Natural killer cell activity following T-cell depleted allogeneic bone marrow transplantation

We have examined the recovery of natural killer (NK) cell function in seven recipients of MHC matched T cell depleted bone marrow allografts. NK cell activity against the erythroblastoid line K562 recovers 2-3 weeks after transplantation. Recipients also show a high level of killing of the T cell target HSB2 and of EBV transformed lymphoblastoid cell lines (B-LCL). This activity peaks at 4-6 weeks and declines towards normal by 12-14 weeks after transplantation. Although killing of HSB2 and B-LCL is usually the property of activated NK cells, few of these patients had any obvious 'trigger' of such activation: none had CMV infection, there were no episodes of graft rejection, and only two patients had mild and transient grade I graft versus host disease (GvHD). We conclude that T cell depletion does not affect the reconstitution of NK cell function and that NK cell activation occurs after T depleted bone marrow transplantation even in the absence of clinically detectable GvHD, graft rejection or CMV infection.