Salk Institute researchers demonstrated in mice that hemophilia B can be completely cured with one single injection of stem cells-derived healthy hepatocytes that can produce missing clotting factor. The results of the study, published on May 1, 2018 in Cell Reports, could drastically change the lives of patients with hemophilia B and could pave a new path toward similar methods of treating diseases caused by genetic disorders.
For most people with hemophilia B, whose bodies can’t properly form blood clots from platelets, constant injections to replenish clotting factors are a vital necessity.
Hemophilia B is a genetic disorder caused by defects in the gene that is responsible for the synthesis of the clotting factor IX (FIX). People suffering from this disease have low levels of clotting factors or their functionality is disrupted, which creates a danger to life even with minimal bleeding.
Currently, treatment involves frequent injections of FIX derived from animal cells. However, this approach is expensive, time-consuming and can become less effective over time.
Recently, Salk scientists developed a new approach, treating mice genetically engineered to have hemophilia B with strands of messenger RNA encoding the FIX gene. However, as with standard methods of treatment, this required repeat injections each time levels of the messenger RNA ran low. Therefore, scientists decided to try a more permanent method: transplanting into patients healthy liver cells, capable of producing FIX.
“The appeal of a cell-based approach is that you minimize the number of treatments that a patient needs”, – says Suvasini Ramaswamy, a former Salk research associate and first author of the new paper. “Rather than constant injections, you can do this in one shot.”
Since donor livers are often in short-supply, the researchers decided to turn to a stem cell strategies for producing healthy liver cells. They obtained blood samples from two patients with severe hemophilia B who cannot produce the clotting factor IX.
Then, in the lab, they reprogrammed the cells into induced pluripotent stem cells (iPSCs), which have the capability to turn into many other types of cells, including hepatocytes.
Using CRISPR/Cas9, a gene editing tool, the researchers corrected the mutations in the FIX gene in each patient. Further, they stimulated the development of “repaired” stem cells into liver progenitor cells, called hepatocyte-like cells, (HLCs), and transplanted them into mice with hemophilia B.
Since carrying out operations with animals with hemophilia carries a risk – their blood can’t always clot, scientists transplanted HLCs through the spleen to evenly distribute the transplanted cells in the liver with blood flow.
Not only did the new hepatocyte-like cells synthesize the clotting factor IX, but they also produced it in sufficient quantities to form normal blood clots in mice. HLCs were able to survive and produce FIX for at least a year after transplantation.
Patients with hemophilia can use their own cells to generate healthy HLCs, which after transplantation will not cause immune complications, often accompanying cell therapies. However, a large amount of work is needed to translate the findings to the clinic.
“A lot of things have to happen before this can go into humans”, – says Ramaswamy. “The work demonstrates the value in combining stem-cell reprogramming and new gene-modifying approaches to treat genetic diseases”.