PURPOSE High levels of circulating tumor plasma cells (CTC-high) in patients with multiple myeloma are a marker of aggressive disease. We aimed to confirm the prognostic impact and identify a possible cutoff value of CTC-high for the prediction of progression-free survival (PFS) and overall survival (OS), in the context of concomitant risk features and minimal residual disease (MRD) achievement. METHODS CTC were analyzed at diagnosis with two-tube single-platform flow cytometry (sensitivity 4 × 10–5) in patients enrolled in the multicenter randomized FORTE clinical trial (ClinicalTrials.gov identifier: NCT02203643 ). MRD was assessed by second-generation multiparameter flow cytometry (sensitivity 10–5). We tested different cutoff values in series of multivariate (MV) Cox proportional hazards regression analyses on PFS outcome and selected the value that maximized the Harrell's C-statistic. We analyzed the impact of CTC on PFS and OS in a MV analysis including baseline features and MRD negativity. RESULTS CTC analysis was performed in 401 patients; the median follow-up was 50 months (interquartile range, 45-54 months). There was a modest correlation between the percentage of CTC and bone marrow plasma cells ( r = 0.38). We identified an optimal CTC cutoff of 0.07% (approximately 5 cells/µL, C-index 0.64). In MV analysis, CTC-high versus CTC-low patients had significantly shorter PFS (hazard ratio, 2.61; 95% CI, 1.49 to 2.97, P < .001; 4-year PFS 38% v 69%) and OS (hazard ratio, 2.61; 95% CI, 1.49 to 4.56; P < .001; 4-year OS 68% v 92%). The CTC levels, but not the bone marrow plasma cell levels, affected the outcome. The only factor that reduced the negative impact of CTC-high was the achievement of MRD negativity (interaction P = .039). CONCLUSION In multiple myeloma, increasing levels of CTC above an optimal cutoff represent an easy-to-assess, robust, and independent high-risk factor. The achievement of MRD negativity is the most important factor that modulates their negative prognostic impact.

Natural killer (NK) cells are innate cytotoxic lymphocytes that play a key role in cancer immunosurveillance thanks to their ability to recognize and kill cancer cells. NKG2D is an activating receptor that binds to MIC and ULBP molecules typically induced on damaged, transformed or infected cells. The release of NKG2D ligands (NKG2DLs) in the extracellular milieu through protease‐mediated cleavage or by extracellular vesicle (EV) secretion allows cancer cells to evade NKG2D‐mediated immunosurveillance. In this work, we investigated the immunomodulatory properties of the NKG2D ligand MICA*008 associated to distinct populations of EVs (i.e., small extracellular vesicles [sEVs] and medium size extracellular vesicles [mEVs]). By using as model a human MICA*008‐transfected multiple myeloma (MM) cell line, we found that this ligand is present on both vesicle populations. Interestingly, our findings reveal that NKG2D is specifically involved in the uptake of vesicles expressing its cognate ligand. We provide evidence that MICA*008‐expressing sEVs and mEVs are able on one hand to activate NK cells but, following prolonged stimulation induce a sustained NKG2D downmodulation leading to impaired NKG2D‐mediated functions. Moreover, our findings show that MICA*008 can be transferred by vesicles to NK cells causing fratricide. Focusing on MM as a clinically and biologically relevant model of tumour‐NK cell interactions, we found enrichment of EVs expressing MICA in the bone marrow of a cohort of patients. All together our results suggest that the accumulation of NKG2D ligands associated to vesicles in the tumour microenvironment could favour the suppression of NK cell activity either by NKG2D down‐modulation or by fratricide of NK cell dressed with EV‐derived NKG2D ligands.

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Daratumumab demonstrated activity in the treatment of AL amyloidosis in two recently concluded phase II clinical trials in relapsed and refractory patients. Its role in upfront therapy is under evaluation in a phase III study. In this report we evaluated the safety and efficacy of 28‐day cycles of daratumumab (single agent or combined with bortezomib or lenalidomide) in 72 previously treated patients with multiple myeloma and AL amyloidosis. Fifty (69%) were refractory to the last line of therapy. After eight infusions of daratumumab, 59 patients (82%) achieved a hematologic response, with 12 (16%) complete responses (CRs) and 30 (42%) very good partial responses (VGPRs). After 16 infusions, the quality of response improved with 22 patients (30%) achieving CR and 21 (29%) attaining VGPR. Cardiac response was observed in 11 of 37 evaluable patients (29%) and renal response in 23 of 38 patients (60%). Daratumumab is highly effective in heavily pretreated patients with relapsed/refractory AL amyloidosis and high bone marrow plasma cell burden. Renal responses, which are usually rare in this setting, were frequently observed.