A newly published study from Karolinska Institutet has illuminated a critical factor that may undermine the effectiveness of cancer immunotherapy—neutrophils, a type of white blood cell traditionally recognized for their role in combating infections. This research, appearing in the distinguished journal Immunity, reveals that neutrophils can actively diminish the potency of immunotherapies by mechanisms triggered within the tumor microenvironment. Their findings offer profound insights into the cellular and molecular intricacies that influence immunotherapeutic outcomes and open new avenues for enhancing treatment efficacy.
Immunotherapy represents a transformative strategy in oncology, aiming to empower the patient’s immune system to recognize and eradicate cancer cells. However, despite remarkable successes, a significant subset of patients exhibits resistance or suboptimal responses. The Karolinska team sought to decipher the cellular dynamics that contribute to these varied outcomes, centering their investigations on neutrophils within two distinct murine cancer models: melanoma and breast carcinoma. These granulocytes, although frontline defenders against pathogens, exhibit complex, often paradoxical, behavior in malignancies.
By employing genetically engineered mice completely lacking neutrophils, researchers created a fundamental contrast with normal counterparts possessing intact neutrophil populations. Remarkably, the absence of neutrophils was associated with amplified effectiveness of multiple immunotherapeutic modalities. Tumor volumes decreased more significantly, paralleled by an influx and heightened activation of cytotoxic T lymphocytes (CTLs) within the tumor niche. This phenomenon underscores a previously underappreciated suppressive influence neutrophils exert over the adaptive immune response prompted by therapy.
Delving deeper, the study elucidates a sophisticated feedback mechanism involving neutrophils and tumor signaling pathways. Following the initiation of immunotherapy, neutrophils themselves undergo a phenotypic modulation wherein they begin expressing programmed death-ligand 1 (PD-L1). PD-L1 is a critical immune checkpoint molecule that suppresses T cell-mediated tumor clearance by binding to PD-1 receptors on T cells, thereby attenuating their cytotoxic functions. This induction of PD-L1 expression on neutrophils is driven by interferon-gamma (IFN-γ), a type II interferon secreted by activated immune cells within the tumor milieu.
Crucially, when the research team selectively ablated PD-L1 or disrupted the IFN-γ receptor specifically on neutrophils, immunotherapeutic efficacy was restored to greater degrees. This compelling evidence demonstrates that the tumor microenvironment dynamically instructs neutrophils to adopt immune checkpoint properties that blunt T cell activity. Such findings challenge the prevailing conception of neutrophils as mere innate immune effectors and highlight their role as modulators of adaptive immune resistance in cancer.
The implications of this discovery are far-reaching. It establishes that the neutrophil response to cancer immunotherapy is not a static trait but is governed by extrinsic signals within the tumor’s immunological landscape. Consequently, therapeutic strategies that target neutrophil-mediated inhibition hold promise to synergize with existing immunotherapies, potentially overcoming resistance and refining treatment responses. This conceptual pivot points toward the development of combination therapies integrating immune checkpoint blockade with interventions designed to neutralize neutrophil-driven suppression.
Moreover, the translational relevance of the study is underscored by observations from human tumor samples. Analysis of specimens from lung cancer patients undergoing immunotherapy revealed similar neutrophil PD-L1 expression patterns, hinting that the interplay observed in murine models reflects conserved phenomena in human malignancies. This cross-species validation bolsters the clinical significance of targeting neutrophil-mediated pathways to augment immunotherapy outcomes.
These insights also invite a broader reconsideration of the tumor microenvironment’s composition and the intricate crosstalk among immune cell subsets. Neutrophils, once relegated to simple categorizations of pro-inflammatory or anti-inflammatory cells, are now appreciated as plastic entities capable of both promoting and suppressing tumor progression, contingent upon microenvironmental cues. The dynamic induction of inhibitory molecules such as PD-L1 represents a striking example of how tumors can hijack immune cells to construct barriers against eradication.
The study was the result of an international collaboration, bringing together expertise from institutions across Sweden, the United States, Germany, and China. Supported by funding from major agencies including the National Institutes of Health, the Swedish Cancer Society, and the Swedish Foundation for Strategic Research, the comprehensive nature of the research reflects a global commitment to advancing cancer immunology. Importantly, the investigators have declared no conflicts of interest, adding credibility to their groundbreaking conclusions.
In practical terms, these findings suggest that future cancer treatment regimens may need to incorporate strategies that either deplete neutrophils or inhibit their PD-L1 induction to unleash maximal T cell function. Such approaches could involve novel pharmacological inhibitors, antibody-based therapies against neutrophil-expressed PD-L1, or modulation of IFN-γ signaling pathways. The goal is to dismantle the immunosuppressive barricades within tumors that limit the curative potential of current immunotherapies.
Ultimately, this research deepens our understanding of the immune landscape in cancer and highlights the nuanced roles played by different leukocyte populations. It emphasizes the importance of a systems biology approach to cancer therapy, where combinatorial treatments targeting multiple cellular and molecular mechanisms stand a better chance of success. As immunotherapy continues to revolutionize cancer care, dissecting the multifaceted interactions within the tumor milieu remains paramount for overcoming resistance and achieving durable remissions.
The Karolinska Institutet study encapsulates a pivotal moment in cancer immunology—recognizing neutrophils not just as effectors but also as modulators of immune evasion. Such nuanced insights will undoubtedly steer the field towards more sophisticated, rationally designed therapies, paving the way for improved patient outcomes in the battle against cancer.
Subject of Research: Neutrophil regulation in cancer immunotherapy through type II interferon signaling.
Article Title: Neutrophil regulation of immunotherapy for cancer is controlled by type II interferon
News Publication Date: 15 June 2026
Web References: https://doi.org/10.1016/j.immuni.2026.05.014
References: Shengduo Pei, Yueyun Pan, Heng Liang, Li Lei, Qirong Lin, Jiarui Mi, Jeffrey V Ravetch, Oliver Soehnlein, Mikael C.I. Karlsson, Immunity, 15 June 2026.
Keywords: Cancer, Immunotherapy, Neutrophils, PD-L1, Interferon-gamma, Tumor microenvironment, T cells, Immune checkpoints, Immunosuppression, Leukocytes, Granulocytes, Tumor resistance
