Introduction:

Regulatory T cells (Treg) are vital in the development and maintenance of immune tolerance.  They function to dampen immune responses and their dysfunction leads to multi-organ autoimmune disease. In cancer, Treg are known to play key roles in the development of cancers including lung, breast, head and neck, and others.  Treg are believed to be used by the tumors to aide in immune evasion.  In bladder cancer, clinical studies have shown an increase in Treg in the tumor or blood of patients correlates with a worse prognosis.  Herein we determine whether Treg play a key role in the development of bladder cancer.

Methods:

Female wild type C57BL/6 mice or transgenic DEREG mice (that express a diptheria toxin [DT] receptor whenever Foxp3, the driver of a Treg phenotype, is expressed) were used for all experiments.  Metastatic cancer was induced by injecting 0.5 x 10⁶ MB49 bladder tumor cells via tail vein into mice on the day of surgery.  Orthotopic (bladder) cancer was induced by catheterizing the bladders of female mice and injecting poly-L-lysine followed by 0.08x10⁶ MB49 cells at day 0.  Treg were depleted in DEREG mice with administration of 50g/kg DT given intraperitoneally every 4 days. Mice were sacrificed at days 21-26 and bladders, lungs, and bladder draining lymph nodes (BLN) were harvested for weight and flow cytometric analysis.

Results:

In mice that received both orthotopic and intravenous bladder tumor challenge, Treg were highly present in the bladder tumors but not the lymph nodes or lung (Fig 1).  In DEREG mice challenged with orthotopic bladder cancer, depletion of Treg with DT administration abrogated the development of bladder cancer (Fig 2A).  Additionally, Treg depleted mice had an increase in the number and percentage of antigen specific CD8+ T cells in the bladder draining lymph nodes as well as an increase in activated CD4+ T cells (Fig 2B).

Conclusion:

Regulatory T cells are necessary for bladder cancer development in the orthotopic model of bladder cancer.  The Treg appear to function in an antigen-specific manner, but pan-T cell activation cannot be excluded.  Development of immunotherapies targeting Treg in the bladder may represent a novel cancer therapeutics.

Funding: AUA Care Foundation and CPRIT Training Grant