Establishing a low-dose x-ray irradiation protocol for experimental acute graft-versus-host disease

The investigation of graft-versus-host disease (GvHD) after allogeneic stem cell transplantation heavily relies on the use of experimental animal models and total body irradiation (TBI) as a conditioning regimen. However, ¹³⁷Cs is gradually being replaced as the main source of radiation due to safety concerns, and the transfer of established irradiation protocols to x-ray irradiators has proven difficult. Here, we describe the establishment of an x-ray-based irradiation protocol in an experimental mouse model for acute GvHD (C57BL6 → BALB/c). Our data show that commonly reported dosages of 6-9 Gy did not result in a viable model. Instead, irradiation with 5 Gy led to the development of clinical symptoms of GvHD in mice after transplantation with allogeneic bone marrow and T cells. Mice with GvHD displayed altered hemograms and increased serum levels of proinflammatory cytokines compared with mice without GvHD, which was accompanied by sequestration of donor lymphocytes within organs. Donor chimerism and hemogram analyses also indicated sufficient myeloablation and hematopoietic reconstitution. Overall, we show that low-dose x-ray TBI effectively promotes acute GvHD in a mismatched mouse model. We also propose that the transfer of previously established gamma-ray TBI protocols should be carefully evaluated according to individual circumstances.