Objective To establish the model of VX2 soft tissue xenograft in rabbit, and choose the best time for PET-CT imaging. To analyze the result of the imaging with semi-quantitative, and evaluate the feasibility of the study with VX2 soft-tissue tumor model in rabbit for PET-CT imaging. Methods 20 Japanese white rabbits were successfully implanted with VX2 tumors in thighs by the injection of tissue mass suspension.Then they were scanned with PET-CT after the diameter of the tumor is ＞2 cm. Results The diameter of the tumor＞2 cm at 14 d post implant. The average volume of tumor was (114.57±9.87) cm3.The average SUVmax of tumor's and normal tissue's in the other thigh was 5.85±0.92 and 0.22±0.09 (t=27.03, P＜0.01). SUVmax was not associated with tumor volume (r=0.02, P=0.93).Conclusion The imaging of VX2 soft tissue xenograft is clear by clinic PET-CT, and it is suitable for the study of PET-CT.PET-CT imaging performed at 14 d post implantation had the highest imaging quality.

Objective To investigate the antigen presentation characteristics of dendritic cells(DC)and B cells in cardiac grafts.Methods The heart of BALB/c mice was transplanted into the abdominal cavity of C57BL/6J mice.CD45+cells in the heart graft were extracted and sorted by flow cytometry at postoperative 5 d,and single cell RNA sequencing was performed.Taking DC and B cell subsets in cardiac grafts as the main study cells,the changing trend,antigen presenting ability and intercellular communication with T cells after heart transplantation were analyzed by bioinformatics analysis and flow cytometry.Gene ontology(GO)function enrichment difference analysis was adopted to prove the specific function and the reliability annotation of cell subsets.Results Germinal center-like B cell(GC-L B)was the B cell subset with the largest increase in quantity during the acute rejection phase,accounting for 87％.Classical DC(cDC)2 was the only DC subset with a significant increase in quantity during acute rejection of heart transplantation,accounting for 44％of DC subset,and it occupied the highest communication intensity with T cells after heart transplantation.Mononucleated DC(moDC)and memory B cell(MBC)were the main transmitters of T cell input signals in non-transplanted hearts,whereas transformed into cDC2 and GC-L B during the acute rejection phase.Among them,MBC and GC-L B were the main sources of T cell input signals in non-transplanted hearts and heart grafts.Conclusions Compared with DC,B cells occupy a higher number and weight in the intercellular communication with T cells in non-transplanted hearts and heart grafts,prompting that the antigen presenting activity of B cells is more active and stronger than DC in the early stage of acute rejection of heart transplantation.

Background::Homoharringtonine (HHT) is an effective anti-inflammatory, anti-viral, and anti-tumor protein synthesis inhibitor that has been applied clinically. Here, we explored the therapeutic effects of HHT in a mouse heart transplant model.Methods::Healthy C57BL/6 mice were used to observe the toxicity of HHT in the liver, kidney, and hematology. A mouse heart transplantation model was constructed, and the potential mechanism of HHT prolonging allograft survival was evaluated using Kaplan–Meier analysis, immunostaining, and bulk RNA sequencing analysis. The HHT-T cell crosstalk was modeled ex vivo to further verify the molecular mechanism of HHT-induced regulatory T cells (Tregs) differentiation. Results::HHT inhibited the activation and proliferation of T cells and promoted their apoptosis ex vivo. Treatment of 0.5 mg/kg HHT for 10 days significantly prolonged the mean graft survival time of the allografts from 7 days to 48 days ( P <0.001) without non-immune toxicity. The allografts had long-term survival after continuous HHT treatment for 28 days. HHT significantly reduced lymphocyte infiltration in the graft, and interferon-γ-secreting CD4 + and CD8 + T cells in the spleen ( P <0.01). HHT significantly increased the number of peripheral Tregs (about 20%, P <0.001) and serum interleukin (IL)-10 levels. HHT downregulated the expression of T cell receptor (TCR) signaling pathway-related genes ( CD4, H2-Eb1, TRAT1, and CD74) and upregulated the expression of IL-10 and transforming growth factor (TGF) -β pathway-related genes and Treg signature genes ( CTLA4, Foxp3, CD74, and ICOS). HHT increased CD4 + Foxp3 + cells and Foxp3 expression ex vivo, and it enhanced the inhibitory function of inducible Tregs. Conclusions::HHT promotes Treg cell differentiation and enhances Treg suppressive function by attenuating the TCR signaling pathway and upregulating the expression of Treg signature genes and IL-10 levels, thereby promoting mouse heart allograft acceptance. These findings may have therapeutic implications for organ transplant recipients, particularly those with viral infections and malignancies, which require a more suitable anti-rejection medication.