Mesenchymal stem cells govern immune cell maturation in the tumor microenvironment of oral squamous cell carcinoma

Mesenchymal stem cells (MSCs) have a role in the recruitment and modulation of immune cells due to their strong immunomodulatory effects. Due to their immunomodulatory properties, it is undeniable that MSCs could also influence the immune landscape of the tumor microenvironment (TME). Our study traced bone marrow-derived cells using GFP ⁺ bone marrow chimeric mice. Compared to the conventional bone marrow transplantation method (BMT), our improved enzyme-cleaved bone marrow harvestation method (cBMT) allows us to collect more bone marrow-derived MSCs than BMT. Using the difference in MSC population in BMT and cBMT, we study the influences of MSCs in the immune environment of oral squamous cell carcinoma (OSCC) tumors. cBMT tumors, which have a higher population of MSCs, created tumors with a histological resemblance to wild-type mice tumors. Interestingly, recruited GFP-positive cells were higher in number in BMT tumors; however, CD45 ⁺ cells in cBMT tumors were higher. The immune cell landscape in cBMT tumors resembled more closely to that of tumors in normal wild mice. Upon detailed examination, we discovered that mature T and B cells were recruited more into cBMT tumors, while immature macrophages and myeloid-derived suppressor cells invaded more into BMT tumors. Here, we provided insight into how MSCs control the immune landscape in the tumor microenvironment.