Immunotherapy of bladder cancer targeting p53

Purpose: Superficial bladder cancer is often responsive to immunotherapy with bacillus Calmette-Guerin (ECG). However, some tumors progress despite BCG treatment, and most of these have mutations in the p53 tumor suppressor gene resulting in its over-expression. Overexpressed p53 is therefore a potential target for immunotherapy. The objective of this study was to demonstrate whether human bladder cancer xenografts in SCID mice could be eliminated by cytotoxic T cells (CTL) which recognize over-expressed p53. Materials and Methods: Murine CTL which are specific for human p53 were previously generated in our laboratory by peptide immunization of HLA A2.1 transgenic mice. These CTL recognize and lyse human tumor cell lines which over-express p53 in the context of HLA A2.1. The p53 over-expressing KLA A2.1(+) human bladder cancer cell line J82 was used to establish subcutaneous or intravesicular tumors in SCID mice. The mice were then administered tail vein injections of 5 x 10(7) p53-specific CTL, control CTL, or phosphate buffered saline(PBS). Results: The subcutaneous tumor mean volume at 5 weeks for the p53-specific CTL treatment group was significantly lower than for both the control CTL or the PBS group (32 mm.(3) versus 185 mm.(3), p = 0.04 and 32 mm.(3) versus 418 mm.(3), p = 0.0001). In the mice with intravesicular tumors, a reduction to nonpalpable tumor size in vivo was seen with specific CTL therapy (14% palpable) versus control CTL treatment (86% palpable), the final tumor volume at necropsy was 127 mm.(3) versus 246 mm.(3) (N.S.). Conclusion: The overall response of the human bladder tumors in the SCID mouse model suggests the possibility of targeting p53 in patients with bladder cancer.