The complement model disease paroxysmal nocturnal hemoglobinuria.

Area of Science:

• Hematology
• Immunology
• Pharmacology

Background:

• Paroxysmal nocturnal hemoglobinuria (PNH) is a rare, severe hematological disorder.
• It is characterized by complement-mediated intravascular hemolysis, leading to anemia and thrombosis.
• The first complement inhibitor, eculizumab, targeting C5, was approved in 2007.

Purpose of the Study:

• To review complement activation and inhibition in PNH.
• To discuss suboptimal responses to C5 inhibitors.
• To explore novel complement therapeutics for PNH.

Main Methods:

• Review of initial, current, and future aspects of complement inhibition in PNH.
• Identification and mechanistic dissection of four causes of suboptimal response to C5 inhibitors.
• Discussion of emerging complement therapeutics targeting proximal cascade proteins.

Main Results:

• Eculizumab stabilized hematologic parameters and reduced thrombotic events in PNH.
• Suboptimal responses are linked to pharmacokinetic/pharmacodynamic breakthrough hemolysis, residual intravascular hemolysis, and extravascular hemolysis.
• Multiple complement inhibitors are approved or in clinical trials for PNH.

Conclusions:

• Despite C5 inhibitor success, residual hemolysis and extravascular hemolysis persist in PNH.
• Novel complement inhibitors targeting proximal pathways are being developed to address these issues.
• PNH research is highly active, with ongoing investigations into unexpected breakthrough events with various complement inhibitors.