CD4 and cancer: In addition, consistent with efficient recognition of MHC class II-negative cancer cell lines (Fig. 2b), MHC class II and CD4 co-ligation was not involved in the TCR activation, as anti-MHC class II and anti-CD4 blocking antibody showed no effects on recognition by 19305DP whereas these antibodies significantly inhibited SK-MEL-37 recognition by MHC class II-restricted TR-CD4 (CD4SP1) (Fig. 2d).