Mitochondrial Regulation of the Muscle Microenvironment in Critical Limb Ischemia

Critical limb ischemia (CLI) is the most severe clinical presentation of peripheral arterial disease and manifests as chronic limb pain at rest and/or tissue necrosis. Current clinical interventions are largely ineffective and therapeutic angiogenesis based trials have shown little efficacy, highlighting the dire need for new ideas and novel therapeutic approaches. Despite a decade of research related to skeletal muscle as a determinant of morbidity and mortality outcomes in CLI, very little progress has been made toward an effective therapy aimed directly at the muscle myopathies of this disease. Within the muscle cell, mitochondria are well positioned to modulate the ischemic cellular response, as they are the principal sites of cellular energy production and the major regulators of cellular redox charge and cell death. In this mini review, we update the crucial importance of skeletal muscle to CLI pathology and examine the evolving influence of muscle and endothelial cell mitochondria in the complex ischemic microenvironment. Finally, we discuss the novelty of muscle mitochondria as a therapeutic target for ischemic pathology in the context of the complex co-morbidities often associated with CLI.

Subacute limb ischemia induces skeletal muscle injury in genetically susceptible mice independent of vascular density

OBJECTIVE

The primary preclinical model of peripheral artery disease, which involves acute limb ischemia (ALI), can result in appreciable muscle injury that is attributed to the acuity of the ischemic injury. A less acute model of murine limb ischemia using ameroid constrictors (ACs) has been developed in an attempt to mimic the chronic nature of human disease. However, there is currently little understanding of how genetics influence muscle injury following subacute arterial occlusion in the mouse.

METHODS

We investigated the influence of mouse genetics on skeletal muscle tissue survival, blood flow, and vascular density by subjecting two different mouse strains, C57BL/6 (BL6) and BALB/c, to ALI or subacute limb ischemia using single (1AC) or double (2AC) AC placement on the femoral artery.

RESULTS

Similar to ALI, the 2AC model resulted in significant tissue necrosis and limb perfusion deficits in genetically susceptible BALB/c but not BL6 mice. In the 1AC model, no outward evidence of tissue necrosis was observed, and there were no differences in limb blood flow between BL6 and BALB/c. However, BALB/c mice displayed significantly greater muscle injury, as evidenced by increased inflammation and myofiber atrophy, despite having no differences in CD31(+) and SMA(+) vascular density and area. BALB/c mice also displayed significantly greater centralized myonuclei, indicating increased muscle regeneration.

CONCLUSIONS

The susceptibility of skeletal muscle to ischemia-induced injury is at least partly independent of muscle blood flow and vascular density, consistent with a muscle cell autonomous response that is genetically determined. Further development of preclinical models of peripheral artery disease that more accurately reflect the nature of the human disease may allow more accurate identification of genetic targets for therapeutic intervention.

Muscle cell derived angiopoietin-1 contributes to both myogenesis and angiogenesis in the ischemic environment

Recent strategies to treat peripheral arterial disease (PAD) have focused on stem cell based therapies, which are believed to result in local secretion of vascular growth factors. Little is known, however, about the role of ischemic endogenous cells in this context. We hypothesized that ischemic muscle cells (MC) are capable of secreting growth factors that act as potent effectors of the local cellular regenerative environment. Both muscle and endothelial cells (ECs) were subjected to experimental ischemia, and conditioned medium (CM) from each was collected and analyzed to assess myogenic and/or angiogenic potential. In muscle progenitors, mRNA expression of VEGF and its cognate receptors (Nrp1, Flt, Flk) was present and decreased during myotube formation in vitro, and EC CM or VEGF increased myoblast proliferation. Angiopoietin-1 (Ang-1), Tie1, and Tie2 mRNA increased during MC differentiation in vitro. Exogenous Ang-1 enhanced myogenic (MyoD and Myogenin) mRNA in differentiating myoblasts and increased myosin heavy chain protein. Myotube formation was enhanced by MC CM and inhibited by EC CM. Ang-1 protein was present in CM from MCs isolated from both the genetically ischemia-susceptible BALB/c and ischemia-resistant C57BL/6 mouse strains, and chimeric Tie2 receptor trapping in situ ablated Ang-1's myogenic effects in vitro. Ang-1 or MC CM enhanced myotube formation in a mixed isolate of muscle progenitors as well as a myoblast co-culture with pluripotent mesenchymal cells (10T1/2) and this effect was abrogated by viral expression of the extracellular domain of Tie2 (AdsTie2). Furthermore, mesh/tube formation by HUVECs was enhanced by Ang-1 or MC CM and abrogated by Tie2 chimeric receptor trapping. Our results demonstrate the ability of muscle and endothelial cell-derived vascular growth factors, particularly Ang-1, to serve as multi-functional stimuli regulating crosstalk between blood vessels and muscle cells during regeneration from ischemic myopathy.

