Maintenance therapy in multiple myeloma

Efficacy of proteasome inhibitor-based maintenance following autologous transplantation in multiple myeloma: A systematic review and meta-analysis

INTRODUCTION

Lenalidomide maintenance, commonly prescribed in the postautologous transplantation (AHCT) setting for multiple myeloma (MM), is associated with development of secondary primary malignancies (SPM). Proteasome inhibitor maintenance (PIM) has also been evaluated in MM. We conduct a systematic review/meta-analysis to assess the efficacy of PIM in MM.

METHODS

Performing a comprehensive search of the medical literature using PubMed/Medline and EMBASE on September 11, 2019, we extracted data on clinical outcomes related to benefits (OS, PFS, and depth of hematologic response [DOHR]) and harms (SPM and adverse events). 2144 references were identified; three studies were eligible for inclusion.

RESULTS

A total of 1760 patients were included in the analysis; 507 patients received bortezomib and 395 received ixazomib maintenance. Control arms were either placebo (n = 261) or thalidomide (n = 358). PIM did not improve OS (HR 0.88, 95% CI 0.73-1.05, P = .15) but improved PFS (HR 0.77, 95% CI 0.69-0.86, P ≤ .00001) and DOHR (HR 0.88, 95% CI 0.79-0.98, P = .02) compared with control. There were no significant differences between PIM and control regarding SPM (p = NS) and ≥grade 3 peripheral neuropathy (PN) (p = NS).

CONCLUSIONS

PIM following AHCT in MM improves PFS and DOHR without an increase in development of SPM or severe PN compared with placebo/thalidomide.

Efficacy and safety of bortezomib maintenance in patients with newly diagnosed multiple myeloma: a meta-analysis

Multiple myeloma (MM) is a B-cell neoplasm with a high incidence of relapse. Bortezomib has been extensively studied for the maintenance treatment of MM. Here, we carried out a meta-analysis to determine the efficacy and safety of maintenance therapy with bortezomib. We searched for clinical trials in PubMed (Medline), Embase (OVID), and the Cochrane Library. Two randomized controlled trials (RCTs) enrolling a total of 1338 patients were included. Bortezomib maintenance statistically significantly improved both progression-free survival (PFS) (hazard ratio (HR) 0.67, 95% confidence interval (CI) = 0.51 to 0.87, P=0.003) and overall survival (OS) (HR = 0.75 therapy, 95% CI = 0.63 to 0.89, P=0.001) more than did non-bortezomib maintenance therapy. Our analysis revealed higher incidence of neutropenia (risks ratios (RR) = 1.39; 95% CI = 1.08 to 1.79), peripheral neuropathy (PN) (RR = 2.23; 95% CI = 1.38 to 3.61, P=0.001), and cardiologic events (RR = 1.91; 95% CI = 1.12 to 3.28, P=0.02) in patients with bortezomib maintenance therapy. Our meta-analysis demonstrates OS and PFS benefits of bortezomib maintenance therapy in patients with newly diagnosed MM. However, the therapy is associated with increased risk of adverse events. Additionally, more RCTs are needed for better understanding and determination of optimal bortezomib maintenance therapy in MM.

Post-Autologous (ASCT) Stem Cell Transplant Therapy in Multiple Myeloma

Autologous stem cell transplant (ASCT) is the standard of care in transplant-eligible multiple myeloma patients and is associated with significant improvement in progression-free survival (PFS), complete remission rates (CR), and overall survival (OS). However, majority of patients eventually relapse, with a median PFS of around 36 months. Relapses are harder to treat and prognosis declines with each relapse. Achieving and maintaining "best response" to initial therapy is the ultimate goal of first-line treatment and sustained CR is a powerful surrogate for extended survival especially in high-risk multiple myeloma. ASCT is often followed by consolidation/maintenance phase to deepen and/or maintain the response achieved by induction and ASCT. Novel agents like thalidomide, lenalidomide, and bortezomib have been used as single agents or in combination. Thalidomide use has been associated with a meaningful improvement in PFS and EFS, however, with substantial side effects. Data with lenalidomide maintenance after-ASCT is favorable, but the optimal duration of lenalidomide maintenance is still unclear. Bortezomib use has been associated with superior outcomes, predominantly in high-risk myeloma patients. Combination regimens utilizing a proteasome inhibitor (i.e., bortezomib) with an immunomodulatory drug (thalidomide or lenalidomide) have provided the best outcomes. This review article serves as a review of the best available evidence in post-ASCT approaches in multiple myeloma.

