Immunotherapy with lymphokine-activated killer (LAK) cells and interleukin 2 (IL-2) has been demonstrated to cause the regression of some human tumors. Expansion of peripheral blood lymphocytes (PBL) in recombinant or naturally produced IL-2, mitogens, and feeder cells results in a progressive expansion of cell number but a decline in lytic activity with time. Lytic activity for fresh tumor is best generated in IL-2 alone from specific purified subpopulations of lymphocytes. The precursor of the LAK cell has been isolated from a nonadherent, sheep erythrocyte receptor negative (E-) lymphocyte subpopulation by the selection of Leu 11+ and Leu 15+ cells by cell sorting. Separation resulted in a significant increase (P2 < 0.05) in lytic activity against fresh tumor by the separated 11+15+ lymphocytes compared to the 11-/15- lymphocytes or PBL. Leu 11+/15+ lymphocytes could be expanded up to eightfold in IL-2 alone with maintenance of lytic activity. We identified two surface antigens on the LAK precursor cell, Leu 15 and Leu 11, and demonstrated a technique for obtaining purified populations of these cells. Purified and expanded LAK cells when administered to patients may have a role in increasing the potency and decreasing the toxicity associated with this therapy.
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