Autologous stem cell transplantation and multiple myeloma cancer stem cells

Newly diagnosed multiple myeloma: current treatment strategies, emerging therapeutic approaches and beyond

INTRODUCTION

As we have just stepped into a new decade of hopes, the mountain of knowledge learned from multiple myeloma (MM) remains unmatched among cancers. In the last decade alone, this rapid-sequence learning curve has led to regulatory approvals of eight drugs with mechanisms of actions representing five different areas of cell biology some of which made to the frontline setting, sparking debates about how to best sequence them in the treatment continuum of induction, consolidation, and maintenance and gained momentum with the realization of the implications of an effective upfront therapeutic approach with potential impact on survival.

AREAS COVERED

This review was written with an intent to introduce the reader to the current treatment approach of a newly diagnosed myeloma patient and acquaint with promising targets and mechanistic strategies. Medline and clinicaltrials.gov databases (2000-2020) and relevant meetings (ASH, ASCO, EHA, ESMO, IMW) reports were queried and guidelines (IMWG) were reviewed to distill to expert opinion in an inundating field.

EXPERT OPINION

Future holds promise with new targets on the horizon. It is likely that the new age of myeloma will belong to quadruplets with the addition of acellular or cellular biologics to first-generation novel agents, leading to new paradigms.

Identification of the xenograft and its ascendant sphere-forming cell line as belonging to EBV-induced lymphoma, and characterization of the status of sphere-forming cells

BACKGROUND

We have characterized the human cell line arised from the Epstein-Barr virus (EBV) positive multiple myeloma aspirate subjected to the long-term cultivation. This cell line has acquired the ability to form free-floating spheres and to produce a xenograft upon transplantation into NOD/SCID mice.

METHODS

Cells from both in vitro culture and developed xenografts were investigated with a number of analytical approaches, including pathomorphological analysis, FISH analysis, and analysis of the surface antigens and of the VDJ locus rearrangement.

RESULTS

The obtained results, as well as the confirmed presence of EBV, testify that both biological systems are derived from B-cells, which, in turn, is a progeny of the EBV-transformed B-cellular clone that supplanted the primordial multiple myeloma cells. Next we assessed whether cells that (i) were constantly present in vitro in the investigated cell line, (ii) were among the sphere-forming cells, and (iii) were capable of internalizing a fluorescent TAMRA-labeled DNA probe (TAMRA+ cells) belonged to one of the three types of undifferentiated bone marrow cells of a multiple myeloma patient: CD34+ hematopoietic stem cells, CD90+ mesenchymal stem cells, and clonotypic multiple myeloma cell.

CONCLUSION

TAMRA+ cells were shown to constitute the fourth independent subpopulation of undifferentiated bone marrow cells of the multiple myeloma patient. We have demonstrated the formation of ectopic contacts between TAMRA+ cells and cells of other types in culture, in particular with CD90+ mesenchymal stem cells, followed by the transfer of some TAMRA+ cell material into the contacted cell.

The role of surface molecule CD229 in Multiple Myeloma

The outcome of Multiple Myeloma (MM) patients has dramatically improved, however, most patients will still succumb to their disease. Additional therapeutic options are urgently needed and novel immunotherapies are enormously promising in the therapeutic armamentarium against MM. The first step in the development of any immunotherapy needs to be the identification of an appropriate target structure. In this review we present the current knowledge on surface molecule CD229, a member of the Signaling Lymphocyte Activation (SLAM) family of immune receptors. We believe that based on its characteristics, including (1) strong and homogenous expression on all myeloma cells, (2) expression on myeloma precursors, (3) absence from most normal tissues, (4) a central function in the biology of MM, CD229 (SLAMF3) represents a promising target for anti-MM immunotherapies. The introduction of novel anti-CD229 approaches into the clinic will hopefully lead to more durable responses, or maybe even cures, in MM.