COGENT (COlorectal cancer GENeTics): an international consortium to study the role of polymorphic variation on the risk of colorectal cancer

It is now recognised that a part of the inherited risk of colorectal cancer (CRC) can be explained by the co-inheritance of low-penetrance genetic variants. The accumulated experience to date in identifying these variants has served to highlight difficulties in conducting statistically and methodologically rigorous studies and follow-up analyses. The COGENT (COlorectal cancer GENeTics) consortium includes 20 research groups in Europe, Australia, the Americas, China and Japan. The overarching goal of COGENT is to identify and characterise low-penetrance susceptibility variants for CRC through association-based analyses. In this study, we review the rationale for identifying low-penetrance variants for CRC and our proposed strategy for establishing COGENT.

Inhibition of BCL11B expression leads to apoptosis of malignant but not normal mature T cells

The B-cell chronic lymphocytic leukemia (CLL)/lymphoma 11B gene (BCL11B) encodes a Krüppel-like zinc-finger protein, which plays a crucial role in thymopoiesis and has been associated with hematopoietic malignancies. It was hypothesized that BCL11B may act as a tumor-suppressor gene, but its precise function has not yet been elucidated. Here, we demonstrate that the survival of human T-cell leukemia and lymphoma cell lines is critically dependent on Bcl11b. Suppression of Bcl11b by RNA interference selectively induced apoptosis in transformed T cells whereas normal mature T cells remained unaffected. The apoptosis was effected by simultaneous activation of death receptor-mediated and intrinsic apoptotic pathways, most likely as a result of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) upregulation and suppression of the Bcl-xL antiapoptotic protein. Our data indicate an antiapoptotic function of Bcl11b. The resistance of normal mature T lymphocytes to Bcl11b suppression-induced apoptosis and restricted expression pattern make it an attractive therapeutic target in T-cell malignancies.

Disruption of the BCL11B gene through inv(14)(q11.2q32.31) results in the expression of BCL11B-TRDC fusion transcripts and is associated with the absence of wild-type BCL11B transcripts in T-ALL

T-cell acute lymphoblastic leukemia (T-ALL) is associated with chromosomal aberrations characterized by juxtaposition of proto-oncogenes to T-cell receptor gene loci (TCR), resulting in the deregulated transcription of these proto-oncogenes. Here, we describe the molecular characterization of a novel chromosomal aberration, inv(14)(q11.2q32.31), in a T-ALL sample, involving the recently described BCL11B gene and the TCRD locus. The inversion joined the 5' part of BCL11B, including exons 1-3, to the TRDD3 gene segment of the TCRD locus, whereas the reciprocal breakpoint fused the TRDV1 gene segment to the fourth exon of BCL11B. The TRDV1-BCL11B joining region was 1344 bp long and contained fragments derived from 20q11.22, 3p21.33 and from 11p12, indicating the complex character of this aberration. A strong expression of in-frame transcripts with truncated BCL11B and TCRD constant region (TRDC) were observed, but in contrast to normal T cells and other T-ALL samples, no wild-type BCL11B transcripts were detected in the T-ALL sample. Screening of 37 other T-ALLs revealed one additional case with expression of the BCL11B-TRDC fusion transcript. As BCL11B appears to play a key role in T-cell differentiation, BCL11B disruption and disturbed expression may contribute to the development of T-cell malignancies in man.

