Another study has found B cells highly expressing programmed death ligand-1 (CD19+PD-L1hi cells) that exert regulatory function through cell-to-cell contact via interaction of CD19+PD-L1hi cells with PD-1 on T cells, resulting in suppression of T follicular helper (Tfh) cell differentiation and expansion, which are the cell type known to be involved in the relapse of MS patients [8, 9]. Here, CD19 is linked to myeloid sarcoma.