Evaluation of LAK-mediated tumor cell killing in a plasma clot clonogenic assay

An assay based on the inhibition of the cloning capacity in a plasma clot semisolid medium assay has been used to test the sensitivity of the Raji cell line to lymphokine-activated killer (LAK) cells. This method overcomes some limitations intrinsic to the widely employed 51Cr release assay and always shows a higher degree of sensitivity. No inhibition of colony growth was found when the effector cells were plated without prior pre-incubation with interleukin 2 or with the addition of the medium derived from the LAK cells. Though more time-consuming than the classic 51Cr release assay, this technique does not require radioactive material. This test may be suitable for a more precise evaluation of LAK activity and for the study of the mechanisms involved in cell killing.