Purpose: Genetically regulated host response to intravesical Bacillus Calmette Guerin (BCG) immunotherapy was assessed using the murine bladder tumor MM45T in Bcgr and Bcgs inbred congenic strains of mice.
Materials and methods: Tumor detection and monitoring of treatment response to BCG was carried out using magnetic resonance imaging (MRI) of BALB/c (Bcgs allele) and BALB/c. CD2 (CD2) (Bcgr allele) mice implanted orthotopically with MM45T tumor cells. Intravesical BCG instillation (3 doses per week for 3 weeks) was used as prophylaxis against tumor implantation in both Bcgr and Bcgs strains and as definitive treatment against MRI-confirmed established tumors. Tumors implanted in both strains of untreated mice served as controls. Intravesical injection of BCG was also performed in established heterotopic subcutaneous tumors in both strains. Immunologic response in all groups was assessed by flow cytometric analysis of the bladder irrigation fluid cell composition, measuring CD4+ (helper/inducer) and CD8+ (cytotoxic/ suppressor) cell subsets.
Results: Intralesional injection of BCG into established heterotopic tumors showed growth inhibition in the Bcgs strain but not in the Bcgr strain. Intravesical BCG treatment against established orthotopic tumors showed significant tumor regression in the Bcgs strain compared to control but there was no effect in the Bcgr strain.
Conclusion: The differential anti-tumor activity of BCG in the Bcgs and Bcgr congenic murine strains supports the notion that Bcg gene-controlled responsiveness to BCG innoculation determines, at least partially, the host response to immunotherapy. These results have potential clinical significance in patient selection for intravesical therapy for bladder cancer.