Study On Clinical And Experimental Features Of BCR-ABL1-like B-cell Acute Lymphoblastic Leukemia With JAK2 Fusion Gene

Objectives1.To summarize the clinical and laboratory characteristics of BCR-ABL1-like B-cell acute lymphoblastic leukemia with JAK2 fusion gene,and to analyze the gene expression profiles of the above patients to explore its possible pathogenetic mechanism.2.To explore the role of JAK2 fusion gene in Philadelphia-chromosomal-like acute lymphoblastic leukemia by cloning novel JAK2 fusion genes.Methods1.In this study,we analyze 12 JAK2-fusion-gene positive B-ALL patients’clinical characteristics,treatment response and survival.RNA sequencing is performed on the above patients in order to analyze their gene expression profiles.The possible pathogenetic mechanism is inferred.2.The breakpoints of JAK2 fusion genes are identified by RNA sequencing and Sanger sequencing.After establishing of various JAK2 fusion gene constructs,the subcellular localization,proliferation/apoptosis in vitro,effect on signaling pathway and response to targeted inhibitors of each cell line expressing fusion gene are analyzed.Results1.There are 8 males and 4 females involved in this study,of which 11 patients are newly diagnosed and 1 patient is recurrent.The median age for the entire study population is 18.5 years(range,5-39 years),which is definitely younger than Ph+ALL control group(p<0.001).These patients have significantly high WBC(white blood cell)count,anemia and low PLT(platelet)level at diagnosis.The proportions of bone marrow blast are higher than that of Other B-ALL group(p=0.013).In terms of karyotype distribution,only 1 patient has abnormal 9p24 translocation,1 patient has 13q-,whereas the remaining 8(80%)patients show normal karyotypes.After one course of standard induced remission therapy,5 8.3%(7/12)patients achieve hematological remission,which is significantly lower than that in the two control groups(p1=0.007,p2=0.020).MRD monitoring is performed in all patients during CR1(complete remission for the first time)period and the result shows that there is still a high level of MRD expression in 81.8%JAK2-rearrangement B-ALL patients.Among the 12 patients,9 patients receive haplotype hematopoietic stem cell transplantation and 3 patients only receive chemotherapy.Additionally,4 patients receive treatment of JAK2-inhibitor ruxolitinib and it turns out to have various clinical effects.41.7%patients(5/12)relapse and there is no significant difference of overall recurrence between JAK2-rearrangment B-ALL group and the control groups.Nevertheless,the event-free survival and overall survival time of B-ALL with JAK2 fusion gene are similar to that of Ph+ALL patients and both of them are worse than that of Other B-ALL group(p=0.0182,p<0.001).B-ALL with JAK2 fusion gene and Ph+ALL patients show similar gene expression,with JAK2-fusion B-ALL up-regulating JAK-STAT signaling pathway.Up-regulating genes are mainly involved in cell components such as plasma membrane,integral component of plasma membrane and integral component of membrane.They also participate in several biological processes like cell adhesion.In addition,JAK2-fusion B-ALL down-regulates B-cell receptor signaling pathway.Down-regulating genes are mainly involved in molecular functions like tumor necrosis factor receptor binding and protease binding,biological processes like positive regulation of interferon-gamma production and activated T cell proliferation and cell components like mitochondrion and endoplasmic reticulum.2.Different JAK2 fusion genes,i.e.,NRF-JAK2、PIK3AP1-JAK2、PAX5(exon8)-JAK2 together with Vector and JAK-WT are established.All the above JAK2 fusion genes retain the JH1(tyrosine kinase)domain.With regard to subcellular localization,except for PAX5-JAK2 located in the nucleus,the other two JAK2 fusion genes are mainly expressed in the cytoplasm with few expressions in the nucleus.JAK2 fusion genes endow leukemia cells with the ability of proliferation advantage and anti-apoptosis in vitro by activating JAK-STAT signaling pathway.While,ruxolitinib,a kind of JAK2 inhibitors,has significant activity against JAK2 activated by gene rearrangement through inhibiting the phosphorylation of JAK-STAT signaling pathway.Conclusions1.JAK2-fusion-gene positive B-ALL patients are characterized by high WBC count,young age at diagnosis and various sensitivity to ruxolitinib.Their gene expression profiles are similar to that of Ph+ALL patients.By analyzing the up-regulated genes,we find that they are enriched in the JAK-STAT signaling pathway which could be one of the pathogenesis of this subtype leukemia.2.In this work,JAK2 is fused to different partner genes,leading to changes in subcelluar localization.These fusion genes gain the proliferation advantage and anti-apoptosis ability in vitro by activating the JAK-STAT signaling pathway.Ruxolitinib could be a promising therapy for treatment of patients with JAK2 fusion genes.