MST1-deficient CD8 T cells exhibit higher expression of T-bet transcription factors, which is associated with higher expression levels of IFNγ and granzyme B. Consistent with this, MST1-deficient CTLs have greater tumoricidal activity in vitro, and suppress tumor progression in mouse models more efficiently, than wild-type CTLs. The gene discussed is MST1; the disease is neoplasm.