Serum B-cell Maturation Antigen Research Articles

Elevated serum levels of soluble B-cell maturation antigen as a prognostic biomarker for multiple myeloma.

Serum B-cell maturation antigen (sBCMA) levels can serve as a sensitive biomarker in multiple myeloma (MM). In the research setting, sBCMA levels can be accurately detected by enzyme-linked immunosorbent assay (ELISA), but the approach has not been approved for clinical use. Here, we used a novel chemiluminescence method to assess sBCMA levels in 759 serum samples from 17 healthy donors and 443 patients with plasma cell (PC) diseases including AL amyloidosis, POEMS syndrome and MM. Serum BCMA levels were elevated 16.1-fold in patients with newly diagnosed MM compared to healthy donors and rare PC diseases patients. Specifically, the sBCMA levels in patients with progressive disease were 64.6-fold higher than those who showed partial response or above to treatment. The sBCMA level also correlated negatively with the response depth of MM patients. In newly diagnosed and relapsed MM patients, survival was significantly longer among those subjects whose sBCMA levels are below the median levels compared with those above the median value. We optimized the accuracy of the survival prediction further by integrating sBCMA level into the Second Revised International Staging System (R2-ISS). Our findings provide evidence that the novel chemiluminescence method is sensitive and practical for measuring sBCMA levels in clinical samples and confirm that sBCMA might serve as an independent prognostic biomarker for MM.

Integrative Analysis of the Tumor and Microenvironment to Model the Molecular Heterogeneity Underlying the Response to Cevostamab in Relapsed/Refractory Multiple Myeloma

Background: Cevostamab is an FcRH5xCD3 bispecific antibody that facilitates T-cell directed killing of myeloma cells and has shown promising activity and a favorable safety profile as monotherapy in patients with relapsed/refractory multiple myeloma (RRMM) in the ongoing Phase I GO39775 trial (NCT03275103; Trudel et al. ASH 2021). We performed an integrative analysis of peripheral blood (PB) and bone marrow aspirate (BMA) samples collected at baseline from patients in GO39775 to understand the heterogeneity of patients with RRMM and potential correlations with clinical outcome. Methods: PB and BMA samples were collected at baseline from 100 patients in GO39775. Patients who had less than 25% missingness in any data layer were selected from the single-step (3.6/90-252mg dose levels [n=49] and 3.6/90mg tocilizumab premedication group [n=14; Trudel et al. ASH 2022]) and double-step (0.3-1.2/3.6-7.2/60-160mg dose levels [n=37]) dose-escalation and dose-expansion cohorts. To characterize immune cells, samples were profiled at a central laboratory by 8-color flow cytometry. Cytokine profiling was performed on baseline plasma samples via electrochemiluminescence and digital ELISA. Serum B-cell maturation antigen (sBCMA) levels were quantified using hybrid immunoaffinity capture by liquid chromatography with tandem mass spectrometry. For the unbiased integrative analysis, a Similarity Network Fusion algorithm was applied to preprocessed flow cytometry data from PB and BMA samples, and to baseline characteristics including demographics, prior therapies, and selected clinical laboratory analytes. Data were imputed in samples with less than 25% missingness using a random forest algorithm. Results: Initial findings from unsupervised machine learning-based integrative clustering analysis of baseline samples from multiple immunological and clinical data types revealed three patient subpopulations with unique biological features, illustrating the molecular heterogeneity of patients with RRMM. Each cluster was characterized by distinct patterns of immune cell proportions and activation states. Interestingly, these immunologically defined clusters also corresponded to clinical outcomes. Cluster 1 had the strongest response to cevostamab, followed by Cluster 2 and Cluster 3. Conclusions: Our novel, unbiased, machine learning, integrative clustering approach not only revealed unique molecular subtypes that illustrate the heterogeneity of patients with RRMM, but also identified immunological features associated with potentially reduced response to cevostamab therapy, which could provide direction for future research.

Early Safety Results of P-BCMA-ALLO1, a Fully Allogeneic Chimeric Antigen Receptor T-Cell (CAR-T), in Patients with Relapsed / Refractory Multiple Myeloma (RRMM)

