NK Cell Therapy Side Effects and What to Ask in Osaka, Japan

Hello, I am Dr. Hidenori Shimada of Grand Green Osaka Umekita Clinic in Osaka, Japan.

If you are considering NK cell therapy, one of the first practical questions is what you might feel during and after treatment. Because the therapy returns your own immune cells to your body, many people wonder whether side effects are expected, how long they last, and who to contact if something changes. This article explains, in general terms, what is known about possible reactions and what international patients can ask at Grand Green Osaka Umekita Clinic in Osaka, Japan.

In short, the clinic’s information describes temporary fever or fatigue as possible reactions, and notes that serious side effects have rarely been reported. That does not mean that no reaction can occur. What you may experience depends on your own condition, and a doctor needs to assess that individually.

Why people ask about side effects with NK cell therapy

NK (natural killer) cells are a type of lymphocyte that circulates in the blood and helps detect abnormal cells. In NK cell therapy, cells obtained from a standard blood draw are activated and expanded at a specialized cell processing facility, then returned by intravenous (IV) infusion. Because the cells come from you, an autologous approach, the concern about rejection is generally considered lower than with cells from another person.

Still, any treatment that involves a blood draw, laboratory processing and an infusion carries some uncertainty. Patients who are already managing cancer, or who are recovering from cancer treatment, often have fatigue, appetite changes or other symptoms of their own. It is therefore reasonable to want a clear picture before you travel or schedule a visit.

What reactions have been described

According to the clinic’s treatment information, temporary fever or fatigue may occur after treatment. In general, reactions to an IV infusion of cells can also include mild discomfort at the needle site or a short-lived feeling of being unwell. These descriptions are general and should not be read as a prediction for any one person.

Published reports on autologous NK cell infusions, which you can search in PubMed, have generally described a limited range of reactions in the studies reviewed. However, studies differ in the cell preparation methods, the cancer types and the patient groups involved, and a single report cannot be applied to everyone. Your doctor can explain how the available evidence relates to your situation, including its limits.

• Temporary fever or a feeling of fatigue after infusion
• Mild discomfort related to the blood draw or the IV needle
• Other changes in how you feel, which should be reported to the medical team promptly

How your own condition and other treatments fit in

NK cell therapy is described as something that can be considered alongside standard cancer treatment such as surgery, chemotherapy or radiation therapy, and the clinic says it can coordinate with the institution providing your standard care. Symptoms you notice may not come from one cause alone. Fatigue, for example, can be related to the underlying illness, to other treatments, to travel, or to the therapy itself.

For this reason, it is helpful to bring your treatment history, recent test results and a list of current medicines to your consultation. Standard treatment remains the foundation of cancer care, and NK cell therapy should not be understood as a replacement for it. Decisions about timing and combination should be made with your doctors.

How treatment is managed under Japanese law

In Japan, cell therapies of this kind are provided under the Act on the Safety of Regenerative Medicine, through a treatment plan submitted to and accepted by the authorities. This framework sets expectations for how cells are processed and how treatment is carried out. It is a system for managing safety, but it does not remove the possibility of side effects, and it does not guarantee any treatment result.

NK cell therapy at the clinic is provided as a self-pay treatment, which means it is not covered by public health insurance. Costs, number of sessions, possible risks and side effects, and whether the therapy is suitable for you must all be confirmed in a medical consultation.

Questions international patients can ask before treatment

If you are visiting from overseas, it can help to write your questions down in advance. Grand Green Osaka Umekita Clinic is located in Umeda, Osaka, and offers a dedicated information page for international patients in multiple languages, so you can review the basics before contacting the clinic.

• Which reactions have been seen with this therapy, and how long do they usually last?
• What should I do if I develop a fever or other symptoms after returning to my hotel or home country?
• How can the clinic coordinate with my current doctors, and what records should I bring?
• Are there conditions or medicines that make this therapy less suitable for me?
• What are the total costs, the number of visits and the expected schedule?
• What are the limits of this therapy, and what outcomes should I not expect?

Because aftercare may continue once you leave Japan, ask in advance how follow-up questions are handled and in which language. Clear communication about symptoms is an important part of any treatment plan.

Key points to remember

NK cell therapy uses your own cells, and the clinic’s information describes temporary fever or fatigue as possible reactions. Even so, individual responses vary, evidence has limits, and the therapy is a self-pay option that does not replace standard cancer treatment. A doctor’s examination is needed to decide whether it is appropriate for you.

If you would like to know more, the NK cell therapy page of Grand Green Osaka Umekita Clinic explains the treatment flow, fees and frequently asked questions, and you can request a consultation to discuss your own circumstances with a physician.

• Ask about reactionsTemporary fever or fatigue may occur
• Standard care stays centralNot a replacement for it
• Japanese legal frameworkSelf-pay, plan accepted by authorities
• Plan aftercare abroadConfirm follow-up and language

This figure is a conceptual diagram that organizes the content of the article

References

• PubMed: Efficacy and safety of allogeneic CD19 CAR NK-cell therapy in systemic lupus erythematosus: a case series in China. (2026)
• PubMed: Optimizing CAR-NK Cell Transduction and Expansion: Leveraging Cytokine Modulation for Enhanced Performance. (2024)
• PubMed: CYAD-01, an autologous NKG2D-based CAR T-cell therapy, in relapsed or refractory acute myeloid leukaemia and myelodysplastic syndromes or multiple myeloma (THINK): haematological cohorts of the dose escalation segment of a phase 1 trial. (2023)
• PubMed: A Phase I Study of Locoregional High-Dose Autologous Natural Killer Cell Therapy With Hepatic Arterial Infusion Chemotherapy in Patients With Locally Advanced Hepatocellular Carcinoma. (2022)
• PubMed: Autologous stem cell transplant recipients tolerate haploidentical related-donor natural killer cell-enriched infusions. (2013)
• PMC: Autologous stem cell transplant recipients tolerate haploidentical related-donor natural killer cell-enriched infusions. (2013)
• PMC: Ex vivo-expanded natural killer cells demonstrate robust proliferation in vivo in high-risk relapsed multiple myeloma patients. (2015)
• PMC: Purification and antibody-free ex-vivo expansion of peripheral blood-derived autologous natural killer cells: A Malaysian case series on patient safety and tolerability. (2026)
• MHLW (Japan): Regenerative Medicine — Ministry of Health, Labour and Welfare, Japan

Supervising Physician

Director, Medical Corporation Shimada Clinic
Head of Clinical Practice, Grand Green Osaka Umekita Clinic

Hidenori Shimada

Graduated from the University of Tokushima Faculty of Medicine in 2005. After his initial residency, he obtained U.S. medical certification (ECFMG) and trained as a sub-intern in general surgery at the University of Washington. After completing the doctoral program at Kyoto University Graduate School of Medicine and working as a researcher at the Center for iPS Cell Research and Application (CiRA), Kyoto University, he founded Shimada Clinic in 2013. At Grand Green Osaka Umekita Clinic (https://umekitaclinic.org), he is engaged in a wide range of care, from internal medicine and pediatrics to cell therapy and aesthetic medicine.

* The physician supervision of this article covers its academic content only and does not constitute a recommendation of any specific treatment or product.