New CAR-T Cells Improve The Treatment of Solid Tumors

The application of CAR-T cell therapy in solid tumors is limited by the suppressive tumor microenvironment (TME), which hinders T cell migration to tumor sites, leads to T cell exhaustion, insufficient T cell persistence, and limited endogenous anti-tumor immune responses. To address these therapeutic challenges, researchers have investigated combination strategies with immune checkpoint inhibitors (such as αPD-1, αCTLA-4, and αPD-L1) and immunomodulatory factors (such as IL-2, IL-7, IL-12, IL-15, and αTGFβ).

Immune checkpoint inhibitors have demonstrated success in treating certain malignancies, including melanoma, renal cell carcinoma, and non-small cell lung cancer. However, immunologically "cold" tumors (such as metastatic castration-resistant prostate cancer, ovarian cancer, and pancreatic cancer) exhibit limited response to immune checkpoint inhibitors. Furthermore, dosing issues, poor biodistribution, and systemic toxicity further complicate the application of immune checkpoint inhibitors and their combinations. Furthermore, combining CAR-T cell therapy with immune checkpoint inhibitors, an obvious combination therapy, has not always yielded the desired results.

Interleukins (ILs) play a key role in both innate and adaptive immune responses, enhancing T cell and natural killer (NK) cell activity and improving anti-tumor responses in preclinical models. However, the clinical application of many cytokines, including IL-12 and IL-15, is limited by their non-tumor-specific activity, which can easily induce cytokine release syndrome (CRS) and other adverse systemic toxicities. This highlights the need for unique, tumor-restricted approaches to combine these therapies to improve the efficacy of solid tumor immunotherapy.

In October 2025, researchers from the Keck School of Medicine of the University of Southern California published a study titled "Solid tumor CAR-T cells engineered with fusion proteins targeting PD-L1 for localized IL-12 delivery" in Nature Biomedical Engineering, a Nature journal. This study used genetic engineering to enable CAR-T cells to express and in situ secrete a bifunctional fusion protein, αPD-L1–IL-12, thereby simultaneously relieving immunosuppression and providing activation signals locally in the tumor, significantly enhancing the efficacy and safety of CAR-T cells in solid tumor models.

Figure 1. Illustration of dual-transduced CAR-T cells engineered to secrete bifunctional fusion proteins with a cytokine modifier (TGFβ^trap, IL-15 or IL-12) linked to an αPD-L1 targeting scFv. (Murad J P, et al., 2025)

The immunosuppressive tumor microenvironment (TME) of solid tumors can "shut down" or "exhaust" CAR-T cells, preventing them from working effectively. Key inhibitory factors include immune checkpoints, such as PD-L1 expressed on the surface of tumor cells, which binds to PD-1 on the surface of T cells, transmitting inhibitory signals; and inhibitory cytokines, such as TGF-β, which strongly suppress T cell immune activity.

The research team designed a self-sufficient CAR-T cell that expresses and in situ secretes a bifunctional fusion protein-αPD-L1–IL-12-making it a "miniature pharmaceutical factory" for localized immunotherapy. The αPD-L1 scFv, acting as an immune checkpoint inhibitor, blocks the PD-1-PD-L1 pathway, removing the "brake" signal on T cells. IL-12, a potent immunostimulatory cytokine, significantly enhances T cell proliferation, cytotoxicity, and persistence. This fusion protein combines these two factors, achieving a synergistic effect of "releasing inhibition and enhancing activation."

Its key advantage lies in its localized effect on tumors. αPD-L1-IL-12 engineered CAR-T cells improve T cell migration and tumor infiltration, while localizing IFNγ production, tumor microenvironment (TME) modulation, and anti-tumor responses to the tumor site. This not only increases drug concentration locally within the tumor, but also reduces systemic inflammatory side effects, such as cytokine release syndrome (CRS).

Why is the αPD-L1–IL-12 combination optimal? The research team compared other combinations (αPD-L1–TGFβ^trap and αPD-L1–IL-15). The results showed that IL-12 provided the strongest activation signal and most effectively promoted T cell function. While TGFβ^trap effectively neutralizes TGF-β, it lacks a positive stimulatory signal. While IL-15 can promote T cell survival, its stimulation may not be as potent as IL-12. Therefore, the αPD-L1–IL-12 combination achieves the best balance between "releasing inhibition + enhancing activation", thus achieving the best performance in efficacy and safety.

This study represents a significant advancement in engineering CAR-T cells to enhance their ability to fight solid tumors, demonstrating the enormous potential of localized delivery and synergistic strategies. It is expected to provide a new approach to addressing the challenges of CAR-T cell therapy in solid tumors and holds broad promise for clinical translation.

Reference

Murad J P, et al. Solid tumour CAR-T cells engineered with fusion proteins targeting PD-L1 for localized IL-12 delivery. Nature Biomedical Engineering, 2025: 1-17.