In vitro induction of cytotoxic effector cells against human neoplasms. I. Sensitization conditions and effect of cryopreservation on the induction and expression of cytotoxic responses to allogeneic leukemia cells

Peripheral blood lymphocytes (PBL) from normal human donors were sensitized in vitro against allogeneic human acute myelocytic leukemia (AML) cells by means of an unidirectional mixed lymphocyte-tumor cell culture (MLTC) technique. The cytotoxic responsiveness of the sensitized lymphocytes, as determined in vitro by the ⁵¹Cr-release assay, varied among individual lymphocyte donors and was greatly dependent on the sensitization culture conditions. Induction of cytotoxic effector cells was augmented appreciably by adding to the cultures minute amounts of the immunopotentiating agent MER-BCG. Responding lymphocytes and stimulating leukemia cells cryopreserved for several weeks in liquid nitrogen were as effective as fresh cells in generating effector lymphocytes; the cytotoxic capacity of already sensitized lymphocytes was fully retained by cryopreservation. The implications of these findings for possible clinical employment of in vitro sensitized lymphocytes in adoptive immunotherapy of cancer are discussed.