Glycosylphosphatidylinositol (GPI) Protein-Negative Population of Leukemic Cells in Patients with De Novo Acute Leukemia.

Paroxysmal nocturnal hemoglobinuria (PNH) is considered to be an acquired stem cell disorder affecting all hematopoietic lineages, which lack GPI-anchored membrane proteins, such as CD59, because of abnormalities in the phosphatidylinositol glycan-class A (PIG-A) gene. Also, PNH is one disorder of the bone marrow failure syndromes, including aplastic anemia and myelodysplastic syndrome, which are considered as pre-leukemic states. In this study, to know some condition of pre-leukemic states in patients with de novo acute leukemia, we investigated the expression of CD59 in leukemic cells from 25 patients (female: male=8: 17; mean age, 57.8 ± 19.5 years) with de novo acute leukemia by single-color flow cytometric analysis. In addition, the PIG-A gene from CD59⁻ leukemic cells, sorted by FACS Vantage, in 10 patients with acute leukemia was examined by sequence analysis. All the patients had no past history of PNH. Based on the French-American-British criteria, the diagnosis and subtypes of acute leukemia were determined. The number of patients with subtypes M1, M2, M3, M4, M5, and M7 was 1, 14, 2, 4, 2, and 2, respectively. Two of the patients were classified into acute myeloid leukemia with trilineage myelodysplasia from morphological findings in bone marrow. Chromosomal analyses presented abnormal karyotypes in 14 of 25 patients. Flow cytometric analyses showed that leukemic cells from 16 of 25 patients (64%) had negative populations of CD59 expression and the mean proportion of the populations was 63.3 ± 25.7%, suggesting the possibility that CD59⁻ leukemic cells from patients with de novo acute leukemia might be derived from PNH clones. In fact, the PIG-A gene analyses showed that single (n=4) or multiple (n=6) PIG-A mutations in coding region were found in leukemic cells from 10 patients with CD59⁻ leukemic cells and all of the clones with the PIG-A mutations were statistically minor. Then, various clinacal parameters, including peripheral blood, bone marrow blood, and laboratory findings and the results of chromosomal analyses were statistically compared between 2 groups of patients with (n=16) and without CD59⁻ leukemic cells (n=9). The reticulocyte counts (mean ± standard deviation; 10.5 ± 13.0 x 10⁴/μl) and proportions of bone marrow erythroblast (17.5 ± 13.9%) in patients with only CD59⁺ leukemic cells were significantly higher than those in patients with CD59⁻ leukemic cells (2.5 ± 1.7 x 10 ⁴/μl; p<0.05 and 5.6 ± 6.2%; p<0.01, respectively). The proportions of bone marrow blasts (69.3 ± 21.1%) in patients with CD59⁻ leukemic cells were significantly higher than that those in patients with only CD59⁺ leukemic cells (45.5 ± 19.3%; p<0.02). In conclusion, our findings indicate that leukemic cells derived from PNH clones may be fairly common in de novo acute leukemia patients, suggesting that bone marrow failure as pre-leukemic states may have already occurred in localized bone marrow even in de novo acute leukemia.