Researchers have developed a protein drug that may teach the body to tolerate, rather than reject, the clotting factor treatment given to hemophilia patients. The new drug, tested in dogs, may lead to novel human therapies.
The study, “Oral Tolerance Induction in Hemophilia B Dogs Fed with Transplastomic Lettuce,” appeared in the journal Molecular Therapy.
“The results were quite dramatic,” Henry Daniell, the study’s lead author, said in a news release. “We corrected blood clotting time in each of the dogs and were able to suppress antibody formation as well. All signs point to this material being ready for the clinic.”
Hemophilia is a rare bleeding disorder caused by low or zero levels of clotting factor VIII (FVIII; hemophilia A) or IX (FIX; hemophilia B). It can lead to a disrupted clotting process, causing uncontrolled bleeding episodes.
Between 30 and 50 percent of patients develop inhibitory antibodies (IgG) directed against treatments with factor VIII or IX; that makes them resistant to replacement therapy. According to the U.S. Centers for Disease Control and Prevention, about one in 5,000 people are born with hemophilia, and about 20,000 Americans have the disease.
For the new study, Daniell — a researcher at Penn Dental Medicine’s Department of Biochemistry — and his colleagues used a patented plant-based drug portfolio in which plants are genetically altered to have specific human proteins in their leaves.
The team looked at how they could prevent patients with hemophilia from developing antibodies that would reject clotting-factor infusions. To that end, they tested if ingesting plant material containing the clotting factor, such as the transformed plant leaves, could promote oral tolerance to the factor protein.
In previous studies, researchers successfully used this technique. Essentially, they found that mice with hemophilia A that were fed plant material containing clotting factor VIII had a reduced formation of inhibitors against that factor.
In this new study, they tested the same technique for hemophilia B by using lettuce genetically altered to produce a fusion protein containing human clotting factor IX, and the cholera non-toxin B subunit — which helps the fused protein to cross the intestinal lining during lettuce digestion — while the plant cell walls protect the protein from digestion.
To do this, they fed the lettuce material to two dogs with hemophilia B twice a week. After 10 months, they observed no adverse reactions, which led researchers to go a bit further and test the technique on more dogs.
Four dogs were fed lettuce material for four weeks, and four other dogs served as controls. Dogs given the modified lettuce also received weekly injections of factor IX for eight weeks. The control dogs received only the injections. The scientists found that dogs in the control group developed antibodies against factor IX, and two of them required antihistamine treatment due to acute allergic reactions.
Three of the four dogs that received both the lettuce and the injections were found to have minimum levels of the antibody IgG2, and had no noticeable levels of two other antibodies, IgG1 or IgE. The fourth dog responded only partially to the treatment, which many have been due to the presence of an antibody, prior to the study, to human factor IX.
Compared to the control dogs, the treated dogs had 32 times lower levels of the antibody IgG2, and suffered no adverse reactions to the treatment.
“Looking at the dogs that were fed the lettuce materials, you can see it’s quite effective,” Daniell said. “They either developed no antibodies to factor IX, or their antibodies went up just a little bit and then came down.”
The researchers will continue to test potential adverse reactions from the treatment, and plan to submit an Investigational New Drug application for their plant-based product to the U.S. Food and Drug Administration before year’s end.