Highly Sensitive Real-Time PCR of V617F-JAK2-Mutation To Monitor Minimal Residual Disease and Guide Donor Lymphocte Infusion after Allogeneic Stem Cell Transplantation in Patients with Myelofibrosis.

The V617F-JAK2-mutation occurs in about 50 % of patients with myelofibrosis and is a reliable marker to monitor residual disease after allogeneic stem cell transplantation. The establishment of valid complete remission criteria for myelofibrosis especially after allogeneic stem cell transplantation remains a major issue. We developed a new, highly sensitive real-time PCR to monitor and quantify V617F-JAK2-positive cells after dose-reduced allogeneic stem cell transplantation. The mutated differs from the wild-type JAK2 allele by just one nucleotide exchange (G à T) leading to the valine to phenylalanine (V à F) transition. Using PrimerExpress^® we designed a TaqMan^® PCR where the reverse primer (RP) terminates at the (3′) nucleotide corresponding to this point mutation. Thus, this reverse primer should bind with higher affinity to the mutated than to the wild-type allele. To increase the specificity while conserving optimal sensitivity of the MRD-specific PCR we generated a set of primers shortened each time by one nucleotide at their 5’ end. In parallel, all those shortened primers were designed to contain an additional mutation at the third to last 3’ position. This allowed us to identify the reverse primer combining high specificity with so far not reported sensitivity(0.01 %). After 22 allogeneic stem cell transplantation procedures in 21 JAK2-positive patients with myelofibrosis, 78 % became PCR-negative. In 15 out of 17 patients (88 %), JAK2 remained negative after a median follow-up of 20 months. JAK2-negativity was achieved after a median of 89 days post allograft (range, 19 – 750 days). A significant inverse correlation was seen for JAK2 positivity and donor cell chimerism (r: −0.91, p<0.001). Four of five patients who never achieved JAK2-negativity fulfilled during the entire follow-up all criteria for complete remission recently proposed by the International Working Group, suggesting a major role for JAK2 measurement to determine depths of remission. In one case, residual JAK2 positive cells could be eliminated by donor lymphocyte infusion, supporting the graft versus myelofibrosis effect. In conclusion, allogeneic stem cell transplantation after dose-reduced conditioning induces high rates of molecular remission in JAK2-positive myelofibrosis-patients and quantification. V617F-JAK2 mutation by real-time PCR allows detecting minimal residual disease to guide adoptive immunotherapy.