Characterization of Philadelphia-like Pre-B Acute Lymphoblastic Leukemia: Experiences in Mexican Pediatric Patients.

Ph-like subtypes with CRLF2 abnormalities are frequent among Hispano-Latino children with pre-B ALL. Therefore, there is solid ground to suggest that this subtype is frequent in Mexican patients. The genomic complexity of Ph-like subtype constitutes a challenge for diagnosis, as it requires diverse genomic methodologies that are not widely available in diagnostic centers in Mexico. Here, we propose a diagnostic strategy for Ph-like ALL in accordance with our local capacity. Pre-B ALL patients without recurrent gene fusions (104) were classified using a gene-expression profile based on Ph-like signature genes analyzed by qRT-PCR. The expressions of the CRLF2 transcript and protein were determined by qRT-PCR and flow cytometry. The P2RY8::CRLF2, IGH::CRLF2, ABL1/2 rearrangements, and Ik6 isoform were screened using RT-PCR and FISH. Surrogate markers of Jak2-Stat5/Abl/Ras pathways were analyzed by phosphoflow. Mutations in relevant kinases/transcription factors genes in Ph-like were assessed by target-specific NGS. A total of 40 patients (38.5%) were classified as Ph-like; of these, 36 had abnormalities associated with Jak2-Stat5 and 4 had Abl. The rearrangements IGH::CRLF2,P2RY8::CRLF2, and iAMP21 were particularly frequent. We propose a strategy for the detection of Ph-like patients, by analyzing the overexpression/genetic lesions of CRLF2, the Abl phosphorylation of surrogate markers confirmed by gene rearrangements, and Sanger sequencing.

High occurrence of CRLF2 abnormalities in Mexican children with B-cell acute lymphoblastic leukemia.

The P2RY8-CRLF2 and IGH-CRLF2 rearrangements induce the overexpression of cytokine receptor-like factor 2 (CRLF2) and have been associated with relapse and poor prognosis in B-cell acute lymphoblastic leukemia (B-ALL). Additionally, they are frequently documented in high-risk Hispanic populations. To better understand the potential causes of the adverse prognosis of childhood B-ALL in Mexico, we analyzed these rearrangements and the CRLF2 mRNA and protein levels in 133 Mexican children with B-ALL. We collected bone marrow samples at diagnosis and evaluated the CRLF2 gene expression by qRT-PCR and the total CRLF2 protein by flow cytometry. P2RY8-CRLF2 and IGH-CRLF2 were detected by RT-PCR and FISH, respectively. The median time of follow-up to determine the prognostic significance of the CRLF2 abnormalities was three years. In 82% of the participants, the mRNA levels correlated with the cell-surface and intracellular CRLF2 protein levels. The P2RY8-CRLF2 rearrangement was present in 31.5% (42/133) of the patients, while the IGH-CRLF2 rearrangement was detected in 13.5% (9/67) of patients with high expression of CRLF2 (6.8% of the total sample). CRLF2 copy number variations (gain) were also detected in 7.5% (5/67) of patients with high protein levels. The overall survival (OS) presented significantly lower rates in patients with high white blood cell count (≥50x109/L) regardless of CRLF2 expression, but high levels of CRLF2 gene expression appears to contribute to the reduction of OS within this group of patients. In conclusion, in our cohort, a high occurrence of CRLF2 abnormalities was documented, particularly the P2RY8-CRLF2 rearrangement, which might represent a characteristic of the Mexican population. Targeted therapy to treat this group of patients could improve OS.