CD19 and cancer: While CAR-T (chimeric antigen receptor T cell) therapy, targeting CD19 and expressing co-stimulatory 4-1BB with CD3ζ signaling domain (151), has achieved great success in enhancing immune responses and tumor regression in hematologic cancers (lymphomas and leukemia), challenges remain in treating CD19-negative tumors, T cell malignancies, and solid tumors (152).