STIMULATION OF NATURAL-KILLER ACTIVITY IN PERIPHERAL-BLOOD LYMPHOCYTES OF HEALTHY DONORS AND MELANOMA PATIENTS IN-VITRO - SYNERGISM BETWEENINTERLEUKIN (IL)-12 AND IL-15 OR IL-12 AND IL-2

Interleukin-2 (IL-2) and IL-12 modify the functional status of T- and natural killer (NK) cells by regulating proliferation, cytolytic activ ity, cytokine induction, and T-cell subset differentiation. These effe cts are exploited in immunotherapy of cancer patients with IL-2 or IL- 12, which, however, is limited by potentially life-threatening side ef fects. IL-15 shares many of the biological activities of IL-2 and may therefore represent a therapeutic alternative. Here we have compared t he ability of these interleukins to stimulate NK activity in periphera l blood lymphocytes (PBLs) isolated from healthy donors (n = 12) as we ll as from patients (n = 12) suffering from metastatic disease (melano ma). Target (K562) cell lysis was assessed by determining the release of Cr-51 and lactate dehydrogenase (LDH) which gave equivalent results . The NK-resistant DAUDI cell line served as control target. Unstimula ted NK activity was significantly lower in PBLs purified from melanoma patients. However? cytolytic activity was readily stimulated by prein cubation of PBLs (18 h) with cytokines such that the maximum target ce ll lysis was comparable to that seen in PBL of healthy donors. Similar ly, the potency of IL-2 (EC50 = 20.2+/-1.3 and 22.0+/-1.3 u/ml in heal thy donors and patients, respectively), IL-12 (EC50 = 11.0+/-1.1 and 4 .3+/-1.6 u/ml) and IL-15 (EC50 = 0.3+/-0.1 and 0.2+/-0.1 u/ml) was com parable. Importantly, if the preincubation was carried out with cytoki ne concentrations in the ECS, range, the effects of two cytokines (tes ted in all combinations) were additive. A synergism was evident in PBL s obtained both from healthy donors and melanoma patients if concentra tion-response curves for IL-12 were determined in the presence of incr easing concentrations of IL-2 (enhanced efficacy) or IL-15 (enhanced e fficacy and potency). Our observations suggest possible alternatives t o the monotherapy with IL-2 (or IL-12) in cancer treatment. Provided t hat the present findings can be extrapolated to the situation in vivo, the combined administration of IL-12 and IL-15 may be as efficacious as the immunotherapy with IL-2; this approach ought to allow for a mar ked reduction in cytokine dose and thereby improve the therapeutic ind ex.