Immunotherapies targeting CD38 in Multiple Myeloma

Recently, the monoclonal antibody daratumumab was approved as a single agent for the treatment of patients with relapsed/refractory Multiple Myeloma (MM). Daratumumab is an antibody targeting surface molecule CD38 on myeloma cells and the agent is already widely being used based on its good tolerability and proven efficacy. We believe, however, that the efficacy of this drug and other anti-CD38 monoclonal antibodies can be further improved by combining it with other types of immunotherapies. Furthermore, surface molecule CD38 can be used as a target for immunotherapies other than just naked monoclonal antibodies. In this report, we review the expression pattern of CD38 among normal tissues and in different types of plasma cell dyscrasias including their progenitor cells, minimal residual disease, and circulating tumor cells. We summarize the physiological role of CD38 as well as its role in the pathophysiology of MM and we present the most recent clinical trials using CD38 as a target. In addition, we highlight possible combination immunotherapies incorporating anti-CD38 monoclonal antibodies and we demonstrate alternative immunotherapeutic approaches targeting the same antigen such as CD38-specific chimeric antigen receptor (CAR) T cells.

Nonadherent Spheres With Multiple Myeloma Surface Markers Contain Cells that Contribute to Sphere Formation and Are Capable of Internalizing Extracellular Double-Stranded DNA

BACKGROUND

The most prominent features of cancer stem cells are asymmetric cell division, tumorigenicity, and clonogenicity. Recently one more feature of poorly differentiated cell types of various origin, including cancer stem cells, has been described. Namely, these cells can internalize extracellular DNA natively, without additional transfection procedures.

PATIENTS AND METHODS

Using our approach to trace internalization of a TAMRA (carboxy tetramethyl-rhodamine [fluorescent dye])-DNA labeled probe by poorly differentiated cell types, we isolated and characterized the cells from free-floating spheres derived from the bone marrow clonogenic aspirate of a multiple myeloma patient.

RESULTS

Nonadherent spheres display a B-cell phenotype (CD73/CD20⁺/CD45⁺/CD19^dim). Further, free-floating spheres contain 1% to 3% cells with a clonogenic potential, and these cells display a marker of poorly differentiated cell types (TAMRA⁺). Upon association with a group of ∼ 10 free-floating TAMRA^- cells, this peculiar cell type forms a sphere-forming cluster that initiates secondary aggregation of cells into a spheric structure. TAMRA⁺ and TAMRA^- cells secrete distinct sets of cytokines indicative of the paracrine regulation. Grafting experiments of intact whole spheres versus cell suspensions prepared from dispersed spheres indicate that successful engraftment only occurs in the former case.

CONCLUSION

Nonadherent 3-D cell colonies (spheres) encompass B cells with CD73/CD20⁺/CD45⁺/CD19^dim phenotype, as well as double-stranded DNA-internalizing cells. The latter cell type appears to function as a sphere-forming center. Different cells in the spheres communicate with each other by secreting specific sets of cytokines. For successful engraftment and tumor growth in mice, intact spheres containing ∼ 10⁶ cells must be used.

CD229 is expressed on the surface of plasma cells carrying an aberrant phenotype and chemotherapy-resistant precursor cells in multiple myeloma

