Manipulation of PD-L1 Endosomal Trafficking Promotes Anticancer Immunity

Rejuvenation of Tumor-Specific T Cells via Ultrahigh DAR Antibody-Polymeric Imidazoquinoline Complexes: Coordinated Targeting of PDL1 and Efficient TLR7/8 Activation in Intratumoral Dendritic Cells

Intratumoral dendritic cells (DCs) are pivotal in tumor treatment due to their immature and pro-tumoral state induced by the tumor microenvironment. Clinically, these immature DCs correlate with disease progression and recurrence, adversely affecting prognosis. Activation of DCs by the TLR7/8 agonist imidazoquinoline (IMDQ) has yielded promising results, but they are limited by systemic inflammation risks, and high programmed death ligand 1 (PDL1) expression on DCs impedes CD8+ T cell activity. Thus, the study introduces an antibody-polymeric IMDQ complex (αPDL1-PLG-IMDQ) with an ultrahigh drug-to-antibody ratio, where αPDL1 is conjugated to Fc-binding peptides on polymeric IMDQ. This complex targets high PDL1-expressing intratumoral DCs with high probability, inducing PDL1-mediated endocytosis to deliver IMDQ to TLR7/8 within endosomes, effectively activating DCs (CD11c+MHC II+: 2.33% versus 1.09%, CD11c+CD86+: 2.49% versus 1.00% on tumors compared to phosphate-buffered saline treatment) and priming T cells. It also blocks PDL1/PD1 interactions, enhancing tumor-specific T-cell activation and memory. Notably, αPDL1-PLG-IMDQ achieved a 97% tumor inhibition rate, prevented tumor regrowth in rechallenge experiments, and reduced lung metastases of tumors by 83%. These findings underscore its potential for intratumoral DC-targeted immunotherapy and novel systemic IMDQ and checkpoint inhibitor combinations.

Profiling Nascent Tumor Extracellular Vesicles via Metabolic Timestamping and Aptamer-Driven Specific Click Chemistry

Tumor-derived extracellular vesicles (tEVs) are essential mediators of tumor progression and therapeutic resistance, yet their secretion dynamics and cargo composition in response to therapies remain poorly understood. Here, we present STAMP, specific click-tagging driven by aptamer for tEV labeled with a metabolic timestamp, which exploits the unique kinetics and thermodynamics of aptamer to significantly enhance the local concentration of clickable probes on tEVs for their covalent attachment to the timestamp, resulting in the selective microfluidic isolation of nascent tEVs following stimulation. In a PD-L1 antibody-treated model, we demonstrated the feasibility of STAMP and revealed a robust positive correlation between the nascent EpCAM+ EV levels and tumor volume. Proteome profiling of isolated nascent tEVs identified previously unknown upregulated vesicle proteins following immunotherapy, including key regulators of immune activation and suppression, suggesting that tumors orchestrate an intricate dual adaptive response through tEV secretion modulation to simultaneously elicit therapeutic sensitivity and resistance. Notably, among the upregulated proteins, we identified HSP70, whose enhanced presentation on tEVs promotes antitumor immunity and inhibits tumor growth. Thus, STAMP provides an effective gateway for studying EV dynamics with cell-origin accuracy and for identifying potential therapeutic targets based on EV transitions.

Protocol for monitoring the endosomal trafficking of membrane proteins in mammalian cells

Here, we present a protocol to study epidermal growth factor (EGF) receptor (EGFR) or transferrin trafficking in mammalian cells. We describe steps for using fluorescent ligands or antibodies, confocal imaging, and quantitative analysis to track their movement. We detail procedures for cell culture preparation, labeling membrane proteins, optimizing imaging, and isolating cell lysates for the biochemical analysis of EGFR degradation after EGF treatment. This protocol is adaptable to various cell types and for assessing genetic or pharmacological impacts on endosomal trafficking. For complete details on the use and execution of this protocol, please refer to Ye et al.,1 Ye et al.,2 and Wang et al.3.

