Analysis of CRLF2/JAK Expression and Mutation Status In Adult ALL Patients

Abstract 758

Adult acute lymphoblastic leukemia (ALL) is a heterogeneous disease with low overall survival. Compared to pediatric ALL, outcomes for adults have not improved despite recent advances in therapy and treatment support. Novel targets and biomarkers will aid in the development of new therapeutic strategies. Recent studies described mutations in the cytokine receptor-like factor 2 (CRLF2), and Janus kinase 1 (JAK1) and JAK2 in ALL patients (pts). These activating mutations have been associated with poor outcome in adult and pediatric series. Interestingly, the gene expression profile (GEP) of pts with these abnormalities overlaps with Philadelphia chromosome (Ph) positive ALL GEP. In order to further assess the prognostic value of these genetic abnormalities in adult ALL we analyzed RNA from available pretreatment bone marrow (BM) and peripheral blood (PB) samples of 138 pts enrolled in SWOG studies S9400, and S0333.

The expression levels of CRLF2 were examined in 85 available specimens with more than 50% blasts. B-glucoronidase, GUSB, was used to correct for RNA integrity. Expression fold change was calculated relative to the pool of RNA from the PB of 7 healthy donors using the comparative Ct analyses (2-^DDCt). CRLF2 levels varied significantly in the examined population, ranging from no detectable expression to 8735-fold greater than the calibrator. High-expressers were defined by expression fold change 10-times above the median (n=21, 25%). Deletion of pseudoautosomal region 1 of chromosomes × and Y, with juxtaposition of the P2RY8 promoter to the CRLF2 coding region, was tested in 126 pts, and 20 pts were positive for P2RY8-CRLF2 (16%). Sixty-seven percent of CRLF2 high-expressers displayed this mutation (14 out of 21). CRLF2 point mutation F232C was identified in 6% of the samples (7 out of 126). Less than 2% of samples (1.6%, 2 out of 120) displayed JAK1 mutations (V658F and V658I). Seven percent of tested pts (9 out of 129) had JAK2 mutations: D869V, L884P, N622T, R683G, and R683S (1, 2, 1, 4, and 1 pts, respectively).

CRLF2 over-expression, the presence of P2RY8-CRLF2, or mutations in CRLF2, JAK1, or JAK2 did not significantly correlate with, gender, age or baseline WBC. No significant correlation with outcome variables (CR, RD, RFS, or OS) was found when the cohort was analyzed as a whole, or when pts with known T-cell lineage ALL are excluded (n=115). Though not a statistically significant result, the two pts with JAK1 were reported living at 9 and 12 years of follow-up. Subgroup analysis of Ph negative non-T-ALL pts (n=86) showed a modest correlation of CRLF2 high expression with a lower CR rate (50% vs. 76% CR rate chi-square test p=0.046). However, this trend in CR rate is not seen in the analysis of continuous CRLF2 expression levels and overall survival is not significantly correlated with CRLF2 expression.