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In most human cells, the average length of telomere repeats at the ends of chromosomes provides indirect information about their mitotic history. To study the turnover of stem cells in patients with bone marrow failure syndromes, the telomere length in peripheral blood granulocytes and lymphocytes from patients with aplastic anemia (AA, n = 56) and hemolytic paroxysmal nocturnal hemoglobinuria (n = 6) was analyzed relative to age-matched controls by means of fluorescence in situ hybridization and flow cytometry. The telomere lengths in granulocytes from patients with AA were found to be significantly shorter than those in age-adjusted controls (P =.001). However, surprisingly, telomere length in granulocytes from AA patients who had recovered after immunosuppressive therapy did not differ significantly from controls, whereas untreated patients and nonresponders with persistent severe pancytopenia showed marked and significant telomere shortening. These results support extensive proliferation of hematopoietic stem cells in subgroups of AA patients. Because normal individuals show significant variation in telomere length, individual measurements in blood cells from AA patients may be of limited value. Whether sequential telomere length measurements can be used as a prognostic tool in this group of disorders remains to be clarified. (Blood. 2001;97:895-900)

Hematopoietic function of some aplastic anemia (AA) patients is dependent on the administration of cyclosporine (CyA). To investigate whether certain HLA class II genes are associated with susceptibility to such CyA-dependent AA, we determined the HLA class II alleles of 59 AA patients treated with CyA. Among 26 patients successfully treated with CyA, 13 required a small dose of CyA to maintain stable hematopoiesis. Of these 13 AA patients, 10 shared an HLA class II haplotype of DRB1*1501-DQA1*0102-DQB1*0602. None of the 13 responders who obtained a sustained remission off CyA therapy possessed this haplotype. In the 10 patients who shared the HLA class II haplotype, single-strand conformation polymorphism analysis of each gene fragment of this haplotype failed to detect a polymorphism in the nucleotide sequence. When the AA patients were assessed for their likelihood to respond to CyA therapy, the response rate in patients with this haplotype (71%) was significantly higher than that of patients with another haplotype associated with HLA-DR2, DRB1*1502-DQA1*0103-DQB1*0601 (36%) and that of patients without HLA-DR2 (35%). These findings indicate that the CyA-dependent response of AA is closely related to an HLA class II haplotype of DRB1*1501-DQA1*0102-DQB1*0602 and suggest that, in AA patients with this haplotype, immune mechanisms play an important role in the pathogenesis of bone marrow failure.

The biphasic shape of the survival curve of 99 patients with aplastic anemia suggested that there may be at least two subgroups of patients with this disease, one with a very short survival and another with a longer survival. Patients who survived for 4 mo or less after the first clinic visit (group A) were different from the patients who survived longer (group B) with respect to their modes of onset, sex, intervals from the onset of symptoms to first clinic visit, and initial hematologic values. These differences suggested that short survival could be predicted from data available at the first contact with the physician. From these measurements, a prognostic index could be calculated which was useful in identifying the patients in group A. Although this method of prognostication needs further testing, if validated, it may prove useful in selecting patients for therapeutic trials and could explain the divergent results in previous studies of androgen treatment of aplastic anemia. When our androgen-treated subjects were compared with subjects with a similar prognostic index who had not received androgens, a beneficial effect of androgen therapy on survival could not be demonstrated.