Four children with thalassemia, a severe genetic blood disorder, have been successfully cured using a domestically developed DNA base editing therapy in China. The breakthrough treatment represents a significant advancement in gene therapy approaches for hereditary conditions.
The clinical research, led by hematologist Professor Zhai Xiaowen at the Children's Hospital of Fudan University in Shanghai, involved administering a single injection of CS-101, an experimental drug developed by CorrectSequence Therapeutics, a biotech firm affiliated with ShanghaiTech University.
Remarkable Clinical Outcomes
The treatment has shown remarkable efficacy across all four pediatric patients—three from China and one from Pakistan. In December 2024, a 14-year-old boy from Jiangxi province became the first patient cured in the trial, showing complete recovery just five weeks after treatment. The most recent case involved a 4-year-old girl from Pakistan who received the injection in January 2025 and was deemed cured after three months.
CS-101 utilizes a transformer base editor (tBE) technology to correct the specific DNA mutation causing thalassemia, effectively restoring normal hemoglobin function. This approach represents a significant advancement over existing treatment options.
Understanding Thalassemia
Thalassemia damages hemoglobin—the protein in red blood cells responsible for oxygen transport—severely reducing the body's ability to deliver oxygen efficiently throughout the system. Patients typically experience fatigue, weakness, stunted growth, and facial bone deformities, with symptoms usually appearing in early childhood.
The condition is particularly prevalent in regions historically affected by malaria, earning it the alternative name "Mediterranean anemia." It is also common throughout Southeast Asia and southern China, especially in Guangdong province and the neighboring Guangxi Zhuang Autonomous Region.
According to a 2020 report, approximately 30 million people in China carry some form of the thalassemia gene, making it one of the most common hereditary blood disorders in the country. Around 300,000 individuals currently live with moderate to severe forms of the disease, with patient numbers increasing by roughly 10% annually.
Disease Classification and Prognosis
Thalassemia is classified into two main types—alpha and beta—depending on which part of the hemoglobin molecule is affected. Each type is further categorized as mild, intermediate, or severe based on symptom intensity and impact.
The prognosis for untreated severe cases is grim. Many infants with severe alpha thalassemia die before or shortly after birth, while patients with severe beta thalassemia who do not receive timely intervention have an average life expectancy of just 15 years.
Traditional Treatment Limitations
Prior to the development of CS-101, treatment options for severe beta thalassemia were limited to two invasive approaches: regular, lifelong blood transfusions or a one-time stem cell or bone marrow transplant, costing between 300,000 and 600,000 yuan ($41,500-83,000). However, transplants remain largely inaccessible due to low donor compatibility rates and significant surgical risks.
The Science Behind Base Editing
Base editing represents a significant advancement over earlier gene editing technologies. Gao Caixia, a geneticist at the Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, explained the approach using a simple analogy: "If one of the four DNA letters—A, T, C, and G—is wrong, you can think of it like using an eraser to remove it, then writing in the correct letter with a pencil."
This method offers greater precision than previous gene editing approaches and reduces the risk of unintended consequences. According to CorrectSequence Therapeutics, the technology "avoids risks such as large-scale DNA deletions, chromosomal mutations, and off-target effects, demonstrating better efficacy and safety."
Development Timeline and Regulatory Progress
The development of CS-101 has progressed rapidly. Professor Zhai's team began collaborating with CorrectSequence Therapeutics in 2023, initially conducting an investigator-initiated trial (IIT)—a small-scale study used to test promising therapies prior to formal regulatory approval.
In January 2024, CorrectSequence partnered with Guangxi Medical University for additional IITs, successfully curing a minor with severe thalassemia—the first successful case using base editing treatment. An adult patient who received the same treatment was later reported to be recovering.
The therapy reached a significant milestone in April 2024 when the CS-101 injection received official approval from China's National Medical Products Administration (NMPA) to begin formal, larger-scale clinical trials. Parallel trials are also underway in the United States and United Kingdom.
Future Considerations
Despite the promising results, scientists maintain a cautious outlook regarding the long-term implications of such gene therapies. Researchers note that the thalassemia gene may have been naturally selected for its malaria-resistant properties, raising questions about potential unforeseen consequences of its removal.
This concern has prompted calls for at least a decade of long-term monitoring and analysis following treatment to fully understand any potential long-term effects.
The successful treatment of these four children represents a significant milestone in genetic medicine and offers new hope for the hundreds of thousands of patients worldwide suffering from this debilitating condition.
