Modification of the clonogenic assay for the detection of lymphokine activated killer cell activity

The soft agar clonogenic assay using [ 3H]thymidine uptake as an endpoint was adapted for the detection of human LAK activity against the Daudi lymphoma cell line and human tumor cells obtained by biopsy. Using Daudi cells as the target population the modified agar assay was more sensitive than the conventional 4 h 51Cr release assay. Use of a single layer agar assay allowed the assessment of LAK cytotoxic/cytostatic activity against Daudi lymphoma cells after cell to cell contact, while a two layer system permitted evaluation of the role of soluble mediators in LAK/target cell interactions. This study shows that LAK cells can either kill or inhibit the proliferation of Daudi cells by two mechanisms: one which requires cell-to-cell contact, and a second via soluble mediators. As determined by the use of neutralizing antisera, the soluble factor(s) are not tumor necrosis factor and interferon-γ. Of the nine individual human tumor samples obtained by biopsy, 89% were sensitive to allogeneic LAK cells when the two populations were admixed. Of these nine tumors 44% were inhibited by LAK-derived soluble factors. The soft agar assay system should serve as a useful tool for determining the sensitivity of human tumors to LAK cells and for studying the mechanisms of LAK anti-tumor activity.