P-BCMA-ALLO1 is an allogeneic CAR-T that targets B-cell Maturation Antigen (BCMA) and is currently being investigated for the treatment of RRMM. P-BCMA-ALLO1 cells are manufactured from healthy donor T-cells using non-viral transposon-based integration (piggyBac® DNA Delivery System) that introduces a human anti-BCMA V H-based CAR and an iCas9 safety switch. The piggyBac® DNA delivery system produces a highly enriched T stem cell memory product. The Cas-CLOVER™ Site-Specific Gene Editing System eliminates endogenous T cell receptor (TCR) expression via knockout of the TCR beta chain 1 gene to prevent graft-vs-host disease (GvHD), and the beta-2 microglobulin gene to reduce Major Histocompatibility Complex (MHC) class I expression to eliminate host-vs-graft responses. P-BCMA-ALLO1 demonstrated compelling activity in MM xenografts, providing rationale for this first-in-human phase I study. The primary objective is to assess the safety and maximum tolerated dose (MTD) of P-BCMA-ALLO1 based on dose limiting toxicity (DLT) in RRMM patients with measurable disease who have received a proteasome inhibitor (PI), immunomodulatory agent (IMiD) and anti-CD38 monoclonal antibody therapy. Key secondary objective will assess the anti-myeloma effect of P-BCMA-ALLO1. Exploratory objectives will assess CAR-T related cytokines, serum BCMA levels and cellular kinetics. The trial utilizes a standard 3 + 3 dose escalation design to test seven planned dose levels of intravenous P-BCMA-ALLO1 ranging from 0.0625 × 10 6 to 15 × 10 6 cells/kg (NCT04960579). Multiple lymphodepletion (LD) strategies and cyclic administration of P-BCMA-ALLO1 are being investigated. Repeat P-BCMA-ALLO1 administration is allowed for patients who do not achieve at least a partial response with the first dose after 4 weeks of follow up. We are currently dosing patients in arm S (Cyclophosphamide (Cy) 300 mg/m 2 + Fludarabine (Flu) 30 mg/m 2 X 3 days), arm P1 (Cy 500 mg/m 2 + Flu 30 mg/m 2 X 3 days), arm P2 (Cy 1,000 mg/m 2 + Flu 30 mg/m 2 X 3 days) and arm C (multiple P-BCMA-ALLO1 doses following Cy 300 mg/m 2 + Flu 30 mg/m 2 X 3 days). The median patient age was 73 (33, 85) years, 61% were female, and median time since MM diagnosis was 6.27 (1.48,18.95) years. Eight (35%) patients had high risk disease by cytogenetic criteria. The enrolled patients were heavily pretreated, having received median 7 (2,16) prior lines of therapy, with 30% having undergone prior BCMA targeting therapy. As of 10 Jul 2023, 24 patients received P-BCMA-ALLO1 at 4 dose levels. Twenty-two were treated in arm S, 1 each in arms P1 and P2. One patient received 0.25 X 10 6 cells/kg (cohort -1, arm S), 7 received 0.75 X 10 6 cells/kg (cohort 1, arm S), 12 received 2 X 10 6 cells/kg (cohort 2, 10 in arm S, 1 in arm P1 and 1 in arm P2), and 4 received 6 X 10 6 cells/kg (cohort 3). One of the cohort 2 patients received a second P-BCMA-ALLO1 infusion at the cohort 2 dose level following disease progression. The median time from enrollment to start of LD chemotherapy was 2 (1-8) days and from enrollment to CAR-T infusion was 7 (6-13) days. No patient needed bridging therapy between enrollment and the start of LD. Twenty-two (all in arm S) of the 24 treated patients completed DLT evaluation by data cutoff. None of the patients treated thus far had DLTs. Most common treatment emergent adverse events (TEAEs) were anemia (36%), neutropenia (36%), constipation (36%) and leukopenia (32%). Most common ≥ grade (G) 3 TEAEs were neutropenia (36%), leukopenia (32%) and anemia (23%). Most of the AEs were considered unrelated to P-BCMA-ALLO1. Three (14%) patients developed grade 1 Cytokine Release Syndrome (CRS). One (4%) patient experienced grade 1 Immune Effector Cell Associated Neurotoxicity Syndrome (ICANS), which resolved with one dose of corticosteroids. None of the patients experienced GvHD by the last follow up. P-BCMA-ALLO1 is a non-viral transposon-generated allogeneic “off-the-shelf” CAR-T that is rapidly available for administration and well tolerated in a heavily pretreated RRMM patient population with minimal CRS/ICANS risk. Updated results including safety, preliminary efficacy, and selected biomarkers will be presented at the American Society of Hematology 2023 meeting.

Clinical Outcomes and Serum B-Cell Maturation Antigen Levels in a Real-World Unselected Population of Newly Diagnosed Multiple Myeloma Patients.

Progression-free survival (PFS) and overall survival (OS) of newly diagnosed multiple myeloma (MM) patients have been widely published in the clinical trials setting, but data published from real-world settings are limited. We determined the survival and factors that predict outcomes among 161 unselected, newly diagnosed MM patients whose frontline therapy was started at a single clinic specializing in the treatment of this B-cell malignancy. None of these patients underwent an autologous stem cell transplantation as part of their initial therapy and the population had a high proportion (35%) of cytogenetic high-risk patients. With a median follow-up of 42.7 months, the cohort had a median PFS of 22.8 months and a median OS of 136.2 months. The 1-, 3-, and 5-year survival rates were 97.5%, 85.3%, and 76.2%, respectively. These results are considerably better than those reported from patients enrolled in clinical trials and those from countries with national registries. Age <65years predicted for a longer OS (p=0.0004). Baseline serum B-cell maturation antigen (sBCMA) levels were also assessed and showed median and mean levels of 320.3 ng/mL and 551.1 ng/mL, respectively. Furthermore, patients with baseline sBCMA levels in the lowest quartile (≤136.2 ng/mL) showed a longer PFS (p=0.0262). These results provide clinicians with a real-world understanding of the survival of unselected, newly diagnosed patients initiating therapy in a clinic specializing in the care of MM patients.

Expression of sBCMA in Newly Diagnosed Multiple Myeloma Patients and Its Relationship with Prognosis

To study the expression level of serum B-cell maturation antigen (sBCMA) in the peripheral blood of newly diagnosed multiple myeloma (MM) patients, and explore its relationship with the prognosis of MM patients. The peripheral blood of 31 newly diagnosed MM patients and 30 healthy volunteers were collected. The level of sBCMA in the peripheral blood was detected by enzyme-linked immunosorbent assay (ELISA). The correlation between the level of sBCMA and the prognosis of MM patients was analyzed. The level of sBCMA in newly diagnosed MM patients was significantly higher than that in healthy controls (P <0.05). The level of sBCMA was closely related to the plasma cells ratio in bone marrow, the M protein level and the treatment (P <0.05). The level of sBCMA was negatively correlated with the overall survival (OS) of MM patients (r =-0.47). MM patients with low expression of sBCMA had significantly longer OS than patients with high expression of sBCMA (P <0.05). The level of sBCMA is significantly increased in MM patients, which is expected to be a new indicator for evaluating the curative efficacy and prognosis of MM patients. Targeting sBCMA may provide new ideas for the treatment of MM.

Serum B-Cell maturation antigen is an independent prognostic marker in previously untreated chronic lymphocytic leukemia

B-Cell maturation antigen (BCMA) is a cell membrane receptor expressed on mature B lymphocytes, with elevated serum levels found among patients with B-cell malignancies, including chronic lymphocytic leukemia (CLL). Serum BCMA (sBCMA) levels were measured in 331 untreated, newly diagnosed CLL patients using an enzyme-linked immunosorbent assay with a polyclonal anti-BCMA antibody. Elevated sBCMA levels were found among patients with CLL compared with age- and sex-matched healthy controls and those with more active CLL based on prognostic factors. The relationships between sBCMA, time to first treatment (TTFT), overall survival (OS) and multiple prognostic factors were compared using Mann-Whitney and Kruskal-Wallis tests. The median sBCMA level in the CLL cohort (48.6 ng/mL) was significantly higher (p < 0.001) compared with those of age- and sex-matched healthy subjects (n=100; 37.8 ng/mL). Serum BCMA correlated with TTFT(hazard ratio [HR]=2.9, 95% confidence interval 2.0-4.2, p < 0.001) and OS (HR=2.5, 95% confidence interval: 1.5-4.0, p < 0.001). Multiple models were used to test the predictive effects of sBCMA, sex, CLL International Prognostic Index (CLL-IPI) and International Prognostic Score for early-stage CLL (IPS-E) on TTFT and OS. The addition of sBCMA to CLL-IPI and IPS-E improved their prognostic ability to predict TTFT and OS. Thus, sBCMA is a new promising prognostic biomarker for CLL.

