Heterodimer‐specific TLR2 stimulation results in divergent functional outcomes in B‐cell precursor acute lymphoblastic leukemia

Abstract

Reports of spontaneous acute lymphoblastic leukemia (ALL) remissions following severe bacterial infections suggest that bacterial components may trigger elimination of ALL. To date, TLR2, which recognizes a broad range of bacterial pathogens through TLR1 or TLR6 heterodimerization, has not been fully evaluated for direct effects on ALL. Studies investigating TLR2 signaling in other tumor cell types utilizing single ligands have yielded contradictory results, and comparative, heterodimer-specific analyses of TLR2 stimulation are lacking. In this study, we report that two well-characterized heterodimer-specific TLR2 ligands, Pam 3 CSK 4 (TLR2/1), and Pam 2 CSK 4 (TLR2/6), induce ALL cell lines and primary ALL samples to upregulate CD40 expression. However, only Pam 3 CSK 4 triggers Caspase-8-mediated apoptosis and sensitizes cells to vincristine-mediated cytotoxicity. Consistent with this result, stimulation of ALL cells through TLR2/1 or TLR2/6 activates Mal, p38 and the NF-κB and PI3K signaling pathways with divergent kinetics that may underlie their distinct downstream effects. Our results reveal a novel branching in downstream responses to heterodimer-specific TLR2 stimulation in ALL cells and emphasize the need for comparative studies to determine differential biological effects observed in specific tumor cells. Based on our results, TLR2/1 ligand Pam 3 CSK 4 possesses potential for generating anti-ALL activity through its direct effects on leukemic blasts.Keywords: CD40 r Caspase-8-mediated apoptotic cell death r Heterodimer-specific TLR2 stimulation r Pediatric acute lymphoblastic leukemia r Signaling kinetics Additional supporting information may be found in the online version of this article at the publisher's web-site IntroductionIt is now widely accepted that tumor remissions induced by the proinflammatory activity of Coley's toxin, which contains various bacterial components, is mediated by the engagement of TollCorrespondence: Dr. Kirk R. Schultz e-mail: kschultz@mail.ubc.ca like receptors (TLRs) on immune cells [1][2][3][4][5]. TLRs are a family of germline-encoded pattern recognition receptors that induce innate and adaptive immune responses after binding pathogenand damage-associated molecular patterns [6][7][8][9][10]. In recent years, many studies have demonstrated that purified TLR ligands exert * These authors contributed equally to this work as senior authors.www.eji-journal.eu Eur. J. Immunol. 2015. 45: 1980-1990 Immunomodulation 1981 potent anti-cancer effects against various types of established tumors in both mice and humans [2,5]. However, while some TLR ligands are currently in clinical trials [11,12], their promising preclinical efficacy as anti-cancer agents has not been consistently observed in the clinic [12]. A greater understanding of the cellular and molecular processes that mediate the beneficial and detrimental outcomes of TLR signaling is needed in order to optimize the translation of this approach. Spontaneous remissions of acute lymphoblastic leukemia (ALL) associated with se...

Immunomodulatory and antitumor effects of type I interferons and their application in cancer therapy

“…It was shown that administration of TLR2 agonists can enhance effector and memory T cell responses, culminating in improved tumor rejection [ 270 , 271 ]. TLR2 agonists can also increase expression of costimulatory molecules in B cell lymphoma, enhancing its sensitivity to NK and CD8 + T cells [ 272 ], or inducing caspase 8-dependent apoptosis [ 273 ].…”

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“…The finding of an enrichment of cell death pathway signatures already 3 hours after Pam3CSK4 treatment of MA9 cells suggests that induction of an apoptosisassociated transcriptional program is an early consequence of TLR1/TLR2 activation. Agonistic targeting of TLR1/TLR2 has previously been shown to sensitize acute lymphoblastic leukemia cells for vincristine-mediated cytotoxicity, 47 to enhance the cytotoxic and apoptotic effects of bortezomib in myeloma cells, and to induce cell death of monocytes from tuberculosis patients, 48,49 but induction of apoptosis after TLR1/TLR2 activation has not previously been described in the context of AML. The observed differentiation of AML cells is consistent with a described cellular response to TLR1/TLR2 activation in normal myeloid progenitor cells.…”

Normal myeloid progenitor cell subset-associated gene signatures for acute myeloid leukaemia subtyping with prognostic impact

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