(A and B) Parental (P) and ZMYND8 KO 4T1 cells were orthotopically implanted into the mammary fat pad of female Balb/c and Rag1 KO mice, respectively. Tumor growth curve is shown in A (n = 5, mean ± SEM). Tumor weight on day 14 is shown in B (n = 5, mean ± SEM). *p < 0.05; ***p < 0.001 by two-way ANOVA with Tukey’s test. (C and D) Flow cytometry quantification of CD8+ (C) and CD4+ (D) T cells in parental and ZMYND8 KO 4T1 tumors harvested from Balb/c mice on day 14 (n = 5, mean ± SEM). (E-G) IHC analysis of CD8+ and CD4+ T cells in parental and ZMYND8 KO 4T1 tumors harvested from Balb/c mice on day 14 (n = 5, mean ± SEM). *p < 0.05 by Student’s t test. (H and I) Parental and ZMYND8 KO 4T1 cells were orthotopically implanted into the mammary fat pad of female Balb/c mice, respectively. Mice were treated with monoclonal anti-CD4/CD8 depleting antibodies (mAbs) or control IgG. Tumor growth curve is shown in H (n = 4, mean ± SEM). Tumor weight on day 26 is shown in I (n = 4, mean ± SEM). *p < 0.05; **p < 0.01, ***p < 0.001 by two-way ANOVA with Tukey’s test. ns, not significant. (J) Immunoblot analysis of ZMYND8 and actin in parental and ZMYND8 KO 4T1 tumors treated with anti-CD4/CD8 depleting mAbs or control IgG.