Targeting Surface Markers in Anaplastic Thyroid Cancer: Future Directions in Ligand-bound Therapy

Anaplastic thyroid cancer (ATC) is the rarest and most aggressive form of thyroid cancer, known for its highly variable nature and poor prognosis, primarily due to the lack of effective treatments. While conventional therapies have had limited success, there remains an urgent need for novel therapeutic approaches to combat this disease. ATC tumors are resistant to the standard radioiodine therapy because they lack the sodium/iodide symporter (NIS), which is necessary for iodine uptake. However, recent advances in theranostics targeting cell surface markers have opened new avenues for treating ATC. We used the PubMed database and Google search engine to identify relevant articles using combinations of specific keywords related to the topic of interest, focusing on each surface marker. This review explores multiple surface markers identified in ATC and their promising roles for delivering therapeutic agents into tumors, inducing cell death. Several promising markers, including prostate-specific membrane antigen, vitamin D receptor, IGF-1 receptor, programmed death-ligand 1, epidermal growth factor receptor, and L-type amino acid transporter 1 (LAT-1), have been found in ATC and could serve as effective targets for delivering therapeutic agents to tumors, inducing cell death. Restoring NIS expression is also explored as a potential therapy for ATC. Additionally, boron neutron capture therapy, which utilizes LAT-1 expression, is highlighted as a future therapeutic option due to its ability to selectively target tumor cells while minimizing damage to surrounding healthy tissue. These strategies offer the potential to overcome many of the challenges associated with ATC, improving patient outcomes and overall survival.

Autophagosomes coated in situ with nanodots act as personalized cancer vaccines

Autophagosome cancer vaccines can promote cross-presentation of multiple tumour antigens and induce cross-reactive T cell responses. However, so far, there is no effective method for obtaining a highly immunogenic autophagosomal cancer vaccine because autophagosomes, once formed, quickly fuse with lysosomes and cannot easily escape from cells. Here we report a functional Ti2NX nanodot that caps the autophagosome membrane lipid phosphatidylinositol-4-phosphate, blocking the fusion of autophagosomes with lysosomes and producing stable nanodot-coated autophagosomes in tumours. The formed nanodot-coated autophagosomes can escape from cancer cells to lymph nodes, where they activate tumour-specific T cells. We show that our approach reduces tumour burden and provide long-term immune surveillance protection for cured mice. This work provides a method for the direct formation of personalized autophagosome-based cancer vaccines in vivo, offering a promising strategy for tumour treatment.

Endosomal trafficking participates in lipid droplet catabolism to maintain lipid homeostasis

The interplay between lipid droplets (LDs) and endosomes remains unknown. Here, we screen and synthesize AP1-coumarin, an LD-specific probe, by conjugating a fluorescent dye coumarin to a triazine compound AP1. AP1-coumarin labels all stages of LDs in live cells and markedly induces the accumulation of enlarged RAB5-RAB7 double-positive intermediate endosomes. The AP1-coumarin-labeled LDs contact these intermediate endosomes, with some LDs even being engulfed in them. When LD biogenesis is inhibited, the ability of AP1-coumarin to label LDs is markedly reduced, and the accumulation of enlarged intermediate endosomes is abolished. Moreover, blocking the biogenesis of LDs decreases the number of late endosomes while increasing the number of early endosomes and inhibits the endosomal trafficking of low-density lipoprotein (LDL) and transferrin. Correspondingly, interference with RAB5 or RAB7, either through knockdown or using dominant-negative mutants, inhibits LD catabolism, whereas the expression of a RAB7 constitutively active mutant accelerates LD catabolism. Additionally, CCZ1 knockdown not only induces the accumulation of intermediate endosomes but also inhibits LD catabolism. These results collectively suggest that LDs and endosomes interact and influence each other's functions, and endosomal trafficking participates in the catabolic process of LDs to maintain lipid homeostasis.

