Report of consensus panel 2 from the 11th international workshop on Waldenström's macroglobulinemia on the management of relapsed or refractory WM patients.

The consensus panel 2 (CP2) of the 11th International Workshop on Waldenström's macroglobulinemia (IWWM-11) has reviewed and incorporated current data to update the recommendations for treatment approaches in patients with relapsed or refractory WM (RRWM). The key recommendations from IWWM-11 CP2 include: (1) Chemoimmunotherapy (CIT) and/or a covalent Bruton tyrosine kinase (cBTKi) strategies are important options; their use should reflect the prior upfront strategy and are subject to their availability. (2) In selecting treatment, biological age, co-morbidities and fitness are important; nature of relapse, disease phenotype and WM-related complications, patient preferences and hematopoietic reserve are also critical factors while the composition of the BM disease and mutational status (MYD88, CXCR4, TP53) should also be noted. (3) The trigger for initiating treatment in RRWM should utilize knowledge of patients' prior disease characteristics to avoid unnecessary delays. (4) Risk factors for cBTKi related toxicities (cardiovascular dysfunction, bleeding risk and concurrent medication) should be addressed when choosing cBTKi. Mutational status (MYD88, CXCR4) may influence the cBTKi efficacy, and the role of TP53 disruptions requires further study) in the event of cBTKi failure dose intensity could be up titrated subject to toxicities. Options after BTKi failure include CIT with a non-cross-reactive regimen to one previously used CIT, addition of anti-CD20 antibody to BTKi, switching to a newer cBTKi or non-covalent BTKi, proteasome inhibitors, BCL-2 inhibitors, and new anti-CD20 combinations are additional options. Clinical trial participation should be encouraged for all patients with RRWM.

Report of Consensus Panel 3 from the 11th International workshop on Waldenström's Macroglobulinemia: Recommendations for molecular diagnosis in Waldenström's Macroglobulinemia.

Apart from the MYD88L265P mutation, extensive information exists on the molecular mechanisms in Waldenström's Macroglobulinemia and its potential utility in the diagnosis and treatment tailoring. However, no consensus recommendations are yet available. Consensus Panel 3 (CP3) of the 11th International Workshop on Waldenström's Macroglobulinemia (IWWM-11) was tasked with reviewing the current molecular necessities and best way to access the minimum data required for a correct diagnosis and monitoring. Key recommendations from IWWM-11 CP3 included: (1) molecular studies are warranted for patients in whom therapy is going to be started; such studies should also be done in those whose bone marrow (BM) material is sampled based on clinical issues; (2) molecular studies considered essential for these situations are those that clarify the status of 6q and 17p chromosomes, and MYD88, CXCR4, and TP53 genes. These tests in other situations, and/or other tests, are considered optional; (3) independently of the use of more sensitive and/or specific techniques, the minimum requirements are allele specific polymerase chain reaction for MYD88L265P and CXCR4S338X using whole BM, and fluorescence in situ hybridization for 6q and 17p and sequencing for CXCR4 and TP53 using CD19+ enriched BM; (4) these requirements refer to all patients; therefore, sample should be sent to specialized centers.

Report of consensus panel 5 from the 11th international workshop on Waldenstrom's macroglobulinemia on COVID-19 prophylaxis and management.

Consensus Panel 5 (CP5) of the 11th International Workshop on Waldenstrom's Macroglobulinemia (IWWM-11; held in October 2022) was tasked with reviewing the current data on the coronavirus disease-2019 (COVID-19) prophylaxis and management in patients with Waldenstrom's Macroglobulinemia (WM). The key recommendations from IWWM-11 CP5 included the following: Booster vaccines for SARS-CoV-2 should be recommended to all patients with WM. Variant-specific booster vaccines, such as the bivalent vaccine for the ancestral Wuhan strain and the Omicron BA.4.5 strain, are important as novel mutants emerge and become dominant in the community. A temporary interruption in Bruton's Tyrosine Kinase-inhibitor (BTKi) or chemoimmunotherapy before vaccination might be considered. Patients under treatment with rituximab or BTK-inhibitors have lower antibody responses against SARS-CoV-2; thus, they should continue to follow preventive measures, including mask wearing and avoiding crowded places. Patients with WM are candidates for preexposure prophylaxis, if available and relevant to the dominant SARS-CoV-2 strains in a specific area. Oral antivirals should be offered to all symptomatic WM patients with mild to moderate COVID-19 regardless of vaccination, disease status or treatment, as soon as possible after the positive test and within 5 days of COVID-19-related symptom onset. Coadministration of ibrutinib or venetoclax with ritonavir should be avoided. In these patients, remdesivir offers an effective alternative. Patients with asymptomatic or oligosymptomatic COVID-19 should not interrupt treatment with a BTK inhibitor. Infection prophylaxis is essential in patients with WM and include general preventive measures, prophylaxis with antivirals and vaccination against common pathogens including SARS-CoV-2, influenza, and S. pneumoniae.

