Injectable 3D-clustered human fibroblastic reticular cells for expanding regulatory t cells - allograft transplant rejection is currently managed mainly by pharmacological immunosuppression

Many organs recipients' quality-of-life are compromised because of the non-specific nature of the current therapies. Induction of allograft immunological tolerance has been the primary goal of new immunotherapies amongst which infusion of regulatory t cells (tregs) is a prominent strategy being evaluated in clinical studies. While the outcomes of some of the human trials are promising, the costly and complex processes of manufacturing several hundred million tregs in clinical grade facilities will limit in the near term the number of transplant recipients who would benefit from the cell-based therapy. In the current project we seek to advance an alternative method to leverage treg-mediated tolerance by formulating fibroblastic reticular cells (frcs) into injectable 3-dimensional (3D) lymphoid niches. Rodent studies have shown that frcs effectively support tregs in vivo and mediate t cell tolerance. While lymph node stromal cells can be isolated from patients in routine biopsies, only a few studies have evaluated the potential of frcs as therapeutics. Injection of single-cell frcs results in their dispersion in the body and destruction of their native physical and biological attributes. The 3D frcs formulation we have developed is enabled by a cross-linking porous biomaterials scaffold. The injectable clustered frcs (clfrcs) will be studied in two specific aims. In aim 1 we will optimize the prototype to generate tregs in vitro by tuning the cross- linking density. In aim 2, the prototype and the top 2 performing optimized clfrcs formulations will be characterized in humanized mouse models to track the migration of frcs and the capacity of the cell depots to support tregs in vivo. Our MPI team is uniquely qualified to advance the research given the complementary expertise in biologics delivery and modeling t cell homeostasis in humanized mouse models. The data generated in this work will pave the way for translational studies of frcs as cell therapies aimed at tolerance induction in allograft transplantations.