An individual bout of vigorous intensity cycling for 20-minutes increases the number of circulating effector memory T-cells by ~450% (44) and circulating CD19+ B-cells by ~100% (44) in healthy humans, and 30-minutes of vigorous intensity run-walk treadmill exercise increases total lymphocytes in blood by ~50% in children with ALL receiving maintenance therapy (144). Here, CD19 is linked to acute lymphoblastic leukemia.