Report of consensus panel 7 from the 11th international workshop on Waldenström macroglobulinemia on priorities for novel clinical trials.

Recent advances in the understanding of Waldenström macroglobulinemia (WM) biology have impacted the development of effective novel agents and improved our knowledge of how the genomic background of WM may influence selection of therapy. Consensus Panel 7 (CP7) of the 11th International Workshop on WM was convened to examine the current generation of completed and ongoing clinical trials involving novel agents, consider updated data on WM genomics, and make recommendations on the design and prioritization of future clinical trials. CP7 considers limited duration and novel-novel agent combinations to be the priority for the next generation of clinical trials. Evaluation of MYD88, CXCR4 and TP53 at baseline in the context of clinical trials is crucial. The common chemoimmunotherapy backbones, bendamustine-rituximab (BR) and dexamethasone, rituximab and cyclophosphamide (DRC), may be considered standard-of-care for the frontline comparative studies. Key unanswered questions include the definition of frailty in WM; the importance of attaining a very good partial response or better (≥VGPR), within stipulated time frame, in determining survival outcomes; and the optimal treatment of WM populations with special needs.

Clonal B cells in Waldenström's macroglobulinemia exhibit functional features of chronic active B-cell receptor signaling.

Waldenström's macroglobulinemia (WM) is a B-cell non-Hodgkin's lymphoma (B-NHL) characterized by immunoglobulin M (IgM) monoclonal gammopathy and the medullary expansion of clonal lymphoplasmacytic cells. Neoplastic transformation has been partially attributed to hyperactive MYD88 signaling, secondary to the MYD88 L265P mutation, occurring in the majority of WM patients. Nevertheless, the presence of chronic active B-cell receptor (BCR) signaling, a feature of multiple IgM+ B-NHL, remains a subject of speculation in WM. Here, we interrogated the BCR signaling capacity of primary WM cells by utilizing multiparametric phosphoflow cytometry and found heightened basal phosphorylation of BCR-related signaling proteins, and augmented phosphoresponses on surface IgM (sIgM) crosslinking, compared with normal B cells. In support of those findings we observed high sIgM expression and loss of phosphatase activity in WM cells, which could both lead to signaling potentiation in clonal cells. Finally, led by the high-signaling heterogeneity among WM samples, we generated patient-specific phosphosignatures, which subclassified patients into a 'high' and a 'healthy-like' signaling group, with the second corresponding to patients with a more indolent clinical phenotype. These findings support the presence of chronic active BCR signaling in WM while providing a link between differential BCR signaling utilization and distinct clinical WM subgroups.

miR-23b/SP1/c-myc forms a feed-forward loop supporting multiple myeloma cell growth.

Deregulated microRNA (miR)/transcription factor (TF)-based networks represent a hallmark of cancer. We report here a novel c-Myc/miR-23b/Sp1 feed-forward loop with a critical role in multiple myeloma (MM) and Waldenstrom's macroglobulinemia (WM) cell growth and survival. We have found miR-23b to be downregulated in MM and WM cells especially in the presence of components of the tumor bone marrow milieu. Promoter methylation is one mechanism of miR-23b suppression in myeloma. In gain-of-function studies using miR-23b mimics-transfected or in miR-23b-stably expressing MM and WM cell lines, we observed a significant decrease in cell proliferation and survival, along with induction of caspase-3/7 activity over time, thus supporting a tumor suppressor role for miR-23b. At the molecular level, miR-23b targeted Sp1 3'UTR and significantly reduced Sp1-driven nuclear factor-κB activity. Finally, c-Myc, an important oncogenic transcription factor known to stimulate MM cell proliferation, transcriptionally repressed miR-23b. Thus MYC-dependent miR-23b repression in myeloma cells may promote activation of oncogenic Sp1-mediated signaling, representing the first feed-forward loop with critical growth and survival role in myeloma.

