Abstract 5386: Immunotherapy of bladder cancer using bacillus calmette guérin (BCG): Generation of cytotoxic T-cells is BCG strain dependent

Abstract

Introduction: Forty years ago Zbar and colleagues demonstrated that bacillus calmette guérin (BCG) is capable of provoking an immune response against experimentally induced tumors. The conditions for successful tumor immunity were defined by a i) limited number of tumor cells in ii) close contact with a iii) sufficient number of bacteria and iv) the ability of the organism to mount a BCG specific immune response. These findings led to the development of what is currently the standard of care for the treatment of patients with non-muscle invasive bladder cancer. Whether the genetic drift between BCG strains that are routinely used in treatment protocols for bladder cancer affects the generation of successful tumor immunity is unknown. Here we compared two of the commonly used BCG strains (Connaught and Tice) in the treatment of bladder cancer in an animal model. Methods: Naïve or bladder cancer bearing (orthotopic implantation of syngeneic MB49 cells) Bl/6 mice received either a single s.c. injection or weekly intravesical instillation of 107 CFUs of BCG Tice or Connaught. Twelve days after the 4th intravesical treatment or after the single s.c. immunization, the bladders, spleens and draining lymph nodes (DLN) were removed, enzymatically digested and the resulting cell suspensions analyzed by flow cytometry, including assessment of BCG specific CD8+ T-cells. Lymph node extracts were cultivated for the enumeration of BCG CFUs. Tumor bearing animals were assessed for their overall survival. Results: In non-tumor bearing animals, BCG Connaught lead to a more robust influx of adaptive immune cells into the bladder and primed significantly more BCG specific cytotoxic CD8+ T-cells. Compared to BCG Connaught, BCG Tice was less capable to disseminate into the draining lymph nodes (DLN), and induced less Th1 polarized CD4+ T-cells in the bladder, DLN and spleens, as assed by intracellular T-bet staining. These findings were independent of BCG preparation (clinical grade versus laboratory grade) and were seen for identical treatment doses. Finally, mice, orthotopically challenged with MB49 bladder cancer cells, showed significantly better survival if treated with BCG Connaught as compared to BCG Tice. Conclusion: Here we show that different BCG strains significantly impact the immunological response of adaptive immunity. Along with a stronger Th1 immune response, favoring the generation of cytotoxic T-cells, BCG Connaught improves survival as compared to BCG Tice in vivo. These findings implicate potential consequences for clinical practice and corroborate testing of different BCG strains in prospective clinical trials. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5386. doi:1538-7445.AM2012-5386