mRNA-LNP Programming of CAR Macrophages for Peritoneal Tumors: Technical Advances and Implications

Study Background and Research Question

Peritoneal metastasis remains a major clinical challenge in oncology, often associated with poor prognosis and limited therapeutic options. Conventional treatments, such as cytoreductive surgery and hyperthermic intraperitoneal chemotherapy, benefit only a fraction of patients with minimal tumor burden. For most individuals with advanced peritoneal disease, the immunosuppressive tumor microenvironment (TME) restricts the efficacy of immunotherapies, necessitating novel strategies to stimulate robust anti-tumor responses. Macrophages, which constitute approximately 45% of immune cells in peritoneal ascites, represent an abundant and potentially reprogrammable population for local immunomodulation. The central research question addressed by Gu et al. (Nature Communications, 2025) is whether in situ programming of chimeric antigen receptor macrophages (CAR-Ms) via mRNA lipid nanoparticles (mRNA-LNPs) can overcome the immunosuppressive barriers of peritoneal metastases and synergize with established immunotherapies.

Key Innovation from the Reference Study

The primary innovation of this study lies in the development of a macrophage-targeted mRNA-LNP delivery system capable of programming peritoneal macrophages with a diverse array of CAR constructs directly in vivo. Unlike traditional ex vivo CAR-M approaches, which require elaborate cell manipulation and expansion outside the body, this intraperitoneal strategy enables rapid, local generation of functional CAR-Ms. Notably, the authors systematically evaluated 36 unique CAR intracellular domain (ICD) formats to identify optimal configurations for anti-tumor efficacy. The incorporation of both CD3ζ and TLR4 ICDs into CARs was found to elicit robust adaptive immune activation and enhance the response to PD-1/PD-L1 immune checkpoint blockade, representing a significant step forward in the design of next-generation cellular immunotherapies for solid tumors.

Methods and Experimental Design Insights

The study utilized a rational screening pipeline to construct and assess 36 CAR designs, each differing in their ICD composition, in primary macrophages. The mRNA encoding these CAR constructs was encapsulated in lipid nanoparticles optimized for macrophage targeting. Intraperitoneal administration of these mRNA-LNPs resulted in efficient transfection and expression of CARs in resident peritoneal macrophages. Functional assessment included in vitro phagocytosis assays, cytokine profiling, and in vivo efficacy studies in murine models of peritoneal metastasis. Of particular note, single-cell RNA sequencing (scRNA-seq) was employed to dissect the phenotypic and transcriptional landscape of CAR-Ms and the broader TME following treatment.

Protocol Parameters

• mRNA-LNP formulation: Use lipid nanoparticle carriers engineered for preferential uptake by peritoneal macrophages. Particle size, mRNA payload, and surface ligands are key optimization points for targeted delivery.
• Intraperitoneal administration: Deliver mRNA-LNPs directly into the peritoneal cavity to maximize local exposure and minimize systemic off-target effects.
• CAR construct selection: Consider screening multiple ICD architectures; the CD3ζ-TLR4 combination showed superior activation and synergy with checkpoint inhibitors in the reference study.
• Verification of programming: Confirm CAR expression and macrophage reprogramming using flow cytometry, bioluminescence imaging (if appropriate reporters are used), and scRNA-seq.
• Functional assays: Evaluate anti-tumor activity through phagocytosis assays, cytokine release, and in vivo tumor burden measurements.

Core Findings and Why They Matter

The systematic screening revealed that CAR-Ms equipped with CD3ζ and TLR4 ICDs not only enhanced phagocytic and proinflammatory activity but also reconditioned the TME. scRNA-seq analysis demonstrated a marked increase in progenitor-exhausted TCF1+PD-1+ CD8+ T cells (Tpex), a population associated with improved response to immunotherapy. Mechanistically, these CAR-Ms upregulated MHC-I and PD-L1 expression via NF-κB pathway perturbation, supporting both antigen presentation and feedback regulation. Importantly, the intraperitoneal administration of mRNA-LNP-programmed CAR-Ms synergized with PD-1/PD-L1 blockade, resulting in significant tumor regression in preclinical models (see study).

These findings underscore the dual benefit of this strategy: direct tumoricidal activity by engineered macrophages and reshaping of the immune landscape to potentiate adaptive responses. The flexibility of mRNA-LNP delivery further positions this platform for rapid iteration and personalization based on tumor antigen expression and immune contexture.

Comparison with Existing Internal Articles

Related internal articles provide practical perspectives and protocol optimizations relevant to this new platform. "Programming CAR Macrophages via mRNA-LNP for Peritoneal Tumors" (read more) discusses the translational implications of mRNA-LNP systems in the context of peritoneal immunotherapy, echoing the reference study's emphasis on in situ cellular programming and TME modulation. Additionally, resources such as "D-Luciferin Sodium Salt: Precision Firefly Luciferase Substrate in Advanced Bioluminescence Assays" (see article) and "D-Luciferin Sodium Salt: Optimizing Firefly Luciferase Workflows" (see protocols) provide detailed guidance on quantitative bioluminescence imaging and cell viability assays, which are instrumental for evaluating CAR-M function and metabolic impact in preclinical workflows. These internal resources complement the reference study by offering troubleshooting strategies and advanced assay design for monitoring cell metabolism and viability, especially using ATP-dependent bioluminescence readouts.

Limitations and Transferability

While the reference study provides compelling preclinical evidence, several limitations warrant discussion. First, the translation of mRNA-LNP programming from murine models to human patients entails challenges, including differences in macrophage biology, immune microenvironment, and potential immunogenicity of delivery components. The study's focus on peritoneal metastases leverages the accessibility and immune cell-rich nature of the peritoneal cavity, which may not be generalizable to other anatomical sites. Furthermore, the safety profile, durability of CAR expression, and risk of off-target effects require systematic investigation in larger animal models and early-phase clinical trials. The transferability of CAR-M programming to other solid tumor contexts remains to be established, though the conceptual framework provides a strong rationale for further exploration.

Research Support Resources

To facilitate similar studies involving bioluminescence imaging of CAR-Ms or metabolic assessments, researchers can utilize D-Luciferin sodium salt (SKU B8311) as a firefly luciferase substrate in ATP-dependent bioluminescence assays. This substrate supports sensitive, quantitative monitoring of cellular viability and metabolic activity, as highlighted in internal articles and product guidelines. For optimal results, follow established protocols for solution preparation and prompt usage, as detailed in the APExBIO product information. Integration of robust bioluminescent substrate workflows is essential for accurate assessment of engineered cell function and tumor regression in preclinical oncology research.