[Lung metastases of colorectal tumors: clinical background and development of care supply]

The incidence of most cancers increases with age, including colorectal-, lung- and breast carcinomas. Each year, approximately 50,000 new cases of colorectal carcinoma (CRC) are diagnosed in Germany with a peak incidence around the age of 65. At diagnosis, 50% of CRC-cases show already metastases. Cure of metastatic disease with chemotherapy, radiology or surgery alone or in combination can be rarely achieved in this situation. However, palliative therapy regimens can significantly prolong life in most cases. Besides systemic therapy, minimal invasive techniques for tumor reduction are an interesting option in the palliative situation, especially in elderly patients. Yet the clinical impact of these new techniques has to be determined in future studies.

Biological evaluation of recombinant human erythropoietin in pharmaceutical products

The potencies of mammalian cell-derived recombinant human erythropoietin pharmaceutical preparations, from a total of five manufacturers, were assessed by in vivo bioassay using standardized protocols. Eight-week-old normocythemic mice received a single subcutaneous injection followed by blood sampling 96 h later or multiple daily injections with blood sampling 24 h after the last injection. Reticulocyte counting by microscopic examination was employed as the end-point using the brilliant cresyl blue or selective hemolysis methods, together with automated flow cytometry. Different injection schedules were investigated and dose-response curves for the European Pharmacopoeia Biological Reference Preparation of erythropoietin were compared. Manual and automated methods of reticulocyte counting were correlated with respect to assay validity and precision. Using 8 mice per treatment group, intra-assay precision determined for all of the assays in the study showed coefficients of variation of 12.1-28.4% for the brilliant cresyl blue method, 14.1-30.8% for the selective hemolysis method and 8.5-19.7% for the flow cytometry method. Applying the single injection protocol, a combination of at least two independent assays was required to achieve the precision potency and confidence limits indicated by the manufacturers, while the multiple daily injection protocol yielded the same acceptable results within a single assay. Although the latter protocol using flow cytometry for reticulocyte counting gave more precise and reproducible results (intra-assay coefficients of variation: 5.9-14.2%), the well-characterized manual methods provide equally valid alternatives for the quality control of recombinant human erythropoietin therapeutic products.

Comparative evaluation of the human whole blood and human peripheral blood monocyte tests for pyrogens

Two different in vitro tests for pyrogens, using human peripheral blood monocytes (PBMNC) and diluted whole blood (WBC), respectively, were applied to different classes of parenteral medicinal products. Many of these products did not have a specified endotoxin limit concentration that was established as the maximum valid dilution to comply with the test. The results of the in vitro tests for pyrogens were compared with the results from the Limulus amoebocyte lysate (LAL) and rabbit pyrogen tests. The Second International Standard for endotoxin was used to calibrate all of the assays and the International Standard for IL-6 was used to calibrate the IL-6 ELISA which provided the readout for the in vitro tests for pyrogens. Preparatory tests were conducted to ensure that the "criteria for validity and precision of the standard curve" were satisfied and that the drugs being tested did not interfere in the tests. The PBMNC/IL-6 test had a detection limit of 0.06 EU/ml and spike recoveries were 62-165%. The whole blood/IL-6 test also had a detection limit of 0.06 EU/ml and spike recoveries were 58-132%. The application to the detection of non-endotoxin pyrogens needs to be evaluated in more detail, but the two in vitro tests for pyrogens showed good agreement overall, both with each other and with the LAL test and the rabbit pyrogen test for the detection of endotoxins.

Quantitative analysis of beta-actin, beta-2-microglobulin and porphobilinogen deaminase mRNA and their comparison as control transcripts for RT-PCR

Quantitation of target mRNAs using the reverse-transcription polymerase chain reaction found a widespread field of application in diverse biomedical diagnostic assays. However, the problem of varying sample quality has to be solved by correcting target molecule amounts through detection of an endogenous control template. The choice of an appropriate reference gene is still object of debate as pseudogene co-amplification and expression level variations may limit the usefulness of some currently used reference reactions. We compared quantitative expression levels of the commonly used endogenous reference genes beta-actin (beta-actin), beta-2-microglobulin (beta2-MG) and porphobilinogen deaminase (PBDG) using the TaqMan chemistry. With these assays we investigated the respective expression patterns in K562 cells and leucocytes of normal individuals as well as of malignoma patients. In K562 cells 1544+246 beta-actin, 65+30 beta2-MG and 22+/-8 PBDG copies/cell were detected. In normal leucocytes 491+/-97 beta-actin, 40+/-17 beta2-MG and <1 PBDG copies/cell were quantified. Leucocytes of various malignancies exhibited 84+/-51 beta-actin, 106+/-8 beta2-MG and <1 PBDG copies/cell. We conclude that beta2-MG is the most suitable reference gene tested as its variation between different sample origins and within distinct cell types was acceptable low.

