Highly homologous T-cell receptor beta sequences support a common target for autoreactive T cells in most patients with paroxysmal nocturnal hemoglobinuria

Abstract

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-␤) 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-␤ 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. IntroductionParoxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal disorder of the hematopoietic stem cell (HSC) 1 characterized by 3 clinical hallmarks: intravascular hemolysis, tendency to venous thrombosis, and variable degrees of bone marrow failure. [2][3][4] The primary molecular lesion responsible for PNH is a somatic mutation of the X-linked PIGA gene in HSCs, 5,6 resulting in either complete or partial deficiency of all glycosylphosphatidylinositol (GPI)-linked proteins from the cell membrane of the progeny of the mutated HSC (GPI Ϫ ). 7,8 The deficiency of the GPI-linked proteins (including the complement-regulating proteins CD59 and CD55) from the surface of blood cells explains the intravascular hemolysis 9 and probably underlies the increased tendency to venous thrombosis. 10 However, a PIGA gene mutation per se does not explain the bone marrow failure and the expansion of the GPI Ϫ clone. In fact, very rare GPI Ϫ blood cells are present in healthy subjects, 11 but only in PNH patients do the GPI Ϫ cells expand and contribute to hematopoiesis to various degrees, side by side with normal (GPI ϩ ) hematopoiesis. 12,13 Clinical observations, 14,15 in vitro hematopoietic colony studies, 16,17 and data from PNH mouse models [18][19][20] indicate that GPI Ϫ HSCs do not have an absolute growth advantage. The close relationship of PNH to idiopathic aplastic anemia (IAA) has suggested that autoreactive T cells against HSCs believed to be responsible for IAA may be at work also in PNH. Specifically, it has been hypothesized that in PNH autoreactive T cells destroy selectively GPI ϩ (normal) HSCs, whereas GPI Ϫ (PNH)HSCs can escape T-cell-mediated damage, thus being able to survive and expand. 21 In r...

A Paroxysmal Nocturnal Haemoglobinuria Progress with Waldenström Macroglobulinemia Along with T Cell Monoclonal Expansion

“…The underlying pathogenesis directly pointed to undefined immune dysregulation [11]. Lucia Gargiulo et al [12] found highly homologous T-cell receptor beta sequences in most PNH patients which supported the hypothesis that autoreactive T cells selective damage the GPI-negative hematopoiesis. AM Risitano [13] definitely pointed out the large granular lymphocyte-like clonal expansion induced the antigendriven lymphocyte attack on hematopoietic progenitors in PNH.…”

Paroxysmal nocturnal hemoglobinuria and myelodysplastic sydromes: clonal expansion of PIG-A-mutant hematopoietic cells in bone marrow failure

“…Thus, mutations other than JAK2 may determine disease phenotype directly or by co-operating with JAK2 mutations. Analysis of the X-chromosome inactivation pattern of clonality in familial cases of myeloproliferative neoplasm 7 has provided support for this hypothesis.…”

“…In a recent publication, Notaro and colleagues described oligoclonal expansion of cytotoxic T cells, belonging to the same T-cell receptor V-β subfamily; sharing of clonotypes, or the sequence of the antigen-binding region of the T-cell receptor, despite histocompatability antigen differences, was interpreted as the result of a (non-protein) antigen-driven process common to PNH patientspossibly to the GPI anchor itself. 7 In the murine system, we observed marked expansion of specific CD8 cell oligoclones in the marrow and spleen of conditional knock-out animals, reproduced even more dramatically after transplantation; these T cells were neither activated nor associated with active marrow failure and thus appeared to result directly from the induced mutation. …”

Phenotypic and functional characterization of a mouse model of targeted Pig-a deletion in hematopoietic cells

“…32 A decline in regulatory T cells might contribute to promote the selective damage to normal GPI + , but not GPI -, hematopoietic cells potentially mediated by an autoimmune attack. 33 However, in our Pig-a deficient mouse model, inadequate effector T-cell activation may account for the lack of autoimmunity and bone marrow failure despite reduced presence of regulatory T cells.…”

“…In humans, oligoclonal expansion of cytotoxic T cells with highly homologous TCR-β molecules suggests an autoimmune process linked to the pathogenesis of PNH. 33 The nature of the target antigens for autoreactive T cells is unknown, but presumably these antigens are expressed on phenotypically normal GPI + hematopoietic stem cells. 33,[39][40][41] We postulate that reduced Tcell activation and decreased response to stimulation-related interferon-γ in GPI -cells would explain why the enlarged pool of clonally-skewed GPI -CD8 T cells did not cause clinical bone marrow failure and PNH in Pig-a deficient mice, even when the proportion of immunosuppressive Treg cells was much reduced.…”