Abstract P008: Effect of route of Bacillus Calmette Guérin administration on the tumor immune microenvironment in a mouse model of non-muscle invasive bladder cancer
Authors: Atallah Aline , Grossman Arielle , Tran William , Paré Jean-Francois , Cotechini Tiziana , Graham Charles H. 
Published: January 2022

Abstract
Background: Bladder cancer is the fifth most common cancer in North America, with up to 80% of cases being non-muscle invasive bladder cancer (NMIBC). The standard of care for high-risk NMIBC involves intravesical immunotherapy with Bacillus Calmette Guérin (BCG), a live attenuated bacterium. Unfortunately, most patients do not respond fully to this therapy, resulting in recurrences that sometimes progress to invasive disease. Moreover, our understanding of how BCG exerts its immunotherapeutic effect is incomplete. Using a mouse model of NMIBC, we compared the bladder tumor immune microenvironment (TiME) following intravesical versus intravenous (IV) administration of BCG.
Methods: Female C57Bl/6 mice (6-8 weeks old) were catheterized and 2.5 × 105 MB49 bladder cancer cells were instilled into the bladders after poly-L-lysine treatment. On day 7 post cancer cell instillation, mice with equal tumor volumes were randomized to receive three weekly intravesical or IV administrations of saline or BCG (2 mg/50 μl). Similarly, following catheterization, 50 μl of poly-L-lysine was administered into the bladders of control non-tumor bearing mice, which was then followed by three weekly intravesical instillations of BCG (2 mg/50 μl). In both cohorts, mice were sacrificed on day 23 and bladders were harvested and enzymatically dispersed to generate single-cell suspensions for analysis by polychromatic flow cytometry.
Results: Compared with intravesical BCG treatment, the TiME of mice treated with BCG intravenously was associated with a significantly higher proportion of CD11b− CD3+, CD3−, and CD4− lymphoid cells, as well as a significantly lower proportion of immature myeloid cells. Furthermore, compared with saline IV treatment, BCG administered IV resulted in a significantly larger CD4− T cell population. There were no significant differences in the TiME of intravesically BCG-treated vs intravesically saline-treated tumor-bearing mice. However, compared with control non-tumor-bearing mice treated with saline intravesically, bladders of non-tumor-bearing mice treated intravesically with BCG had a significantly higher proportion of leukocytes, which were predominantly immature myeloid cells.
Conclusion/Significance: These results provide evidence that the route of BCG administration is an important determinant of the composition of the TiME in bladder cancer. Understanding the link between the TiME and BCG therapy may facilitate the development of new approaches to improve outcomes and reduce recurrence rates in patients with NMIBC. This knowledge may also help optimize BCG treatment regimen to avoid unnecessary therapy and induce an optimal anti-tumor immune response.
Citation Format: Aline Atallah, Arielle Grossman, William Tran, Jean-Francois Paré, Tiziana Cotechini, Charles H. Graham. Effect of route of Bacillus Calmette Guérin administration on the tumor immune microenvironment in a mouse model of non-muscle invasive bladder cancer [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2021 Oct 5-6. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(1 Suppl):Abstract nr P008.