Leukemic B cells clonally identical to myeloma plasma cells are myelomagenic in NOD/SCID mice

Molecular and immunological mechanisms of clonal evolution in multiple myeloma

Multiple myeloma (MM) is a hematologic malignancy characterized by the proliferation of clonal plasma cells in the bone marrow (BM). It is known that early genetic mutations in post-germinal center B/plasma cells are the cause of myelomagenesis. The acquisition of additional chromosomal abnormalities and distinct mutations further promote the outgrowth of malignant plasma cell populations that are resistant to conventional treatments, finally resulting in relapsed and therapy-refractory terminal stages of MM. In addition, myeloma cells are supported by autocrine signaling pathways and the tumor microenvironment (TME), which consists of diverse cell types such as stromal cells, immune cells, and components of the extracellular matrix. The TME provides essential signals and stimuli that induce proliferation and/or prevent apoptosis. In particular, the molecular pathways by which MM cells interact with the TME are crucial for the development of MM. To generate successful therapies and prevent MM recurrence, a thorough understanding of the molecular mechanisms that drive MM progression and therapy resistance is essential. In this review, we summarize key mechanisms that promote myelomagenesis and drive the clonal expansion in the course of MM progression such as autocrine signaling cascades, as well as direct and indirect interactions between the TME and malignant plasma cells. In addition, we highlight drug-resistance mechanisms and emerging therapies that are currently tested in clinical trials to overcome therapy-refractory MM stages.

New generation drugs for treatment of multiple myeloma

Multiple myeloma (MM), a plasma cell malignancy, is characterised by lesions in multiple bones involving transformed, matured post-follicular B cells. The course of the disease involves an initial development of monoclonal gammopathy of undetermined significance (MGUS), followed by smouldering MM, before the full MM disease emerges. Despite novel therapies, MM remains incurable, managed by combination therapies, including proteasome inhibitors (PIs), immunomodulators (IMiDs) and anti-human CD38 (daratumumab). MM patients have an increased risk of thromboembolic events due to combination treatments with IMiDs, PIs and anti-human CD38 antibody, and steroids. This review will examine the efficacy and pro-thrombotic effects of MM therapies.

Definition of a multiple myeloma progenitor population in mice driven by enforced expression of XBP1s

Multiple myeloma (MM) is an incurable plasma cell malignancy with frequent treatment failures and relapses, suggesting the existence of pathogenic myeloma stem/progenitor populations. However, the identity of MM stem cells remains elusive. We used a murine model of MM with transgenic overexpression of the unfolded protein response sensor X-box binding protein 1 (XBP1s) in the B cell compartment to define MM stem cells. We herein report that a post-germinal center, pre-plasma cell population significantly expands as MM develops. This population has the following characteristics: (a) cell surface phenotype of B220+CD19+IgM-IgD-CD138-CD80+sIgG-AA4.1+FSChi; (b) high expression levels of Pax5 and Bcl6 with intermediate levels of Blimp1 and XBP1s; (c) increased expression of aldehyde dehydrogenase, Notch1, and c-Kit; and (d) ability to efficiently reconstitute antibody-producing capacity in B cell-deficient mice in vivo. We thus have defined a plasma cell progenitor population that resembles myeloma stem cells in mice. These results provide potentially novel insights into MM stem cell biology and may contribute to the development of novel stem cell-targeted therapies for the eradication of MM.

Anti-CD19 CAR T cells with high-dose melphalan and autologous stem cell transplantation for refractory multiple myeloma

BACKGROUND

Multiple myeloma is usually fatal due to serial relapses that become progressively refractory to therapy. CD19 is typically absent on the dominant multiple myeloma cell population but may be present on minor subsets with unique myeloma-propagating properties. To target myeloma-propagating cells, we clinically evaluated autologous T cells transduced with a chimeric antigen receptor (CAR) against CD19 (CTL019).

METHODS

Subjects received CTL019 following salvage high-dose melphalan and autologous stem cell transplantation (ASCT). All subjects had relapsed/refractory multiple myeloma and had previously undergone ASCT with less than 1 year progression-free survival (PFS).

RESULTS

ASCT + CTL019 was safe and feasible, with most toxicity attributable to ASCT and no severe cytokine release syndrome. Two of 10 subjects exhibited significantly longer PFS after ASCT + CTL019 compared with prior ASCT (479 vs. 181 days; 249 vs. 127 days). Correlates of favorable clinical outcome included peak CTL019 frequency in bone marrow and emergence of humoral and cellular immune responses against the stem-cell antigen Sox2. Ex vivo treatment of primary myeloma samples with a combination of CTL019 and CAR T cells against the plasma cell antigen BCMA reliably inhibited myeloma colony formation in vitro, whereas treatment with either CAR alone inhibited colony formation inconsistently.

CONCLUSION

CTL019 may improve duration of response to standard multiple myeloma therapies by targeting and precipitating secondary immune responses against myeloma-propagating cells.

TRIAL REGISTRATION

Clinicaltrials.gov identifier NCT02135406.

FUNDING

Novartis, NIH, Conquer Cancer Foundation.

Clonal Expansion and Interrelatedness of Distinct B-Lineage Compartments in Multiple Myeloma Bone Marrow

Multiple myeloma is characterized by the clonal expansion of malignant plasma cells in the bone marrow. But the phenotypic diversity and the contribution of less predominant B-lineage clones to the biology of this disease have been controversial. Here, we asked whether cells bearing the dominant multiple myeloma immunoglobulin rearrangement occupy phenotypic compartments other than that of plasma cells. To accomplish this, we combined 13-parameter FACS index sorting and t-Stochastic Neighbor Embedding (t-SNE) visualization with high-throughput single-cell immunoglobulin sequencing to track selected B-lineage clones across different stages of human B-cell development. As expected, the predominant clones preferentially mapped to aberrant plasma cell compartments, albeit phenotypically altered from wild type. Interestingly, up to 1.2% of cells of the predominant clones colocalized with B-lineage cells of a normal phenotype. In addition, minor clones with distinct immunoglobulin sequences were detected in up to 9% of sequenced cells, but only 2 out of 12 of these clones showed aberrant immune phenotypes. The majority of these minor clones showed intraclonal silent nucleotide differences within the CDR3s and varying frequencies of somatic mutations in the immunoglobulin genes. Therefore, the phenotypic range of multiple myeloma cells in the bone marrow is not confined to aberrant-phenotype plasma cells but extends to low frequencies of normal-phenotype B cells, in line with the recently reported success of B cell-targeting cellular therapies in some patients. The majority of minor clones result from parallel nonmalignant expansion. Cancer Immunol Res; 5(9); 744-54. ©2017 AACR.

