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Regulatory T cells (Tregs) play an important role in immunological self-tolerance and protect the host from autoimmune disease. However, in cancer immunity, Tregs might block anti-tumor immune responses. Therefore, the depletion of Tregs using a specific agent that suppresses its function or population, such as an anti-CD25 antibody, could promote anti-tumor immune responses. In the present study, a cytotoxicity assay, enzyme-linked immunosorbent spot (ELISPOT) assay and measuring cytokine secretion, were used to study the efficacy of Treg depletion by anti-CD25 antibody added to a dendritic cell/tumor cell (DC/TC) fusion hybrid vaccine in a murine pancreatic cancer model. All the mice treated with the combined therapy of fusion hybrid vaccine and Treg depletion rejected tumor growth in a challenging test, although the rejection rate was 20% both for mice that received the fusion hybrids alone or Treg depletion alone. In addition, combined therapy showed a significantly improved survival in comparison to other treatment or control groups. The NK cell activity for DC/TC fusion + Treg depletion was significantly higher than that for the other treatment groups. Cytotoxic T lymphocyte (CTL) activity for DC/TC could potentially be enhanced by the addition of Treg depletion therapy. The treatments including DC/TC fusion induced IFN-gamma secreting effector cells in ELISPOT assays. Furthermore, a cytometric beads array assay used to measure cytokine secretion showed that DC/TC fusion + Treg depletion stimulated the highest levels of IFN-gamma Th1/Th2 ratios and Th17. These results demonstrate that Treg depletion combined with DC/TC fusion hybrid vaccine enhanced the efficacy of immunotherapy in pancreatic cancer by activating CTLs and NK cells.

Dendritic cells (DCs) have been used successfully for inducing effective anti-tumor immune responses in advanced cancer patients undergoing tumor-specific immunotherapy. Appropriate antigen pulsing is a crucial parameter for optimizing the efficacy of immunotherapy as well as anti-tumor protection therapy. Using a murine colon cancer model, we evaluated the anti-tumor efficacy of four different preparations of DC vaccines that contained either a whole tumor or its derivatives, including i) DCs pulsed with tumor lysate, ii) DCs pulsed with necrotic tumor cells, iii) DCs pulsed with apoptotic tumor cells, and iv) DC-tumor cell fusion hybrids. Our data show that DC-tumor cell fusion hybrids and DCs pulsed with irradiated apoptotic tumor cells were more potent than DCs with freeze-thawed necrotic tumor cells for the induction of protective anti-tumor responses. The vaccination of DCs pulsed with tumor lysate failed to elicit any anti-tumor effect. In animals administered with higher doses of a tumor-cell challenge, DC-tumor cell fusion hybrids elicited the most effective anti-tumor response. Among the preparations tested, mice immunized with DC-tumor cell fusion hybrids resulted in the greatest induction of cytotoxicity as measured by the cytotoxic T lymphocyte activity of both the splenocytes and the Thy1.2-positive T lymphocytes. Furthermore, the in vitro production of IFN-gamma polarized to the Th1 cytokine responses was highest in the splenocytes derived from mice vaccinated with DC-tumor cell fusion hybrids. Our results suggest that DC-tumor cell fusion hybrids are more potent inducers of protection against solid tumors, such as colon cancer, than other antigen-loading strategies using whole tumor cell materials.

The calcium-binding protein S100A4 has been characterized as a metastasis-inducing molecule, and regulates cell motility and invasiveness of cancer cells. In order to clarify the significance of the expression of S100A4 as a prognostic factor in gallbladder cancer, S100A4 expression in resected gallbladder cancers were examined using an immunohistochemical staining technique. The relationship between S100A4 expression and clinicopathological factors including prognosis were evaluated. Twenty-five of 60 cases (42%) demonstrated positive staining for S100A4. There was no statistically significant association between S100A4 and histological grade, T, N, M factor, presence of stone, or stage. Kaplan-Meier method showed the 5-year survival rate of the group staining positive for S100A4 (31.5%) to be statistically poorer than that of the group staining negative for S100A4 (78.2%). Also in T2 cases, the 5-year survival rate of the group staining positive for S100A4 (57.1%) was statistically poorer than that of the group staining negative for S100A4 (83.3%). On univariate analysis, positive staining for S100A4 was a significant prognostic factor, and the hazard ratio was 4.05. On multivariate analysis, positive staining for S100A4 is also a significant predictor of prognosis second to T factor. These results indicate that positive staining for S100A4 is useful in assessing the prognosis of patients with gallbladder cancer as well as TNM factors.

