Circulating Endothelial Cells Are an Indicator of Response to Treatment in Acute Myeloid Leukemia Patients.

Introduction. The circulating endothelial cells (CEC) are proposed to be a noninvasive marker of angiogenesis. The number of CEC in peripheral blood of patients (pts) with acute myeloid leukemia (AML) has not been investigated so far.

Patients and Methods. We evaluated the count of resting (rCEC) and activated (aCEC) CEC and circulating endothelial progenitor cells (CEPC) as well as apoptotic CEC (CEC^AnnV+) in 62 AML pts at the time of diagnosis and 30 healthy controls. Additionally in 26 pts measurements were performed at the time of response evaluation and in 15 pts also 24 h after the first and last dose of chemotherapy. The levels of CEC were correlated with known prognostic factors and response to treatment. CEC were evaluated by the four colour flow cytometry using a panel of previously described monoclonal antibodies and an appropriate analysis gate. CEPC were defined as negative for hematopoietic marker CD45 and positive for endothelial cells markers CD34, CD31 and the endothelial progenitor marker CD133. Resting CEC were defined as CD45−, CD133−, CD31+, CD34+, CD146+ and negative for activation markers (CD105, CD106). CD105 or CD106 positive mature endothelial cells were classified as activated CEC. Apoptotic CEC were CD146 and Annexin V positive.

Results. In untreated AML pts we observed 10-fold higher CEC level (median 29,3/μL) than in the control group (2,95/μL) p<0,0001. The numbers of aCEC (12,7/μL), rCEC (12,3/μL) and CEPC (1,7/μL) were significantly higher in AML pts at diagnosis when compared to healthy controls (aCEC 0,9/μL, rCEC 1,6/μL and 0,1/μL; p<0,0001). CEC^AnnV+ count was also 10-fold higher in AML (1,5/μL) than in controls (0,15/μL; p<0,0001). Both CEC and CEC^AnnV+ counts did not correlate with WBC, hemoglobin and platelets count as well as percentage of blasts in bone marrow and absolute blast count. The positive correlations between CEC number and CEPC count (r=0,435; p<0,001), CEC^AnnV+ count (r=0,502; p<0,01) as well as LDH activity (r=0,328; p<0,02) were found. The significant decrease of aCEC and rCEC numbers 24 hours after the first dose of chemotherapy was noted in patients who achieved complete remission (CR)(p<0,04) but not in pts refractory to treatment. Moreover aCEC, rCEC, CEPC and CEC^AnnV+ counts determined at the time of response’s evaluation were significantly lower then at the time of diagnosis in pts who achieved CR (p<0,01) and did not differ in refractory AML. There was no difference between levels of both viable and apoptotic CEC in AML pts in CR and in the control group (p>0,05).

Conclusions. The CEC and CEC^AnnV+ levels are significantly higher in AML patients than in healthy subjects and correlate with response to treatment. Further investigation should be undertaken to better determine their prognostic and therapeutic value.