4 days ago
This startup's mission to extend human life sounds like sci-fi, and investors are betting $20M on it
Startup profile: Tolerance Bio
Founded by: Francisco Leon
Year founded: 2023
Headquarters: Philadelphia, PA
Sector: Life sciences
Funding and valuation: $20.2 million raised at an undisclosed valuation, according to the company
Key ecosystem partners: Columbus Venture Partners, Ben Franklin Technology Partners
When Francisco Leon talks about the medical science behind the biotech company he founded in 2023, it sounds like something out of a movie.
The company, Tolerance Bio, focuses on preserving the body's immune system by restoring the function of an organ called the thymus. The organ, long believed to be as useful in adults as the appendix (that is, not at all), may actually be the key to slower aging and prolonged life spans.
'Immune tolerance is at the core of almost all medical needs,' Leon told
Now, Tolerance Bio is moving toward the first trials of its proprietary stem cell therapy, focusing first on children born without a thymus.
The thymus, a small gland located behind the breastbone in the upper chest, controls immune tolerance by creating T-cells, white blood cells that fight infections and cancerous cells, and can also prevent the body from attacking healthy cells.
It's a vital organ, but even in a perfectly healthy person, it only functions at 100% for the first two years of life, and then, Leon said, it starts to shrink.
By adulthood, the thymus functions at just 10%, which is why the medical community didn't think it was needed in adults.
That changed in 2023, when an article published in the New England Journal of Medicine concluded that the surgical removal of the residue of the thymus in adults led to an increase in the five-year mortality rates due to cancer and autoimmunity.
Subsequent research in nursing homes, Leon said, found that the better the thymic function, the lower the incidence of cancer, autoimmunity and infection.
'That's why we started the company,' Leon said, 'we are trying to restore thymic function.'
From genetic diseases to anti-aging
One of the main focuses of Tolerance Bio's research and development is using its cell implantation therapy to cure DiGeorge syndrome, also known as 22q11.2 deletion syndrome, a genetic condition where a baby is born without a thymus, or with one that is underdeveloped. Children with this condition struggle to fight infections and often have heart problems or other serious medical issues.
Restoring the thymus has the potential to save babies who, with cases of complete DiGeorge syndrome, have a life expectancy of two to three years without medical intervention.
Since the thymus naturally loses functionality as a person ages, Leon and his team also aim to develop treatments for adults, including a drug for healthy people that could potentially delay aging and increase longevity.
'We can regenerate the thymus by implanting cells intramuscularly; it's a new science,' Leon said.
It's yet to be proven in humans, but if they can show the principle in human patients, he said, they can potentially apply it to other conditions, including Type 1 diabetes, cancer, organ diseases, other immune deficiencies, and, potentially, Alzheimer's disease.
A $20 million seed round
Leon, who leads a hybrid team of 10 from Tolerance Bio headquarters at the B+labs incubator at the Cira Centre in Philadelphia, is an immunologist who came to the US from Spain 25 years ago.
After starting out working for pharmaceutical companies, including helping to develop drugs in immunology and oncology, he became an entrepreneur, cofounding the drug development companies Celimmune (acquired by Amgen in 2017) and Provention (acquired by Sanofi in 2023). Provention developed the drug Tzield, which can delay the onset of Type 1 diabetes in at-risk patients.
'It was the first drug ever to delay the onset of an autoimmune disease,' Leon said. 'You give it to children that show signs of being about to become diabetic, but still don't need insulin.'
By the time Sanofi acquired Provention, Leon was ready to turn his focus to preventing and regenerating the thymus. He started Tolerance Bio, initially as a concept, bringing two members of the Provention team with him and partnering with University of Florida academic Holger Russ as Tolerance Bio's scientific cofounder.
Tolerance Bio closed a $20.2 million seed round in December 2024. Led by Columbus Venture Partners, it included Ben Franklin Technology Partners, Criteria Bio Ventures, Sessa Capital, BioAdvance, Pacific 8 Ventures and individual biotechnology investors with an interest in thymus regeneration.
'We now know that thymic evolution is the main limiter of human life — it is the beginning of aging,' Leon said. 'There is a strong correlation between thymic function and longevity in humans and animals.'
'This almost sounds like science fiction'
Even the Tolerance Bio team is amazed at the potential.
'This almost sounds like science fiction, in some respects,' said Phil Ball, Tolerance Bio's SVP and head of business development and operations, who previously worked with Leon at Provention. 'The technology that science needed to get to this point is, even for me, who's worked in the industry for so long, is absolutely amazing.'
Translating that technology into actual products that reach as many patients as possible is a priority for the team.
'Ultimately, if we don't have approved products, it's been wasted time,' said Ball, who has spent 25 years in the industry, starting in the UK, where he worked for small biotech companies before moving to the US and eventually settling in Chapel Hill, North Carolina.
The team's expert on scaling up clinical manufacturing, Poh Yeh-Chuin, is based in Cambridge, Massachusetts. He previously worked for Beam Therapeutics, where he led a cell process development group that developed products currently being manufactured — one, a stem cell program for sickle cell disease, the other a CAR-T therapy program for cancer treatment.
Prior to that, he was part of the startup Semma Therapeutics (since acquired by Vertex), helping to develop a Type 1 diabetes treatment using pancreatic stem cells.
'It's very related to the work that we're doing here at Tolerance,' Poh said. 'Especially the cell therapy part, because both the pancreas as well as the thymus are derived from what we call the endoderm lineage.'
Simply put, the endocrine system — including the pancreas, the thymus and the thyroid — comes from the same type of embryonic cells, which can be used in the treatment of endocrine disorders.
Justin Vogel, Tolerance's chief financial officer and the other former Provention team member, grew up at the Jersey Shore and still lives in New Jersey. While the team is spread out, Vogel frequently comes to work at the Philadelphia office.
While much of what they do at Tolerance Bio is focused on complex biotechnology, Vogel also stressed the importance of getting involved with the people and organizations they are trying to help. Members of the team attended the recent 22q at The Zoo event in Philadelphia, part of a global awareness event held at zoos around the world led by the International 22q11.2 Foundation.
'We're a very patient-focused organization,' Vogel said. 'It's so important to hear all the stories and meet the families, and it really resonates with us and gives meaning to what we try to do for these kids.'