HIF-1α and rapamycin act as gerosuppressant in multiple myeloma cells upon genotoxic stress

Multiple myeloma (MM) is still an incurable hematological malignancy. Despite recent progress due to new anti-myeloma agents, the pathology is characterized by a high frequency of de novo or acquired resistance. Delineating the mechanisms of MM resistance is essential for therapeutic advances. We previously showed that long-term genotoxic stress induces the establishment of a senescence-associated secretory phenotype, a pro-inflammatory response that favors the emergence of cells with cancer stem-like properties. Here, we studied the short-term response of MM cells following treatment with various DNA damaging agents such as the energetic C-ion irradiation. MM cells are highly resistant to all treatments and do not enter apoptosis after they arrest cycling at the G2 phase. Although the DNA damage response pathway was activated, DNA breaks remained chronically in damaged MM cells. We found, using a transcriptomic approach that RAD50, a major DNA repair gene was downregulated early after genotoxic stress. In two gerosuppression situations: induction of hypoxia and inhibition of the mammalian target of rapamycin (mTOR) pathway, we observed, after the treatment with a DNA damaging agent, a normalization of RAD50 expression concomitant with the absence of cell cycle arrest. We propose that combining inhibitors of mTOR with genotoxic agents could avoid MM cells to senesce and secrete pro-inflammatory factors responsible for cancer stem-like cell emergence and, in turn, relapse of MM patients.

FGFR3 preferentially colocalizes with IGH in the interphase nucleus of multiple myeloma patient B-cells when FGFR3 is located outside of CT4

Many B-cell malignancies are characterized by chromosomal translocations involving IGH and a proto-oncogene. For translocations to occur, spatial proximity of translocation-prone genes is necessary. Currently, it is not known how such genes are brought into proximity with one another. Although decondensed chromosomes occupy definitive, non-random spaces in the interphase nucleus known as chromosome territories (CTs), chromatin at the edges of CTs can intermingle, and specific genomic regions from some chromosomes have been shown to "loop out" of their respective CTs. This extra-territorial positioning of specific genomic regions may provide a mechanism whereby translocation-prone genes are brought together in the interphase nucleus. FGFR3 and MAF recurrently participate in translocations with IGH at different frequencies. Using 3D, 4-color FISH, and 3D analysis software, we show frequent extra-territorial positioning of FGFR3 and significantly less frequent extra-territorial positioning of MAF. Frequent extra-territorial positioning may be characteristic of FGFR3 in B-cells from healthy adult donors and non-malignant B-cells from patients, but not in hematopoietic stem cells from patients with translocations. The frequency of extra-territorial positioning of FGFR3 and MAF in B-cells correlates with the frequency of translocations in the patient population. Most importantly, in patient B-cells, we demonstrate a significant proportion of extra-territorial FGFR3 participating in close loci pairs and/or colocalizing with IGH. This preliminary work suggests that in patient B-cells, extra-territorial positioning of FGFR3 may provide a mechanism for forming close loci pairs and/or colocalization with IGH; indirectly facilitating translocation events involving these two genes. © 2016 Wiley Periodicals, Inc.

Drug resistance in multiple myeloma: latest findings and new concepts on molecular mechanisms

In the era of new and mostly effective therapeutic protocols, multiple myeloma still tends to be a hard-to-treat hematologic cancer. This hallmark of the disease is in fact a sequel to drug resistant phenotypes persisting initially or emerging in the course of treatment. Furthermore, the heterogeneous nature of multiple myeloma makes treating patients with the same drug challenging because finding a drugable oncogenic process common to all patients is not yet feasible, while our current knowledge of genetic/epigenetic basis of multiple myeloma pathogenesis is outstanding. Nonetheless, bone marrow microenvironment components are well known as playing critical roles in myeloma tumor cell survival and environment-mediated drug resistance happening most possibly in all myeloma patients. Generally speaking, however; real mechanisms underlying drug resistance in multiple myeloma are not completely understood. The present review will discuss the latest findings and concepts in this regard. It reviews the association of important chromosomal translocations, oncogenes (e.g. TP53) mutations and deranged signaling pathways (e.g. NFκB) with drug response in clinical and experimental investigations. It will also highlight how bone marrow microenvironment signals (Wnt, Notch) and myeloma cancer stem cells could contribute to drug resistance in multiple myeloma.

Next-generation sequencing of peripheral B-lineage cells pinpoints the circulating clonotypic cell pool in multiple myeloma

The identity of the proliferative compartment of myeloma progenitor cells remains a matter of debate. Polymerase chain reaction-based studies suggested pre-switch "clonotypic" B cells sharing the immunoglobulin (Ig) rearrangement of the malignant plasma cell (M-PC), to circulate in the blood and possess stem cell-like properties. Here, we disprove this hypothesis. We screened peripheral blood IgM, IgG, and IgA repertoires of myeloma patients for the clonotypic rearrangement by next-generation sequencing. None of 12 cases showed pre-switch clonotypic transcripts. In the post-switch IgG/IgA repertoires, however, the clonotypic rearrangement was detected at high frequency in 6 of 8 patients with active disease, whereas it was undetectable after treatment, correlating with flow cytometric presence or absence of circulating M-PCs. Minor subclones with alternative post-switch isotypes suggested ongoing switch events and clonal evolution at the M-PC level. Our findings consistently show an absence of pre-switch clonotypic B cells, while M-PCs circulate in the peripheral blood and may contribute to spreading of the disease.

Targeting the biophysical properties of the myeloma initiating cell niches: a pharmaceutical synergism analysis using multi-scale agent-based modeling

Multiple myeloma, the second most common hematological cancer, is currently incurable due to refractory disease relapse and development of multiple drug resistance. We and others recently established the biophysical model that myeloma initiating (stem) cells (MICs) trigger the stiffening of their niches via SDF-1/CXCR4 paracrine; The stiffened niches then promote the colonogenesis of MICs and protect them from drug treatment. In this work we examined in silico the pharmaceutical potential of targeting MIC niche stiffness to facilitate cytotoxic chemotherapies. We first established a multi-scale agent-based model using the Markov Chain Monte Carlo approach to recapitulate the niche stiffness centric, pro-oncogenetic positive feedback loop between MICs and myeloma-associated bone marrow stromal cells (MBMSCs), and investigated the effects of such intercellular chemo-physical communications on myeloma development. Then we used AMD3100 (to interrupt the interactions between MICs and their stroma) and Bortezomib (a recently developed novel therapeutic agent) as representative drugs to examine if the biophysical properties of myeloma niches are drugable. Results showed that our model recaptured the key experimental observation that the MBMSCs were more sensitive to SDF-1 secreted by MICs, and provided stiffer niches for these initiating cells and promoted their proliferation and drug resistance. Drug synergism analysis suggested that AMD3100 treatment undermined the capability of MICs to modulate the bone marrow microenvironment, and thus re-sensitized myeloma to Bortezomib treatments. This work is also the first attempt to virtually visualize in 3D the dynamics of the bone marrow stiffness during myeloma development. In summary, we established a multi-scale model to facilitate the translation of the niche-stiffness centric myeloma model as well as experimental observations to possible clinical applications. We concluded that targeting the biophysical properties of stem cell niches is of high clinical potential since it may re-sensitize tumor initiating cells to chemotherapies and reduce risks of cancer relapse.

