IL-2 complex therapy enhanced NK cell numbers and antipathogen immunity in HSCT recipients. (A) IL-2_S4B6 therapy elicited large numbers of NK cells in the peritoneal cavity of intraperitoneally vaccinated HSCT recipients 5 days following the third treatment. NK1.1⁺ cell numbers in the peritoneal cavity; n = 2. (B) IL-2_S4B6-treated HSCT recipients displayed fewer splenic bacterial CFU following intravenous inoculation with 1.0 × 10⁴ CFU L monocytogenes 14 days after HSCT and 4 infusions of IL-2_S4B6 starting 3 days after HSCT and repeated every 3 days. CFU numbers in the spleen 7 days after infection; n = 5 from representative of 2 experiments; x, no HSCT; ●, HSCT; ■, HSCT + IL-2_S4B6.