Considering the absolute decrease in the number of immune cells, B lymphocytes were most affected by the genetic loss of CCR4 (CCR4−/−: 2534 ± 809 CD19+ cells per 1 × 105 tumor cells vs. WT: 6287 ± 2426 CD19+ cells per 1 × 105 tumor cells; n = 9, p = 0.1616). The gene discussed is CD19; the disease is neoplasm.