Icariin protects against acute graft-versus-host disease while preserving graft-versus-leukemia activity after allogeneic hematopoietic stem cell transplantation.

Background: Acute graft-versus-host disease (aGVHD), which is mainly mediated by allogeneic T cells, is a decisive factor in the success of allogeneic hematopoietic stem cell transplantation (allo-HCT). Prophylaxis for aGVHD in clinical patients is unsatisfactory, and there is still a huge unmet need for novel approaches. Icariin (ICA) shows potent anti-inflammatory activity and suppresses T cell-mediated immune responses. Thus, ICA is a potential drug for the prevention of aGVHD. However, there is no data assessing the impact of ICA on aGVHD after allo-HCT.

Purpose: This study aimed to investigate the protective effect of ICA against aGVHD and its mechanisms. Moreover, the impact of ICA on the graft-versus-leukemia (GVL) effect and engraftment of donor hematopoietic and immune cells were assessed.

Methods: Different murine models of allo-HCT were developed to study the influence of the ICA on GVHD and GVL effect. Flow cytometry was used to analyze the growth of leukemia cells, alterations in different immune cells, and apoptosis. Cell proliferation was determined using a CCK-8 assay. RNA sequencing and quantitative proteomic analysis were performed to elucidate the underlying mechanisms, which were further verified by polymerase chain reaction or functional experiments.

Results: Different concentrations of ICA exhibited opposite effects: low-concentration ICA promoted, while high concentrations suppressed the proliferation and function of T cells. A high dose of ICA administration during days +3 to +5 post-allo-HCT can alleviate murine aGVHD but does not affect the course of chronic GVHD (cGVHD), the GVL effect against both acute myeloid and lymphoblastic leukemia, or the recovery of donor hematological and immune cells. ICA extensively represses the expansion, function, and infiltration of donor alloreactive T cells, while preserving regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSC). Quantitative proteomic analysis showed that downregulation of integrin-linked kinase (ILK) and lymphocyte cytosolic protein 2 (LCP2) expression was possibly associated with ICA-mediated aGVHD protective effects. Furthermore, an inhibitor of ILK, which can alleviate murine aGVHD administered early after allo-HCT.

Conclusion: These findings suggest that the bioactivities of ICA are associated with its concentration and that ICA can effectively mitigate aGVHD without losing GVL activity or engraftment of donor hematopoietic and immune cells. Thus, ICA may be a promising drug for preventing aGVHD in clinical settings.