Current laboratory lymphokine-activated killer (LAK) cell activation procedures require culture of peripheral blood mononuclear cells (PBMC) in the presence of 1000–1500 units/ml of interleukin 2 (IL-2) for 3–7 days. However, we have observed that a brief exposure (15 min-1 h) of PBMC to a high concentration of IL-2 results in the maturation of LAK precursor cells to cytolytic effector cells over the course of 1–3 days. These IL-2-pulsed LAK cells express cytolytic activity comparable to that of nonpulsed PBMC (cultured continuously in IL-2) at 3 days of culture. The acquisition of cytolytic activity followed the same kinetics for both pulsed and nonpulsed mononuclear cells and was maintained when tested at day 7. The pulsed LAK cells were capable of significantly lysing 11 different tumor targets tested and flow cytometric analysis revealed that pulsed LAK cells were phenotypically similar to nonpulsed LAK cells. Serum obtained from cancer patients undergoing IL-2/LAK cell therapy did not inhibit the maturation of the pulsed mononuclear cells into LAK cells. Interestingly, only PBMC obtained from cancer patients receiving in vivo IL-2 infusions could be induced to generate the same levels of cytolytic activity as those in nonpulsed cells using this pulse procedure. PBMC obtained from healthy, normal donors could not be pulsed to the same levels of activation as nonpulsed LAK cultures. Our study demonstrates that for the generation of maximum LAK cell cytolytic activity, LAK cell precursors must be primed in vivo with IL-2. Implementation of this procedure could eliminate the high cost of cell culture which normally accompanies IL-2/LAK cell therapy. Such an approach could make IL-2/LAK cell therapy more accessible for cancer patients.

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