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Association of clonal T‐cell large granular lymphocyte disease and paroxysmal nocturnal haemoglobinuria (PNH): further evidence for a pathogenetic link between T cells, aplastic anaemia and PNH

There is mounting evidence to suggest that T‐cell‐mediated suppression of haemopoiesis is a pathogenetic mechanism in three bone marrow failure syndromes: aplastic anaemia (AA), paroxysmal nocturnal haemoglobinuria (PNH) and myelodysplasia (MDS). T‐cell microclones can be detected by sensitive polymerase chain reaction (PCR)‐based methods in all three disorders. Recently, larger clonal populations of T‐cell large granular lymphocytes (T‐LGLs) have been observed in some patients with AA and MDS. Here, we report the development of a large clonal T‐LGL population in a patient with bona fide PNH. In this patient, we defined part of the sequence of the T‐cell receptor (TCR) β‐chain gene, and we have shown that the large T‐LGL population emerged from a background of multiple smaller T‐cell clones. Thus, T‐LGL clones in AA, MDS and PNH probably expand as a result of antigenic stimulation. It is postulated that the antigen driving clonal T‐cell proliferations in these disorders exists on haemopoietic stem cells.