Deficiency of glycosylphosphatidylinositol (GPI)-anchored molecules on blood cells accounts for most features of paroxysmal nocturnal hemoglobinuria (PNH) but not for the expansion of PNH (GPI-) clone(s). A plausible model is that PNH clones expand by escaping negative selection exerted by autoreactive T cells against normal (GPI+) hematopoiesis. By a systematic analysis of T-cell receptor beta (TCR-β) clonotypes of the CD8+ CD57+ T-cell population, frequently deranged in PNH, we show recurrent clonotypes in PNH patients but not in healthy controls: 11 of 16 patients shared at least 1 of 5 clonotypes, and a set of closely related clonotypes was present in 9 patients. The presence of T-cell clones bearing a set of highly homologous TCR-β molecules in most patients with hemolytic PNH is consistent with an immune process driven by the same (or similar) antigen(s) - probably a nonpeptide antigen, because patients sharing clonotypes do not all share identical HLA alleles. These data confirm that CD8+ CD57+ T cells play a role in PNH pathogenesis and provide strong new support to the hypothesis that the expansion of the GPI- blood cell population in PNH is due to selective damage to normal hematopoiesis mediated by an autoimmune attack against a nonpeptide antigen(s) that could be the GPI anchor itself.
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