Characteristics and Prognostic Significance of CRLF2 High Expression and the Co-Existence with JAK1 Mutations and Ikaros Deletion in Adult Acute Lymphoblastic Leukemia

Objective Cytokine receptor-like factor 2 (CRLF2) play an important role in differentiation and proliferation of lymphoid precursor cells through activation of JAK signaling pathway. Increased CRLF2 expression associates with mutations in JAK2, a combination that transforms hematopoietic cells, suggesting that mutants in JAK family members and CRLF2 may cooperate to contribute to acute lymphoblastic leukemia (ALL) pathogenesis. Moreover, the Ikaros deletion is also associated with the development of T-/B-cell ALL with poor outcome and relapse of high-risk leukemia. The aim of this study was to determine the clinical characterization and prognostic values of CRLF2 high expression and its concomitant expression with JAK1 mutations and Ikaros deletion in adult ALL patients.

Methods Quantitative PCR (qPCR) was performed to detect the expression of CRLF2 in 133 newly diagnosed adult patients with ALL. Genomic DNA was amplified to detect the mutations of the exon 13, 14, 16, 18 and 19 of JAK1, and IKZF1 exons 4 through 7 deletions (△4–7) by direct sequencing or sequencing after cloning. The CD34, CD13, CD33 and other markers were detected on the leukemia cells from bone marrow of the patients by flow cytometry, and the correlations of the CRLF2 high expression with the clinical features, survival, and with co-expression of JAK1 mutations and Ikaros deletion were statistically analyzed with Pearson's chi-square test or Fisher's exact test and Kaplan–Meier curves analysis.

Results CRLF2 high expression was detected in 22.8% of newly diagnosed adult ALL. The patients with CRLF2 high expression has significantly higher percentage of CD34, CD13 or CD33 positive than those with low expression（91.3% vs 62%, P=0.008; 76.2% vs 46.3%, P=0.016; 80.0% vs 37.9%, P=0.001), higher frequency of splenomegaly（60.0% vs 32.0%, P=0.040) in the adult ALL and shorter overall survival and event-free survival（9.5 months vs 16 months, P=0.029; 3 months vs 9 months, P=0.030）in the Philadelphia chromosome negative ALL. Moreover, the 4 JAK1 point mutations with amino acid changes were detected in the patients, which had significant CRLF2 high expression compared to that without mutation（75% vs 21.3%, P=0.037). The co-existence of CRLF2 high expression and IKZF1 exons 4-7 deletion (isoform Ik6) was found in 4 of 10 patients.

Conclusion CRLF2 high expression predicts poor survival, and significantly co-exists with JAK1 mutation and Ikaros deletion in adult ALL patients. Our result also suggested that CRLF2, JAK1 and IKZF1 could be integrated in future prognostic model of adult ALL as possible markers for high-risk leukemia.