A multicenter phase II study of single-agent enzastaurin in previously treated multiple myeloma

Enzastaurin is an oral serine/threonine kinase inhibitor of the protein kinase C (PKC) and phosphatidylinositol 3 (PI3) kinase/Akt pathways that induces apoptosis in multiple myeloma (MM) cell lines in a caspase-independent manner. A phase II study was conducted to assess response rate, time to progression (TTP), safety and biomarker association with clinical outcomes after monotherapy with the PKC inhibitor enzastaurin in previously treated patients with MM. Eligible patients (n = 14) were treated with enzastaurin 250 mg twice daily after receiving loading doses on day 1. One minimal response was observed. The median TTP was 5.11 months. There were two grade 3 adverse events, anemia and prolonged QTc interval, and no grade 4 adverse events. Single-agent enzastaurin was well tolerated but not effective in this heavily pretreated population with MM.

Strategies for induction, autologous hematopoietic stem cell transplantation, consolidation, and maintenance for transplantation-eligible multiple myeloma patients

There have been major advances in the past decade in the continuum of therapy for transplantation-eligible multiple myeloma patients. For patients requiring therapy, recommended induction treatment consists of triple drug regimens followed by the collection of hematopoietic stem cells. The question of early versus delayed transplantation is under investigation and may identify patients for whom early transplantation is optimal therapy and those for whom it may be delayed. For transplantation-eligible patients, high-dose melphalan remains the standard regimen. After transplantation, consolidation can be considered for patients with less than a complete remission. Maintenance therapy with bortezomib or lenalidomide (or both in very-high-risk patients) is a reasonable option for long-term disease control and improvement in overall survival. Incorporation of new agents into the continuum of multiple myeloma care should result in improved outcomes and long-term disease control.

MTI-101 (cyclized HYD1) binds a CD44 containing complex and induces necrotic cell death in multiple myeloma

Our laboratory recently reported that treatment with the d-amino acid containing peptide HYD1 induces necrotic cell death in multiple myeloma cell lines. Because of the intriguing biological activity and promising in vivo activity of HYD1, we pursued strategies for increasing the therapeutic efficacy of the linear peptide. These efforts led to a cyclized peptidomimetic, MTI-101, with increased in vitro activity and robust in vivo activity as a single agent using two myeloma models that consider the bone marrow microenvironment. MTI-101 treatment similar to HYD1 induced reactive oxygen species, depleted ATP levels, and failed to activate caspase-3. Moreover, MTI-101 is cross-resistant in H929 cells selected for acquired resistance to HYD1. Here, we pursued an unbiased chemical biology approach using biotinylated peptide affinity purification and liquid chromatography/tandem mass spectrometry analysis to identify binding partners of MTI-101. Using this approach, CD44 was identified as a predominant binding partner. Reducing the expression of CD44 was sufficient to induce cell death in multiple myeloma cell lines, indicating that multiple myeloma cells require CD44 expression for survival. Ectopic expression of CD44s correlated with increased binding of the FAM-conjugated peptide. However, ectopic expression of CD44s was not sufficient to increase the sensitivity to MTI-101-induced cell death. Mechanistically, we show that MTI-101-induced cell death occurs via a Rip1-, Rip3-, or Drp1-dependent and -independent pathway. Finally, we show that MTI-101 has robust activity as a single agent in the SCID-Hu bone implant and 5TGM1 in vivo model of multiple myeloma.

Autologous hematopoietic stem cell transplantation and maintenance therapy for multiple myeloma

SUMMARY Multiple myeloma is highly treatable with novel agents such as proteasome inhibitors (bortezomib) and the immunomodulatory drugs thalidomide and lenalidomide. However, it remains an incurable disease. Induction regimens incorporating novel agents, as well as autologous hematopoietic stem cell transplantation (AHSCT), have deepened response. Following AHSCT, consolidation and maintenance therapy strategies have been developed to improve response, delay progression and improve overall survival (OS). Maintenance therapy should be effective with minimal toxicity and easily administered. The bisphosphonate zoledronate, thalidomide, lenalidomide and bortezomib improve time to progression and OS when used for maintenance therapy after AHSCT, although it is uncertain whether this improvement in OS can be attributed to the maintenance phase in the case of zoledronate. It is also important to note that few data are available regarding the exact role of bortezomib in the maintenance phase. New therapies alone or in combination with existing agents may lead to further improvement of multiple myeloma disease control after AHSCT for transplant-eligible patients.

