Paroxysmal nocturnal hemoglobinuria associated with in vitro inhibition oferythropoiesis by bone marrow T lymphocytes

Background: The etiology of bone marrow failure, a prominent feature of par oxysmal nocturnal hemoglobulinuria, is presently unknown. Objectives: To evaluate the possible influence of cellular immune mechanism s in the bone marrow failure of PNH. Methods: We studied marrow erythroid colony formation in a patient with par oxysmal nocturnal hemoglobinuria without hypoplastic/aplastic marrow compli cations. Results: In vitro assays revealed a pronounced inhibition of primitive eryt hroid (BFU-E) progenitor cell growth by marrow T lymphocytes. Removal of T cells prior to culture resulted in a 4.5-fold enhancement of BFU-E numbers. Reevaluation of in vitro erythropoiesis during steroid administration indi cated a persistent, albeit less prominent, T cell inhibitory effect. Conclusion: Our findings provide the first direct evidence for a cellular i mmune inhibitory phenomenon accompanying PNH.