‘Reverse Vaccination’ Has Broad Clinical Potential As Immunotherapy Strategy
By Deborah Borfitz
November 3, 2021 | Researchers at the University of Buffalo (UB) have come up with a nanoparticle platform for oral prophylactic immunotherapy designed to pre-expose the immune system to medications it might otherwise perceive as foreign and attack. If translated to the clinic, their novel “reverse vaccination” approach could be used to desensitize patients to key proteins in drug treatments for rare conditions, autoimmune diseases, and allergies, according to Sathy Balu-Iyer, Ph.D., professor of pharmaceutical sciences and associate dean for research in the UB School of Pharmacy and Pharmaceutical Sciences.
Put to the test in mouse models for hemophilia A and Pompe disease, the methodology succeeded in preventing an unwanted immune response to protein therapies, as discussed in an article recently published in Scientific Reports (DOI: 10.1038/s41598-021-97333-0). In addition to preventing anti-drug antibody development, Balu-lyer says, it might also help address the immunogenicity problem associated with gene therapy products that can be curative for the monogenic disorders.
The U.S. Food and Drug Administration reports that over 90% of the population has preexisting antibodies to some of the adeno-associated viruses (AAV) commonly used as vectors for gene delivery. In some cases, the antibodies render gene therapy ineffective on the first dose.
The new nanoparticle platform houses phosphatidylserine (PS), a fatty substance that covers and protects the cells in the body and plays a key role in cell cycle signaling. In earlier studies, Balu-lyer and his colleagues showed that PS-containing nanoparticles, when given subcutaneously, can reduce unwelcome immunogenicity in animal models of hemophilia A treated with recombinant Factor VIII (FVIII) and Pompe disease receiving recombinant acid alpha glucosidase (GAA).
Critically, PS surface density and externalization to the outer leaflet of the bilayer membrane of dendritic cells are what determine if it gets recognized by immune-regulatory PS receptors, he says. Those considerations informed the design of the nanoparticle platform with the ideal size and surface characteristics for cellular uptake, binding, and survival in the digestive tract.
Specifically, the approach uses single-acyl chain lysophosphatidylserine (Lyso-PS), a fatty acid that helps the immune system tolerate foreign substances. Lyso-PS is much more readily taken up by the adaptive immune system than double chain phosphatidylserine and lysophosphatidylcholine (another form of lysophospholipid), he notes.
The reverse vaccination strategy is “exactly opposite” of the wanted immunogenicity of vaccines that use pre-exposure to provoke an immune response against a pathogen, says Balu-lyer. Pre-exposure of proteins in the presence of Lyso-PS nanoparticles rouses immune tolerance of those proteins, thereby reducing adverse reactions to treatment regimens such as FVIII and GAA.
PS primarily resides in the inner leaflet of healthy cells but flips to the outer leaflet when cells undergo apoptosis, Balu-lyer explains. This sends the “eat me” signal to the immune system to silently clear cell debris and helps to maintain tolerance of proteins that originate in the body.
But, as the UB research team has demonstrated, externalization of PS can also be leveraged to induce tolerance of specific nonhuman proteins. Animals orally immunized with Lyso-PS along with a therapeutic protein learned not to respond by manufacturing anti-drug antibodies.
As reported several months ago in the Journal of Thrombosis and Haemostasis (DOI: 10.1111/jth.15497), co-administering Lyso-PS with FVIII for four weeks significantly reduced the development of antibodies without impacting the effectiveness of the protein. In the latest research, the optimized Lyso-PS nanoparticle was found to prevent development of antibodies against FVIII in the majority of pre-clinical models of Hemophilia A.
The treatment was effective when delivered intravenously as well as orally, says Balu-lyer. But a therapy that can be taken by mouth allows for easier consumption and improved medication compliance by patients.
The prospect of an oral tolerance pathway means that in the future patients might briefly be pre-treated with a user-friendly, perhaps cherry-flavored pill pairing Lyso-PS with a challenge dose of a specific protein-based drug prior to the start of usual treatment with that drug. From a clinical perspective, it appears that inhibiting the anti-drug antibody in hemophilia requires only 15 or 20 such pre-exposures, Balu-lyer says.
Hemophilia and Pompe disease were good starting points for several reasons, he continues, which includes his personal “rare disease inclination.” For nearly one-third of patients with hemophilia A and about 90% of patients with Pompe disease, their own immune system is the greatest treatment obstacle.
A major and growing issue with protein-based drugs is their tendency to trigger an unwanted immune response against themselves, says Balu-lyer, including activation of B cells producing antibodies that bind to the proteins and reduce or eliminate their therapeutic effects. “Once antibodies develop, clinical options available for patients become expensive [upwards of $700,000 per year for hemophilia] and, in several cases, ineffective.”
People with rare and orphan diseases typically have few other options, he adds. But it is also relatively easy to test the reverse vaccination approach for monogenic disorders characterized by a specific protein deficiency.
The nanoparticle platform has “broad clinical potential” because of its ability to desensitize the immune system, Balu-lyer says. For patients with autoimmune conditions, the nanoparticle could potentially be used to retrain their immune system to tolerate rather than attack their body’s own proteins.
In multiple sclerosis (MS), for example, the myelin sheath protein is recognized as foreign, so the body mounts a response. But early in the disease, patients might be given a few doses of the nanoparticle containing myelin sheath, so their body learns how to tolerate the protein, he continues. Preliminary testing in animals suggests the approach might substantially delay progression of MS and the same could hold true for other autoimmune conditions.
It’s a similar story with allergies, which are also triggered by an immune system malfunction, says Balu-lyer. People with gluten allergies, for instance, recognize the structural protein in wheat as foreign. Potentially, a cereal protein could be delivered via the Lyso-PS nanoparticle to desensitize patients and prevent them from ever going into life-threatening anaphylactic shock.
Gene therapy, including CRISPR, is another promising area of investigation for the nanoparticle platform, he says. Some people are ineligible for gene therapy because of pre-existing antibodies from exposure to wild-type AAV, but the body also tends to mount an immune response to viral vectors before they infect their target cells, and this could potentially be prevented using the new reverse vaccination approach.
Balu-Iyer recently received investment funding and scientific support to continue preclinical R&D from the Empire Discovery Institute (EDI), which is licensing the technology and advancing the treatment to market in “multiple directions.” EDI is an integrated drug discovery and development accelerator located in Upstate New York focused on critical unmet needs.
“My hope is that [EDI] will take this up to phase 1,” says Balu-lyer, adding that the immediate next step is a robust preclinical safety trial.