UPREGULATED COBLL1 IN CHRONIC LYMPHOCYTIC LEUKAEMIA (CLL) PATIENTS WITH UNMUTATED IGHV IDENTIFIES A COHORT WITH INFERIOR PROGNOSIS

Background
Chronic lymphocytic leukaemia (CLL) is a heterogeneous disease; patients are stratified into two prognostic groups with either mutated (M-CLL) or unmutated (U-CLL) IGHV. CLL cells are also characteristic by upregulated expression of a transmembrane tyrosine-protein kinase (ROR1), a member of Wnt/planar cell polarity (PCP) pathway, which influences migration of CLL cells and chemotaxis. We have identified recently Cordon-bleu protein-like 1 (COBLL1) as a ROR1 binding partner. The significance of COBLL1 for CLL patient stratification remains unknown.

Aims
Our aim was (i) to examine expression of COBLL1 in CLL cells and (ii) to analyse COBLL1 expression in relation to the patients’ prognosis.

Methods

We analysed COBLL1 expression in 174 previously untreated patients (82 U-CLL, 92 M-CLL) by qRT-PCR and correlated the results with prognostic markers (TP53 defect, IGHV status, del 11q, del 13q, trisomy 12, ATM, BIRC3, MYD88 and NOTCH1mutation). We also examined how chemotaxis of CLL cells towards chemokines CCL19 and CXCL12 differs depending onCOBLL1 expression (11 M-CLL, 10 U-CLL COBLL1-low, 6 U-CLL COBLL1-high).

Results

COBLL1 expression in CLL cells is heterogeneous. COBLL1 is upregulated in all M-CLL (M-CLL vs. U-CLL, p<0.0001, Mann Whitney test), whereas its expression in U-CLL shows a bimodal pattern and distinguishes two prognostically different subgroups. Intriguingly, the U-CLL COBLL1-high patients suffer from more aggressive disease than the U-CLL COBLL1-low patients, which results in their shorter time to first treatment (TTFT), time to second treatment (TTST) and overall survival (OS) (TTFT: medians 20 vs. 33 months, p=0.0226; TTST: 36 vs. 57, p=0.0055; OS: 75 vs. 207, p=0.0037, Mantle Cox test). Analysis of biological markers revealed lower somatic hypermutation load in U-CLL COBLL1-high cells (p=0.0062, Mann Whitney test). No other genomic differences which might result in survival differences within U-CLL patients have been found. Frequency of TP53 defect was not statistically significant (29% U-CLL COBLL1-high vs. 22% U-CLL COBLL1-low). Therefore, we analysed the cell migration abilities of U-CLL COBLL1-high towards chemokines CCL19 and CXCL12 and found impaired migration compared to M-CLL and U-CLL COBLL1-low cells (CCL19: M-CLL vs. U-CLL COBLL1-high, p=0.0182, Mann Whitney test). In basal migration, the trend was reversed, i.e. basal migration of U-CLL COBLL1-high cells was increased compared to the M-CLL and U-CLL COBLL1-low cells.

Summary

COBLL1 expression in CLL cells differs dramatically and identifies a novel subgroup within U-CLL patients with inferior prognosis. Their shorter survival cannot be explained by any other prognostic marker tested. Aggressive disease course of U-CLL COBLL1-high patients can be a result of a deregulated response to microenvironment stimuli caused by deregulated Wnt/PCP pathway.

Supported by MUNI/A/1180/2014, IGA NT13493-4/2012, GACR P301/11/0747, 15-29793A, CZ.1.07/2.3.00/30.0009.

Keyword(s): Chronic lymphocytic leukemia, Prognostic groups, Wnt

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