Search

CD99, a type I transmembrane protein, emerges as a promising therapeutic target due to its heightened expression in T cell acute lymphoblastic leukemia (T-ALL). This characteristic renders it a potential marker for minimal residual disease detection and an appealing target for antibody-based treatments. Previous studies have revealed that a mouse monoclonal antibody, mAb MT99/3, selectively binds to CD99, triggering apoptosis in T-ALL/T-LBL cells while preserving the integrity of healthy cells. By targeting CD99, mAb MT99/3 suppresses antigen presentation and disrupts T cell functions, offering promise for addressing hyperresponsive T cell conditions. To facilitate clinical translation, we developed a humanized ScFv variant of mAb MT99/3, termed HuScFvMT99/3 in "ScFvkh" design. Structural analysis confirms its resemblance to the original antibody, and the immunoreactivity of HuScFvMT99/3 against CD99 is preserved. The fully humanized version of antibody HuMT99/3 was further engineered, exhibiting similar binding affinity at the 10−10 M level and specificity to the CD99 epitope without antigenic shift. HuMT99/3 demonstrates remarkable selectivity, recognizing both malignant and normal T cells but inducing apoptosis only in T-ALL/T-LBL cells, highlighting its potential for safe and targeted therapy. [ABSTRACT FROM AUTHOR]

CD99 was demonstrated to be a potential target for antibody therapy on T-acute lymphoblastic leukemia (T-ALL). The ligation of CD99 by certain monoclonal antibodies (mAbs) induced T-ALL apoptosis. However, the molecular basis contributing to the apoptosis of T-ALL upon anti-CD99 mAb engagement remains elusive. In this study, using our generated anti-CD99 mAb clone MT99/3 (mAb MT99/3), mAb MT99/3 engagement strongly induced apoptosis of T-ALL cell lines, but not in non-malignant peripheral blood cells. By transcriptome analysis, upon mAb MT99/3 ligation, 13 apoptosis-related genes, including FOS, TNF, FASLG, BCL2A1, JUNB, SOCS1, IL27RA, PTPN6, PDGFA, NR4A1, SGK1, LPAR5 and LTB, were significantly upregulated. The epitope of CD99 recognized by mAb MT99/3 was then identified as the VDGENDDPRPP at residues 60–70 of CD99, which has never been reported. To the best of our knowledge, this is the first transcriptome data conducted in T-ALL with anti-CD99 mAb engagement. These findings provide new insights into CD99 implicated in the apoptosis of T-ALL. The identification of a new epitope and apoptosis-related genes that relate to the induction of apoptosis by mAb MT99/3 may serve as a new therapeutic target for T-ALL. The anti-CD99 mAb clone MT99/3 might be a candidate for further development of a therapeutic antibody for T-ALL therapy. [ABSTRACT FROM AUTHOR]