Multiple Myeloma (MM) is a plasma cell (PC) malignancy, which despite significant therapeutic advances, is still considered incurable. This is due to the persistence of chemotherapy-resistant minimal residual disease in the patients' bone marrow (BM) after an effective induction therapy. Immunotherapies targeting surface molecules expressed on the bulk of tumor cells and the chemotherapy-resistant, myeloma-propagating cells could play a central role in this clinical setting. We recently described surface molecule CD229 as a potential therapeutic target for MM. In our current study we assessed the expression of CD229 on different PC subtypes and on cells with a myeloma-propagating phenotype in a total of 77 patients with PC dyscrasias independently at 2 different cancer centers. We found that CD229 was strongly and homogeneously overexpressed on the PC of patients with monoclonal gammopathy of undetermined significance (MGUS), smoldering myeloma, MM, and PC leukemia. CD229 was particularly overexpressed on those PC showing an abnormal phenotype such as expression of CD56. Most importantly, CD229 was also highly expressed on those cells in the patients' BM displaying the phenotype of chemotherapy-resistant and myeloma-propagating cells. In conclusion, our combined findings suggest that immunotherapies targeting CD229 will not only be effective for the bulk of tumor cells but will also help to eradicate chemotherapy-resistant cells remaining in the patients' BM after induction treatment. Hopefully, the design of CD229-specific monoclonal antibodies or chimeric antigen receptor-transduced T cells will help to achieve prolonged remissions or even cures in MM patients.

Cancer-testis antigen SLLP1 represents a promising target for the immunotherapy of multiple myeloma

Background

Most patients with multiple myeloma (MM) will relapse after an initial response and eventually succumb to their disease. This is due to the persistence of chemotherapy-resistant tumor cells in the patients’ bone marrow (BM) and immunotherapeutic approaches could contribute to eradicating these remaining cells. We evaluated SLLP1 as a potential immunotherapeutic target for MM.

Methods

We determined SLLP1 expression in myeloma cell lines and 394 BM samples from myeloma patients (n = 177) and BM samples from healthy donors (n = 11). 896 blood samples and 64 BM samples from myeloma patients (n = 263) and blood from healthy donors (n = 112) were analyzed for anti-SLLP1 antibodies. Seropositive patients were evaluated regarding SLLP1-specific T cells.

Results

Most cell lines showed SLLP1 RNA and protein expression while it was absent from normal BM. Of 177 patients 41% evidenced SLLP1 expression at least once during the course of their disease and 44% of newly diagnosed patients were SLLP1-positive. Expression of SLLP1 was associated with adverse cytogenetics and with negative prognostic factors including the patient’s age, number of BM-infiltrating plasma cells, serum albumin, β₂-microglobulin, creatinine, and hemoglobin. Among patients treated with allogeneic stem cell transplantation those with SLLP1 expression showed a trend towards a reduced overall survival. Spontaneous anti-SLLP humoral immunity was detectable in 9.5% of patients but none of the seropositive patients evidenced SLLP1-specific T cells. However, antigen-specific T cells could readily be induced in vitro after stimulation with SLLP1.

Conclusions

SLLP1 represents a promising target for the immunotherapy of MM, in particular for the adoptive transfer of T cell receptor-transduced T cells.

Tumoricidal Effects of Macrophage-Activating Immunotherapy in a Murine Model of Relapsed/Refractory Multiple Myeloma

Myeloma remains a virtually incurable malignancy. The inevitable evolution of multidrug-resistant clones and widespread clonal heterogeneity limit the potential of traditional and novel therapies to eliminate minimal residual disease (MRD), a reliable harbinger of relapse. Here, we show potent anti-myeloma activity of macrophage-activating immunotherapy (αCD40+CpG) that resulted in prolongation of progression-free survival (PFS) and overall survival (OS) in an immunocompetent, preclinically validated, transplant-based model of multidrug-resistant, relapsed/refractory myeloma (t-Vκ*MYC). αCD40+CpG was effective in vivo in the absence of cytolytic natural killer, T, or B cells and resulted in expansion of M1-polarized (cytolytic/tumoricidal) macrophages in the bone marrow. Moreover, we show that concurrent loss/inhibition of Tpl2 kinase (Cot, Map3k8), a MAP3K that is recruited to activated CD40 complex and regulates macrophage activation/cytokine production, potentiated direct, ex vivo anti-myeloma tumoricidal activity of αCD40+CpG-activated macrophages, promoted production of antitumor cytokine IL12 in vitro and in vivo, and synergized with αCD40+CpG to further prolong PFS and OS in vivo. Our results support the combination of αCD40-based macrophage activation and TPL2 inhibition for myeloma immunotherapy. We propose that αCD40-mediated activation of innate antitumor immunity may be a promising approach to control/eradicate MRD following cytoreduction with traditional or novel anti-myeloma therapies.

