An anion exchange membrane sensor detects EGFR and its activity state in plasma CD63 extracellular vesicles from patients with glioblastoma.

We present a quantitative sandwich immunoassay for CD63 Extracellular Vesicles (EVs) and a constituent surface cargo, EGFR and its activity state, that provides a sensitive, selective, fluorophore-free and rapid alternative to current EV-based diagnostic methods. Our sensing design utilizes a charge-gating strategy, with a hydrophilic anion exchange membrane functionalized with capture antibodies and a charged silica nanoparticle reporter functionalized with detection antibodies. With sensitivity and robustness enhancement by the ion-depletion action of the membrane, this hydrophilic design with charged reporters minimizes interference from dispersed proteins, thus enabling direct plasma analysis without the need for EV isolation or sensor blocking. With a LOD of 30 EVs/µL and a high relative sensitivity of 0.01% for targeted proteomic subfractions, our assay enables accurate quantification of the EV marker, CD63, with colocalized EGFR by an operator/sample insensitive universal normalized calibration. We analysed untreated clinical samples of Glioblastoma to demonstrate this new platform. Notably, we target both total and "active" EGFR on EVs; with a monoclonal antibody mAb806 that recognizes a normally hidden epitope on overexpressed or mutant variant III EGFR. Analysis of samples yielded an area-under-the-curve (AUC) value of 0.99 and a low p-value of 0.000033, surpassing the performance of existing assays and markers.

CD63 + tumor-associated macrophages drive the progression of hepatocellular carcinoma through the induction of epithelial-mesenchymal transition and lipid reprogramming.

BACKGROUND: Tumor-associated macrophages (TAMs) constitute a substantial part of human hepatocellular carcinoma (HCC). The present study was devised to explore TAM diversity and their roles in HCC progression. METHODS: Through the integration of multiple 10 × single-cell transcriptomic data derived from HCC samples and the use of consensus nonnegative matrix factorization (an unsupervised clustering algorithm), TAM molecular subtypes and expression programs were evaluated in detail. The roles played by these TAM subtypes in HCC were further probed through pseudotime, enrichment, and intercellular communication analyses. Lastly, vitro experiments were performed to validate the relationship between CD63, which is an inflammatory TAM expression program marker, and tumor cell lines. RESULTS: We found that the inflammatory expression program in TAMs had a more obvious interaction with HCC cells, and CD63, as a marker gene of the inflammatory expression program, was associated with poor prognosis of HCC patients. Both bulk RNA-seq and vitro experiments confirmed that higher TAM CD63 expression was associated with the growth of HCC cells as well as their epithelial-mesenchymal transition, metastasis, invasion, and the reprogramming of lipid metabolism. CONCLUSIONS: These analyses revealed that the TAM inflammatory expression program in HCC is closely associated with malignant tumor cells, with the hub gene CD63 thus representing an ideal target for therapeutic intervention in this cancer type.

Metastasizing aneurysmal dermatofibroma initially diagnosed as angiosarcoma confirmed by CD63::PRKCD fusion gene detection with nanopore sequencing.

Dermatofibroma (DF) is a benign tumor that forms pedunculated lesions ranging in size from a few millimeters to 2 cm, usually affecting the extremities and trunks of young adults. Histopathologically, DF is characterized by the storiform proliferation of monomorphic fibroblast-like spindle cells. In addition to neoplastic cells, secondary elements such as foamy histiocytes, Touton-type giant cells, lymphoplasmacytes, and epidermal hyperplasia are characteristic histological features. Several histological variants, including atypical, cellular, aneurysmal, and lipidized variants, have been reported; cases with variant histologies are sometimes misdiagnosed as sarcomas. We present a case of metastasizing aneurysmal DF that was initially diagnosed as an angiosarcoma on biopsy. A 26-year-old woman was referred to our hospital with a gradually enlarging subcutaneous mass in her lower left leg. Positron emission tomography-computed tomography revealed high fluorodeoxyglucose uptake not only in the tumor but also in the left inguinal region. On biopsy, ERG and CD31-positive atypical spindle cells proliferated in slit-like spaces with extravasation, leading to the diagnosis of angiosarcoma. Histology of the wide-resection specimen was consistent with DF, and lymph node metastasis was also observed. Nanopore DNA sequencing detected CD63::PRKCD fusion and copy number gain, although CD63 was not included in the target region of adaptive sampling. This report highlights the importance of recognizing the unusual clinical, radiological, and pathological features of DF to avoid misdiagnosis, and the potential diagnostic utility of nanopore sequencer.

