Profound Alterations in expression of PD-1 on CD8⁺ T Cell Accumulation within the Tumor Microenvironment upon Foxp3⁺ T Cell Depletion. In this experiment, DEREG mice (six individuals per group) were injected intraperitoneally with 1 µg DT or PBS 24 h before 1 × 10⁶ ID8 cells injection. Subsequently, 1 µg DT was administered on day 7 following tumor implantation. Control mice were treated with PBS injection. (A and B) On day 14 post DT or PBS injection, we sacrificed tumor-bearing mice that had received either PBS or DT treatment. Tumor-infiltrating lymphocytes were isolated and analyzed via FACS. The frequencies of CD8⁺TIGIT⁺PD-1⁺ (9.248 ± 1.518 vs. 20.52 ± 1.439, p < 0.01) and CD8⁺TIGIT⁻PD-1⁺ (8.482 ± 0.6521 vs. 19.95 ± 1.583, p < 0.01) tumor-infiltrating lymphocytes were calculated, comparing PBS control with DT-treated tumor-bearing mice. (C) The impact of Foxp3⁺ Tregs depletion on tumor growth is depicted (Mean ± SD, n = 4), p = 0.1502 on day 10, p = 0.0018 on day 15, p = 0.001 on day 20, p = 0.0004 on day 25. All data were collected from three independent experiments, and the results are presented as means ± standard deviation