Generation of cytotoxic effector lymphocytes by MLTC using tumor cells genetically modified to secrete interleukin-2

The in vitro generation of effector lymphocytes cytotoxic to cancer cells, was investigated with a mixed lymphocyte-tumor culture (MLTC) system using genetically modified human cancel cells, followed by stimulation with the i nterleukin (IL)-2 plus immobilized anti-CD3 antibody (IL-2/CD3) system. A g astric cancer cell line, GC022588 (HLA-A2, 24, B35, 55, C1,3), was retrovir ally transduced with the human interleukin (IL)-2 gene (GC/IL-2) or the neo mycin-resistance gene (GC/Neo). The secretion of biologically active IL-2 w as detectable in GC/IL-2 cells brit not in GC/Neo or parental GC022588 cell s. The cytotoxic activity against the parental GC022588 cells of peripheral blood mononuclear cells (PBMC) was greater among PBMC activated with MLTC using GC/IL-2 than among those activated with MLTC using GC/Neo ol without MLTC. The IL-2/CD3 stimulation could efficiently expand the effector lympho cytes without any reduction of the cytotoxic activity generated. The cytoto xic activity generated by this system was reproducible in several HLA-A2- o r A24-positive donors. The effector lymphocytes could kill the other adenoc arcinoma cells expressing HLA-A2 or A24. The phenotypes of the effector lym phocytes generated with the system were 40% CD4+ and 70% CD8+. Both phenoty pes may have been responsible for the cytotoxicity. The removal of adherent cells from PBMC before the MLTC did not affect the generation of cytotoxic ity, whereas neutralization of tumor-derived IL-2 with a specific antibody during the MLTC significantly inhibited the generation of cytotoxicity. The se results suggest that IL-2 gene-transduction augments the immunogenicity of the tumor cells that efficiently stimulate lymphocytes to be cytotoxic, and that the IL-2/CD3 system may be practical for the expansion of effector lymphocytes for use in adoptive immunotherapy for cancer. The mechanism by which IL-2 gene-modified tumor cells stimulate immune reactivity was discu ssed.