Allogeneic Hematopoietic Cell Transplantation Promotes Atherosclerosis in Mice Driven By Donor CD8+ T Cells

Allogeneic hematopoietic cell transplantation (allo-HCT) stands as the primary, often sole treatment option for many malignant and non-malignant haematological disorders. Despite the continuous advancements of allo-HCT protocols over recent decades, graft-versus-host disease (GvHD) remains a primary adverse side effect, contributing significantly to morbidity and mortality after allo-HCT. One of the major concerns for long-term post-HCT patients is the heightened cumulative incidence of dyslipidaemia, hypertension, and diabetes mellitus all of which are significant cardiovascular risk factors (Visseren et al., Eur Heart J 2021). Indeed, a 2.7-fold increased risk of premature cardiovascular event-related mortality is observed in long-term survivors compared to the general population (Bhatia et al., Blood 2007). The main underlying cause of these cardiovascular events, such as stroke and myocardial infarction, is atherosclerosis – a chronic inflammatory disease of the artery wall, however, the potential connection between allo-HCT and atherosclerosis remained unclear so far.

Here we established a novel GvHD-atherosclerosis mouse model of minor histocompatibility antigen-(miHAg)-mismatch allo-HCT from BALB/b donors into C57BL/6 mice deficient for low density lipoprotein receptor (BALB/b, H-2^b  B6.LDLr^-/-, H-2^b) and fed them with high fat diet (HFD) to recapitulate western diet intake.

Allo-HCT resulted in mild clinical GvHD symptoms, with low disease activity in typical GvHD target organs. However, (T cells + bone marrow) BMT-recipients displayed increased atherosclerotic lesion formation compared to (bone marrow) BM controls accessed by Oil-Red-O staining of complete aorta and aldehyde-fuchsin stained aortic root. Aortic atherosclerotic lesions showed a heightened infiltration of donor CD8⁺ T cells but not CD4⁺ T cells in the aorta as evaluated by single cell RNA sequencing (scRNA seq) and spectral flow cytometry, with an expression signature of inflammation (Mif, Ccr2, Ccr5, Cxcr4, Cxcr6, Il7r, Il2rb) and cytotoxicity (FasI, Tnfrsf9, Gzmb, Tnf), suggesting alloreactive CD8⁺ T cell-mediated pathology. Furthermore, BMT recipients exhibited significantly higher serum cholesterol levels than BM recipients without significant differences in liver damage (AST, ALT and bilirubin levels). Indeed, expression of Hmgcr and Srebf2 regulating cholesterol metabolism were decreased in BMT recipients with elevated expression of cellular cholesterol removing transporters. Importantly, the expression of hydroxylases, which are important for the synthesis of bile acids from cholesterol via the classical (Cyp7a1) but not the alternative pathway (Cyp27a1), was increased in BMT- vs BM-recipients suggesting induction of genes towards compensatory pathways to lower cholesterol levels in the liver.

Notably, antibody mediated depletion of CD8⁺ T cells in B6.LDLr^-/- BMT recipients reduced atherosclerotic lesion formation, increased α-smooth muscle cell actin (αSMA), diminished necrotic cores and decreased cholesterol levels. Taken together, these findings demonstrate a critical function of allogeneic CD8⁺ T cells in promoting atherosclerotic lesion formation in mice after allo-HCT.

Our findings furnish novel insights into the underlying mechanisms of cardiovascular disease in long-term GvHD survivors. Furthermore, the utilization of this innovative mouse model offers a promising avenue for future research into the signalling pathways implicated in GvHD induced atherosclerosis.