Intraperitoneal mRNA-LNP Programming of CAR Macrophages: A New Paradigm in Solid Tumor Immunotherapy

Study Background and Research Question

Peritoneal metastasis in solid tumors, such as ovarian and gastrointestinal cancers, remains a formidable clinical challenge. Conventional treatments—including cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC)—offer benefits primarily to patients with limited tumor burden, leaving the majority of advanced cases with few effective options. The tumor microenvironment (TME) in peritoneal metastasis is particularly immunosuppressive, frequently leading to immune evasion and poor outcomes. Macrophages, which constitute approximately 45% of immune cells in peritoneal ascites, are abundant but often co-opted by the tumor. This scenario raises a pivotal research question: Can in situ programming of macrophages to express chimeric antigen receptors (CARs) overcome local immunosuppression and enhance antitumor immunity in the peritoneal cavity?

Key Innovation from the Reference Study

The study by Gu et al. (Nature Communications, 2025) introduces a macrophage-targeted mRNA lipid nanoparticle (mRNA-LNP) platform for direct intraperitoneal delivery and programming of tailored CAR macrophages (CAR-Ms). Unlike previous approaches that rely on ex vivo engineering and reinfusion, this strategy programs endogenous peritoneal macrophages in situ using mRNA-LNPs encoding a panel of 36 CAR constructs. Through systematic evaluation, the authors identify a construct containing CD3ζ and TLR4 intracellular domains (ICDs) as particularly effective in eliciting robust antitumor responses and synergizing with PD-1/L1 checkpoint therapy.

Methods and Experimental Design Insights

The research employs a multi-faceted experimental design:

• Macrophage-targeted mRNA-LNP Formulation: The mRNA-LNPs are engineered to selectively transfect peritoneal macrophages upon intraperitoneal injection, achieving high transfection efficiency without significant off-target effects.
• Systematic CAR Design: Thirty-six CAR formats are screened, focusing on combinations of signaling domains (notably CD3ζ and TLR4 ICDs) to optimize immune activation.
• In Vivo Functional Assessment: Mouse models of peritoneal metastasis are used to evaluate antitumor efficacy, CAR-M persistence, and synergy with immune checkpoint blockade.
• Single-Cell RNA-seq: This technology is leveraged to dissect the cellular and molecular changes in the TME following CAR-M programming, including effects on T cell subpopulations.
• Bioluminescence Imaging: Cellular viability and metabolic activity are monitored non-invasively using ATP-dependent bioluminescence assays, a workflow underpinned by the use of high-purity firefly luciferase substrates such as D-Luciferin sodium salt (see related review).

Core Findings and Why They Matter

The study demonstrates that intraperitoneally programmed CAR-Ms with CD3ζ-TLR4 ICDs not only enhance phagocytic function and maintain a proinflammatory phenotype but also upregulate MHC-I and PD-L1 by modulating NF-κB signaling. Notably, CAR-M therapy leads to a reshaping of the TME, promoting infiltration and expansion of TCF1+PD-1+ progenitor-exhausted CD8+ T cells (Tpex), which are associated with improved responses to checkpoint inhibition. When combined with PD-1/L1 blockade, this approach produces synergistic antitumor effects. These insights broaden our mechanistic understanding of how engineered macrophages can modulate both innate and adaptive immunity within solid tumors, and position in situ mRNA-LNP programming as a highly adaptable strategy for overcoming immunosuppressive niches.

Comparison with Existing Internal Articles

The current study builds upon and extends concepts discussed in internal resources such as "Illuminating the Path from Mechanism to Medicine", which highlights the central role of D-Luciferin sodium salt in ATP-dependent bioluminescence assays for metabolic and gene expression monitoring. Gu et al.'s use of bioluminescence imaging exemplifies the translational application of these assays in preclinical immunotherapy models, providing sensitive, real-time readouts of cell viability and metabolic status. Other internal articles, such as "Intraperitoneal mRNA-LNP Programming of CAR Macrophages in Oncology", overview the innovation of in situ macrophage engineering but do not provide the same systematic, mechanistic insights into CAR intracellular domain selection or TME modulation as the reference study does.

Additionally, the workflow challenges and solutions for high-sensitivity cell viability monitoring discussed in "D-Luciferin Sodium Salt: Reliable Bioluminescence Workflows" are directly relevant to the imaging strategies employed in this study. The reference work reinforces the importance of robust, ATP-dependent bioluminescence assays for tracking engineered cell therapies in vivo.

Limitations and Transferability

While the study establishes a powerful proof-of-concept for intraperitoneal programming of CAR-Ms, several limitations remain. The preclinical mouse models, while informative, may not fully recapitulate the complexity or heterogeneity of human peritoneal metastases. The durability and safety of repeated mRNA-LNP administration, as well as the long-term fate of engineered macrophages, require further investigation. Moreover, the approach’s applicability to other anatomical sites or tumor types is yet to be established. While the study’s findings are promising, translation to clinical practice will need careful evaluation of immune-related adverse events and off-target effects.

Protocol Parameters

• mRNA-LNP Administration: Intraperitoneal injection; dosing and schedule optimized for macrophage transfection efficiency in murine models.
• CAR Construct Screening: 36 formats assessed; CD3ζ-TLR4 ICDs identified as optimal for immune activation.
• Bioluminescence Imaging: Use of ATP-dependent firefly luciferase substrate (e.g., D-Luciferin sodium salt); imaging performed at defined intervals to monitor cell viability and therapy response.
• Checkpoint Inhibitor Combination: PD-1/L1 antibodies administered per standard protocols to test synergy with CAR-M therapy.

Research Support Resources

To replicate or extend ATP-dependent bioluminescence workflows for cell viability and metabolism monitoring in similar immunotherapy models, researchers may utilize D-Luciferin sodium salt (SKU B8311), a validated firefly luciferase substrate. This reagent is widely applied in non-invasive imaging of gene expression and cellular metabolism in oncology research, as noted in the internal workflow guidance. For optimal results, freshly prepared solutions should be used, adhering to recommended solubility and storage conditions. APExBIO’s substrate supports sensitive and reproducible bioluminescence assays that are integral to evaluating engineered cell therapies in preclinical models.