Stefan Wöhrer

Cancer stem cell definitions and terminology: the devil is in the details

The cancer stem cell (CSC) concept has important therapeutic implications, but its investigation has been hampered both by a lack of consistency in the terms used for these cells and by how they are defined. Evidence of their heterogeneous origins, frequencies and their genomic, as well as their phenotypic and functional, properties has added to the confusion and has fuelled new ideas and controversies. Participants in The Year 2011 Working Conference on CSCs met to review these issues and to propose a conceptual and practical framework for CSC terminology. More precise reporting of the parameters that are used to identify CSCs and to attribute responses to them is also recommended as key to accelerating an understanding of their biology and developing more effective methods for their eradication in patients.

High-throughput analysis of single hematopoietic stem cell proliferation in microfluidic cell culture arrays

Heterogeneity in cell populations poses a major obstacle to understanding complex biological processes. Here we present a microfluidic platform containing thousands of nanoliter-scale chambers suitable for live-cell imaging studies of clonal cultures of nonadherent cells with precise control of the conditions, capabilities for in situ immunostaining and recovery of viable cells. We show that this platform mimics conventional cultures in reproducing the responses of various types of primitive mouse hematopoietic cells with retention of their functional properties, as demonstrated by subsequent in vitro and in vivo (transplantation) assays of recovered cells. The automated medium exchange of this system made it possible to define when Steel factor stimulation is first required by adult hematopoietic stem cells in vitro as the point of exit from quiescence. This technology will offer many new avenues to interrogate otherwise inaccessible mechanisms governing mammalian cell growth and fate decisions.

Prospective isolation and molecular characterization of hematopoietic stem cells with durable self-renewal potential

Hematopoietic stem cells (HSCs) are generally defined by their dual properties of pluripotency and extensive self-renewal capacity. However, a lack of experimental clarity as to what constitutes extensive self-renewal capacity coupled with an absence of methods to prospectively isolate long-term repopulating cells with defined self-renewal activities has made it difficult to identify the essential components of the self-renewal machinery and investigate their regulation. We now show that cells capable of repopulating irradiated congenic hosts for 4 months and producing clones of cells that can be serially transplanted are selectively and highly enriched in the CD150(+) subset of the EPCR(+)CD48(-)CD45(+) fraction of mouse fetal liver and adult bone marrow cells. In contrast, cells that repopulate primary hosts for the same period but show more limited self-renewal activity are enriched in the CD150(-) subset. Comparative transcriptome analyses of these 2 subsets with each other and with HSCs whose self-renewal activity has been rapidly extinguished in vitro revealed 3 new genes (VWF, Rhob, Pld3) whose elevated expression is a consistent and selective feature of the long-term repopulating cells with durable self-renewal capacity. These findings establish the identity of a phenotypically and molecularly distinct class of pluripotent hematopoietic cells with lifelong self-renewal capacity.

The Lin28b–let-7–Hmga2 axis determines the higher self-renewal potential of fetal haematopoietic stem cells

Mouse haematopoietic stem cells (HSCs) undergo a postnatal transition in several properties, including a marked reduction in their self-renewal activity. We now show that the developmentally timed change in this key function of HSCs is associated with their decreased expression of Lin28b and an accompanying increase in their let-7 microRNA levels. Lentivirus-mediated overexpression of Lin28 in adult HSCs elevates their self-renewal activity in transplanted irradiated hosts, as does overexpression of Hmga2, a well-established let-7 target that is upregulated in fetal HSCs. Conversely, HSCs from fetal Hmga2−/− mice do not exhibit the heightened self-renewal activity that is characteristic of wild-type fetal HSCs. Interestingly, overexpression of Hmga2 in adult HSCs does not mimic the ability of elevated Lin28 to activate a fetal lymphoid differentiation program. Thus, Lin28b may act as a master regulator of developmentally timed changes in HSC programs with Hmga2 serving as its specific downstream modulator of HSC self-renewal potential.

Assessment of Disease Dissemination in Gastric Compared With Extragastric Mucosa-Associated Lymphoid Tissue Lymphoma Using Extensive Staging: A Single-Center Experience

