TRGC1 and primary cutaneous T-cell non-Hodgkin lymphoma: One of the first studies on biomarkers for ECP response in GvHD investigated whether circulating clonal T cells in peripheral blood (PB) and clonal T cell receptor γ (TCRγ) rearrangement, could be linked to response to ECP, as was previously demonstrated in cutaneous T cell lymphoma (CTCL) (142, 143).