The Interim Analysis of the Optima (observation of GPI-anchored protein-deficient [PNH-type]) Cells in Japanese Patients with Bone Marrow Failure Syndrome and in Those Suspected of Having PNH) Study

[Background] Paroxysmal nocturnal hemoglobinuria (PNH) is a hematopoietic　stem cell disorder derived from an acquired mutation of the phosphatidylinositol glycan class A (PIGA) gene in the hematopoietic stem cells which results in the expansion of glycosylphospatidylinositol-anchored protein (GPI-AP)-deficient (PNH-type) hematopoietic cells. PNH-type blood cells are also observed in patients with bone marrow failure (BMF). PNH is conventionally diagnosed when patients have >1% of GPI-AP-deficient erythrocytes and granulocytes determined by flow cytometry. Analyses with high resolution flow cytometry by several different groups have shown that patients with aplastic anemia (AA) or low-risk types of myelodysplastic syndromes (MDS) have small percentages of PNH-type erythrocytes, granulocytes, and/or other lineages of blood cells and that these patients respond better to immunosuppressive therapies compared with BMF patients lacking PNH-type cells. In order to determine the prevalence and clinical significance of PNH-type cells in BMF patients, we conducted a nationwide multi-center prospective observational investigation, the OPTIMA study.

[Methods] From July 2011, Japanese patients with PNH, AA, MDS or BMF of uncertain origin have been prospectively enrolled into the study. Six laboratories in different cities in Japan were assigned as regional analyzing centers and measured the percentages of PNH-type cells in the study population as well as collecting clinical and laboratory data. The high-resolution flow cytometry assessments used a liquid fluorescein-labeled proaerolysin (FLAER) method and a cocktail method with anti-CD55 and anti-CD59 antibodies for the detection of PNH-type granulocytes and erythrocytes, respectively. Periodic blind cross validation tests using a standard blood sample containing 0.01% PNH-type cells and a normal control were conducted to minimize inter-laboratory variations. From analysis of 68 healthy individuals >0.003% of PNH-type granulocytes and >0.005% of PNH-type erythrocytes were considered to be abnormal (Sugimori et al, Blood, 2006).

[Results] As of May 2014, flow cytometry data have been collected from 1685 patients and are included in this interim analysis. Of these patients, 65 (4%) were diagnosed with PNH, 523 (31%) with AA, 459 (27%) with MDS, and 638 (38%) with BMF of unknown etiology. Overall, 154 (9%) patients had ≥1% of both PNH-type erythrocytes and granulocytes: 63 (97%) patients with PNH; 57 (11%) with AA; 18 (4%) with MDS; and 16 (3%) with BMF of unknown etiology. In total, 545 (32%) patients had ≥0.005% PNH-type erythrocytes and ≥0.003% PNH-type granulocytes. These consisted of the followings; all 65 (100%) patients with PNH; 264 (51%) with AA; 76 (17%) with MDS; and 140 (22%) with BMF of unknown origin. Lactate dehydrogenase (LDH) levels ≥1.5 × upper limit of normal range were seen in 14/329 (4%) patients with 0.005-1% PNH-type erythrocytes, 23/62 (37%) patients with 1-10% PNH-type erythrocytes, and 69/71 (97%) patients with ≥10% PNH-type erythrocytes. Periodic blind validation tests revealed that inter-laboratory differences in absolute measurements of PNH-type cells were always within 0.02%.

[Conclusion] A high-resolution flow cytometry-based method, based on the Kanazawa method, that enables the detection of very low percentages of PNH-type cells was successfully transferred to 6 laboratories across Japan. Our results demonstrated that the proportion of patients identified as having small percentages of PNH-type cells differed depending on diagnosis (PNH, AA, MDS, or unknown BMF) and that elevated LDH levels (>1.5 x upper limits of normal range) were more frequently associated with higher percentages of PNH-type erythrocytes. Our findings suggest that the high resolution method is helpful as a diagnostic tool in BMF syndromes, including AA, MDS, and PNH, and may prove useful in understanding the pathophysiology of these disorders.