Phase I/II trial of everolimus in combination with bortezomib and rituximab (RVR) in relapsed/refractory Waldenstrom macroglobulinemia.

We examined the combination of the mammalian target of rapamycin inhibitor everolimus with bortezomib and rituximab in patients with relapsed/refractory Waldenstrom macroglobulinemia (WM) in a phase I/II study. All patients received six cycles of the combination of everolimus/rituximab or everolimus/bortezomib/rituximab followed by maintenance with everolimus until progression. Forty-six patients were treated; 98% received prior rituximab and 57% received prior bortezomib. No dose-limiting toxicities were observed in the phase I. The most common treatment-related toxicities of all grades were fatigue (63%), anemia (54%), leucopenia (52%), neutropenia (48%) and diarrhea (43%). Thirty-six (78%) of the 46 patients received full dose therapy (FDT) of the three drugs. Of these 36, 2 (6%) had complete response (90% confidence interval (CI): 1-16). In all, 32/36 (89%) of patients experienced at least a minimal response (90% CI: 76-96%). The observed partial response or better response rate was 19/36 (53, 90 CI: 38-67%). For the 36 FDT patients, the median progression-free survival was 21 months (95% CI: 12-not estimable). In summary, this study demonstrates that the combination of everolimus, bortezomib and rituximab is well tolerated and achieved 89% response rate even in patients previously treated, making it a possible model of non-chemotherapeutic-based combination therapy in WM.

The WHIM-like CXCR4(S338X) somatic mutation activates AKT and ERK, and promotes resistance to ibrutinib and other agents used in the treatment of Waldenstrom's Macroglobulinemia.

CXCR4(WHIM) somatic mutations are common Waldenstrom's Macroglobulinemia (WM), and are associated with clinical resistance to ibrutinib. We engineered WM cells to express the most common WHIM (Warts, Hypogammaglobulinemia, Infections and Myelokathexis), CXCR(S338X) mutation in WM. Following SDF-1a stimulation, CXCR4(S338X) WM cells exhibited decreased receptor internalization, enhanced and sustained AKT kinase (AKT) and extracellular regulated kinase (ERK) signaling, decreased poly (ADP-ribose) polymerase and caspase 3 cleavage, and decreased Annexin V staining versus CXCR4 wild-type (WT) cells. CXCR4(S338X)-related signaling and survival effects were blocked by the CXCR4 inhibitor AMD3100. SDF-1a-treated CXCR4(S338X) WM cells showed sustained AKT and ERK activation and decreased apoptotic changes versus CXCR4(WT) cells following ibrutinib treatment, findings which were also reversed by AMD3100. AKT or ERK antagonists restored ibrutinib-triggered apoptotic changes in SDF-1a-treated CXCR4(S338X) WM cells demonstrating their role in SDF-1a-mediated ibrutinib resistance. Enhanced bone marrow pAKT staining was also evident in CXCR4(WHIM) versus CXCR4(WT) WM patients, and remained active despite ibrutinib therapy in CXCR4(WHIM) patients. Last, CXCR4(S338X) WM cells showed varying levels of resistance to other WM relevant therapeutics, including bendamustine, fludarabine, bortezomib and idelalisib in the presence of SDF-1a. These studies demonstrate a functional role for CXCR4(WHIM) mutations, and provide a framework for investigation of CXCR4 inhibitors in WM.

Detection of MYD88 L265P in peripheral blood of patients with Waldenström's Macroglobulinemia and IgM monoclonal gammopathy of undetermined significance.

