CD44

Overview

CD44 is a multifunctional transmembrane glycoprotein and cell surface receptor broadly expressed across mammalian tissues, where it plays central roles in cell adhesion, migration, proliferation, and survival. It functions primarily as a receptor for hyaluronic acid (hyaluronan), a major component of the extracellular matrix, as well as for other ligands including osteopontin, collagens, and matrix metalloproteinases. Through these interactions, CD44 mediates intracellular signaling cascades — notably the PI3K/Akt and JAK2/signal transducer and activator of transcription 3 (STAT3) pathways — that govern fundamental cellular processes including epithelial-to-mesenchymal transition (EMT), stem cell maintenance, and immune modulation. CD44 exists in multiple isoforms generated by alternative splicing of up to 10 variant exons, allowing context-dependent expression across cell types and disease states.

In oncology, CD44 is widely recognized as a cancer stem cell (CSC) marker, often co-expressed with other stemness-associated proteins such as Epithelial Cell Adhesion Molecule (EpCAM) (EPCAM). Its overexpression has been documented across a broad spectrum of malignancies — including liver cancer, colorectal cancer, bladder cancer, breast cancer, and prostate cancer, among others — where it is associated with tumor aggressiveness, therapy resistance, and metastatic potential. Because of its consistent surface overexpression on tumor cells and immunological relevance, CD44 has also emerged as a high-value target for receptor-mediated drug delivery systems, particularly those utilizing hyaluronic acid as a targeting ligand.

Recent Publications Summary

Recent studies have continued to position CD44 as a multifunctional target in cancer, inflammation, and tissue injury, with several reports leveraging hyaluronic acid-based delivery systems to exploit CD44-mediated uptake. In triple-negative breast cancer, a dual-trigger hyaluronic acid nanoprodrug was designed for CD44-targeted and glutathione-responsive doxorubicin delivery, showing selective internalization in CD44-high MDA-MB-231 cells with intracellular prodrug activation and nuclear accumulation of doxorubicin 42401301Jul. Similarly, hyaluronic acid-coated nanoparticle and polymersome platforms were developed to target CD44-overexpressing cells or macrophages, including a polymersome for co-delivery of melittin and celecoxib that reduced uptake after anti-CD44 antibody blocking in RAW 264.7 macrophages, and an inhalable nitric oxide nanotherapeutic that selectively targeted CD44-overexpressing M1 macrophages in chronic obstructive pulmonary disease 42493250Jul42312473Jun. Additional CD44-directed systems included glutathione-responsive chitosan nanoparticles carrying ginsenoside Rg1 for diabetic kidney disease and hyaluronic acid-modified polymersomes encapsulating gemcitabine and copper peroxide for CD44-overexpressing triple-negative breast cancer 41707746Feb41780685Mar.

Beyond drug delivery, CD44 was highlighted as a biologically active receptor involved in tumor progression, immune regulation, and stromal signaling. In hepatocellular carcinoma, endotrophin was identified as a CD44 receptor that activated STAT3 signaling and promoted epithelial-mesenchymal transition, proliferation, and sorafenib resistance; disruption of the endotrophin-CD44 axis suppressed malignant phenotypes and reduced tumor burden in mouse models 41671381Feb. In gastric cancer, tumor cell-derived serglycin signaled through CD44 on T cells to drive differentiation and suppressive function of LAG3-positive Tregs via CD44-TGFβRI-SMAD3 signaling, with associated metabolic effects including glycolysis and reduced reactive oxygen species clearance 41734377Feb. CD44 also appeared in a fibrotic immune crosstalk axis in pulmonary fibrosis, where CHI3L1 promoted profibrotic macrophage activation and myofibroblast transformation through a CD44/PD-L1 axis 42048160Apr.

CD44 was also linked to stemness, invasion, and metastasis-associated programs. In triple-negative breast cancer, adapalene was reported to inhibit the activity of CD44, described as a cancer stem cell biomarker 42397497Jul. In hepatocellular carcinoma, AFP knockout reduced stemness markers including CD44 and suppressed PI3K/Akt signaling, supporting a role for CD44-associated stemness in tumor progression 41651174Feb. Spatial functional genomics work using SPAC-seq further identified Cd44 as a regulator of CD8+ T-cell spatial phenotypes through interaction with Spp1 on macrophages, underscoring a role for CD44 in intercellular communication within tissue microenvironments 42190664May. Finally, integrative bioinformatics analysis of high-risk primary biliary cholangitis nominated CD44 among six core candidate genes associated with gut microbiota-derived metabolites and immune signatures, suggesting CD44 may also participate in inflammatory liver disease-associated host responses 42594087Aug.

What Changes, What Holds

1. CD44-directed delivery is being refined into triggerable, cell-selective cargo uptake
REINFORCES CD44’s established value as a surface target for hyaluronic-acid-mediated delivery is strengthened rather than altered. The new systems mainly show that targeting can be combined with extra release controls, such as redox responsiveness or inhaled formulations, to improve intracellular drug delivery in CD44-high cancer cells and inflammatory myeloid cells 42401301Jul42312473Jun. That supports the baseline view of CD44 as a useful receptor for receptor-mediated delivery, without adding a new biological role.

2. CD44 is now implicated in stromal and immune crosstalk beyond its classic cancer-cell functions
NEW DIRECTION Endotrophin acting through CD44 in hepatocellular carcinoma, serglycin signaling through CD44 on T cells, and CHI3L1 engaging a CD44/PD-L1 axis in fibrosis extend CD44 beyond the Overview’s emphasis on adhesion, migration, stemness, and immune modulation in general 41671381Feb41734377Feb. These findings suggest CD44 can serve as a signaling node in tumor resistance, T-cell suppression, and profibrotic macrophage programming. The baseline does not explicitly cover these stromal and immune-interaction axes.

3. CD44 remains tied to stemness and tissue microenvironment communication, but the new roles are context-specific
REINFORCES Findings linking CD44 to reduced stemness markers in hepatocellular carcinoma, inhibitor-sensitive cancer-stem-cell activity in triple-negative breast cancer, and macrophage-to–CD8+ T-cell communication are consistent with the established picture of CD44 as a stemness- and microenvironment-associated receptor 42397497Jul41651174Feb. The PBC bioinformatics signal adds a disease-association hypothesis, but not a contradiction or new mechanism. Overall, these reports sharpen where CD44 matters rather than changing what it is understood to do.

Overview update candidates: CD44-mediated stromal and immune crosstalk in hepatocellular carcinoma; gastric cancer; and pulmonary fibrosis; CD44-linked regulation of CD8+ T-cell spatial phenotypes in tissue microenvironments.