Léolène J. Carrington

"Lymphoid tissue stromal cells are highly sensitive to immune-mediated damage after allogeneic bone marrow transplantation"

Léolène J. Carrington, Ashley Vanderbeck, Daniela Gómez Atria, Samantha Kelly, Frederick Allen, Gloria Jih, Anneka Allman, Eric Perkey, and Ivan Maillard

In preclinical models of hematopoietic cell transplantation (allo-HCT), lymphoid tissue stromal cells expressing Delta-like Notch ligands deliver pathogenic Notch signals to drive T cell alloimmunity and acute graft-versus-host disease (GVHD). However, previous work from our lab and others indicates that lymph node fibroblastic stromal cells can be targeted and damaged by the alloreactive T cell response after allo-HCT. This immune-mediated injury impairs the supportive functions of stromal cells in immune cell trafficking and activation, thus contributing to defective immunity (e.g., poor responses to vaccination and immunization). In addition, it has the potential to impair peripheral tolerance mechanisms. We hypothesize that defective lymphoid tissue stromal cells play a key role in the immune dysregulation of chronic GVHD. To start testing this hypothesis, we have adapted a parent/F1 model to conditions with limited mortality within 30-60 days after allo-HCT, allowing us to track the magnitude and impact of stromal injury in the presence of low level systemic GVHD as well as thymic GVHD. In preliminary results, we observed no significant loss of blood endothelial cells and lymphatic endothelial cells (LECs). However, there was profound depletion of gp38/podoplanin+ LN fibroblastic stromal cells in mice with GVHD compared to T-cell depleted bone marrow recipients. Specialized immune-interacting fibroblasts such as MAdCAMhi marginal reticular cells and “floor LECs”, which line the marginal zone sinus and support filtering of lymph node antigens were markedly decreased in LNs. Furthermore, CD157hi fibroblastic stromal cells, which we have shown to be important in early priming of alloreactive T cells via Dll4 Notch ligand expression were also particularly sensitive to immune-mediated damage. Whereas thymopoiesis was preserved in our low grade GVHD model, naïve T cells were profoundly decreased in GVHD-damaged lymph nodes, suggesting defective recruitment or retention of newly formed T cells by lymph node stroma. Damage was profound up to day 60 after transplantation with no recovery of immune-interacting fibroblast populations. Immunofluorescence imaging showed defective compartmentalization of T and B cell zones, with evidence of increased collagen deposition. Altogether, our data suggest that stromal cells in secondary lymphoid organs are even more sensitive to GVHD than thymic epithelial cells, with no evidence of functional recovery. Through continued profiling of the fibroblastic subsets most susceptible to injury, we are exploring the impact of stromal damage in secondary lymphoid organs on immune dysfunction after allo-HCT.