Strategies for induction, autologous hematopoietic stem cell transplantation, consolidation, and maintenance for transplantation-eligible multiple myeloma patients

There have been major advances in the past decade in the continuum of therapy for transplantation-eligible multiple myeloma patients. For patients requiring therapy, recommended induction treatment consists of triple drug regimens followed by the collection of hematopoietic stem cells. The question of early versus delayed transplantation is under investigation and may identify patients for whom early transplantation is optimal therapy and those for whom it may be delayed. For transplantation-eligible patients, high-dose melphalan remains the standard regimen. After transplantation, consolidation can be considered for patients with less than a complete remission. Maintenance therapy with bortezomib or lenalidomide (or both in very-high-risk patients) is a reasonable option for long-term disease control and improvement in overall survival. Incorporation of new agents into the continuum of multiple myeloma care should result in improved outcomes and long-term disease control.

Fucoidan prevents multiple myeloma cell escape from chemotherapy-induced drug cytotoxicity

Minimal residual disease (MRD) occurrence with some chemotherapy drugs that promote tumor cell escape is also a key factor in blood malignancy relapse. We observed that cytarabine promotes multiple myeloma (MM) cell escape and that the number of cells in the lower chamber increased with increasing clinical disease stage in in vitro model which was constructed by a Boyden chamber, matrigel glue and serum from MM patients in different disease stages. The mechanism of cytarabine that promotes MM cell escape is closely associated with the up-regulation of CXCR4. SDF-1α can up-regulate the expression of MMP9 and RHoC proteins in MM cells with up-regulated CXCR4, and further promote the cell escape. Fucoidan, a sulfated polysaccharide in the cell wall matrix of brown algae, has attracted much attention for its multiple biological activities, and we further explored the effects and possible underlying mechanisms of fucoidan on MM cell escape from cytarabine cytotoxicity. The results show that fucoidan may decrease MM cell escape from cytarabine cytotoxicity, and that fucoidan can down-regulate CXCR4, MMP9 and RHoC expression. This research provides new direction for investigating MRD occurrence and prevention.

Bortezomib-thalidomide-dexamethasone is superior to thalidomide-dexamethasone as consolidation therapy after autologous hematopoietic stem cell transplantation in patients with newly diagnosed multiple myeloma

In a randomized, phase 3 study, superior complete/near-complete response (CR/nCR) rates and extended progression-free survival were demonstrated with bortezomib-thalidomide-dexamethasone (VTD) versus thalidomide-dexamethasone (TD) as induction therapy before, and consolidation after, double autologous stem cell transplantation for newly diagnosed myeloma patients (intention-to-treat analysis; VTD, n = 236; TD, n = 238). This per-protocol analysis (VTD, n = 160; TD, n = 161) specifically assessed the efficacy and safety of consolidation with VTD or TD. Before starting consolidation, CR/nCR rates were not significantly different in the VTD (63.1%) and TD arms (54.7%). After consolidation, CR (60.6% vs 46.6%) and CR/nCR (73.1% vs 60.9%) rates were significantly higher for VTD-treated versus TD-treated patients. VTD consolidation significantly increased CR and CR/nCR rates, but TD did not (McNemar test). With a median follow-up of 30.4 months from start of consolidation, 3-year progression-free survival was significantly longer for the VTD group (60% vs 48% for TD). Grade 2 or 3 peripheral neuropathy (8.1% vs 2.4%) was more frequent with VTD (grade 3, 0.6%) versus TD consolidation. The superior efficacy of VTD versus TD as induction was retained despite readministration as consolidation therapy after double autologous transplantation. VTD consolidation therapy significantly contributed to improved clinical outcomes observed for patients randomly assigned to the VTD arm of the study. The study is registered at www.clinicaltrials.gov as #NCT01134484.

Maintenance therapy for myeloma: how much, how long, and at what cost?

