CD36 cell surface expression as a surrogate marker to identify ABL/JAK-class kinase fusions in pediatric BCP-ALL

Genetic alterations are the cornerstone of risk stratification in B-cell precursor acute lymphoblastic leukemia (BCP-ALL), and their accurate identification is critical for optimal treatment. Most cases with ABL-class fusion are classified as high-risk yet display good responses to tyrosine kinase inhibitors (TKIs). Current clinical protocols recommend adding a TKI to chemotherapy as soon as possible, making it mandatory to rapidly identify these alterations. We investigated here whether the identification of immunophenotypic features associated with these molecular alterations could be a valuable screening tool. CD36 expression was shown to be a characteristic feature of ABL- or JAK-class kinase fusions. The main genetic subgroups clustering in the subset with Philadelphia (Ph)-like features were also found to display specific immunophenotypic characteristics. A predictive multiparameter scoring system was generated, segregating genetic subtypes with aberrant kinase activation (PAX5/CRLF2alt, BCR::ABL1, ABL/JAK-class). The most robust markers identified were the TSLPR with CD19/22/9/38/81/304 and CD49f. As TKI adjunction is currently limited to the ABL-class kinase fusions, immunophenotypes distinguishing ABL from JAK-class were also investigated. The flow cytometry method reported here, accessible to most hematology departments, is thus a new useful tool to quickly screen for Ph-like kinase fusion with a good sensitivity (95%) and specificity (96%).