S1PR5 regulates NK cell responses in preventing graft-versus-host disease while preserving graft-versus-tumour activity in a murine allogeneic haematopoietic stem cell transplantation model.

Graft-versus-host disease (GVHD) remains a major complication following allogeneic haematopoietic stem cell transplantation (allo-HSCT) leading to high transplant-related mortality. Natural killer (NK) cells have been found to mitigate GVHD without attenuating the graft-versus-tumour (GVT) activity in the murine model of haematopoietic stem cell transplantation. Sphingosine-1-phosphate receptor 5 (S1PR5) is a very important chemokine receptor on NK cells that governs NK cell distribution in vivo and trafficking at lesion sites. Our preliminary studies showed that the incidence of GVHD was negatively correlated with S1PR5 expression in the NK cells of patients after allo-HSCT. In the present study, we found that S1PR5 deficiency in murine NK cells blocked the migration of NK cells from the bone marrow to the GVHD target organs and attenuated the inhibitory effects on the alloreactive T cells, especially CD3+ CD8+ T cells, which may be the reason why the loss of S1PR5 in NK cells could aggravate GVHD in recipient mice. Furthermore, we also demonstrated that the absence of S1PR5 expression in NK cells did not interfere with the antitumour effects of NK cells and T cells in vivo. Taken together, our data indicate that S1PR5 plays an essential role in balancing GVHD and GVT activity.