Cross-talk between 4-1BB and TLR1–TLR2 Signaling in CD8+ T Cells Regulates TLR2′s Costimulatory Effects

Abstract

The activation of TLR-MyD88 (Toll-like receptor- Myeloid differentiation factor 88) signaling within T cells functions as a potent costimulatory signal that boosts antitumor and antiviral responses. However, the molecular mechanisms underlying the costimulatory processes are poorly understood. We compared microarray gene analysis data between TLR1–TLR2 stimulated and unstimulated T-cell receptor transgenic ‘pmel’ and MyD88−/− pmel CD8+ T cells and identified changes in the expression of several TNF family members. In particular, TLR-stimulation increased 4-1BB levels in pmel but not in MyD88−/−pmel T cells. A link between 4-1BB and TLR1–TLR2 signaling in CD8+ T cells was highlighted by the suboptimal responses of 4-1BB−/− T cells to TLR1–TLR2 agonist, but their normal response to CD28 or OX40 costimulation. Blocking 4-1BB signaling with antibodies also hindered the costimulatory effects of the TLR1–TLR2 agonist. The elevated levels of 4-1BB transcripts in TLR1–TLR2–stimulated cells were not due to increased mRNA stability nor increased histone activation, but instead were associated with increased binding of p65 and c-Jun to two distinct 4-1BB promoter sites. Combining TLR1–TLR2 ligand with an agonistic antibody to 4-1BB enhanced the antitumor activity in mice with established melanoma tumors. These studies reveal that the costimulatory effects of TLR1–TLR2 signaling in CD8+ T cells are in part mediated by 4-1BB and are important for mounting an effective antitumor immune response.

A Synthetic CD8α:MyD88 Coreceptor Enhances CD8+ T-cell Responses to Weakly Immunogenic and Lowly Expressed Tumor Antigens

“…Changes in the expression of 89 surface proteins were identified comparing the fold change between vector control and CD8α:MyD88 or CD8α:ΔIC T cells (Figure 2F). CD8α:MyD88 increased expression of IL-2 receptor chains CD25 and CD132, co-stimulatory molecules involved in T cell proliferation and cytolytic function such as CD71, CD26, and CD137 (4-1BB)(14), and various activation-associated adhesion molecules including CD44 and CD69. CD8α:MyD88 also decreased the expression of co-inhibitory molecules including CD160, CD73, Tim3, and CD39 (Figure 2F).…”

Toll‐like receptor‐2/7‐mediated T cell activation: An innate potential to augment CD8+ T cell cytokine production

“…As such, TLR2 might be better suited for use in a therapeutic setting, especially in situations where antigen levels and T cell functionality are limited, such as in cancer. Indeed, in a murine melanoma model, TLR2 stimulation enhanced tumor‐specific T cell responses to weakly immunogenic tumor antigens 120 and delayed tumor outgrowth in a B16‐OVA melanoma model 26,29 …”

“…22,23 Recently, it was shown that TLR stimulation can also function in a costimulatory fashion to enhance TCR triggering (Table 1). Combined TCR and TLR triggering enhances the activation, proliferation, memory formation and effector function of murine and human CD4 + and CD8 + T cells, 10,13,14,16,19,[24][25][26][27][28][29][30] enhancing the production of the pro-inflammatory cytokines IFN-γ, TNF-α and IL-2. 10,14,16,19,[24][25][26][28][29][30][31][32][33] Furthermore, similar to CD28, 22,23 TLR triggering also lowers the antigen threshold required for TCR triggering.…”

“…Combined TCR and TLR triggering enhances the activation, proliferation, memory formation and effector function of murine and human CD4 + and CD8 + T cells, 10,13,14,16,19,[24][25][26][27][28][29][30] enhancing the production of the pro-inflammatory cytokines IFN-γ, TNF-α and IL-2. 10,14,16,19,[24][25][26][28][29][30][31][32][33] Furthermore, similar to CD28, 22,23 TLR triggering also lowers the antigen threshold required for TCR triggering. 16,24 Due to their stimulatory capacity to enhance the effector function of both innate and adaptive immune cells, 16,34,35 TLR ligands or the exploitation of TLR signalling could provide novel opportunities for immunotherapy approaches.…”

mTORC1 Signaling Controls TLR2-Mediated T-Cell Activation by Inducing TIRAP Expression

“…Indeed, stimulation of T cells with TLR2 ligands enhances T-cell proliferation and cytokine production when they are co-stimulated via the TCR ( Komai-Koma et al, 2004;Cottalorda et al, 2006), modulates the suppressive functions of CD4 + CD25 + regulatory T cells (Sutmuller et al, 2006;Liu et al, 2006), and promotes Th17 responses (Reynolds et al, 2010). Furthermore, TLR2-induced functional activation of T cells has been shown to be critical for the induction of inflammatory diseases and protective immunity to pathogens and tumor in vivo (Reynolds et al, 2010;Geng et al, 2010;Quigley et al, 2009;Asprodites et al, 2008;Chodisetti et al, 2015;Joseph et al, 2016). We have shown that TLR2 ligands directly trigger Th1 effector functions, including interferon-g (IFN-g) production, cell proliferation, and cell survival without requiring TCR co-stimulation.…”