Image by James Thomson
Induced pluripotent stem cells
Cell therapy could produce lasting effects in hemophilia B, according to a group of researchers.
They genetically modified induced pluripotent cells (iPSCs) derived from patients with hemophilia B and converted those iPSCs into hepatocyte-like cells (HLCs).
When transplanted into mouse models of hemophilia B, the HLCs remained functional for months, increasing levels of factor IX (FIX) and clotting efficiency.
However, the HLCs were substantially less effective than cryopreserved human hepatocytes (hHeps), which were able to correct clotting defects in mice long-term.
“The appeal of a cell-based approach is that you minimize the number of treatments that a patient needs,” explained Suvasini Ramaswamy, PhD, of The Boston Consulting Group in Massachusetts.
“Rather than constant injections, you can do this in one shot.”
Dr Ramaswamy and her colleagues described their results with this approach in Cell Reports. Study authors include employees of Shire Therapeutics, Vertex Pharmaceuticals, and Thermo Fisher Scientific.
The researchers first developed a quadruple knockout mouse model of hemophilia B that allows for the engraftment and expansion of hHeps. The team crossed transgenic FIX-/--deficient mice with Rag2-/- IL2rg -/- Fah-/- mice to create this model.
The researchers transplanted cryopreserved hHeps into the mice and observed a sustained increase in circulating levels of human albumin, human FIX, and clusters of FIX- or Fah-positive cells in the liver.
The team said the hHeps were able to restore clotting function to wild-type levels in the mice—at least 10-fold higher than levels needed for a significant improvement in hemophilia B.
The hHeps remained functional for up to a year, and the researchers believe the cells could persist even longer. The team noted that there was no difference in the efficacy of hHeps from different donors or vendors.
The researchers then tested the cell therapy they developed using iPSCs. They collected blood samples from 2 patients with severe hemophilia B, reprogrammed peripheral blood-derived mononuclear cells into iPSCs, and used CRISPR/Cas9 to repair the mutations in each patient’s FIX gene.
The team coaxed those repaired cells into HLCs and tested the HLCs in the mouse model of hemophilia B. The HLCs were transplanted through the spleen so the cells were distributed uniformly in the liver.
The researchers said the HLCs were present and functional in the liver for up to a year, but they were less effective than hHeps. Mice that received HLCs experienced “modest” increases in clotting efficiency, from less than 10% to about 25% of wild-type activity.
The researchers believe this work demonstrates the value of combining stem cell reprogramming and gene-modifying approaches to treat genetic diseases. However, more work is needed to optimize this approach for hemophilia B.