IN-VITRO AND IN-VIVO CHARACTERISTICS OF HUMAN SQUAMOUS-CELL CARCINOMAOF THE HEAD AND NECK CELLS ENGINEERED TO SECRETE INTERLEUKIN-2

Two human squamous cell carcinoma of the head and neck (SCCHN) cell li nes, PCI-13 and PCI-52, were transduced with the retroviral construct containing human interleukin-2 (IL-2) cDNA and selected for neomycin r esistance in G418 medium. Stably transduced SCCHN cells produced and s ecreted IL-2, which was shown to have biologic activity in a bioassay, using an IL-2-dependent CTLL-2 cell line. By immunohistochemistry, IL -2 gene-transduced PCI-13 cells were strongly positive for IL-2, and b y flow cytometry showed both cell surface and intracytoplasmic express ion of IL-2 protein. Expression of IL-2 mRNA was measured by quantitat ive RT-PCR and found to be considerably increased in transduced SCCHN relative to that in parental cells. There was no difference in express ion of IL-2R between the parental and IL-2 gene-transduced cells, In v itro proliferation of IL-2 gene-transduced tumor cells was consistentl y more rapid than that of parental cells. Sensitivity of the parental and IL-2 gene-transduced targets to lysis or apoptosis mediated by pur ified human natural killer (NK) cells or IL-2-activated NK (A-NK) cell s was comparable as measured in 4-hour Cr-51-release and 1-hour [H-3]t hymidine-release assays, respectively. However, transduced cells were significantly more sensitive than parental cells to these effecters in 24-hour MTT assays, most likely due to IL-2 production by the transdu ced targets. PCI-52 cells selected for in vivo experiments formed larg e subcutaneous tumors in immunosuppressed nude mice. Tumors establishe d by subcutaneous injections of 1 X 10(7) IL-2 gene-transduced cells r egressed completely by day 25, while those formed by parental or LacZ gene-transduced tumor cells grew progressively, Tumor regression was m ediated by numerous mononuclear cells, identified as murine NK cells a nd macrophages by immunohistochemistry, which accumulated around the I L-2-secreting, but not parental, tumors within 5-6 days after tumor ce ll injections. Thus, IL-2 gene-transduced SCCHN cells produce function al IL-2 in vivo in amounts sufficient to support the recruitment to th e tumor site and antitumor activity of cytotoxic effector cells. IL-2- secreting SCCHN cells may be a useful component of vaccines designed t o induce and sustain effector cell activation at the tumor site.