Despite the increased expression of markers of immaturity in the transcriptome of canine CD4+ PTCL, the enrichment of these tumor cells for early thymocyte gene signatures, and downregulation of TCR signaling, canine CD4+ PTCL cells do still express mature T-cell surface antigens CD3 and CD5, although surface expression of the latter may be variable. The gene discussed is CD4; the disease is mature T-cell and NK-cell non-Hodgkin lymphoma.