A Novel, Highly Sensitive, Rapid, Non-PCR Based Method for the Detection of the JAK2 ^V617F Mutation in Chronic Myeloproliferative Neoplasms.

The point mutation G1849T (V617F) of the JAK2 gene occurs at high frequency in several Ph-negative chronic myeloproliferative neoplasms (Ph-neg-CMNs), such as Polycythemia Vera (PV), Essential Thrombocythemia (ET) and Myelofibrosis (MF). The molecular analysis of this mutation is mandatory in the diagnostic work up of these diseases. Several molecular diagnostic techniques are currently used but each of them present some important limitations such as a low sensitivity and the requirement of labor intensive procedures performed with expensive specialized equipment that may not always be readily available in clinical laboratories.

We have developed a non-PCR method for the identification of the JAK2^V617F mutation called Allele Specific (AS)-LAMP, based on the Loop mediated isothermal AMPlification (LAMP) principle (Notomi et al. NAR 2000). LAMP reaction efficiently produces, within one hour, a large amount of amplified DNA and does not require gel separation of the amplified product which is indirectly detected by measuring the loss of intensity of a light beam through the reaction solution in which suspended particles of magnesium pyrophosphate are generated as a result of the DNA amplification process. Pyrophosphate salts produce turbidity which is both visible to the naked-eye and monitorable in Real-Time turbidimetry. AS-LAMP consists of 4 primers suitable for LAMP and a self-annealed primer highly specific for the mutated target sequence. To ensure efficiency and sensitivity a Peptide Nucleic Acid (PNA) probe specific for the wild-type allele was added thus resulting in absence of normal allele amplification within the reaction time. The AS-LAMP assay was optimized on plasmid controls and on human genomic DNA extracted from the HEL and K562 cell lines, respectively carrying or not the JAK2^V617F mutation. The level of sensitivity was determined by testing serial dilutions of mutant HEL DNA in K562 DNA at concentrations of 100, 10, 1, 0.5, 0.1, 0.05, 0.01 and 0%.

This simple, easy to perform and rapid AS-LAMP assay selectively detects the JAK2^V617F mutated DNA down to 0.05%. Moreover, when mutant DNA is present in the range of 1%-100% in wild type DNA, we observed a linear relationship between the mutant allele burden and the amplification time. We have validated this AS-LAMP assay on DNA obtained from 87 patient samples previously analyzed by conventional Allele Specific PCR (ASO-PCR): 19 PV, 58 TE, 3 IMF, 1 post ET Acute Myeloid Leukemia (AML), 1 post PV and 1 post ET Myelofibrosis, 2 Idiopathic Erythrocytosis (IE) and 2 unclassified CMNs. All samples which proved positive by ASO-PCR resulted positive with our AS-LAMP assay (100% concordance). In addition, 6 ET and 1 IE previously found negative by ASO-PCR were found to be low-positive (<1%) with AS-LAMP. Interestingly, the molecular monitoring in one patient with post-PV MF achieving complete remission after allogenic transplantation, proved repeatedly negative by ASO-PCR but positive by AS-LAMP. Sequencing analysis after PCR amplification with PNA confirmed the presence of the JAK2^V617F mutation in all these LAMP-low-positive samples. None of the negative controls, (1 AML, 2 Acute Lymphoblastic Leukemia, 2 Follicular Non Hodgkin's Lymphoma, 2 Chronic Lymphocytic Leukemia, and 1 healthy donor) gave false positive results.

This novel, non-PCR based allele-specific LAMP assay is rapid and reduces the risk of contamination related to post amplification manipulations. Most importantly, it is highly specific and sensitive and significantly increases our ability to detect a low JAK2^V617F tumor allele burden. For all these reasons, the AS-LAMP assay can be a valid and powerful tool in the routine diagnostic work up and the molecular monitoring of these diseases.

Minnucci:Diasorin S.p.A.: Employment. Amicarelli:Diasorin S.p.A: Employment. Salmoiraghi:Diasorin S.p.A.: Consultancy, Honoraria. Spinelli:Diasorin S.p.A: Consultancy, Honoraria. Adlerstein:Diasorin S.p.A.: Employment. Rambaldi:Diasorin S.p.A.: Consultancy, Honoraria.