Calorimetric markers of Bence Jones and nonsecretory multiple myeloma serum proteome

The present work provides a thermodynamic description of blood serum from patients diagnosed with Bence Jones myeloma (BJMM) and nonsecretory myeloma (NSMM) by means of differential scanning calorimetry (DSC), serum protein electrophoresis, and free light chain assay. Specific alterations in the thermodynamic behavior of both BJMM and NSMM proteome have been revealed. On the basis of the transition temperature of the main transition in the calorimetric profiles and the shape similarity criterion, we defined BJMM and NSMM sets/subsets of thermograms with very similar thermodynamic features. We show that some of the BJMM and NSMM subsets correlate with previously defined secretory myeloma subsets (Todinova et al. Anal. Chem. 2011, 83, 7992). The established analogies strongly suggest that common molecular markers contribute to the calorimetric profiles of the different, secretory and nonsecretory, myeloma types; our data show robust evidence that these are ligands stabilizing the major serum proteins. We demonstrate that the DSC approach might be highly beneficial, especially for NSMM patients, since the characteristic modifications in the DSC profiles might serve as calorimetric markers when no monoclonal proteins can be detected in the bloodstream and the diagnosis heavily relies on invasive methods.

Rapamycin-resistant effector T-cell therapy

Pharmacologic inhibition of the mechanistic target of rapamycin (mTOR) represents a stress test for tumor cells and T cells. Mechanisms exist that allow cells to survive this stress, including suboptimal target block, alternative signaling pathways, and autophagy. Rapamycin-resistant effector T (T-Rapa) cells have an altered phenotype that associates with increased function. Ex vivo rapamycin, when used in combination with polarizing cytokines and antigen-presenting-cell free costimulation, is a flexible therapeutic approach as polarization to T-helper 1 (Th1)- or Th2-type effectors is possible. Murine T-Rapa cells skewed toward a Th2-type prevented graft rejection and graft-versus-host disease (GVHD) more potently than control Th2 cells and effectively balanced GVHD and graft-versus-tumor (GVT) effects. A phase II clinical trial using low-intensity allogeneic hematopoietic cell transplantation demonstrated that interleukin-4 polarized human T-Rapa cells had a mixed Th2/Th1 phenotype; T-Rapa cell recipients had a balanced Th2/Th1 cytokine profile, conversion of mixed chimerism toward full donor chimerism, and a potentially favorable balance between GVHD and GVT effects. In addition, a phase I clinical trial evaluating autologous T-Rapa cells skewed toward a Th1- and Tc1-type is underway. Use of ex vivo rapamycin to modulate effector T-cell function represents a promising new approach to transplantation therapy.

Gastric cancer stem cells in gastric carcinogenesis, progression, prevention and treatment

In recent decades, the study of the mechanism of tumorigenesis has brought much progress to cancer treatment. However, cancer stem cell (CSC) theory has changed previous views of tumors, and has provided a new method for treatment of cancer. The discovery of CSCs and their characteristics have contributed to understanding the molecular mechanism of tumor genesis and development, resulting in a new effective strategy for cancer treatment. Gastric CSCs (GCSCs) are the basis for the onset of gastric cancer. They may be derived from gastric stem cells in gastric tissues, or bone marrow mesenchymal stem cells. As with other stem cells, GCSCs highly express drug-resistance genes such as aldehyde dehydrogenase and multidrug resistance, which are resistant to chemotherapy and thus form the basis of drug resistance. Many specific molecular markers such as CD44 and CD133 have been used for identification and isolation of GCSCs, diagnosis and grading of gastric cancer, and research on GCSC-targeted therapy for gastric cancer. Therefore, discussion of the recent development and advancements in GCSCs will be helpful for providing novel insight into gastric cancer treatment.

