Reprograming the tumor immunologic microenvironment by neoadjuvant chemotherapy in osteosarcoma.

Tumor-infiltrating immune cells play a crucial role in tumor progression and response to treatment. However, limited studies on infiltrating immune cells have shown inconsistent and even controversial results in osteosarcoma (OS). In addition, the dynamic changes of infiltrating immune cells after neoadjuvant chemotherapy are largely unknown. We downloaded the RNA expression matrix and clinical information of 80 osteosarcoma patients from the TARGET database. CIBERSORT was used to evaluate the proportion of 22 immune cell types based on gene expression data. M2 macrophages were found to be the most abundant immune cell type and associated with improved survival in OS. Another cohort of pretreated OS samples was evaluated by immunohistochemistry (IHC) to validate the results from CIBERSORT analysis. Matched biopsy and surgical samples from 27 patients were collected to investigated the dynamic change of immune cells and factors before and after neoadjuvant chemotherapy. Neoadjuvant chemotherapy was associated with increased densities of CD3+ T cells, CD8+ T cells, Ki67+CD8+ T cells and PD-L1+ immune cells. Moreover, HLA-DR-CD33+ myeloid derived suppressive cells (MDSCs) were decreased after treatment. We inferred that the application of chemotherapy may activate the local immune status and convert OS into an immune "hot" tumor. These findings provide rationale for investigating the schedule of immunotherapy treatment in OS patients in future clinical trials.