AbstractA serum free lymphokine preparation derived from human buffy-coat mononuclear cells [buffy coat interleukins (BC-IL)], also named Leukocyte Interleukin, Inj. (LI), trade name Multikine™, containing glycosylated interleukin-2 (IL-2) among other interleukins, was tested in three head and neck cancer patients. They responded with tumor regressions associated with increased tumor infiltration of lymphocytes and tumor cell lysis indicating an LI Interleukin-2 induced tumor-specific immune response. to determine whether these responses elicited by LI were IL-2 driven, augmentation of natural killer cells (NKC) and cytolytic T cells (CTL), was tested bothin vitroandin vivo. A single intraperitoneal (ip) injection of LI in adult BALB/c mice at doses of 3, 10, 30 and 100 of IL-2 equivalence International Units per mouse, led to significant (psubcutaneous(sc). Significant (p<0.05 to<0.01) NKC cytotoxicity was achieved by all four routes.In vitroincubation of murine splenocytes with 30 and 100 International Units/ml (IU/ml) of IL-2 equivalent elevated NKC cytotoxicity significantly (p<0.01) at all effector to target cell ratios tested and exceeded the response achieved with rhIFNy. NKC cytotoxicity of human peripheral blood lymphocytes (HPBL) against the K562 human tumor cell was also significantly elevated (p<0.01) at the 30 and 100 IU/ml doses and (p<0.05) at 3 and 10 IU/ml doses. of particular interest was the significant increase of CTL response in HPBL generated by LI. Significant activity (p<0.01) was achieved with levels of 10, 30 and 100 IU/ml at effector to target cell ratios as low as 6 to 1. These results indicate that the LI containing IL-2 led to the significant increase in NKC and CTL cytolytic activities. Relatively lower doses of LI were needed to attain equivalent cytolytic activities as achieved with rhIL-2 or rhIFNy.