Lactate dehydrogenase-release assay: a reliable, nonradioactive technique for analysis of cytotoxic lymphocyte-mediated lytic activity against blasts from acute myelocytic leukemia.

Treatment of patients in remission of acute myelocytic leukemia using immunotherapy with interleukin 2 is a new approach to prolonging remission duration in this disease. As an important mechanism for the pathophysiology of eradication of residual myelocytic blast populations, activation of cytotoxic effector lymphocytes has frequently been discussed. However, the associated immunological research has been complicated to some extent, because in conventional chromium 51-release assays, blast cells frequently fail to incorporate sufficient amounts of 51Cr and/or spontaneously release high amounts of 51Cr. Recently, we established a culture system which promotes the outgrowth of cytotoxic T lymphocytes in bone marrow-derived mononuclear cells cultured in IL-2. To study cytotoxicity and the responsible mechanisms of the obtained T-cell lines and clones, we modified a previously described cytotoxicity assay, based on the release of lactate dehydrogenase (LDH-release assay) for use in cryopreserved blasts obtained from the bone marrow of patients with acute myelocytic leukemia. Using this assay, we were able to detect cytotoxicity of IL-2-activated peripheral blood lymphocytes from three healthy controls against a number of blast samples obtained from the bone marrow of patients with AML (up to more than 40% lysis at an effector target cell ratio of 20:1). However, a minority of AML blasts seem to be resistant to lysis by IL-2-activated lymphocytes. In bone marrow-derived T-cell lines from patients with AML we detected lytic activity against autologous blasts in three of seven cases tested by LDH release, ranging from 29 to 63% at an effector target ratio of 10:1. Additionally, T-cell clones with different phenotypes were established which were able to mediate cytotoxicity against autologous blast cells. Thus, cytotoxicity against freshly isolated blasts from patients with acute myelocytic leukemia can be analyzed reliably, reproducibly, and without the use of isotopes by the LDH-release assay.