CD33 and leukemia: In the past, therapeutic monoclonal antibodies (mAbs) [e.g., rituximab (anti-CD20), cetuximab (anti-EGFR), lintuzumab (anti-CD33), and alemtuzumab (anti-CD52)] against the corresponding surface antigens on leukemia cells have positively contributed to the treatment but still lead to the development of resistance and an unsatisfactory response rate.