CD38 expression levels on immune cell subsets in PB samples obtained during treatment with daratumumab monotherapy followed by daratumumab with ATRA. (A) CD38 expression levels on monocytes, B cells, T cells, NK cells, and activated NK cells (CD16⁺) in sequential PB samples obtained before start of daratumumab monotherapy (C1D1 of part A; n = 55), and after 1 cycle of daratumumab monotherapy (C2D1 of part A; n = 51). (B) CD38 expression levels on these immune cell subsets in sequential PB samples obtained before start of ATRA treatment (C1D1 of part B; n = 51), before first dose of daratumumab after initiation of ATRA (C1D3 of part B; n = 42), after 1 cycle of daratumumab and ATRA treatment (C2D3 of part B; n = 36), and at disease progression during daratumumab and ATRA treatment (EOT, part B; n = 33). Dots represent individual expression levels; error bars represent median and IQR. Median fluorescence intensity is provided for each timepoint. Differences between indicated groups were calculated using Wilcoxon matched-pairs rank test. *P < .05; **P < .01; ***P < .001; ****P < .0001. EOT, end of treatment; IQR, interquartile range; MFI, median fluorescence intensity; ns, not significant.