Novel T-cell receptor delta gene rearrangement involving a recombining element located 2.6 kb 3' from the Vdelta2 gene segment

In this study, we describe a novel T-cell receptor delta (TCRdelta) gene rearrangement observed in acute myeloid leukemia with coexpression of T-lymphoid antigens (Ly+AML) and in peripheral blood leukocytes (PBL) from one out of ten healthy donors. The rearrangement was identified by Southern blot analysis using a joining region (Jdelta1) specific probe and amplified by polymerase chain reaction (PCR) with a variable region (Vdelta2) and Jdelta1 specific primers. The nucleotide sequence analysis of an atypical 3000 bp PCR product allowed localization of the breakpoint within the TCRdelta gene locus, 2.6 kb 3' from the Vdelta2 gene segment. A regular Ddelta2-Ddelta3-Jdelta1 joining was found at the 3' end of the breakpoint, indicating that the rearrangement was mediated by the VDJ recombinase, but no TCRdelta gene segment was detected at the 5' end. Analysis of the germline sequence 3' from the breakpoint revealed an isolated recombination signal sequence (RSS) capable of initiating a rearrangement. The RSS motif described by us is the second TCRdelta recombining element (deltaRec2). The deltaRec2(Ddelta)Jdelta1 recombination is a rather rare event and can be found in acute leukemia and in PBL from healthy individuals. Most likely, the nonfunctional deltaRec2(Ddelta)Jdelta1 rearrangement is a transient step during the VDJ recombination. It may potentially lead to deletion of the deltaRec2(Ddelta)Jdelta1 complex and either to direct joining of a Vdelta region to one of the downstream Jdelta regions or to a rearrangement of the TCRalpha gene.

Selection of B-cell chronic lymphocytic leukemia cell variants by therapy with anti-CD20 monoclonal antibody rituximab

OBJECTIVE

Anti-CD20 chimeric monoclonal antibody rituximab (Mabthera; IDEC-C2B8) is currently tested in several clinical trials for the treatment of B-cell chronic lymphocytic leukemia (B-CLL). In the present study, we investigated whether rituximab therapy may select for CD20(-) subclones.

MATERIALS AND METHODS

Leukemic B-CLL cells were isolated from patients with B-CLL and sensitivity to rituximab-induced cell death was examined. Levels of CD20 protein and mRNA were determined using flow cytometry and real-time PCR, respectively. Clonality analyses of leukemic cells throughout rituximab therapy were performed by GeneScan analysis of patient clone specific rearrangements of the complementarity determining region III of the heavy chain immunoglobulin.

RESULTS

Cytotoxicity of rituximab in vitro did not depend on the protein levels of CD20. During therapy with rituximab CD20(+) B-CLL cells were depleted and CD20(-) leukemic cells emerged. After treatment, the initial CD20(+) B-CLL cell clone reexpanded. CD20(-) B-CLL cells retained their capacity to synthesize the CD20 molecule.

CONCLUSIONS

These data support the concept that in B-CLL rituximab treatment may not lead to the emergence of CD20(-) leukemic variants. Our findings support clinical studies investigating the benefit of prolonged period of rituximab therapy in B-CLL disease.

Prospective randomized trial to assess the value of preemptive oral therapy for CMV infection following liver transplantation

BACKGROUND

With the development of sensitive tests to detect cytomegalovirus (CMV) viremia, preemptive approaches become a reasonable alternative to general CMV prophylaxis. We performed a randomized trial comparing pp65-antigenemia guided preemptive therapy using oral ganciclovir with symptom-triggered intravenous ganciclovir treatment.

