Plexin domain-containing 1 may be a biomarker of poor prognosis in hepatocellular carcinoma patients,may mediate immune evasion

BACKGROUND For the first time,we investigated the oncological role of plexin domain-containing 1(PLXDC1),also known as tumor endothelial marker 7(TEM7),in hepatocellular carcinoma(HCC).AIM To investigate the oncological profile of PLXDC1 in HCC.METHODS Based on The Cancer Genome Atlas database,we analyzed the expression of PLXDC1 in HCC.Using immunohistochemistry,quantitative real-time polymerase chain reaction(qRT-PCR),and Western blotting,we validated our results.The prognostic value of PLXDC1 in HCC was analyzed by assessing its correlation with clinicopathological features,such as patient survival,methylation level,tumor immune microenvironment features,and immune cell surface checkpoint expression.Finally,to assess the immune evasion potential of PLXDC1 in HCC,we used the tumor immune dysfunction and exclusion(TIDE)website and immunohistochemical staining assays.RESULTS Based on immunohistochemistry,qRT-PCR,and Western blot assays,overexpression of PLXDC1 in HCC was associated with poor prognosis.Univariate and multivariate Cox analyses indicated that PLXDC1 might be an independent prognostic factor.In HCC patients with high methylation levels,the prognosis was worse than in patients with low methylation levels.Pathway enrichment analysis of HCC tissues indicated that genes upregulated in the high-PLXDC1 subgroup were enriched in mesenchymal and immune activation signaling,and TIDE assessment showed that the risk of immune evasion was significantly higher in the high-PLXDC1 subgroup compared to the low-PLXDC1 subgroup.The high-risk group had a significantly lower immune evasion rate as well as a poor prognosis,and PLXDC1-related risk scores were also associated with a poor prognosis.CONCLUSION As a result of this study analyzing PLXDC1 from multiple biological perspectives,it was revealed that it is a biomarker of poor prognosis for HCC patients,and that it plays a role in determining immune evasion status.

Accurate Diagnosis of SARS-CoV-2 JN.1 by Sanger Sequencing of Receptor-Binding Domain Is Needed for Clinical Evaluation of Its Immune Evasion

Background: Omicron JN.1 has become the dominant SARS-CoV-2 variant in recent months. JN.1 has the highest number of amino acid mutations in its receptor binding domain (RBD) and has acquired a hallmark L455S mutation. The immune evasion capability of JN.1 is a subject of scientific investigation. The US CDC used SGTF of TaqPath COVID-19 Combo Kit RT-qPCR as proxy indicator of JN.1 infections for evaluation of the effectiveness of updated monovalent XBB.1.5 COVID-19 vaccines against JN.1 and recommended that all persons aged ≥ 6 months should receive an updated COVID-19 vaccine dose. Objective: Recommend Sanger sequencing instead of proxy indicator to diagnose JN.1 infections to generate the data based on which guidelines are made to direct vaccination policies. Methods: The RNA in nasopharyngeal swab specimens from patients with clinical respiratory infection was subjected to nested RT-PCR, targeting a 398-base segment of the N-gene and a 445-base segment of the RBD of SARS-CoV-2 for amplification. The nested PCR amplicons were sequenced. The DNA sequences were analyzed for amino acid mutations. Results: The N-gene sequence showed R203K, G204R and Q229K, the 3 mutations associated with Omicron BA.2.86 (+JN.1). The RBD sequence showed 24 of the 26 known amino acid mutations, including the hallmark L455S mutation for JN.1 and the V483del for BA.2.86 lineage. Conclusions: Sanger sequencing of a 445-base segment of the SARS-CoV-2 RBD is useful for accurate determination of emerging variants. The CDC may consider using Sanger sequencing of the RBD to diagnose JN.1 infections for statistical analysis in making vaccination policies.

