In adoptive cell therapy (ACT) of cancer patients are transfused with a large number of ex-vivo-activated and expanded tumor-reactive T cells. Yet, a network of suppressive mechanisms operating at the tumor site, T cell exhaustion, downregulated effector mechanisms and low persistence of the transferred cells are critical factors which still limit clinical efficacy and broader use of ACT.
Human T cells express several members of the toll-like receptor (TLR) family and are directly activated by their ligands. TLR ligands have been shown to induce T cell survival and proliferation, boost the production of IL-2, IFN-γ and render effector T cells refractory to suppression by regulatory T cells. Genetic removal of the TLR ligand-binding region results in constitutive signaling triggered by the remaining cytosolic TIR domain. This constitutively active (ca)TLR derivative offers an ideal means for equipping tumor-infiltrating lymphocytes (TILs) with the arsenal of functional attributes required for improving current ACT protocols.
Here we report the assembly of caTLR4 and the evaluation of its function in human T cells and in anti-melanoma TILs. We show that the mere expression of caTLR4 mRNA induced massive production of IFN-γ and upregulated a panel of cytokines, chemokines and surface molecules important for T cell effector functions. We then examined the reactivity of anti-melanoma TILs electroporated with caTLR4 mRNA and co-cultured with melanoma target cells. We found that caTLR4 enhanced the anti-melanoma reactivity of transfected TILs and augments secretion of the proinflammatory cytokines GM-CSF, TNF-α and IFN-γ
Expression of caTLR4 in T cells as a genetic adjuvant is, to the best of our knowledge, unprecedented in the field of cancer ACT.
