Hello, I am Dr. Hidenori Shimada of Grand Green Osaka Umekita Clinic in Osaka, Japan.
When people first read about NK cell therapy, one of the earliest questions is usually about side effects. It is a sensible place to start. Any medical treatment carries some degree of uncertainty, and a good decision begins with a clear picture of what is known, what is not known, and what your own doctor can tell you about your situation. This article explains how side effects and risks are generally discussed for NK cell therapy and suggests questions you can bring to a consultation at Grand Green Osaka Umekita Clinic in Osaka (Umeda).
The short answer: what to expect from the conversation
NK cell therapy uses your own natural killer cells. A blood sample is taken, the NK cells are activated and expanded at a specialized facility, and they are returned to you by intravenous infusion. Because the cells come from you, the risk of rejection is considered low, and serious side effects have rarely been reported. However, “rarely reported” is not the same as “none”. Temporary reactions such as fever or fatigue may occur, and every patient’s situation is different. The most useful step is a frank discussion with a physician who knows your medical history.
Please also keep in mind that NK cell therapy is offered in Japan as a self-pay (non-insured) treatment. It is not a replacement for standard cancer treatment, and it does not promise any particular outcome. The aim of this article is to help you prepare better questions, not to predict how you would respond.
Why using your own cells matters for risk discussions
The term for this approach is autologous therapy, meaning the cells come from the same person who receives them. In many other kinds of cell or organ treatment, the body’s immune system may react against donor material. With autologous cells, that particular concern is much smaller. This is one reason the therapy is described as relatively gentle on the body.
That said, using your own cells does not remove every question. The cells are handled outside the body for a period of time, so the quality of the processing facility, the testing carried out on the cells, and the way they are delivered all deserve attention. Published studies of NK cell infusions in people with cancer have generally described mild and temporary reactions, but these studies differ in design, cell preparation methods, and patient groups. A single report cannot be applied to every individual, and it is reasonable to ask your doctor how the evidence relates to your own diagnosis.
Temporary reactions that may be discussed
On the day of an infusion, some patients may notice a temporary rise in temperature, chills, or tiredness. Other reactions can occur as well, because any intravenous treatment may involve discomfort at the needle site, a drop in energy, or an individual response to the infusion itself. Whether these reactions appear, how strong they feel, and how long they last can vary from person to person.
It is helpful to ask the clinic how infusion days are monitored, what you should do if symptoms appear after you return to your hotel or home, and whom you can contact. If you are traveling from overseas, ask about contact options in your language and what the plan would be if you felt unwell outside clinic hours.
Questions to bring to your consultation
A written list makes a consultation more productive, especially if you are using an interpreter or speaking in a second language. You may wish to include the following points.
- Which side effects have been reported with this therapy, and how often are they described as mild or temporary?
- Are there medical conditions, medicines, or recent treatments that could make this therapy unsuitable for me?
- How would this therapy fit with my current surgery, chemotherapy, or radiation plan?
- How are the cells prepared and checked before they are returned to me?
- What happens if my blood sample cannot be processed as planned, or if I need to postpone an infusion?
- What are the total costs, including consultations, tests, and each infusion, since the treatment is self-pay?
- How will you share information with the doctor who is treating me at home?
If you have a treating oncologist, share this list with them as well. They know your diagnosis and current medicines, and can tell you whether anything about the timing of NK cell therapy should be coordinated with your standard care. We can also coordinate with the medical institution providing your standard treatment when you wish.
How Japanese regulation relates to patient protection
In Japan, cell-based treatments such as this are provided under the Act on the Safety of Regenerative Medicine, which requires a treatment plan to be submitted to and accepted by the authorities and requires cells to be processed at licensed facilities. This framework is intended to set rules for how the treatment is delivered and reviewed. It does not mean the therapy is covered by public health insurance, and it does not guarantee any result for an individual patient.
When you speak with any clinic, you can ask which plan covers the treatment you are being offered, who performs the cell processing, and how adverse events are recorded and handled. Clear answers to these questions help you judge how transparent a provider is.
Planning a consultation in Osaka as an international patient
Grand Green Osaka Umekita Clinic is located in the Umeda area of Osaka and offers information pages for international patients in several languages, so you can review the basics of the therapy before you arrive. A first consultation is the place where a doctor can review your records, explain the potential benefits and limits, and discuss risks and side effects in the context of your own health. Bringing recent test results, a summary of your current treatment, and a list of medicines will make the discussion more specific.
You are under no obligation to decide on the day. Many patients prefer to take time, talk with family, and consult their home physician before choosing. Fees, treatment schedule, indications, and risks are all confirmed individually at the consultation, and it is perfectly reasonable to ask for them in writing. For more detail on the therapy itself, please see the NK cell therapy information page on this website.
Summary
NK cell therapy uses your own cells and involves a blood draw and an intravenous infusion, and temporary reactions such as fever or fatigue may occur. Serious side effects have rarely been reported, but no treatment is free of uncertainty, and evidence from studies cannot be applied to every individual. Because the therapy is self-pay and provided under Japan’s regenerative medicine framework, it is wise to confirm costs, risks, side effects, and suitability directly with a physician. Prepare your questions in advance, involve your treating oncologist, and treat NK cell therapy as an option to discuss alongside, not instead of, standard cancer care.
- Ask about side effectsTemporary reactions may occur
- Check Japan's frameworkRegenerative medicine rules
- Confirm self-pay costsFees explained at consultation
- Decide with your doctorAlongside standard care
This figure is a conceptual diagram summarizing 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: Adoptive Transfer of Autologous Invariant Natural Killer T Cells as Immunotherapy for Advanced Hepatocellular Carcinoma: A Phase I Clinical Trial. (2021)
- 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)
- PMC: Autologous stem cell transplant recipients tolerate haploidentical related-donor natural killer cell-enriched infusions. (2013)
- PMC: Autologous NK cells as consolidation therapy following stem cell transplantation in multiple myeloma. (2022)
- PMC: Targeting immune checkpoints: how to use natural killer cells for fighting against solid tumors. (2023)
- 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.