origin and function of adherent lymphokine activated killer cells in patients with chronic myeloid leukaemia who relapse following bone marrow transplantation adherent lymphokine activated killer alak cells are a subpopulation of activated natural killer nk cells with mhc unrestricted antitumour activity distinguished by their propensity to adhere to plastic in the presence of interleukin2 il2 we generated alak cells from seven patients with chronic myeloid leukaemia cml following campath1depleted bone marrow transplantation bmt five had relapsed and were in chronic phase one had cytogenetic evidence of relapse and one had prior evidence of cytogenetic relapse but was in complete remission at time of study phenotypically the alak cells included both cd56cd3 nk cells and cd56cd3 t cells the cd3 subpopulation were studied cytogenetically and their functional activity tested in a 4 h 51cr release cytotoxicity assay using the pretransplant leukaemia cells as targets cytogenetic studies showed that the alak cells from six patients were ph negative and where donor and recipient were sex mismatched alak cells were exclusively of donor origin in one patient alak cells were ph positive and of recipient origin in eight of nine metaphases in the 51cr release assay the alak cells showed significant lysis of the pretransplant leukaemia in five of the seven patients tested these data indicate that in cml patients who relapse postbmt the nk cells are usually of donor origin but may be recipientderived in most patients these alak cells have antileukaemic activity in vitro