INDUCTION OF LYMPHOKINE-ACTIVATED KILLER ACTIVITY IN CANINE LYMPHOCYTES WITH LOW HUMAN RECOMBINANT INTERLEUKIN-2 IN-VITRO

Interleukin-2 (IL-2) is an immunostimulatory cytokine that induces act ivation of peripheral blood lymphocytes (PBL) which can mediate augmen ted rumor cytotoxicity. Several regimens using IL-2 as treatment for m etastatic melanoma and renal carcinoma have shown measurable tumor res ponses in 10-20% of human patients. Our overall goals ave to determine the efficacy of IL-2 as an adjuvant treatment for canine tumors. In o rder to evaluate the possibility to extend the use of IL-2 in vivo in the dog, we examined the ability of a clinically relevant (low) dose o f human recombinant IL-2 (100 units/ml) to enhance the tumoricidal pro perties of canine PBL in vitro. This was particularly important consid ering the need to establish the effects on canine PBL by IL-2 at a dos e that is potentially achievable in vivo with acceptable side effects. Our data show, for the first time, the ability to separate canine nat ural killer (NK) cell activity from lymphokine-activated killer (LAK) cell activity (induced with a low IL-2 dose) mediated by canine PBL ag ainst two canine cell lines (CTAC and CML-10) used as targets in 4 vs. 16 hour killing assays. LAK cells generated by stimulation of canine PBL with 100 units/ml of lL-2 for 72 hours, could kill CTAC or CML-10 targets up to 11 or 18 times more efficiently, respectively, than fres h PBL in a 4 hour assay. However, the killing efficiency of the LAK ce lls was only 2- to 3-fold greater than that of the fresh PBL in a 16 h our assay. This apparent reduction in the killing efficiency of the LA K cells was mostly due to increased spontaneous NK activity by the fre sh PBL after 16 hours in culture; both the LAK cells and the fresh PBL (NK cells) mediated a greater overall cytotoxicity after 16 hours tha n they did in the 4 hour assays. These results indicate that a low dos e of human recombinant IL-2 can augment tumor killing by canine PBL in vitro, and suggest that it may be feasible to examine the potential u se of IL-2 as an immunotherapeutic agent in tumor-bearing dogs.