Immune evasion and therapeutic opportunities based on natural killer cells

Natural killer(NK)cells can elicit an immune response against malignantly transformed cells without recognizing antigens,and they also exhibit cytotoxic effects and immune surveillance functions in tumor immunotherapy.Although several studies have shown the promising antitumor effects of NK cells in immunotherapy,their function is often limited in the tumor microenvironment because tumor cells can easily escape NK cell-induced death.Thus,for efficient tumor immunotherapy,the mechanism by which tumor cells escape NK cell-induced cytotoxicity must be fully understood.Various novel molecules and checkpoint receptors that mediate the disruption of NK cells in the tumor microenvironment have been discovered.In this review,we analyze and detail the major activating and inhibitory receptors on the surface of NK cells to delineate the mechanism by which tumor cells suppress NKG2D ligand expression and increase tumor receptor and inhibitory receptor expression[NKG2A,programmed cell death1(PD-1),and T-cell immunoglobulin and immunoreceptor tyrosine inhibitory motif(TIGIT)]on the NK cell surface,and thus inhibit NK cell activity.We also reviewed the current status of treatments based on these surface molecules.By comparing the therapeutic effects related to the treatment status and bypass mechanisms,we attempt to identify optimal single or combined treatments to suggest new treatment strategies for tumor immunotherapy.

Research Hotspot and Application Status of Immune Evasion Mechanism in Ovarian Cancer

Ovarian cancer is one of the three major malignant tumors in gynecology, with increasing incidence and mortality rates. Currently, the main treatment methods remain surgical intervention in combination with chemotherapy. However, due to its high recurrence rate and the risk of drug resistance, the overall prognosis is poor. Ovarian cancer has been identified as an immunegenic tumor, and in recent years, with the continued advancement of research into immune evasion mechanisms, immunotherapy has emerged as a groundbreaking treatment modality. This article will focus on the immune escape mechanisms and their application in ovarian cancer, providing a comprehensive overview of its current status and the challenges it faces.

Immune evasion mechanisms and therapeutic strategies in gastric cancer

Gastric cancer(GC)is a malignancy with a high incidence and mortality.The tumor immune microenvironment plays an important role in promoting cancer development and supports GC progression.Accumulating evidence shows that GC cells can exert versatile mechanisms to remodel the tumor immune microenvironment and induce immune evasion.In this review,we systematically summarize the intricate crosstalk between GC cells and immune cells,including tumor-associated macrophages,neutrophils,myeloid-derived suppressor cells,natural killer cells,effector T cells,regulatory T cells,and B cells.We focus on how GC cells alter these immune cells to create an immunosuppressive microenvironment that protects GC cells from immune attack.We conclude by compiling the latest progression of immune checkpoint inhibitor-based immunotherapies,both alone and in combination with conventional therapies.Anti-cytotoxic Tlymphocyte-associated protein 4 and anti-programmed cell death protein 1/programmed death-ligand 1 therapy alone does not provide substantial clinical benefit for GC treatment.However,the combination of immune checkpoint inhibitors with chemotherapy or targeted therapy has promising survival advantages in refractory and advanced GC patients.This review provides a comprehensive understanding of the immune evasion mechanisms of GC,and highlights promising immunotherapeutic strategies.

EXPRESSION OF FLIP IN HUMAN COLON CARCINOMAS: A NEW MECHANISM OF IMMUNE EVASION

Objective： It has been proposed that Fas ligand （FasL） may play an important role in immune escape of tumors and FLIP is an important mediator of Fas/FasL pathway. In this study, the expression of FLIP was determined in human colon carcinoma cell lines and tissue to investigate the new mechanism of immune evasion of human colon carcinomas. Methods： RT-PCR and immunohistochemistry （IHC） were performed to investigate the expression of FLIP in human colon carcinoma cell lines SW480, LS174 and twenty human primary colon carcinoma specimens. Results： It was shown that SW480 cells, LS174 cells and primary colon carcinoma specimen constitutively expressed FLIP at the mRNA and protein level. The expression of FLIP was not found in the epithelial cells of normal colon mucosa. Conclusion： FLIP was expressed in human primary colon carcinoma specimens but not in the normal counterpart. It suggested that the expression of FLIP may occur during the malignant transformation from normal colon epithelial cells to colon carcinoma cells. Tumor cells might obtain the ability to resist the Fas-mediated apoptosis by expressing FLIP. The expression of FLIP might contribute to the formation of colon carcinomas.

Targeting pancreatic cancer immune evasion by inhibiting histone deacetylases

The immune system plays a vital role in maintaining the delicate balance between immune recognition and tumor development.Regardless,it is not uncommon that cancerous cells can intelligently acquire abilities to bypass the antitumor immune responses,thus allowing continuous tumor growth and development.Immune evasion has emerged as a significant factor contributing to the progression and immune resistance of pancreatic cancer.Compared with other cancers,pancreatic cancer has a tumor microenvironment that can resist most treatment modalities,including emerging immunotherapy.Sadly,the use of immunotherapy has yet to bring significant clinical breakthrough among pancreatic cancer patients,suggesting that pancreatic cancer has successfully evaded immunomodulation.In this review,we summarize the impact of genetic alteration and epigenetic modification(especially histone deacetylases,HDAC)on immune evasion in pancreatic cancer.HDAC overexpression significantly suppresses tumor suppressor genes,contributing to tumor growth and progression.We review the evidence on HDAC inhibitors in tumor eradication,improving T cells activation,restoring tumor immunogenicity,and modulating programmed death 1 interaction.We provide our perspective in targeting HDAC as a strategy to reverse immune evasion in pancreatic cancer.

