PNH cells are as sensitive to T-cell-mediated lysis as their normal counterparts: implications for the pathogenesis of paroxysmal nocturnal haemoglobinuria.

ABSTRACT

The mechanism responsible for the bone marrow failure that is almost invariable in paroxysmal nocturnal haemoglobinuria (PNH) is unknown. Based on the close association between PNH and idiopathic aplastic anaemia, a plausible pathogenetic model predicts that, in PNH, autoreactive T cells specific for haemopoietic stem cells (HSCs) cause depletion of normal HSCs, whereas PNH HSCs escape this T-cell-mediated attack. In this study, we addressed the hypothesis that PNH HSCs are resistant to the cytotoxic effect of T cells because they lack surface expression of one or more glycosylphosphatidylinositol (GPI)-linked molecules. We tested the sensitivity of normal and PNH Epstein-Barr virus (EBV)-transformed B-cell lymphoblastoid cell lines (BLCLs) to the cytotoxic effect of autologous EBV-specific T-cell lines and clones from a patient with PNH in an in vitro experimental system. We found that the PNH BLCLs were no less sensitive to T-cell-mediated cytotoxicity than non-PNH isogenic BLCLs, indicating that GPI-linked molecules on the surface of target cells are not required for killing by T cells. This suggests that the mechanism whereby PNH HSCs survive T-cell attack is not because of the lack of surface expression of one or more GPI-linked molecules. By implication, other mechanisms become more probable.