Abstract Body (Do not enter title and authors here): BackgroundCardiac transplantation remains the single most effective treatment for end-stage heart failure. Despite the routine use of anti-rejection drugs in clinical practice, approximately 40% of cardiac transplant patients still experience unavoidable rejection. Timely diagnosis of early acute rejection (AR) is essential to prevent further tissue damage. Transplant rejection and graft damage is primarily mediated by recipient cytotoxic CD8⁺ T cells, which attack allografts by releasing perforin and granzyme B (GzmB).
AimThis study aimed to evaluate whether GzmB-targeted positron emission tomography (PET) imaging agent (⁶⁸Ga-grazytracer) can characterize T lymphocyte infiltration in AR.
Method Mice were subjected to GzmB-targeted PET/CT on POD 3, 5, and 7. Autoradiography, Masson staining, immunohistochemistry, and flow cytometry were performed to verify the inflammatory infiltration and graft damage . Allograft-bearing mice were intraperitoneally administered with tacrolimus (2 mg kg⁻¹) daily from operative day to post-operative day (POD) 7.
ResultThe uptake of ⁶⁸Ga-grazytracer was observed increased with the extension of rejection time(SUVmax:0.54 ± 0.07 vs. 0.19 ± 0.05 at POD 7 days, P<0.001). To assess ⁶⁸Ga-grazytracer sensitivity and specificity between isograft and allograft groups, POD 7 PET/CT imaging were analyzed for their catalytic activities by receiver-operating-characteristic(ROC)analysis (AUC=0.95, 95% CI = 0.8143–1). HE staining of the myocardium indicated massive inflammatory cell infiltration and disruption of the myocardial integrity in the allograft myocardium. Immunohistochemistry and flow cytometry showed significantly high expression of GzmB and CD8, in line with the PET/CT imaging results. Autoradiography revealed ⁶⁸Ga-grazytracer accumulation in the transplanted heart. The ⁶⁸Ga-grazytracer uptake of treated mice was significantly reduced compared with that in the allograft group (SUVmax: 0.262±0.05% vs. 0.54±0.07 at POD 7 days; P<0.001). Daily treatment with tacrolimus improved heart allograft outcome and graft survival curves revealed complete rejections of the allograft within POD 15±3 days.
ConclusionThis study demonstrated the potential of ⁶⁸Ga-grazytracer imaging to delineate early non-invasive diagnosis of heart allograft rejection. This study provides an entirely imaging-based method for monitoring allograft status. In the future, the development of imaging of GzmB may be more readily translated into clinical applications.