CD4 and neoplasm: Three days later, we found significantly enhanced proliferation of Ptpn22−/− OT-1 T cells compared to control cells in individual mice (Fig. 3d, **p < 0.01 using two-way ANOVA with Tukey’s post test) showing that Ptpn22−/− T cells indeed proliferate more in response to the weak T4 antigen expressed by the tumor.