A label-free colorimetric biosensor utilizing natural material for highly sensitive exosome detection.

Exosomes, extracellular vesicles secreted by cells, play a crucial role in intercellular communication by transferring information from source cells to recipient cells. These vesicles carry important biomarkers, including nucleic acids and proteins, which provide valuable insights into the parent cells' status. As a result, exosomes have emerged as noninvasive indicators for the early diagnosis of cancer. Colorimetric biosensors have garnered significant attention due to their cost-effectiveness, simplicity, rapid response, and reproducibility. In this study, we employ sporopollenin microcapsules (SP), a natural biopolymer material derived from pollen, as a substrate for gold nanoparticles (AuNPs). By modifying the SP-Au complex with CD63 aptamers, we develop a label-free colorimetric biosensor for exosome detection. In the absence of exosomes, the SP-Au complex catalyzes the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB), resulting in a color change from colorless to blue. However, the addition of exosomes inhibits the catalytic activity of the SP-Au complex due to coverage of exosomes on AuNPs. This colorimetric biosensor exhibits high sensitivity and selectivity for exosome detection, with a detection limit of 10 particles/µL and a wide linear range of 10 - 108 particles/µL. Additionally, the SP-Au biosensor demonstrates remarkable resistance to serum protein adsorption and excellent catalytic stability even in harsh environments, making it highly suitable for clinical diagnostics.

Fusion with ARRDC1 or CD63: A Strategy to Enhance p53 Loading into Extracellular Vesicles for Tumor Suppression.

Small extracellular vesicles (sEVs) have emerged as promising therapeutic agents and drug delivery vehicles. Targeted modification of sEVs and their contents using genetic modification strategies is one of the most popular methods. This study investigated the effects of p53 fusion with arrestin domain-containing protein 1 (ARRDC1) and CD63 on the generation of sEVs, p53 loading efficiency, and therapeutic efficacy. Overexpression of either ARRDC1-p53 (ARP) or CD63-p53 (CDP) significantly elevated p53 mRNA and protein levels. The incorporation of ARRDC1 and CD63 significantly enhanced HEK293T-sEV biogenesis, evidenced by significant increases in sEV-associated proteins TSG101 and LAMP1, resulting in a boost in sEV production. Importantly, fusion with ARRDC1 or CD63 substantially increased the efficiency of loading both p53 fusion proteins and its mRNA into sEVs. sEVs equipped with ARP or CDP significantly enhanced the enrichment of p53 fusion proteins and mRNA in p53-null H1299 cells, resulting in a marked increase in apoptosis and a reduction in cell proliferation, with ARP-sEVs demonstrating greater effectiveness than CDP-sEVs. These findings underscore the enhanced functionality of ARRDC1- and CD63-modified sEVs, emphasizing the potential of genetic modifications in sEV-based therapies for targeted cancer treatment.

Endocytosis blocks the vesicular secretion of exosome marker proteins.

Exosomes are secreted vesicles of ~30 to 150 nm diameter that play important roles in human health and disease. To better understand how cells release these vesicles, we examined the biogenesis of the most highly enriched human exosome marker proteins, the exosomal tetraspanins CD81, CD9, and CD63. We show here that endocytosis inhibits their vesicular secretion and, in the case of CD9 and CD81, triggers their destruction. Furthermore, we show that syntenin, a previously described exosome biogenesis factor, drives the vesicular secretion of CD63 by blocking CD63 endocytosis and that other endocytosis inhibitors also induce the plasma membrane accumulation and vesicular secretion of CD63. Finally, we show that CD63 is an expression-dependent inhibitor of endocytosis that triggers the vesicular secretion of lysosomal proteins and the clathrin adaptor AP-2 mu2. These results suggest that the vesicular secretion of exosome marker proteins in exosome-sized vesicles occurs primarily by an endocytosis-independent pathway.

A highly sensitive and selective fluorescent biosensor for breast cancer derived exosomes using click reaction of azide-CD63 aptamer and alkyne-polymer dots.

