Published online 9 February 2010
(Haematologica 2010, 10.3324/haematol.2009.007229)
Copyright © 2010 by Ferrata Storti Foundation

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Original Article

Eculizumab prevents intravascular hemolysis in patients with paroxysmal nocturnal hemoglobinuria and unmasks low-level extravascular hemolysis occurring through C3 opsonization

Anita Hill^1,2, Russell P Rother³, Louise Arnold¹, Richard Kelly¹, Matthew J Cullen¹, Stephen J Richards¹, Peter Hillmen¹

¹ Department of Haematology, St James’ University Hospital, Leeds, UK
² Department of Haematology, Bradford Teaching Hospitals NHS Foundation Trust, Bradford, UK
³ Alexion Pharmaceuticals, Inc., Cheshire, CT USA

Correspondence: Anita Hill, St. James’ Institute of Oncology, Department of Haematology, Level 3 Bexley Wing, Beckett Street Leeds LS9 7TF, UK. E-mail: anitahill{at}nhs.net

ABSTRACT

Background: Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired hemolytic anemia characterized by intravascular hemolysis which has been demonstrated to be effectively controlled with eculizumab. LDH levels however remain slightly elevated and haptoglobin levels remain low in some patients suggesting residual low-level hemolysis. This may be due to C3-mediated clearance of PNH red cells (RBCs) through the reticuloendothelial system.

Design and Methods: Thirty-nine samples from patients not treated with eculizumab and 31 samples from patients treated with eculizumab (17 of these 31 samples had pre-eculizumab samples) were obtained. Membrane bound complement was assessed by flow cytometry. Direct antiglobulin testing was carried out using 2 methods. LDH was used to assess degree of hemolysis.

Results: Three of 39 PNH patients (8%), not on eculizumab, were DAT-positive, while 21 of 31 (68%) were DAT-positive during eculizumab treatment. Of the 21 DAT-positive patients during eculizumab treatment, 17 were tested prior treatment; only one was positive. Flow cytometry using anti-C3 mAbs was performed on the 21 DAT-positive eculizumab-treated patients; the median proportion of C3 positive total RBCs was 26%. Sixteen (76.2%) DAT-positive eculizumab-treated patients received at least one transfusion compared with 1 of 10 (10.0%) DAT-negative eculizumab-treated patients p<0.01). The mean hemoglobin value for 21 DAT-positive eculizumab-treated patients was 9.6±0.3 g/dL compared with 11.0±0.4 g/dL in 10 DAT-negative eculizumab patients (p=0.02).

Conclusions: These data demonstrate previously masked mechanism of red cell clearance in PNH and suggests that blockade of complement C5 allows C3 fragment accumulation on some PNH red cells, explaining the residual low-level hemolysis occurring in some eculizumab treated patients.

Key words: paroxysmal nocturnal hemoglobinuria, eculizumab, complement, hemolysis, C3.

Related Article

Paroxysmal nocturnal hemoglobinuria and eculizumab

Lucio Luzzatto, Antonio Maria Risitano, Rosario Notaro
Haematologica 2010 95: 523-526. [Full Text] [PDF]

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				L. Luzzatto, A. M. Risitano, and R. Notaro Paroxysmal nocturnal hemoglobinuria and eculizumab Haematologica, April 1, 2010; 95(4): 523 - 526. [Full Text] [PDF]