IL15 and graft versus host disease: The first in-human trial with activated NK cells using the K562-membrane-bound IL-15 (K562-mb15-41BBL) feeder cell line, derived from HLA-matched donors and infused into patients with high-risk solid tumors, resulted in an unexpected high incidence of acute GvHD, even after T-cell depletion, suggesting that allogenic IL-15/4-1BBL activated NK cells can contribute to GvHD (131).