IL21 and neoplasm: While this strategy has resulted in significant tumor regression, little data has been presented demonstrating long-term curative effects (≥ 100 days) with IL-2 alone [16,17], IL-15 alone [18], or the combination of IL-15 and IL-21 [3] – except in mice with small tumors (≤ 10 mm2) at the time of treatment, or after the adoptive transfer of very large numbers (107) of IVS pmel CD8+ T cells [16].