Intraperitoneal Programming of CAR Macrophages Using mRNA-LNP: A New Paradigm in Cancer Immunotherapy

Study Background and Research Question

Peritoneal metastasis in solid tumors remains a pressing clinical challenge, with standard interventions such as cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (HIPEC) benefiting only a minority of patients with minimal tumor burden [source_type: paper][source_link: https://doi.org/10.1038/s41467-025-67674-9]. The peritoneal cavity is highly immunologically active, notably harboring abundant macrophages, which can comprise approximately 45% of immune cells in malignant ascites [source_type: paper][source_link: https://doi.org/10.1038/s41467-025-67674-9]. Yet, these macrophages are generally not harnessed effectively in current immunotherapeutic strategies. The central research question addressed by Gu et al. (2025) is whether tailored programming of macrophages with chimeric antigen receptors (CARs) directly within the peritoneal cavity—using an mRNA-lipid nanoparticle (mRNA-LNP) delivery approach—can overcome the immunosuppressive environment and enhance antitumor immunity in solid tumor metastasis [source_type: paper][source_link: https://doi.org/10.1038/s41467-025-67674-9].

Key Innovation from the Reference Study

The core innovation lies in the development of a macrophage-targeted mRNA-LNP platform that enables rapid, in situ programming of native macrophages into CAR-Ms within the peritoneal cavity, bypassing the need for ex vivo cell engineering. This strategy allows for the systematic screening of 36 CAR designs with various intracellular domains (ICDs), ultimately identifying a CD3ζ-TLR4 ICD combination that confers robust antitumor functionality [source_type: paper][source_link: https://doi.org/10.1038/s41467-025-67674-9]. Two aspects distinguish this work:

1. Demonstration of in vivo reprogramming of resident peritoneal macrophages with high efficiency and specificity via mRNA-LNPs.
2. Comprehensive comparison of CAR constructs, revealing that inclusion of TLR4 costimulatory domains synergizes with canonical CD3ζ to enhance both innate and adaptive immune responses.

Methods and Experimental Design Insights

The study utilized a rational, modular approach to CAR design, constructing 36 distinct CARs with varying ICDs to dissect the impact on macrophage phenotype and function. The mRNA-LNP system was engineered for macrophage tropism and optimized for efficient intraperitoneal delivery. High-throughput single-cell RNA sequencing (scRNA-seq) and flow cytometry were employed to characterize immune cell populations and functional phenotypes post-treatment. Bioluminescence imaging was used to monitor tumor burden and CAR-M function in vivo, leveraging ATP-dependent bioluminescence assays—a field in which firefly luciferase substrate systems (such as D-Luciferin sodium salt) are standard for tracking cell viability and metabolism [source_type: workflow_recommendation][source_link: https://fireflyluciferase.com/index.php?g=Wap&m=Article&a=detail&id=11081].

Protocol Parameters

• assay | 24-48 hours post-injection | applicability: in vivo CAR-M persistence | rationale: correlates with peak CAR expression post-mRNA-LNP delivery | source_type: paper [source_link: https://doi.org/10.1038/s41467-025-67674-9]
• bioluminescence substrate (D-Luciferin sodium salt) | 150 mg/kg (mouse) | applicability: tumor burden quantification | rationale: optimal signal-to-noise ratio for in vivo imaging | source_type: workflow_recommendation [source_link: https://fireflyluciferase.com/index.php?g=Wap&m=Article&a=detail&id=11081]
• scRNA-seq cell loading | 5,000-10,000 cells/sample | applicability: immune population profiling | rationale: sufficient depth for TME analysis | source_type: paper [source_link: https://doi.org/10.1038/s41467-025-67674-9]

Core Findings and Why They Matter

Gu et al. demonstrated that their mRNA-LNP system effectively reprograms peritoneal macrophages into functional CAR-Ms, with the CD3ζ-TLR4 ICD variant displaying superior antitumor activity and a pronounced ability to reshape the tumor microenvironment (TME) [source_type: paper][source_link: https://doi.org/10.1038/s41467-025-67674-9]. Key mechanistic findings include:

• Cytokine analysis and scRNA-seq revealed that CAR-Ms with TLR4 costimulatory domains promoted a proinflammatory phenotype, upregulated MHC-I and PD-L1, and enhanced the infiltration and activation of TCF1+PD-1+ progenitor-exhausted CD8+ T cells (Tpex).
• Combining CAR-M therapy with PD-1/PD-L1 blockade resulted in synergistic tumor control, indicating that this approach can potentiate existing immune checkpoint therapies.
• NF-κB pathway perturbation was identified as a critical axis for maintaining the proinflammatory, antitumor activity of engineered CAR-Ms.

The use of ATP-dependent bioluminescence assays and in vivo imaging provided quantitative, non-invasive measures of cell viability and tumor progression, underscoring the importance of robust firefly luciferase substrate systems for workflow reproducibility.

Comparison with Existing Internal Articles

Several internal resources have articulated the central role of D-Luciferin sodium salt in enabling precise bioluminescence imaging for CAR macrophage studies:

• D-Luciferin Sodium Salt: Illuminating New Frontiers in CAR Macrophage Imaging contextualizes the workflow established by Gu et al., highlighting protocol best practices for non-invasive imaging and underscoring how substrate purity and solubility affect assay sensitivity [source_type: workflow_recommendation][source_link: https://uo126.com/].
• D-Luciferin Sodium Salt: Unveiling Cellular Energy Dynamics provides mechanistic insights into the link between bioluminescence imaging, cellular energy metabolism assessment, and immunotherapeutic efficacy. This aligns with the reference study's focus on cellular phenotype and energy status in vivo.
• D-Luciferin Sodium Salt (SKU B8311): Precision in ATP-Dependent Workflows offers technical guidance for ensuring substrate stability and assay reproducibility, directly supporting protocols used in the current study.

These resources collectively reinforce the translational importance of optimized firefly luciferase substrate selection in immuno-oncology workflows and provide practical recommendations for experimental design.

Limitations and Transferability

While the study establishes proof-of-concept for intraperitoneal programming of CAR-Ms, several limitations merit consideration:

• The findings are currently restricted to murine models; translation to human peritoneal immunobiology and clinical settings requires further validation [source_type: paper][source_link: https://doi.org/10.1038/s41467-025-67674-9].
• Long-term persistence, safety, and potential for off-target effects of in situ engineered macrophages were not fully elucidated and warrant extended follow-up.
• Optimization of mRNA-LNP formulation for selective macrophage targeting in the presence of heterogeneous immune populations in the peritoneal cavity remains an ongoing challenge.

Transferability to other metastatic sites or tumor types should be approached with caution, pending additional evidence for efficacy and safety beyond the peritoneal setting.

Research Support Resources

Researchers aiming to implement ATP-dependent bioluminescence assays or track engineered cell populations in vivo can leverage validated substrates such as D-Luciferin sodium salt (SKU B8311). This firefly luciferase substrate is highly soluble and widely adopted for cell viability and metabolism monitoring in preclinical models [source_type: product_spec][source_link: https://www.apexbt.com/d-luciferin-sodium-salt.html]. For further technical guidance and best practices, the internal articles referenced above provide scenario-driven recommendations tailored to oncology and immunotherapy assay workflows.