When the immune system remembers the carrier

Your immune system is designed to remember. That is what makes vaccines work. It is also a problem for drug delivery.

Many modern therapies do not travel through the body on their own. They are packaged inside carriers, tiny particles that protect the drug, help it reach the right tissue and control how it is released. A good carrier can make a drug safer and more effective. But the carrier itself is something the body can see.

Coated, but not invisible

Many synthetic nanoparticles are coated with a polymer called PEG to help them avoid detection. It works, up to a point. Studies have found that some people carry antibodies against PEG, and that repeated doses can trigger faster clearance of PEG-coated particles.

PEG is common in everyday products, including cosmetics and some medicines, so prior exposure is not surprising. The coating forms a water-attracting layer that reduces how quickly immune proteins stick to a particle. That buys time in the bloodstream. But once antibodies against the coating exist, the same feature that was meant to hide the particle can become the thing the immune system recognizes.

Why that matters

If the body learns to recognize the carrier, the drug may be cleared before it reaches its target, or cause a reaction. A carrier that works once is not the same as a carrier that works for a full course of treatment.

The question is not just “does it work?” It is “does it keep working?”

This is especially important for chronic conditions and cancer, where patients receive many doses over weeks or months. A first dose that performs well in testing can give a misleading picture if later doses behave differently. Effectiveness can drop, and in some cases the immune response itself becomes a safety issue.

The case for natural carriers

Extracellular vesicles are made by our own cells, so the hope is that they are better tolerated. Hope is not data. That is why immunogenicity testing, how human immune cells respond to them, is central to my work.

Vesicles are not automatically invisible. They carry proteins and lipids from the cells that made them, and depending on the source and how they are prepared, those molecules can be recognized. A vesicle from a different species, or one loaded with a new cargo, is a new object for the immune system to evaluate. Testing has to be done carefully, with human immune cells, and ideally across repeated exposures rather than only once.

My perspective

I think immunogenicity is one of the most underappreciated questions in drug delivery. It is less exciting than showing a carrier reaches a tumour, and it rarely makes headlines. But it often decides whether a promising technology becomes a usable therapy, and whether patients can rely on it. I would rather find a problem early, in a dish, than discover it in patients.

In drug delivery, the question is not just “does it work?” It is “does it keep working?”