Maintenance therapy in multiple myeloma has been under investigation for more than 3 decades and has been without evidence of clear advantage in terms of progression-free survival (PFS) until the mid-2000s. Neither conventional chemotherapy, prednisone, nor interferon-based maintenance regimens offered any benefit after conventional or high-dose therapy. Thalidomide was the first drug, mainly given as maintenance after high dose therapy, to demonstrate clinical benefits in terms of PFS and, in some studies, of overall survival (OS). The role of other novel agents such as lenalidomide and bortezomib as maintenance therapy is emerging. Lenalidomide has been shown to reduce the risk of relapse with longer follow-up needed to see if this will translate into a survival benefit. At present, a number of key questions remain unanswered. What are the optimal dose and duration of those treatments? Is the risk of toxicity and second primary malignancies acceptable? Will the disease be more aggressive at time of relapse? Is the clinical benefit predicted by initial prognostic factors and response to previous therapy? Does maintenance therapy work by further eradication of minimal residual disease or by immunological control of the malignant clone? Ongoing randomized trials are evaluating lenalidomide and bortezomib, both in the transplant and nontransplant settings, to better define the role of these drugs as maintenance in multiple myeloma.

Changes in renal function after different tandem hematopoietic stem-cell transplantation approaches in patients with multiple myeloma

This study was done to observe the alteration of the estimated glomerular filtration rate (eGFR) in multiple myeloma patients according to type of tandem hematopoietic stem cell transplantation (HSCT). Forty-one patients were enrolled in this study. Twenty patients underwent autologous HSCT (auto-HSCT) and 21 patients underwent allogeneic HSCT (allo-HSCT). The changes in eGFR after the two tandem HSCT modalities were different between the two groups, according to the donor of stem cells (P = 0.016). In the auto-HSCT group, the eGFR, recorded 12 months after secondary HSCT, was significantly decreased compared with the eGFR recorded before stem cell mobilization (P = 0.005). Although there was no significant difference, the trend showed that the eGFR after allo-HSCT decreased from the previous HSCT until a month after secondary HSCT. In addition, after 6 months of secondary HSCT, the eGFR recovered to the level recorded prior to the HSCT (P = 0.062). This difference may be due to total body irradiation, a calcineurin inhibitor, or maintenance therapy. Changes in renal function would be monitored closely for these patients. The recovery of the eGFR would be a main focus for the patients treated with the total body irradiation or the calcineurin inhibitor, a progressive decline of the eGFR would be also crucial for the patients treated with maintenance therapy.

International Myeloma Working Group consensus approach to the treatment of multiple myeloma patients who are candidates for autologous stem cell transplantation

The role of high-dose therapy followed by autologous stem cell transplantation (ASCT) in the treatment of multiple myeloma (MM) continues to evolve in the novel agent era. The choice of induction therapy has moved from conventional chemotherapy to newer regimens incorporating the immunomodulatory derivatives thalidomide or lenalidomide and the proteasome inhibitor bortezomib. These drugs combine well with traditional therapies and with one another to form various doublet, triplet, and quadruplet regimens. Up-front use of these induction treatments, in particular 3-drug combinations, has affected unprecedented rates of complete response that rival those previously seen with conventional chemotherapy and subsequent ASCT. Autotransplantation applied after novel-agent-based induction regimens provides further improvement in the depth of response, a gain that translates into extended progression-free survival and, potentially, overall survival. High activity shown by immunomodulatory derivatives and bortezomib before ASCT has recently led to their use as consolidation and maintenance therapies after autotransplantation. Novel agents and ASCT are complementary treatment strategies for MM. This article reviews the current literature and provides important perspectives and guidance on the major issues surrounding the optimal current management of younger, transplantation-eligible MM patients.

Combination of IFN-α/Gm-CSF as a Maintenance Therapy for Multiple Myeloma Patients After Autologous Stem Cell Transplantation (ASCT): A Prospective Phase II Study

Interferon alpha (IFN-α) has been used as a maintenance therapy after autologous stem cell transplantation (ASCT) for multiple myeloma (MM) patients. In this study, we combined GM-CSF with IFN-α in order to improve IFN tolerance in post-ASCT myeloma patients. Primary aims were to evaluate myelotoxicity and effectiveness of this maintenance therapy. The treatment included 4 × 10⁶ units of IFN-α and 125 μg/m² of GM-CSF given three times a week for twelve months. Twenty seven patients were enrolled within 120 days after ASCT. One patient discontinued treatment due to thrombocytopenia and seven others were taken off study due to flu-like symptoms and/or increase in liver enzymes. With a median follow-up of 45.5 months, the median overall survival was not reached while the median progression-free survival was 28 months. Eleven patients (42%) have remained in very good partial remission or complete remission since ASCT. In conclusion, our results demonstrate that maintenance with GM-CSF and IFN-α is safe and effective.

