Extracellular vesicles, or EVs, are tiny membrane-enclosed packages that cells release into their surroundings. Ranging from 30 nanometers to 5,000 nanometers in diameter, these particles carry proteins, genetic material, and lipids from one cell to another, functioning as a built-in communication system throughout the body. Once dismissed as cellular waste, EVs are now recognized as key players in health, disease, and a growing number of medical technologies.
The Three Main Types of EVs
EVs come in three broad categories, distinguished mainly by how they form and how large they are.
Exosomes are the smallest, typically 30 to 150 nanometers across. They form inside the cell through a process where the inner wall of a cellular compartment (called an endosome) folds inward, creating small internal bubbles. When that compartment eventually fuses with the cell’s outer membrane, those bubbles are released outside the cell as exosomes.
Microvesicles range from about 100 to 1,000 nanometers. Instead of forming inside the cell, they bud directly outward from the cell’s surface membrane, pinching off like a soap bubble separating from a wand. The cell generates internal tension through its structural skeleton, which pushes the membrane outward until a piece breaks free.
Apoptotic bodies are the largest, ranging from 50 to 5,000 nanometers, though most skew toward the bigger end of that range. These form when a dying cell breaks apart in a controlled process called apoptosis. Rather than the cell simply bursting open and spilling its contents, it packages its material into neat membrane-wrapped fragments that neighboring cells can safely clean up.
What EVs Carry Inside
The cargo inside an EV is what makes it biologically meaningful. EVs transport a mix of RNA, proteins, and lipids, and the specific combination reflects the cell that produced them.
The RNA payload is remarkably diverse. EVs carry messenger RNA, which contains instructions for building proteins, along with microRNAs, which are short molecules that can silence or regulate genes in the receiving cell. They also carry fragments of transfer RNA, ribosomal RNA, long non-coding RNAs, and circular RNAs. This means a single vesicle can potentially alter gene activity in a distant cell without any direct contact between the two cells.
Proteins in EVs include surface markers like tetraspanins (a family of proteins embedded in the vesicle membrane) and a range of RNA-binding proteins that help sort and stabilize the genetic cargo during transit. The lipid membrane itself is enriched with cholesterol and sphingomyelin, giving EVs structural rigidity and helping them fuse with target cells upon arrival.
How EVs Communicate Between Cells
EVs act as long-distance communication vehicles. A cell in one tissue can release vesicles into the bloodstream, where they travel to a completely different organ, get taken up by cells there, and deliver their cargo. The receiving cell then responds to the new instructions, whether that means producing a new protein, changing its behavior, or altering the surrounding tissue environment.
This is not random. Surface proteins on the vesicle, particularly integrins, help determine which organ or cell type will absorb them. Think of it as an address label: the integrin profile on a vesicle’s surface directs it toward specific tissues, making EV communication surprisingly targeted.
EVs in Cancer and Disease
The same communication system that keeps healthy tissues coordinated can be hijacked by disease. In cancer, tumor cells release EVs that travel to distant organs and prepare the ground for metastasis, a process researchers call building a “pre-metastatic niche.”
Tumor-derived EVs accomplish this in several ways. They reprogram immune cells in the target organ, shifting certain white blood cells (macrophages) into a state that supports tumor growth rather than fighting it. They modify the tissue environment, remodeling the structural framework of distant organs to make it more hospitable for incoming cancer cells. They also promote a cellular transformation called epithelial-mesenchymal transition, which helps tumor cells become more mobile and invasive.
Cancer-specific EVs called oncosomes carry molecular cargo tailored for this purpose. The integrins on their surface determine which organs they target, which helps explain why certain cancers consistently spread to particular organs. Breast cancer, for example, preferentially metastasizes to bone and lung, and the integrin profiles on its EVs appear to play a role in that pattern.
EVs as Diagnostic Tools
Because EVs circulate in blood and other body fluids, they offer a way to detect disease without invasive tissue biopsies. This concept, known as liquid biopsy, is especially relevant for cancers where traditional biopsies are difficult or risky to obtain.
Lung cancer is one of the most actively studied areas. Researchers have found that the nucleic acids inside small EVs are more sensitive than free-floating tumor DNA in blood (called ctDNA) for detecting common mutations like BRAF, KRAS, and EGFR in non-small cell lung cancer. Combining EV analysis with ctDNA and RNA testing further improves detection accuracy. A clinical trial called ALCINA 1, which enrolled 60 patients with metastatic lung cancer, was among the studies evaluating these circulating biomarkers.
EVs also carry surface markers that reflect the tumor’s characteristics. Levels of PD-L1, a protein that helps tumors evade the immune system, measured on circulating EVs reliably mirror PD-L1 levels in the actual tumor. Certain membrane proteins on lung cancer EVs can even distinguish between patients with metastatic disease and those without spread. These approaches are particularly valuable for lung cancer because obtaining tissue samples from the lungs is often complicated and carries procedural risks.
Engineered EVs for Drug Delivery
The natural ability of EVs to deliver molecular cargo to specific cells has made them attractive as drug delivery vehicles. Researchers are engineering EVs to carry therapeutic payloads directly to diseased tissue while leaving healthy cells alone.
In breast cancer research, EVs have been modified to display a targeting molecule on their surface that binds specifically to HER2, a protein overexpressed in some breast tumors. These engineered vesicles carry small interfering RNA (siRNA) that silences cancer-promoting genes inside the tumor cells. A similar approach has been developed for prostate cancer, where EVs fitted with a targeting molecule called an aptamer deliver siRNA that shuts down a specific gene involved in tumor growth and metastasis.
The applications extend beyond cancer. Engineered EVs loaded with siRNA targeting inflammatory genes have shown the ability to reduce kidney inflammation and fibrosis while restoring metabolic function in animal models. In obesity research, EVs carrying mRNA for a bone-related growth factor successfully triggered the conversion of white fat to calorie-burning brown fat in abdominal tissue. These examples illustrate why EVs are generating excitement as a delivery platform: they are naturally biocompatible, can be directed to specific tissues, and can carry a variety of genetic instructions.
How Researchers Isolate EVs
Studying EVs requires separating them from the complex mix of proteins and other particles in blood or cell culture fluid. Two dominant methods each come with trade-offs.
Ultracentrifugation spins samples at extremely high speeds to pellet EVs based on their density. An optimized version of this method removes more than 95% of contaminating blood proteins, making it the better choice when researchers need high-purity samples for protein analysis. The downside is that it recovers fewer total vesicles.
Size-exclusion chromatography filters particles through a column that separates them by size. It recovers more EVs overall, yielding roughly 1.3 billion vesicles per milliliter of serum, and retains more of the vesicles’ native protein content. However, it also lets through significantly more blood proteins as contaminants. This makes it better suited for RNA analysis, where the protein background matters less, but problematic for protein-focused studies where contamination can obscure results.
The 2023 update of the Minimal Information for Studies of Extracellular Vesicles guidelines (MISEV2023) provides standardized recommendations for how researchers should produce, separate, and characterize EVs. These guidelines exist because inconsistent methods across laboratories have historically made it difficult to compare results, and they now cover everything from basic isolation techniques to advanced approaches for studying EV release, uptake, and behavior in living organisms.