Serum B-cell maturation antigen level in multiple myeloma

Background Multiple myeloma (MM) is a malignant neoplasm of plasma cells that accumulate in the bone marrow producing excessive amounts of monoclonal immunoglobulins (Ig) and suppression of other normal polyclonal Igs, leading to bone destruction and marrow failure. B-cell maturation antigen (BCMA) is known to bind to B-cell-activating factor (BAFF) or a proliferation-inducing ligand (APRIL), leading to the activation of cell proliferation pathways and upregulation of antiapoptotic proteins, which is considered the main step in the pathogenesis of MM. Aim This study was planned to evaluate serum BCMA levels in MM patients and its clinical significance. Patients and methods This study was carried out on 40 newly diagnosed MM patients and 40 apparently healthy individuals served as the control. The two studied groups were compared as regards serum BCMA levels using the enzyme-linked immunosorbent assay technique. Results Results showed that there was a statistically significant increase in MM patients when compared with the control group, and there was a significant positive correlation between BCMA level and plasma cells in bone marrow, M protein, number of bone lesions, and beta-2 microglobulin. However there was no correlation between BCMA level and age, creatinine, and hemoglobin. Conclusion Serum BCMA level was significantly elevated in MM patients compared with healthy controls that may suggest the role of BCMA in the pathogenesis of MM. The high sensitivity of BCMA suggests that it may be a novel diagnostic marker, and its level was positively correlated with other prognostic markers. It may be used as a prognostic marker in MM patients.

Treatment of Patients with T Cells Expressing a Fully-Human Anti-BCMA CAR with a Heavy-Chain Antigen-Recognition Domain Caused High Rates of Sustained Complete Responses and Relatively Mild Toxicity

Multiple myeloma (MM) is a malignancy of plasma cells that is nearly always incurable. T cells expressing chimeric antigen receptors (CAR) that target B-cell maturation antigen (BCMA) can recognize and eliminate MM. The murine or other non-human sequences in the single-chain variable fragments (scFv) of many anti-BCMA CARs can elicit recipient immune responses against CAR T cells. We constructed a CAR incorporating an anti-BCMA fully-human heavy-chain variable domain designated FHVH33. FHVH33 lacks the light chain, the artificial linker sequence, and the 2 linker-associated junctions of a scFv, so FHVH33 is smaller than a scFv and is likely to be less immunogenic. The FHVH33-containing CAR utilized in this clinical trial also incorporated a CD8a hinge and transmembrane domain, a 4-1BB domain, and a CD3z domain. The CAR was designated FHVH33-CD8BBZ and was encoded by a gamma-retroviral vector. T cells expressing FHVH33-CD8BBZ were designated FHVH33-T. The FHVH33-T production process was initiated with unsorted peripheral blood mononuclear cells and took 7 days. The treatment protocol was 300 mg/m 2 of cyclophosphamide and 30 mg/m 2 of fludarabine on days -5 to -3 followed by infusion of FHVH33-T on day 0.Twenty-five patients received FHVH33-T infusions. Median age of the treated patients was 62 (range 39-73). Patients received a median of 6 prior lines of therapy (range 3-10). Five dose levels were assessed (Table). Dose level 4, 6x10 6 CAR + T cells/kg was identified as the maximum feasible dose after considering efficacy and manufacturing factors.Twenty-three of 25 patients (92%) obtained objective responses (OR) of partial response (PR) or better. Seventeen patients (68%) attained a best response of stringent complete response (sCR) or very good partial response (VGPR). Thirteen patients have ongoing responses. To date, the median duration of response is 50 weeks for the highest two dose levels. At present, the overall median progression free survival (PFS) is 78 weeks; as responses are ongoing in 13 patients (52%), PFS will likely improve. Nine of 25 patients had extramedullary plasmacytomas at baseline; patients with extramedullary plasmacytomas at baseline were less likely to achieve sCR (P=0.011).All 25 treated patients were evaluable for toxicity. Eighteen patients had grade 1 or 2 cytokine-release syndrome (CRS), and 6 patients had grade 3 CRS. One patient had no CRS. No patients had grade 4 CRS. Five patients received tocilizumab and 4 patients received corticosteroids for CRS. Two of twenty-five patients had grade 3 neurological toxicity possibly attributable to FHVH33-T. No patient had grade 4 neurologic toxicity attributable to CAR T cells. One patient died of influenza pneumonia.We assessed blood CAR+ cells by quantitative PCR. The median peak blood CAR+ cell level was 126.5 cells/µl (range 3-1071 cells/µl), and the median time post-infusion of peak blood CAR + cell levels was 10.5 days (range 7-14). Peak CAR T-cell level was not associated with obtaining a sCR. In contrast, blood CAR+ T cell levels at both 1 and 2 months after infusion were statistically higher for patients obtaining sCR. For the 1-month time-point, blood CAR+ cell levels in cells/mL were 20 for sCR patients and 4 for not sCR patients (P=0.04). Pretreatment serum BCMA was not statistically different when patients obtaining or not obtaining sCR were compared (median serum BCMA in pg/mL: sCR patients 86,243; not sCR patients 261,675, P=0.20). We assessed cell-surface BCMA expression level on MM cells by antibody binding capacity (ABC) flow cytometry. Cell-surface BCMA expression level was not statistically different in sCR versus not sCR patients (median ABC in sites/cell: sCR patients 844; not sCR patients 535, P=0.29). Patients with MM expressing low levels of BCMA obtained durable responses of greater than 2 years duration, which suggests that FHVH33-T can recognize low levels of cell-surface BCMA. Eight patients had extramedullary plasmacytomas at relapse; 4 patients had plasmacytomas biopsied. Two of the biopsied plasmacytomas were BCMA+, and two were BCMA-negative by immunohistochemistry.FHVH33-CD8BBZ CAR T cells caused relatively mild toxicity and a high rate of sCRs in patients with relapsed MM including MM with low cell-surface BCMA expression. [Display omitted] DisclosuresBrudno: Kyverna Therapeutics: Membership on an entity's Board of Directors or advisory committees. Lam: Kite, a Gilead Company: Patents & Royalties. Kochenderfer: Kite, a Gilead Company: Patents & Royalties: on anti-CD19 CARs, Research Funding; Bristol Myers Squibb: Research Funding.