A replicative self-renewal model for long-lived plasma cells: questioning irreversible cell cycle exit

Plasma cells are heterogenous in terms of their origins, secretory products, and lifespan. A current paradigm is that cell cycle exit in plasma cell differentiation is irreversible, following a pattern familiar in short-lived effector populations in other hemopoietic lineages. This paradigm no doubt holds true for many plasma cells whose lifespan can be measured in days following the completion of differentiation. Whether this holds true for long-lived bone marrow plasma cells that are potentially maintained for the lifespan of the organism is less apparent. Added to this the mechanisms that establish and maintain cell cycle quiescence in plasma cells are incompletely defined. Gene expression profiling indicates that in the transition of human plasmablasts to long-lived plasma cells a range of cell cycle regulators are induced in a pattern that suggests a quiescence program with potential for cell cycle re-entry. Here a model of relative quiescence with the potential for replicative self-renewal amongst long-lived plasma cells is explored. The implications of such a mechanism would be diverse, and the argument is made here that current evidence is not sufficiently strong that the possibility should be disregarded.

Fact or fiction--identifying the elusive multiple myeloma stem cell

Multiple Myeloma (MM) is a debilitating disease of proliferating and malignant plasma cells that is currently incurable. The ability of monoclonal recurrence of disease suggests it might arise from a stem cell-like population capable of self-renewal. The difficulty to isolate the cancer stem-like cell in MM has introduced confusion toward this hypothesis. However, recent evidence has suggested that MM originates from the B cell lineage with memory-B cell like features, allowing for self-renewal of the progenitor-like status and differentiation to a monoclonal plasma cell population. Furthermore, this tumor-initiating cell uses signaling pathways and microenvironment similar to the hematopoietic stem cell, though hijacking these mechanisms to create and favor a more tumorigenic environment. The bone marrow niche allows for pertinent evasion, either through avoiding immunosurveillance or through direct interaction with the stroma, inducing quiescence and thus drug resistance. Understanding the interaction of the MM stem cell to the microenvironment and the mechanisms utilized by various stem cell-like populations to allow persistence and therapy-resistance can enable for better targeting of this cell population and potential eradication of the disease.

Breaking the invulnerability of cancer stem cells: two-step strategy to kill the stem-like cell subpopulation of multiple myeloma

In multiple myeloma, the presence of highly resistant cancer stem cells (CSC) that are responsible for tumor metastasis and relapse has been proven. Evidently, for achieving complete response, new therapeutic paradigms that effectively eradicate both, CSCs and bulk cancer populations, need to be developed. For achieving that goal, an innovative two-step treatment combining targeting of thymidine de novo synthesis pathway and a nanoirradiation by the Auger electron emitting thymidine analogue (123/125)I-5-iodo-4'-thio-2'-deoxyuridine ((123/125)I-ITdU) could be a promising approach. The pretreatment with thymidylate synthase inhibitor 5-fluoro-2'-deoxyuridine (FdUrd, 1 μmol/L for 1 hour) efficiently induced proliferation and terminal differentiation of isolated myeloma stem-like cells. Moreover, FdUrd stimulation led to a decreased activity of a functional CSC marker, aldehyde dehydrogenase (ALDH). The metabolic conditioning by FdUrd emerged to be essential for enhanced incorporation of (125)I-ITdU (incubation with 50 kBq/2 × 10(4) cells for 4 days) and, consequently, for the induction of irreparable DNA damage. (125)I-ITdU showed a pronounced antimyeloma effect on isolated tumor stem-like cells. More than 85% of the treated cells were apoptotic, despite activation of DNA repair mechanisms. Most important, exposure of metabolically conditioned cells to (125)I-ITdU resulted in a complete inhibition of clonogenic recovery. This is the first report showing that pretreatment with FdUrd sensitizes the stem-like cell compartment in multiple myeloma to apoptosis induced by (125)I-ITdU-mediated nanoirradiation of DNA.

Frequent occurrence of highly expanded but unrelated B-cell clones in patients with multiple myeloma

Clonal diversity in multiple myeloma (MM) includes both MM-related and MM-unrelated clonal expansions which are subject to dominance exerted by the MM clone. Here we show evidence for the existence of minor but highly expanded unrelated B-cell clones in patients with MM defined by their complementary determining region 3 (CDR3) peak. We further characterize these clones over the disease and subsequent treatment. Second clones were identified by their specific IgH-VDJ sequences that are distinct from those of dominant MM clones. Clonal frequencies were determined through semi-quantitative PCR, quantitative PCR and single-cell polymerase chain reaction of the clone-specific sequence. In 13/74 MM patients, more than one dominant CDR3 peak was identified with 12 patients (16%) being truly biclonal. Second clones had different frequencies, were found in different locations and were found in different cell types from the dominant MM clone. Where analysis was possible, they were shown to have chromosomal characteristic distinct from those of the MM clone. The frequency of the second clone also changed over the course of the disease and often persisted despite treatment. Molecularly-defined second clones are infrequent in monoclonal gammopathy of undetermined significance (MGUS, 1/43 individuals or 2%), suggesting that they may arise at relatively late stages of myelomagenesis. In further support of our findings, biclonal gammopathy and concomitant MM and CLL (chronic lymphocytic leukemia) were confirmed to originate from two unrelated clones. Our data supports the idea that the clone giving rise to symptomatic myeloma exerts clonal dominance to prevent expansion of other clones. MM and second clones may arise from an underlying niche permissive of clonal expansion. The clinical significance of these highly expanded but unrelated clones remains to be confirmed. Overall, our findings add new dimensions to evaluating related and unrelated clonal expansions in MM and the impact of disease evolution and treatment on clonal diversity.

Differential nuclear organization of translocation-prone genes in nonmalignant B cells from patients with t(14;16) as compared with t(4;14) or t(11;14) myeloma

Gene organization in nonmalignant B cells from t(4;14) and t(11;14) multiple myeloma (MM) patients differs from that of healthy donors. Among recurrent IGH translocations in MM, the frequency of t(4;14) (IGH and FGFR3) or t(11;14) (IGH and CCND1) is greater than the frequency of t(14;16) (IGH and MAF). Gene organization in t(14;16) patients may influence translocation potential of MAF with IGH. In patients, three-dimensional FISH revealed the positions of IGH, CCND1, FGFR3, and MAF in nonmalignant B cells that are likely similar to those when MM first arose, compared with B cells from healthy donors. Overall, IGH occupies a more central nuclear position while MAF is more peripherally located. However, for B cells from t(4;14) and t(11;14) patients, IGH and FGFR3, or IGH and CCND1 are found in spatial proximity: IGH and MAF are not. This differs in B cells from t(14;16) patients and healthy donors where IGH is approximately equidistant to FGFR3, CCND1, and MAF, suggesting that gene organization in t(14;16) patients is different from that in t(4;14) or t(11;14) patients. Translocations between IGH and MAF may arise only in the absence of close proximity to the more frequent partners, as appears to be the case for individuals who develop t(14;16) MM.