METHODS

Eighty-eight of 372 liver transplant recipients developed antigenemia early after orthotopic liver transplantation. Twenty-eight symptomatic patients with antigenemia were excluded from randomization and treated with intravenous ganciclovir. Sixty pp65-antigen-positive asymptomatic patients were randomized to receive either oral ganciclovir 3x1 g/day for 14 days (group 1) or no preemptive treatment (group 2). Patients that developed CMV disease were treated with intravenous ganciclovir 2x5 mg/kg body weight for 14 days. The high-risk (Donor+/Recipient-) patients were equally distributed in the two study groups.

RESULTS

Three of 30 (10%) patients on oral ganciclovir developed mild to moderate CMV disease compared with 6/30 (20%) patients in the control group. In the Donor+/Recipient- patients, the incidence of CMV disease was 1/6 and 3/7. All disease episodes resolved after intravenous treatment. The 1- and 3-year patient and organ survival was the same in the study groups and in the patients with or without CMV infection. No deaths related to CMV occurred.

CONCLUSIONS

The positive predictive value of pp65-antigenemia for the development of CMV disease was very low, and, in 28/88 patients (32%), antigenemia did not precede symptoms. Therefore, pp65-antigenemia is of limited value in deciding on the timing and need for ganciclovir therapy after liver transplantation.

Fluorescent 5'-exonuclease assay for the absolute quantification of Wilms' tumour gene (WT1) mRNA: implications for monitoring human leukaemias

The Wilms' tumour gene (WT1) has been suggested as a powerful parameter for molecular monitoring of minimal residual disease (MRD) in leukaemias. However, molecular monitoring via WT1 RNA levels is far from being routinely performed, which is possibly owing to the complex and inaccurate quantitative reverse transcription polymerase chain reaction (RT-PCR) procedures. Using a newly-developed quantitative real time RT-PCR, we measured WT1 transcripts in peripheral blood leucocytes of patients with acute myeloid (AML), acute lymphoid (ALL) and chronic myeloid leukaemia (CML). While healthy blood donors did not show measurable amounts of WT1 transcripts, WT1 RNA levels were detectable in all types of leukaemia. Furthermore, intraindividual WT1 transcript kinetics were exclusively dependent on disease progression, treatment and subsequent disease outcome. Using this approach, we could distinguish between treatment response and failure within the first days of therapeutic intervention. Moreover, gradually rising WT1 levels over a period of weeks and months paralleled long-term disease progression and appeared to be a prognostic indicator for subsequent clinical relapse. A linear correlation between quantities of WT1 and bcr/abl fusion transcripts could be seen in CML. We conclude that quantitative assessment of WT1 transcripts using real-time PCR is an appropriate method for molecular monitoring of AML, ALL and CML, and can be used independently for both short- and long-term monitoring of leukaemia patients.

Elevated p21 mRNA level in skeletal muscle of DMD patients and mdx mice indicates either an exhausted satellite cell pool or a higher p21 expression in dystrophin-deficient cells per se

Abnormalities in proliferation and differentiation of the dystrophin-deficient muscle are a controversial aspect of the pathogenesis of Duchenne muscular dystrophy (DMD). Analyses of molecules involved in cell cycle modulation do not exist in this context. Cells withdrawn from the cell cycle permanently express p21. The fact that p2 1, in contrast to other cell cycle proteins, is not diminished when myotubes are reexposed to growth media, allocates this cyclin-dependent kinase inhibitor a special function. Here we report for the first time statistically increased p21 mRNA levels in dystrophin-deficient muscle tissue. Only 42% of conventional RT-PCRs from six muscle samples of human controls yielded positive results but almost all skeletal muscle biopsy samples (87%) from DMD patients (n=5). For p21 mRNA quantification in murine muscle samples we were able to use the exact real-time TaqMan PCR method due to generally higher p21 mRNA levels than in human muscles. In addition, contamination with fibroblasts can be excluded for the murine samples because they do not demonstrate fibrosis at the age of 350 days but start to lose their regenerative capacity. In accord with the results in humans, we observed p21 mRNA levels in mdx mice that were approx. four times as high as those in control mice. Elevated p21 mRNA level may indicate a shift in cell composition towards differentiated p21 expressing cells as a result of an exhausted pool of undifferentiated, non-p21-expressing satellite cells due to previous cycles of de- and regeneration. Alternatively, dystrophin-deficient cells per se may express higher p21 levels for unknown reasons. Although we cannot distinguish between these possibilities, the eventual transfec tion of a patient's own satellite cells with p21 antisense oligonucleotides may enable the dystrophic process to be influenced.

