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Genome editing by the CRISPR/Cas9 system has recently been used to produce gene knockout lines in many plant species. We applied this system to analyze Japanese gentian plants that produce blue flowers because of the accumulation of a polyacylated anthocyanin, gentiodelphin. Mutant lines in which anthocyanin modification genes were knocked out were examined to assess the contribution of each gene to the blue pigmentation of flowers. The targeted genes encoded anthocyanin 5-O-glycosyltransferase (Gt5GT), anthocyanin 3'-O-glycosyltransferase (Gt3'GT), and anthocyanin 5/3'-aromatic acyltransferase (Gt5/3'AT). The Gt5GT knockout lines accumulated delphinidin 3G, whereas the Gt3'GT knockout lines accumulated delphinidin 3G-5CafG as the major flower pigment. Knocking out Gt5/3'AT resulted in the accumulation of delphinidin 3G-5G-3'G and delphinidin 3G-5G as the primary and secondary pigments, respectively. These results indicated the existence of two pathways mediating the modification of delphinidin 3G-5G in flowers, with one involving a glycosylation by 3'GT and the other involving an acylation by 5/3'AT. The Gt5GT, Gt3'GT, and Gt5/3'AT transformants produced pale red violet, dull pink, and pale mauve flowers, respectively, unlike the vivid blue flowers of wild-type plants. Thus, the glycosylation and subsequent acylation of the 3'-hydroxy group of the B-ring in delphinidin aglycone is essential for the development of blue gentian flowers.

The central nervous system shows tolerance for activated host immune reactions, and this relative unresponsiveness may lessen the efficacy of an immunotherapy for brain tumors. Using interleukin-2 (IL-2)-producing 9L rat gliosarcoma cells (9L/IL-2), we examined whether secretion of IL-2 from subcutaneous (s.c.) and/or intracerebral (i.c.) tumors can elicit augmented immunological responses to brain tumors. Syngeneic rats could reject 9L/IL-2 cells inoculated s.c., but developed 9L/IL-2 brain tumors by i.c. inoculation. The growth of i.c. 9L/IL-2 tumors was, however, significantly retarded compared with that of i.c. wild-type tumors. The growth of i.c. wild-type tumors was significantly suppressed when the rats concurrently received 9L/IL-2 cells s.c. Moreover, most of the rats that were inoculated i.c. with 9L/IL-2 cells did not develop brain tumors when concurrently injected s.c. with 9L/IL-2 cells. Immunohistochemical analysis on i.c. 9L/IL-2 tumors, when the rats were concurrently inoculated s.c. with 9L/IL-2 cells, revealed that migration of CD4+ or CD8+ T cells, monocytes/microglias, and macrophages was markedly augmented to a similar level as found in the s.c. 9L/IL-2 tumors. These results showed that systemic immune responses to brain tumor were induced in an immunologically privileged site by concurrent s.c. inoculation of the same tumors that produce IL-2. The present study may also raise the possibility of a therapeutic strategy for brain tumors by the combinatory expression of IL-2 gene using s.c. immunization followed by direct gene transfer into brain tumors.

Uracil phosphoribosyltransferase (UPRT) of Escherichia coli origin can convert 5-fluorouracil (5-FU), a chemotherapeutic agent widely used for solid tumors, to an active intermediate, 5-fluorouridine-5'-monophosphate, as mammalian orotate phosphoribosyltransferase does. To examine whether the E. coli UPRT gene expressed in tumor cells can confer increased sensitivity to 5-FU, we retrovirally transduced Colon 26 cells, a murine colon carcinoma cell line, with the UPRT gene (Colon 26/UPRT cells) and tested the in vivo antitumoral effect of 5-FU in syngeneic immunocompetent mice. After 5-FU administration, tumors of Colon 26/UPRT cells regressed, whereas those of wild-type cells were unaffected. The mice that once eliminated Colon 26/UPRT tumors after 5-FU treatment rejected wild-type cells that were subsequently inoculated but not irrelevant syngeneic tumor cells. This suicide gene/prodrug system was less efficient in nude mice, suggesting that mature alphabeta T cells play a role in the antitumoral effect. The cytotoxicity mediated by the bystander effect was marginal in this system, contrary to the herpes simplex virus-thymidine kinase gene/ganciclovir system. Therefore, expression of the UPRT gene in tumor cells followed by 5-FU administration is a possible strategy for cancer gene therapy, but potentiation of the bystander effect is required for its therapeutic application.

We investigated the antitumor effects induced by the production of interleukin-12 (IL-12) or IL-18, which influence the function of T helper type 1 cells, in murine colon carcinoma cells (Colon 26). Retrovirally transduced cells with IL-12 genes that encoded both p35 and p40 (Colon 26/IL-12) lost their tumorigenicity when inoculated subcutaneously or intraperitoneally into syngeneic immunocompetent mice. Moreover, the mice that had rejected the Colon 26/IL-12 cells generated protective immunity to wild-type (wt) cells when subsequently challenged. Colon 26 cells transduced with the IL-18 gene (Colon 26/IL-18) could not form subcutaneous tumors in immunocompetent mice, and the mice became resistant to inoculated wt cells. Immunohistochemical analysis revealed that the numbers of blood vessels in Colon 26/IL-12 or Colon 26/IL-18 tumors were markedly reduced, and that the expression of adhesion molecules such as intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 increased on the endothelium in the stroma of Colon 26/IL-12 tumors. The loss of tumorigenicity of Colon 26/IL-12 or Colon 26/IL-18 cells was not observed in immunocompromised mice. However, the survival days of the immunocompromised mice inoculated with Colon 26/IL-12 but not Colon 26/IL-18 cells were significantly longer than those inoculated with wt cells. The secretion of cytokines that stimulate T helper type 1 cells from tumor cells can thereby induce an antitumor response. However, the effector cells involved in these antitumor effects could differentially migrate to the tumors, and the inhibition of angiogenesis may partially contribute to the antitumor responses observed.