Multiple myeloma-initiating cells

Multiple myeloma (MM) is characterized by the clonal expansion of malignant plasma cells. As in other cancers, MM plasma cells are thought to be derived from MM-initiating cells, although these remain unidentified. MM patients harbor phenotypic CD19(+) B cells expressing the immunoglobulin gene sequence and the idiotype unique to the individual myeloma clone. Some previous studies have reported that CD19(+) clonotypic B cells can serve as MM-initiating cells. However, we and another group have recently showed that CD19(+) B cells from many MM patients do not reconstitute MM disease upon transplantation into NOD/SCID IL2Rγc(-/-) mice. In the SCID-rab and SCID-hu models, which enable engraftment of human MM in vivo, CD19(-)CD38(++) plasma cells engrafted and rapidly propagated MM, while engraftment of CD19(+) B cells was not detected. Both CD138(-) and CD138(+) plasma cells have the potential to propagate MM clones in vivo in the absence of CD19(+) B cells. Distinct from acute myeloid leukemia-initiating cells, which are derived from undifferentiated stem or progenitor cells, MM-initiating cells are derived from plasma cells, which are terminally differentiated cells. An improved understanding of how the bone marrow microenvironment supports MM-initiating plasma cells, which can initiate MM disease in the SCID-hu (or rab) model, is thus now essential.

Differential protein expression profile between CD20 positive and negative cells of the NCI-H929 cell line

At present, multiple myeloma (MM) remains an incurable disease and cologenic cells may be responsible for disease relapse. It has been proposed that CD20+/CD138- NCI-H929 cells could be hallmarks of MM clonogenic cells. Here, the immunology phenotype of NCI-H929 cells is described. Only a small population of CD20+/CD138- cells (<1%) was found in the NCI-H929 cell line, but CD20+/CD138- cells were not detected. We found that CD20+/CD138+ cells were able to exhibit cologenic capacity by colony formation assay and continuous passage culture. Proteins were analyzed by 1D-SDS-PAGE and TMT based quantitative differential liquid chromatography tandem mass spectrometry (LC-MS/MS). 1,082 non-redundant proteins were identified, 658 of which were differentially expressed with at least a 1.5-fold difference. 205 proteins in CD20+ cells were expressed at higher levels and 453 proteins were at lower levels compared with CD20- cells. Most proteins had catalytic and binding activity and mainly participated in metabolic processes, cell communication and molecular transport. These results proved that there are different biological features and protein expression profile between CD20+ and CD20- cells in the NCI-H929 cell line.

Senescence-associated secretory phenotype favors the emergence of cancer stem-like cells

The molecular mechanisms underlying cancer resistance remain elusive. One possible explanation is that cancer stem cells (CSCs) elude drug treatment, emerge and reproduce a tumor. Using multiple myeloma as a paradigm, we showed that cancer stem-like cells (CSLCs) appear after genotoxic stress because of their intrinsic properties. However, these properties do not drive the emergence of the CSLCs. Following genotoxic stress, remaining DNA damages lead to a senescence-associated secretory phenotype (SASP). Senescent cells, which are the non-CSLCs, secrete chemokines contributing to the emergence, maintenance and migration of CSLCs. Downregulation of checkpoint protein 2, a key player of SASP, significantly reduced the emergence of CSLCs. Our results unravel a novel molecular mechanism by which SASP might promote malignancy, underlining the dual role of senescence in tumorigenesis. This mechanism, based on mutual cooperation among tumor cells, illustrates how cancer may relapse; its targeting could represent new therapeutic opportunities.

Clinical drug resistance linked to interconvertible phenotypic and functional states of tumor-propagating cells in multiple myeloma

The phenotype and function of cells enriched in tumor-propagating activity and their relationship to the phenotypic architecture in multiple myeloma (MM) are controversial. Here, in a cohort of 30 patients, we show that MM composes 4 hierarchically organized, clonally related subpopulations, which, although phenotypically distinct, share the same oncogenic chromosomal abnormalities as well as immunoglobulin heavy chain complementarity region 3 area sequence. Assessed in xenograft assays, myeloma-propagating activity is the exclusive property of a population characterized by its ability for bidirectional transition between the dominant CD19(-)CD138(+) plasma cell (PC) and a low frequency CD19(-)CD138(-) subpopulation (termed Pre-PC); in addition, Pre-PCs are more quiescent and unlike PCs, are primarily localized at extramedullary sites. As shown by gene expression profiling, compared with PCs, Pre-PCs are enriched in epigenetic regulators, suggesting that epigenetic plasticity underpins the phenotypic diversification of myeloma-propagating cells. Prospective assessment in paired, pretreatment, and posttreatment bone marrow samples shows that Pre-PCs are up to 300-fold more drug-resistant than PCs. Thus, clinical drug resistance in MM is linked to reversible, bidirectional phenotypic transition of myeloma-propagating cells. These novel biologic insights have important clinical implications in relation to assessment of minimal residual disease and development of alternative therapeutic strategies in MM.

In multiple myeloma, bone-marrow lymphocytes harboring the same chromosomal abnormalities as autologous plasma cells predict poor survival

Chromosomal abnormalities in plasma cells (PCs) from multiple myeloma (MM) provide a clonal signature to identify malignant cells. BM-lymphocytes from MM aspirates, defined by stringent criteria, were screened for the same chromosomal abnormalities as autologous PCs, including translocations, deletions, and amplifications. For 200 MM patients, we evaluated BM mononuclear cells to identify lymphocytes and autologous PCs on the same slide, followed by interphase fluorescence in situ hybridization to characterize their chromosomal abnormalities. Of all patients having a given chromosomal abnormality(s) in PCs, 45% showed that same abnormality(s) in 2–37% (median = 5%) of BM-lymphocytes. Most translocations, amplifications, and deletions found in MM PCs were also detected in lymphocytes, above the healthy-donor “cut-off.” In patients having chromosomally abnormal CD20⁻ PCs, chromosomally abnormal lymphocytes were found among CD20+ cells confirming them as B cells. Exceptions were amplification of 1q21 or p53 deletion, which characterize PCs but were undetectable in BM-lymphocytes, suggesting that processes leading to these abnormalities may be exclusive to PCs. For a set of 75 patients whose BM-lymphocytes and PCs were analyzed by all six probe sets, 58% of those with abnormal PC also had abnormal BM-lymphocytes harboring from one to five different abnormalities. Confirming the clinical significance of chromosomally abnormal BM-lymphocytes, MM patients having abnormalities in both lymphocytes and PC had significantly worse survival than those with abnormalities only in PC (HR = 2.68). The presence of at least one chromosomal abnormality in BM-lymphocytes appears to have greater clinical significance than particular abnormalities. Chromosomally abnormal BM-lymphocytes correlate with poor outcome and by extrapolation with more aggressive disease.