Immune evasion by Plasmodium falciparum parasites: converting a host protection mechanism for the parasite′s benefit

Immune evasion is a strategy used by pathogenic microbes to evade the host immune system in order to ensure successful propagation. Immune evasion is particularly important for the blood stages of Plasmodium falciparum, the causative agent of the deadly disease malaria tropica. Because Plasmodium blood stage parasites require human erythrocytes for replication, their ability to evade attack by the human immune system is essential for parasite survival. In order to escape immunity-induced killing, the intraerythrocytic parasites have evolved a variety of evasion mechanisms, including expansion of plasmodial surface proteins, organ-specific sequestration of the infected red blood cells and acquisition of immune-regulatory proteins by the parasite. This review aims to highlight recent advances in the molecular understanding of the immune evasion strategies by P. falciparum, including antigenic variation, surface protein polymorphisms and invasion ligand diversification. The review will further discuss new findings on the regulatory mechanisms applied by P. falciparum to avoid lysis by the human complement as well as killing by immune factors of the mosquito vector.

Elevated nuclear PIGL disrupts the cMyc/BRD4 axis and improves PD-1 blockade therapy by dampening tumor immune evasion

To improve the efficacy of lenvatinib in combination with programmed death-1(PD-1)blockade therapy for hepatocellular carcinoma(HCC),we screened the suppressive metabolic enzymes that sensitize HCC to lenvatinib and PD-1 blockade,thus impeding HCC progression.After analysis of the CRISPR‒Cas9 screen,phosphatidylinositol-glycan biosynthesis class L(PIGL)ranked first in the positive selection list.PIGL depletion had no effect on tumor cell growth in vitro but reprogrammed the tumor microenvironment(TME)in vivo to support tumor cell survival.Specifically,nuclear PIGL disrupted the interaction between cMyc/BRD4 on the distant promoter of target genes and thus decreased the expression of CCL2 and CCL20,which are involved in shaping the immunosuppressive TME by recruiting macrophages and regulatory T cells.PIGL phosphorylation at Y81 by FGFR2 abolished the interaction of PIGL with importinα/β1,thus retaining PIGL in the cytosol and facilitating tumor evasion by releasing CCL2 and CCL20.Clinically,elevated nuclear PIGL predicts a better prognosis for HCC patients and presents a positive correlation with CD8+T-cell enrichment in tumors.Clinically,our findings highlight that the nuclear PIGL intensity or the change in PIGL-Y81 phosphorylation should be used as a biomarker to guide lenvatinib with PD-1 blockade therapy.

Emerging role of metabolic reprogramming in tumor immune evasion and immunotherapy

Mounting evidence has revealed that the therapeutic efficacy of immunotherapies is restricted to a small portion of cancer patients.A deeper understanding of how metabolic reprogramming in the tumor microenvironment(TME)regulates immunity remains a major challenge to tumor eradication.It has been suggested that metabolic reprogramming in the TME may affect metabolism in immune cells and subsequently suppress immune function.Tumor cells compete with infiltrating immune cells for nutrients and metabolites.Notably,the immunosuppressive TME is characterized by catabolic and anabolic processes that are critical for immune cell function,and elevated inhibitory signals may favor cancer immune evasion.The major energy sources that supply different immune cell subtypes also undergo reprogramming.We herein summarize the metabolic remodeling in tumor cells and different immune cell subtypes and the latest advances underlying the use of metabolic checkpoints in antitumor immunotherapies.In this context,targeting both tumor and immune cell metabolic reprogramming may enhance therapeutic efficacy.

