Natural killer cells are innate immune lymphocytes that patrol the bloodstream and tissues, eliminating virus-infected and malignant cells without the antigen-specific training that T cells require. Their cytotoxicity is governed by a balance of activating and inhibitory receptors, and when they encounter a target cell they can deploy perforin and granzymes to trigger apoptosis. Beyond direct killing, NK cells are prolific producers of interferon-gamma, a cytokine that shapes both innate and adaptive immune responses. This dual capacity — cytotoxicity and cytokine output — is what makes them attractive candidates for adoptive cell therapy in solid tumors like breast cancer.

But translating that promise into a clinical product requires large numbers of functional cells, and that is where the difficulty lies. Autologous NK cells must be isolated from a patient’s peripheral blood mononuclear cells and expanded ex vivo under cytokine-driven culture conditions to reach therapeutic doses. The expansion capacity of these cells varies enormously from one individual to another, and clinicians have had few reliable ways to gauge that potential in advance. Age, circulating leukocyte counts, the frequency of NK cells in peripheral blood, and the initial number of NK cells available for culture have all been examined as possible predictors, but none has proven consistently informative.

The research team, led by Dai Khac Do and including Trang Thi Vu, Hai The Phung, Kien Trung Hoang, Tuan Ngoc Nguyen, Dung Dang Nguyen, Hai Anh Vu, and Thuc Cong Luong, approached the problem with a deceptively simple assay. They drew peripheral blood from 33 patients with breast cancer and subjected whole-blood samples to a standardized interferon-gamma release assay. This test measures how much IFN-γ circulating immune cells — NK cells chief among them — release when stimulated, providing a functional readout of NK cell activity rather than a mere count of cells present. The assay requires no complex cell isolation and can be performed on whole blood, making it potentially suitable for routine clinical laboratories.

After establishing each patient’s baseline NK cell activity, the researchers isolated peripheral blood mononuclear cells and expanded the NK cells ex vivo under cytokine-based culture conditions. Once the expansion period concluded, they compared the laboratory-measured growth against the pre-treatment IFN-γ signal. The result was striking: baseline NK cell activity showed a significant positive correlation with expansion capacity, with a Spearman rank correlation coefficient of 0.46 and a p-value of 0.007. In plain terms, patients whose blood produced a stronger IFN-γ response at the outset tended to have NK cells that multiplied more vigorously in culture.

Just as telling was what did not predict expansion. Age, total leukocyte counts, the proportion of NK cells within the peripheral blood lymphocyte pool, and the absolute number of NK cells available at the start of culture showed no significant association with how well the cells expanded. This is a crucial distinction for the field. It suggests that the functional fitness of NK cells — their readiness to respond and produce cytokines — matters more than how many are present. A patient could have a robust circulating NK cell population yet still yield cells that expand poorly, while another with a modest frequency might harbor cells with superior proliferative potential once stimulated.

The implications reach beyond breast cancer. Adoptive NK cell therapy is being explored across a range of malignancies, and the inter-individual variability in expansion has been a recurring frustration for clinicians and manufacturers alike. A biomarker that can be measured from a simple blood draw before any culture begins would allow treatment teams to stratify patients, set realistic expectations for cell yield, and potentially adjust culture strategies or choose alternative cell sources — such as allogeneic or cell-line-derived NK products — for those whose autologous cells are unlikely to reach therapeutic numbers.

The study’s authors are careful to frame their finding as a candidate biomarker rather than a validated clinical tool. The cohort of 33 patients is modest, and the correlation, while statistically significant, explains only a portion of the variability in expansion outcomes. Larger studies across diverse patient populations and cancer types will be needed to confirm the relationship and to determine whether the IFN-γ signal can reliably guide treatment decisions. The researchers also note that the assay’s standardization — the precise stimulation conditions and measurement protocol — will require refinement before it can be deployed as a routine pre-treatment screen.

Still, the conceptual advance is significant. For the first time, a functional, cytokine-based readout from whole blood has been linked to the ex vivo expansion potential of a patient’s own NK cells in a solid tumor setting. The finding moves the field away from a purely quantitative view of cell availability toward a qualitative assessment of cell fitness. If validated, the IFN-γ release assay could become a standard pre-treatment evaluation, helping clinicians decide which patients are best suited for autologous NK cell therapy and which might benefit from alternative strategies.

The research, published in BMC Cancer, was conducted with ethics approval from Vietnam Military Medical University and the National Cancer Hospital, and all participants provided written informed consent. The study received no external funding, and the authors declare no competing interests. As NK cell-based immunotherapy continues to advance toward broader clinical application, this work offers a practical step toward personalized cell therapy — one that begins not in the culture flask, but with a single measurement from a tube of blood.

Subject of Research: Immunology

Article Title: Baseline IFN-γ-based natural killer cell activity is associated with ex vivo expansion capacity of autologous NK cells in patients with breast cancer

Article References: Vu, T. T., Phung, H. T., Hoang, K. T., Nguyen, T. N., Nguyen, D. D., Vu, H. A., Luong, T. C., & Do, D. K. (2026). Baseline IFN-γ-based natural killer cell activity is associated with ex vivo expansion capacity of autologous NK cells in patients with breast cancer. BMC Cancer. https://doi.org/10.1186/s12885-026-16978-0

Image Credits: AI Generated

DOI: 10.1186/s12885-026-16978-0

Keywords: natural killer cells, breast cancer, immunotherapy, interferon-gamma, biomarker, cell therapy, Baseline, IFN-, based, natural, killer, cell