Scientists at the University of Florida in Gainesville have developed a gene immunotherapy method that can stop the development of multiple sclerosis (MS) in a mouse model of the autoimmune disorder, and even reverse paralysis in animals with pre-existing disease. “We were very impressed with the results,” commented Brad E. Hoffman, Ph.D., associate professor in the departments of pediatrics and neuroscience at the University of Florida College of Medicine, speaking with GEN at a press briefing. “We expected there to be a reversal or at least a dampening of the disease. We were quite surprised we had that level and magnitude of response, and how long the reversal lasted.”
MS affects about 2.3 million people worldwide. The neurological disease is thought to result from the activation of self-reactive effector T cells that attack proteins in the myelin sheath that surrounds nerve cells. These rogue cells somehow escape control by regulatory T cells (Tregs) that normally prevent self-destructive activity and gradually destroy the protective myelin sheath.
Rather than use gene therapy to deliver a therapeutic or curative protein for MS, Dr. Hoffman’s team is using gene therapy to exploit the liver’s ability to induce immune tolerance. The approach uses an adeno-associated viral (AAV) vector to deliver the gene for the myelin sheath protein, myelin oligodendrocyte glycoprotein (MOG), to the liver. Expression of MOG by liver cells triggers the immune system to produce highly specific Tregs that prevent the rogue autoreactive effector T cells from attacking the protein in the myelin sheath.
The researchers report on their research in Molecular Therapy, in a paper entitled, “Gene Therapy-Induced Antigen-Specific Tregs Inhibit Neuro-inflammation and Reverse Disease in a Mouse Model of Multiple Sclerosis.”
Previous research has shown that administering Tregs to a murine model of MS, known as experimental autoimmune encephalomyelitis (EAE), can halt or reduce neurological symptoms, but the effects are temporary. Treg cell injections have also been shown to be a safe treatment approach for patients with other autoimmune disorders, such as type 1 diabetes and graft-versus host disease. The problem with this method, however, is generating enough of the cells.
Dr. Hoffman’s team has instead developed a liver-targeting AAV vector encoding the full coding sequence for MOG, which they delivered to the mouse EAE model. It’s not the first time that this approach has been tried in animals, the team noted in their published paper. “Leveraging the tolerogenic nature of the liver, hepatic gene transfer has successfully been used to induce robust transgene tolerance in large- and small-animal disease models.” MOG was chosen as the Treg-stimulating antigen because although the protein accounts for only about 0.05% to 0.1% of total myelin proteins, it has been found to induce a more potent T-cell response than other myelin antigens in patients with MS.
EAE is a progressive disease in mice.The animals initially have no discernible deficits, but as the disease progresses they develop tail paralysis, then hind leg paralysis, and in late-stage disease forearm paralysis occurs. The researchers first confirmed that administering the liver-targeting AAV vector to mice stimulated hepatocytes to express MOG, which triggered the production of functionally suppressive MOG-specific Tregs.
When the researchers next administered the gene therapy prophylactically to the mouse EAE model, they found that treatment had an immunosuppressive effect, which prevented mice from developing the disease. Whereas control mice started to develop neurological deficits within 10 days of EAE induction, mice receiving the AAV vector developed no clinical signs of EAE.
Importantly, liver cells in the prophylactically treated mice continued to express Treg-stimulating MOG over the whole 200-day experimental timeline, without any discernible adverse immune effects. “Notably, throughout this protracted timeline, mice never developed any observable signs of neurological disability or general distress, suggesting that hepatocyte expression of MOG does not provoke any deleterious immune responses,” the authors noted. Encouragingly, the protective effects of the vector injection were also robust and long lasting. Mice were protected from developing EAE even if they received a single injection of the gene therapy as early as seven months prior to disease induction.
Importantly, the gene therapy completely reversed clinical symptoms, including paralysis, in animals that were treated for the first time after they had already developed moderate disease. Mice with hind leg paralysis gradually began to regain the use of their legs following treatment and were eventually able to move around freely again. “Within a very short amount of time, we saw a nearly complete reversal of all the clinical signs and symptoms of the disease,” Dr. Hoffman noted. Examination of the animals’ tissues also confirmed that while control mice exhibited tell-tale inflammation in the spinal cord, there was no inflammation in the treated mice. “These results suggest that AAV gene immunotherapy reverses the clinical symptoms associated with EAE disease through a mechanism that suppresses tissue-specific inflammation,” the authors stated.
Animals with much more severe, late-, or end-stage disease also derived some clinically relevant, but less dramatic, benefits following the MOG vector therapy. The disease had progressed too far for gene therapy alone to completely reverse the symptoms. However, even in these animals, combining the MOG-encoding AAV vector therapy with a course of treatment using the immunosuppressive drug rapamycin led—“remarkably” the authors admit—to near-complete remission. Among the two groups of end-stage disease animals with either complete tail and hind-limb paralysis or near quadriplegia, 71%, and 80% of treated animals demonstrated near-complete remission.
Hoffman said his team is continuing to develop the gene immunotherapy platform into a technology that could potentially be used to treat MS in humans. Clinical use of the AAV technology is well documented, and rapamycin is a widely used drug that is used to coat stents and treat organ transplant recipients, so the main elements of the technology have been well studied. There are still some hurdles to overcome and potential safety issues that need to be addressed, however, he stated. “We are putting a neural protein into the liver,” and while no adverse effects of the gene therapy were observed in mice, the potential for adverse effects in humans will need very careful study.
A human gene therapy will also likely require the development of vectors for additional proteins, and not just MOG, Hoffman told GEN at the briefing. “We are actively developing additional vectors that target several other neuroproteins to have a complement of vectors that will offer a broader range of coverage in the patient. Hopefully that paper will come out in the next couple of months.”
So what is the takeaway message for MS patients? Dr. Hoffman has worked for many years with the National Multiple Sclerosis Society, and says the aim is to tackle MS early and provide a long-term treatment modality that will give patients a higher quality of life. If it is possible to suppress the early immune response, then the disease won’t have long-term neurodegenerative effects.
The technology is also setting the stage for studies in several other autoimmune diseases, he commented to GEN. “We have a tremendous amount of data showing that the tolerogenic effect would be conducive to other autoimmune diseases. MS works because we know what the proteins are that are causing the autoimmune disease, but the technology can definitely be applied and looked at in other autoimmune diseases.”