Serum B-Cell Maturation Antigen As a Biomarker for Chronic Lymphocytic Leukemia Treated with Ibrutinib

INTRODUCTIONEarly assessment of tumor response in chronic lymphocytic leukemia (CLL) can be difficult during ibrutinib therapy due to treatment-related lymphocytosis and concern for radiation exposure that limits the frequency of computed tomography (CT). B-cell maturation antigen (BCMA), a member of the tumor necrosis factor super family receptors, is overexpressed in CLL. In another mature B-cell malignancy, multiple myeloma, elevated serum (s) BCMA has been associated with inferior therapeutic response and survival. It was previously shown that sBCMA levels are increased in CLL and correlated with time to first treatment and overall survival. To evaluate its utility as a biomarker in the context of targeted therapy, we assessed sBCMA in CLL patients during treatment with ibrutinib. METHODSBCMA levels were measured in the serum of 46 patients enrolled on a phase 2 study of ibrutinib for CLL (NCT01500733). The following time points were evaluated: baseline, day 2, and 1, 2, 6, 12, 24, 36, 48 months (M) after starting ibrutinib, as well as at the time of progressive disease (PD), if available. sBCMA was measured using a sandwich ELISA (R&D Systems). Lymphadenopathy was measured by the sum of the product of the diameters (SPD). Signed-rank test, rank-sum test and Spearman correlation were performed to compare sBCMA between categorical and continuous variables. RESULTSBaseline disease characteristics included relapsed or refractory CLL in 15 patients (33%), 17p deletion in 31 (67%), unmutated IGHV in 33 (72%), and advanced Rai stage in 32 (70%). The median age was 67 years (range 39-81) and 26 patients (57%) were male. At baseline, the median sBCMA was 145 ng/mL (range 24-376) and significantly higher among patients with 17p deletion than those without (median 179.6 versus 75.8, P = 0.033). sBCMA was not different with respect to prior treatment status, IGHV mutation, or Rai stage. A weak correlation between sBCMA and known serologic indicators of tumor burden and activity, β2-microglobulin (r = 0.36, P = 0.02) and lactate dehydrogenase (r = 0.41, P = 0.006), was also observed.sBCMA decreased as early as day 2 (median decrease 15%, P = 0.003) and progressively decreased during the first year of ibrutinib therapy (median decrease 79%, P < 0.0001 at 12M). To assess whether early changes in sBCMA predict tumor response, we compared lymph node response at 12M between patients dichotomized by the median decrease in sBCMA at 1M. Patients with a decrease in sBCMA above the median of 65% at 1M showed a greater reduction in lymph node SPD at 12M (median reduction 84% versus 74%, P = 0.0487). However, the decrease in sBCMA at 1M was not different between patients who achieved partial remission (n = 29) and those in complete remission (n = 16) at best response per modified iwCLL criteria.Next, we retrospectively measured sBCMA in 13 patients from whom serum was collected within 3M of PD to evaluate whether it could be used to predict PD. Baseline sBCMA was not significantly different between patients who later developed PD and those who did not. Among patients who developed PD, sBCMA reached a nadir after a median of 12M on ibrutinib therapy before gradually increasing until the time of PD (median increase 153% [interquartile range, IQR 81%-314%] from nadir). The initial increase in sBCMA was observed at a median of 8.4M (range 0-20.2) before clinical progression. In contrast, patients who remained in remission experienced lesser fluctuations in sBCMA (median increase 20% [IQR 0%-43%] from nadir). The increase in sBCMA from nadir among PD cases was significantly greater than non-PD cases (P < 0.0001). CONCLUSIONsBCMA rapidly decreased during treatment with ibrutinib. Decrease in sBCMA was associated with reduction in lymphadenopathy, while an increase in sBCMA from nadir often preceded clinical PD. sBCMA represents a potential biomarker for monitoring response and detecting disease progression in CLL patients treated with ibrutinib.This research was supported by the Intramural Research Program of NHLBI. Pharmacyclics, an Abbvie company provided ibrutinib and research support. DisclosuresBerenson:OncoTracker, Inc.: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy, Research Funding. Wiestner:Acerta Pharma: Research Funding; Pharmacyclics: Research Funding.

Changes in Serum B-Cell Maturation Antigen Levels Rapidly Indicate Changes in Clinical Status Among Multiple Myeloma Patients Undergoing New Treatments

