CXCR5 and plasma cell myeloma: Moreover, the high expression of CD38 in WT B cells may suppress even further the CXCR5+PD1hi Tfr cell function via adenosine-receptor signaling as it occurs in multiple myeloma tumor cells, which are highly positive for CD38 expression and where CD38 promotes tumor progression via the suppression of CD8+ T-cell function (58).