XIAP and neoplasm: Moreover, the expression of Xiap (X-linked inhibitor of apoptosis protein), a member of the inhibitor of apoptosis family of proteins, was diminished in these T cells treated with tumor supernatant (Fig. 5A), making them more susceptible to execution by caspases, as Xiap is known to inhibit caspases-3, -7 and -9 [48].