Pro- and Antiapoptotic Proteins Expression on Bone Marrow and Peripheral Blood CD34+Cells in Acute Leukemia (AL) Patients

Abstract 4996

It was shown that drug resistance, poor-risk cytogenetics and poor prognosis in AL is associated with high level of Bcl-2 expression and low Bax/Bcl-2 ratio (<0,3). Fas-antigen (CD95) as a protein triggering the extrinsic apoptotic pathway is differently expressed on hematopoietic precursors. More immature CD34+/CD38- AML blast cells have lower expression of Fas/Fas-L and lower Fas-induced apoptosis than CD34⁺/CD38⁺cells. CD34⁺/CD38⁻ leukemia precursors also have a reduced sensitivity to daunorubicin in vitro and increased expression of multidrug resistance genes (mrp/lrp). CD34+ leukemia cells have not yet been properly characterized regarding the expression of angiotensin converting enzyme (ACE) which regulatory influence on hematopoiesis is now beeing extensively investigated. ACE expression on blast cells is high, but it's still unknown how CD34+ACE+ leukemia cells behave after chemotherapy. Recent publications indicate that CD34+ACE+ hematopoietic precursors transplanted into NOD/SCID mice contribute 10-fold higher numbers of multilineage blood cells than their CD34+ACE- counterparts.

We have studied the dynamics of Bcl-2, Bax, CD95 and ACE expression on CD34+ cells in peripheral blood (PB) and bone marrow (BM) in AL pts during treatment. PB and BM samples were collected before and on +36 day after chemotherapy. The antigens were detected by flow cytometry using monoclonal antibodies. We calculated 10 000 cells in each sample.

19 pts were included in the study: 10 - AML and 9 - ALL. The control group comprised 8 healthy donors. At time of diagnosis there were 40±5,7% of CD34+ cells in BM and 26±4,9% - in PB. There was no significant difference between AML and ALL. CD34+ cells in BM and PB of healthy donors constituted 1,6% and 0,27%, respectively. After induction therapy (+36 day) CD34+ cells decreased in BM to 6,1%±3,3 (p=0,0001), in PB to 3,7%± 2,7 (p=0,0008) in all pts. The data on antigens expression on CD34+ cells of BM and PB are presented in table 1 

CD34/Bcl-2 expression in BM in AML pts is significantly higher (p=0,04) at the diagnosis comparing with donors. CD34/Bcl-2 expression in PB in AML pts and in BM and PB in ALL pts is higher too, but not significantly. This expression level decreased substantially in BM and PB in AML pts on +36 day comparing with day 0 (p<0,05). We did not found significant changes in ALL pts. CD34/Bax expression in PB is significantly lower (p=0,003) both in AML and ALL pts in comparison with donors. In AML, not in ALL, chemotherapy caused augmentation of Bax expression in CD34+ BM and PB cells on +36 day.

BM and PB CD34+ cells in donors had different expression characteristics of Bcl-2 and Bax, demonstrating much higher level of pro- and antiapoptotic markers in PB cells. On the contrast CD34+ leukemia cells in BM and PB had similar characteristics regarding CD34/Bcl-2 and CD34/Bax expression. This fact demonstrates the heterogeneity of donor CD34+cells in BM and PB and points that leukemia CD34+cells in BM and PB are rather similar.

CD95 expression on CD34+ BM and PB before treatment is significantly lower (p=0,01, p=0,008) in ALL pts in comparison with donors, and this expression level increased after chemotherapy (p<0,05). CD34/CD95 expression in AML pts is similar with donors, and we didn't find changes after treatment.

CD34/ACE coexpression in BM cells of leukemia pts and donors did not differ much at any time of evaluation. But CD34/ACE expression in PB cells of AML and ALL pts was much lower (p<0,05) than in donors and substantially increased on the day 36.

So, our data demonstrate that Bcl-2, Bax, CD95 and ACE expression on CD34+ cells in AL pts and donors significantly differs. The chemotherapy provokes critical changes in CD34/CD95 expression in BM and PB in ALL pts, CD34/Bcl-2 expression in AML pts and ÑÂ34/ACE expression in PB in all AL pts.