Both PI3K p110α and p110δ Isoforms Control CD160-Mediated CLL Cell Viability and Cytokine Production

Expression of CD160 on normal immune cells is primarily observed on human and murine circulating cytotoxic lymphocytes (NK cells and a small subset of T-cells). CD160 exhibits a broad specificity for major histocompatibility complex molecules. While normal B-cells do not express CD160, malignant B-cells of CLL (and HCL) are CD160+.¹ Triggering of CD160 on CLL cells mediates increased viability, PI3K dependent growth signals and marked IL-6 and IL-8 secretion.² In this study, the role of the different PI3K subunits in CD160 effector functions in CLL have been investigated in terms of cytokine/chemokine secretion and cell viability.

Unstimulated CLL cells underwent apoptosis over 5 days in culture, which was significantly inhibited by the anti-CD160 antibody, CL1-R2 (p<0.01). Similarly, the viability of purified CLL cells was enhanced by addition of a microenvironment milieu (CD19 negative fraction from BM samples) and further improved by CL1-R2 triggering of CD160 (p=0.03).

Without stimulation, CLL cells secreted minimal levels of IL-2, IL-4, IL-10, TNF-alpha, INF-gamma, CCL2 and CCL5 (as assessed by cytokine bead array (BD Biosciences). At baseline, low levels of IL-6 (median: 23 pg/ml) and IL-8 (median: 114 pg/ml) were detected. Incubating CL1-R2 with CLL cells led to a significant increase in IL-6 (median: 1431 pg/ml, p<0.01), IL-8 (median: 7945 pg/ml, p<0.01), CCL2 (monocyte chemotactic protein-1, median: 813.3 pg/ml, p=0.01) and CCL5 (median: 53.61 pg/ml, p=0.03). These effects of CD160 triggering were suppressed, in a dose-dependent manner, by the pan PI3K inhibitors LY294002 (p=0.01) and Wortmannin (p<0.01, Table 1).

The roles of the different p110-catalytic subunits of PI3K in CD160 mediated activation were investigated. CLL cells from 5 different patients were incubated with the specific isoform-selective inhibitors PI103 (p110α), TGX-115 (p110β) and IC87114 (p110δ) at concentrations of 0.5, 1 and 10μM, in the presence of CL1-R2. CD160 induced cell viability was significantly reduced in a dose dependent manor by both PI103 (p=0.004) and IC87114 (p=0.002). Although the p110β inhibitor demonstrated a reduction in CD160 mediated cell viability it was not significant. Combining the p110α and p110δ inhibitors, a further decrease in CD160 mediated cell viability was observed (p<0.01), but not in a synergistic manner.

Upon performing cytokine and chemokine bead array assays on the same patients, the CD160 induced cytokine and chemokine production of IL-6, IL-8, CCL2 and CCL5 were suppressed by all the inhibitors at a concentration of 10 μM (Table 2). However, only p110α and p110δ subunit inhibition resulted in significant reductions, with a further decrease in both CD160 mediated cytokine and chemokine secretion when both were inhibited together (IL-6: p<0.01, IL-8: p=0.03, CCL2: p=0.02, CCL5: p=0.03), but not with a synergistic or additive effect (Table 2).

These results demonstrate that CL1-R2 engagement of CD160 leads to: (1) a direct survival signal in CLL cells; and (2) production of IL-6, IL-8, CCL2 and CCL5. These functions are PI3K-dependent. These PI3K dependent responses signal largely through the p110α and p110δ isoform-selective catalytic subunits. From a clinical perspective, this data lends further support to targeting the p110α subunit, in addition to p110δ, as a therapeutic strategy. However, none of the inhibitors, alone or in combination, reduced cytokine secretion to basal levels, suggesting that CD160 is also signalling via other undefined pathways.

References:

1. Farren TW et al. Blood. 2011; 118 (8): 2174-2183.

2. Liu FT et al. Blood. 2010; 115 (15): 3079-3088