Natural Killer (NK) cells and innate lymphoid cells (ILCs) function as critical components of the immune system, playing essential roles in detecting and eliminating virally infected and malignant cells. The study spearheaded by Deppe et al. explored the acute immune responses triggered by a 20-minute bicycle ergometer HIIT session in a cohort of AYA cancer patients, comparing their immune responses with those of healthy peers matched by age.

Prior to this investigation, the immune status of cancer patients undergoing treatment was known to be compromised, leading to increased vulnerability to infections and potentially hampered anti-tumor immunity. By focusing on the dynamic behavior of NK cells and ILCs — which include several subpopulations such as CD56^dim^ and CD56^bright^ NK cells, ILC1-like, ILC2, and innate lymphoid cell precursors (ILCPs) — the researchers aimed to elucidate how acute exercise interventions might enhance immune cell mobilization even in this vulnerable demographic.

Blood samples were collected at three critical junctures: immediately before the exercise bout (T0), immediately after exercise cessation (T1), and following one hour of recovery (T2). This temporal approach allowed the researchers to capture rapid immune system fluctuations in response to acute physical stress. Using sophisticated flow cytometry techniques, the team quantified changes in cell counts and subpopulations, offering a detailed immunophenotypic characterization unprecedented in this clinical context.

The study revealed that total NK cells, along with cytotoxic CD56^dim^ NK cells, increased significantly immediately following HIIT in both the cancer group and healthy controls. This suggests that the mobilization of cytotoxic immune cells is a conserved physiological response to intense exercise. Notably, while CD56^bright^ NK cells increased only in healthy individuals, the other subpopulations such as ILC1-like cells, ILC2, and ILCPs surged robustly in both groups. These findings indicate that HIIT triggers a comprehensive mobilization of innate immune effectors in adolescents and young adults, irrespective of their health status.

The kinetics of immune cell populations during recovery were equally revealing. Total NK cells, including both CD56^dim^ and CD56^bright^ subsets, as well as ILC2 and ILCP populations, exhibited significant declines during the hour following exercise cessation. However, ILC1-like cells maintained elevated levels, reflecting possibly distinct regulatory mechanisms governing their circulation or recruitment. The sustained plateau of ILC1-like cells could be indicative of their crucial role in orchestrating post-exercise immune responses.

The absence of significant changes in NKp44^+^ ILC3 cells and the lack of notable inter-group differences in percentage changes of immune cell counts suggest that certain innate lymphoid subsets are less responsive to acute exercise stimuli or may require chronic intervention to manifest mobilization. This nuance underscores the complexity of immune regulation in cancer patients and highlights the need for prolonged or repeated exercise interventions to harness broader immunomodulatory effects.

Intriguingly, the data demonstrated a positive correlation between younger age and greater heart rate intensity—measured as a percentage of predicted maximal heart rate—and immune cell mobilization. This finding aligns with the hypothesis that both biological age and exercise intensity modulate the immune system’s responsiveness, offering practical insights for tailoring exercise prescriptions in clinical oncology settings.

This pilot trial fundamentally challenges the long-held notion that cancer patients might be too frail for intense physical activity. Instead, it demonstrates that even a single, well-supervised HIIT session can transiently boost critical immune components that may contribute to enhanced tumor surveillance and pathogen defense. The translational potential of this knowledge is far-reaching, suggesting that integrating HIIT into supportive care protocols may yield immunological benefits without exacerbating treatment-related burden.

The implications of this study extend beyond immunology, touching upon the broader field of exercise oncology where researchers are actively exploring how physical activity can improve patients’ quality of life, reduce fatigue, and potentially improve treatment efficacy. The ability of HIIT to trigger rapid immune cell mobilization may lead to improved resilience against infections during immunosuppression, a common and dangerous side-effect of chemotherapy and radiation.

Moreover, understanding the mechanistic underpinnings of exercise-induced immune mobilization could open new therapeutic windows combining physical activity with immunotherapies. As the immune microenvironment becomes an increasingly targeted battleground in cancer treatment, strategies that optimize immune cell availability and function are paramount.