CD19-CD45 low/- CD38 high/CD138+ plasma cells enrich for human tumorigenic myeloma cells

Multiple myeloma is a hematological neoplasm characterized by the accumulation of clonal plasma cells in the bone marrow. Its frequent relapse following achievement of clinical remissions implicates the existence of therapy-resistant myeloma-initiating cells. To date, results on the identity of myeloma-initiating cells have differed. Here, we prospectively identified a myeloma-initiating population by fractionating and transplanting patient bone marrow cells into human bone-bearing immunocompromised mice. Xenotransplantation of fractionated CD138(+)/CD38(high) cells from 40% of patients (8/20) led to a repopulation of CD19(+)CD38(low) or CD138(+)CD38(+) B-lineage cells in human bone grafts; and these grafts were clonally derived from patient myeloma cells. Meanwhile, CD19(+)CD38(low) xenografts were detected in human bone-bearing mice transplanted with CD19(+)CD38(low/-) B cells from 8 of 22 samples but were not clonally related to patient myeloma cells. Further fractionation and xenotransplantation of CD138(+)CD38(high) cells demonstrated that (CD45(low/-) or CD19(-)) CD38(high)/CD138(+) plasma cells, but not (CD45(high) or CD19(+)) CD38(high)/CD138(+) plasmablasts enrich for myeloma-initiating cells. Quantitative reverse transcription-PCR of two serially transplantable xenografts, which were CD19(-)CD138(+), revealed that they were Pax5 (a B-cell-specific transactivator)-negative. These results suggest that CD19(-)CD45(low/-) fully differentiated plasma cells enrich for long-lived and tumor-initiating cells whereas B cells or plasmablasts do not.

Autologous stem cell transplantation and multiple myeloma cancer stem cells

It is well established that high-dose therapy (HDT) combined with autologous stem cell transplantation (ASCT) produces superior response rates and progression-free survival compared with conventional chemotherapy in patients with multiple myeloma (MM). Accordingly, MM currently represents the most common indication for ASCT. Despite these clinical improvements, the impact of ASCT on overall survival is unclear because the vast majority of patients eventually experience disease relapse and progression. The continual risk of relapse suggests that malignant cells resistant to HDT possess the clonogenic growth potential to mediate tumor regrowth, and in several diseases cancer stem cells (CSCs) have been identified that are both highly tumorigenic and resistant to standard anticancer approaches. Putative CSCs have been identified in MM, and their characterization may lead to the development of novel maintenance strategies that inhibit the production of new tumor cells, prevent disease relapse, and improve overall survival.

CD138-negative clonogenic cells are plasma cells but not B cells in some multiple myeloma patients

Clonogenic multiple myeloma (MM) cells reportedly lacked expression of plasma cell marker CD138. It was also shown that CD19(+) clonotypic B cells can serve as MM progenitor cells in some patients. However, it is unclear whether CD138-negative clonogenic MM plasma cells are identical to clonotypic CD19(+) B cells. We found that in vitro MM colony-forming cells were enriched in CD138(-)CD19(-)CD38(++) plasma cells, while CD19(+) B cells never formed MM colonies in 16 samples examined in this study. We next used the SCID-rab model, which enables engraftment of human MM in vivo. CD138(-)CD19(-)CD38(++) plasma cells engrafted in this model rapidly propagated MM in 3 out of 9 cases, while no engraftment of CD19(+) B cells was detected. In 4 out of 9 cases, CD138(+) plasma cells propagated MM, although more slowly than CD138(-) cells. Finally, we transplanted CD19(+) B cells from 13 MM patients into NOD/SCID IL2Rγc(-/-) mice, but MM did not develop. These results suggest that at least in some MM patients CD138-negative clonogenic cells are plasma cells rather than B cells, and that MM plasma cells including CD138(-) and CD138(+) cells have the potential to propagate MM clones in vivo in the absence of CD19(+) B cells.

Phenotypic detection of clonotypic B cells in multiple myeloma by specific immunoglobulin ligands reveals their rarity in multiple myeloma

In multiple myeloma, circulating “clonotypic” B cells, that express the immunoglobulin rearrangement of the malignant plasma cell clone, can be indirectly detected by PCR. Their role as potential “feeder” cells for the malignant plasma cell pool remains controversial. Here we established for the first time an approach that allows direct tracking of such clonotypic cells by labeling with patient-specific immunoglobulin ligands in 15 patients with myeloma. Fifty percent of patients showed evidence of clonotypic B cells in blood or bone marrow by PCR. Epitope-mimicking peptides from random libraries were selected on each patient's individual immunoglobulin and used as ligands to trace cells expressing the idiotypic immunoglobulin on their surface. We established a flow cytometry and immunofluorescence protocol to track clonotypic B cells and validated it in two independent monoclonal B cell systems. Using this method, we found clonotypic B cells in only one out of 15 myeloma patients. In view of the assay's validated sensitivity level of 10⁻³, this surprising data suggests that the abundance of such cells has been vastly overestimated in the past and that they apparently represent a very rare population in myeloma. Our novel tracing approach may open perspectives to isolate and analyze clonotypic B cells and determine their role in myeloma pathobiology.

The bone marrow stroma in hematological neoplasms--a guilty bystander

In the setting of hematological neoplasms, changes in the bone marrow (BM) stroma might arise from pressure exerted by the neoplastic clone in shaping a supportive microenvironment, or from chronic perturbation of the BM homeostasis. Under such conditions, alterations in the composition of the BM stroma can be profound, and could emerge as relevant prognostic factors. In this Review, we delineate the multifaceted contribution of the BM stroma to the pathobiology of several hematological neoplasms, and discuss the impact of stromal modifications on the natural course of these diseases. Specifically, we highlight the involvement of BM stromal components in lymphoid and myeloid malignancies, and present the most relevant processes responsible for remodeling the BM stroma. The role of bystander BM stromal elements in the setting of hematological neoplasms is discussed, strengthening the rationale for treatment strategies that target the BM stroma.

Cancer stem cells of differentiated B-cell malignancies: models and consequences

The concept of cancer stem cells has revolutionized our current vision of cancer development and was validated in solid tumors and cancers of the primitive hematopoietic compartment. Proof of the principle is still lacking, however, in malignancies of differentiated B-cells. We review here the current literature, which nevertheless suggests hierarchical organizations of the tumor clone for mostly incurable B-cell cancers such as multiple myeloma, lymphomas and B-chronic lymphocytic leukemia. We propose two models accounting for cancer stem cells in these contexts: a “top-to-bottom” clonal hierarchy from memory B-cells and a “bottom-to-top” model of clonal reprogramming. Selection pressure on the growing tumor can drive such reprogramming and increase its genetic diversity.

Identification of translocation products but not K-RAS mutations in memory B cells from patients with multiple myeloma

BACKGROUND

Several laboratories have shown that cells with a memory B-cell phenotype can have the same clonotype as multiple myeloma tumor cells.

DESIGN AND METHODS

The aim of this study was to determine whether some memory B cells have the same genetic alterations as their corresponding multiple myeloma malignant plasma cells. The methodology included sorting multiple myeloma or memory B cells into RNA stabilizing medium for generation of subset-specific polymerase chain reaction complementary DNA libraries from one or 100 cells.

RESULTS

Cells with the phenotype of tumor plasma cells (CD38(++)CD19(-)CD45(-/+)CD56(-/+/++)) or memory B cells (CD38(-)/CD19(+)/CD27(+)) were isolated by flow activated cell sorting. In samples from all four patients with multiple myeloma and from two of the three with monoclonal gammopathy of undetermined significance, we identified memory B cells expressing multiple myeloma-specific oncogenes (FGFR3; IGH-MMSET; CCND1 high) dysregulated by an IGH translocation in the respective tumor plasma cells. By contrast, in seven patients with multiple myeloma, each of whom had tumor plasma cells with a K-RAS61 mutation, a total of 32,400 memory B cells were analyzed using a sensitive allele-specific, competitive blocker polymerase chain reaction assay, but no K-RAS mutations were identified.