PURPOSE Molecular data and preliminary clinical findings have suggested mucosa-associated lymphoid tissue (MALT) lymphoma as a multifocal disease in a high percentage of patients. We report our findings with an extensive staging routine applied in patients diagnosed with MALT lymphoma at our institution. PATIENTS AND METHODS A total of 140 consecutive patients (61 with gastric and 79 with extragastric MALT lymphoma) underwent staging according to a standardized protocol. Staging included gastroscopy with multiple biopsies, endosonography of the upper GI tract, computed tomography of thorax and abdomen, lymph node sonography, colonoscopy with multiple biopsies, otorhinolaryngologic assessment, magnetic resonance imaging of salivary and lacrimal glands, and bone marrow biopsy. All lesions suggestive of lymphoma involvement were subjected to biopsy, if accessible, and biopsies were evaluated for MALT lymphoma-specific genetic aberrations by means of reverse transcriptase polymerase chain reaction and/or fluorescent in situ hybridization. RESULTS Fifteen (25%) of 61 patients with gastric MALT lymphoma had multiorgan involvement, with dissemination beyond the GI tract in six patients. By contrast, significantly more patients with extragastric MALT lymphoma had dissemination to another MALT organ (37 of 79 patients, 46%; P = .045). Nine of these 37 patients had dissemination to the stomach. Only three (2%) of 140 patients had bone marrow involvement. Multifocality was significantly associated with t(11;18)(q21;q21) in gastric lymphomas (P = .045) and with trisomy 18 in extragastric lymphomas (P = .011). CONCLUSION Our findings suggest that MALT lymphoma frequently presents as a multifocal disease. Extragastric MALT lymphomas are significantly more prone to dissemination than gastric MALT lymphomas.

Successful antibiotic treatment of Helicobacter pylori negative gastric mucosa associated lymphoid tissue lymphomas

Background and aims: The role of antibiotic treatment in early stage gastric mucosa associated lymphoid tissue (MALT) lymphoma not associated with Helicobacter pylori infection has not been investigated. Patients and methods: Six patients with localised gastric MALT lymphoma underwent antibiotic treatment with clarithromycin, metronidazole, and pantoprazole. Staging, including endosonography plus gastroscopy, computed tomography of the thorax and abdomen, colonoscopy, magnetic resonance imaging of the salivary glands, and bone marrow biopsy were performed to rule out distant spread of the disease. In addition, MALT specific genetic changes, including reverse transcriptase-polymerase chain reaction for t(11;18)(q21;q21), were tested in all patients. H pylori infection was ruled out by histology, urease breath test, serology, and stool antigen testing. Results: All six patients had MALT lymphoma restricted to the stomach, and no evidence of infection with H pylori was found. Only one patient tested positive for t(11;18)(q21;q21) while the remaining five displayed no genetic aberrations. Following antibiotic treatment, endoscopic controls were performed every three months. Five patients responded with lymphoma regression between three and nine months following antibiotic treatment (one partial remission and four complete responses). One patient had stable disease for 12 months and was then referred for chemotherapy. Conclusions: Patients with early stage gastric MALT lymphoma negative for H pylori might still benefit from antibiotic treatment as the sole treatment modality.

Antibiotic Treatment Is Not Effective in Patients Infected With Helicobacter pylori Suffering From Extragastric MALT Lymphoma

PURPOSE Apart from anecdotal reports implicating Helicobacter pylori (HP) in the development of extragastric mucosa associated lymphoid tissue (MALT) lymphoma, no large scale prospective studies have been performed on this topic. PATIENTS AND METHODS A total of 77 patients with extragastric MALT lymphoma were prospectively studied. The presence or absence of HP was tested by histology, urease breath test, and serology. Patients were also tested for hepatitis A, B, and C and autoimmune conditions along with assessment of MALT lymphoma-specific genetic changes. RESULTS Evidence for infection with HP was present in 35 of 77 patients (45%), and three of 75 patients tested (4%) were positive for hepatitis C and one for hepatitis B. All patients with HP-infection underwent eradication, 16 before initiation of further therapy. Apart from one patient with lymphoma involving parotid and colon, who achieved regression of the colonic lesions, none of these 16 patients showed regression of the lymphoma after a median follow-up of 14 months (range, 8 to 48+ months) before initiation of definitive treatment. No correlation between HP-status, localization, stage, autoimmune diseases, and genetic findings was seen. CONCLUSION In our series, HP-eradication was ineffective for treatment of extragastric MALT lymphomas. This finding, along with an infection rate of 45%-as could also be expected in the general Austrian population-suggests that HP does not play a role in the development of these lymphomas. Antibiotic treatment targeting HP should, therefore, be discouraged in patients with extragastric MALT lymphomas.

