Thytech has successfully developed a pioneering cell therapy to prevent rejection in infant heart transplant recipients. The startup is now seeking to expand its applications to treat autoimmune diseases in adults.

Congenital heart defects affect one in every 100 newborns. They are the most common birth-related conditions in Spain, with around 4,000 new cases each year. Seventy percent of affected babies undergo surgery before their first birthday, most within the first three months of life. While these procedures generally have a good prognosis, the most severe cases may require a transplant.

Irene was one of those cases. Born during the pandemic at the Hospital General Universitario Gregorio Marañón, she underwent a heart transplant at just six months old. The first months after surgery are the riskiest, as the likelihood of rejection is highest. At that time, a new cell therapy designed to regulate the immune response in transplant patients had just received approval to begin its first clinical trials.

This pioneering therapy was developed by Thytech, a spin-off of the Gregorio Marañón Health Research Institute (IISGM) focused on treating diseases related to immune dysfunction. The goal was to prevent rejection of the transplanted organ — and Irene became the first baby in the world to receive it. Three years later, she has shown no signs of rejection.

“She’s a child who now goes to school and her progress has been wonderful. She’s in perfect health, and after her, we’ve treated seven more babies with this therapy, with no adverse events,” explains Dr. Rafael Correa Rocha, one of Thytech’s four founders, alongside Marta Martínez Bonet, Marjorie Pion, and Esther Bernaldo de Quirós.

“The immune system, which protects us from pathogens and other threats, can under certain circumstances also cause disease. It is responsible for transplant rejection, allergies, and autoimmune diseases. These processes can become very serious and are highly prevalent. Until now, the only available treatment has been immunosuppressive drugs that suppress all immune defenses,” says Correa.

Thytech’s innovative therapy emerged “as an attempt to find alternatives to immunosuppressants. The originality of our approach lies in using cells — and the body’s own natural mechanisms — rather than chemical molecules to tackle these diseases.”

The Secret Lies in the Thymus

The thymus is a small organ located in the upper chest whose primary function is to produce T lymphocytes, including a subtype called regulatory T cells (Treg cells). These cells are essential mediators of immune responses because “in healthy individuals, they prevent allergies and autoimmune processes,” Correa explains.

During childhood, the thymus produces the T lymphocytes needed for life. Once generated, they enter peripheral blood and remain distributed throughout the body for decades.

The thymus is often discarded during infant cardiac surgeries because it is proportionally larger in babies than in adults, and surgeons must remove it to access the heart.

“At Thytech, we realized we could make use of this discarded tissue and explore whether it could be turned into a cell therapy. What surprised us was the enormous quantity of regulatory cells present in this tissue — with unique characteristics. These are cells taken directly from the ‘factory,’ before they age in peripheral blood.”

These thymus-derived Treg cells are more potent, can be cultured and expanded, and allow for the production of large numbers of therapeutic doses. Thytech estimates that around 500 thymuses are discarded annually in Spain. “If each thymus can yield hundreds of doses, in our hospital alone — where 100 thymuses are discarded each year — thousands of doses could be produced annually,” Correa notes.

Once produced, the cells are reintroduced into the patient to modulate immune response and prevent the body from recognizing the transplanted organ as foreign. So far, a single administration of Thytech’s therapy has successfully prevented immune rejection of transplanted hearts in children.

From Transplants to Autoimmune Diseases

The therapy continues to be used in infant transplant recipients, and Thytech aims to treat 15 babies in the first phase of its clinical trial. At the same time, the company is exploring its use in adult autoimmune diseases. In 2025, the first clinical trial has been approved to test the therapy in Crohn’s disease, an autoimmune condition affecting the digestive tract.

“Our initial goal was to treat children with heart transplants using these cells. We demonstrated the therapy was feasible and safe. Now we want to leverage this mechanism to treat other diseases,” says Correa.

The major challenge ahead is scaling production: harvesting cells from discarded thymus tissue, producing hundreds of doses, and storing them frozen and ready for use when patients need them.

Could cells from a baby treat an adult’s disease? According to Correa, thymus-derived cells are so immature that they are “invisible” to the immune system. When administered to adults, they are not recognized as foreign because they do not yet express the defining characteristics of mature cells.

This allogeneic use of cells dramatically expands the therapy’s potential. Unlike many cell therapies that require personalized manufacturing for each patient — such as CAR-T treatments for cancer — Thytech can generate thousands of doses from a single donor. From half a liter of blood, only around 10 million regulatory cells can be obtained; from a single thymus, up to 10 billion cells have been achieved.

From Laboratory to Company

Turning scientific research into a company is no small step. Thytech’s goal is to bring this therapy beyond infant heart transplants and make it accessible to both children and adults across multiple diseases.

Developing such a therapy is long and expensive, requiring clinical trials, regulatory approvals, and industrial-scale manufacturing. “The cost makes it impossible to develop solely within an academic lab,” explains Correa. “That’s why we created Thytech S.L., to attract private investment and industrialize the therapy.”

Private funding came through Banco Sabadell via its BStartup program, alongside contributions from friends, family, and a business angel. The funding enabled Thytech to secure intellectual property, hire regulatory experts, scale manufacturing processes, and build partnerships with pharmaceutical companies.

In biomedicine, it can take a decade before a product reaches commercialization. “You may not generate revenue for five or ten years, but you need significant capital to develop it. Programs like Banco Sabadell’s, along with public grants, have been essential in positioning our technology as attractive to investors and pharmaceutical partners,” Correa concludes.

Thytech’s journey — from discarded surgical tissue to a potential platform therapy for transplants and autoimmune diseases — reflects a shift in medicine: harnessing the body’s own regulatory mechanisms to restore immune balance rather than suppress it.

More info: elespanol.com