CONCLUSIONS

The increased expression of a specific "early" oncogene of multiple myeloma (monoclonal gammopathy of undetermined significance) in some memory B cells suggests that dysregulation of the oncogene occurs in a precursor B-cell that can generate memory B cells and transformed plasma cells. However, if memory B cells lack "late" oncogene (K-RAS) mutations but express the "early" oncogene, they cannot be involved in maintaining the multiple myeloma tumor, but presumably represent a clonotypic remnant that is only partially transformed.

Cancer stem cells and the cellular hierarchy in haematological malignancies

Malignancies in the haematopoietic system seem to depend on a small subset of so-called cancer stem cells (CSC) for their continued growth and progression - this was first described as the "sleeper-feeder theory" for leukaemia. The leukaemia stem cell was the first of such subsets to be described although the origins of these cells have been difficult to dissect. Consequently, their biology is not fully elucidated, which also holds true for the normal-tissue counterparts. The stem cell concept describes stem cells to be of low frequency, self renewing and with multilineage potential based on phenomenology - a definition which may not hold strictly true for CSCs when studied in animals and humans in vivo and in vitro. Several studies have analysed the cellular hierarchy of the haematopoietic system by cell sorting of few and even single cells, tracking acquired genetic changes and performing transplantation model studies to document subsets within the differentiating hierarchy as potential CSC compartments. In leukaemia the CSC has been described in the bone marrow compartment of haematopoietic stem cells (HSC); however, in other bone marrow disorders like multiple myeloma it is likely that the cell of origin is a more differentiated cell, like post-germinal memory B cells or plasmablasts. Studies performed so far have even indicated that the genetic events may occur in different B cell subsets in accordance with the stepwise oncogenesis of the disease. Although our understanding of the nature and biology of these initiating cells remains unknown, the obvious existence of such cells has implications for understanding initial malignant transformation and disease metastasis or progression and, most important, the selection of individualised therapeutic strategies targeting the subsets harbouring the CSC function. In the present review on stem cells in haematological malignancies we have focused on two topics, first, describing the stem cell concept in health and disease, and its "phenomenology", and second, describing the CSC compartments in leukaemia and multiple myeloma.

A novel Rag2-/-gammac-/--xenograft model of human CLL

Easily reproducible animal models that allow for study of the biology of chronic lymphocytic leukemia (CLL) and to test new therapeutic agents have been very difficult to establish. We have developed a novel transplantable xenograft murine model of CLL by engrafting the CLL cell line MEC1 into Rag2(-/-)gamma(c)(-/-) mice. These mice lack B, T, and natural killer (NK) cells, and, in contrast to nude mice that retain NK cells, appear to be optimal recipient for MEC1 cells, which were successfully transplanted through either subcutaneous or intravenous routes. The result is a novel in vivo model that has systemic involvement, develops very rapidly, allows the measurement of tumor burden, and has 100% engraftment efficiency. This model closely resembles aggressive human CLL and could be very useful for evaluating both the biologic basis of CLL growth and dissemination as well as the efficacy of new therapeutic agents.

The proteasome inhibitor CEP-18770 enhances the anti-myeloma activity of bortezomib and melphalan

The anti-multiple myeloma (MM) efficacy of bortezomib has led to the development of other proteasome inhibitors (PI), including CEP-18770 which has shown anti-MM effects in preclinical studies. However, the efficacy of orally (PO) or intravenously (IV) administered CEP-18770 in multiple MM models and in combination with conventional anti-MM therapies has not been evaluated. Herein, we show that CEP-18770 combined with melphalan or bortezomib induces synergistic inhibition of MM cell viability in vitro. In MM xenograft models, the addition of CEP-18770 IV to melphalan completely prevented the growth of both melphalan-sensitive and melphalan-resistant tumours. The combination of CEP-18770 IV and bortezomib induced complete regression of bortezomib-sensitive tumours and markedly delayed progression of bortezomib-resistant tumours compared to treatment with either agent alone. Single agent CEP-18770 PO also showed marked anti-MM effects in these xenograft models. These studies provide strong preclinical rationale for further development of this novel PI in the treatment of MM as a monotherapy as well as combined with either melphalan or bortezomib.

The search for multiple myeloma stem cells: the long and winding road

Recent years have brought significant breakthroughs in the understanding of tumor biology, related to discovery of cancer stem cells (CSCs) in acute myelogenous leukemia as well as in a number of solid tumors. This finding revealed that not all tumor cells are able to divide indefinitely, and that the bulk of tumor cells are expanded because of divisions and differentiation of CSC fraction. Although the CSCs identified in acute leukemia have a phenotype of early hematopoietic progenitors, it seems that CSCs in multiple myeloma (MM) may resemble the memory B cell fraction. Previous studies in patients with MM have documented the existence of cells without plasma cell characteristics expressing MM-type immunoglobulin genes--so-called "clonotypic" B cells. These cells have been characterized functionally and phenotypically as chemoresistant recirculating B cells. They have been found to self-renew and to be capable of initiating MM growth in immunocompromised animals. Controversy exists as to whether these cells truly belong to an MM clone, however; they may represent only the remaining clones of premalignant B cells. The identification of MM stem cells responsible for the recurrence of MM is of primary importance in designing targeted therapies to definitely cure this disease. This article summarizes the current state of knowledge on these hypothetical "MM stem cells."

Cancer stem cells: controversies in multiple myeloma

Increasing data suggest that the initiation, relapse, and progression of human cancers are driven by specific cell populations within an individual tumor. However, inconsistencies have emerged in precisely defining phenotypic markers that can reliably identify these "cancer stem cells" in nearly every human malignancy studied to date. Multiple myeloma, one of the first tumors postulated to be driven by a rare population of cancer stem cells, is no exception. Similar to other diseases, controversy surrounds the exact phenotype and biology of multiple myeloma cells with the capacity for clonogenic growth. Here, we review the studies that have led to these controversies and discuss potential reasons for these disparate findings. Moreover, we speculate how these inconsistencies may be resolved through studies by integrating advancements in both myeloma and stem cell biology.

Altered expression of fibronectin and collagens I and IV in multiple myeloma and monoclonal gammopathy of undetermined significance

Multiple myeloma (MM) is an incurable B-cell malignancy that arises in the bone marrow (BM). The malignant cells within the BM have extensive interaction with the structural components of their microenvironment. It has been previously shown that the interactions between MM cells and the BM extracellular matrix (ECM) proteins contribute to drug resistance. To understand the underlying causes of adhesion-mediated drug resistance in MM, the components of human BM ECM available for interactions with MM cells must be characterized. We analyzed the expression and localization of fibronectin, laminin, and collagens I and IV in the core biopsies of normal donors and patients with monoclonal gammopathy of undetermined significance (MGUS) or MM. In addition, we compared the patterns of ECM expression in MM patients with low-, mid-, and high-level plasmacytosis of the BM. Although expression of laminin was the same for all groups tested, levels of fibronectin and collagen I were reduced in MM patients with high-level plasmacytosis. Expression of collagen IV in the BM of MGUS and MM patients was higher than in the BM from normal donors. Compared with the plasma cells isolated from the patients with low- and mid-level plasmacytosis, sorted CD138(+) plasma cells from MM patients with high-level plasmacytosis overexpressed collagen IV. Our findings show that, compared with normal controls, the ECM composition of the bone, endosteum, and BM is aberrant in patients with MM, further establishing ECM as a key player in the MM disease process.