Exosomes have gained recognition as valuable reservoirs of biomarkers, holding immense potential for early cancer detection. Consequently, there is a pressing need for the development of an economical and highly sensitive exosome detection methodology. In this work, we present a fluorescence method for breast cancer-derived exosome detection based on Cu-triggered click reaction of azide-modified CD63 aptamer and alkyne functionalized Pdots. The detection threshold for the exosomes obtained from the breast cancer serum was determined to be 6.09 × 107 particles per µL, while the measurable range spanned from 6.50 × 107 to 1.30 × 109 particles per µL. The employed methodology achieved notable success in accurately distinguishing breast cancer patients from healthy individuals through serum analysis. The application of this method showcases the significant potential for early exosome analysis in the clinical diagnosis of breast cancer patients.

Arf GTPase-Activating proteins ADAP1 and ARAP1 regulate incorporation of CD63 in multivesicular bodies.

Arf GTPase-activating proteins (ArfGAPs) mediate the hydrolysis of GTP bound to ADP-ribosylation factors. ArfGAPs are critical for cargo sorting in the Golgi-to-ER traffic. However, the role of ArfGAPs in sorting into intralumenal vesicles (ILVs) in multivesicular bodies (MVBs) in post-Golgi traffic remains unclear. Exosomes are extracellular vesicles (EVs) of endosomal origin. CD63 is an EV marker. CD63 is enriched ILVs in MVBs of cells. However, the secretion of CD63 positive EVs has not been consistent with the data on CD63 localization in MVBs, and how CD63-containing EVs are formed is yet to be understood. To elucidate the mechanism of CD63 transport to ILVs, we focused on CD63 localization in MVBs and searched for the ArfGAPs involved in CD63 localization. We observed that ADAP1 and ARAP1 depletion inhibited CD63 localization to enlarged endosomes after Rab5Q79L overexpression. We tested epidermal growth factor (EGF) and CD9 localization in MVBs. We observed that ADAP1 and ARAP1 depletion inhibited CD9 localization in enlarged endosomes but not EGF. Our results indicate ADAP1 and ARAP1, regulate incorporation of CD63 and CD9, but not EGF, in overlapped and different MVBs. Our work will contribute to distinguish heterogenous ILVs and exosomes by ArfGAPs.

Septin-coated microtubules promote maturation of multivesicular bodies by inhibiting their motility.

The microtubule cytoskeleton consists of microtubule subsets with distinct compositions of microtubule-associated proteins, which instruct the position and traffic of subcellular organelles. In the endocytic pathway, these microtubule-associated cues are poorly understood. Here, we report that in MDCK cells, endosomes with multivesicular body (MVB) and late endosome (LE) markers localize preferentially to microtubules coated with septin GTPases. Compared with early endosomes, CD63-containing MVBs/LEs are largely immotile on septin-coated microtubules. In vitro reconstitution assays revealed that the motility of isolated GFP-CD63 endosomes is directly inhibited by microtubule-associated septins. Quantification of CD63-positive endosomes containing the early endosome antigen (EEA1), the Rab7 effector and dynein adaptor RILP or Rab27a, showed that intermediary EEA1- and RILP-positive GFP-CD63 preferentially associate with septin-coated microtubules. Septin knockdown enhanced GFP-CD63 motility and decreased the percentage of CD63-positive MVBs/LEs with lysobiphosphatidic acid without impacting the fraction of EEA1-positive CD63. These results suggest that MVB maturation involves immobilization on septin-coated microtubules, which may facilitate multivesiculation and/or organelle-organelle contacts.

Enhanced immune capture of extracellular vesicles with gelatin nanoparticles and acoustic mixing.

Extracellular vesicles (EVs) originating from cancer cells incorporate various critical biomolecules that can aid in early cancer diagnosis. However, the rapid analysis of these micro vesicles remains challenging due to their nano-scale size and overlapping dimensions, hindering sufficient capture in terms of quantity and purity. In this study, an acoustofluidic device was developed to enhance the yield of immune-captured EVs. The channel of the device was modified with degradable gelatin nanoparticles (∼220 nm) to increase the surface roughness, and subsequently treated with CD63 antibodies. The acoustic-induced streaming would prolong the rotation time of the EVs in the targeted continuous flow area, improving their aggregation towards the surrounding pillars and subsequent capture by the specific CD63 antibodies. Consequently, the capture efficiency of the device was improved when the signal was on, as evidenced by enhanced fluorescence intensity in the main channel. It is demonstrated that the acoustofluidic device could enhance the immune capture of EVs through acoustic mixing, showcasing great potential in the rapid and fast detection of EVs in liquid biopsy applications.

