Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of malignant B lymphocytes in the peripheral blood that are regarded as poorly antigenic to the host immune system. Nonetheless, they are thought to be able to undergo stimulation and become antigen-presenting cells possibly through
Toll-like receptors (TLRs). Several studies have examined the effect of TLR7 and TLR9 stimulation on the biology of CLL cells, revealing contradictory results in terms of cell proliferation and apoptosis. On the other hand, suppression of TLRs has not been studied in CLL so far, and the rationale for this may be increasing evidence of the supportive role of TLR signaling in CLL. In our study we assessed the effect of a synthetic
oligodeoxynucleotide with immunoregulatory sequences (
IRS 954) on peripheral blood cells from patients with untreated CLL, in terms of expression of costimulatory molecules, production of
cytokines and cell viability ex vivo. Agonists of TLR7 (
imiquimod, IMI) and TLR9 (
oligodeoxynucleotide ODN 2006) acted as positive internal controls. ODN 2006 most markedly induced CD86 expression compared to IMI and
IRS 954. Both
oligodeoxynucleotides -
IRS 954 and ODN 2006 - caused 1.5- and 5-fold increases of CD40 on CLL cells, respectively. Immunostimulatory ODN 2006 induced CD95 expression 1.5-fold. Changes in costimulatory molecule expression were accompanied by a moderate response from CD4 + and CD8 + T lymphocytes. TLR7 and TLR9 agonists led to significantly higher production of
interleukin 6 (IL-6) and
IL-10.
IRS 954 and ODN 2006 markedly increased the concentration of
tumor necrosis factor α (TNFα).
IL-17A was significantly decreased by 50% after IMI.
IRS 954 and IMI induced significant
necrosis at all concentrations, and the effect was augmented by the addition of
cladribine (2CdA). ODN 2006 presented a dual effect on cell viability, which was related to disease stage and baseline
IL-17A concentration. The addition of 2CdA had little effect in a group where ODN 2006 supported cell survival, and further enhanced cytotoxicity of ODN 2006 in the second group. Inhibitory
oligodeoxynucleotides seem to exert promising antileukemic effects regardless of sample background, and thus may become a new modality in CLL. The response of leukemic cells to ODN 2006 varies between samples and cannot yet be predicted.