To examine the role of cancer-derived CS on tumor-specific CD4+ T-cell responses, we expressed the I-Ab molecule covalently bound to OVA323–339 (I-Ab/OVA complex; Fig. 4C) as an ‘artificial tumor-specific antigen’ on E0771 and 3LL with or without Sult2B1b expression (E0771-SULT-I-Ab/OVA; 3LL-SULT-I-Ab/OVA; E0771-control-I-Ab/OVA; 3LL-control-I-Ab/OVA) (Supplementary Figures 2A and 7). Here, CD4 is linked to cancer.