To investigate the effects of tumor-specific B cells on tumor eradication by CD4+ T cells, we set up a mouse model combining B cell receptor transgenic hen egg lysozyme (HEL)-specific B cells capable of antibody isotype switching (SWHEL mouse model [24]) and TCR transgenic moth cytochrome c (MCC)-specific CD4+ T cells (5C.C7 TCR model [25]). Here, CD4 is linked to neoplasm.