CD63+ cancer-associated fibroblasts confer CDK4/6 inhibitor resistance to breast cancer cells by exosomal miR-20.

Cyclin-dependent kinase 4 (CDK4) and CDK6 inhibitors (CDK4/6i) have rapidly received Food and Drug Administration (FDA) approval as a new type of therapy for patients with advanced hormone receptor-positive breast cancer. However, with the widespread application of CDK4/6i, drug resistance has become a new challenge for clinical practice and has greatly limited the treatment effect. Here, the whole microenvironment landscape of ER+ breast cancer tumors was revealed through single-cell RNA sequencing, and a specific subset of cancer-associated fibroblasts (CD63+ CAFs) was identified as highly enriched in CDK4/6i resistant tumor tissues. Then, we found that CD63+ CAFs can distinctly promote resistance to CDK4/6i in breast cancer cells and tumor xenografts. In addition, it was discovered that miR-20 is markedly enriched in the CD63+ CAFs-derived exosomes, which are used to communicate with ER+ breast cancer cells, leading to CDK4/6i resistance. Furthermore, exosomal miR-20 could directly target the RB1 mRNA 3'UTR and negatively regulate RB1 expression to decrease CDK4/6i sensitivity in breast cancer cells. Most importantly, we designed and synthesized cRGD-miR-20 sponge nanoparticles and found that they can enhance the therapeutic effect of CDK4/6i in breast cancer. In summary, our findings reveal that CD63+ CAFs can promote CDK4/6i resistance via exosomal miR-20, which induces the downregulation of RB1 in breast cancer cells, and suggest that CD63+ CAFs may be a novel therapeutic target to enhance CDK4/6i sensitivity.

The subtilisin-like protease furin regulates hemin-induced CD63 surface expression on platelets.

Accumulation of free heme B in the plasma can be the result of severe hemolytic events, when the scavenger system for free hemoglobin and heme B is overwhelmed. Free heme B can be oxidized into toxic hemin, which has been proven to activate platelet degranulation and aggregation and promote thrombosis. In the present study we analyzed the effect of hemin on the activation-mediated lysosomal degranulation and CD63 surface expression on platelets using classic flow cytometry and fluorescence microscopy techniques. Classical platelet activators were used as control to distinguish the novel effects of hemin from known activation pathways. CD63 is a tetraspanin protein, also known as lysosomal-associated membrane protein 3 or LAMP-3. In resting platelets CD63 is located within the membrane of delta granules and lysosomes of platelet, from where it is integrated into the platelet outer membrane upon stimulation. We were able to show that hemin like the endogenous platelet activators ADP, collagen or thrombin does provoke CD63 re-localization. Interestingly, only hemin-induced CD63 externalization is dependent on the subtilisin-like pro-protein convertase furin as shown by inhibitor experiments. Furthermore, we were able to demonstrate that hemin induces lysosome secretion, a source of the hemin-mediated CD63 presentation. Again, only the hemin-induced lysosome degranulation is furin dependent. In summary we have shown that the pro-protein convertase furin plays an important role in hemin-mediated lysosomal degranulation and CD63 externalization.

Combining avidin with CD63 improves basophil activation test accuracy in classifying peanut allergy.

BACKGROUND: Conventional basophil activation tests (BATs) measure basophil activation by the increased expression of CD63. Previously, fluorophore-labeled avidin, a positively-charged molecule, was found to bind to activated basophils, which tend to expose negatively charged granule constituents during degranulation. This study further compares avidin versus CD63 as basophil activation biomarkers in classifying peanut allergy. METHODS: Seventy subjects with either a peanut allergy (N = 47), a food allergy other than peanut (N = 6), or no food allergy (N = 17) were evaluated. We conducted BATs in response to seven peanut extract (PE) concentrations (0.01-10,000 ng/mL) and four control conditions (no stimulant, anti-IgE, fMLP (N-formylmethionine-leucyl-phenylalanine), and anti-FcεRI). We measured avidin binding and CD63 expression on basophils with flow cytometry. We evaluated logistic regression and XGBoost models for peanut allergy classification and feature identification. RESULTS: Avidin binding was correlated with CD63 expression. Both markers discriminated between subjects with and without a peanut allergy. Although small by percentage, an avidin+ /CD63- cell subset was found in all allergic subjects tested, indicating that the combination of avidin and CD63 could allow a more comprehensive identification of activated basophils. Indeed, we obtained the best classification accuracy (97.8% sensitivity, 96.7% specificity) by combining avidin and CD63 across seven PE doses. Similar accuracy was obtained by combining PE dose of 10,000 ng/mL for avidin and PE doses of 10 and 100 ng/mL for CD63. CONCLUSIONS: Avidin and CD63 are reliable BAT activation markers associated with degranulation. Their combination enhances the identification of activated basophils and improves the classification accuracy of peanut allergy.