We examined the antitumor effect of locally secreted interleukin (IL)-12 or IL-15 on human pancreatic cancer cells (AsPC-1). We subcutaneously inoculated AsPC-1 cells retrovirally transduced with IL-12 or IL-15 cDNA into nude mice. Tumors derived from these cells showed retarded growth compared with those from wild-type (wt) cells. Nude mice inoculated intraperitoneally with the cytokine producers survived longer than those injected with wt cells. These cytokine producers were also tested for their tumor growth in severe combined immunodeficient mice. The tumor growth of IL-12 producers was similarly suppressed as found in nude mice, but the average tumor volumes of IL-15 producers were not statistically different from those of wt tumors. In nude mice that were administered anti-asialo GM1 antibody before the inoculation of the tumor cells, growth retardation of tumors of IL-12 producers remained the same as in untreated animals, but that of IL-15 producers was markedly reduced. Immunohistochemical analysis revealed that CD11b+ cells migrated into the tumors of cytokine producers and that the number of CD31+ endothelial cells within the tumors was not different between IL-12 producers and wt cells. Taken together with other data, it is possible that granulocytes are candidate cells for the IL-12-mediated antitumor effect, and that natural killer cells and gammadelta T cells are involved in the IL-15-induced antitumor effect. We did not observe synergistic effects of these cytokines to suppress subcutaneous tumors.

We examined the antitumor effects caused by murine colon carcinoma cells (Colon 26) transduced with interleukin-15 (IL-15) gene. Although the in vitro proliferation rate of IL-15-secreting Colon 26 (Colon 26/IL-15) cells was not different from that of wild-type (wt) cells, small subcutaneous tumors of Colon 26/IL-15 cells that developed in syngeneic immunocompetent mice regressed spontaneously in contrast to tumors of wt cells. The mice that had eliminated tumors of Colon 26/IL-15 cells rejected wt cells when subsequently challenged. The survival of the mice that had been inoculated intraperitoneally with Colon 26/IL-15 cells was significantly prolonged compared with that of the mice injected with wt cells. However, in an experimental lung metastasis model, the survival of the mice inoculated with Colon 26/IL-15 cells remained the same as that of the mice inoculated with wt cells. The inoculation of Colon 26/IL-15 cells into immunocompromised nude or severe combined immunodeficient mice produced tumors, but the survival of the immunocompromised mice was significantly longer than that of the mice inoculated with wt cells. The nude mice inoculated with Colon 26/IL-15 cells also survived longer than the severe combined immunodeficient mice with Colon 26/IL-15 cells. Depletion of natural killer cells in nude mice with anti-asialo GM1 antibody did not influence the survival of the mice injected with Colon 26/IL-15 cells. Immunohistological examination revealed that CD31+ cells migrated into tumors of Colon 26/IL-15 cells that developed in immunocompetent and immunocompromised mice. Taken together, our results indicate that an inoculation of IL-15-producing tumor cells can produce antitumor effects that are mediated by a variety of immunocompetent cells.

We have examined the antitumor effect of the retrovirally expressed interleukin-2 (IL-2) gene in murine colon carcinoma cells (Colon 26) on a disseminated model within the peritoneal cavity. Intraperitoneal injection of IL-2-producing Colon 26, but not wild-type cells, into syngeneic mice did not cause animal death and conferred T-cell-dependent, tumor-specific protective immunity on the inoculated mice. Direct administration of the retrovirus harboring IL-2 gene into the peritoneal cavity of the mice that had intraperitoneal tumor of wild-type cells significantly prolonged the survival of the mice compared with that of the mice that received control retrovirus. In the surviving mice treated with the retrovirus we also observed the induction of protective immunity with tumor specificity. Integrated retrovirus DNA was not detected in any organs examined. Thus, in vivo IL-2 gene transfer by retrovirus enabled tumor-bearing mice to generate antitumor immunity without unnecessary retroviral insertion into host genome.

We have examined the antitumor effect of murine neuroblastoma cells (C1300) engineered to produce cytokines. Retrovirally transduced cells with human interleukin-2 (IL-2) or murine GM-CSF gene, but not murine IL-4 gene, abolished their tumorigenicity in syngeneic mice, although their in vitro growth rate and expression of class I antigens of the major histocompatibility complex were unchanged. Inoculation of wild-type cells into the mice, which had rejected IL-2 or GM-CSF producers, did not develop tumors, indicating that protective immunity was induced. In an experimental hematogenous metastasis model, we found that the numbers of metastatic foci in the liver caused by intravenous administration of IL-2 or GM-CSF producers were significantly reduced compared with those by the injection of wild-type or vector virus-transduced cells. No significant differences in their adhesiveness to extracellular matrices and ability to differentiate were observed among parent and transduced cells. Thus, these results indicate that IL-2 or GM-CSF secretion, in the vicinity of neuroblastoma cells, produced antitumor effect and reduced metastatic ability.