Patients at maximum response on anti-CD38 antibodies express background level CD38. (A) Swimmers plot for samples from patients who were at maximum response on or within 6 months from last dose on anti-CD38 antibody therapy. Tan brown bar indicates complete response, dark brown bar indicates very good partial response, yellow bars indicate partial response, and orange bars indicate stable disease (SD). (B) Example of a patient on Dara-based therapy who had achieved maximum response, with flow cytometry showing that CD38 expression on the residual MM cells is not distinguishable from the background expression on normal BM MNCs (non-MM). Residual MM cells were identified from BM samples as double-positive for CD138 and CD46, then verified to have BCMA. (C) For patients tested at maximum response, the ratio of CD38 expression on MM vs non-MM was below the sixfold threshold correlated to ex vivo sensitivity for most of the patients tested. (D) In contrast, in a patient who was Dara-naïve on maintenance therapy, residual MM cells gated in the same manner of greatly overexpressed CD38 expression.