Regulation of the nuclear proteasome activity in myelomonocytic human leukemia cells after adriamycin treatment

Treatment of different human leukemia cell variants with the anthracycline adriamycin was associated with a rapid activation of the proteasome. Thus, proliferating U937, TUR, and retrodifferentiated U937 cells exhibited a 4.3-fold, 5.8-fold, and 4.3-fold proteasome activation within 15 minutes after adriamycin treatment, respectively. In contrast, little if any proteasome activation was detectable in a growth-arrested differentiated U937 population following adriamycin treatment. Further analysis of this mechanism revealed a significant reduction of adriamycin-induced proteasome activity after inhibition of poly(ADP-ribose) polymerase (PARP) by 3-aminobenzamide (3-ABA) in the proliferating leukemic cell types. These findings suggested that PARP is involved in the regulation of drug-induced proteasome activation. Indeed, anti-PARP immunoprecipitation experiments of adriamycin-treated cells revealed increasing levels of coprecipitated, enzymatically active proteasome particularly in the proliferating cell variants in contrast to the differentiated U937 cells, with a maximum after 15 minutes, and sensitivity to PARP inhibition by 3-ABA. The specific role of the PARP was investigated in U937 and TUR cell clones stably transfected with a constitutively active antisense PARP (asPARP) vector. Thus, asPARP-TUR cells developed a 25-fold increased sensitivity to adriamycin treatment. Furthermore, we investigated leukemic blasts isolated from acute myelogenous leukemia patients and obtained a similarly enhanced proteasome activity after adriamycin treatment, which was dependent on the PARP and thus could be coprecipitated with anti-PARP antibodies. Transient transfection of leukemic blasts with the asPARP vector significantly reduced the adriamycin-induced proteasome activation. These data suggest that the PARP-associated nuclear proteasome activation represents a potential target within chemotherapeutic defense mechanisms developed by leukemia cells.

Epstein-Barr virus DNA quantitation assessed by a real-time polymerase chain reaction in a case of Burkitt's lymphoma

A real-time PCR technique was used to quantify EBV DNA load in plasma, leukocytes, peritoneal cells, ascites and cerebrospinal fluid (CSF) at diagnosis and during the follow-up of a 21-year-old patient suffering from an abdominal form of EBV-associated Burkitt's lymphoma. The EBV DNA load correlated well with the clinical and biological remission status of the patient after chemotherapy confirming that EBV DNA quantitation in plasma and leukocytes from peripheral blood can be considered as a marker of the tumor load and can be analyzed in parallel for monitoring of EBV-related malignancies.

Molecular quantification of response to therapy and remission status in TEL-AML1-positive childhood ALL by real-time reverse transcription polymerase chain reaction

Although TEL-AML1 positivity [translocation t(12;21)(p13;q22)], detected in 20-25% of initial childhood acute lymphoblastic leukemia (ALL), has been associated with an excellent prognosis, its positive predictive value is insufficient for appropriate treatment stratification considering reported prevalence in relapsed ALL (3-28%). Molecular quantification of response to therapy by PCR-based methods has been shown to improve risk assessment. Here, we report on the sensitive quantification of leukemia-specific TEL-AML1 fusion transcript levels normalized to beta-actin expression (sensitivity threshholds, 10(-5)) by a novel real-time reverse transcription-PCR (RQ-RT-PCR) based on fluorescent TaqMan technique providing early and rapid evidence on the treatment efficacy of children with initial or relapsed TEL-AML1+ ALL enrolled in frontline or relapse trials of the Berlin-Frankfurt-Münster (BFM)-Study Group. In initial ALL, TEL-AML1/beta-actin decrease was > or =10(5)-fold in 50% of patients after induction therapy (day 33) and stayed TEL-AML1-negative throughout therapy, which suggested high sensitivity of leukemic cells to antineoplastic therapy. The remaining patients were still TEL-AML1+ before reintensification (ratios, 0.7 x 10(-2):10(-4)). In relapsed ALL, TEL-AML1/beta-actin decrease was generally less pronounced at corresponding time points, and conversion to TEL-AML1 negativity was observed in 40% of patients. Most notably, subsequent relapses occurred only among molecular poor responders, whereas all early responders remain in their second complete remission. In conclusion, real-time quantification of TEL-AML1/beta-actin kinetics distinguishes distinct molecular response groups, and provides indications capable of directing therapeutic interventions for patients with TEL-AML1+ ALL. Before considering modification of therapy, results should be interpreted cautiously taking into account the long duration of remission associated with TEL-AML1+ ALL.

