Hello, I am Dr. Hidenori Shimada of Grand Green Osaka Umekita Clinic in Osaka, Japan.
When patients and families begin researching immune cell therapy, one of the first questions is often practical: what might I feel during and after treatment? This article explains, in general terms, what is known about side effects of NK cell therapy and how patients considering treatment in Japan can prepare for a consultation at Grand Green Osaka Umekita Clinic in Osaka (Umeda). It is educational information, not medical advice, and it cannot replace an examination by a physician.
The short answer: what is generally reported
NK cell therapy uses your own cells. A small amount of blood is collected, NK (natural killer) cells are activated and expanded at a specialized facility, and the cells are returned by intravenous infusion. Because the cells are autologous, meaning they come from the same person who receives them, the risk of rejection is thought to be low. Serious side effects have rarely been reported, but that does not mean side effects cannot happen. The effects most often described are temporary, such as a mild fever or tiredness around the time of the infusion.
Published studies of adoptive NK cell and related immune cell approaches have generally described mild, short-lived reactions, yet study designs, cell types, and patient groups vary widely. For that reason, it is wise not to treat any single report as a prediction of what you will personally experience. Your own medical history, current cancer treatment, and overall condition all matter.
Why side effects can still occur with your own cells
Using your own cells lowers some risks, but the process still involves several steps that can affect the body. A blood draw can cause bruising or lightheadedness. An intravenous infusion can cause local discomfort at the needle site. The returned cells are immune cells, and the immune system may respond to them with signals that people feel as a short fever, chills, or fatigue. Some people may also notice headache or a general sense of being unwell for a short time.
Another consideration is the culture process. Cells are grown outside the body under controlled conditions, so quality control and hygiene management at the processing facility are important. In Japan, such facilities are subject to rules under the Act on the Safety of Regenerative Medicine, which is one reason patients are encouraged to ask how the clinic handles cell processing, testing, and record keeping.
Possible reactions to be aware of
The following reactions are examples that patients commonly ask about. Whether any of them occurs, and how strongly, differs from person to person, and only a doctor who knows your case can discuss your individual situation.
- Temporary fever or chills, usually around the day of infusion
- Fatigue or a feeling of heaviness for a short period
- Mild headache or muscle aches
- Discomfort, redness, or bruising where the needle was placed
- Less commonly, allergic-type reactions or other symptoms that need prompt medical attention
If you already have a fever, an infection, or side effects from chemotherapy or radiation, it is important to tell the clinic in advance. A doctor may decide to adjust the timing of an infusion or to check your condition more closely before proceeding.
How side effects are monitored and discussed in Japan
NK cell therapy in Japan is provided as a self-pay (not covered by national health insurance) treatment under a regenerative medicine provision plan that has been submitted to and accepted by the government, as required by the Act on the Safety of Regenerative Medicine. This framework asks providers to explain risks to patients, obtain informed consent, and have procedures for reporting health problems. It does not guarantee any particular result, and it does not remove the need for your own careful questions.
Because treatment is delivered on an outpatient basis, patients are typically observed for a period after the infusion and told which symptoms should prompt them to call the clinic. For international patients, the follow-up question matters especially: if a symptom appears after you return home, who will you contact, and can your local doctor receive information about what was given? Clarifying this before you travel is far easier than trying to arrange it afterward.
Side effects when combined with standard cancer treatment
Many people considering NK cell therapy are also receiving or have recently received surgery, chemotherapy, or radiation therapy. NK cell therapy is described as something that can be used alongside standard treatment and is not intended to replace it. However, symptoms such as fever or fatigue can have several causes, including the cancer itself and its standard treatment, which can make it harder to tell where a symptom came from.
For this reason, keeping your oncologist informed is important. A short written summary of your diagnosis, current medicines, recent blood tests, and treatment schedule helps a physician in Osaka assess the situation, and it helps your home team interpret any symptoms that arise. Standard treatment decisions should always remain with the doctors responsible for your cancer care.
Questions to ask before you decide
A consultation is the right place to turn general information into guidance for your own case. Bringing a prepared list can make the visit more productive, particularly when you are working across languages. Grand Green Osaka Umekita Clinic offers an information page in multiple languages for international patients, and you can use it to check how to arrange a consultation.
- Which side effects are most likely to occur in my situation, and which would need urgent attention?
- How long am I observed after each infusion, and what should I do if symptoms start later?
- How does this therapy fit with my current chemotherapy, radiation, or other treatment?
- What are the total costs, how many sessions are planned, and how long will treatment take?
- What are the limits of this therapy, and what might I expect if it does not help?
- How will information be shared with my doctor at home?
Asking about limits is just as important as asking about benefits. Evidence for NK cell therapy is still developing, results vary between individuals, and it should be understood as one option to discuss with your physicians, not a certain solution.
Summary
Side effects reported with NK cell therapy are generally described as mild and temporary, such as fever or fatigue, in part because the treatment uses your own cells. Even so, reactions can occur, individual differences are real, and conditions such as ongoing cancer treatment can complicate how symptoms are interpreted. NK cell therapy in Japan is a self-pay treatment provided under the Act on the Safety of Regenerative Medicine. Costs, risks, side effects, and whether it suits you must be confirmed through a physician’s examination. If you are considering a consultation in Osaka, prepare your medical records, write down your questions, and involve your current oncologist in the decision.
- Possible mild reactionsFever or fatigue may occur
- Alongside standard careKeep your oncologist informed
- Self-pay treatmentConfirm costs and risks
- Ask your doctorIndividual advice needs an exam
This figure is a conceptual summary of the article content
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: Treatment of cancer patients with ex vivo anti-CD3-activated killer cells and interleukin-2. (1993)
- PubMed: Anti-GD2 CAR-NKT cells in patients with relapsed or refractory neuroblastoma: an interim analysis. (2020)
- 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)
- PMC: Natural Killer Cell Recognition and Control of Epithelial Cancers. (2022)
- PMC: Current progress in NK cell biology and NK cell-based cancer immunotherapy. (2020)
- PMC: Advances in natural killer cell immunotherapy for hematologic malignancies. (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.