Autologous Hematopoietic Recovery with Aberrant Antigen Expression after Allogeneic Bone Marrow Transplantation

Abstract

A 50-year-old woman was admitted in December 2006 with progressive petechiae. Bone marrow (BM) aspiration showed massive proliferation of leukemic myeloblasts with myeloperoxidase staining. Three-color flow cytometry (FCM) with a CD45 gate for the BM cells was performed in our laboratory ; the blasts were positive for CD7, CD11c, CD13, CD15, CD33, myeloperoxidase and HLA-DR and negative for CD34 and CD117. Karyotypes of the BM cells were normal. A diagnosis of acute myeloblastic leukemia (AML)M2 was made on the basis of French-American-British classification. The patient needed standard induction chemotherapy twice to achieve complete remission. Refractoriness to platelet transfusions due to anti-HLA antibody developed. She received an allogeneic BM transplant from an ABOmatched and HLA-DR-mismatched unrelated female donor in September 2007. The conditioning regimen consisted of total body irradiation (2 Gy twice daily for 3 days) followed by cyclophosphamide (60 mg/kg/day for 2 days). On day 0, 4.0 × 10 BM cells per recipient body weight were infused. Tacrolimus and short-course methotrexate were used as prophylaxis for graft-versus-host disease. After BM transplantation, severe pancytopenia persisted. BM aspiration on day 22 revealed marked hypocellularity, suggesting graft rejection. Peripheral blood neutrophils gradually increased from day 50. BM aspiration smears on day 75 showed recovery of the BM cells, especially myeloid cells, without significant morphologic abnormalities and proliferation of myeloblasts, indicating that complete remission was maintained. Chromosomal analysis of the BM cells showed various cytogenetic abnormalities (Table 1). A chimerism-based analysis of the BM cells using short tandem repeat-polymerase chain reaction showed that 100% of the cells originated from the recipient. A diagnosis of autologous (recipient) hematopoietic recovery after graft rejection was made. Multiparametric FCM based on a four-color method (ReproCELL, Yokohama, Japan), which had been approved by the Jichi Medical University Institutional Review Board (no. 06-70), did not show the abnormal expression of antigens in the blasts in the BM on days 75 and 183. However, it showed small populations of CD34CD7 cells and CD34CD15 cells in the blasts on day 253 (Fig. 1). The latter cells were characterized by a high intensity of CD34, which indicates abnormal expression of the antigen. BM aspiration was performed every three to six months ; various chromosomal abnormalities of BM cells were found in each sample (Table 1). After day 253, routine three-color FCM instead of the multiparametric FCM was conducted to analyze phenotypes of the blasts in the BM. This FCM can detect CD34CD7 cells but not CD34CD15 cells because of antibody combinations. The proportions of CD34CD7 cells among the blasts of the BM were as follows : on day 323, 37.2% ; on day 421, 30.9% ; on day 603, 35.5% ; on day 785, 21.5% ; on day 975, 49.2% ; on day 1,149, 36.0% ; and on day 1,232, 24.5%. Although chromosomal abnormalities were detected on and after day 75, obvious dysplastic features associated with myelodysplastic syndrome (MDS) were not found. The patient is clinically well with normal peripheral blood cell counts. There are several reports on autologous (recipient) hematopoietic recovery after allogeneic hematopoietic stem cell transplantation. All patients received total body irradiation