Clonal expansions of CD8+ T cells have been identified in muscle and blood of polymyositis patients by PCR techniques, including T cell receptor (TCR) complementarity-determining region (CDR)3 length analysis (spectratyping). To examine a possible pathogenic role of these clonally expanded T cells, we combined CDR3 spectratyping with laser microdissection and single-cell PCR of individual myocytotoxic T cells that contact, invade, and destroy a skeletal muscle fiber.
First, we screened cDNA from muscle biopsy specimens by CDR3 spectratyping for expanded TCR beta chain variable region (BV) sequences. To pinpoint the corresponding T cells in tissue, we stained cryostat sections with appropriate anti-TCR BV mAbs, isolated single BV+ T cells that directly contacted or invaded a muscle fiber by laser-assisted microdissection, and amplified their TCR BV chain sequences from rearranged genomic DNA. In this way, we could relate the oligoclonal peaks identified by CDR3-spectratype screening to morphologically characterized microdissected T cells.
In one patient, a large fraction of the microdissected T cells carried a common TCR-BV amino acid CDR3 motif and conservative nucleotide exchanges in the CDR3 region, suggesting an antigen-driven response.
In several cases, we tracked these T cell clones for several years in CD8+ (but not CD4+) blood lymphocytes and in two patients also in consecutive muscle biopsy specimens.
During immunosuppressive therapy, oligoclonal CDR3-spectratype patterns tended to revert to more polyclonal Gaussian distribution-like patterns.
Our findings demonstrate that CDR3 spectratyping and single-cell analysis can be combined to identify and track autoaggressive T cell clones in blood and target tissue. This approach should be applicable to other inflammatory and autoimmune disorders.
