研究背景和目的：2022年底由猴痘病毒（Mpox Virus, MPXV）引起的猴痘（Monkeypox, Mpox）疫情在全球暴发，对人类健康造成了严重危害。痘苗病毒（Vaccinia Virus, VACV）和MPXV同属正痘病毒属，是研究猴痘的常用模式毒株。CAST/EiJ小鼠对正痘病毒易感，已被用于MPXV和VACV的感染模型研究。复制缺陷型痘苗病毒天坛株（Non-replicating Tiantan Vaccinia Virus Strain, NTV）疫苗是在我国自主研发的天花疫苗-痘苗病毒天坛株（Vaccinia Virus Tiantan Strain, VTT）疫苗的基础上删除与宿主范围和毒力相关的26个基因获得。本研究旨在探究MPXV和VACV在CAST/EiJ小鼠中的致病力、免疫机制及NTV疫苗的保护效果。

材料与方法：本研究通过在CAST/EiJ小鼠中通过腹腔途径分别感染MPXV和VACV构建正痘病毒小鼠感染模型，并通过转录组测序进一步分析两种毒株感染导致小鼠脾脏肿大差异的信号通路变化。通过比较两种毒株感染小鼠的体重变化、死亡率以及血浆、组织中的病毒载量、滴度和病理变化，评价两种毒株在小鼠模型中的致病力。并基于正痘病毒小鼠感染模型验证NTV疫苗保护效果。

结果：本研究成功构建了VACV和MPXV感染动物模型。低剂量VACV（VACV-L）和MPXV组小鼠出现脾脏肿大现象，但高剂量VACV（VACV-H）的小鼠脾脏肿大并不明显；VACV-L组与MPXV组脾脏中髓外造血和巨噬细胞浸润增多。转录组分析结果显示，VACV-L组、VACV-H组和MPXV组均与Calcium、MAPK及PI3K-Akt信号通路相关；与VACV-H组的致死性感染相比，VACV-L组与MPXV组在脾脏肿大方面的差异主要体现于Wnt、TNF和TGF-β信号通路。NTV疫苗保护性实验结果显示，双针免疫程序不仅完全阻断VACV致死性感染，使免疫组小鼠无体重下降及死亡，且脾肺组织病理损伤和病毒复制均被完全抑制；而对MPXV感染，单针免疫即可降低组织病毒载量（约降低100倍），双针免疫效果更加显著（降幅超1000倍），并可抑制病毒滴度至检测限以下，同时有效缓解脾脏肿大和肺组织炎症损伤的产生。

结论：本研究成功构建了VACV和MPXV感染CAST/EiJ小鼠模型，并发现低剂量VACV和MPXV感染可诱导CAST/EiJ小鼠脾脏肿大。脾脏转录组分析结果表明MPXV通过Wnt、TNF和TGF-β信号通路调控脾脏免疫反应影响脾脏肿大。NTV疫苗可显著降低VACV与MPXV在CAST/EiJ小鼠血浆和组织中的复制，并减轻脾肺组织病理损伤，能够为VACV和MPXV感染的小鼠提供有效保护。

Background and objective: At the end of 2022, a global outbreak of Monkeypox (Mpox) caused by the Monkeypox Virus (MPXV) emerged, posing significant threats to public health. The Vaccinia virus (VACV) belongs to the genus Orthopoxvirus, similar to the monkeypox virus, and is extensively utilized as a model strain in monkeypox research. CAST/EiJ mice, which are susceptible to orthopoxviruses, have been employed in infection model studies for both MPXV and VACV. The Non-replicating Tiantan Vaccinia Virus Strain (NTV) vaccine is a vaccine based on the Chinese-developed smallpox vaccine Vaccinia Virus Tiantan Strain. This vaccine was derived through the deletion of 26 genes associated with host range and virulence. The present study aims to investigate the pathogenic mechanisms and immune responses elicited by MPXV and VACV, as well as the protective efficacy of the NTV vaccine in CAST/EiJ mice.

Methods: In this study, CAST/EiJ mice were infected with MPXV and VACV via i.p. to construct an orthopoxvirus infection model, and transcriptome sequencing was used to further analyze the changes in signaling pathways related to the difference in splenomegaly caused by the two strains. The pathogenicity of the two strains in the mouse model was evaluated by comparing the weight change, mortality rate, viral load, titer and pathological changes in plasma and tissues of CAST/EiJ mice infected with the two strains. The protective effect of NTV vaccine was verified based on a mouse model of orthopoxvirus infection.

Results: Animal models of VACV and MPXV infection were successfully constructed in this study. The mice with low dose VACV (VACV-L) and MPXV showed splenomegaly, but the mice with high dose VACV (VACV-H) showed no obvious splenomegaly. 

Conclusion: In this study, a CAST/EiJ mouse model of VACV and MPXV infection was successfully constructed, and it was found that low dose VACV and MPXV infection induced splenomegaly in CAST/EiJ mice. The results of spleen transcriptome analysis showed that MPXV regulated the spleen immune response through Wnt, TNF and TGF-β signaling pathways and affected splenomegaly. NTV vaccine significantly reduces the replication of VACV and MPXV in plasma and tissues of CAST/EiJ mice, alleviates pathological damage in spleen and lung tissues, and provides effective protection against infections.