Extracellular vesicles in tumor immunity: mechanisms and novel insights

Extracellular vesicles (EVs), nanoscale vesicles secreted by cells, have attracted considerable attention in recent years due to their role in tumor immunomodulation. These vesicles facilitate intercellular communication by transporting proteins, nucleic acids, and other biologically active substances, and they exhibit a dual role in tumor development and immune evasion mechanisms. Specifically, EVs can assist tumor cells in evading immune surveillance and attack by impairing immune cell function or modulating immunosuppressive pathways, thereby promoting tumor progression and metastasis. Conversely, they can also transport and release immunomodulatory factors that stimulate the activation and regulation of the immune system, enhancing the body's capacity to combat malignant diseases. This dual functionality of EVs presents promising avenues and targets for tumor immunotherapy. By examining the biological characteristics of EVs and their influence on tumor immunity, novel therapeutic strategies can be developed to improve the efficacy and relevance of cancer treatment. This review delineates the complex role of EVs in tumor immunomodulation and explores their potential implications for cancer therapeutic approaches, aiming to establish a theoretical foundation and provide practical insights for the advancement of future EVs-based cancer immunotherapy strategies.

Resetting the Hsc70-mediated lysosomal degradation of PD-L1 via a supramolecular meso peptide for the restoration of acquired anti-tumor T cell immunity

The reduction of cellular PD-L1 abundance through lysosomal degradation is recognized as essential for effective and sustained targeting of PD-L1-dependent immune evasion in cancer. While Hsc70 can interact with PD-L1 to promote its lysosomal degradation, the overexpression of CMTM6 competitively inhibits this interaction, leading to the blockade of PD-L1 lysosomal degradation. To overcome this issue, a meso chimeric peptide PEPPDL1 was designed to specifically bind the PD-1 binding domain of PD-L1 instead of the Hsc70/CMTM6 binding domain, while also binding to Hsc70 to facilitate the dragging of PD-L1 into Hsc70-mediated chaperone-mediated autophagy (CMA), thereby achieving lysosomal degradation. In order to enable internalization into tumor cells, supramolecular engineering techniques were employed through terminal modification involving sulfydryl and monovalent gold ion (Au(I)), both facilitating self-assembly of modified PEPPDL1 into supramolecular nanospheres termed CTAC-PDL1 driven by aurophilic interaction. Furthermore, based on bioinformatics analysis of mRNA expression data from 30 types of tumors obtained from TCGA database, malignant melanoma was identified as the most suitable indication for CTAC-PDL1 due to its specific characteristics of tumor immune. As expected, CTAC-PDL1 effectively reactivated Hsc70-mediated lysosomal degradation of PD-L1 and consequently restored anti-tumor T cell immunity in a B16F10-derived mouse model of malignant melanoma while maintaining a favorable safety profile. Overall, this work not only presents an alternative approach for targeting PD-L1-dependent cancer immune evasion, but also provides a modularized strategy for discovering specific regulators for target proteins in various diseases.

Fluorescence Lifetime Imaging Enables In Vivo Quantification of PD-L1 Expression and Intertumoral Heterogeneity

Patient selection for cancer immunotherapy requires precise, quantitative readouts of biomarker expression in intact tumors that can be reliably compared across multiple subjects over time. The current clinical standard biomarker for assessing immunotherapy response is PD-L1 expression, typically quantified using IHC. This method, however, only provides snapshots of PD-L1 expression status in microscopic regions of ex vivo specimens. Although various targeted probes have been investigated for in vivo imaging of PD-L1, nonspecific probe accumulation within the tumor microenvironment has hindered accurate quantification, limiting the utility for preclinical and clinical studies. Here, we demonstrated that in vivo time-domain fluorescence imaging of an anti-PD-L1 antibody tagged with the near-infrared fluorophore IRDye 800CW (αPDL1-800) can yield quantitative estimates of baseline tumor PD-L1 heterogeneity across untreated mice, as well as variations in PD-L1 expression in mice undergoing clinically relevant anti-PD-1 treatment. The fluorescence lifetime (FLT) of PD-L1-bound αPDL1-800 was significantly longer than the FLT of nonspecifically accumulated αPDL1-800 in the tumor microenvironment. This FLT contrast allowed quantification of PD-L1 expression across mice both in superficial breast tumors using planar FLT imaging and in deep-seated liver tumors (>5 mm depth) using the asymptotic time-domain algorithm for fluorescence tomography. These findings suggest that FLT imaging can accelerate the preclinical investigation and clinical translation of new immunotherapy treatments by enabling robust quantification of receptor expression across subjects. Significance: Fluorescence lifetime imaging can quantify PD-L1 expression across multiple mice undergoing anti-PD-1 treatment, providing a critically needed noninvasive imaging method to quantify immunotherapy targets in vivo.

Targeting secretory autophagy in solid cancers: mechanisms, immune regulation and clinical insights

Secretory autophagy is a classical form of unconventional secretion that integrates autophagy with the secretory process, relying on highly conserved autophagy-related molecules and playing a critical role in tumor progression and treatment resistance. Traditional autophagy is responsible for degrading intracellular substances by fusing autophagosomes with lysosomes. However, secretory autophagy uses autophagy signaling to mediate the secretion of specific substances and regulate the tumor microenvironment (TME). Cytoplasmic substances are preferentially secreted rather than directed toward lysosomal degradation, involving various selective mechanisms. Moreover, substances released by secretory autophagy convey biological signals to the TME, inducing immune dysregulation and contributing to drug resistance. Therefore, elucidating the mechanisms underlying secretory autophagy is essential for improving clinical treatments. This review systematically summarizes current knowledge of secretory autophagy, from initiation to secretion, considering inter-tumor heterogeneity, explores its role across different tumor types. Furthermore, it proposes future research directions and highlights unresolved clinical challenges.

Known and unknown: Exosome secretion in tumor microenvironment needs more exploration

Exosomes, extracellular vesicles originating from endosomes, were discovered in the late 1980s and their function in intercellular communication has since garnered considerable interest. Exosomes are lipid bilayer-coated vesicles that range in size from 30 to 150 nm and appear as sacs under the electron microscope. Exosome secretion is crucial for cell-to-cell contact in both normal physiology and the development and spread of tumors. Furthermore, cancer cells can secrete more exosomes than normal cells. Scientists believe that intercellular communication in the complex tissue environment of the human body is an important reason for cancer cell invasion and metastasis. For example, some particles containing regulatory molecules are secreted in the tumor microenvironment, including exosomes. Then the contents of exosomes can be released by donor cells into the environment and interact with recipient cells to promote the migration and invasion of tumor cells. Therefore, in this review, we summarized the biogenesis of exosome, as well as exosome cargo and related roles. More importantly, this review introduces and discusses the factors that have been reported to affect exosome secretion in tumors and highlights the important role of exosomes in tumors.

DRG2 as a Biomarker to Enhance the Predictive Efficacy of PD-L1 Immunohistochemistry Assays

PD-L1 immunohistochemistry (IHC) assays are used as a companion diagnostic for immunotherapy with immune checkpoint inhibitors (ICIs). However, despite the association between PD-L1 expression and clinical benefit from ICIs, the PD-L1 IHC assay is not sufficiently accurate in predicting response to ICIs; some patients with high PD-L1 expression do not respond to ICIs. Recently, researchers provided insights into why some patients with high PD-L1 expression fail to respond to ICIs. They discovered that DRG2 is a critical regulator of PD-L1 endosomal trafficking in cancer cells, which is essential for the proper localization of PD-L1 on the cell surface. Although DRG2-depleted cells express high levels of PD-L1 and are PD-L1 IHC-positive, the PD-L1 sequestered in early endosomes does not respond to ICIs. Therefore, a companion diagnostic combining DRG2 expression with a PD-L1 IHC assay may improve the therapeutic response to PD-1/PD-L1 ICIs.

