DiMeN Doctoral Training Partnership: Determining risk for drug-induced complications of anti-complement therapy in PNH

This cutting edge project brings together an inter-disciplinary team of clinicians, geneticists, and complement experts and engages the two National Centres for complement mediated disease (in haematological disease, Leeds, and in renal disease, Newcastle). Complement is part of the innate immune system responsible for recognition and destruction of pathogens. It opsonises bacteria and dead and dying cells thereby triggering phagocytosis and clearance, and it punches holes in target cells resulting in death by osmotic lysis.

Self-cells are protected from damage by complement due to the presence of control proteins in blood and on cell membranes. However, problems with these control proteins, often triggered by mutant genes, can cause disease. Paroxysmal nocturnal haemoglobinuria (PNH) is one of these diseases, it is a haematological disorder characterised by clonal expansion of haematopoietic stem cells which cannot synthesise glycosylphosphatidylinositol (GPI) anchors (1). Daughter cells lack essential GPI-anchored complement control proteins and are therefore exquisitely sensitive to complement attack. Erythrocytes (E) are particularly susceptible to lysis and patients develop thromboses, anaemia and become transfusion-dependent.

Treatment of PNH was revolutionised in 2007 by clinical use of an antibody (eculizumab) which blocked complement C5, a protein responsible for generating the lytic ‘pore’ or ‘membrane attack complex’, thereby preventing catastrophic haemolysis (2). However, as C3 is activated prior to C5, C3-derived activation products (opsonins) can still accumulate on circulating E and cause extravascular haemolysis by binding complement receptors (CRs) on phagocytic cells, thereby triggering cell death by an alternative (phagocytic) mechanism. This maintains a requirement for transfusion in a portion of patients and is purely a drug-induced phenomenon as eculizumab blocks removal of these opsonised cells by complement-mediated lysis (3).

We have recently described the ‘complotype’ –an inherited pattern of complement gene variants which together influence the ability of complement to amplify and deposit C3 on targets and to be processed to different opsonins (4,5). We believe that a patient’s complotype can be used to identify those at risk for extravascular haemolysis and who might benefit from targeted complement therapies which modulate C3-derived opsonins on the erythrocyte surface. The successful candidate will assess PNH patients who are being treated with eculizumab (Hillmen) for their variation in complement genes (Kavanagh). Using bioinformatics, they will correlate patient complotype with a range of biological and clinical outcomes, including C3 deposition on erythrocytes (Harris, Newton), signs of complement activation in blood (Harris) and clinical parameters including need for transfusion (Newton). An in vitro model of erythrocyte phagocytosis will be developed using in-house methodologies to opsonise erythrocytes with activated C3 and to quantitate C3 fragments; fragment density and type will be correlated with opsonophagocytic activity. This powerful combination of patient analyses and in vitro experimentation will provide insight into disease mechanism and will result in a clinically-invaluable prognostic tool, enabling risk stratification for extravascular haemolysis in PNH.

Suitable candidates are likely to have a background in biomedical sciences, biochemistry or biology with a keen interest in clinical science.

1. http://mp.bmj.com/content/55/3/145.long
2. http://www.bloodjournal.org/content/bloodjournal/106/7/2559.full.pdf
3. http://www.bloodjournal.org/content/bloodjournal/113/17/4094.full.pdf
4. http://www.cell.com/trends/immunology/pdf/S1471-4906(12)00106-8.pdf
5. http://www.pnas.org/content/108/21/8761.full.pdf