Ex vivo evaluation of the effect of regulatory T cells on the anti-tumor activity of bortezomib in multiple myeloma

•A primary multiple myeloma cell culture and a co-culture with host Treg cells were established.•The interaction between Treg cell expansion and the anti-tumor effect of bortezomib was revealed.•Treg cells had varied effects on bortezomib, increasing, decreasing, or not changing its anti-tumor effect on multiple myeloma.•Treg cells increased the ex vivo anti-tumor effect of bortezomib in patients who did not develop bortezomib resistance in...