Simultaneous absolute quantification of target and control templates by real-time fluorescence reverse transcription-PCR using 4-(4'-dimethylaminophenylazo)benzoic acid as a dark quencher dye

BACKGROUND

Despite the many advantages of real-time fluorescence reverse transcription-PCR (RT-PCR) as a quantitative analytical tool, simultaneous quantification of target and reference templates within one reaction has not been reported. We developed such an assay with an internal reference template.

METHODS

For quantification of target and reference sequences, we used two fluorescent probes in one reaction vessel on an ABI PRISM 7700 SDS instrument. Fluorescent probes were labeled with either 6-carboxy-fluorescein or hexachloro-6-carboxy-fluorescein as reporter dye and 4-(4'-dimethylaminophenylazo)benzoic acid (DABCYL) as a dark quencher fluorophore. To test the sensitivity and specificity of this assay, serial dilutions of reference and target templates were analyzed in one PCR reaction. In the presence of 10 beta-actin molecules as control templates, 10(5) bcr/abl molecules were amplified, and 10(5) beta-actin molecules were amplified in the presence of 10 bcr/abl copies. We also performed single and duplex measurements on samples from five patients with documented Philadelphia chromosome-positive chronic myelogenous leukemia disease courses (72 samples) and three with minor bcr/abl+ acute myelogenous leukemias (26 samples).

RESULTS

For M-bcr/abl duplex RT-PCR, the correlation coefficient (r) for starting template amounts and threshold cycle values was 0.99; for m-bcr/abl, r = 0.96, indicating a precise log-linear relation for 10-10(5) copies/100 ng of cDNA. In the same PCR reactions, r = 0.99 for beta-actin (coamplified with M-bcr/abl or m-bcr/abl) for 10(3)-10(7) copies/100 ng cDNA. The linear correlation coefficient for single and duplex measurements was 0.98 for M- and m-bcr/abl in patient samples.

CONCLUSIONS

DABCYL can be used as dark quencher fluorophore in real-time fluorescence PCR. The duplex fluorescence RT-PCR assay for bcr/abl and beta-actin transcripts allows monitoring of bcr/abl+ leukemias.

What can we learn from leukemia as for the process of lineage commitment in hematopoiesis?

Most contemporary models of hematopoiesis assume lineage fidelity of early progenitor cells. Along with this concept normal hematopoietic cells and the majority of leukemias express exclusively myeloid or lymphoid specific antigens. On the other hand, growing evidence exists challenging the lineage fidelity model. Chronic myeloid leukemia (CML) in the blast crisis may switch to acute lymphoblastic leukemia (ALL) and as a result of the chemotherapy ALL may converse to acute myeloid leukemia (AML). Furthermore, a substantial portion of leukemia cases, named acute mixed-lineage leukemia (AMLL), show simultaneous expression of both myeloid and lymphoid antigens. Immunoglobulin (Ig) and T-cell receptor (TCR) gene rearrangements, correlating with myeloid-lymphoid immunophenotype in AMLL, support the hypothesis of lineage infidelity of early progenitor cells, rather than the aberrant antigen expression. Based on a detailed characterization of AMLL we present a modified model of a "common myeloid/lymphoid progenitor cell". This hypothetical very early hematopoietic progenitor cell shows a transient expression of myeloid and B- or T-lymphoid antigen and may also have rearranged its Ig and/or TCR genes. Subsequently, myeloid or lymphoid markers are downregulated and the hematopoietic cell enters either myeloid, T-lymphoid or B-lymphoid differentiation pathway.