Transcriptional characterization of tissue-Tregs and whole tissues of skeletal muscles in muscle Treg TCR transgenic mice.

Foxp3+CD4+ regulatory T cells (Tregs) play important roles in controlling both homeostatic processes and immune responses at the tissue and organismal levels. For example, Tregs promote muscle regeneration in acute or chronic injury models by direct effects on local muscle progenitor cells as well as on infiltrating inflammatory cells. Muscle Tregs have a transcriptome, a T cell receptor (TCR) repertoire and effector capabilities distinct from those of classical, lymphoid-organ Tregs, but it has proven difficult to study the provenance and functions of these unique features due to the rarity of muscle Tregs and their fragility upon isolation. Here, we attempted to side-step these hindrances by generating, characterizing and employing a line of mice carrying rearranged transgenes encoding the TCRα and TCRβ chains from a Treg clone rapidly and specifically expanded within acutely injured hindlimb muscle of young mice. Tregs displaying the transgene-encoded TCR preferentially accumulated in injured hindlimb muscle in a TCR-dependent manner both in the straight transgenic model and in adoptive-transfer systems; non-Treg CD4+ T cells expressing the same TCR did not specifically localize in injured muscle. The definitive muscle-Treg transcriptome was not established until the transgenic Tregs inhabited muscle. When crossed onto the mdx model of Duchenne muscular dystrophy, the muscle-Treg TCR transgenes drove enhanced accumulation of Tregs in hindlimb muscles and improved muscle regeneration. These findings invoke the possibility of harnessing muscle Tregs or their TCRs for treatment of skeletal muscle pathologies.

Foxp3+CD4+调节性T细胞（Foxp3+CD4+ regulatory T cells, Tregs）在组织与机体层面调控稳态进程及免疫应答过程中发挥关键作用。例如，在急性或慢性损伤模型中，Tregs可通过直接作用于局部肌肉祖细胞及浸润的炎症细胞，促进肌肉再生。肌肉驻留Tregs拥有与经典淋巴器官来源Tregs截然不同的转录组、T细胞受体（T cell receptor, TCR）库及效应功能，但由于肌肉Tregs数量稀少且分离后极易失活，对其独特特征的起源与功能开展研究始终存在诸多阻碍。本研究通过构建、表征并应用一批转基因小鼠，该小鼠携带经重排的转基因，编码源自年轻小鼠急性损伤后肢肌肉中快速特异性扩增的Treg克隆的TCRα链与TCRβ链，以此规避上述研究障碍。无论是单纯转基因模型还是过继转移系统中，携带该转基因编码TCR的Tregs均以TCR依赖的方式优先在损伤后肢肌肉中聚集；而表达相同TCR的非Treg CD4阳性T细胞则无法特异性定位至损伤肌肉组织。直至转基因Tregs定植于肌肉组织后，肌肉Tregs的特异性转录组才得以明确。当将该模型与杜氏肌营养不良症（Duchenne muscular dystrophy, DMD）的mdx小鼠模型杂交后，肌肉Treg的TCR转基因可促进Tregs在后肢肌肉中的聚集，并改善肌肉再生过程。上述研究结果提示，我们有望通过靶向肌肉Tregs或其TCR来治疗骨骼肌相关疾病。