Syanne Landron just turned two, and she spent her birthday the same way she has spent most of her short life: inside a hospital room, surrounded by doctors and nurses instead of friends her own age. Born without a functioning immune system, the toddler has now been hospitalized for six weeks at UCLA Mattel Children's Hospital, where her body has not developed the infection-fighting T cells her medical team had hoped to see by now.
Syanne's condition traces back to a routine screening days after her August 2024 birth, when California's mandatory newborn blood panel flagged an absence of T cells, a hallmark of severe immune deficiency. According to BioPharm International, that screening tool, which uses T-cell receptor excision circle assays, has been used to test all California newborns for severe combined immunodeficiency since 2010. Doctors eventually diagnosed Syanne with congenital athymia, an ultra-rare condition affecting an estimated 17 to 24 newborns nationwide each year, in which infants are born without a functioning thymus gland and cannot naturally produce T cells to fight infection.
As CBS News Los Angeles reports, Syanne received a thymus implant intended to help her body produce those infection-fighting T cells on its own. Any exposure to germs or infection could still prove fatal for the toddler, whose family has lived in near-total isolation for two years near Santa Clarita. The outlet's report, written by Laurie Perez, notes that Syanne's body has not rejected the transplant itself, even though her immune system has developed less than doctors had hoped.
A Cross-Country Trip for a One-Of-A-Kind Treatment
Syanne's transplant came from Rethymic, the only FDA-approved regenerative tissue therapy for immune reconstitution in children with congenital athymia, according to a statement from Sumitomo Pharma, which developed the therapy over nearly three decades of research led by Dr. M. Louise Markert at Duke University. The federal agency approved the treatment in October 2021. Duke University Hospital in Durham, North Carolina, remains the only medical center in the country that performs the cultured thymus tissue implantation, per Duke Health, which meant the Landron family had to travel across the country for the surgery itself.
Before that trip, the family relocated from Ventura to Canyon Country in the Santa Clarita Valley to stay closer to UCLA Mattel Children's Hospital for urgent medical care, as the Santa Clarita Valley Signal reported in May 2025. Syanne's father serves in the U.S. Navy, and her mother paused her middle school teaching career in Oxnard to help maintain the strict isolation protocols her daughter's condition required. The wholesale cost of Rethymic runs approximately $2.7 million, and the family received official medical and financial approval for the transplant in May 2025, before Syanne could travel for the procedure.
Doctors Call Reaching Age Two Remarkable
Dr. Caroline Kuo, Syanne's primary care physician at UCLA Mattel Children's Hospital and an associate professor specializing in pediatric allergy, immunology, and gene therapy research, said Syanne reaching her second birthday is remarkable. Long-term clinical trial data submitted for the therapy's FDA approval showed that 21 of 95 treatment-naive athymic infants died within their first year after implantation, but those who survived past that milestone achieved a 94% long-term survival rate over a median follow-up of more than a decade. Doctors and nurses joined Syanne's second-birthday party at the hospital, even as she celebrated the milestone in isolation rather than at home.
The lag in Syanne's immune development falls within a known biological window. It typically takes six to 12 months for implanted thymus tissue to begin producing new T cells, according to Duke Health, a delay that leaves patients severely immunocompromised and vulnerable to life-threatening infections during the transition. The U.S. Food and Drug Administration has also identified specific risks tied to the non-vascularized tissue implants, including graft-versus-host disease, cytokine release syndrome, autoimmune complications, and low blood magnesium or platelet levels, all of which doctors continue to monitor during Syanne's hospital stays.
A Rollercoaster That Has Not Let Up
Syanne's father, Alex Landron, described his daughter's medical experience as a rollercoaster. Her mother, Marilyn Landron, said their life is not like everybody else's, and recalled that Syanne has told her she wanted the procedures to stop, a sign that even at two years old, the toddler can verbalize her pain. Marilyn Landron also said a second transplant chance for children like Syanne is uncommon, underscoring how much rides on her daughter's fragile recovery.
Doctors are now waiting to see how Syanne's condition develops further, and she is set to undergo more hospital tests in the days ahead. Per the article, Syanne has not had the expected immune-system development doctors were hoping for at this stage of her recovery. For now, her family remains in the same holding pattern they have lived in for two years, watching for the moment her body finally begins to fight back on its own.
