Tissue origin of cytotoxic natural killer cells dictates their differential roles in mouse digit tip regeneration and progenitor cell survival

Summary

Regeneration of amputated digit tips relies on mesenchymal progenitor cells and their differentiation into replacement bone and tissue stroma. Natural killer (NK) cells have well-characterized roles in antigen-independent killing of virally infected, pre-tumorous, or stressed cells; however, the potential for cytotoxic activity against regenerative progenitor cells is unclear. We identified NK cell recruitment to the regenerating digit tip, and NK cytotoxicity was observed against osteoclast and osteoblast progenitors. Adoptive cell transplants of spleen NK (SpNK) or thymus NK (ThNK) donor cells into immunodeficient mice demonstrated ThNK cell-induced apoptosis with a reduction in osteoclasts, osteoblasts, and proliferative cells, resulting in inhibition of regeneration. Adoptive transfer of NK cells deficient in NK cell activation genes identified that promotion of regeneration by SpNK cells requires Ncr1, whereas inhibition by ThNK cells is mediated via Klrk1 and perforin. Successful future therapies aimed at enhancing regeneration will require a deeper understanding of progenitor cell protection from NK cell cytotoxicity.

Graphical abstract

Highlights

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  NK cell ablation delays regeneration, demonstrating a regulatory role in vivo

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  Spleen-derived NK (SpNK) and thymus-derived (ThNK) cells are cytotoxic ex vivo

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  SpNK cells enhance regeneration in vivo without progenitor cell cytotoxicity

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  ThNK cells inhibit regeneration in vivo via progenitor cell destruction

Abstract

Dastagir et al. identified two NK cell subsets with divergent activity on osteoclast and osteoblast progenitor cells critical for successful digit tip regeneration. Spleen-derived NK cells are non-cytotoxic in vivo and enhance regeneration, but thymus-derived NK cells maintain cytotoxicity and inhibit regeneration. These findings reveal new insights into potential mechanisms of regenerative failure in human tissue.