Cytomegalovirus immune evasion by perturbation ot endosomal trafficking

Cytomegaloviruses （CMVs）, members of the herpesvirus family, have evolved a variety of mechanisms to evade the immune response to survive in infected hosts and to establish latent infection, They effectively hide infected cells from the effector mechanisms of adaptive immunity by eliminating cellular proteins （major histocompatibility Class I and Class II molecules） from the cell surface that display viral antigens to CD8 and CD4 T lymphocytes, CMVs also successfully escape recognition and elimination of infected cells by natural killer （NK） cells, effector cells of innate immunity, either by mimicking NK cell inhibitory ligands or by downregulating NK cell-activating ligands, To accomplish these immunoevasion functions, CMVs encode several proteins that function in the biosynthetic pathway by inhibiting the assembly and trafficking of cellular proteins that participate in immune recognition and thereby, block their appearance at the cell surface, However, elimination of these proteins from the cell surface can also be achieved by perturbation of their endosomal route and subsequent relocation from the cell surface into intracellular compartments, Namely, the physiological route of every cellular protein, including immune recognition molecules, is characterized by specific features that determine its residence time at the cell surface, In this review, we summarize the current understanding of endocytic trafficking of immune recognition molecules and perturbations of the endosomal system during infection with CMVs and other members of the herpesvirus family that contribute to their immune evasion mechanisms,

Germline genomes have a dominant-heritable contribution to cancer immune evasion and immunotherapy response

Background:Immune evasion is a fundamental hallmark for cancer.At the early stages of tumor development,immune evasion strategies must be implemented by tumors to prevent attacks from the host immune systems.Blocking tumors5 immune evasion will re-activate the host immune systems to eliminate tumors.Immune-checkpoint therapy(ICT)which applies anti-PD-l/PD-Ll or anti-CTLA4 treatment has been a remarkable success in the past few years.However,〜70%of patients cannot gain any clinical benefits from ICT treatment due to the tumorimmunity system's complexity・In the past,germline pathogenic variants have been thought to have only minorheritable contributions to cancer.Results:Emerging evidence has shown that germline genomes play a dominant-heritable contribution to cancer via encoding the host immune system.The functional components of the immune system are encoded by the host genome,thus the germline genome might have a profound impact on cancer immune evasion and immunotherapy response.Indeed,recent studies showed that germline pathogenic variants can influence immune capacity in cancer patients at a population level by(i)shaping tumor somatic mutations,altering methylation patterns and antigen-presentation capacity or(ii)influencing NK cell's function to modulate lymphocyte infiltration in the tumor microenvironment.In addition,the HLA(types A,B or C)genotypes also shape the landscape of tumor somatic mutations.Conclusion:These results highlight the indispensable roles of germline genome in immunity and cancer development and suggest that germline genomics should be integrated into the research field of cancer biology and cancer immunotherapy.

Prognostic value of lactate transporter SLC16A1 and SLC16A3 as oncoimmunological biomarkers associating tumor metabolism and immune evasion in glioma

Background:Hypoxic microenvironment is immunosuppressive and protu-morigenic,and elevated lactate is an intermediary in the modulation of immune responses.However,as critical lactate transporters,the role of SLC16A1 and SLC16A3 in immune infiltration and evasion of glioma is not fully elucidated.Methods:Gene expression in low‐and high‐grade glioma(LGG and GBM)was evaluated with TCGA database.The TISIDB,TIMER and CIBERSORT databases were utilized for the analysis of the correlation between SLC16A1 or SLC16A3 and immunocyte infiltration as well as immune checkpoints.Results:Compared with normal tissues,a significant increase of both SLC16A1 and SLC16A3 was found in LGG and GBM,and closely related to the poor prognosis only in LGG.Cancer SEA indicated that SLC16A1 was involved in hypoxia while SLC16A3 contributed to metastasis and inflamma-tion in glioma.The SLC16A3 expression was significantly correlated with neutrophil activation by GO analysis.TISCH showed the distribution of SLC16A1 on glioma cells and SLC16A3 on immune cells,which was correlated to tumor‐associated macrophages and neutrophils that are immunosuppressive.SLC16A1 and SLC16A3 were identified to tightly interacted with diverse immune checkpoints(especially PD1,PD‐L1,PD‐L2,Tim‐3)and immunosuppressive factors(TGF‐βand IL‐10)in glioma.Furthermore,SLC16A3 had a positive correlation to activation markers of tumor‐associated neutrophils and chemokines such as CCL2,CCL22,CXCR2,CXCR4 in LGG and CCL7,CCL20 CXCL8 in GBM,which could enhance infiltration of immunosuppressive cells to the tumor microenvironment.Conclusion:In general,our results suggest that SLC16A1 and SLC16A3 act as a bridge between tumor metabolism and immunity by promoting immuno-suppressive cell infiltration,which contributes to immune evasion and a worse prognosis in glioma.Targeting SLC16A1 and SLC16A3 may provide novel therapeutic strategy for immunotherapy in glioma.