Hsc70 promotes anti-tumor immunity by targeting PD-L1 for lysosomal degradation

Immune checkpoint inhibition targeting the PD-1/PD-L1 pathway has become a powerful clinical strategy for treating cancer, but its efficacy is complicated by various resistance mechanisms. One of the reasons for the resistance is the internalization and recycling of PD-L1 itself upon antibody binding. The inhibition of lysosome-mediated degradation of PD-L1 is critical for preserving the amount of PD-L1 recycling back to the cell membrane. In this study, we find that Hsc70 promotes PD-L1 degradation through the endosome-lysosome pathway and reduces PD-L1 recycling to the cell membrane. This effect is dependent on Hsc70-PD-L1 binding which inhibits the CMTM6-PD-L1 interaction. We further identify an Hsp90α/β inhibitor, AUY-922, which induces Hsc70 expression and PD-L1 lysosomal degradation. Either Hsc70 overexpression or AUY-922 treatment can reduce PD-L1 expression, inhibit tumor growth and promote anti-tumor immunity in female mice; AUY-922 can further enhance the anti-tumor efficacy of anti-PD-L1 and anti-CTLA4 treatment. Our study elucidates a molecular mechanism of Hsc70-mediated PD-L1 lysosomal degradation and provides a target and therapeutic strategies for tumor immunotherapy.

DDX3 regulates cancer immune surveillance via 3' UTR-mediated cell-surface expression of PD-L1

Programmed death-1 (PD-1)/PD ligand-1 (PD-L1)-mediated immune escape contributes to cancer development and has been targeted as an anti-cancer strategy. Here, we show that inhibition of the RNA helicase DDX3 increased CD8+ T cell infiltration in syngeneic oral squamous cell carcinoma tumors. DDX3 knockdown compromised interferon-γ-induced PD-L1 expression and, in particular, reduced the level of cell-surface PD-L1. DDX3 promoted surface PD-L1 expression by recruiting the adaptor protein 2 (AP2) complex to the 3' UTR of PD-L1 mRNA. DDX3 depletion or 3' UTR truncation increased the binding of the coatomer protein complexes to PD-L1, leading to its intracellular accumulation. Therefore, this 3' UTR-dependent mechanism may counteract cellular negative effects on surface trafficking of PD-L1. Finally, pharmaceutic disruption of DDX3's interaction with AP2 reduced surface PD-L1 expression, supporting that the DDX3-AP2 pathway routes PD-L1 to the cell surface. Targeting DDX3 to modulate surface trafficking of immune checkpoint proteins may provide a potential strategy for cancer immunotherapy.

Challenges Coexist with Opportunities: Spatial Heterogeneity Expression of PD-L1 in Cancer Therapy

Cancer immunotherapy using anti-programmed death-ligand 1 (PD-L1) antibodies has been used in various clinical applications and achieved certain results. However, such limitations as autoimmunity, tumor hyperprogression, and overall low patient response rate impede its further clinical application. Mounting evidence has revealed that PD-L1 is not only present in tumor cell membrane but also in cytoplasm, exosome, or even nucleus. Among these, the dynamic and spatial heterogeneous expression of PD-L1 in tumors is mainly responsible for the unsatisfactory efficacy of PD-L1 antibodies. Hence, numerous studies focus on inhibiting or degrading PD-L1 to improve immune response, while a comprehensive understanding of the molecular mechanisms underlying spatial heterogeneity of PD-L1 can fundamentally transform the current status of PD-L1 antibodies in clinical development. Herein, the concept of spatial heterogeneous expression of PD-L1 is creatively introduced, encompassing the structure and biological functions of various kinds of PD-L1 (including mPD-L1, cPD-L1, nPD-L1, and exoPD-L1). Then an in-depth analysis of the regulatory mechanisms and potential therapeutic targets of PD-L1 is provided, seeking to offer a solid basis for future investigation. Moreover, the current status of agents is summarized, especially small molecular modulators development directed at these new targets, offering a novel perspective on potential PD-L1 therapeutics strategies.

Identification of monocyte-associated biomarkers in systemic lupus erythematosus and their pan-cancer analysis

Immune dysregulation is not only a pathogenic mechanism in systemic lupus erythematosus (SLE) but also a potential cause of the link between SLE and cancer. The current understanding of SLE monocyte-associated biomarkers is limited, and the precise mechanism behind the link between SLE and cancer is uncertain. By using WGCNA and immune infiltration to analyze the GSE72326 dataset, we determined the most pertinent modules for monocytes and discovered eight candidate hub genes from them. The limma software was used to find genes that were differently expressed in SLE. The genes that overlapped between the two were chosen using a Venn diagram as the essential genes related to monocytes in SLE, and the essential genes were verified by several datasets. Correlation analysis and GSEA analysis were used to examine the probable immunological pathways connected to key genes. We examined the expression of hub genes in cancer and their interaction with monocytes using the GEPIA and TIMER databases to understand the significance of essential genes in tumorigenesis. In addition, we performed transcription factor identification. We discovered three biomarkers (IFI30, BLVRA, and RIN2) that are mostly involved in interferon-related signaling pathways and are associated with monocyte-mediated immune responses in SLE. The three important genes are also strongly expressed in a number of malignancies and have a relationship with monocytes. As a result, IFI30, BLVRA, and RIN2 may act as SLE-associated biomarkers of monocytes and as a bridge between SLE and tumors. We proposed that interferon-related signaling pathways might function as possible mediators of cancer risk in SLE.

Extracellular Vesicles Facilitate the Transportation of Nanoparticles within and between Cells for Enhanced Tumor Therapy

The interaction between nanoparticles and cells is closely associated with the therapeutic effects of nanomedicine. Nanoparticles could be transported among cells, but the process-related mechanism remains to be further explored. In this study, it was found that endocytosed cationic polymer nanoparticles (cNPs) could be excreted in an extracellular vesicle (EV)-coated form (cNP@EVs). It was deduced that cNPs may pass through early endosomes, multivesicular bodies (MVBs), and autophagic MVBs within cells. Moreover, a high level of autophagy facilitated the exocytosis process. Since EVs were the effective vehicles for conveying biological information and substances, cNP@EVs were proved to be efficient forms for the intercellular transportation of nanoparticles and have the potential as efficient biomimetic drug delivery systems. These properties endowed cNP@EVs with deep penetration and enhanced antitumor activity. Our findings provided a proof-of-concept for understanding the transfer process of nanoparticles among cells and may help us to further utilize EV-mediated transportation of nanoparticles, therefore, expanding its clinical application.

Local Delivery of Immunomodulatory Antibodies for Gastrointestinal Tumors

Cancer therapy has experienced a breakthrough with the use of immune checkpoint inhibitors (ICIs) based on monoclonal antibodies (mAbs), which are able to unleash immune responses against tumors refractory to other therapies. Despite the great advancement that ICIs represent, most patients with gastrointestinal tumors have not benefited from this therapy. In addition, ICIs often induce adverse effects that are related to their systemic use. Local administration of ICIs in tumors could concentrate their effect in the malignant tissue and provide a higher safety profile. A new and attractive approach for local delivery of ICIs is the use of gene therapy vectors to express these blocking antibodies in tumor cells. Several vectors have been evaluated in preclinical models of gastrointestinal tumors to express ICIs against PD-1, PD-L1, and CTLA-4, among other immune checkpoints, with promising results. Vectors used in these settings include oncolytic viruses, self-replicating RNA vectors, and non-replicative viral and non-viral vectors. The use of viral vectors, especially when they have replication capacity, provides an additional adjuvant effect that has been shown to enhance antitumor responses. This review covers the most recent studies involving the use of gene therapy vectors to deliver ICIs to gastrointestinal tumors.