Introduction : B-cell maturation antigen (BCMA) is a protein that is expressed on the plasma cells from patients (pts) with multiple myeloma (MM). Our group has previously shown that MM pts have higher levels of serum (s) BCMA than healthy subjects and that sBCMA levels can be used to monitor the disease course of MM pts. Notably, we have shown that the half-life of soluble BCMA is only 24-36 hours which is much shorter than sM-protein, and its levels are independent of renal function. With the expanding therapeutic options for the treatment (Tx) of MM, there is a need for more rapid and accurate ways to assess the efficacy of new therapies. To this end, we compared changes in levels of sBCMA with sM-protein among MM patients undergoing new treatments.Methods : Serum was obtained at least weekly during each pt's first cycle of a new therapy (C1) and the first day of their second cycle (C2D1) and at least monthly thereafter from all MM pts receiving a new Tx regimen (n=83) at a single clinic from March 2015 to July 2017. sM-protein levels were measured, and sBCMA levels were determined using an enzyme-linked immunosorbent assay (R&D Systems; Minneapolis, MN). Percentage changes in sBCMA and sM-protein throughout Tx were determined relative to levels measured at their start of treatment (C1D1). Kaplan-Meier analysis was used to assess differences in time on therapy (TOT) based on the percentage changes in sBCMA levels at cycle 1 day 8 (C1D8) and day 15 (C1D15) of the pt's new Tx. All patient samples were obtained following proper informed consent in accordance with the Declaration of Helsinki.Results : Forty-nine MM pts (IgG [n=37], IgA [n=12]) receiving 83 Tx regimens were analyzed. Regimens that resulted in a > 25% increase in sBCMA by C1D8 (n=10) had a shorter median TOT than all other regimens (n=71; median TOT: 1.73 months vs. 5.76 months; P=.0037). Regimens that showed a > 25% decrease in sBCMA levels on C1D8 (n=27) had a longer TOT (median TOT: 6.91 months) when compared with all other regimens (median TOT: 2.89 months). In contrast, sM-protein levels did not show > 25% changes at these early time points.For those patients who achieved at least a minimal response (MR) using IMWG criteria (n=30), the time to achieve at least a 25% decrease in sBCMA was much shorter (median 7 days) than the time for sM-protein (median 21 days; P=.0004). For those that progressed during the first cycle (n=5), the time to achieve at least a 25% increase in sBCMA was similarly much shorter (median 7 days) than the time for sM-protein (median 21 days).Because the half-life of IgG is long (approximately 3-4 weeks), we studied the 64 regimens among the 37 pts with IgG MM. Twenty-four (38%) achieved at least an MR. Among these pts, sBCMA levels reduced by an average of 31% on C1D8, whereas sM-protein decreased by an average of only 7.6%.The regimens that resulted in a > 25% decrease on C1D8 (n=23) had a longer TOT than regimens that did not reach this reduction (n=41; median TOT: 7.8 months vs. 2.8 months, P=.023). Those regimens with a confirmed > 25% increase in sBCMA levels (n=6) at C1D15 had a shorter TOT than those with a confirmed > 25% decrease in sBCMA levels (n=22) at C1D15 (median 0.9 months vs. 6.9 months, P <.0001), and had a shorter TOT than all other Tx regimens (n=75; median 0.9 months vs. 5.8 months, P <.0001).There were six regimens for which pts did not achieve a response during the first cycle but did so during subsequent cycles. At C1D8, sBCMA levels decreased > 25% in four pts and 24% in another pt. During the second week of therapy, sBCMA levels continued to decrease in these five pts. In contrast, sM-protein did not show a response (> 25% decrease) in any of these regimens during C1 and decreased by an average of only 9.7% and 13.3% on days 8 and 15, respectively.Conclusions: We have shown that relative changes in sBCMA levels from baseline can much more rapidly determine changes in clinical status than the standard sM-protein biomarker among MM pts starting new treatments. By C1D8, sBCMA establishes changes in clinical status whereas sM-protein takes much longer to show the effect of treatment on response status. In addition, a > 25% increase or decrease in sBCMA levels at C1D8 indicates a much shorter or longer TOT, respectively for these pts. Thus, relative changes in sBCMA levels among MM pts on new therapies allows more rapid determination of changes in their clinical status, and these early changes predict the length of time on those treatments. DisclosuresBerenson:OncoTracker, Inc.: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy, Research Funding.

Serum Bcma May Interfere with Anti-Bcma-CAR-Transduced T Cells or Other Anti-Bcma Antibody-Based Immunotherapy in Multiple Myeloma

Introduction: CAR T cell-based immunotherapy has shown clinical activity in a variety of B-cell malignancies. Specifically, the engineered CAR-transduced T cells targeting B-cell maturation antigen (BCMA) on multiple myeloma (MM) have shown promising activity for the treatment of relapsed/refractory (RR) MM patients. However, MM patients have high levels of solubilized BCMA (sBCMA) in the blood especially those with RR disease. Due to these findings, we hypothesized that circulating levels of sBCMA may interfere with the efficacy of CAR T cell immunotherapy or other anti-BCMA antibody (Ab)-based therapeutic approaches for treating MM patients.Study design: Sera were collected from MM patients and healthy subjects after obtaining institutional review board approval (IRB). Serum levels of human BCMA were determined using an ELISA kit (R&D Systems, Minneapolis, MN). For the BCMA antibody binding assay, 50 µL of human BCMA fluorescein-conjugated polyclonal Ab or monoclonal Ab was incubated with 100 µL of diluent buffer and 100 µL of serum from human subjects with varying sBCMA concentrations. To demonstrate the effects of sBCMA interference with anti-BCMA CAR T function, we utilized a wide range of concentrations (0ng/ml, 3ng/ml, 18 ng/mL, 32ng/ml, 37ng/ml, 110ng/ml, 156ng/ml, 390ng/ml, 530ng/ml and 2167 ng/mL); recombinant BCMA (0ng/ml, 65ng/ml, 130ng/ml, 400ng/ml, 1200ng/ml). After one hour of incubation at room temperature (RT), each sample was added to primary tumor cells from MM patients with progressive disease. These cells were incubated for two hours at RT away from light. Following incubation, cells were washed three times using PBS. Flow cytometric analysis was performed using a Beckman Coulter Cytomics FC 500 with Cytomics CXP software. The same procedure was followed to observe the effects of recombinant human BCMA. To assess immunofluorescent (IFC) analysis of anti-BCMA binding to MM tumor cells, IFC staining was completed following a standard IFC assay protocol and the BCMA binding markers were identified under the microscope (Olympus BX51).Results and discussion: The experimental results demonstrate a concentration dependent response of anti-BCMA antibody binding to primary MM tumor cells. At sBCMA levels lower than 150ng/mL, there was no significant difference in anti-BCMA antibody binding to tumor cells. However, at concentrations greater than 150 ng/mL, a significant decrease in binding was observed. At 390ng/ml, serum sBCMA blocked 50% of anti-BCMA antibody binding to the tumor cells. At 2000ng/ml, serum sBCMA interfered with anti-BCMA antibody binding to tumor cells by more than 80%. When using recombinant BCMA, we observed the same concentration dependent effects on anti-BCMA binding to MM cells. As the levels of recombinant BCMA increased, the antibody binding to MM cells decreased. These results suggest that higher BCMA levels that are present in patients with MM interfere with binding to MM tumor cells; and, thus, could reduce the efficacy of CAR T cell and other immunotherapy approaches targeting BCMA. The fluorescent image further demonstrated serum sBCMA blocked anti-BCMA antibody binding to primary MM tumor cells in a concentration dependent fashion. In 2013 Carpenter et al . showed that sBCMA levels do not interfere with CAR-T-cells. However, the sBCMA concentrations used in those experiments are based on low sBCMA levels (10ng/ml). We have consistently detected concentrations much higher than 150ng/ml of sBCMA in MM patients. Our experimental data showed 30-35% serum BCMA level was above 150ng/ml in 500 MM serum samples and 50% serum BCMA level was above 150ng/ml in relapsed/refractory patients.Conclusion: The results demonstrated that higher serum sBCMA concentrations do interfere with anti-BCMA antibody directed CAR T cells immunotherapy therapies or any anti-BCMA antibody therapeutic agents in MM. We suggest determining serum sBCMA level before anti-BCMA antibody directed CAR T cells immunotherapy therapy or use of any anti-BCMA antibody therapeutic agents. DisclosuresBerenson:OncoTracker, Inc.: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy, Research Funding.

