For decades, drug discovery has been built around a familiar idea: Design a molecule, manufacture it, and administer it. But that model is now being challenged by a class of therapies that don’t fit neatly within it. So-called “living drugs” — engineered immune cells — do not behave like conventional pharmaceuticals. Once infused, they can expand, migrate, respond to biological signals, and persist long after administration. In effect, they function less like static interventions and more like dynamic biological systems.
That shift is forcing a rethink of what a drug is, and how this class of therapies should be classified, developed, and scaled.
Cell therapies harness the immune system to fight cancer or immune diseases, using either a patient’s own immune cells or those from a donor. Scientists then genetically or functionally enhance these cells so they can recognize and destroy diseased cells more effectively. Once reinfused, the cells can proliferate, migrate through the body, and maintain long-term activity — behaviors more typical of living systems than pharmaceuticals.
A drug that doesn’t fit the drug model
That biological complexity is also creating structural tension in how therapies are developed.
“As CAR T cells or T cell receptor therapies are living drugs, the field doesn’t really fit the way pharma has traditionally been organized,” explained Margot Pont, Vice President of Translational Development at Integra Therapeutics. “If you think about biomarkers or clinical pharmacology, these things are in silos. If you're talking about a living drug, they're all interconnected.”
Pont argued that the conventional separation between biomarkers, pharmacology, and clinical development breaks down in this context. In living systems, these domains are inseparable. That forces a shift not only in laboratory science, but in how companies and regulators think about development pipelines.
Regulators, she added, have begun adapting in response to clinical success. But the broader industry is still catching up.
Rewriting the rules of immunotherapy
Three major classes of these therapies are now approved by the FDA, marking a turning point for oncology and immune diseases.
Tumor-infiltrating lymphocyte (TIL) therapy is one of the earliest approaches. It involves extracting immune cells already present within a tumor, expanding them in the lab with immune-stimulating cytokines, and reinfusing them into the patient. The aim is to amplify a naturally occurring anti-tumor response. In 2024, the FDA approved the first TIL therapy, targeting metastatic melanoma.
T cell receptor (TCR) therapies take a more engineered approach. T cells are modified to recognize specific peptide fragments displayed on cancer cells via human leukocyte antigen (HLA) molecules — a system that acts like a cellular identity code. This allows highly precise targeting, and in 2024 the FDA approved the first TCR therapy for synovial sarcoma, a rare soft-tissue cancer.
Chimeric antigen receptor (CAR) T cell therapy has arguably had the greatest clinical impact so far. Instead of relying on HLA presentation, CAR T cells are engineered to directly bind proteins on the surface of cancer cells. This broader targeting strategy has enabled multiple approvals since 2017, particularly in blood cancers such as lymphoma and multiple myeloma.
These are just the start of what is now broadly referred to as adoptive cell therapy (ACT), a field that is steadily expanding from cancer into autoimmune disease and beyond. Currently, most therapies are targeting blood cancers, where immune cells can more easily circulate and engage malignant cells. But this is quickly changing as research reveals better targets, improved engineering strategies, and a deeper understanding of how immune cells behave within complex tissue environments.
Engineering control into biology
New gene-editing and gene-writing technologies are being developed to make cell therapies more programmable — enabling more precise genomic integration, larger genetic payloads, and built-in safety mechanisms such as inducible kill switches that allow clinicians to deactivate engineered cells if necessary.
These advances point toward a future in which living drugs can be actively controlled after administration, rather than simply delivered. For clinicians, this offers the ability to tune therapeutic activity in real time, manage toxicity, and preserve efficacy without compromising safety.
At the same time, cell therapy design is moving beyond single engineered cell types toward more complex, combinatorial immune strategies — programming T cells not only to kill target cells directly, but also to recruit and coordinate broader immune responses that amplify anti-tumor or immunomodulatory activity.
These developments are extending the boundaries of what ACTs can treat. While early clinical success has been most pronounced in blood cancers, many of the most common and lethal cancers present a far more complex challenge.
Solid tumors in particular behave less like static targets and more like evolving ecosystems. Physical barriers can restrict immune cell infiltration, while immunosuppressive signalling within the tumor microenvironment dampens T cell activity and drives exhaustion. Even when engineered cells reach their target, tumors can adapt under therapeutic pressure — losing antigen expression, rewiring signalling pathways, or reshaping their immune landscape to evade detection.
The manufacturing bottleneck
Despite rapid scientific progress, scalability remains a major obstacle. Unlike many traditional drugs, living therapies require complex manufacturing workflows, skilled personnel, and tightly controlled infrastructure.
Cells need to be extracted, genetically modified, expanded under good manufacturing practice conditions, and reinfused — a process that can take weeks and cost hundreds of thousands of dollars per patient, limiting scalability. Additionally, many of these steps are still done manually, limiting throughput and driving up costs.
“That creates a real challenge for global access,” Pont noted. “We need trained people, robust infrastructure, and better ways to reduce the cost of goods if these therapies are going to reach patients widely.”
Beyond the traditional drug paradigm
Living drugs are not just a new category of therapy. They are forcing a redefinition of what drug discovery means. They blur the boundary between drug and system, between intervention and ongoing biological process. They collapse traditional silos in development. And they demand new thinking in manufacturing, regulation, and clinical design.
The defining question is no longer whether living drugs work. It is how far they can be pushed as a therapeutic system — and whether healthcare systems can adapt quickly enough to deliver them safely, efficiently, and at scale.
Watch our interview with Margot Pont, Vice President of Translational Development at Integra Therapeutics:
