CD19 and myeloid sarcoma: Another study showed that B cells carry programed death ligand (CD19+PD-L1hi cells) that produces its regulatory effects through cell-to-cell contact through the interaction of (CD19+PD-L1hi cells) with PD-1 on T cells, which results in the termination of T follicular helper (Tfh) cell differentiation and proliferation, leading to the relapse of symptoms of MS patients [3,4].