MicroRNA-146a reduces MHC-II expression via targeting JAK/STAT signaling in dendritic cells after stem cell transplantation.

Acute Graft-versus-host disease (GVHD) is a major immunological complication after allogeneic hematopoietic cell transplantation and a better understanding of the molecular regulation of the disease could help to develop novel targeted therapies. Here we found that a G/C polymorphism within the human microRNA-146a (miR-146a) gene of transplant recipients, which causes reduced miR-146a levels, was strongly associated with the risk of developing severe acute GVHD (n=289). In mice, deficiency of miR-146a in the hematopoietic system or transfer of recipient-type miR-146a-/- dendritic cells (DCs) enhanced GVHD, while miR-146a mimic-transfected DCs ameliorated disease. Mechanistically, lack of miR-146a enhanced JAK2-STAT1 pathway activity, which led to higher expression of class II-transactivator (CIITA) and consecutively increased MHCII-levels on DCs. Inhibition of JAK1/2 or CIITA knockdown in DCs prevented miR-146a-/- DC-induced GVHD exacerbation. Consistent with our findings in mice, patients with the miR-146a polymorphism rs2910164 in hematopoietic cells displayed higher MHCII levels on monocytes, which could be targeted by JAK1/2 inhibition. Our findings indicate that the miR-146a polymorphism rs2910164 identifies patients at high risk for GVHD before allo-HCT. Functionally we show that miR-146a acts as a central regulator of recipient-type DC activation during GVHD by dampening the pro-inflammatory JAK-STAT/CIITA/MHCII axis, which provides a scientific rationale for early JAK1/2 inhibition in selected patients.

[The role of microRNAs for immunoregulation after allogeneic hematopoietic cell transplantation]. / Mikro-RNA: Rolle bei der Immunregulation nach allogener hämatopoetischer Stammzelltransplantation.

Immunoregulation following allogeneic hematopoietic stem cell transplantation (allo-HSCT) involves the delicate balance between the desirable graft-versus-leukemia (GvL) effect and the prevention of the undesirable graft-versus-host disease (GvHD). Emerging evidence has shown that microRNAs (miRNAs) play a role in the pathogenesis of different inflammatory and malignant diseases. Especially in autoimmune diseases, allergy and GvHD numerous dysregulated miRNAs have been identified. In this review, we provide an overview of current knowledge about the role of miRNAs in the immunoregulation after allo-HSCT. Moreover, we give an outlook on potential new diagnostic and therapeutic approaches, including the use of miRNAs as clinical biomarkers and the manipulation of immune responses using miRNA mimetics.