Use of an extracellular matrix material as a vaccine carrier and adjuvant.

BACKGROUND: The addition of adjuvants frequently enhances the efficacy of vaccine preparations. Interest in the use of vaccines as a means to treat cancer has led to the search for improved adjuvants. Because cancer vaccines based on whole cell preparations might benefit from an adjuvant which enhances expression of antigens expressed during tumor cell growth, we evaluated the utility of an extracellular matrix material, porcine small intestinal submucosa (SIS), as a cancer vaccine adjuvant. MATERIALS AND METHODS: After tumors were produced in Lobund-Wistar (LW) rats by subcutaneous administration of PAIII prostate adenocarcinoma cells, rats underwent surgical debulking of the tumor mass. Groups of ten rats were then vaccinated directly on the tumor bed with glutaraldehyde-treated tumor (GFT) cells harvested from a PAIII tumor; a 2 x 2 cm section of glutaraldehyde-treated SIS; or a 2 x 2 cm section of SIS on which harvested tumor cells were grown for either 3 days (GFT-S3) or 28 days (GFT-S28) and then treated with glutaraldehyde. In addition, a group was left untreated after debulking. RESULTS: When tumors and lungs were harvested 21 days later, there were no significant differences between mean tumor weights of rats vaccinated with GFT cells or SIS and those which were left untreated. In contrast, rats vaccinated with GFT-S3 had a significant (p<0.01) reduction of greater than 65% and 58% in mean tumor weight compared to untreated rats and GFT cell-vaccinated rats, respectively. GFT-S28 rats had a significant (p<0.05) reduction of 59% and 49% compared to untreated rats and GFT cell-vaccinated rats, respectively. There was no significant difference in mean tumor weight between GFT-S3 and GFT-S28 rats. Furthermore, while most untreated rats had at least one metastatic focus in the lungs, a reduction was seen in rats vaccinated with GFT (7/10 positive), GFT-S3 (2/5 positive) and GFT-S28 (2/5 positive) cells. CONCLUSION: SIS enhanced the efficacy of a tissue vaccine for prostate cancer, demonstrating the potential utility of extracellular matrices as novel vaccine adjuvants.

Inhibition of prostate cancer metastasis by administration of a tissue vaccine.

Immunotherapy by vaccination represents a novel method for treatment of cancer. In this regard, vaccines with the broadest possible menu of relevant antigens stand the greatest chance of success. Tissue vaccines are composed of material harvested directly from tumors and contain not only antigens associated with neoplastic epithelium, but also those that may be unique to in vivo growth and antigens associated with the tumor stroma. To test the hypothesis that a tissue vaccine, produced by glutaraldehyde fixation of harvested syngeneic prostate tumors (GFT vaccine), could be used for treatment of prostate cancer, male Lobund-Wistar (LW) rats were treated with methylnitrosourea (MNU) and testosterone propionate to induce autochthonous prostate tumors. Tumor-bearing rats were randomly assigned to one of three treatment groups: no treatment (11 rats); vaccination with media (10 rats); or vaccination with the GFT vaccine (19 rats). Vaccination was given initially with Freund's complete adjuvant and booster doses were given with incomplete Freund's adjuvant every week until the time of euthanasia. There were no significant differences in mean tumor weight between groups; however, GFT-vaccinated rats had a prolonged survival time; and 4/19 (21%) GFT-vaccinated rats were found to be tumor-free compared to none of the untreated or media-treated controls. Further, pulmonary metastasis occurred in only 5/15 (33%) of GFT-vaccinated rats compared to 10/11 (91%) and 10/10 (100%) of untreated and media-vaccinated controls, respectively. Supernatants of cultured splenocytes from similarly media- and GFT-vaccinated rats demonstrated significant (P < 0.001) increases in IFN-gamma and TNF-alpha from splenocytes of GFT-vaccinated rats, suggesting that GFT vaccination stimulates a Th1 response. In summary, treatment of tumor-bearing rats with a tissue vaccine stimulated a protective immune response that resulted in complete tumor regression in 21% of animals and reduced the number of animals with any evidence of metastasis by nearly 70%. These results suggest that tissue vaccines may be useful for the treatment of prostate cancer.

Immunization with a tissue vaccine enhances the effect of irradiation on prostate tumors.

Recent studies on immunotherapy as a means to treat prostate cancer presents an interesting opportunity for combination therapy with radiation. This work was undertaken to determine if immunization with a prostate cancer tissue vaccine could enhance the effect of radiation treatment. Groups of Lobund-Wistar (LW) rats were subcutaneously administered PAIII prostate cancer cells (Day 0). Tumor-bearing rats were then either left untreated, vaccinated on Days 11 and 14 with a vaccine composed of glutaraldehyde-fixed harvested tumor tissue (GFT), irradiated with 15 Gy on Days 21 and 23 (Irr), or vaccinated with the GFT vaccine on Days 11 and 14 and irradiated on Days 21 and 23 (GFT/Irr). The tumors were measured on Day 11 and at the time of euthanasia (Day 30) and tumor volume was calculated. On Day 30, the tumors were harvested, weighed and fixed for histopathological evaluation. The mean tumor weight was significantly less (p < or = 0.05) in the Irr rats (7.21 g) compared to the untreated (13.04 g) and GFT-treated (10.64 g) rats. In contrast, the mean tumor weight of the GFT/Irr rats (3.37 g) was significantly less than the untreated and the GFT-treated tumors (p < or = 0.001), as well as the Irr tumors (p < or = 0.01). The GFT/Irr rats were the only group in which the tumor volume decreased during the study (14% decrease) compared to the untreated (147% increase), the GFT-treated (115% increase), and the Irr (12% increase) rats. Immunization with a tissue vaccine prior to radiation treatment enhances the therapeutic effect of radiation.

Prevention of human PC-346C prostate cancer growth in mice by a xenogeneic tissue vaccine.

Vaccination, as an approach to prostate cancer, has largely focused on immunotherapy utilizing specific molecules or allogeneic cells. Such methods are limited by the focused antigenic menu presented to the immune system and by immunotolerance to antigens recognized as "self". To examine if a xenogeneic tissue vaccine could stimulate protective immunity in a human prostate cancer cell line, a vaccine was produced by glutaraldehyde fixation of harvested PAIII prostate cancer cells tumors (GFT cell vaccine) from Lobund-Wistar rats. Immunocompetent Ncr-Foxn1 mice were vaccinated with the GFT cell vaccine four times, 7 days apart. The control animals were either not vaccinated or vaccinated with media or glutaraldehyde-fixed PC346C human prostate cancer cells and adjuvant. About 8 days after the final boost, serum and spleens were harvested. The splenocytes were co-incubated with PC346C cells and then transplanted orthotopically into sygneneic immunodeficient nude mice. About 10 weeks later, the prostates were weighed and sampled for histolologic examination. The spleens were harvested from additional mice, and the splenocytes were cultured, either with or without pulsing by GFT cells, and the supernatants harvested 72 h later for cytokine analysis. Results showed that vaccination with GFT cells resulted in increased serum antibody to a PAIII cell lysate; reduced weight of the prostate/seminal vesicle complex and reduced incidence of prostate cancer in nude mice; increased splenocyte supernatant levels of TNF-alpha, IL-2, IFN-gamma and IL-12, cytokines associated with Th1 immunity; and increased splenocyte supernatant levels of IL-4 and IL-10, cytokines associated with Th2 immunity. In summary, the results suggest that use of a xenogeneic tissue vaccine can stimulate protective immunity against human prostate cancer cells.