Lenalidomide in multiple myeloma: an evidence-based review of its role in therapy

INTRODUCTION

Multiple myeloma (MM) is a relatively common and incurable hematological malignancy. Currently, there is no single standard therapy, with choice of treatment dependent on individual patient factors. Lenalidomide is an immunomodulatory drug with potent antitumor, antiangiogenic, immunomodulatory, and proapoptotic activity in MM.

AIMS

To evaluate the evidence for the use of lenalidomide in its current indication in relapsed or refractory MM, and additionally its investigational use for the treatment of newly diagnosed MM.

EVIDENCE REVIEW

In patients with relapsed and refractory MM, adding lenalidomide to high-dose dexamethasone significantly improves response rates and time-to-progression, relative to high-dose dexamethasone alone. This translates into a significant extension of overall survival (with a median extension of 9.1 months in a pivotal phase III study). Outcome is independent of patient age, number of previous therapies, type of previous therapy (including thalidomide or autologous stem cell transplantation), renal impairment, and beta(2)-microglobulin level. Evidence suggests that combining lenalidomide with low-dose dexamethasone improves outcomes in patients with newly diagnosed disease and is superior to lenalidomide combined with high-dose dexamethasone. Myelosuppression is the predominant toxicity observed, although some studies have shown high incidences of venous thromboembolism in the absence of prophylactic antithrombotic anticoagulation therapy. There is currently only limited evidence regarding the health economics of lenalidomide. ROLE IN THERAPY: The encouraging results obtained with lenalidomide alone and in combination with dexamethasone in patients with relapsed or refractory MM have led to its adoption as a recommended therapy in patients who have received at least one prior treatment. Emerging evidence supports the ongoing investigation of lenalidomide in combination with low-dose dexamethasone, and in other combinations including bortezomib, for use both in relapsed, refractory, and newly diagnosed MM.

Lipid raft-targeted therapy in multiple myeloma

Despite recent advances in treatment, multiple myeloma (MM) remains an incurable malignancy. By using in vitro, ex vivo and in vivo approaches, we have identified here that lipid rafts constitute a new target in MM. We have found that the phospholipid ether edelfosine targets and accumulates in MM cell membrane rafts, inducing apoptosis through co-clustering of rafts and death receptors. Raft disruption by cholesterol depletion inhibited drug uptake by tumor cells as well as cell killing. Cholesterol replenishment restored MM cell ability to take up edelfosine and to undergo drug-induced apoptosis. Ceramide addition displaced cholesterol from rafts, and inhibited edelfosine-induced apoptosis. In an MM animal model, edelfosine oral administration showed a potent in vivo antimyeloma activity, and the drug accumulated preferentially and dramatically in the tumor. A decrease in tumor cell cholesterol, a major raft component, inhibited the in vivo antimyeloma action of edelfosine and reduced drug uptake by the tumor. The results reported here provide the proof-of-principle and rationale for further clinical evaluation of edelfosine and for this raft-targeted therapy to improve patient outcome in MM. Our data reveal cholesterol-containing lipid rafts as a novel and efficient therapeutic target in MM, opening a new avenue in cancer treatment.

Short-term thalidomide incorporated into double autologous stem-cell transplantation improves outcomes in comparison with double autotransplantation for multiple myeloma

PURPOSE

To assess potential benefits with thalidomide incorporated into double autologous stem-cell transplantation (ASCT) for younger patients with newly diagnosed multiple myeloma (MM).

PATIENTS AND METHODS

One hundred thirty-five patients who received thalidomide from induction until the second ASCT were retrospectively analyzed in comparison with an equal number of pair mates treated with double ASCT not including thalidomide.

RESULTS

On an intention-to-treat basis, the addition of thalidomide to double ASCT effected a significant improvement in the rate (68% v 49%; P = .001) and duration (62% v 33% at 4 years; P < .001) of at least very good partial response (VGPR), time to progression (TTP; 61% v 41% at 4 years; P < .001) and progression-free survival (PFS; 51% v 31% at 4 years; P = .001). A trend was also noted for extended overall survival (OS) among thalidomide-treated patients (69% at 5 years v 53% for the control group), although the difference between the two groups was not statistically significant (P = .07). Benefits with thalidomide in increasing the rate of VGPR or better response, TTP, and PFS were confirmed in a multivariate analysis. Median OS after relapse was 24 months for patients receiving thalidomide added to double ASCT and 25 months for the control group. Overall, 17% of patients discontinued thalidomide, including 8% because of drug-related adverse events.

