Co-activation of macrophages and T cells contribute to chronic GVHD in human IL-6 transgenic humanised mouse model

Background: Graft-versus host disease (GVHD) is a complication of stem cell transplantation associated with significant morbidity and mortality. Non-specific immune-suppression, the mainstay of treatment, may result in immune-surveillance dysfunction and disease recurrence. Methods: We created humanised mice model for chronic GVHD (cGVHD) by injecting cord blood (CB)-derived human CD34 ⁺ CD38 ⁻ CD45RA ⁻ haematopoietic stem/progenitor cells (HSPCs) into hIL-6 transgenic NOD/SCID/Il2rgKO (NSG) newborns, and compared GVHD progression with NSG newborns receiving CB CD34 ⁻ cells mimicking acute GVHD. We characterised human immune cell subsets, target organ infiltration, T-cell repertoire (TCR) and transcriptome in the humanised mice. Findings: In cGVHD humanised mice, we found activation of T cells in the spleen, lung, liver, and skin, activation of macrophages in lung and liver, and loss of appendages in skin, obstruction of bronchioles in lung and portal fibrosis in liver recapitulating cGVHD. Acute GVHD humanised mice showed activation of T cells with skewed TCR repertoire without significant macrophage activation. Interpretation: Using humanised mouse models, we demonstrated distinct immune mechanisms contributing acute and chronic GVHD. In cGVHD model, co-activation of human HSPC-derived macrophages and T cells educated in the recipient thymus contributed to delayed onset, multi-organ disease. In acute GVHD model, mature human T cells contained in the graft resulted in rapid disease progression. These humanised mouse models may facilitate future development of new molecular medicine targeting GVHD.