IMMUNOTHERAPY FOR MEDULLARY-THYROID CARCINOMA BY A REPLICATION-DEFECTIVE ADENOVIRUS TRANSDUCING MURINE INTERLEUKIN-2

We have evaluated the feasibility of gene transduction using replicati on-defective adenovirus vector as a novel therapy for medullary thyroi d carcinoma (MTC), a thyroid C cell neoplasm. Replication-defective ad enoviruses were constructed to express murine interleukin-2 (mIL-2) ge ne and Escherichia coli beta-galactosidase (beta-gal; lacZ) gene under the control of the human cytomegalovirus (CMV) promoter (AdCMVmIL2, A dCMV beta-gal) by homologous recombination. The efficiency of transduc tion was evaluated using AdCMV beta-gal at different conditions. The g ene transduction efficiency was dependent on multiplicity of infection , duration of exposure to the virus, and viral concentration. The expr ession of functional mIL-2 in transduced tumor cells was verified both in vitro and in vivo. Two cell lines (rat MTC and mMTC) secreted larg e amounts of functional mIL-2 after transduction, as tested in cytotox ic T lymphocyte (CTL) L-2 cells. When AdCMVmIL2-infected mMTC cells we re injected sc into their host animals, tumors developed in 2 of 10 an imals, in contrast to 9 of 10 animals injected with AdCMV beta-gal-inf ected mMTC cells and all 10 animals injected with parental mMTC cells. Moreover protected animals developed a long lasting immunity against mMTC tumor cells and their splenocytes, showing cytotoxicity to parent al tumor cells, and active natural killer (NK) cell activity. BALB/c-S CID (severe combined immune deficiency) mice were also used to evaluat e the function of NK cells in antitumor activities. No tumor developed in SCID) mice injected with AdCMVmIL2-infected cells, whereas all ani mals injected with either AdCMV beta-gal-infected or parental mMTC cel ls developed tumors. Our data indicate that IL-2 production by MTC cel ls leads to rejection in syngeneic animals and suggest that both cytot oxic T cells and NK cells may play an important role. In addition, tra nsduction of adenoviral vectors into tumor cells produces some nonspec ific antitumor effects.