotype, and transplantation potential. Development of enhanced and species-specific transplantation protocols enabled serial HuSC xenotransplantation and recovery. These protocols and models provide an accessible system for basic and translational investigation and clinical development of HuSCs.