Expression of B Cell Maturation Antigen (BCMA) and Transmembrane Activator and Caml Interactor (TACI) Are Correlated and Can be Targeted at Multiple Points during the Course of Multiple Myeloma

Therapies directed to specific antigens expressed on multiple myeloma [MM] cells are desirable given the high likelihood of relapse in patients [pts] and the toxicities associated with current treatment options. BCMA and TACI are surface proteins of interest as they promote the survival and proliferation of mature plasma cells. Given that their gene expression by RT-PCR is higher in MM cells compared to normal plasma cells [PCs], and the association of increasing serum BCMA levels with disease progression, we sought to assess if similar patterns were seen on PCs measured by flow cytometry. We specifically examined changes in BCMA/TACI expression (frequency and intensity) with progression of MM, whether expression of BCMA and TACI are correlated, and if levels of their expression correlates with PC burden as determined by IHC.Flow cytometric data were collected using a validated multi-color panel used for clinical assessment of PC burden, with the addition of antibodies to BCMA and TACI, by the Flow Cytometry Clinical Laboratory at our Center. In total, 29 myeloma pts samples were analyzed, and a retrospective chart review of these individuals was performed under an IRB-approved protocol.Pts were separated into 4 sets of groups based on their number of prior lines of therapy, status of disease, prior autologous stem cell transplant [ASCT], and early relapse post-ASCT. Frequency and intensity of BCMA/ TACI expression were examined across these groups by assessing the following variables within each set of groups: % BCMA+ total PCs, % TACI+ total PCs, as well as BCMA/TACI mean fluorescence intensity (MFI). Correlation analysis was performed to assess whether BCMA expression correlated to TACI expression (n=25). To evaluate the correlation of PC burden in BM aspirate with antigen expression, correlation analysis was performed between PC burden and the BCMA/TACI expression (frequency and intensity). Statistical analysis was performed using GraphPad Prism 7 Software. Statistical tests included 1 way ANOVA (comparison of ≥3 means), student t-test (comparison of 2 means), and Pearson correlation (correlation analysis).The median patient age was 62, with 65.5% male and 34.5% female. IgG kappa (37.9%) was the most common type of MM. 17.2% were newly diagnosed, 27.6% had stable disease, 20.7% were in remission, and 39.5% had relapsed/refractory disease. A majority of pts (41.4%) received 1-3 prior lines of therapy. 51.7% underwent ASCT, 10% of which had relapsed, with 13.8% of relapses occurring ≤ 1 year post-ASCT.Four of 29 pts were excluded from data analysis due to insufficient PCs as detected by flow cytometry. ≥Four lines of therapy (n=9), relapsed/refractory disease (n=8), relapse post-ASCT (n=7), and relapse ≤ 1 year post-ASCT (n=2), were all markers of disease progression. There were no significant differences in BCMA/ TACI expression (frequency and intensity) among these groups and their counterparts, but less variability of expression was observed in newly diagnosed pts.There was a positive correlation between % BCMA+ total PCs with % TACI+ total PCs (r= 0.6051, p= 0.0014, n=25), and BCMA MFI with TACI MFI (r=0.5191, p=0.0078, n=25). A similar relationship was noted where aberrant PCs were identified (r=0.9199, p= 0.0094, n=6).Of the patients without minimal residual disease, there was a negative correlation between PCs in BM aspirate with % TACI+ total PCs(r= -0.5211, p= 0.0320, n=17). There were no significant correlations with PCs in BM aspirate and % of BCMA+ total PCs, BCMA MFI, and TACI MFI. BCMA/TACI expression was spread across a broad range for pts with ≤ 10% clonal PCs in BM aspirate, and a narrower range in pts with > 10% clonal PCs in BM aspirate.BCMA and TACI expression alone are not markers of progression of MM and should be used in conjunction with other antigens associated with progressive disease. However, the persistent and frequent expression of BCMA and TACI identified suggests that BCMA and TACI directed therapies can be used at multiple points during the course of disease. Since expression seems to be more uniform in newly diagnosed patients, patients treated at later time points may benefit from quantitative assessment of BCMA and/or TACI expression prior to receiving therapies targeting these molecules. Finally, expression of BCMA and TACI are correlated, but it remains to be seen if loss of one antigen could precipitate obligate loss of the other. DisclosuresNo relevant conflicts of interest to declare.

Baseline serum B-cell maturation antigen levels predict time to disease progression for patients with smoldering multiple myeloma.

Multiple myeloma (MM) patients with smoldering (S) disease are defined by a lack of CRAB/SLiM criteria but may transform into disease requiring treatment. The International Myeloma Working Group risk stratification model for SMM uses serum M-protein, serum-free light chain ratio, and bone marrow plasma cell percentage. We investigated whether baseline serum B-cell maturation antigen (sBCMA) levels are predictive of disease progression among 65 patients with SMM. A receiver operating characteristic curve was used to establish a definition for high-risk baseline sBCMA. Mantel Byar analysis was used to examine whether high-risk sBCMA was correlated with shorter time to transformation, and a time-dependent cox proportional hazard was used to determine whether it is independent of other risk factors. A z test for proportions was used to compare the percentage of patients that progressed among high-risk versus low-risk sBCMA patients. A baseline sBCMA level ≥137.5mg/ml was found to be the optimal cutoff between high- and low-risk SMM patients. Patients with high-risk sBCMA levels had a shorter time to transformation (P=.000332). sBCMA was also higher at the time of transformation than baseline levels (P=.0116). sBCMA was the only variable found to be significantly predictive of time to transformation and additionally was found to be independent of other risk factors. In this study, we have shown for the first time that sBCMA levels predict transformation of SMM to active disease and that these levels increase at the time of transformation. These results are consistent with other studies showing that active MM patients undergoing therapy with higher baseline sBCMA levels are more likely to progress early and its levels increase at the time of disease progression.

Baseline and Changes in Serum B-Cell Maturation Antigen Levels Rapidly Indicate Changes in Clinical Status Among Patients with Relapsed/Refractory Multiple Myeloma Starting New Therapy.