MYD88 L265P is highly prevalent in Waldenstrom's Macroglobulinemia (WM) and IgM monoclonal gammopathy of unknown significance (MGUS). We investigated whether MYD88 L265P could be identified by peripheral blood (PB) allele-specific PCR. MYD88 L265P was detected in untreated WM (114/118; 96.6%); previously treated WM (63/102; 61.8%); and IgM MGUS (5/12; 41.7%) but in none of 3 hyper-IgM or 40 healthy individuals. Median PB MYD88 L265P ΔCt was 3.77, 7.24, 10.89, 12.33 and 14.07 for untreated WM, previously treated WM, IgM MGUS, hyper-IgM and healthy individuals, respectively (P<0.0001). For the 232 IgM MGUS and WM patients, PB MYD88 L265P ΔCt moderately correlated to bone marrow (BM) disease (r=-0.3553; P<0.0001), serum IgM (r=-0.3262; P<0.0001) and hemoglobin (r=0.3005; P<0.0001) levels. PB MYD88 L265P ΔCt and serum IgM correlated similarly with BM disease burden. For positive patients, PB MYD88 L265P ΔCt was <6.5 in 100/114 (88%) untreated WM, and >6.5 in 4/5 (80%) IgM MGUS patients (P=0.0034). Attainment of a negative PB MYD88 L265P mutation status was associated with lower BM disease (P=0.001), serum IgM (P=0.019) and higher hemoglobin (P=0.004) levels in treated patients. These studies show the feasibility for detecting MYD88 L265P by PB examination, and the potential for PB MYD88 L265P ΔCt use in the diagnosis and management of WM patients.

Absence of somatic MYD88 L265P mutations in patients with primary Sjogren's syndrome.

Sjogren's syndrome (SS) is a chronic autoimmune disorder with the highest risk for lymphoma development among all autoimmune diseases. In order to evaluate whether the presence of the recently described MYD88 L265P mutation in patients with Waldenström's macroglobulinemia (WM) is contributory to SS-associated lymphomagenesis, a quantitative allele-specific PCR method was performed in peripheral blood derived from 90 SS patients as well as in minor salivary gland tissues derived from 12 primary SS patients with or without lymphoma. MYD88 L265P was not detected in either of the samples tested. Although the absence of the MyD88 L265P somatic mutation in our SS cohort does not exclude a common germline susceptibility gene in SS, it might suggest a distinct operating pathogenetic mechanism in SS-related lymphoma compared with WM and other hematological malignancies.

Mast cells in Waldenstrom's macroglobulinemia support lymphoplasmacytic cell growth through CD154/CD40 signaling.

Bone marrow (BM) mast cells (MC) are commonly found in association with lymphoplasmacytic cells (LPC) in patients with Waldenström's macroglobulinemia (WM). We therefore sought to clarify the role of MC in WM. Co-culture of sublethally irradiated HMC-1 MC, KU812 basophilic cells, or autologous BM MC along with BM LPC from WM patients resulted in MC dose-dependent tumor colony formation and/or proliferation as assessed by 3H-thymidine uptake studies. Furthermore, by immunohistochemistry, multicolor flow cytometry and/or RT-PCR analysis, CD40 ligand (CD154), a potent inducer of B-cell expansion, was expressed on BM MC from 32 of 34 (94%), 11 of 13 (85%), and 7 of 9 (78%) patients, respectively. In contrast, MC from five healthy donors did not express CD154. By multicolor flow cytometry, CD154 was expressed on BM LPC from 35 of 38 (92%) patients and functionality was confirmed by CD154 and CD40 agonistic antibody stimulation, which induced proliferation, support survival and/or pERK phosphorylation of LPC. Moreover, MC induced expansion of LPC from 3 of 5 patients was blocked in a dose dependent manner by use of a CD154 blocking protein. These studies demonstrate that in WM, MC may support tumor cell expansion through constitutive CD154-CD40 signaling and therefore provide the framework for therapeutic targeting of MC and MC-WM cell interactions in WM.

Characterization of familial Waldenstrom's macroglobulinemia.

BACKGROUND: Familial clustering of B-cell disorders among Waldenström's macroglobulinemia (WM) patients has been reported, though the frequency and any differences in disease manifestation for familial patients remain to be defined. PATIENTS AND METHODS: We therefore analyzed clinicopathological data from 257 consecutive and unrelated WM patients. Forty-eight (18.7%) patients had at least one first-degree relative with either WM (n = 13, 5.1%), or another B-cell disorder including non-Hodgkin's lymphoma (n = 9, 3.5%), myeloma (n = 8, 3.1%), chronic lymphocytic leukemia (n = 7, 2.7%), monoclonal gammopathy of unknown significance (n = 5, 1.9%), acute lymphocytic leukemia (n = 3, 1.2%) and Hodgkin's disease (n = 3, 1.2%). Patients with a familial history of WM or a plasma cell disorder (PCD) were diagnosed at a younger age and with greater bone marrow involvement. RESULTS: Deletions in 6q represented the only recurrent structural chromosomal abnormality and were found in 13% of patients, all non-familial cases. Interphase FISH analysis demonstrated deletions in 6q21-22.1 in nearly half of patients, irrespective of familial background. CONCLUSIONS: The above results suggest a high degree of clustering for B-cell disorders among first-degree relatives of patients with WM, along with distinct clinical features at presentation based on familial disease cluster patterns. Genomic studies to delineate genetic predisposition to WM are underway.

