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Why Does NK Cell Activity Decline, and What Does It Mean for Therapy in Osaka?

Published 2026.10.09 7 min read

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

If you or a family member has been diagnosed with cancer, you may have come across the idea that immune activity can change over time, and that natural killer (NK) cells play a part in it. Many international patients ask a practical question: why would NK cell activity decline, and what does that have to do with NK cell therapy offered in Osaka, Japan? This article explains the background in plain language so that you can prepare better questions before a consultation.

In short, NK cell activity has been reported to vary with age, stress, and the effects of cancer itself. NK cell therapy is an option that aims to return a larger number of activated NK cells to the body, but it is a self-pay treatment, its effects differ from person to person, and it is not a substitute for standard cancer care. Whether it is suitable for you is a decision to make with a physician after a consultation.

What are NK cells, and what do they do in the body?

NK cells, short for natural killer cells, are a type of lymphocyte that circulates in the blood. They belong to the innate immune system, which means they can recognize and attack abnormal cells, such as cancer cells and virus-infected cells, without waiting for instructions from other immune cells. This ability to act on their own is the main reason they attract attention in cancer immunology.

Researchers often describe their role as part of immune surveillance. Even in healthy people, abnormal cells that could develop into cancer are thought to appear from time to time. Immune cells, including NK cells, are believed to find and remove many of them. When this monitoring weakens, abnormal cells may be able to escape detection more easily. This is a general scientific concept, and it should not be read as a promise about any individual outcome.

Why can NK cell activity decline?

Published research, which can be explored through public databases such as PubMed, suggests that NK cell function is not constant throughout life. Several factors are commonly discussed.

Age: immune function in general changes as people get older, and NK cell activity is known to decline with age.
Stress: prolonged psychological or physical stress has been associated with changes in immune activity.
Cancer itself: tumors can create conditions that make it harder for immune cells to work effectively.
Cancer treatment: some standard treatments can temporarily affect the immune system as a whole.

It is important to be careful here. These associations come from different kinds of studies, and a reduced NK cell measurement does not by itself tell you how a particular person will respond to any treatment. Your own doctors can explain what tests mean in your situation.

How does NK cell therapy relate to this decline?

At Grand Green Osaka Umekita Clinic, NK cell therapy is described as a cancer immune cell therapy that uses your own cells. NK cells are obtained from a standard blood draw, then activated and expanded at a specialized cell processing facility. After that, they are returned to the body by intravenous infusion. The idea is to reinforce weakened immune function by returning NK cells that are greater in number and higher in activity.

Because the cells come from you, the therapy is called autologous. The risk of rejection is considered low, and serious side effects have rarely been reported, although temporary fever or fatigue may occur. Treatment involves a blood draw and an IV infusion without hospitalization, so many people are able to continue their daily routines. Even so, individual reactions vary, and any symptoms should be discussed with the treating physician.

The therapy can be considered alongside surgery, chemotherapy, or radiation therapy, and the clinic can coordinate with the medical institution providing your standard treatment. It should be understood as one option to discuss, not as a replacement for the care recommended by your oncology team.

What limits and legal points should international patients understand?

NK cell therapy is provided in Japan as a self-pay treatment, which means it is not covered by public health insurance. Fees, the number of infusions, the treatment period, and possible risks and side effects should be confirmed in writing and explained by a physician during a consultation. Please do not rely on general articles for those details.

In Japan, this kind of treatment is provided under the Act on the Safety of Regenerative Medicine, through a plan submitted to and accepted by the authorities. This framework helps structure how cells are handled and how treatment is reported, but it does not mean that results can be predicted. The evidence for NK cell therapy continues to develop, and eligibility depends on your diagnosis, stage, current treatments, and overall health.

How can you prepare before consulting in Osaka?

A clear set of questions makes a consultation more useful, especially when you are travelling or living abroad. Consider preparing the following information and questions.

Your diagnosis, stage, and treatment history, ideally with English medical records or summaries.
The treatments you are currently receiving or planning, and the name of your home oncologist.
Questions about how NK cell therapy might fit with your standard treatment, and what its limits are.
Questions about total costs, the schedule of visits, and how follow-up would work after you return home.
Any medicines, allergies, or other conditions that your doctor should know about.

Grand Green Osaka Umekita Clinic is located in the Umeda area of Osaka and offers an information page for international patients, with multilingual support available. You can use it to review the treatment flow and fees before deciding whether to book a consultation.

To summarize, NK cell activity can change with age, stress, and illness, and NK cell therapy is one approach that aims to support the immune system by returning activated cells from your own body. It is a self-pay option provided under Japanese regenerative medicine rules, with limits and uncertainties that a physician should explain to you in person. Please consult a doctor, and speak with your current oncology team, before making any decision.

NK cell activity and therapy

NK cells in immunityInnate immune cells
Activity can declineAge, stress, cancer
Own cells returnedBlood draw and IV
Alongside standard careDiscuss with a doctor

This figure is a conceptual summary of the article content

Learn more about NK Cell Therapy

References

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.

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