New Gene Therapy Strategy Rejuvenates CAR T-Cell Effectiveness Against Glioblastoma

Researchers at the San Raffaele-Telethon Institute for Gene Therapy (SR-TIGET, Milan), led by Nadia Coltella and Luigi Naldini, have developed a powerful new strategy to enhance the efficacy of Chimeric Antigen Receptor (CAR) T-cell therapy for glioblastoma, one of the most aggressive and treatment-resistant brain tumors. Published in Science Translational Medicine, their findings demonstrate how genetically engineered macrophages can transform the immunosuppressive tumor microenvironment (TME), enabling CAR T-cells to effectively combat the tumor and prolong survival in preclinical models.

Addressing the CAR T-Cell Challenge in Solid Tumors

While CAR T-cells have revolutionized treatment for blood cancers, their success in solid tumors, such as glioblastoma, has been limited due to the hostile and immunosuppressive nature of the tumor microenvironment. The SR-TIGET team’s innovative approach directly addresses this challenge.

The Innovative “Cross-Talk” Strategy

Building on prior work from the Naldini laboratory, which involved genetically engineering hematopoietic progenitors to generate tumor-infiltrating monocytes/macrophages that selectively release immune-stimulating payloads, this new study integrates this strategy with CAR T-cell therapy:

1. Reprogrammed Macrophages: A population of tumor-infiltrating macrophages is reprogrammed through gene therapy to selectively release two key cytokines directly into the tumor microenvironment.
2. Targeted Cytokine Delivery:

   • Interferon-α (IFN-α): This potent immune stimulator counteracts local immunosuppression and enhances antigen presentation and the activity of immune effector cells.
   • Engineered Interleukin-2 (IL-2 mutant): This modified IL-2 is designed to activate only a cognate mutant receptor co-introduced with the CAR into the T-cells. This “private cross-talk” ensures that the IL-2 specifically boosts the proliferation of the administered CAR T-cells engaged in fighting the tumor, preventing systemic toxicity and collateral damage to other cells.

3. TME Transformation: By delivering these cytokines directly into the tumor, the immunosuppressive TME is “morphed” into an environment that supports immune cells, allowing CAR T-cells to better persist, activate, and attack tumor cells.

As Dr. Rossari, first author, explains, this method “[reprograms] a population of tumor-infiltrating macrophages to deliver cytokines directly into the tumor, we’ve morphed the immunosuppressive TME into one supportive of immune cells, thus allowing CAR T cells to better persist, become activated and attack tumor cells.”

Preclinical Success and Broader Immune Response

In a mouse model of glioblastoma, this combined strategy rescued the activity of CAR T-cells that were ineffective when given alone. The engineered macrophages and CAR T-cells synergized, significantly delaying tumor growth and extending mouse survival. Strikingly, the strategy also engaged endogenous T-cells, enabling effective control of tumors even when only a fraction of cells expressed the CAR-targeted antigen B7-H3, indicating a broader anti-tumor immune response beyond just the CAR T-cells.

This work highlights a promising new avenue for overcoming the challenges of CAR T-cell therapy in solid tumors and could pave the way for more effective treatments for aggressive cancers like glioblastoma. This strategy is also being pursued in clinical testing as a stand-alone glioblastoma treatment by Genenta Science, a NASDAQ-listed biotech spin-off from the San Raffaele Institute.