Abstract
This study investigates the effect of different cytokines on the growth and antitumor activity of the alpha CD3-induced killer cells CD3-AK, and the potential of the use of CD3-AK cells in cancer immunotherapy. Eight cytokines were tested. Only three (interleukin-2, -4 and -7) were able to support the growth of CD3-AK cells, which selectively killed different tumor targets of diversified origin. Culturing in interleukin-4 (IL-4) or IL-7 alone could maintain the growth of CD3-AK cells for 6-8 days. Only IL-2 could maintain long-term growth, but further addition of IL-4 exerted an inhibitory effect, which terminated the cell growth in 2 weeks. In contrast, despite the fact that IL-7 inhibited the proliferation of CD3-AK cells cultured in IL-2, as determined by [3H]thymidine uptake, the recovery of viable cells was not reduced. In 10 days, CD3-AK cells cultured in IL-2 alone or IL-2 plus IL-7 increased 160- or 176-fold respectively. There is an inverse relationship between the in vitro growth ability and Fas expression on the CD3-AK cells. Further, IL-7 increased the cytolytic activity of the CD3-AK cells two- to threefold. CD3-AK cells could be maintained in IL-2 or IL-2 plus IL-7 for 60-240 days or more. The long-term-cultured CD3-AK cells not only possessed a high level of cytolytic activity, but also showed a wide spectrum of killing with different tumor targets; the normally "resistant" targets, such as EL-4 lymphoma, fibrosarcoma, or melanoma, became susceptible. When the in vivo antitumor activity of the CD3-AK cells against a non-immunogenic tumor. EL-4, was tested by tumor-neutralization experiments, we found that only the long-term-cultured cells gave significant protection, with those maintained in both IL-2 and IL-7 giving the highest degree of protection. Thus, these long-term-cultured CD3-AK cells may have the potential to be used for immunotherapy of a variety of tumors whatever their immunogenicity.