Extended rituximab therapy in Waldenström's macroglobulinemia.

BACKGROUND: Waldenström's macroglobulinemia (WM) is a CD20 expressing B-cell malignancy represented by the pathological diagnosis of IgM secreting lymphoplasmacytic lymphoma. Major response rates of 30% have been reported in most studies with standard dose rituximab, i.e. 4 weekly infusions at 375 mg/m(2)/week. METHODS: In an effort to increase rituximab activity in WM, an extended dose schedule employing two sets of four (375 mg/m(2)/week) infusions at weeks 1-4 and 12-16 was evaluated. Expression of the complement resistance antigens CD46, CD55 and CD59 was also evaluated on tumor cells pre- and post-therapy to determine impact on response. RESULTS: Twenty-nine patients were enrolled and 26 patients completed the intended therapy. On an intent to treat analysis, 14 (48.3%) patients achieved a partial response, and 5 (17.2%) patients achieved a minor response. Responses were observed in 18/24 (75%) patients with a serum IgM level of <6000 mg/dl, and only 1 of 5 (20%) patients with a level of >6000 mg/dl (P=0.03). The median time to best response was 17 months, and only 2 of 19 responding patients progressed with a median follow-up of 29 months. No differences in baseline expression of the complement resistance antigens CD46, CD55 and CD59 were observed among responding and non-responding patients, although post-therapy CD55 expression was higher in non-responding patients (P=0.002). CONCLUSIONS: These data show that extended rituximab therapy is active and may lead to more major responses over standard dose rituximab in WM. WM patients with serum IgM levels of <6000 mg/dl are more likely to benefit from extended rituximab therapy.

Paradoxical increases in serum IgM and viscosity levels following rituximab in Waldenstrom's macroglobulinemia.

BACKGROUND: The anti-CD20 monoclonal antibody rituximab is an important therapeutic in Waldenstrom's macroglobulinemia (WM), producing response rates of 50-70%. Responses, which are based on serum IgM levels, have typically been evaluated at 12 weeks. Paradoxically, we have observed that serum IgM levels can abruptly rise following rituximab therapy in patients with WM, and can often lead to morbidity on the basis of hyperviscosity. PATIENTS AND METHODS: Eleven WM patients with CD20+ tumor cells who received rituximab at our Institution and had serum IgM levels measured within a 12-week period following start of therapy were evaluated. Therapy consisted of four weekly infusions of rituximab at 375 mg/m(2). Pre- and post-therapy serum IgM levels were determined by nephelometry and corresponding serum viscosity levels were determined by viscometry. RESULTS: Ten of the 11 patients demonstrated an abrupt rise in serum IgM levels, with a >25% increase occurring in eight (73%) patients. Mean serum IgM levels for all 10 spiking patients rose from 4370 (range, 655-7940) to a peak of 5865 (range, 872-11 800) mg/dl (P=0.004), which occurred at a mean of 4 (range, 1-8) weeks following initiation of therapy. Mean serum viscosity levels also increased from 3.5 to 5.6 centipoise (CP) (P=0.09) in eight patients for whom pre- and post-therapy studies were obtained. A subdural hemorrhage occurred in one patient when serum IgM levels rose from 7530 to 11 800 mg/dl, and serum viscosity increased from 3.9 to 10.1 CP. Two other spiking patients with pre-therapy IgM levels of >5000 mg/dl experienced worsening headaches and/or epistaxis attributed to increasing serum viscosity. CONCLUSIONS: Abrupt increases in serum IgM levels commonly occur following rituximab therapy in WM. Careful clinical and laboratory monitoring is warranted, particularly if patients have pre-therapy serum IgM levels of >5000 mg/dl. The mechanism of this effect is under active investigation, and may be related to CD20 signaling triggered by rituximab.

Adherence of multiple myeloma cells to bone marrow stromal cells upregulates vascular endothelial growth factor secretion: therapeutic applications.

