KRAS and CREBBP mutations: a relapse-linked malicious liaison in childhood high hyperdiploid acute lymphoblastic leukemia

High hyperdiploidy defines the largest genetic entity of childhood acute lymphoblastic leukemia (ALL). Despite its relatively low recurrence risk, this subgroup generates a high proportion of relapses. The cause and origin of these relapses remains obscure. We therefore explored the mutational landscape in high hyperdiploid (HD) ALL with whole-exome (n=19) and subsequent targeted deep sequencing of 60 genes in 100 relapsing and 51 non-relapsing cases. We identified multiple clones at diagnosis that were primarily defined by a variety of mutations in receptor tyrosine kinase (RTK)/Ras pathway and chromatin-modifying genes. The relapse clones consisted of reappearing as well as new mutations, and overall contained more mutations. Although RTK/Ras pathway mutations were similarly frequent between diagnosis and relapse, both intergenic and intragenic heterogeneity was essentially lost at relapse. CREBBP mutations, however, increased from initially 18-30% at relapse, then commonly co-occurred with KRAS mutations (P<0.001) and these relapses appeared primarily early (P=0.012). Our results confirm the exceptional susceptibility of HD ALL to RTK/Ras pathway and CREBBP mutations, but, more importantly, suggest that mutant KRAS and CREBBP might cooperate and equip cells with the necessary capacity to evolve into a relapse-generating clone

Immunobiological diversity in infant acute lymphoblastic leukemia is related to the occurrence and type of MLL gene rearrangement.

The aim of this study was to identify immunobiological subgroups in 133 infant acute lymphoblastic leukemia (ALL) cases as assessed by their immunophenotype, immunoglobulin (Ig) and T-cell receptor (TCR) gene rearrangement pattern, and the presence of mixed lineage leukemia (MLL) rearrangements. About 70% of cases showed the pro-B-ALL immunophenotype, whereas the remaining cases were common ALL and pre-B-ALL. MLL translocations were found in 79% of infants, involving MLL-AF4 (41%), MLL-ENL (18%), MLL-AF9 (11%) or another MLL partner gene (10%). Detailed analysis of Ig/TCR rearrangement patterns revealed IGH, IGK and IGL rearrangements in 91, 21 and 13% of infants, respectively. Cross-lineage TCRD, TCRG and TCRB rearrangements were found in 46, 17 and 10% of cases, respectively. As compared to childhood precursor-B-ALL, Ig/TCR rearrangements in infant ALL were less frequent and more oligoclonal. MLL-AF4 and MLL-ENL-positive infants demonstrated immature rearrangements, whereas in MLL-AF9-positive leukemias more mature rearrangements predominated. The immature Ig/TCR pattern in infant ALL correlated with young age at diagnosis, CD10 negativity and predominantly with the presence and the type of MLL translocation. The high frequency of immature and oligoclonal Ig/TCR rearrangements is probably caused by early (prenatal) oncogenic transformation in immature B-lineage progenitor cells with germline Ig/TCR genes combined with a short latency period

Optimization of PCR-based minimal residual disease diagnostics for childhood acute lymphoblastic leucemia in a multi-center setting .

Minimal residual disease (MRD) diagnostics is used for treatment stratification in childhood acute lymphoblastic leukemia. We aimed to identify and solve potential problems in multicenter MRD studies to achieve and maintain consistent results between the AIEOP/BFM ALL-2000 MRD laboratories. As the dot-blot hybridization method was replaced by the real-time quantitative polymerase chain reaction (RQ-PCR) method during the treatment protocol, special attention was given to the comparison of MRD data obtained by both methods and to the reproducibility of RQ-PCR data. Evaluation of all key steps in molecular MRD diagnostics identified several pitfalls that resulted in discordant MRD results. In particular, guidelines for RQ-PCR data interpretation appeared to be crucial for obtaining concordant MRD results. The experimental variation of the RQ-PCR was generally less than three-fold, but logically became larger at low MRD levels below the reproducible sensitivity of the assay (<10(-4)). Finally, MRD data obtained by dot-blot hybridization were comparable to those obtained by RQ-PCR analysis (r(2)=0.74). In conclusion, MRD diagnostics using RQ-PCR analysis of immunoglobulin/T-cell receptor gene rearrangements is feasible in multicenter studies but requires standardization; particularly strict guidelines for interpretation of RQ-PCR data are required. We further recommend regular quality control for laboratories performing MRD diagnostics in international treatment protocol