BLOG

What Affects NK Cell Activity, and Why It Matters in Japan

Published 2026.10.03 7 min read

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

If you are researching cancer immune cell therapy, you may have read that natural killer (NK) cell activity can decline over time. It is a reasonable thing to wonder about: what actually lowers NK cell activity, and what does that mean for a treatment that uses your own NK cells? This article explains the topic in plain language for international patients, including those considering care at Grand Green Osaka Umekita Clinic in Osaka, Japan.

In short, NK cell activity is known to vary with age, stress, and the effects of cancer itself, and NK cell therapy is designed to return a larger number of activated NK cells to the body. However, it is a self-pay treatment whose suitability depends on your individual condition, so it should be discussed with a doctor and not assumed to be right for everyone.

What NK cells do and why their activity matters

NK cells are a type of lymphocyte that circulates in the blood. Unlike many other immune cells, they can recognize and attack abnormal cells, such as cancer cells and virus-infected cells, without waiting for instructions from other parts of the immune system. This is why they are often described as part of the body’s front-line, or innate, immune defense.

Researchers believe that abnormal cells with the potential to become cancer may arise in healthy people from time to time, and that immune cells including NK cells help find and remove many of them. This idea is called immune surveillance. When NK cells are fewer in number or less active, this monitoring is thought to become less effective, although the exact relationship in any one person is complex and cannot be predicted from a single factor.

Factors that are known to affect NK cell activity

Published research has described several factors that may be linked to changes in NK cell activity. The main ones discussed in relation to NK cell therapy are listed below.

Aging: NK cell function is reported to change as people get older, and this is one reason immune health is a common topic in later life.
Stress: Ongoing psychological or physical stress has been associated with changes in immune cell activity in several studies.
The effects of cancer itself: Tumors can create an environment that suppresses immune cells, which may reduce how well NK cells work.
Treatment-related factors: Some cancer treatments can affect blood and immune cells, so the timing of any additional therapy should be planned with your treating team.

It is important not to over-interpret these findings. Results come from studies of different designs and populations, and they do not mean that any individual person will have low NK cell activity or that raising it will lead to a particular outcome.

How NK cell therapy relates to this issue

In NK cell therapy at Grand Green Osaka Umekita Clinic, NK cells are obtained from a standard blood draw. They are then activated and expanded outside the body at a specialized cell processing facility, and returned to your body by intravenous infusion. The aim is to return NK cells that are greater in number and higher in activity than before, in order to reinforce immune function that may have weakened.

Because the therapy uses your own cells, called autologous cells, the risk of rejection is considered low, and serious side effects have rarely been reported. Temporary fever or fatigue may still occur. Treatment consists of a blood draw and an infusion without hospitalization, so many people are able to continue their daily lives during the course of therapy. Even so, every person responds differently, and the therapy does not promise any specific result.

Where NK cell therapy fits alongside standard cancer treatment

NK cell therapy is not a replacement for surgery, chemotherapy, or radiation therapy. Standard treatment remains the foundation of cancer care, and any decision to add or change treatment should be made with your oncologist. The therapy is generally not considered to interfere with these standard treatments, so it may be considered alongside them, and the clinic can coordinate with the medical institution providing your standard treatment.

Some people also consider the therapy after their main treatment has finished, with the aim of supporting immune function during follow-up. Whether this is appropriate depends on your cancer type, stage, treatment history, and overall health, which only a doctor can assess after a consultation.

Legal framework and costs in Japan

In Japan, this type of cell therapy is provided under the Act on the Safety of Regenerative Medicine. Facilities provide treatment under a plan submitted to and accepted by the government, and cell processing is carried out at licensed facilities. This framework is about how treatment is managed, and it does not by itself mean that a therapy is effective for a given patient.

NK cell therapy is a self-pay treatment that is not covered by Japan’s national health insurance. Fees, the number of infusions, and the treatment period are explained during consultation, and you should confirm them, together with the risks, possible side effects, and whether you are a candidate, before you decide.

Questions to ask before you decide

If you are considering NK cell therapy as an international patient, preparing questions in advance can make your consultation more productive. You may wish to ask the following.

Is NK cell therapy suitable for my type and stage of cancer, and for my current standard treatment?
What are the realistic goals, and what are the limits of this therapy?
What side effects can occur, and when should I contact a doctor?
What is the full cost, how many infusions are recommended, and over what period?
How will the clinic coordinate with my current oncologist and share information?

The clinic is located in Osaka, in the Umeda area, and provides information pages for international patients in multiple languages, so you can review the basics before contacting the clinic. A consultation with a doctor is the right place to discuss your own situation, because general information in an article like this cannot replace a medical assessment.

Summary

NK cell activity is reported to be influenced by age, stress, and the effects of cancer, and NK cell therapy aims to return a larger number of activated NK cells to the body. It is an option to understand carefully, not a guaranteed solution. It is a self-pay treatment provided in Japan under a regulated framework, and it is considered alongside standard cancer treatment, not instead of it. Costs, risks, side effects, and suitability should always be confirmed with a doctor before you decide.

NK Cell Activity at a Glance

NK cellsFront-line immune cells
Age and stressLinked to activity changes
Alongside standard careNot a replacement
Ask a doctorCost, risks, suitability

This diagram 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.

Back to article list › Back to NK Cell Therapy ›