Increased angiogenesis has recently been recognized in active multiple myeloma (MM). Since vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) are two key mediators of angiogenesis, we characterized the production of VEGF, b-FGF and interleukin-6 (IL-6) (a MM growth and survival factor) in MM cell lines and Epstein-Barr virus (EBV) transformed B cell lines from MM patients, patient MM cells, as well as bone marrow stromal cells (BMSCs) from normal healthy donors and MM patients. We detected secretion of VEGF, but no bFGF and IL-6, in MM cell lines (MM.1S, RPMI 8226 and U266); EBV transformed B cell lines from MM patients (IM-9, HS-Sultan and ARH77); MM cell lines resistant to doxorubicin (RPMI-DOX40), mitoxantrone (RPMI-MR20), melphalan (RPMI-LR5) and dexamethasone (MM.1R); and patient MM cells (MM1 and MM2). BMSCs from MM patients and normal donors secreted VEGF, b-FGF and IL-6. Importantly, when MM cells were adhered to BMSCs, there was a significant increase in VEGF (1.5- to 3.1-fold) and IL-6 (1.9- to 56-fold) secretion. In contrast, the bFGF decreased in co-cultures of BMSCs and MM cells. Paraformaldehyde fixation of BMSCs or MM cells prior to adhesion revealed that VEGF was produced both from BMSCs and MM cells, though it may come primarily from BMSCs in some cultures. IL-6 was produced exclusively in BMSCs, rather than MM cells. Moreover, when MM cells were placed in Transwell insert chambers to allow their juxtaposition to BMSCs without cell to cell contact, induction of VEGF and IL-6 secretion persisted, suggesting the importance of humoral factors. Addition of exogenous IL-6 (10 ng/ml) increased VEGF secretion by BMSCs. Conversely, VEGF (100 ng/ml) significantly increased IL-6 secretion by BMSCs. Moreover, anti-human VEGF (1 microg/ml) and anti-human IL-6 (10 microg/ml) neutralizing antibodies reduced IL-6 and VEGF secretion, respectively, in cultures of BMSCs alone and co-cultures of BMSCs and MM cells. Finally, thalidomide (100 microM) and its immunomodulatory analog IMiD1-CC4047 (1 microM) decreased the upregulation of IL-6 and VEGF secretion in cultures of BMSCs, MM cells and co-cultures of BMSCs with MM cells. These data demonstrate the importance of stromal-MM cell interactions in regulating VEGF and IL-6 secretion, and suggest additional mechanisms whereby thalidomide and IMiD1-CC4047 act against MM cells in the BM millieu.

TRAIL/Apo2L ligand selectively induces apoptosis and overcomes drug resistance in multiple myeloma: therapeutic applications.

Multiple myeloma (MM) remains incurable and novel treatments are urgently needed. Preclinical in vitro and in vivo evaluations were performed to assess the potential therapeutic applications of human recombinant tumor necrosis factor (TNF)-related apoptosis-inducing ligand/Apo2 ligand (TRAIL/Apo2L) in MM. TRAIL/Apo2L potently induced apoptosis of MM cells from patients and the majority of MM cell lines, including cells sensitive or resistant to dexamethasone (Dex), doxorubicin (Dox), melphalan, and mitoxantrone. TRAIL/Apo2L also overcame the survival effect of interleukin 6 on MM cells and did not affect the survival of peripheral blood and bone marrow mononuclear cells and purified B cells from healthy donors. The status of the TRAIL receptors (assessed by immunoblotting and flow cytometry) could not predict TRAIL sensitivity of MM cells. The anti-MM activity of TRAIL/Apo2L was confirmed in nu/xid/bg mice xenografted with human MM cells; TRAIL (500 microg intraperitoneally daily for 14 days) was well tolerated and significantly suppressed the growth of plasmacytomas. Dox up-regulated the expression of the TRAIL receptor death receptor 5 (DR5) and synergistically enhanced the effect of TRAIL not only against MM cells sensitive to, but also against those resistant to, Dex- or Dox-induced apoptosis. Nuclear factor (NF)-kappaB inhibitors, such as SN50 (a cell-permeable inhibitor of the nuclear translocation and transcriptional activity of NF-kappaB) or the proteasome inhibitor PS-341, enhanced the proapoptotic activity of TRAIL/Apo2L against TRAIL-sensitive MM cells, whereas SN50 reversed the TRAIL resistance of ARH-77 and IM-9 MM cells. Importantly, normal B lymphocytes were not sensitized to TRAIL by either Dox, SN50, or PS-341. These preclinical studies suggest that TRAIL/Apo2L can overcome conventional drug resistance and provide the basis for clinical trials of TRAIL-based treatment regimens to improve outcome in patients with MM. (Blood. 2001;98:795-804)

CD20-directed antibody-mediated immunotherapy induces responses and facilitates hematologic recovery in patients with Waldenstrom's macroglobulinemia.

