Durable complete molecular remission of chronic myeloid leukemia following dasatinib cessation, despite adverse disease features.

Patients with chronic myeloid leukemia, treated with imatinib, who have a durable complete molecular response, might remain in complete molecular response after stopping treatment. Previous reports of patients stopping treatment in complete molecular response have included only patients with a good response to imatinib. We describe 3 patients with stable complete molecular response on dasatinib treatment following imatinib failure. Two of the 3 patients remain in complete molecular response more than 12 months after stopping dasatinib. In these 2 patients we used highly sensitive patient-specific BCR-ABL1 DNA PCR to show that the leukemic clone remains detectable, as we have previously shown in imatinib-treated patients. Dasatinib-associated immunological phenomena, such as the emergence of clonal T-cell populations, were observed both in one patient who relapsed and in one patient in remission. Our results suggest that the characteristics of complete molecular response on dasatinib treatment may be similar to that achieved with imatinib, at least in patients with adverse disease features.

Antisense PCR: A simple and robust method for performing nested single-tube PCR.

To overcome the disadvantages of two-round nested PCR, we developed a simple and robust closed single-tube nested PCR method (antisense PCR). The method uses antisense oligonucleotides that carry a 5' tag and that can potentially hybridize to the 3' ends of the outer primers, depending on the annealing temperature. During initial cycles, which are performed at a high annealing temperature, the antisense oligonucleotides do not hybridize and amplification is directed by the outer primers. During later cycles, for which the annealing temperature is decreased, the outer primers hybridize to the antisense oligonucleotides, extend to produce sequences that are mismatched to the amplicon templates, and consequently become inactivated, whereas the inner primers hybridize to the amplicon templates and continue amplification. Antisense quantitative PCR (qPCR) was compared with one-round qPCR for real-time amplification of four PCR targets (BCR, APC, N-RAS, and a rearranged IGH gene). It had equal amplification efficiency but produced much less nonspecific amplification. Antisense PCR enables both endpoint detection and real-time quantification. It can substitute for two-round nested PCRs but may also be applicable to instances of one-round PCR in which nonspecificity is a problem.

Rapid isolation of translocation breakpoints in chronic myeloid and acute promyelocytic leukaemia.

Isolation and sequencing of the translocation breakpoint in chronic myeloid leukaemia-(CML) and acute promyelocytic leukaemia (APML) may help to elucidate the mechanism of translocation and provide a molecular marker for monitoring of minimal residual disease. Amplification across the translocation breakpoint was performed in samples from 91 patients with CML and 15 patients with APML using single-tube multiplex polymerase chain reaction (PCR) involving 308 primers for CML and 40 primers for APML. Nonspecific amplification was removed by a modification of PCR, termed sequential hybrid primer PCR (SHP-PCR), which involved two sequential rounds of PCR, each of which used a low concentration of a specially designed hybrid primer. The resultant amplified material was sequenced. The method as finally developed was simple quick and robust. The translocation breakpoint was successfully isolated and sequenced in all 106 samples. The strategy of highly multiplexed PCR followed by SHP-PCR is thus an effective method for isolating the translocation breakpoint in CML and APML. It may also be applicable to other haematological disorders characterised by translocation, deletion or inversion.

Gene walking using sequential hybrid primer polymerase chain reaction.

We developed a simple and robust method for removing nonspecific amplification produced during gene walking with a gene-specific primer and a degenerate primer. The primary walking polymerase chain reaction (PCR) was followed by two or three PCR rounds, each incorporating a low concentration of a reverse hybrid primer, where the 3' end was bound to a target sequence generated in the preceding PCR round and the 5' end was a new sequence that generated a target sequence for the next PCR round. The low concentration of the hybrid primer and the extent of amplicon stem-loop formation inhibited nonspecific amplification and enabled successful walking along three genes.

BCR-ABL1 expression, RT-qPCR and treatment decisions in chronic myeloid leukaemia.

AIMS: RT-qPCR is used to quantify minimal residual disease (MRD) in chronic myeloid leukaemia (CML) in order to make decisions on treatment, but its results depend on the level of BCR-ABL1 expression as well as leukaemic cell number. The aims of the study were to quantify inter-individual differences in expression level, to determine the relationship between expression level and response to treatment, and to investigate the effect of expression level on interpretation of the RT-qPCR result. METHODS: BCR-ABL1 expression was studied in 248 samples from 65 patients with CML by determining the difference between MRD quantified by RT-qPCR and DNA-qPCR. The results were analysed statistically and by simple indicative modelling. RESULTS: Inter-individual levels of expression approximated a normal distribution with an SD of 0.36 log. Expression at diagnosis correlated with expression during treatment. Response to treatment, as measured by the number of leukaemic cells after 3, 6 or 12 months of treatment, was not related to the level of expression. Indicative modelling suggested that interpretation of RT-qPCR results in relation to treatment guidelines could be affected by variation in expression when MRD was around 10% at 3 months and by both expression variation and Poisson variation when MRD was around or below the limit of detection of RT-qPCR. CONCLUSIONS: Variation between individuals in expression of BCR-ABL1 can materially affect interpretation of the RT-qPCR when this test is used to make decisions on treatment.

Regulation of the gene encoding glutathione S-transferase M1 (GSTM1) by the Myb oncoprotein.

The identification of Myb 'target' genes will not only aid in the understanding of how overexpression of Myb, or expression of activated forms of Myb, leads to cellular transformation but will also shed light on its role in normal cells. Using a combination of an estrogen-regulated Myb-transformed cell line (ERMYB) and PCR-based subtractive hybridization, we have identified the gene (GSTM1) encoding the detoxification enzyme glutathione S-transferase M1 as being transcriptionally upregulated by Myb. Functional analysis of the GSTM1 promoter using reporter assays indicated that both the DNA binding and transactivation domains of Myb were required for transcriptional activation. Mutational ana-lysis of consensus Myb-binding sites (MBS) in the promoter and electrophoretic mobility gel shift analysis indicated that one of the three potential MBS can bind Myb protein, and is the primary site involved in the regulation of this promoter by Myb.

