Figure 3.

CD25⁺ T cell depletion before vaccination enhances efficacy of treatment. (A) Survival data of mice challenged subcutaneously with 2.5 × 10³ B16-BL6 tumor cells. Mice received either no treatment (n = 6, ▪), or depleting anti-CD25 on day −4 (n = 6, ⋄) or vaccination with GM-CSF–producing B16 on days 0, 3, and 6. The vaccinated mice were divided over three groups that received the following Ab: CTLA-4 blocking Ab on days 0, 3, and 6 (n = 8, •); depleting anti-CD25 Ab on day −4 (n = 8, ×); or depleting anti-CD25 Ab on day −4 plus CTLA-4–blocking Ab on days 0, 3, and 6 (n = 8, ▴). (B) Survival data of mice challenged subsutaneously (day 0) with 5 × 10³ B16-BL6 tumor cells. Mice received either depleting anti-CD25 Ab on day −4 (n = 6, ⋄) or were vaccinated on days 0, 3, and 6 with GM-CSF–producing B16. The vaccinated mice were divided over two groups that received the following Ab: blocking anti–CTLA-4 Ab on days 0, 3, and 6 (n = 9, •); or depleting anti-CD25 Ab on day −4 combined with blocking anti-CTLA-4 Ab on days 0, 3, and 6 (n = 9, ▴). See Materials and Methods for details. Significant (A, P = 0.025; B, P = 0.0004, log rank test) differences were found between B16-GM-CSF vaccinated mice that received either anti–CTLA-4 Ab (•) or were injected with anti-CD25 Ab plus anti-CTLA-4 Ab (▴). Representative results from two independent experiments are shown.