PURPOSE: Proper induction of the T-helper type 1 immune response is required for effective bacillus Calmette-Guérin immunotherapy for bladder cancer. Interleukin-10 down-regulates the T-helper 1 response and is associated with bacillus Calmette-Guérin failure. We investigated whether blocking interleukin-10 receptor 1 would enhance the bacillus Calmette-Guérin induced T-helper type 1 immune response and anti-bladder cancer immunity in a mouse model. MATERIALS AND METHODS: Splenocytes were incubated with bacillus Calmette-Guérin or bacillus Calmette-Guérin plus control IgG1, anti-interleukin-10 receptor 1 mAb or anti-interleukin-10 neutralizing mAb, followed by enzyme-linked immunosorbent assay of interferon-γ production. Bladder RNA was extracted after intravesical bacillus Calmette-Guérin plus intraperitoneal IgG1 or anti-interleukin-10 receptor 1 mAb and analyzed by reverse transcriptase and/or quantitative polymerase chain reaction. Urine was collected and analyzed by enzyme-linked immunosorbent assay. Mice bearing a luciferase expressing MB49 orthotopic tumor were treated with intravesical bacillus Calmette-Guérin plus intraperitoneal IgG1 or anti-interleukin-10 receptor 1 mAb. Tumor response was assessed by bioluminescent imaging and bladder weight measurement. RESULTS: Bacillus Calmette-Guérin plus anti-interleukin-10R1 mAb induced significantly higher interferon-γ production by splenocytes than bacillus Calmette-Guérin plus anti-interleukin-10 mAb. Bacillus Calmette-Guérin plus anti-interleukin-10 receptor 1 mAb also induced significantly higher interferon-γ mRNA and protein in bladder and urine, respectively, in a dose dependent manner. Treatment with phosphate buffered saline, bacillus Calmette-Guérin plus control IgG1 and bacillus Calmette-Guérin plus anti-interleukin-10 receptor 1 mAb showed a 0% tumor-free rate with a 20% death rate, a 20% tumor-free rate with a 20% death rate and a 40% tumor-free rate with a 0% death rate, respectively. Bladder weight also revealed the effect of anti-interleukin-10 receptor 1 mAb on the bacillus Calmette-Guérin induced bladder tumor response. CONCLUSIONS: Anti-interleukin-10 receptor 1 mAb enhanced the bacillus Calmette-Guérin induced T-helper type 1 immune response and anti-bladder cancer immunity. A humanized form of this mAb warrants future investigation for bacillus Calmette-Guérin treatment of bladder cancer.