Cancer stem cells in multiple myeloma

Several key observations providing evidence for the cancer stem cell hypothesis and insights into the unique biology of these cells have come from the study of multiple myeloma. These include evidence that cancer cells may be functionally heterogeneous in spite of their genetic homogeneity and that malignant progenitors share many biological features with normal adult stem cells including drug resistance and regulatory processes governing self-renewal. We review studies that have examined clonogenic cells in multiple myeloma, highlight controversies regarding the cell of origin in multiple myeloma, and discuss potential targeting strategies.

Analysis of clonotypic switch junctions reveals multiple myeloma originates from a single class switch event with ongoing mutation in the isotype-switched progeny

Multiple myeloma (MM) is a cancer of plasma cells (PCs) expressing immunoglobulin heavy chain (IgH) postswitch isotypes. The discovery of earlier stage cells related to postswitch PCs, called preswitch clonotypic IgM (cIgM) cells led to the hypothesis that cIgM cells may be MM progenitors, replenishing the tumor throughout malignancy. cIgM cells may do this by undergoing class switch recombination (CSR), a process detectable in postswitch PCs as multiple IgH switch junctions associated with a single clonotypic IgH V/D/J. We addressed this with a specific clonotypic-switch polymerase chain reaction (PCR), informative for 32 of 41 cases. Here we made 2 significant discoveries: (1) in all cases, we detected only a single clonotypic switch fragment that persists over time (1-7.6 years), and (2) we detected ongoing mutation upstream of the switch junction in 5 of 6 patients, often targeting the intronic enhancer, a key control region in IgH expression. The presence of a single, unchanging clonotypic switch junction suggests that cIgM cells are not MM-PC progenitors; rather, postswitch PCs arise from a single cIgM cell, and MM-PC progenitors reside in the postswitch population. Furthermore, mutations revealed here provide a new marker to identify MM-PC progenitors and aggressive clones that evolve throughout malignancy.

Multiple myeloma cancer stem cells

Multiple myeloma is characterized by the clonal expansion of neoplastic plasma cells within the bone marrow, elevated serum immunoglobulin, and osteolytic bone disease. The disease is highly responsive to a wide variety of anticancer treatments including conventional cytotoxic chemotherapy, corticosteroids, radiation therapy, and a growing number of agents with novel mechanisms of action. However, few if any patients are cured with these modalities and relapse remains a critical issue. A better understanding of clonogenic multiple myeloma cells is essential to ultimately improving long-term outcomes, but the nature of the cells responsible for myeloma regrowth and disease relapse is unclear. We review evidence that functional heterogeneity exists in multiple myeloma and discuss potential strategies and clinical implications of the stem-cell model of cancer in this disease.

A unique three-dimensional model for evaluating the impact of therapy on multiple myeloma

Although the in vitro expansion of the multiple myeloma (MM) clone has been unsuccessful, in a novel three-dimensional (3-D) culture model of reconstructed bone marrow (BM, n = 48) and mobilized blood autografts (n = 14) presented here, the entire MM clone proliferates and undergoes up to 17-fold expansion of malignant cells harboring the clonotypic IgH VDJ and characteristic chromosomal rearrangements. In this system, MM clone expands in a reconstructed microenvironment that is ideally suited for testing specificity of anti-MM therapeutics. In the 3-D model, melphalan and bortezomib had distinct targets, with melphalan targeting the hematopoietic, but not stromal com-partment. Bortezomib targeted only CD138(+)CD56(+) MM plasma cells. The localization of nonproliferating cells to the reconstructed endosteum, in contact with N-cadherin-positive stroma, suggested the presence of MM-cancer stem cells. These drug-resistant CD20(+) cells were enriched more than 10-fold by melphalan treatment, exhibited self-renewal, and generated clonotypic B and plasma cell progeny in colony forming unit assays. This is the first molecularly verified demonstration of proliferation in vitro by ex vivo MM cells. The 3-D culture provides a novel biologically relevant preclinical model for evaluating therapeutic vulnerabilities of all compartments of the MM clone, including presumptive drug-resistant MM stem cells.

Multiple Myeloma Includes Phenotypically Defined Subsets of Clonotypic CD20+ B Cells that Persist During Treatment with Rituximab

Potential progenitor B cell compartments in multiple myeloma (MM) are clinically important. MM B cells and some circulating MM plasma cells express CD20, predicting their clearance by treatment with anti-CD20. Here we describe two types of clonotypic CD20+ B cell in peripheral blood of myeloma patients, identified by their expression of CD19 and CD20 epitopes, their expression of CD45RA and their light scatter properties. Thus, the circulating component of the MM clone includes at least two distinct CD19+ CD20+ B cell compartments, as well as CD138+ CD20+ plasma cells. To determine whether either or both B cell subsets and the CD20+ plasma cell subset were depleted by anti-CD20 therapy, they were evaluated before, during and after treatment of patients with rituximab (anti-CD20), followed by quantifying B cell subsets over a 5 month period during and after treatment. Overall, all three types of circulating B lineage cells persist despite treatment with rituximab. The inability of rituximab to prolong survival in MM may result from this failure to deplete CD20+ B and plasma cells in MM.

Clonogenic multiple myeloma progenitors, stem cell properties, and drug resistance

Many agents are active in multiple myeloma, but the majority of patients relapse. This clinical pattern suggests most cancer cells are eliminated, but cells with the clonogenic potential to mediate tumor regrowth are relatively chemoresistant. Our previous data suggested that CD138(+) multiple myeloma plasma cells cannot undergo long-term proliferation but rather arise from clonogenic CD138(neg) B cells. We compared the relative sensitivity of these distinct cell types to clinical antimyeloma agents and found that dexamethasone, lenadilomide, bortezomib, and 4-hydroxycyclophosphamide inhibited CD138(+) multiple myeloma plasma cells but had little effect on CD138(neg) precursors in vitro. We further characterized clonogenic multiple myeloma cells and stained cell lines using the Hoechst side population and Aldefluor assays. Each assay identified CD138(neg) cells suggesting that they possess high drug efflux capacity and intracellular drug detoxification activity. We also found that multiple myeloma cells expressing the memory B-cell markers CD20 and CD27 could give rise to clonogenic multiple myeloma growth in vitro and engraft immunodeficient nonobese diabetes/severe combined immunodeficient mice during both primary and secondary transplantation. Furthermore, both the side population and Aldefluor assays were capable of identifying circulating clonotypic memory B-cell populations within the peripheral blood of multiple myeloma patients. Our results suggest that circulating clonotypic B-cell populations represent multiple myeloma stem cells, and the relative drug resistance of these cells is mediated by processes that protect normal stem cells from toxic injury.

