Elena Vendramini

Down syndrome acute lymphoblastic leukemia, a highly heterogeneous disease in which aberrant expression of CRLF2 is associated with mutated JAK2: a report from the International BFM Study Group.

We report gene expression and other analyses to elucidate the molecular characteristics of acute lymphoblastic leukemia (ALL) in children with Down syndrome (DS). We find that by gene expression DS-ALL is a highly heterogeneous disease not definable as a unique entity. Nevertheless, 62% (33/53) of the DS-ALL samples analyzed were characterized by high expression of the type I cytokine receptor CRLF2 caused by either immunoglobulin heavy locus (IgH@) translocations or by interstitial deletions creating chimeric transcripts P2RY8-CRLF2. In 3 of these 33 patients, a novel activating somatic mutation, F232C in CRLF2, was identified. Consistent with our previous research, mutations in R683 of JAK2 were identified in 10 specimens (19% of the patients) and, interestingly, all 10 had high CRLF2 expression. Cytokine receptor-like factor 2 (CRLF2) and mutated Janus kinase 2 (Jak2) cooperated in conferring cytokine-independent growth to BaF3 pro-B cells. Intriguingly, the gene expression signature of DS-ALL is enriched with DNA damage and BCL6 responsive genes, suggesting the possibility of B-cell lymphocytic genomic instability. Thus, DS confers increased risk for genetically highly diverse ALLs with frequent overexpression of CRLF2, associated with activating mutations in the receptor itself or in JAK2. Our data also suggest that the majority of DS children with ALL may benefit from therapy blocking the CRLF2/JAK2 pathways.

Poor prognosis for P2RY8-CRLF2 fusion but not for CRLF2 over-expression in children with intermediate risk B-cell precursor acute lymphoblastic leukemia

Pediatric B-cell precursor acute lymphoblastic leukemia (BCP-ALL) has achieved an 80% cure rate as a result of a risk-adapted therapy largely based on minimal residual disease (MRD) monitoring. However, relapse is still the most frequent adverse event, occurring mainly in the patients with intermediate MRD levels (intermediate risk, IR), emphasizing the need for new prognostic markers. We analyzed the prognostic impact of cytokine receptor-like factor 2 (CRLF2) over-expression and P2RY8-CRLF2 fusion in 464 BCP-ALL patients (not affected by Down syndrome and BCR-ABL negative) enrolled in the AIEOP-BFM ALL2000 study in Italy. In 22/464 (4.7%) samples, RQ-PCR showed CRLF2 over-expression (⩾20 times higher than the overall median). P2RY8-CRLF2 fusion was detected in 22/365 (6%) cases, with 10/22 cases also showing CRLF2 over-expression. P2RY8-CRLF2 fusion was the most relevant prognostic factor independent of CRLF2 over-expression with a threefold increase in risk of relapse. Significantly, the cumulative incidence of relapse of the P2RY8-CRLF2+ patients in the IR group was high (61.1%±12.9 vs 17.6%±2.6, P<0.0001), similar to high-risk patients in AIEOP-BFM ALL2000 study. These results were confirmed in a cohort of patients treated in Germany. In conclusion, P2RY8-CRLF2 identifies a subset of BCP-ALL patients currently stratified as IR that could be considered for treatment intensification.

Treatment outcome of CRLF2-rearranged childhood acute lymphoblastic leukaemia: a comparative analysis of the AIEOP-BFM and UK NCRI-CCLG study groups.

The prognostic relevance of CRLF2 ‐rearrangements in childhood acute B‐cell precursor lymphoblastic leukaemia (ALL), was assessed by a comparative analysis of 114 non‐Down‐syndrome patients (99 P2RY8‐CRLF2+ , 15 IGH@‐CRLF2+ ), 76 from the AIEOP‐BFM ALL 2000 and 38 from the MRC ALL97 trials. The 6‐year cumulative relapse incidence of P2RY8‐CRLF2+ patients treated on the two trials was not statistically different: 0·37 ± 0·06 vs. 0·25 ± 0·08 (P = 0·194). In contrast, 0/9 IGH@‐CRLF2+ AIEOP‐BFM, but 5/6 ALL97 patients relapsed. Conclusively, P2RY8‐CRLF2+ patients had an intermediate protocol‐independent outcome while the different prognosis of IGH@‐CRLF2+ patients could be related to the different structures of the applied treatment protocols.

High expression of miR-125b-2 and SNORD116 noncoding RNA clusters characterize ERG-related B cell precursor acute lymphoblastic leukemia

ERG-related leukemia is a B cell precursor acute lymphoblastic leukemia (BCP ALL) subtype characterized by aberrant expression of DUX4 and ERG transcription factors, and highly recurrent ERG intragenic deletions. ERG-related patients have remarkably favorable outcome despite a high incidence of inauspicious IKZF1 aberrations. We describe clinical and genomic features of the ERG-related cases in an unselected cohort of B-other BCP ALL pediatric patients enrolled in the AIEOP ALL 2000 therapeutic protocol. We report a small noncoding RNA signature specific of ERG-related group, with up-regulation of miR-125b-2 cluster on chromosome 21 and several snoRNAs in the Prader-Willi locus at 15q11.2, including the orphan SNORD116 cluster.