Waldenstrom's macroglobulinemia (WM, lymphoplasmacytic lymphoma) is a B-cell lymphoproliferative disorder in which CD20 is expressed on tumor cells from most patients. Several small studies have suggested a benefit from the anti-CD20 monoclonal antibody rituximab (Rituxan, MabThera) in patients with WM. In this retrospective study, we examined the outcome of 30 previously unreported patients with WM who received treatment with single-agent rituximab (median age 60; range 32-83 years old). The median number of prior treatments for these patients was 1 (range 0-6), and 14 patients (47%) received a nucleoside analogue before rituximab therapy. Patients received a median of 4.0 (1-11.3) infusions of rituximab (375 mg/m2). Three patients received steroids with their infusions for prophylaxis of rituximab-related infusion syndrome. Overall, treatment was well tolerated. Median immunoglobulin M (IgM) levels for all patients declined from 2,403 mg/dL (range 720-7639 mg/dL) to 1,525 mg/dL (range 177-5,063 mg/dL) after rituximab therapy (p = 0.001), with 8 of 30 (27%) and 18 of 30 (60%) patients demonstrating >50% and >25% decline in IgM, respectively. Median bone marrow lymphoplasmacytic (BM LPC) cell involvement declined from 60% (range 5-90%) to 15% (range 0-80%) for 17 patients for whom pre- and post-BM biopsies were performed (p < 0.001). Moreover, 19 of 30 (63%) and 15 of 30 (50%) patients had an increase in their hematocrit (HCT) and platelet (PLT) counts, respectively. Before rituximab therapy, 7 of 30 (23.3%) patients were either transfusion or erythropoietin dependent, whereas only 1/30 (3.3%) patients required transfusions (no erythropoietin) after rituximab. Overall responses after treatment with rituximab were as follows: 8 (27%) and 10 (33%) of the patients achieved a partial (PR) and a minor (MR) response, respectively, and an additional 9 (30%) of patients demonstrated stable disease (SD). No patients attained a complete response. The median time to treatment failure for responding (PR and MR) patients was 8.0 months (mean 8.4: range 3-20+ months), and 5.0 months (mean 6.1; range 3-12+ months) for patients with SD. These studies therefore demonstrate that rituximab is an active agent in WM. Marked increases in HCT and PLT counts were noted for most patients, including patients with WM who had MR or SD. A prospective clinical trial to more completely define the benefit of single-agent rituximab in patients with WM has been initiated by many of our centers.

Tumor cell expression of CD59 is associated with resistance to CD20 serotherapy in patients with B-cell malignancies.

The anti-CD20 chimeric monoclonal antibody rituximab (Rituxan) is used to treat patients with various B-cell tumors, including patients with plasma cell dyscrasias who have CD20+ disease. Many patients with CD20+ disease have either primary unresponsive disease or progress after initially responding to rituximab; therefore, understanding how tumor cells are, or become, resistant to rituximab is of clinical relevance. In this report, we determined whether tumor cells express antigens that block complement-mediated lysis or antibody-dependent cell-mediated cytotoxicity (ADCC) and thereby contribute to rituximab resistance. We demonstrate that expression of the complement regulator CD59 is associated with resistance to rituximab-mediated complement lysis of multiple myeloma (MM) and non-Hodgkin's lymphoma (NHL) cell lines. Moreover, neutralization of CD59 using a blocking monoclonal antibody reversed resistance to rituximab-mediated complement lysis of CD20++ CD59++ ARH-77 MM cells. In addition, we demonstrate the presence of CD59 and rituximab binding on viable tumor cells from patients with MM and Waldenstrom's macroglobulinemia with progressive disease despite rituximab therapy. Last, we also examined MM and NHL B-cell lines, as well as patient tumor cells, for the expression of other antigens that may have a role in blocking ADCC activity, such as Fas ligand (FasL), MUCI, or TRAIL. FasL, MUC1, and/or TRAIL were coexpressed with complement regulators on many of these cells. These studies therefore show that complement regulators, particularly CD59 and antigens that may block ADCC, are present on various B-cell tumors and associated with rituximab resistance in patients. A prospective, clinical study is assessing the role of these antigens in mediating rituximab resistance.

