Significance of CD99 expression in T-lineage acute lymphoblastic leukemia.

BACKGROUND: CD99 was first isolated as an antigen on the T acute lymphoblastic leukemia cells. It has been shown to participate in T cell adhesion and is widely expressed on a variety of hematopoietic and non-hematopoietic cell types. AIM OF WORK: Detection of the expression pattern of CD99 on leukemic and normal T cells and assessing the possibility of its use as a tool for the diagnosis and monitoring of T-ALL cases. METHODOLOGY: We used flow cytometry technique to determine the expression level of CD99 in 62 newly diagnosed TALL patients. Patients were followed up for the presence of minimal residual disease on day 15 and day 42 post-therapy. 20 age and sex matched healthy controls were enrolled in our study. RESULTS: CD99 was expressed in all T-ALL patients, with a higher median expression level when compared to controls (58.5% versus 1.38%, p < 0.001). On day 42 post-therapy, 100% of follow up patients who had initial CD99 expression <= 50% had no minimal residual disease, while only 45.5% of those who had initial CD99 expression > 50% had no minimal residual disease (P = 0.03). There was no significant influence of CD99 expression on the 1-year overall survival probability (P = 0.82). CONCLUSION: CD99 could be used to complement current strategy relying on TdT for diagnosis and monitoring of minimal residual disease during the post-therapy follow up of T-ALL patients. Further studies are needed to confirm these findings.