B-cell maturation antigen (BCMA) is expressed on malignant plasma cells from patients with multiple myeloma (MM). These patients have higher levels of serum (s)BCMA than healthy subjects, and levels correlate with disease status. The half-life of sBCMA is only 24-36 h, and levels are independent of renal function. We determined whether baseline sBCMA values, a ≥ 25% increase, and a ≥ 50% decrease during treatment predicted progression-free survival (PFS) and overall survival (OS) among 81 patients with relapsed/refractory MM (RRMM) starting new treatments. Serum was obtained on day 22 of each patient's 28-day cycle of new therapy. Kaplan-Meier survival analysis and log-rank comparison tests were used to determine the effect of baseline sBCMA. The effect of percentage change in sBCMA was investigated using time-dependent Cox proportional hazard models. Patients with baseline sBCMA levels above the median had a shorter PFS (p=0.0077), and those in the highest quartile had a shorter PFS (p = 0.0012) and OS (p=0.0022). A ≥ 25% increase at week 4, week 8, and anytime through week 12 predicted a shorter PFS (p = 0.0011, p = 0.0005, and p < 0.0001, respectively). A ≥ 50% decrease at week 4, week 8, and anytime through week 12 predicted a longer PFS (p = 0.0045, p = 0.029, p = 0.0055, respectively). A ≥ 25% increase in sBCMA occurred before progression according to International Myeloma Working Group criteria in 67.5% of patients. Our results indicate the potential for the use of sBCMA as a new biomarker for monitoring patients with RRMM.

P0344NEFECON® (BUDESONIDE) SELECTIVELY REDUCES CIRCULATING LEVELS OF BAFF (BLYS) AND SOLUBLE BCMA AND TACI IN IGA NEPHROPATHY

Abstract Background and Aims There is increasing evidence to support a pivotal role for the gut-associated lymphoid tissue (GALT) as a major source of the poorly O-galactosylated immunoglobulin A1 (IgA1) that triggers the formation of nephritogenic immune complexes in IgA nephropathy (IgAN). Critical to the regulation of IgA synthesis in GALT are two cytokines, which regulate B-cell maturation, function and survival: BAFF (B-cell activating factor [also known as BLyS (B-lymphocyte stimulator)]) and APRIL (A PRoliferation-inducing ligand). BAFF and APRIL bind to specific cell-surface receptors: TACI (transmembrane activator and calcium modulator and cyclophilin-ligand interactor), BCMA (B-cell maturation antigen) and the BAFF receptor. Several studies have shown elevated levels of BAFF and APRIL in IgAN linked to worse clinical outcomes. The therapeutic potential of selectively targeting GALT was demonstrated in the NEFIGAN trial (NCT01738035), which assessed the safety and efficacy of a novel targeted-release formulation of budesonide (NEFECON®), designed to deliver budesonide to the GALT-rich distal ileum in patients with IgAN. The trial comprised a 6-month run-in, 9-month treatment and 3-month follow-up phase: 48 patients received NEFECON® 16 mg/day, 51 patients received NEFECON® 8 mg/day and 50 patients received placebo. The headline result of the study was that NEFECON® 16 mg/day, added to optimised renin–angiotensin system blockade, reduced proteinuria and stabilised estimated glomerular filtration rate in patients with IgAN. In this study, we aimed to determine whether NEFECON® treatment altered synthesis of the BAFF and APRIL B-cell maturation modulators. Method Serum levels of BAFF, APRIL, BCMA and TACI were measured using Luminex technology. Changes in the levels of each biomarker between randomisation (T0), end of treatment (T1) and the end of study (T2) and between treatments arms were compared using a one-way analysis of variance. Significance was set at p&amp;lt;0.05. Results A significant, dose-dependent reduction in serum BAFF levels was seen with NEFECON®, which reversed on cessation of NEFECON®. There were similar significant reductions in the levels of soluble BCMA and TACI with treatment but no effect was seen on circulating levels of APRIL. These changes were mirrored by parallel changes in soluble CD27 levels and are consistent with our previous reports describing a dose-dependent reduction in circulating IgA–IgG immune complexes, secretory IgA and galactose-deficient IgA levels with NEFECON®. Conclusion Delivering budesonide to the GALT-rich distal ileum modulates key regulators of GALT B-cell maturation in IgAN. Although the samples available are not sufficient to determine that the observed changes in serum BAFF, BCMA and TACI levels are due to a direct action on GALT, it is intriguing to note that BAFF-transgenic mice develop an IgAN-like disease, principally due to IgA overexpression in the intestinal lamina propria.

Normalization of serum B-cell maturation antigen levels predicts overall survival among multiple myeloma patients starting treatment.

Serum B-cell maturation antigen (sBCMA) is a novel biomarker for B-cell malignancies. A normal reference range (<82·59ng/ml) has been recently established but the impact of achieving normal levels to outcomes for patients receiving treatment for B-cell malignancies has not been studied. We first found that among multiple myeloma (MM) patients starting a new treatment, those who begin treatment within normal sBCMA limits (<82·59ng/ml) have improved progression-free survival (PFS; P=0·0398) and overall survival (OS; P=0·0217) than those who do not. Furthermore, among patients who begin treatment with elevated (≥82·59ng/ml) sBCMA levels, we assessed the relationship of a decrease in sBCMA to the normal range to OS and found that those who normalize sBCMA demonstrated improved OS (P=0·0078). Normalizing patients also experienced a markedly improved overall response rate (P<0·0001). Moreover, all patients who achieved complete remission (CR) showed normalization of sBCMA, and time to normalization (median 0·9months) was faster than time to CR (5·0months; P=0·0036) for these patients. These results suggest that normalization of sBCMA may be an accurate predictor of OS for MM patients during treatment and predict for a higher likelihood of response.

Estimating a normal reference range for serum B-cell maturation antigen levels for multiple myeloma patients.

The serum B-cell maturation antigen (sBCMA) has been identified as a novel serum biomarker for patients with multiple myeloma. However, no study has yet established a reference range for sBCMA levels. Its levels were determined in 196 healthy subjects and showed a right-tailed distribution with a median value of 37·51ng/ml with a standard deviation of 22·54ng/ml (range 18·78-180·39ng/ml). Partitioning of subgroup reference ranges was considered but determined to be irrelevant. A non-parametric method using the median±2 standard deviations suggests using a universal reference interval of <82·59ng/ml.

