The Transcription Factor Nuclear Factor Erythroid-2 Related 2 Regulates Hematopoietic Stem Cell Function And T-Cell Alloreactivity

Abstract

Coordinating the balance between haematopoietic stem cell (HSC) quiescence and self-renewal is crucial for maintaining haematopoiesis lifelong. Equally important for haematopoietic function is modulating their localisation within their bone marrow niches, as maintenance of HSC function is tightly controlled by a complex network of intrinsic molecular mechanisms and extrinsic signalling interactions with their surrounding microenvironment. Recent findings have suggested that a common mediator of these functions is the CXCR4-CXCL12 axis. In the first part of the dissertation, we demonstrate that nuclear factor erythroid 2-related factor 2 (Nfe2l2, or Nrf2), well-established as a global regulator of oxidative stress response, plays a regulatory role in all these aspects of HSC homeostasis. Nrf2-deficiency results in an expansion of haematopoietic stem and progenitor cells (HSPCs) due to cell-intrinsic hyperproliferation, which was accomplished at the expense of HSC quiescence and self-renewal. We further show that Nrf2 mediates both migration and retention of HSCs in their niche. Moreover, we identify a previously unrecognized link between Nrf2 and CXCR4, contributing, at least partially, to the maintenance of the main modalities of HSC function. While there is mounting evidence including ours suggesting a critical role of Nrf2 in HSC homeostasis and lymphohematopoietic malignancies, little is known about its role in T-cell biology. In the second part of the dissertation, we evaluate the relative contribution of Nrf2 to alloreactive T cells in the context of allogeneic bone marrow transplant (allo-BMT). Allogeneic bone marrow transplant (allo-BMT) is the most potent modality of cellular immune therapy for lymphohematologic malignancies. The therapeutic benefits of allo-BMT are derived from the cytoreductive conditioning, as well as the immune-mediated graft-versus-tumor (GVT) effect. However, one of the main drawbacks to the widespread use of allo-BMT is graft-versus-host disease (GVHD). Allogeneic donor T (allo-T) lymphocytes are the primary mediators facilitating both GVT and GVHD responses. We validate the biological significance of Nrf2 in T lymphocytes by showing nuclear translocation of Nrf2 upon T cell activation in vitro, and an increased cellular Nrf2 level specifically within CD4+ donor T cells upon alloactivation in vivo. We demonstrate that Nrf2-deficiency in donor T cells leads to attenuated acute GVHD, which is associated with stabilization of Helios+ regulatory T cells, present in the graft at the time of transplant, as well as defective upregulation of the gut homing receptor LPAM-1 of CD8+ allo-T cells. However, Nrf2-/- donor CD8+ T cells possess intact killing ability against alloantigens and A20 lymphoma cells. With their preserved GVT activity and ameliorated GVHD severity, Nrf2-/- donor T cells conferred an overall improved survival in the tumor-bearing allo-BMT recipients. Our findings not only characterize a novel role of Nrf2 in T cell function, but also reveal an exciting target for therapeutic manipulation as a useful clinical strategy to improve the outcomes of allo-BMT.