CONCLUSION

In comparison with double ASCT, the addition of first-line thalidomide to double ASCT improved clinical outcomes. Short-term thalidomide was generally well tolerated and had no adverse impact on postrelapse survival.

Identification and characterization of the interferon-beta-mediated p53 signal pathway in human peripheral blood mononuclear cells

The relationship between the p53 signal pathway and the response of human peripheral blood mononuclear cells (PBMC) to interferon (IFN)-beta has hitherto not been examined. Using an oligonucleotide microarray, we found differential expression of at least 70 genes involved in the p53 signal pathway, including p53, which regulate cell proliferation and cell death following stimulation with IFN-beta. We verified our observations on a limited set of p53-regulated genes at the transcriptional and translational levels. We also examined the consequences of the activation of the p53 signal pathway by IFN-beta in PBMC. When cultured in the presence of T-cell mitogens, IFN-beta restricted the entry of lymphocytes from the G0/G1 phase to the S phase and reduced the number of cells in the G2 phase. The addition of IFN-beta alone did not increase apoptosis. However, in the presence of actinomycin D, a DNA-damaging agent, addition of IFN-beta enhanced the susceptibility of PBMC to apoptosis. These observations suggest that, in spite of the activation of a number of mutually overlapping pathways mediating cell death, cell cycle arrest was the most evident consequence of IFN-beta signalling in PBMC.

Emerging combination treatment strategies containing novel agents in newly diagnosed multiple myeloma

Treatment strategies for multiple myeloma have changed substantially over the past 10 years following the introduction of bortezomib and the immunomodulatory drugs thalidomide and lenalidomide. In the front-line setting, combination regimens incorporating these novel agents are demonstrating substantial activity, which is translating into improved outcomes compared with previous standards of care. Response rates and depth of response that were previously only seen with high-dose therapy plus stem-cell transplantation (HDT-SCT) can now be achieved with new induction regimens utilizing these novel agents. This has raised the need for trials that will determine the clinical benefit of early SCT in patients that have already achieved a high quality of response. Here, we review the improvements in response and outcome that are seen with these novel-agent regimens, both as induction therapy prior to HDT-SCT and in non-transplant patients, and highlight the latest data from key studies of various novel combinations, including regimens featuring bortezomib plus thalidomide or lenalidomide. We also review data on response and outcomes in patients with poor prognostic characteristics that indicate that the adverse impact typically seen with these factors may be overcome using novel-agent therapy.

Therapeutic antitumor efficacy of anti-CD137 agonistic monoclonal antibody in mouse models of myeloma

PURPOSE

Eradication of post-treatment residual myeloma cells is needed to prevent relapses, and immunostimulatory monoclonal antibodies (mAb) such as anti-CD137, CTLA-4, CD40, etc., which enhance the immune response against malignancies, represent a means of achieving this purpose. This study explores anti-CD137 mAbs for multiple myeloma treatment in preclinical models of the disease because they safely augment tumor immunity and are in clinical trials for other cancers.

EXPERIMENTAL DESIGN

The antitumor effect of anti-CD137 mAb on mouse plasmacytomas derived from HOPC and NS0 cell lines was studied and compared with that of anti-CTLA-4, anti-CD40, and anti-ICAM-2 mAbs. The antitumor effect of anti-CD137 mAb was also examined in a mouse syngeneic disseminated myeloma (5TGM1) model, which more closely resembles human multiple myeloma. Depletions of specific cell populations and gene-targeted mice were used to unravel the requirements for tumor rejection.

RESULTS

Agonistic mAb against CD137 and blocking anti-CTLA-4 mAb showed activity against i.p. HOPC tumors, resulting in extended survival of mice that also became immune to rechallenge. Anti-CD137 mAbs induced complete eradications of established s.c. NS0-derived tumors that were dependent on IFN-gamma, natural killer cells, and CD8(+) T lymphocytes. Natural killer cells accumulated in tumor draining lymph nodes and showed increased IFN-gamma production. Antitumor efficacy of anti-CD137 mAb was preserved in CD28-deficient mice despite the fact that CD28 signaling increases the expression of CD137 on CD8(+) T cells. Importantly, anti-CD137 mAb treatment significantly decreased systemic tumor burden in the disseminated 5TGM1 model.

CONCLUSIONS

The immune-mediated antitumor activity of anti-CD137 mAb in mouse models holds promise for myeloma treatment in humans.