PCA revealed consistent clustering of control canine CD4 and CD8 lymphocytes away from tumor samples, and close clustering of canine CD4+ PTCLs (Fig. 2A), corroborating previous findings that CD4 expression by flow cytometry corresponds to a distinct subgroup of canine PTCL with a uniform gene expression profile [8]. The gene discussed is CD4; the disease is mature T-cell and NK-cell non-Hodgkin lymphoma.