Milestones of Post Transplant Monitoring of JAK2 p.V617F Positive MPN Patients.

Abstract 3462

Detection of JAK2 p.V617F point mutation plays an important role in the initial diagnosis of myeloproliferative neoplasms (MPN) and also in the monitoring of JAK2 p.V617F positive MPN following allogeneic stem cell transplantation (SCT). Therefore it is of great interest to optimize molecular monitoring techniques and to define milestones for clinical decisions after SCT. We analyzed 146 probes of 14 patients with a median age of 61 (range 52–70) and with JAK2 p.V617F positive MPN prior and post SCT after reduced (n=10) or myeloablative conditioning (n=4) using related (n=6) or unrelated (n=8) donors. DNA from 70 peripheral blood (PB) samples and 76 bone marrow biopsies (BMB) were analyzed both by a quantitative allele-specific oligonucleotides (ASO) PCR assay (sensitivity 0.01% JAK2 p.V617F mutated alleles per HCK) and a allele specific quantitative real-time (Q) PCR (sensitivity 1%) followed by a JAK2 p. V617F wild type blocking (WTB) PCR in case of a negative result (sensitivity 0.001%). 144 samples has been analyzed with both assays and showed 100% and 89% concordance in samples containing ≥1% and <1% JAK2 p. V617F, respectively. In order to select the optimal compartment, 26 BMB and simultaneously drawn PB samples showed 77%, 92% and 100% concordance for negative or positive results by ASO, (WTB) Q-PCR or both methods. A total of 146 samples from 14 patients, among them 40 samples prior allo-SCT, were analyzed for molecular follow-up. A cut-off of >1% (ASO) and/ or a JAK2 p.V617F positive result in the QPCR was seen in 7 patients. Six (86%) died due to relapse and disease persistence (n=5) or TRM with significant persistence of JAK2 p.V617F. In contrast, all patients with engraftment post allo-SCT exhibited episodes of molecular negativity if the JAK2 p.V617F allele burden was < 1% one month after SCT. We conclude that (1) adequate monitoring post allo-SCT requires a sensitivity of at least 0.01%, (2) monitoring can be performed on full blood samples as peripheral blood and bone marrow biopsies showed identical results, (3) a cut-off of > 1% JAK2 p.V617F allele burden one month post allo-SCT indicates an adverse course of the disease