Mouse models of human myeloma

Multiple myeloma (MM) remains incurable despite high-dose chemotherapy with stem cell support. There is need, therefore, for continuous efforts directed toward the development of novel rational-based therapeutics for MM, which requires a detailed knowledge of the mutations driving this malignancy. In improving the success rate of effective drug development, it is equally imperative that biologic systems be developed to better validate these target genes. Here we review the recent developments in the generation of mouse models of MM and their impact as preclinical models for designing and assessing target-based therapeutic approaches.

Microfluidic chips for detecting the t(4;14) translocation and monitoring disease during treatment using reverse transcriptase-polymerase chain reaction analysis of IgH-MMSET hybrid transcripts

Diagnosis platforms incorporating low-cost microfluidic chips enable sensitive, rapid, and accurate genetic analysis that could facilitate customized therapies tailored to match the vulnerabilities of any types of cancer. Using ex vivo cancer cells, we have detected the unique molecular signature and a chromosomal translocation in multiple myeloma. Multiple myeloma is characterized by IgH rearrangements and translocations that enable unequivocal identification of malignant cells, detected here with integrated microfluidic chips incorporating genetic amplification via reverse transcriptase-polymerase chain reaction and capillary electrophoresis. On microfluidic chips, we demonstrated accurate and versatile detection of molecular signatures in individual cancer cells, with value for monitoring response to therapy, detecting residual cancer cells that mediate relapse, and evaluating prognosis. Thus, testing for two clinically important molecular biomarkers, the IgH VDJ signature and hybrid transcripts signaling the t(4;14) chro-mosomal translocation, with predictive value in diagnosis, treatment decisions, and monitoring has been efficiently implemented on a miniaturized microfluidic system.

Sensitive detection using microfluidics technology of single cell PCR products from high and low abundance IgH VDJ templates in multiple myeloma

Human cancer is inherently heterogeneous, so the ability to monitor individual cancer cells at every clinic visit would be a valuable tool. This work describes the first step towards developing handheld and automated devices for molecular and phenotypic analysis of cancer cells. Here, we show that use of capillary electrophoresis to detect PCR product amplified from either transcripts (high abundance template) or genomic DNA (low abundance template) encoding clonotypic immunoglobulin heavy chain VDJ of plasma cells from patients with multiple myeloma. High abundance IgH VDJ transcripts amplified in conventional systems or by capillary electrophoresis through channels on microfluidic chips or, alternatively, PCR product amplified from individual myeloma plasma cells in a single stage RT-PCR reaction was readily detectable on microfluidic chips. For low abundance templates, a nested PCR strategy was needed to detect PCR product by any method. Using microfluidic chips, PCR products amplified from genomic IgH VDJ DNA were detected in six out of eight plasma cells. Comparison of the ABI3100 and the microfluidic chip indicates that approximately 20 times more sample is injected into the ABI 3100 capillary than for the microfluidics chip. Overall, for high and low abundance template in individual cells, the microfluidic separation/detection system is at least as sensitive as the ABI 3100. In the future, integrated microfluidic platforms that incorporate both PCR cycling and product detection on the same chip are likely to exceed conventional systems in sensitivity and speed of genetic analysis by RT-PCR or PCR.

Antigen-specific memory B cell development

Helper T (Th) cell-regulated B cell immunity progresses in an ordered cascade of cellular development that culminates in the production of antigen-specific memory B cells. The recognition of peptide MHC class II complexes on activated antigen-presenting cells is critical for effective Th cell selection, clonal expansion, and effector Th cell function development (Phase I). Cognate effector Th cell-B cell interactions then promote the development of either short-lived plasma cells (PCs) or germinal centers (GCs) (Phase II). These GCs expand, diversify, and select high-affinity variants of antigen-specific B cells for entry into the long-lived memory B cell compartment (Phase III). Upon antigen rechallenge, memory B cells rapidly expand and differentiate into PCs under the cognate control of memory Th cells (Phase IV). We review the cellular and molecular regulators of this dynamic process with emphasis on the multiple memory B cell fates that develop in vivo.

RHAMM expression and isoform balance predict aggressive disease and poor survival in multiple myeloma

Multiple myeloma (MM) plasma cells (PCs) express receptor for hyaluronan-mediated motility (RHAMM), a hyaluronan-binding, cytoskeleton and centrosome protein. The most abundant RHAMM isoforms in MM are full-length RHAMM (RHAMMFL) and the splice variant RHAMM-exon4. We separately examined the significance of RHAMM expression, and isoform balance, in 2 groups of MM patients. In oligonucleotide microarray experiments (n=210, Arkansas), increasing RHAMM mRNA expression in MM PCs is strongly associated with osteolytic bone lesions (P <.001), and event-free (P =.05) and overall (P =.04) survival. Semiquantitative determination of RHAMM isoform expression (Alberta, Canada) used capillary electrophoretic detection and measurement of RHAMM-exon4/RHAMMFL reverse-transcriptase-polymerase chain reaction (RT-PCR) products. RHAMM isoforms are rarely expressed concurrently in single MM PCs; the pattern of isoform expression, at the single-cell level, is approximated in larger numbers of cells by the RHAMM-exon4/RHAMMFL ratio. Absolute RHAMM expression and the RHAMM-exon4/RHAMMFL ratio are only partially correlated in MM PCs; in cell lines, absolute RHAMM expression is elevated in mitosis, while RHAMM ratios remain stable. Temporal examination of MM patients' peripheral blood reveals that the RHAMM-exon4/RHAMMFL ratio increases with disease burden. The RHAMM-exon4/RHAMMFL ratio in diagnostic bone marrow samples (n=101, Alberta) is an independent prognostic factor. Thus, expression and splicing of RHAMM are important molecular determinants of disease severity in MM.

Nonirradiated NOD/SCID-human chimeric animal model for primary human multiple myeloma: a potential in vivo culture system

The NOD/SCID human chimeric animal model was generated by implanting of human fetal bones (FBs) into subcutaneous sites of NOD/SCID mice (NOD/SCID-hu(+)), followed by inoculation of primary bone marrow mononuclear cells (BMNCs) obtained from patients with multiple myeloma (MM) into the FBs. The BMNCs from 30 patients with MM were inoculated, and 28 (93%) of them revealed evidence of tumor growth of myeloma cells (MCs) in the NOD/SCID-hu(+) mice. Intriguingly, 17 (61%) of the 28 patients' BMNCs inoculated developed not only myeloma in the bone marrow of the FBs, but also extramedullary macrotumors (EMTs) along the periosteum of the FBs. The tumor cells in these EMTs had plasmacytoid morphology and preserved antigens and cytogenetics similar, if not identical, to those in the parent MCs. Moreover, small tumor blocks from nine EMTs were transplanted into subcutaneous sites of subsequent recipient NOD/SCID mice without human FBs (NOD/SCID-hu(-)), and all but one grew successfully. Two of the EMTs have been maintained in the animal model for more than 12 months. The NOD/SCID-hu(+) chimeric animal model is highly efficient for growth of primary MCs and presents clinical features of human MM. The engrafted MCs can be maintained subsequently in NOD/SCID-hu(-) mice as in vivo culture.