Baseline and Increases in Serum B-Cell Maturation Antigen Levels Rapidly Indicate Changes in Clinical Status Among Relapsed/Refractory Multiple Myeloma Patients Undergoing New Treatments

Baseline and Increases in Serum B-Cell Maturation Antigen Levels Rapidly Indicate Changes in Clinical Status Among Relapsed/Refractory Multiple Myeloma Patients Undergoing New Treatments

Normalization of Serum B-Cell Maturation Antigen Levels from Treatment Predicts Progression Free and Overall Survival in Multiple Myeloma Patients

Introduction: B-cell maturation antigen (BCMA) is increased in the serum (s) of multiple myeloma (MM) patients (pts). We have previously shown that baseline sBCMA levels predict outcomes for MM pts. The purpose of this study was to determine whether a decrease of sBCMA to normal levels (&lt; 82.69 ng/mL) after initiating treatment predicts both progression free survival (PFS) and overall survival (OS) among MM pts and its relationship to clinical response status in this pt population. Methods: sBCMA levels were determined using an ELISA (R&amp;D Systems; Minneapolis, MN) in 147 consecutive MM pts whose first treatment was in the frontline (n=87 [59%]) or salvage (n=60 [41%]) settings in a single clinic specializing in MM from February 2009 to April 2019 (observation cut-off: May 31, 2019). We determined sBCMA weekly during the first cycle and then monthly thereafter (median follow-up= 28 mo). An age-matched analysis of 206 healthy donors was used to determine a median normal sBCMA level of 37.6 ng/mL (SD 22.5 ng/mL). A reference threshold value of 82.7 ng/mL was determined using 2 SDs above the median. We defined normalization of sBCMA as a decrease in levels to &lt; 82.7 ng/mL on two consecutive measurements. Kaplan-Meier analysis was used to compare PFS and OS among these pts and compared with responses as defined using the IMWG criteria. All pt samples were obtained following informed consent in accordance with the Declaration of Helsinki. Results: One hundred thirteen pts (77%) had a baseline sBCMA ≥ upper threshold of normal (82.7 ng/mL) with a median of 435.3 ng/mL (range, 84.5-9,153.8 ng/mL) whereas the remaining 34 pts (23%) had baseline levels below 82.7 ng/mL and were excluded from analyses in relationship to normalizing sBCMA during their treatment. sBCMA levels normalized (&lt; 82.7 ng/mL) in over half (55%) of evaluable pts (n=62), and these pts showed a markedly longer PFS (median 33.2 mo) than pts that did not (n=51; median 4.0 mo; p&lt;0.0001). Furthermore, those normalizing their sBCMA levels showed improved OS (p&lt;0.0001). Among those evaluated during their frontline treatment (n=75), those who normalized (n=50) also showed a longer PFS (median 33.9 mo) than those who did not (n=25; median 12.8 mo; p&lt;0.0001). Only 12 of 38 pts undergoing salvage treatment normalized their sBCMA, but these pts experienced both improved PFS (median 8.3 mo vs 3.1 mo; p=0.0115) and OS (p=0.0345). We also compared the PFS and OS of pts in CR to normalization of sBCMA. Pts whose sBCMA normalized (n=62) had both similar PFS (p=0.6257) and OS (p=0.7346) to those who achieved CR (n=26). Notably, every pt who achieved CR had normalized sBCMA and all pts who failed to normalize did not achieve CR (n=51). Pts who failed to normalize had shorter PFS (median 4.0 mo; n=51) than those who did not achieve CR (median 12.7 mo; n=87; p=0.0091). Among the pts who normalized sBCMA, pts who achieved CR (n=26) had similar PFS (p=0.4029) and OS (p=0.6354) to those who did not achieve CR (n=36). Conversely, among the 87 pts who did not achieve CR, pts who normalized their sBCMA (n=36) had markedly longer PFS (median 29.4 mo) than those who did not (n=51; median 4.0 mo; p&lt;0.0001); normalizing pts also showed improved OS (p=0.0072). We examined pts whose best clinical response was ≥ MR to determine if normalization of sBCMA improved upon determination of their PFS and OS. We found that among pts who achieved PR, those who normalized sBCMA (n=26) experienced improved PFS (median 33.2 mo) than those who did not (n=18; median 12.8 mo; p=0.0173); OS was also improved in those PR pts who normalized their sBCMA (p=0.0350). Similar findings were found when analyzing those achieving MR or PR, with PFS (p=0.0006) and OS (p=0.0326) for pts who normalized (n=30) being longer than for pts who did not normalize sBCMA (n=28). Of those achieving at least an MR, both PFS (median 33.9 vs 12.8 mo; p&lt;0.0001) and OS (p=0.0052) were longer for normalizing pts (n=59) than pts who failed to normalize (n=28). Conclusion: We have demonstrated that among MM pts starting new treatment with baseline elevated sBCMA levels, normalization of sBCMA levels (&lt; 82.7 ng/mL) predicts markedly longer PFS and OS. Patients who achieve normalization have similar outcomes to those in CR. Additionally, our findings suggest that normalization of sBCMA predicts longer PFS and OS for pts who achieve ≥ MR. Therefore, normalization of sBCMA may be a novel approach to predict clinical outcomes for MM pts starting new treatment. Disclosures Chen: Oncotraker Inc: Equity Ownership. Swift:Bristol Mayers Squib: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Jansen: Consultancy, Honoraria. Berenson:Sanofi: Consultancy; Janssen: Consultancy, Speakers Bureau; Bristol-Myers Squibb: Honoraria, Research Funding; Incyte Corporation.: Consultancy, Research Funding; OncoTracker: Equity Ownership, Other: Officer; Amgen: Consultancy, Speakers Bureau; Amag: Consultancy, Speakers Bureau; Takeda: Consultancy, Speakers Bureau.

Changes in Serum B-Cell Maturation Antigen Levels Rapidly Predict Progression Free Survival among Multiple Myeloma Patients undergoing New Treatment

We have previously shown that MM patients (pts) have higher levels of serum (s) BCMA than healthy subjects and these levels can be used to monitor the course of disease of MM pts. There is a need for more rapid and accurate ways to assess the efficacy of therapy (Tx) for these pts. Thus, we compared changes in levels of sBCMA, sM-protein and SFLC among MM patients undergoing new treatments.