Cutting-edge research examines inhibitors, measurement discrepancies and more

Researchers presented six new studies on hemophilia during a Monday afternoon session. Presentations included:

Generation of IPS Cell Lines from Haemophilia A patients

Author Heike Singer said this study focused on nonsense mutations versus inhibitor risk. Noting that there’s a higher inhibitor risk in the light chains of proteins versus heavy chains, the research team posed the following questions: Why do different nonsense mutations have a higher risk of inhibitors? Does this have to do with cross-reactive material status? RNA? Protein?

The research team generated induced pluripotent stem cells (iPSCs) from a hemophilia A patient. They then reprogramed the cells and differentiated them into endothelial cells. “This cellular system will help us to further study the mutation-specific effect on factor VIII formation,” Singer said.

Macrovascular and Microvascular Endothelial Function in Adult Males with Hemophilia

Author Shannon Jackson said several studies have shown that hemophilia is associated with a lower cardiovascular mortality compared to the general population. This may have to do with atherosclerotic plaque formation.

In a study of about 1,600 healthy firemen, microvascular endothelia function (EF)—but not macrovascular EF—was identified as an independent predictor of cardiovascular risk.

In the first similar study on hemophilia patients, Jackson and her team gathered 81 males with all severities of hemophilia A and B, along with controls from the firemen study. The researchers measured macrovascular and microvascular EF functions in all subjects. They found similar macrovascular EF between hemophilia patients and controls, but significantly lower microvascular EF.

Results from a randomized controlled trial on inhibitor development in PUPs: the SIPPET study 

Manuel Carcao said the choice of factor may affect inhibitor development in young children with hemophilia A. The Study on Inhibitors in Plasma-Product Exposed Toddlers (SIPPET) was designed to measure whether there is more inhibitor development with recombinant factor VIII versus plasma-derived factor VIII.

The study involved 42 centres in 14 countries, and included 251 males age 6 or younger with severe hemophilia A, randomized to recombinant or plasma-derived factor VIII groups.

Results showed that 73.3 percent of the plasma VIII group did not develop an inhibitor, compared to 55.5 percent for the recombinant group. The recombinant group also had a 1.87 percent higher incidence of developing an inhibitor compared to the plasma-derived group. The high-titer rate was 1.69.

For both products, Carcao said 90 percent of inhibitor development occurred in the first 58 exposure days. No individual country results changed the hazard ratio. Overall, Carcao said toddlers given recombinant factor VIII had an 87 percent higher risk of developing all inhibitors, and a 69 percent higher risk of developing high-titer inhibitors.

Manufacturers should investigate what it is about plasma product that makes it less immunogenic, and incorporate those discoveries into recombinant product, Carcao said.

Inhibitor Neutralizing Capacity of FVIII Therapeutic Concentrates Depends on VWF-Natural FVII/VWF Complex Versus Isolated FVIII. Study of Eleven Products

Author Juan Ignacio Jorquera said many plasma FVIII concentrates contain natural FVIII/VWF complexes. These concentrates may have some benefits for immunogenic response.

His team’s in vitro study was designed to analyze the VWF role on FVIII. The researchers used both a hemophilia-mimic case and a pre-mixture case. Both cases behaved similarly to plasma in the in vitro assay. But concentrates of FVII with low VFW or without VFW showed higher inhibitor titers, even when pre-mixed with VFW for the assay.

“Is it possible that what people with hemophilia lack is not only FVIII, but FVIII with VWF?” Jorquera asked.

Discrepancies Between the One-Stage Clotting Assay and the Chromogenic Assay in Haemophilia B

Author Jan Astermark discussed this study dealing with discrepancies in the measurement of factor VIII:C in hemophilia B patients.

Plasma samples from 32 patients with mild and moderate hemophilia B were analyzed by both one-stage assay and chromogenic assay. The assays measured the patients’ mean factor IX levels. Fourteen samples from seven patients showed a twofold or greater difference between the results of the two methods, with the chromogenic method presenting the higher value.

Mutation at the N-terminal site of the activation peptide at Arg191 was associated with a higher Factor IX:C activity measured by chromogenic rather than one-stage assay. The bleeding phenotype may correlate better to the activity defined by the chromogenic assay, Astermark said.

Platelet Function Measured Using the Multiplate (R) Analyzer in Pediatric Patients with Severe Hemophilia A (SHA)

Author Margaret Rand said this study of pediatric patients with severe hemophilia A in two Canadian centres found dose-response curves in ADP, collagen, arachidonic acid and thrombin receptor active peptide (TRAP), as measured by the Multiplate® analyzer.

The patients were then compared to healthy male adult controls. There was no significant difference in measurements between the two groups at site 1. At site 2, the aggregation responses were increased in patients versus the controls. But when both sites were combined, there was no significant difference in responses between controls and patients. Rand said the same results occurred in overall platelet aggregation responses between sites.