CD99 tumor associated antigen is a potential target for antibody therapy of T-cell acute lymphoblastic leukemia.

Monoclonal antibodies (mAbs) are an effective drug for targeted immunotherapy in several cancer types. However, so far, no antibody has been successfully developed for certain types of cancer, including T-cell acute lymphoblastic leukemia (T-ALL). T-ALL is an aggressive hematologic malignancy. T-ALL patients who are treated with chemotherapeutic drugs frequently relapse and become drug resistant. Therefore, antibody-based therapy is promising for T-ALL treatment. To successfully develop an antibody-based therapy for T-ALL, antibodies that induce death in malignant T cells but not in nonmalignant T cells are required to avoid the induction of secondary T-cell immunodeficiency. In this review, CD99 tumor associated antigen, which is highly expressed on malignant T cells and lowly expressed on nonmalignant T cells, is proposed to be a potential target for antibody therapy of T-ALL. Since certain clones of anti-CD99 mAbs induce apoptosis only in malignant T cells, these anti-CD99 mAbs might be a promising antibody drug for the treatment of T-ALL with high efficiency and low adverse effects. Moreover, over the past 25 years, many clones of anti-CD99 mAbs have been studied for their direct effects on T-ALL. These outcomes are gathered here.