Anti-ABCG2 monoclonal antibody in combination with paclitaxel nanoparticles against cancer stem-like cell activity in multiple myeloma

Aim: To investigate the effects of anti-ABCG2 monoclonal antibodies (mAbs) in combination with paclitaxel iron oxide nanoparticles (PTX-NPs) on CD138-CD34- multiple myeloma (MM) cancer stem cells (CSCs) in JJN3 cells. Materials & methods: PTX-NPs were prepared using the hydrophobic interaction of the polyoxypropylene chain and oleic acid on the surface of iron oxide NPs and were targeted to the ABCG2 transporter overexpressing MM CSCs with mAbs. Results: The data showed that MM CSCs have strong drug resistance and tumorigenicity compared with non-MM CSCs. PTX-NPs combined with mAbs led to a significant reduction in the tumor volume, a visible alleviation of lytic bone lesions and a markedly increased survival rate in contrast to using a single agent in MM CSCs when it was transplanted to nonobese diabetic/severe combined immunodeficiency mice. Conclusion: This study is the first to report on the anti-MM CSC activity by PTX-NPs as a single agent or used together with anti-ABCG2 mAbs to treat MM. These findings provide a rationale for future clinical trials.

Original submitted 18 June 2012; Revised submitted 29 November 2012; Published online 27 March 2013

Autologous hematopoietic stem cell transplantation for multiple myeloma: frequently asked questions

When caring for patients with multiple myeloma, questions often arise about the role and timing of autologous hematopoietic stem cell transplantation. As a complement to the other articles in this supplement, as well as to ensure that readers are provided with the insight needed to feel comfortable speaking to patients and other practitioners about this topic, the authors address eight frequently asked questions about common decision points in the process of autologous hematopoietic stem cell transplantation as a treatment for patients with multiple myeloma.

Progressive changes in chromatin structure and DNA damage response signals in bone marrow and peripheral blood during myelomagenesis

The molecular pathways implicated in multiple myeloma (MM) development are rather unknown. We studied epigenetic and DNA damage response (DDR) signals at selected model loci (N-ras, p53, d-globin) in bone marrow plasma cells and peripheral blood mononuclear cells (PBMCs) from patients with monoclonal gammopathy of undetermined significance (MGUS; n=20), smoldering/asymptomatic MM (SMM; n=29) and MM (n=18), as well as in healthy control-derived PBMCs (n=20). In both tissues analyzed, a progressive, significant increase in the looseness of local chromatin structure, gene expression levels and DNA repair efficiency from MGUS to SMM and finally to MM was observed (all P<0.002). Following ex vivo treatment with melphalan, a gradual suppression of the apoptotic pathway occurred in samples collected at different stages of myelomagenesis, with the severity and duration of the inhibition of RNA synthesis, p53 phosphorylation at serine15 and induction of apoptosis being higher in MGUS than SMM and lowest in MM patients (all P<0.0103). Interestingly, for all endpoints analyzed, a strong correlation between plasma cells and corresponding PBMCs was observed (all P<0.0003). We conclude that progressive changes in chromatin structure, transcriptional activity and DDR pathways during myelomagenesis occur in malignant plasma cells and that these changes are also reflected in PBMCs.

A new system for quality control in hematopoietic progenitor cell units before reinfusion in autologous transplant

BACKGROUND

In our Center, the cell viability, the integrity of the bag, and the clonogenic assay were evaluated before the reinfusion of hematopoietic progenitor cells-apheresis (HPC-A). This quality control (QC) should be made 14 days before the reinfusion to the patient to have the result of the functional test on the proliferative capacity of hematopoietic progenitors.

