How a 17‑Year‑Old’s Immunotherapy Success Is Shaping the Future of Pediatric Cancer Care
When Mailo Grühn from Thuringia was diagnosed with a malignant kidney tumor at age seven, doctors removed the primary growth and launched conventional chemotherapy. Two years later the disease had spread to his liver, spleen, lungs and brain. By early 2025, after ten years of battling cancer, the prognosis was bleak – physicians gave him only three months to live.
Why Mailo’s Case Was Different
At the Hopp‑Kidney Tumor Center (KiTZ) in Heidelberg, oncologist Christian Seitz discovered that all of Mailo’s tumor cells expressed the protein PRAME. This marker opened the door to a cellular immunotherapy that had never before been used on a child with a solid tumor.
Mailo’s own T‑cells were harvested, genetically re‑programmed with a viral vector to express a receptor that recognises PRAME, and reinfused on 2 July 2025. Within days he developed a high fever – a sign that the engineered T‑cells were proliferating – and twelve days later the first MRI showed that visible tumor lesions had vanished. After 120 days, no living tumor tissue could be detected in scans or blood samples.
From “Last Resort” to “New Standard” – Emerging Trends
- Targeted protein markers: PRAME is only one of many tumour‑associated antigens being screened for in pediatric cancers. Identifying such markers enables personalised cell therapies.
- Regulatory pathways for “single‑patient trials”: Mailo’s treatment required a special exemption for a “Einzelheilversuch” (single‑patient compassionate use). Streamlining this process could accelerate access for other children.
- Expansion beyond blood cancers: Although cellular immunotherapy is already approved for adult leukaemia, Mailo’s success demonstrates its potential for solid tumours in adolescents.
- Clinical‑study pipelines: KiTZ is preparing a study with 15‑18 young patients to verify whether Mailo’s outcome can be replicated.
Key Challenges on the Road Ahead
Even with promising results, several hurdles remain:
- Manufacturing complexity – each therapy is custom‑made from a patient’s own cells.
- Risk of cytokine‑release syndrome, where an overactive immune response can endanger the patient.
- Limited data on long‑term effects in children, especially regarding growth and development.
Pro Tip for Parents and Caregivers
If your child faces a relapse, inquire the treating team whether their tumour expresses any known antigens (e.g., PRAME, HER2) and whether a targeted immunotherapy trial is available. Early molecular profiling can open doors to experimental options before standard therapies run out.
Frequently Asked Questions
- What is PRAME?
- PRAME (Preferentially Expressed Antigen in Melanoma) is a protein found on certain cancer cells that can be recognised by engineered T‑cells.
- Is cellular immunotherapy only for adults?
- No. While most approved cell therapies target adult leukaemia, Mailo’s case shows they can be adapted for solid tumours in adolescents.
- How long does it take to prepare the engineered T‑cells?
- In Mailo’s treatment the cells were infused within a few weeks after blood collection.
- What are the main side effects?
- Patients may experience fever, flu‑like symptoms, or more severe cytokine‑release syndrome. intensive monitoring is essential.
Where to Find More Information
Read the full German report on Mailo’s breakthrough on RP‑Online and the detailed analysis on Tagesspiegel. For broader statistics on childhood cancer in Germany, visit the Thüringische Krebsgesellschaft.
What’s Next?
Mailo now aims to finish his secondary school exams and study medicine in Heidelberg. His story fuels optimism that personalized cell therapies will turn into a regular part of paediatric oncology, offering hope where traditional treatments have failed.
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