INTERLEUKIN-12 SYNERGIZES WITH INTERLEUKIN-2 TO GENERATE LYMPHOKINE-ACTIVATED KILLER ACTIVITY IN PERIPHERAL-BLOOD MONONUCLEAR-CELLS CULTURED IN OVARIAN-CANCER ASCITIC FLUID

OBJECTIVE: The ascites-associated lymphocytes in ovarian cancer have a ltered immunologic function, and cell-free ascitic fluid has immunomod ulating properties. We determined (1) whether interleukin (IL)-2 could induce lymphokine-activated killer (LAK) activity in normal periphera l blood mononuclear cells (PBMC) cultured in ovarian cancer ascitic fl uid, and (2) whether IL-12 could synergize with IL-2 to generate LAK a ctivity in normal PBMC cultured in ascitic fluid. METHODS: Normal PBMC were cultured in control medium and in media consisting of 50% asciti c fluid (ascitic medium), with and without IL-2 and IL-12. Cell activa tion to assess LAK activity (cell lysis) was determined in a Cr-51-rel ease array with the tumor cell lines FMEX and SKOV3 as target cells. T o determine a possible mechanism for any synergistic effect, the expre ssion of perforin, a pore-forming protein, was determined by Northern blot analysis. RESULTS: Interleukin-2 alone could not induce LAK activ ity in normal PBMC cultured in 50% ascitic fluid for up to 3 days. Int erleukin-12 did mediate some or minimal LAK activity after 1, 2, or 3 days of incubation in control medium or in 50% ascitic fluid. When IL- 2 and IL-12 were used in combination, PBMC cultured for 3 days in 50% ascitic fluid had remarkably high lytic activity against FMEX and SKOV 3 tumor cells. In some experiments, this cytotoxicity was greater than that in PBMC cultured in control medium with IL-2 and IL-12. Lower co ncentrations of IL-12 (1 U/mL) with IL-2 (100 U/mL) were as effective as, and often more effective than, higher doses of IL-12 with IL-2. Ve ry low-dose IL-12 (0.01-0.03 U/mL) in combination with IL-2 also induc ed a range of cytotoxicities. Only the combination of IL-2 and IL-12 u p-regulated expression of perforin mRNA in ascitic medium. CONCLUSIONS : The cytotoxicity responses of PBMC cultured in ascitic fluid in the presence of IL-2 and IL-12 are complex. Low-dose IL-2 and IL-12 can ov ercome the inhibitory property of ascitic fluid on LAK generation and can restore and enhance cytotoxic activity, possibly by reconstituting the expression of perforin. These findings may have therapeutic poten tial.