When Mailo was 7 years old, doctors found a tumor growing in his kidney. For the next ten years, the cancer kept coming back, spreading to his lungs, liver, pelvis, and even his brain. By the time he was 17, Mailo had run out of treatment options. No clinical trials could help him. His doctors had one last idea: reprogram his own immune cells to hunt down the cancer.
In July 2025, Mailo received an infusion of his own T cells — immune cells that had been genetically engineered in a laboratory to recognize a protein called PRAME, which was present on his cancer cells. The modified cells were made at the National Center for Tumor Diseases in Heidelberg, Germany, using a genetic tool provided by Immatics, a biotechnology company in Tübingen. The entire manufacturing process took just seven days.
Nine days after Mailo received the infusion, doctors did a biopsy and found something remarkable: immune cells had flooded into the tumor, and cancer cells were dying. Over the following weeks and months, the disease retreated from every organ it had invaded. Three months after treatment, a second biopsy showed no living tumor cells anywhere. Imaging scans and blood tests confirmed what seemed impossible: Mailo's cancer was gone.
Nearly one year later, Mailo is doing things any teenager should do. He trains regularly, competes in cycling races, finished his vocational training, and is now planning to earn his Abitur — the German equivalent of a high school diploma. His doctor, Christian Seitz of the Hopp Children's Cancer Center Heidelberg (KiTZ) and Heidelberg University Hospital, described Mailo's condition as excellent.
The treatment worked because researchers identified that Mailo's cancer carried the PRAME protein, a target already well-studied in adult cancers like melanoma. Immatics had developed a way to engineer T cells to attack cells carrying this marker, and their adult clinical trials had shown promising results. Mailo's team decided to try the same approach in a teenager with no other options.
The case was published in the New England Journal of Medicine and is now inspiring a larger clinical trial called PRAMEtime, expected to begin enrolling children and adolescents with PRAME-positive tumors in 2027. The trial will manufacture personalized T-cell therapies for multiple patients, building on what worked for Mailo. Researchers say the story shows how partnerships between university hospitals and biotech companies can bring experimental treatments to the young patients who need them most.
For Mailo, the future looks nothing like the one he faced two years ago.