A multi-institutional study was performed to evaluate the appropriate duration of oral administration of Carmofur (1-hexylcarbamoyl-5-fluorouracil, HCFU), a 5-fluorouracil (5-FU) derivative, for postoperative adjuvant chemotherapy in patients with colorectal cancer undergoing curative operation. Patients were divided into two: i) short duration group receiving 6 months of HCFU administration and ii) long duration group receiving 1 year of the administration, using a centralized registration system. Among 364 patients entered in this study, 293 evaluable cases were analyzed to investigate the appropriate duration of adjuvant oral chemotherapy. No statistical differences were found in the cumulative 5-year disease-free or survival rates between the groups. However, the actual duration of oral HCFU administration differed in the patients of short and long duration groups from the protocol. Namely, more than 70% of the patients received a different duration of oral adjuvant chemotherapy in each of the groups. Therefore, apart from this division of two groups, correlation between the actual duration of oral HCFU administration and the prognosis was examined in these patients. As a result, it was suggested that oral adjuvant chemotherapy with HCFU would be effective in colon cancer patients when the duration of administration exceeded 330 days. In rectal cancer patients, however, adjuvant chemotherapy with HCFU alone was considered to be not sufficient to affect the prognosis.

The clinical and therapeutic significance of thymidylate synthase (TS) in cancers of the ampulla of Vater have not yet been reported. We immunohistochemically evaluated TS expression in 33 ampullary cancers using an anti-TS antibody. TS expression, clinicopathologic variables, and survival rates were examined and the correlations between these parameters were identified. Fifteen patients were found to express high levels of TS (high TS group), while 18 patients expressed low levels of TS (low TS group). No significant difference was found between TS expression and clinicopathologic factors. Univariate and multivariate analysis revealed that lymph node metastasis and pancreatic invasion are important variables for independently predicting post-operative survival. Although TS expression was not identified as an important factor for postoperative survival, recurrent cases in patients with chemotherapy existed only in the high TS group. In the present study, it was found that TS expression itself in cancers of the ampulla of Vater has no impact in predicting the prognosis of ampullary cancers, but a chemotherapeutic benefit of evaluating TS expression may exist.

The change of proliferating cell nuclear antigen (PCNA) expression was examined in three gastric cancer cell lines, MKN28, MKN45 and MKN74, during continuous or bolus exposure to 5-fluorouracil (5-FU). The cytotoxic effect of 5-FU was almost the same in all the cells. PCNA expression was higher at 24 and 72 h after continuous 5-FU treatment than before treatment. Continuous 5-FU treatment of cells revealed higher expression of PCNA protein and mRNA than did bolus treatment. Flow cytometry revealed that 5-FU increased cell population at the late G1 or S phase 24 and 72 h after treatment. PCNA values at the late G1 and S phase were significantly higher than those at other phases 24 h after treatment. These results suggest that PCNA expression increased due to cell cycle accumulation at late G1 and S phases. Thus PCNA values just after chemotherapy of gastric cancer may be useful in predicting the therapeutic effects of continuous 5-FU administration.

We investigated the effect of stabilized Fab oligomerization by disuccinimidyl suberate on tumor uptake in a pancreatic carcinoma xenograft model in nude mice. Recombinant mouse/human chimeric Fab of the anti-carcinoembryonic antigen (CEA) monoclonal antibody A10, which was previously shown to react specifically with gastrointestinal cancers was used in this study. Fab homo-oligomers (dimers and trimers) chemically linked with ethylene bonds (C-C oligomers) were produced by linkage of chimeric Fab. Oligomers with C-C bonds had similar immunoreactivity against human CEA to parental Fab monomer. In biodistribution studies in animals bearing pancreatic carcinoma xenografts, at 12 and 24 h after infusion, C-C oligomers showed significantly greater uptakes in tumors than Fab or F(ab')2 but lower than IgG. However, oligomers with C-C bonds maintained higher tumor to normal tissue specificity ratios than IgG 24 h post-infusion. In conclusion, tumor uptake was enhanced by Fab oligomerization with C-C bonds, compared to Fab or F(ab')2, perhaps due to the larger molecular size. It was also shown that C-C Fab oligomers could have a potency to deliver high-dose radionuclides with reduced radio-uptakes in normal tissues for the radioimmunotherapy of gastrointestinal carcinomas.

We have investigated tissue- and serum-selective growth or migration activities of two hamster pancreatic carcinoma cell lines, KH-PC and HapT1. In experimental metastatic models, multiple liver metastases were observed for hamsters injected with KH-PC cells, while HapT1 had little tendency to metastasize to the liver. Micrometastases in the lung were observed for both KH-PC and HapT1. Liver extract inhibited the growth of HapT1 cells when compared to a 1% bovine serum albumin control, while KH-PC growth was not inhibited by liver extract. Liver extract showed chemoattractive activity to KH-PC but not to HapT1 cells. No notable differences were shown in either chemoattractive or growth properties of lung extract toward either cell line. These activities of lung extracts were weaker than those of liver extract to KH-PC. Hamster portal vein serum (PVS) had higher mitogenic activity toward both KH-PC and HapT1 cells, compared with serum derived from the vena cava (VS). Chemokinetic activity of PVS or VS toward KH-PC was slightly higher than that toward HapT1. In a chemoinvasion assay with liver extract and PVS, a 6-fold greater number of invasive cells was observed for KH-PC cells when compared to HapT1 cells. In a chemoinvasion assay with lung extract and VS, there was no difference between the cell lines. Our results suggest that complex activities of tissue- and serum-selective growth or migration were related to organ preferential metastasis of these hamster pancreatic carcinoma cell lines.