Future research is warranted to investigate whether repeated HIIT interventions yield sustained or cumulative immunological benefits and whether these transient changes translate into meaningful clinical improvements in infection rates, tumor progression, or overall survival. Additionally, exploring the molecular signals that govern the trafficking and activation of NK cells and ILCs post-exercise could lead to novel drug targets mimicking the beneficial effects of physical activity.

In conclusion, this groundbreaking trial firmly establishes that even amidst the rigors of cancer treatment, adolescents and young adults retain a remarkable capacity for immune mobilization in response to high-intensity exercise. These findings advocate for the inclusion of tailored HIIT programs in multidisciplinary cancer care frameworks, potentially transforming supportive oncology into a domain where exercise is recognized not only as a quality-of-life intervention but as a vital adjunct to immunological defense and therapeutic efficacy.

With the global cancer burden continuing to rise, particularly in young populations, this study injects a dose of optimism and scientific rigor into the evolving narrative that exercise is medicine—capable of empowering the immune system to mount a stronger defense against disease. As guidelines evolve, clinicians, exercise physiologists, and patients alike may soon view HIIT not as a strenuous challenge but as a vital catalyst for immune resilience during cancer therapy.

Subject of Research: The acute mobilization of natural killer (NK) cells and innate lymphoid cells (ILCs) induced by a single session of high-intensity interval training (HIIT) in adolescents and young adults undergoing cancer treatment.

Article Title: The impact of a single HIIT intervention on the mobilization of NK cells and ILCs in adolescents and young adults (AYA) undergoing cancer treatment: an interventional controlled trial.

Article References:
Deppe, I., Beller, R., Kiehl, F. et al. The impact of a single HIIT intervention on the mobilization of NK cells and ILCs in adolescents and young adults (AYA) undergoing cancer treatment: an interventional controlled trial. BMC Cancer 25, 689 (2025). https://doi.org/10.1186/s12885-025-14058-3

Image Credits: Scienmag.com

DOI: https://doi.org/10.1186/s12885-025-14058-3

The study, which also involved the Karolinska Institutet in Sweden, the biotechnology firm Miltenyi, and Glycostem Therapeutics from the Netherlands, originated from a collaborative European research network. The multi-institutional team included experts from the Hospital Clínic-IDIBAPS, the CIBER Cancer Unit (CIBERONC), CIBER Hepatic and Digestive Disorders Unit (CIBERehd), and the CIBER Infectious Diseases Unit (CIBERinfec). This robust collaboration reflects the concerted efforts within the scientific community to tackle one of the most significant challenges in cancer therapy: the tumor microenvironment’s ability to neutralize immune responses.

To enhance NK cell performance in combating tumors, the research team employed the CRISPR/Cas9 gene-editing technology to disrupt a gene known to hinder NK cell efficacy. More specifically, they targeted the SMAD4 gene, which plays a critical role in the signaling of TGF-β and Activin A, two molecules notoriously abundant in solid tumors. These molecules serve as protective agents for tumors, effectively shielding them from an immune assault. By knocking out the SMAD4 gene in NK cells, the researchers aimed to establish a more robust immune response capable of penetrating the tumor’s defenses.

The primary objective of this ambitious study was to ascertain if genetically modified NK cells could indeed surmount the inhibitory effects posed by TGF-β and Activin A in preclinical models of HER2-positive breast cancer and metastatic colorectal cancer. Solid tumors are replete with these molecules, which work diligently to shield themselves against immune system attacks. The findings from both in vitro studies and murine models were promising, demonstrating that the modified NK cells not only reached the tumors but also penetrated and effectively destroyed them, thereby overcoming the protective barriers presented by these malignancies.

Dr. Aura Muntasell, a key researcher from the Immunity and Infection Research Group at the Hospital del Mar Research Institute, articulated the significance of these results. "When we compare genetically modified NK cells with their non-modified counterparts, the former exhibit a significantly improved capacity to control tumor growth in vivo, whether administered alone or in combination with existing therapies, such as targeted HER2 antibodies," she emphasized. This dramatic enhancement in NK cell efficacy marks a pivotal development in the ongoing battle against cancer.

