CD4 and lymphoma: CD4:CD8b ratio in unstimulated koala PBMCs was markedly higher in the KoRV-B-positive, KoRV-C-negative individual (KM, which showed lymphoma) than in koalas with endogenous infection only (KoRV-A); however, this ratio showed no other significant differences between KoRV subtype infection profiles (Figure 3A).