Transfer of MSC mitochondria to T lymphocytes: impact on T cell metabolism, phenotype and recirculation in autoimmunity – MitoStem

Mesenchymal Stromal Cells (MSCs) were firstly described in the bone marrow but are also present in secondary lymphoid organs. They play an important physiological role in T cell homeostasis because they secrete survival cytokines such as IL-7. Additionally, we and others have demonstrated that they are immunosuppressive in vitro and in vivo, when systemically injected under inflammatory conditions. In particular, they are able to inhibit T cell proliferation and Th17 differentiation, induce T cell anergy and Treg activation, and, notably, can prevent collagen-induced arthritis in mice. Immunosuppression is mediated, at least in part, by prostaglandin E2, transforming growth factor-ß, interleukins- 6 and 10, indoleamine-2,3-dioxygenase and nitric oxide. Although the interactions between MSCs and T cells, in a physiological and in a pathological context, are known to require both direct contacts and soluble factors, the precise pathways involved in the immunomodulatory capacity of MSCs remain still unclear. Interestingly, the ability of MSCs to reprogram cell functions through mitochondrial transfer has been recently described. We have established a protocol for artificially transferring mitochondria, isolated from MSCs, and shown their effects on metabolic reprogramming and, in turn, on the functional properties of the recipient cells. Furthermore, our preliminary results demonstrate, for the first time, that MSCs can transfer mitochondria to T cells. Since a critical checkpoint for T cell survival and differentiation is the establishment of specific metabolic programs, our hypothesis is that MSCs, via mitochondria transfer, induce a switch between glycolytic and oxidative metabolism resulting in the modulation of T cell differentiation programs. Utilizing human and mouse MSCs isolated from bone marrow, our in vitro artificial mitochondrial transfer in 2D cultures, as well as a newly designed 3D scaffold to mimic the MSC niche and mouse models in vivo, our objective is to determine the impact of the uptake of MSC mitochondria by different human and mouse T cell subsets on their metabolic status and, consequently, on their differentiation programs.Finally, we will access whether mitochondrial induced reprogramming of Tcells can be exploited therapeutically in a mouse model of autoimmune diabetes.To meet the objective, this 3-year project is organized in 4 tasks:

1. Assessing the molecular pathways and the extent of mitochondrial transfer from MSCs to T cells in vitro
2. Generating a 3D niche scaffold for modeling of the human bone marrow stromal microenvironment and T cell interactions
3. Assessing the metabolic and biological outcome for T cells that have acquired MSC mitochondria
4. Assessing the occurrence and impact of the MSC mitochondria transfer to T cells in vivo.

The financial instrument chosen to perform these tasks is in the form of a multidisciplinary collaborative project with two complementary partners that have already collaborated in the past. Partner 1 has an extensive expertise in the biology and physiology of MSCs and is a reference in the development of immunotherapies for inflammatory diseases. Partner 2 provides his expertise in the field of biopolymer chemistry, in order to recreate novel artificial 3D structures, and approaching physiological conditions, in the study of MSC-T cell interactions.

Our network is focusing on the comprehension of mechanisms that are responsible for the T cell immunomodulatory properties of MSCs under both physiological and pathological conditions. One of the strengths of this project is that understanding the pathways via which MSCs interact with T cells, and modulating their functionality, could set the basis for the design of novel immunotherapeutic strategies for inflammatory diseases.