In the quest for increasing NK cell potency, the team specifically deactivated the SMAD4 gene—critical in the signaling cascade initiated by TGF-β and Activin A, as well as other growth factors. "To achieve this disruption, we transiently exposed NK cells to the CRISPR/Cas9 system, designed to specifically target and cleave the SMAD4 gene," explained Marc Güell, who serves as an ICREA research lecturer and heads the Synbio Lab at Pompeu Fabra University. This precise editing approach ensures that while the tumor-suppressive signals from TGF-β are inhibited, other supportive signaling pathways remain functional, allowing NK cells to navigate toward and infiltrate tumors more effectively.

Dr. Muntasell further elaborated on the implications of targeting SMAD4. "By knocking out SMAD4, we confer resistance to TGF-β’s inhibitory effects while still leveraging the remaining signaling pathways from the molecule, thereby enhancing NK cells’ overall capacity for tumor engagement and penetration." The study also robustly demonstrates the safety and efficacy of this innovative approach.

In a significant extension of their findings, the research team ascertained that this strategy could synergistically enhance the immune-mediated effects when applied in conjunction with other developing therapies centered on NK cells. Such advances could broaden the potential applications of this method across various cancer types, especially considering that TGF-β is known to subdue immune responses in numerous malignancies.

Despite the success of NK cell therapies in hematological cancers, their effectiveness in solid tumors has not reached a comparable level. Dr. Clara Montagut, heading a project concurrently supported by an independent research grant from the Instituto de Salud Carlos III, underscores the pivotal opportunity this research presents. "These genetically modified NK cells represent a promising avenue for treating patients with solid tumors that currently show resistance to immunotherapies," she noted, highlighting the urgency and necessity of such innovations.

This multidisciplinary research project paves the way for the initiation of a phase I clinical trial aimed at evaluating the safety and tolerability of CRISPR/Cas9-modified NK cells, in conjunction with other existing treatments. This innovative trial holds particular significance for patients with refractory colon and rectal cancer, where conventional treatment options may be limited or ineffective.

By advancing the understanding of NK cell modulation and establishing the groundwork for clinical trials, this research not only holds promise for immediate benefits in oncological therapies but also sets the stage for further exploration into the potential of gene editing technologies in improving cancer immunotherapy efficacy.

As the scientific community continues to explore the myriad possibilities inherent in manipulating the immune system, the results of this research serve as a beacon of hope for advancing cancer treatment strategies. The potential for genetically modified NK cells to reshape therapeutic approaches presents a significant leap toward more effective cancer management.

With the promise of ushering in a new era in immunotherapy, this study paves the way for ongoing advancements and captivates the imagination of oncologists and researchers alike, inspiring efforts that could eventually translate into clinical success.

The research underscores a broader understanding that, as scientists deepen their knowledge of the molecular intricacies around cancer immunology, the ability to modify immune responses will hold increasingly transformative implications for patient outcomes. The successful application of CRISPR technology elucidated in this study provides an evocative glimpse into the future of personalized cancer therapies that harness the body’s own defenses to combat malignancies.

Ultimately, as therapies evolve and improve, the dream of achieving durable responses even in the toughest cancers may soon be realized. With the commitment and innovation showcased by this team, the fight against cancer continues to forge ahead, more resolute than ever.

Subject of Research: Enhancing NK cell anti-tumor function through genetic modification
Article Title: Enhancing human NK cell antitumor function by knocking out SMAD4 to counteract TGFβ and activin A suppression
News Publication Date: 21-Mar-2025
Web References: http://dx.doi.org/10.1038/s41590-025-02103-z
References: Nature Immunology
Image Credits: Hospital del Mar Research Institute

Keywords: Natural Killer cells, Gene editing, Immunotherapy, Cancer treatment, SMAD4, CRISPR/Cas9, TGF-β, Activin A, HER2-positive breast cancer, Metastatic colorectal cancer.