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 T-ALL 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.