Limited impact of imatinib in a murine model of sclerodermic chronic graft-versus-host disease

Background: Graft-versus-host disease (GVHD) remains one of the major complications following
haematopoietic stem cell transplantation (HSCT). Approximately 15% of the patients with chronic GVHD develop the sclerodermatous form of the disease characterized by multiple organ fibrosis and loss of skin elasticity. Several studies have shown the potential benefits of imatinib, a tyrosine kinase inhibitor, as a treatment of fibrosis in cGVHD due to its
ability to inhibit simultaneously PDGF-R and c-Abl pathways which are both involved in fibrosis mechanisms. This work investigates the possible benefits of imatinib on fibrosis in a murine model of sclerodermatous chronic GVHD (sclcGVHD).
Methods: Lethally irradiated Balb/cJ mice (7 Gy TBI) were injected i.v. with 10.106 bone marrow cells and 70.106 splenocytes from B10.D2 donnor mice. Mice were then treated with sterile water or imatinib (150 mg/kg/day) by oral gavage from day +7 to day +52 following transplantation. GVHD severity was assessed three times/week with a scoring system encompassing 5 criteria (mice posture, weight loss, activity, hair loss, skin integrity ; 0-1-2 point(s)/criteria).
Results: Our results show that imatinib failed to prevent/improve GVHD with a similar evolution of the GVHD severity with no differences between groups. Histological analyses indicate a significant reduction of the phosphorylation level of the PDGR receptor (p = 0,033) and a trend to a decreased level of phosphorylated c-Abl (p = 0,1854). In vivo cell proliferation assay with CFSE were also performed and showed a reduced proliferation of T cells and subsets (CD4, CD8
and Tregs) in spleen, lymph nodes, bone marrow and blood after imatinib treatment. Finally, FACS analyses performed on days +21 and +35 after transplantation did not show any differences in the absolute T-cell counts.
Conclusion: Although we have observed a decreased phosphorylation level of PDGR receptor and less proliferation of T cells and subsets in vivo, imatinib failed to alleviate scl-cGVHD in a murine model of severe scl-cGVHD.