Thalidomide and immunomodulatory derivatives augment natural killer cell cytotoxicity in multiple myeloma.

The antiangiogenic activity of thalidomide (Thal), coupled with an increase in bone marrow angiogenesis in multiple myeloma (MM), provided the rationale for the use of Thal in MM. Previously, the direct anti-MM activity of Thal and its analogues (immunomodulatory drugs, IMiDs) on MM cells was demonstrated, suggesting multiple mechanisms of action. In this study, the potential immunomodulatory effects of Thal/IMiDs in MM were examined. It was demonstrated that Thal/IMiDs do not induce T-cell proliferation alone but act as costimulators to trigger proliferation of anti-CD3-stimulated T cells from patients with MM, accompanied by an increase in interferon-gamma and IL-2 secretion. However, an increase in autologous T-cell killing of patient MM cells could not be demonstrated. A role for natural killer (NK)- and LAK-cell-mediated killing is suggested because IL-2-primed peripheral blood mononuclear cells (PBMCs) treated with Thal/IMiDs demonstrated significantly increased lysis of MM cell lines. Cold target inhibition assays suggested NK- rather than LAK-cell-mediated killing. Furthermore, this killing was not major histocompatibility complex-class restricted, and the depletion of CD56(+) cells blocked the drug-induced MM cell lysis. It was significant that increased killing of patient MM cells by autologous PBMCs treated with Thal/IMiDs was also observed. Although the in vivo relevance of NK-cell-mediated MM cell killing is unknown, phenotypic analysis performed in MM patients receiving Thal therapy demonstrated an increase in CD3(-)CD56(+) cells in patients responding to therapy. Thus in vitro and in vivo data support the hypothesis that Thal may mediate its anti-MM effect, at least in part, by modulating NK cell number and function.

Concepts in the use of TRAIL/Apo2L: an emerging biotherapy for myeloma and other neoplasias.

TNF-related apoptosis inducing ligand/Apo2 ligand (TRAIL/Apo2L) is a member of the TNF superfamily of death ligands that selectively induces apoptosis in tumour cells of diverse origins. In this report, we have reviewed recent studies examining TRAIL/Apo2L-induced apoptosis in multiple myeloma (MM), a B-cell malignancy which, in spite of its initial sensitivity to steroids, cytotoxic and high-dose chemotherapy, remains incurable. Recently, we demonstrated that TRAIL/Apo2L induces apoptosis of steroid- and chemotherapy-sensitive and resistant MM cell lines. Moreover, TRAIL/Apo2L selectively induced apoptosis of patient MM tumour cells while sparing non-malignant bone marrow and peripheral blood mononuclear cells. In addition, TRAIL/Apo2L inhibited the growth of human plasmacytomas xenografted into mice. Importantly, TRAIL/Apo2L-induced apoptosis was unaffected by IL-6, a potent growth and survival factor for MM cells which, as we and others have previously shown, blocks various pro-apoptotic signals including Fas ligand, which like TRAIL/Apo2L is also a member of the TNF family of ligands. In view of the potential clinical application of TRAIL/Apo2L to the treatment of MM, we have attempted to discern intracellular mechanisms of action and resistance for TRAIL/Apo2L in MM, along with strategies to increase sensitivity and overcome resistance of MM cells to TRAIL/Apo2L. These studies demonstrated that doxorubicin, an agent which is commonly used to treat MM patients, upregulated the expression of the DR5 death-signalling TRAIL receptor and synergistically enhanced the pro-apoptotic effect of TRAIL on MM cells. Moreover, NF-kappaB inhibitors such as SN50 (a cell permeable inhibitor of NF-kappaB nuclear translocation) as well as the proteasome inhibitor PS-341, which is currently in Phase II clinical trials, also enhanced the pro-apoptotic activity of TRAIL/Apo2L in MM cells. Lastly, TRAIL/Apo2L-induced apoptosis in MM cells was dependent on caspase-8 activation and inhibited by the caspase regulatory proteins FLIP and cIAP2. These studies provide a framework for the use of TRAIL/Apo2L as a single agent or as part of combination therapy for the treatment of MM.