Ex Vivo-Generated Autologous iTregs as a Cell-Based Therapy for Acquired Aplastic Anemia
Abstract
Central tolerance refers to a mechanism that generates a very small population of protective, regulatory cells that circulate throughout our bodies and prevent our immune system from attacking and destroying our own tissues. These regulatory cells are frequently deficient in patients with AA. Either they are reduced in number, or they somehow lose their ability to suppress effector cells that destroy the blood re-populating cells in the bone marrow. We identify these regulatory cells by a signature molecule they express, called FOXP3. The level of FOXP3 expressed in regulatory cells correlates with their ability to suppress the activity of effector cells: the higher the FOXP3 expression, the better cells are at performing their suppressive functions. Furthermore, high FOXP3 expression is also associated with regulatory cells being very stable – that is they cannot easily be converted into effector cells. Many factors regulate FOXP3 expression, including whether the gene that codes for FOXP3 can be readily turned on. One specific way this on-off switch is regulated, is by adding chemical groups to the FOXP3 DNA, through a process referred to as promoter methylation. When a promoter is highly methylated, the DNA is no longer accessible for other factors to bind to it and to turn the gene on. Regulatory cells with demethylated FOXP3 are much more stable and are much better at suppressing effector cells than regulatory cells that have more methylated FOXP3. We discovered an unexpected function for PCMT1, a molecule known to repair aged proteins in cells by adding methyl groups. We found that PCMT1 can add methyl groups to FOXP3 DNA in regulatory cells. Furthermore, we can use special synthetic cell-penetrating compounds to carry an antibody against PCMT1 into cells and prevent it from binding to and methylating FOXP3 DNA. We predict that if we make regulatory cells using cell-penetrating compounds and antibodies against PCMT1, we will permanently lock the regulatory cells, and they will function better to suppress the destruction in the bone marrow caused by effector cells. In proof-of-concept experiments, we used a humanized mouse model of AA to test how well these regulatory cells performed when they were given at the same time bone marrow failure was induced. We found they were much better at decreasing disease severity and extending survival in AA mice, compared to conventionally prepared regulatory cells. In this project we will test their efficacy under more clinically-relevant conditions, and in combination with other immunosuppressive treatments that AA patients are likely to be given. To better predict how effective this regulatory cell-based therapy may be as a new treatment for AA patients, we will also create unique humanized mouse models of AA, which we call avatar mice. Individual mice, whose bone marrow failure is induced by cells transferred from an AA patient, will then be treated with regulatory cells from that same patient, that were generated as described above. We will also examine how cyclosporin A and rapamycin, two immunosuppressive drugs frequently given to AA patients, impact, the expansion and function of patient-derived regulatory cells in our avatar mice. The probability of finding a genetically-matched sibling or unrelated matched donor for a bone marrow transplantation is low for AA patients. Using regulatory cells to treat immune-mediated diseases is gaining momentum, but these therapies rely on isolating and expanding the naturally occurring regulatory cells that are defective in most AA patients. Through our approach, we predict we can generate stable, highly-suppressive regulatory cells that can be reinfused into patients as a cell-based immunosuppressive therapy. By gaining a greater understanding of how certain drugs, such as cyclosporin A and rapamycin act on regulatory cells, we expect we can maximize the efficacy of our regulatory cells once they are transferred
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 19, 2019
- Source ID
- W81XWH1910540
Entities
People
- Lisa M Minter
Organizations
- United States Army
- University of Massachusetts Amherst