CD28 and myeloid sarcoma: We summarize three inhibitory feedback loops to explain the protective crosstalk mechanism between DCs and Tregs in the context of MS/EAE: the CD28/cytotoxic T lymphocyte antigen (CTLA)-4/B7 pathway, the PD-L1/PD-1 inhibitory feedback loop, and the lymphocyte activation gene 3 (LAG-3)/T cell receptor (TCR)/MHC-II inhibitory feedback loop (Figure 2).