Evolution of disease activity and biomarkers on and off rapamycin in 28 patients with autoimmune lymphoproliferative syndrome

Mutations in CCAAT/enhancer binding protein (CEBPA) occur in 5-10% of acute myeloid leukemia. CEBPA-double mutated (CEBPA-dm) cases usually bear bi-allelic N- and C-terminal mutations and are associated with favorable clinical outcome. Due to variability of mutation, gene-intrinsic and technical issues, the identification of CEBPA mutants is challenging. Several screening methods (fragment-length analysis, gene expression array) have been proposed especially for large-scale clinical use; although efficient, they are limited by specific concerns. In our study we have investigated the phenotypic profile of blast and maturing bone marrow cell compartments at diagnosis in 251 cases. In our cohort, 16 (6.4%) patients had two CEBPA mutations, whereas 10 (4.0%) had a single mutation. First, we highlighted that CEBPA-dm subset displays recurrent phenotypic abnormalities in all cell compartments. By mutational analysis after cell sorting, we demonstrated that this common phenotypic signature depends upon CEBPA-dm multi-lineage involvement. From the multi-dimensional study of phenotypic data, we have developed a classifier including 10 core and widely available parameters. The selected markers on blasts (CD34, CD117, CD7, CD15, CD65), neutrophil (SSC, CD64), monocytic (CD14, CD64) and erythroid (CD117) compartments were able to provide clustering of CEBPA-dm cases. In a validation set of 259 AML cases from 3 independent centers, our classifier showed excellent performance with 100% specificity, 100% sensitivity. We established a reliable screening method, based upon multi-dimensional analysis of widely available phenotypic parameters. As such, it provides early results and is suitable for large-scale detection of CEBPA-dm status allowing to focus gene sequencing only in selected cases.