Opportunities and challenges of CD47-targeted therapy in cancer immunotherapy

Cancer immunotherapy has emerged as a promising strategy for the treatment of cancer,with the tumor microenvironment(TME)playing a pivotal role in modulating the immune response.CD47,a cell surface protein,has been identified as a crucial regulator of the TME and a potential therapeutic target for cancer therapy.However,the precise functions and implications of CD47 in the TME during immunotherapy for cancer patients remain incompletely understood.This comprehensive review aims to provide an overview of CD47’s multifaced role in TME regulation and immune evasion,elucidating its impact on various types of immunotherapy outcomes,including checkpoint inhibitors and CAR T-cell therapy.Notably,CD47-targeted therapies offer a promising avenue for improving cancer treatment outcomes,especially when combined with other immunotherapeutic approaches.The review also discusses current and potential CD47-targeted therapies being explored for cancer treatment and delves into the associated challenges and opportunities inherent in targeting CD47.Despite the demonstrated effectiveness of CD47-targeted therapies,there are potential problems,including unintended effects on healthy cells,hematological toxicities,and the development if resistance.Consequently,further research efforts are warranted to fully understand the underlying mechanisms of resistance and to optimize CD47-targeted therapies through innovative combination approaches,ultimately improving cancer treatment outcomes.Overall,this comprehensive review highlights the significance of CD47 as a promising target for cancer immunotherapy and provides valuable insight into the challenges and opportunities in developing effective CD47-targeted therapies for cancer treatment.

FasL Expression in Colorectal Carcinoma and Its Significance in Immune Escape of Cancer

To study the significance of FasL expression in immune escape of colorectal carcinoma, FasL protein expression and the number of tumor infiltrating lymphocytes （TILs） in 80 specimens of colorectal carcinoma were detected by immunohistochemitry. The mRNA of FasL was measured by in situ hybridization in the consecutive tissue slices of 80 colorectal carcinomas respectively. Using terminal deoxynucleotidyl transferase-mediaed dUTP nick end labeling （TUNEL）, apoptotic cells were detected in 80 specimens of colorectal carcinoma. The expression of FasL was detected in all 80 specimens, but it was not even in the same or among different tissues. In the consecutive tissue slices, the location of expression of FasL protein corresponded with that of FasL mRNA. In those with FasL extensive expression, the number of TILs was less than that of FasL weak expression （P〈0. 05）, and the apoptotic index （AI） of TILs was higher and that of tumor cells was lower than that of FasL with weak expression respectively （P〈0. 01）. The AI of TILs was correlated with that of tumor cells （r=-0. 631, P〈0. 01）. It was suggested that colorectal carcinoma cells can induce the apoptosis of TILs through the expression of FasL, which can counterattack the immune system. This may be one of the mechanisms of immune evasion in colorectal carcinoma.

Understanding the immune response and the current landscape of immunotherapy in pancreatic cancer

Pancreatic ductal adenocarcinoma(PDAC)is an aggressive tumor with high lethality.Even with surgery,radiotherapy,chemotherapy,and other locoregional or systemic therapies,the survival rates for PDAC are low and have not significantly changed in the past decades.The special characteristics of the PDAC’s microenvironment and its complex immune escape mechanism need to be considered when designing novel therapeutic approaches in this disease.PDAC is characterized by chronic inflammation with a high rate of tumor-associated macrophages and myeloid-derived suppressor cells and a low rate of natural killer and effector T cells.The pancreatic microenvironment is a fibrotic,microvascularized stroma that isolates the tumor from systemic vascularization.Immunotherapy,a novel approach that has demonstrated effectiveness in certain solid tumors,has failed to show any practice-changing results in pancreatic cancer,with the exception of PDACs with mismatch repair deficiency and high tumor mutational burden,which show prolonged survival rates with immunotherapy.Currently,numerous clinical trials are attempting to assess the efficacy of immunotherapeutic strategies in PDAC,including immune checkpoint inhibitors,cancer vaccines,and adoptive cell transfer,alone or in combination with other immunotherapeutic agents,chemoradiotherapy,and other targeted therapies.A deep understanding of the immune response will help in the development of new therapeutic strategies leading to improved clinical outcomes for patients with PDAC.