A DNA real-time quantitative PCR method suitable for routine monitoring of low levels of minimal residual disease in chronic myeloid leukemia.

The BCR-ABL1 sequence has advantages over the BCR-ABL1 transcript as a molecular marker in chronic myeloid leukemia and has been used in research studies. We developed a DNA real-time quantitative PCR (qPCR) method for quantification of BCR-ABL1 sequences, which is also potentially suitable for routine use. The BCR-ABL1 breakpoint was sequenced after isolation by nested short-range PCR of DNA from blood, marrow, and cells on slides, obtained either at diagnosis or during treatment, or from artificial mixtures. PCR primers were chosen from a library of presynthesized and pretested BCR (n = 19) and ABL1 (n = 568) primers. BCR-ABL1 sequences were quantified relative to BCR sequences in 521 assays on 266 samples from 92 patients. For minimal residual disease detectable by DNA qPCR and RT-qPCR, DNA qPCR gave similar minimal residual disease results as RT-qPCR but had better precision at low minimal residual disease levels. The limit of detection of DNA qPCR depended on the amount of DNA assayed, being 10(-5.8) when 5 µg was assayed and 10(-7.0) when 80 µg was assayed. DNA qPCR may be useful and practical for monitoring the increasing number of patients with minimal residual disease around or below the limit of detection of RT-qPCR as the assay itself is simple and the up-front costs will be amortized if sequential assays are performed.

Incorporation of measurement of DNA integrity into qPCR assays.

Optimal accuracy of quantitative PCR (qPCR) requires correction for integrity of the target sequence. Here we combine the mathematics of the Poisson distribution and exponential amplification to show that the frequency of lesions per base (which prevent PCR amplification) can be derived from the slope of the regression line between cycle threshold (Ct) and amplicon length. We found that the amplifiable fraction (AF) of a target can be determined from this frequency and the target length. Experimental results from this method correlated with both the magnitude of a damaging agent and with other measures of DNA damage. Applying the method to a reference sequence, we determined the values for lesions/base in control samples, as well as in the AFs of the target sequence in qPCR samples collected from leukemic patients. The AFs used to calculate the final qPCR result were generally >0.5, but were <0.2 in a few samples, indicating significant degradation. We conclude that DNA damage is not always predictable; quantifying the DNA integrity of a sample and determining the AF of a specific qPCR target will improve the accuracy of qPCR and aid in the interpretation of negative results.

Absence of platelet endothelial cell adhesion molecule-1 (CD31) leads to increased severity of local and systemic IgE-mediated anaphylaxis and modulation of mast cell activation.

Platelet endothelial cell adhesion molecule-1 (PECAM-1) is a newly assigned member of the Ig-immunoreceptor tyrosine-based inhibitory motif superfamily, and its functional role is suggested to be an inhibitory receptor that modulates immunoreceptor tyrosine-based activation motif-dependent signaling cascades. In this study, we hypothesized that PECAM-1 plays an essential in vivo role as a counterregulator of immediate hypersensitivity reactions. We found that PECAM-1 was highly expressed on the surface of immature bone marrow mast cells and at a lower density on mature peritoneal mast cells. Examination of skin biopsies from PECAM-1(+/+) and PECAM-1(-/-) mice revealed that absence of PECAM-1 did not affect mast cell development or the capacity of mast cells to populate tissues. To examine whether the absence of PECAM-1 would influence immediate hypersensitivity reactions, PECAM-1(+/+) and PECAM-1(-/-) mice were presensitized with anti-DNP mouse IgE and then challenged 20 h later with DNP-BSA or PBS. PECAM-1(-/-) mice exhibited elevated serum histamine concentrations after Ag stimulation compared with PECAM-1(+/+) mice, indicating an increased severity of systemic IgE-mediated anaphylaxis. PECAM-1(-/-) mice have increased sensitivity to local cutaneous IgE-dependent anaphylaxis compared with PECAM-1(+/+) mice, as assessed by greater tissue swelling of their ears and mast cell degranulation in situ. PECAM-1(-/-) bone marrow mast cells showed enhanced dense granule serotonin release after Fc epsilon RI cross-linking in vitro. These results suggest that PECAM-1 acts as a counterregulator in allergic disease susceptibility and severity and negatively modulates mast cell activation.

Platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31) acts as a regulator of B-cell development, B-cell antigen receptor (BCR)-mediated activation, and autoimmune disease.

Platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31) is an immunoglobulin-immunoreceptor tyrosine-based inhibitory motif (Ig-ITIM) superfamily member that recruits and activates protein-tyrosine phosphatases, SHP-1 and SHP-2, through its intrinsic ITIMs. PECAM-1-deficient (PECAM-1(-/-) ) mice exhibit a hyperresponsive B-cell phenotype, increased numbers of B-1 cells, reduced B-2 cells, and develop autoantibodies. In the periphery, there are reduced mature recirculating B-2 cells and increased B-1a cells within the peritoneal cavity. In addition, PECAM-1(-/-) B cells display hyperproliferative responses to lipopolysaccharide and anti-IgM stimulation and showed enhanced kinetics in their intracellular Ca(++) response following IgM cross-linking. PECAM-1(-/-) mice showed increased serum levels of IgM with elevated IgG isotypes and IgA antidinitrophenol antibody in response to the T-independent antigen, dinitrophenol-Ficoll. Finally, PECAM-1(-/-) mice developed antinuclear antibodies and lupuslike autoimmune disease with age.