Differential proteomics argues against a general role for CD9, CD81 or CD63 in the sorting of proteins into extracellular vesicles.

The tetraspanins CD9, CD81 and CD63 are major components of extracellular vesicles (EVs). Yet, their impact on EV composition remains under-investigated. In the MCF7 breast cancer cell line CD63 was as expected predominantly intracellular. In contrast CD9 and CD81 strongly colocalized at the plasma membrane, albeit with different ratios at different sites, which may explain a higher enrichment of CD81 in EVs. Absence of these tetraspanins had little impact on the EV protein composition as analysed by quantitative mass spectrometry. We also analysed the effect of concomitant knock-out of CD9 and CD81 because these two tetraspanins play similar roles in several cellular processes and associate directly with two Ig domain proteins, CD9P-1/EWI-F/PTGFRN and EWI-2/IGSF8. These were the sole proteins significantly decreased in the EVs of double CD9- and CD81-deficient cells. In the case of EWI-2, this is primarily a consequence of a decreased cell expression level. In conclusion, this study shows that CD9, CD81 and CD63, commonly used as EV protein markers, play a marginal role in determining the protein composition of EVs released by MCF7 cells and highlights a regulation of the expression level and/or trafficking of CD9P-1 and EWI-2 by CD9 and CD81.

Revisiting the Role of CD63 as Pro-Tumorigenic or Anti-Tumorigenic Tetraspanin in Cancers and its Theragnostic Implications.

Cluster of differentiation antigen 63 (CD63) belongs to a superfamily of proteins, usually defined as tetraspanins which are known to transverse the bilayer membranes four times. The expression of CD63 has been shown to get altered in several cancers, where it has been demonstrated to act as both a tumor promoter and tumor suppressor. The present review describes the mechanism of how CD63 promotes tumor formation in certain cancer types while inhibiting in some other specific cancers. Glycosylation, a post-translational process plays a significant role in regulating the expression and function of these membrane proteins. Being a crucial exosomal flag protein, CD63 has been found to get involved in endosomal cargo sorting as well as the production of extracellular vesicles. Increased expression of exosomal CD63 derived from advanced tumors has demonstrated its role in promoting metastasis. CD63 also regulates the characteristic and function of stem cells on which they get expressed. This particular tetraspanin has been discovered to participate in gene fusion to perform distinctive roles in certain specific cancer types like breast cancer and pigmented epithelioid melanocytoma. Furthermore, this review mentions twelve different microRNAs obtained from miRDB that might target CD63. A few theragnostic uses of this membrane protein are also discussed. Thereby, the review indicates that further studies on CD63 might prove it to be an effective therapeutic target in different cancers in the coming future.

Lack of involvement of CD63 and CD9 tetraspanins in the extracellular vesicle content delivery process.

Extracellular vesicles (EVs) are thought to mediate intercellular communication by transferring cargoes from donor to acceptor cells. The EV content-delivery process within acceptor cells is still poorly characterized and debated. CD63 and CD9, members of the tetraspanin family, are highly enriched within EV membranes and are respectively enriched within multivesicular bodies/endosomes and at the plasma membrane of the cells. CD63 and CD9 have been suspected to regulate the EV uptake and delivery process. Here we used two independent assays and different cell models (HeLa, MDA-MB-231 and HEK293T cells) to assess the putative role of CD63 and CD9 in the EV delivery process that includes uptake and cargo delivery. Our results suggest that neither CD63, nor CD9 are required for this function.

Exosome secretion kinetics are controlled by temperature.