Innate immune recognition and modulation in hepatitis D virus infection

Hepatitis D virus(HDV)is a global health threat with more than 15 million humans affected.Current treatment options are largely unsatisfactory leaving chronically infected humans at high risk to develop liver cirrhosis and hepatocellular carcinoma.HDV is the only human satellite virus known.It encodes only two proteins,and requires Hepatitis B virus(HBV)envelope protein expression for productive virion release and spread of the infection.How HDV could evolve and why HBV was selected as a helper virus remains unknown.Since the discovery of Na+-taurocholate co-transporting polypeptide as the essential uptake receptor for HBV and HDV,we are beginning to understand the interactions of HDV and the immune system.While HBV is mostly regarded a stealth virus,that escapes innate immune recognition,HBV-HDV coinfection is characterized by a strong innate immune response.Cytoplasmic RNA sensor melanoma differentiation antigen 5 has been reported to recognize HDV RNA replication and activate innate immunity.Innate immunity,however,seems not to impair HDV replication while it inhibits HBV.In this review,we describe what is known up-to-date about the interplay between HBV as a helper and HDV’s immune evasion strategy and identify where additional research is required.

Unsynchronized butyrophilin molecules dictate cancer cell evasion of Vγ9Vδ2 T-cell killing

Vγ9Vδ2 T cells are specialized effector cells that have gained prominence as immunotherapy agents due to their ability to target and kill cells with altered pyrophosphate metabolites.In our effort to understand how cancer cells evade the cell-killing activity of Vγ9Vδ2 T cells,we performed a comprehensive genome-scale CRISPR screening of cancer cells.We found that four molecules belonging to the butyrophilin(BTN)family,specifically BTN2A1,BTN3A1,BTN3A2,and BTN3A3,are critically important and play unique,nonoverlapping roles in facilitating the destruction of cancer cells by primary Vγ9Vδ2 T cells.The coordinated function of these BTN molecules was driven by synchronized gene expression,which was regulated by IFN-γsignaling and the RFX complex.Additionally,an enzyme called QPCTL was shown to play a key role in modifying the N-terminal glutamine of these BTN proteins and was found to be a crucial factor in Vγ9Vδ2 T cell killing of cancer cells.Through our research,we offer a detailed overview of the functional genomic mechanisms that underlie how cancer cells escape Vγ9Vδ2 T cells.Moreover,our findings shed light on the importance of the harmonized expression and function of gene family members in modulating T-cell activity.

Intracellular life of protozoan Toxoplasma gondii:Parasitophorous vacuole establishment and survival strategies

Toxoplasma gondii is a protozoan of worldwide distribution and the agent of toxoplasmosis.It is estimated that 30%–50%of the world population could be infected with this parasite.Although the infection in immunocompetent individuals is mostly asymptomatic,the disease in immunosuppressed and pregnant is a risk condition.As a member of the phylum Apicomplexa,T.gondii has an obligatory intracellular lifestyle;therefore,invading a host cell and establishing it inside a parasitophorous vacuole(PV)are mandatories for the survival of this parasite.The construction of a perfect intracellular niche for T.gondii requires the secretion of an arsenal of proteins from unique secretory organelles.These proteins will remodel the vacuolar environment and the host cell organization and functions,allowing the parasite to access essential nutrients and stay“invisible”inside a host cell.In the present review,we will discuss the main steps involved in the PV formation and its differentiation to tissue cyst,focusing mainly on the strategies employed in the acquisition of nutrients and proteins involved in host cell modification.

Circulating tumor cells: Biological features and survival mechanisms

Circulating tumor cells(CTCs)are neoplastic cells that are detached from primary tumors and enter circulation.Enumeration and characterization of CTCs are of significance in cancer diagnosis,prognosis,and treatment monitoring.CTC survival in the bloodstream is a limiting step for the development of metastases in distant organs.Recent technological advances,especially in single-cell molecular analyses have uncovered heterogeneous CTC survival mechanisms.Undergoing epithelial-to-mesenchymal transition(EMT),increasing stem cell-like properties,and forming cell clusters enable CTCs to adapt to the harsh microenvironment of the circulation.Expressing and releasing several immunosuppressive molecules help CTCs escape from anti-cancer immune mechanisms.This review article summarizes the biological characteristics of CTCs and focuses on the recent understanding of the mechanisms by which CTCs survive in circulation.Additionally,the clinical and therapeutic implications of CTCs are discussed.