Endothelial cell MHC molecules are necessary and sufficient to reject 3D-printed human skin grafts in an advanced human immune system mouse.

Vascularized skins were 3D-printed using single donor human fibroblasts, pericytes, keratinocytes and endothelial cells (ECs), the latter either unmodified (WT-ECs) or deleted of MHC molecules (KO-ECs). Adult MISTRG6 immunodeficient mice neonatally inoculated with adult human hematopoietic stem cells (HSCs) received printed skin allogeneic to the HSCs and were boosted 3 weeks post-grafting with human peripheral blood mononuclear cells (PBMCs) autologous to the HSCs. HSC inoculation alone produced low levels of circulating human myeloid and lymphoid cells without affecting grafts; PBMC boosting dramatically increased circulating human CD4+ T cells and boosted CD8+ T cells only in mice with WT-EC grafts. These grafts became infiltrated by human macrophages, dendritic cells, CD4+ and CD8+ T cells, and showed evidence of rejection. Shared T cell clones were present in skin and spleen. KO-EC grafts had minimal infiltration of graft or spleen without rejection despite MHC molecule expression on other graft cell types.