CD27 and hepatocellular carcinoma: Moreover, we co‐cultured mouse B cells with HCC cells and investigated B cell subtypes, including mature B cells (CD19+B220+CD22+), germinal center B cells (CD19+ B220+CD38+), memory B cells (CD19+ B220+CD27+ CD138‐), and plasma cells (CD19+ B220‐/low CD138+).[21] We found that the proportion of plasma cells was significantly increased when co‐cultured with PRP19 knockout HCC cells; nevertheless, mature B, germinal center B, and memory B exhibited fewer differences (Figure S4C,D, Supporting Information).