CD49d expression is an independent predictor of overall survival in patients with chronic lymphocytic leukaemia: a prognostic parameter with therapeutic potential

Abstract

In vitro studies have demonstrated that surface expression of CD49d on chronic lymphocytic leukaemia (CLL) B cells facilitates leukaemic cell-stromal interactions by binding to fibronectin. This interaction reduces both spontaneous and drug-induced apoptosis. The present study measured CD49d expression by flow cytometry in a cohort of untreated CLL patients previously accrued to a prospective observational study and evaluated the relationship with overall survival (OS). Among the 158 CLL patients tested, the percentage of leukaemic B cells expressing CD49d ranged from 0 to 100%. When all risk factors were treated as continuous variables, CD49d expression showed moderate correlation with expression of ZAP-70 (r = 0.54; P < 0.0001) and CD38 (r = 0.58; P < 0.0001) but not %IGHV mutation. As a continuous variable, CD49d expression strongly correlated with OS (P < 0.0001). Recursive partitioning analysis suggested the 45% threshold of CD49d expression best predicted OS. Multivariate analysis, controlling for disease stage, ZAP-70, IGHV status and fluorescent in situ hybridization defects identified CD49d as an independent predictor of OS and was a better predictor of clinical outcome than ZAP-70, IGHV, or cytogenetics. This observational cohort study suggests that CLL B-cell expression of CD49d is an easily measurable and independent predictor of OS and CD49d expression in CLL. Importantly, anti-CD49d antibodies are already approved for treatment of other human diseases. Clinical testing of anti-CD49d therapy in CLL appears warranted.

Fig 1

Relationship of CD49d with other prognostic parameters. (A) Examples of dot plots for CLL cells stained with antibodies specific for CD19 (x-axis) and CD49d (y-axis) assessed by flow cytometry. After gating on lymphocytes on forward and side scatter, CD49d expression was measured in CD19⁺ cells using antibodies specific for CD19 and CD49d. Dots in the upper right quadrant represent leukaemic B cells with higher CD49d expression while the dots in the lower right quadrant represent leukaemic B cells with lower CD49d expression. The percentage of CD19⁺ cells in the right upper quadrant is given for each patient (i.e. CD19 negative cells are not included in this calculation). Cells in the left upper quadrant represent CD19 negative lymphoid cells (i.e. T cells). (B) Distribution of CD49d expression in B cells of 158 patients. (C) Distribution of CD49d expression by ZAP-70 status (n = 158). (D) Distribution of CD49d expression by IGHV mutation status (n = 126). (E) Distribution of CD49d expression by CD38 status (n = 158). (F) Distribution of CD49d expression by FISH prognostic category (n = 152).

Fig 2

Time to treatment and overall survival according to 30% threshold to categorize CD49d. (A) TTT from date of diagnosis based on CD49d expression (n = 156). (B) TTT from on study date based on CD49d expression (n = 156). (C) OS from date of diagnosis based on CD49d expression (n = 158). (D) OS from on study date based on CD49d expression (n = 158).

Fig 3

Time to treatment and overall survival based on 45% threshold to categorize CD49d. (A) TTT from date of diagnosis based on CD49d expression (n = 156). (B) TTT from on study date based on CD49d expression (n = 156). (C) OS from date of diagnosis based on CD49d expression (n = 158). (D) OS from on study date based on CD49d expression (n = 158).