1.0 INTRODUCTION AND BACKGROUND 
1.1 Need for novel therapeutics 
Most patients with disseminated and/or locally far-advanced cancer can 
not be cured using conventional therapies Including surgical resection, 
radiation therapy, and chemotherapy. Thus, it is apparent that additional 
therapeutic strategies are needed. We, and others, have previously 
demonstrated that interleukin-2 (IL-2) -based immunotherapy induces clinically 
significant tumor regression in 20 to 30 percent of treated patients who have 
metastatic melanoma or renal cell carcinoma, respectively (Rosenberg et al, • 
1989), Responses have been noted, albeit much less frequently, among treated 
patients wno have other malignancies Including colon carcinoma, ovarian 
carcinoma, breast carcinoma, lung cancer, and non-Hodgkin's lymphoma (Rubin et 
al, 1992). Although a small proportion of patients manifest durable clinical 
responses, prolonged survival, cure, or even palliation have yet to be clearly 
demonstrated. 
To improve the clinical outcome of existing systemic cytokine therapies, 
alternative strategies for immunotherapy have been tested to show their 
efficiency in in vitro and in vivo tumor models. In such studies, we have been 
accumulating evidence which suggests that the cytokine microenvironment at the 
tumor site may determine, in part, the outcome of the immune response (Fearon 
et al, 1990. Gansbacher et al , 1990. Tepper et al, 1989). 
1.2 Interleukin-12 (IL-12) Biology 
IL-12, formerly termed natural-killer cell stimulatory factor 
(NKSF) (Kobayashi et al, 1989) or cytotoxic lymphocyte maturation factor 
(CLMFKStern et al , 1990), is a disulfide - linked heterodimeric cytokine 
composed of a 35 kD light chain (p35) and a 40 kD heavy chain (p40) (Kobayashi 
et al, 1989, Stem et al, 1990). The cDNAs encoding the p35 and p40 chains of 
IL-12 from both the mouse and human have been cloned. Unlike most other 
cytokines, simultaneous transfection of mammalian cells with two different 
f enes is necessary for production of biologically active IL-12 (Wolf et al, 
991. Gubler, 1991). This cytokine exerts a variety of biological effects on 
human T and NK cells in vitro . These Include the ability to synergize with 
IL-2 in augmenting allogeneic CTL response (Wong et al, 1988), LAK activity 
(Stern et al, 1990), and INF-g production from peripheral blood lymphocytes 
(Kobayashi et al, 1989. Chan et al, 1991). IL-12 also directly stimulates the 
production of IFN-g and other cytokines from peripheral blood T and NK cells 
(9,10), enhances the lytic activity of NK cells (Kobayashi et al, 1989; Naume 
et al , 1992), and promotes the expansion of activated NK cells and activated T 
cells (CD4+ and CD8+ subsets) (Gately et al , 1991). IL-12 has also been shown 
to induce primarily a Tul (cellular immune) response in vitro (Hsieh et al, 
1993), In addition to the in vitro results, recent studies with the 
administration of recombinant murine IL-12 to normal mice revealed that IL-12 
enhances NK and CTL activity and induces IFN-g production in vivo (Gately et 
al, 1993). Immunization with IL-12 in a murine Leishmania model suggests the 
role of IL-12 as a potent adjuvant (Afonso et al, 1994). 
Based on these results which suggested profound immunologic effects of 
IL-12 alone or in combination with IL-2, we initiated murine therapeutic 
studies to investigate the possible anti- tumor effect of IL-12 (Tanara et al , 
1994; Nastala et al, 1994). These experiments demonstrated that systemic 
application of IL-12 can suppress and prolong the survival of tumor bearing 
mice even when IL-12 treatment is started as late as 14 days after tumor 
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Recombinant DNA Research, Volume 19 
