Platelet-mediated circulating tumor cell evasion from natural killer cell killing via immune checkpoint CD155-TIGIT.

e14552 Background: Circulating tumor cells (CTCs) are precursors of cancer metastasis. However, how CTCs evade immunosurveillance during hematogenous dissemination remains unclear. The interaction between platelets and CTCs is the most extensively studied of all blood cells, and it is well known that CTCs are surrounded by platelets, which form microplots on their surface and play a crucial role in cancer metastasis. The precise mechanisms platelets employ to contribute to CTC immune evasion have not been fully elucidated. Our previous single-cell RNA sequencing data indicated high expression of platelet-related genes in CTCs. Here, our study demonstrated that platelet adhesion to CTCs is prevalent in multiple cancers and is indispensable for CTCs metastasis. Methods: CTC isolation was performed by our self-established ChimeraX-i120 platform. CTC-platelet adhesions were identified by single-cell RNA sequencing and multiplex immunofluorescence of blood samples from multiple cancer types. The cytotoxicity of natural killer (NK) cells was assessed by the reduction in tumor cell numbers measured using the xCELLigence system. In vitro and ex vivo co-culture systems were established by using platelets and NK cells isolated from the peripheral blood of patients for direct or indirect co-culturing with cell lines and patient-derived organoids (PDOs). The effects of platelets and NK cells on metastasis and immune responses were investigated in vivo by utilizing mouse models. Results: Clinically, CTC-platelet aggregates were associated with significantly shorter progression-free survival and overall survival in hepatocellular carcinoma patients. In vitro, ex vivo, and in vivo assays demonstrated direct platelet adhesions gifted cancer cells with an evasive ability from NK cell killing by upregulating inhibitory checkpoint CD155, therefore facilitating distant metastasis. Mechanistically, CD155 was transcriptionally regulated by the FAK/JNK/c-Jun cascade in a platelet contact-dependent manner. Further competition assays and cytotoxicity experiments revealed that CD155 on CTCs inhibited NK cell cytotoxicity only by engaging with immune receptor TIGIT, but not CD96 and DNAM1, another two receptors for CD155. Interrupting the CD155-TIGIT interactions with a TIGIT antibody restored NK cell immunosurveillance on CTCs and markedly attenuated tumor metastasis. Conclusions: Our results demonstrated CTC evasion from NK cell-mediated innate immunosurveillance mainly via immune checkpoint CD155-TIGIT, potentially offering an immunotherapeutic strategy for eradicating CTCs.