Frequency of chromosomal aberrations involving MALT1 in mucosa-associated lymphoid tissue lymphoma in patients with Sjögren's syndrome

Purpose: Mucosa-associated lymphoid tissue (MALT) lymphoma develops in the context of longstanding antigenic stimulation such as infection with Helicobacter pylori or autoimmune disease, including Sjögren’s syndrome (SS). Recently, two chromosomal aberrations involving the MALT1 gene, i.e., t(11;18)(q21;q21) and t(14;18)(q32;q21) have been reported as genetic events specific for MALT lymphoma. In view of the association between SS and the development of MALT lymphoma, we have analyzed the frequency of t(11;18)(q21;q21) and t(14;18)(q32;q21) in patients with MALT lymphomas arising in the background of SS. Experimental Design: A retrospective analysis of patients diagnosed with MALT lymphoma and SS was performed. The t(11;18)(q21;q21) was analyzed using reverse transcriptase-PCR, whereas t(14;18)(q32;q21) was assessed by two-color interphase fluorescence in situ hybridization. Results: Twenty-six patients (20 female and 6 male) with MALT lymphoma and SS could be identified. The lymphoma was located in the parotid (n = 14), orbit (n = 2), and submandibular gland (n = 1), whereas 9 patients had gastric MALT lymphoma. Seven of 26 patients (27%) harbored t(11;18)(q21;q21). Interestingly, only 1 of 17 patients (6%) with extragastrointestinal lymphoma was positive, as opposed to 6 of 9 patients (67%) with gastric MALT lymphoma. Four of 26 patients were positive for t(14;18)(q32;q21): 3 of 17 extragastrointestinal (18%) and 1 of 9 gastric lymphomas (11%). Conclusions: The overall frequency of MALT1 rearrangement appears to be low in patients with extragastrointestinal MALT lymphoma associated with SS. By contrast, MALT1 rearrangement was demonstrated in 7 of 9 patients (78%) with gastric MALT lymphoma and SS. This finding may explain at least in part why gastric MALT lymphomas in patients with SS are refractory to H. pylori eradication therapy.

Monoclonal Immunoglobulin Production Is a Frequent Event in Patients with Mucosa-Associated Lymphoid Tissue Lymphoma

Purpose: Mucosa-associated lymphoid tissue (MALT) lymphoma comprises 7% of all newly diagnosed non-Hodgkin’s lymphomas and is therefore among the most common lymphoma entities. Monoclonal gammopathy due to production of a monoclonal immunoglobulin by lymphoma cells is a well-known phenomenon associated with various types of B-cell non-Hodgkin’s lymphomas. The objective of the present study was to evaluate the incidence and clinical relevance of paraprotein (PP) production in patients with MALT lymphoma. Experimental Design: Fifty two patients were prospectively evaluated with regard to differentiation of the MALT lymphoma cells, t(11;18) translocation, monoclonal immunoglobulin production, Helicobacter pylori (HP) status, stage, treatment, and clinical outcome. Results: Nineteen of 52 MALT lymphoma patients (36%) had PP (8 IgMκ, 6 IgGκ, 4 IgMλ, and 1 IgAκ). The histologic feature of plasmacytic differentiation correlated significantly with the production of PP (P = 0.001). No correlation was found between PP and clinical stage, HP status, and t(11;18) status. PP was, however, negatively associated with response to eradication of HP in gastric MALT lymphoma, and PP levels declined significantly in patients responding to chemotherapy or radiation. Importantly, both immunofixation and serum electrophoresis have to be performed to detect low PP levels. Conclusions: In conclusion, PP levels may probably be used as a potential prognostic tool for response to HP eradication, and serial measurements may also allow for noninvasive assessment of response to radiation or chemotherapy in patients with MALT lymphoma.

Activity of Rituximab plus Cyclophosphamide, Doxorubicin/Mitoxantrone, Vincristine and Prednisone in Patients with Relapsed MALT Lymphoma

Background: Various chemotherapeutic agents as well as the anti-CD20 antibody rituximab (R) have been tested in patients with mucosa-associated lymphoid tissue (MALT) lymphoma, but no standard chemotherapeutic regimen has emerged so far. Judging from the data obtained in various types of lymphoma, the activity of R appears to be enhanced by combination with chemotherapy. As no data on this topic exist for MALT lymphoma, we have retrospectively analysed our experience with R plus cyclophosphamide, doxorubicin/mitoxantrone, vincristine and prednisone (R-CHOP/R-CNOP) in patients with relapsed MALT lymphoma. Patients and Methods: A total of 26 patients were identified, 15 were administered R-CHOP while 11 patients were given R-CNOP due to age >65 years or pre-existing cardiac conditions. Cycles were repeated every 21 days, and restaging was performed after 4 cycles of therapy. In case of complete remission, 2 further cycles were administered for consolidation while patients achieving partial remission or stable disease after restaging were given 4 further courses. Results: A total of 170 cycles were administered to our patients (median 6, range 2–8). Twenty of the 26 patients (77%) achieved a complete remission and 6 (23%) a partial remission. Toxicities were mainly haematological, with WHO grade III/IV leukocytopenia occurring in 5 patients. After a median follow-up of 19 months (range 10–45), all patients are alive: 22 are in ongoing remission, while 4 have relapsed between 12 and 19 months after treatment. Conclusions: Our data demonstrate a high activity of R-CHOP/R-CNOP in relapsing MALT lymphoma irrespective of prior therapy.