On the other hand, FasLE163A, FasLE271A, FasLED163-164AA, and FasLEE270-271AA mutants lost both binding (S3b,c), apoptotic cytotoxicity, and Fas clustering activity against tumor and T cells (Fig. 3D–G and Supplementary Fig. S3D–F). The gene discussed is FAS; the disease is neoplasm.