In a breakthrough that could revolutionize cancer immunotherapy, a research team at Baylor College of Medicine, led by the late Dr. Bert O’Malley, has unveiled the critical role of the steroid receptor coactivator 3 (SRC-3) in regulatory T cells (Tregs) that govern the immune system’s response to tumors. Their pioneering 2023 study demonstrated that SRC-3 acts as a molecular switch within Tregs, influencing whether these cells suppress or facilitate the anti-cancer immune response. Building upon this foundational work, the researchers have now expanded their investigation to encompass multiple aggressive solid tumors, publishing compelling new findings in the prestigious journal OncoImmunology.
The immune microenvironment surrounding tumors is pivotal in either enabling or thwarting cancer progression. Tumors categorized as ‘cold’ maintain an immunosuppressive atmosphere that limits infiltration by cytotoxic T cells and natural killer (NK) cells, key players in tumor eradication. Conversely, ‘hot’ tumors are characterized by substantial immune cell presence and heightened anti-tumor activity. Central to maintaining the ‘cold’ phenotype are Tregs, a subset of immune cells that suppress excessive immune activation but, paradoxically, can be co-opted by tumors to dampen immune attack. SRC-3, a transcriptional coactivator within Tregs, has emerged as an influential modulator of this immunosuppressive function.
In their early work with mouse models of breast and prostate cancer, the researchers employed genetic ablation techniques to delete SRC-3 specifically in Tregs. This intervention transformed these regulatory cells from tumor protectors into potent tumor antagonists. SRC-3 knockout (KO) Tregs showed an enhanced ability to infiltrate tumors and orchestrate the recruitment of effector immune cells capable of destroying cancer cells. Remarkably, this approach elicited robust tumor eradication without inducing the deleterious side effects commonly associated with conventional immunotherapies, such as autoimmunity or systemic toxicity. Moreover, the SRC-3 KO Tregs appeared to confer durable immunity, preventing tumor recurrence in these mouse models.
At the molecular level, SRC-3 KO Tregs exhibited an altered secretion profile, releasing chemokines that act as chemical beacons to attract cytotoxic CD8+ T cells and NK cells into the tumor milieu. Simultaneously, they impeded immune suppressive cells that would otherwise inhibit this anti-tumor assault. This dual mechanism effectively reshaped the tumor microenvironment, turning ‘cold’ tumors into ‘hot’ ones, thereby facilitating an immune-permissive state conducive to tumor destruction.
Encouraged by these promising outcomes, the research team delved deeper, exploring the applicability of SRC-3-deficient Tregs across a broader spectrum of solid tumors, including glioblastoma, melanoma, and lung cancer. These cancers are notorious for their aggressive progression, resistance to therapy, and poor prognosis, highlighting the urgent need for novel immunotherapeutic strategies.
Glioblastoma, an exceptionally lethal brain cancer, is classically associated with an immune-deserted environment, rendering immunotherapies largely ineffective. In mouse models harboring glioblastoma tumors, those lacking SRC-3 in their Tregs demonstrated a remarkable complete suppression of tumor growth. All control animals succumbed to rapidly progressing tumors by 41 days post-implantation, whereas SRC-3 KO mice survived the entire 52-day study duration without detectable tumor burden. Histological analyses revealed substantial infiltration of cytotoxic T cells within tumor tissues, confirming that SRC-3 ablation in Tregs effectively turns the brain tumor microenvironment from immunologically inert into one actively engaged in anti-tumor warfare.
Melanoma, though somewhat more immunologically active than glioblastoma, also leverages Treg-mediated suppression to evade immune elimination. In this context, SRC-3 KO Tregs conferred significant protection against melanoma development in murine models. While every control mouse developed tumors, an impressive 75% of SRC-3 KO mice remained tumor-free and lived beyond 50 days. The elevated presence of tumor-infiltrating lymphocytes in these subjects underscores the enhanced anti-tumor immunity enabled by the SRC-3 knockout in regulatory T cells.
Lung cancer represents another formidable challenge due to its propensity for rapid progression and immune resistance. Studies revealed that both control mice and those with SRC-3 KO Tregs initially exhibited transient tumor regression. Notably, mice with normal Tregs experienced subsequent tumor resurgence followed by mortality within a month. In contrast, animals harboring SRC-3-deficient Tregs achieved sustained tumor clearance, with 60% surviving long-term and exhibiting no signs of tumor recurrence. This longevity was accompanied by amplified infiltration of immune cells within lung tumor tissues, reiterating the capacity of SRC-3 KO Tregs to remodel the tumor microenvironment favorably.
At the immunological mechanism’s core is the capacity of SRC-3 KO Tregs to proliferate extensively and deploy chemokines that attract and activate effector immune cells while simultaneously inhibiting the recruitment or function of immunosuppressive counterparts. This multifaceted mode of action orchestrates a dynamic shift in the local tumor ecosystem, overriding tumor-induced immune evasion strategies.
These collective experimental findings not only underscore the universality of SRC-3’s role in modulating Treg function across diverse tumor types but also affirm the translational potential of targeting SRC-3 as an innovative cancer immunotherapy approach. By harnessing the intrinsic plasticity of Tregs and reprogramming their activity from tumor-supporting to tumor-fighting, this strategy overcomes significant barriers that have historically limited the efficacy of immunotherapies for solid tumors.
Given these advances, Baylor College of Medicine, in collaboration with CoRegen, Inc., is actively pursuing the commercialization and clinical translation potential of SRC-3-targeted therapies. The intellectual property protecting these discoveries has been licensed to CoRegen, reflecting a commitment to advancing these findings from bench to bedside.
Importantly, the absence of severe immune-related adverse events in these preclinical studies suggests that manipulating SRC-3 in Tregs offers a safer alternative to existing immunomodulatory treatments that often provoke autoimmunity. The promising results also hint at the possibility of durable cancer remission with reduced risk of relapse, a longstanding goal in oncology.
Further research is warranted to unravel the detailed molecular pathways through which SRC-3 governs Treg-mediated immunosuppression and to optimize delivery methods for targeted SRC-3 inhibition in human patients. Additionally, expanding trials to encompass other challenging tumor entities may elucidate the broader applicability of this therapeutic paradigm.
In summation, the innovative manipulation of SRC-3 within Tregs represents a transformative leap forward in cancer immunotherapy. By converting immunosuppressive cells into allies of tumor eradication, this approach promises to reshape the landscape of solid tumor treatment, offering hope for more effective, durable, and side-effect-free therapeutic options in the fight against cancer.
Subject of Research: Animals
Article Title: Steroid receptor coactivator 3-deficient regulatory T cells eradicate multiple solid tumors in syngeneic mouse models
News Publication Date: 2-Mar-2026
Web References:
- https://www.pnas.org/doi/10.1073/pnas.2221707120
- https://www.tandfonline.com/doi/full/10.1080/2162402X.2026.2640261#abstract
References:
Han S.J., Lonard D.M., et al. (2026). Steroid receptor coactivator 3-deficient regulatory T cells eradicate multiple solid tumors in syngeneic mouse models. OncoImmunology. https://doi.org/10.1080/2162402X.2026.2640261
Image Credits: Baylor College of Medicine
Keywords: cancer immunotherapy, regulatory T cells, SRC-3, tumor microenvironment, glioblastoma, melanoma, lung cancer, immune suppression, solid tumors, chemokines, immune infiltration, immunomodulation
