Cyclin B1 is commonly expressed in the cytoplasm of primary human acute myelogenous leukemia cells and serves as a leukemia-associated antigen associated with autoantibody response in a subset of patients.

OBJECTIVES Aberrant expression of cyclin B1, a cell cycle regulator, is related to prognosis in various human malignancies. Additionally, cytoplasmic expression of cyclin B1 in epithelial malignancies is associated with a specific T-cell response and presumably also a humoral immune response. We therefore investigated (i) whether a similar expression pattern could be detected in native human acute myelogenous leukemia (AML) cells and (ii) whether cyclin B1 specific antibodies could be detected in AML. METHODS AML cell expression of cyclin B1 was analyzed by flow cytometry and confocal microscopy. Humoral immune response in AML patient sera against cyclin B1 was analyzed by ELISA. RESULTS AML cell expression of cyclin B1 was detected for all 42 patients; but the percentage of cyclin B1 positive cells showed a wide variation between patients. Confocal microscopy demonstrated that 32/42 (76%) patient samples showed abnormal cytoplasmic expression. Furthermore, the cytoplasmic expression was maintained after 14 d of in vitro culture and differentiation of the AML cells towards a dendritic cell phenotype. Cyclin B1 specific serum antibodies could be detected for seven of 65 patients with untreated AML. CONCLUSIONS Our studies demonstrate that primary human AML cells show aberrant cytoplasmic expression of cyclin B1 for a majority of patients and a specific humoral immune response was also detected for a subset of patients with untreated leukemia.