Enhanced Antitumor Efficacy Through Microwave Ablation In Combination With Immune Checkpoints Blockade

As a minimally invasive therapy for focal cancer,microwave ablation(MWA)is widely used in the treatment of liver,thyroid,lung,and kidney tumors.In addition to directly destroy tumor tissues,MWA can lead to the release of large amounts of cellular debris in situ,which can serve as a source of tumor antigens to elicit hosting adaptive immune responses against tumors.However,the responses induced by MWA are weak and not sufficient to prevent tumor recurrence.Immune checkpoints are a series of inhibitory pathways that are crucial for modulating the intensity and duration of immune responses.Among these checkpoints,cytotoxic T-lymphocyte-associated protein 4(CTLA-4)and programmed cell death protein 1(PD-1)have shown to be two key regulators of the activation and proliferation of T cells.CTLA-4 is rapidly up-regulated on activated T-cell surface following immune activation,and binds to B7 molecules on antigen presenting cells(APCs)with a higher affinity than does CD28 molecules on T cells.PD-1 is also increasingly expressed on T-cell surface following activation,and binds to its ligands PD-L1 and PD-L2 on tumor cells or other immune cells,which promotes T-cell anergy,apoptosis and exhaustion.Whether immune checkpoints blockade can enhance and mantain the adaptive immune responses induced by MWA,and whether a combination of immune checkpoints blockade and MWA can synergistically enhance antitumor efficacy.In order to testify the hypothesis,we treated 4T1 tumor-bearing mice with MWA,PD-1 and CTLA-4 blockade,MWA plus PD-1 and CTLA-4 blockade.Immune cells were identified by immunohistochemistry and flow cytometry,and the concentrations of plasma interferon-γ(IFN-γ)were identified by enzyme-linked immunosorbent assay(ELISA).The results showed that the frequencies of CD8+ T cells and the concentrations of IFN-y in the peripheral blood of tumor-bearing mice were significantly increased in the early stage after MWA,but reduced in the middle and late stages after MWA,which implys that the adaptive immune responses induced by MWA weaked gradually.However,PD-1 and CTLA-4 blockade maintained the adaptive immune responses induced by MWA to the late stage after MWA,with increased CD8+ T cells frequencies and IFN-γ concentrations in the peripheral blood.In addition,administration of anti-PD-1 and anti-CTLA-4 without MWA showed no change in overall survival,peripheral blood immune cells and IFN-y of 4T1 tumor bearing mice,which confirmed that weak immunogenicity tumors were refractory to immune checkpoints blockade.Although MWA inhibited the lung metastases of 4T1 tumor bearing mice in the early stage after MWA,it induced the tumor immunosuppressive microenvironment,accelerating the growth and invasiveness of tumors,which failed to prolong overall survival of tumor-bearing mice.MWA combined with PD-1 and CTLA-4 blockade not only significantly inhibited the lung metastases,but also remodeled the tumor microenvironment,which significantly prolonged overall survival of tumor-bearing tumors.Therefore,this study provides a theoretical basis for the clinical study of microwave ablation combined with immune checkpoints blockade.