Donor T-Cell DNA Methylation in GVHD and the Graft-vs-Tumor Effect after Allogeneic Hematopoietic Stem Cell Transplant
Bone marrow transplantation, also known as hematopoietic stem cell transplantation (HSCT) is the only curative treatment for many malignant disorders, such as aggressive types of leukemia and lymphoma. It is also increasingly used to treat disorders other than cancer. Unfortunately, successful outcomes following HSCT can be limited by either cancer relapse, or graft-versus-host disease (GVHD), a complication wherein the new, donor, immune system attacks the patient causing significant multi-organ injury and dysfunction, which can be fatal. Of interest, such graft-versus-host effects can be beneficial when residual cancer cells are targeted, a process known as graft-versus-tumor (GVT) activity. While progress has been made in our understanding of GVHD, significant improvements in the treatment and prevention of GVHD that will also allow for continued GVT effects have yet to be fully appreciated.
Project Goal:
Our project aims to better understand and identify new strategies to control GVHD and optimize GVT activity in order to reduce relapse rates and improve outcome for cancer patients undergoing HSCT. It is well known that T lymphocytes, a type of white blood cell, play a major role in the development of GVHD and GVT activity. We also know that one way that our body controls the function of T cells, is through a DNA change called DNA methylation. DNA methylation is not only an important way of regulating T cell function (and therefore, we believe, GVHD and GVT activity) but also could be a great target for future therapies because it is reversible with medications that are already available (called demethylating agents). In this project, we will use mice that have been genetically engineered so that they are unable to control their T cells via DNA methylation. We will use these mice as donors in HSCT experiments and then study GVHD and GVT effects that occur in groups of mice that receive the engineered T cells as compared to mice that receive “normal” T cells. This will allow us to directly examine the effect that methylation has on GVHD and GVT activity and therefore identify new ways in which to improve outcomes for patients who require a bone marrow transplantation.
Project Update 2024:
Blood marrow transplantation (BMT) remains the only curative option for many pediatric and adult patients with cancer of the blood and lymphoid systems (such as aggressive leukemias).
However, successful outcomes can be limited either by cancer relapse, or by the development of graft-versus-host disease (GVHD). GVHD is a complication wherein the new, donor, immune system (the “graft”) attacks the patient (the “host”) causing targeted multi-organ injury and dysfunction, which can be fatal. It is well known that T lymphocytes, a type of white blood cell, play a major role in the development of GVHD activity. We also know that one way that our body controls the function of T cells and the immune system is through changes in DNA and gene expression called epigenetic modifications. A process known as DNA methylation is one form of epigenetic regulation. In this project, we have used mice that have been genetically engineered so that they are unable to control their T cells via new DNA methylation (“DNMT3a knock-out T cells”). These experiments allow us to directly examine the effects that T cell DNA methylation has on GVHD activity.
We have shown that donor T cell DNA methylation plays a significant role in regulating GVHD. Mice that receive transplantation with DNMT3a knock-out T cells develop accelerated severe GVHD, associated with skin, liver, and intestinal damage. We have confirmed this finding in several different mouse models, and we have shown that the exacerbated GVHD is mainly driven by a T cell subpopulation called CD8+ T cells, rather than CD4+ T cells. Additionally, we have identified an unusual population of T cells (CD4+CD8+ double positive) in our experimental mice that may be contributing to our findings. Subsequent experiments revealed that DNMT3a knock-out T cells divide earlier than “normal” T cells and have an advantage in migrating to organs such as the spleen, lymph nodes, and intestine. We have shown these knock-out T cells have distinct DNA methylation changes, which correspond to pathways that are closely related to the activation and function of T cells. Importantly, these changes may represent new therapeutic targets that can help to improve outcomes for patients who require blood and marrow transplantation as a curative option for their underlying disease. Our lab has used a small molecule inhibitor to target one of the new pathways we have identified, with promising preliminary results in the improvement of GVHD in treated mice.