STUDY DESIGN AND METHODS

This study was designed to assess the potential of an automatic cell counting system (NucleoCounter NC-3000, ChemoMetec) in our clinical routine as a support of the clonogenic assay and the cytofluorimetric analysis for the QC of the cryopreserved HPC-A. The cell viability was evaluated by flow cytometry using the modified International Society of Hematotherapy and Graft Engineering protocol. The proliferative potential was assessed by specific clonogenic tests using a commercial medium. Furthermore, we evaluated the cellular functionality with NucleoCounter NC-3000, by using two protocols: "vitality assay" and "mitochondrial potential assay."

RESULTS

The evaluation of the total nucleated cells in preapoptosis measured by 5,5,6,6-tetrachloro-1,1,3,3-tetraethylbenzimidazol-carbocyanine iodide (JC-1) assay showed a negative correlation (r=-0.43) with the total number of colonies (colony-forming unit [CFU]-granulocyte-macrophage progenitors plus burst-forming unit-erythroid progenitors plus CFU-granulocyte, erythroid, macrophage, megakaryocyte progenitors) obtained after seeding of 50 × 10(6) /L viable total nucleated cells. We observed a significant difference (p<0.0001) comparing the median number of colonies (166.70; SD, ± 136.36) obtained with a value of JC-1 less than 30% to the number of colonies (61.75; SD, ± 59.76) obtained with a value of JC-1 more than 30%.

CONCLUSION

The evaluation of cell functionality by the use of the NucleoCounter NC-3000 is in agreement with results from clonogenic assay and can be considered an effective alternative in the routine laboratory.

Macrophages in multiple myeloma: emerging concepts and therapeutic implications

Multiple myeloma, a clonal plasma cell malignancy, has long provided a prototypic model to study regulatory interactions between malignant cells and their microenvironment. Myeloma-associated macrophages have historically received limited scrutiny, but recent work points to central and non-redundant roles in myeloma niche homeostasis. The evidence supports a paradigm of complex, dynamic and often mutable interactions between macrophages and other cellular constituents of the niche. We and others have shown that macrophages support myeloma cell growth, viability and drug resistance through both contact-mediated and non-contact-mediated mechanisms. These tumor-beneficial roles have evolved in opposition to, or in parallel with, intrinsic pro-inflammatory and tumoricidal properties. Thus, simple blockade of protective "don't eat me" signals on the surface of myeloma cells leads to macrophage-mediated myeloma cell killing. Macrophages also enhance the tumor-supportive role of mesenchymal stem/stromal cells (MSCs) in the niche: importantly, this interaction is bidirectional, producing a distinct state of macrophage polarization that we termed "MSC-educated macrophages." The intriguing pattern of cross-talk between macrophages, MSCs and tumor cells highlights the myeloma niche as a dynamic multi-cellular structure. Targeted reprogramming of these interactions harbors significant untapped therapeutic potential, particularly in the setting of minimal residual disease, the main obstacle toward a cure.

The systemic cytokine environment is permanently altered in multiple myeloma

Multiple myeloma (MM) is an incurable bone marrow malignancy of the B cell lineage. Utilizing multiplex Luminex technology we measured levels of 25 cytokines in the plasma of normal donors (n = 177), those with monoclonal gammopathy of undetermined significance (n = 8), and MM patients (n = 55) with either active disease, on treatment, or in remission. The cytokine levels were compared between normal donors and MM patients as well as between various phases of MM, and discriminant analysis was used to create a predictive classification model based on the differentially expressed cytokines. Evaluating age- and gender-dependence of cytokine expression, we determined that with age there is a shift toward a pro-inflammatory environment. Moreover, we observed a strong gender bias in cytokine expression. However, the profile of differentially expressed cytokines was heavily skewed toward an anti-inflammatory, pro-tumorigenic response in patients with MM. Significantly, our predictive model placed all patients in remission in the same category as those with active disease. Thus, our study demonstrates that the homeostasis of systemic cytokines is not restored when MM patients enter remission, suggesting that once an individual has cancer, the microenvironment is permanently altered and the system is primed for a relapse.