When multivesicular endosomes (MVEs) fuse with the plasma membrane, exosomes are released into the extracellular space where they can affect other cells. The ability of exosomes to regulate cells nearby or further away depends on whether they remain attached to the secreting cell membrane. The regulation and kinetics of exosome secretion are not well characterized, but probes for directly imaging single MVE fusion events have allowed for visualization of the fusion and release process. In particular, the design of an exosome marker with a pH-sensitive dye in the middle of the tetraspanin protein CD63 has facilitated studies of individual MVE fusion events. Using TIRF microscopy, single fusion events were measured in A549 cells held at 23-37°C and events were identified using an automated detection algorithm. Stable docking precedes fusion almost always and a decrease in temperature was accompanied by decrease in the rate of content loss and in the frequency of fusion events. The loss of CD63-pHluorin fluorescence was measured at fusion sites and fit with a single or double exponential decay, with most events requiring two components and a plateau because the loss of fluorescence was typically incomplete. To interpret the kinetics, fusion events were simulated as a localized release of tethered/untethered exosomes coupled with the membrane diffusion of CD63. The experimentally observed decay required three components in the simulation: 1) free exosomes, 2) CD63 membrane diffusion from the endosomal membrane into the plasma membrane, and 3) tethered exosomes. Modeling with slow diffusion of the tethered exosomes (0.0015-0.004 µm2/s) accurately fits the experimental data for all temperatures. However, simulating with immobile tethers or the absence of tethers fails to replicate the data. Our model suggests that exosome release from the fusion site is incomplete due to postfusion, membrane attachment.

Glial cells expressing visual cycle genes are vital for photoreceptor survival in the zebrafish pineal gland.

Photoreceptors in the vertebrate eye are dependent on the retinal pigmented epithelium for a variety of functions including retinal re-isomerization and waste disposal. The light-sensitive pineal gland of fish, birds, and amphibians is evolutionarily related to the eye but lacks a pigmented epithelium. Thus, it is unclear how these functions are performed. Here, we ask whether a subpopulation of zebrafish pineal cells, which express glial markers and visual cycle genes, is involved in maintaining photoreceptors. Selective ablation of these cells leads to a loss of pineal photoreceptors. Moreover, these cells internalize exorhodopsin that is secreted by pineal rod-like photoreceptors, and in turn release CD63-positive extracellular vesicles (EVs) that are taken up by pdgfrb-positive phagocytic cells in the forebrain meninges. These results identify a subpopulation of glial cells that is critical for pineal photoreceptor survival and indicate the existence of cells in the forebrain meninges that receive EVs released by these pineal cells and potentially function in waste disposal.

LAMP3/CD63 Expression in Early and Late Endosomes in Human Vaginal Epithelial Cells Is Associated with Enhancement of HSV-2 Infection.

Herpes simplex virus 2 (HSV-2) is a lifelong sexually transmitted virus that disproportionately infects women through heterosexual transmission in the vaginal tract. The vaginal epithelium is known to be highly susceptible to HSV-2 infection; however, the cellular mechanism of HSV-2 uptake and replication in vaginal epithelium has not been extensively studied. Previously, we observed that lysosomal-associated membrane protein-3 (LAMP3/CD63) was among the highly upregulated genes during HSV-2 infection of human vaginal epithelial cell line VK2, leading us to posit that LAMP3/CD63 may play a role in HSV-2 infection. Consequently, we generated two gene-altered VK2-derived cell lines, a LAMP3-overexpressed (OE) line and a LAMP3 knockout (KO) line. The wild-type VK2 and the LAMP3 OE and KO cell lines were grown in air-liquid interface (ALI) cultures for 7 days and infected with HSV-2. Twenty-four hours postinfection, LAMP3 OE cells produced and released significantly higher numbers of HSV-2 virions than wild-type VK2 cells, while virus production was greatly attenuated in LAMP3 KO cells, indicating a functional association between LAMP3/CD63 expression and HSV-2 replication. Fluorescence microscopy of HSV-2-infected cells revealed that HSV-2 colocalized with LAMP3 in both early endosomes and lysosomal compartments. In addition, blocking endosomal maturation or late endosomal/lysosomal fusion using specific inhibitors resulted in reduced HSV-2 replication in VK2 cells. Similarly, LAMP3 KO cells exhibited very low viral entry and association with endosomes, while LAMP3 OE cells demonstrated large amounts of virus that colocalized with LAMP3/CD63 in endosomes and lysosomes. IMPORTANCE Collectively, these results showed that HSV-2 is taken up by human vaginal epithelial cells through an endosomal-lysosomal pathway in association with LAMP3, which plays a crucial role in the enhancement of HSV-2 replication. These findings provide the basis for the future design of antiviral agents for prophylactic measures against HSV-2 infection.