On August 18, 2026, in Japan, the Department of New Experimental Therapeutics and Early-Phase 1 Drug Development Service at Kansai Medical University Hospital, led by Professor Toshio SHIMIZU, administered DS1025 to the first patient worldwide as part of a global, multicenter First-in-Human Phase 1 clinical trial sponsored by Daiichi Sankyo. This Global First Patient First Dose milestone makes Kansai Medical University Hospital the first clinical trial site anywhere in the world to administer this potential first-in-class CD25-directed ADC to a patient.
DS1025 is directed to recognize and bind to CD25 on immunosuppressive regulatory T cells (Treg cells) and deliver an immuno-oncology optimized cytotoxic payload. Treg cells are immune cells that normally help control excessive immune activity, preventing issues like allergic reactions and excessive inflammation. Within tumors, however, Treg cells can accumulate and block the body’s immune response. By suppressing the immune system’s ability to recognize tumors and attacking them, Treg cells act as a shield for cancer cells, helping them spread.
Treg cells, including those found in tumor tissue, carry high levels of a surface protein called CD25, making it an important marker in cancer immunotherapy. Assessing its potential as a promising therapeutic target to combat tumor immunosuppression, DS1025, is an investigational, potential first-in-class CD25 directed that builds on the DXd ADC Technology of Daiichi Sankyo.
By targeting immunosuppressive Treg cells in the tumor microenvironment, DS1025 is intended to reduce a mechanism that can limit the body's immune response against cancer. The approach is investigational, and the outcomes of this clinical trial will determine whether DS1025 can be suitable for further clinical development.
This Phase 1 trial is the first stage of clinical testing in humans and is primarily designed to assess the safety and tolerability of DS1025 and identify a dose suitable for further clinical development. Participants will be monitored closely as researchers gradually increase the dose across groups, looking for dose-limiting toxicities and other adverse events. The study will also examine how DS1025 behaves in the body, including its pharmacokinetic and pharmacodynamic characteristics, and will assess biological markers and preliminary signs of antitumor activity. At this stage, the study is not intended to establish DS1025’s efficacy or confirm its safety for routine clinical use. DS1025 is an investigational medicine and has not been approved for any indication. Its safety and efficacy have not been established.
The trial is expected to enroll up to 45 adults with advanced, metastatic, or unresectable solid tumors who have experienced disease progression following at least one line of standard treatment and for whom further standard treatment is not suitable. Clinical sites are located across Asia, including Japan, and Europe, making the study an international effort to investigate DS1025 in patients with advanced solid tumors.
For Kansai Medical University Hospital, achieving the Global First Patient First Dose milestone also reflects its growing role in early-stage international cancer drug development. While early clinical development requires same level of developmental speed globally, access to Phase 1 clinical trials for new drugs has been limited in Japan. The establishment of Department of New Experimental Therapeutics at Kansai Medical University Hospital in November 2024 has strengthened the ability to conduct early-phase clinical trials of new cancer treatments in Japan. Since February 2025, the department has conducted multiple international collaborative Phase 1 trials, including First-in-Human studies of investigational cancer drugs.
Through its collaboration with Daiichi Sankyo and other domestic and international partners, Kansai Medical University will continue to contribute to early-stage clinical research and the development of new approaches to cancer treatment.
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About Kansai Medical University
Kansai Medical University (KMU) is a private medical university in Osaka, Japan. Originally established in 1928 as Osaka Women’s Medical College, KMU became co-educational and adopted its current name in 1954. Guided by its founding spirit of Jijinshinkyo—“Benevolence, Compassion, and Empathy”—the university fosters skilled medical professionals across its faculties of Medicine, Nursing, and Rehabilitation. Today, KMU operates an extensive network including four affiliated hospitals, advanced institutes like the Near InfraRed Photo-ImmunoTherapy (NIR-PIT) Research Institute, and global facilities such as the KMU Tower. Approaching its one-hundredth anniversary in 2028, KMU continues to advance medical education, clinical research, and public health.
Website: https://www.kmu.ac.jp/en/index.html