A physiological role of interferon (IFN)-beta derived from tumor: tumor growth of a mouse bladder carcinoma line MBT-2 is partially suppressed by autocrine IFN-beta

Retrovirus-mediated transfer of prothymosin gene inhibits tumor growth and prolongs survival in murine bladder cancer

To explore the potential use of prothymosin alpha(ProT), a putative thymic hormone, in gene therapy for bladder cancer, we generated a replication-defective recombinant retroviral vector encoding ProT and tested its antitumor effect on the MBT-2 murine bladder cancer. C3H/HeN mice injected with MBT-2 cells in conjunction with retroviruses encoding ProT exhibited smaller tumor mass, lower tumor incidence and higher survival rate, as well as higher antitumor cytotoxic activities compared with those injected with control viruses. However, such effects were not observed in severe combined immunodeficiency mice, suggesting that ProT exerts antitumor effects through its immunomodulatory activities. Cell growth in monolayer culture and colony formation in soft agar were enhanced in ProT gene-modified MBT-2 clones, and such growth-promoting activities of ProT could be reversed if its nuclear localization signal (NLS) was deleted. To circumvent the proliferation-promoting effect of ProT on tumor cells, a retroviral vector encoding ProT lacking NLS was constructed. Our results showed that retroviruses encoding NLS-deleted ProT was more efficacious than those encoding wild-type ProT in prolonging survival of tumor-bearing mice. This is the first report indicating that ProT, in particular NLS-deleted ProT, delivered by retroviral vectors may be further explored for the treatment of bladder cancer.

Immune response in Stat2 knockout mice

Type I IFNs induce gene expression through Stat1 and Stat2, which can in turn associate either to form Stat1 homodimers or the transcription factor ISGF-3. Stat1 homodimers also transduce signals for IFN-gamma. To explore the unique properties of Stat2 and ISGF-3 in type I IFN signaling, its gene was targeted for deletion. Stat2 null mice exhibit a number of defects in immune response. This includes an increased susceptibility to viral infection and the loss of a type I IFN autocrine/ paracrine loop, which in turn regulates several aspects of immune response. Intriguingly, Stat2-deficient fibroblasts exhibit a more significant defect in their response to type I IFNs than macrophages, highlighting tissue-specific differences in the response to this family of ligands.

Gene expression and antitumor effects following direct interferon (IFN)-gamma gene transfer with naked plasmid DNA and DC-chol liposome complexes in mice

Gene expression was assessed in three types of mouse solid tumors after direct injection of naked plasmid DNA encoding the luciferase gene (pCMV-Luc) and its DC-chol liposome complexes. Intratumoral injection of 5 or 100 micrograms naked pCMV-Luc into subcutaneously inoculated mouse colon tumor (CT-26), fibrosarcoma (MCA-15) and bladder carcinoma (MBT-2) resulted in significant gene expression. A DC-chol liposome formulation (5 micrograms pCMV-Luc complexed with 25 micrograms DC-chol liposome) showed lower level of gene expression in the tumor models. Based on the results using the reporter gene, we examined the antitumor effect after direct interferon-gamma (IFN-gamma) gene transfer into CT-26 tumors. A significant IFN-gamma production and growth inhibition were obtained following direct intratumoral injection of IFN-gamma gene with naked plasmid DNA (pCMV-Mu gamma). Interestingly, pCMV-Mu gamma/DC-chol liposome complexes exhibited more pronounced growth inhibitory effect despite lower IFN-gamma production. Induction of CT-26 specific antitumor immunity by IFN-gamma gene transfer was confirmed by rejection of a CT-26 tumor challenge in the mice showing complete regression of CT-26 tumors after both treatments. Further analysis demonstrated that a significant cDNA-independent induction of IFN-beta and TNF-alpha occurred following injection with the liposome complexes, suggesting a nonspecific suppressive effect on CT-26 tumor growth by these cytokines. Thus, the present study has demonstrated that tumor tissue might be a promising target for direct IFN-gamma gene transfer with plasmid-based nonviral vectors. It is also suggested that immunomodulatory effects by various cytokines could be involved in antitumor effects after direct intratumoral injection of plasmid DNA formulations.