Immunosuppressive chemoresistance is a major barrier in lung cancer treatment. Tumor immunosuppressive environments mediated by myeloid-derived suppressor cells (MDSCs) play a key role in chemotherapy induced MDSC development and differentiation but their mechanistic role has not been elucidated. Here, we define a role for carboplatin based chemotherapy in potentiating an MDSC-dependent pathway that triggers the chemoresistance mechanism. Findings reveal MDSC differentiation and activation of IL-13/IL-33-mediated pathway through VCAM/RANTES following carboplatin treatment. Furthemore, secretion of T regulatory IL-10-producing CD4+Foxp3+ cells was increased followed by expression of co-inhibitory receptor TIGIT on T cells, leading to a dysfunctional T cell phenotype. These cells were characterized by an immunosuppressive phenotype with impaired activation, proliferation and cytokine production. Lung cancer tissues expressed CD155, which bound TIGIT receptors and inactivated CD8 T cells. This TIGIT expression on tumor-infiltrating T cells was found to be associated with tumor progression and was linked to functional exhaustion of T cells. In addition, the presence of plasmacytoid dendritic cells (pDCs) exposed to tumor-derived factors further enhanced tumor progression through IL-10 production and up-regulation of the inducible co-stimulatory ligand (ICOS-L). Deciphering these deranged immune mechanisms and how they are impacted by chemotherapy induction is essential for incorporation of novel immune-based strategies in order to restore immunity and inhibit the immunosuppressive phenotype of metastatic lung cancer.
Keywords: Carboplatin; Chemoresistance; MDSCs; T cell exhaustion; TIGIT.
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