Microbial Rhamnolipid-Stabilized mRNA Nanovaccines Target DCs for Enhanced Immunity

Study Background and Research Question

Lipid nanoparticles (LNPs) have transformed the landscape of mRNA delivery, underpinning the success of mRNA-based vaccines for infectious diseases and other applications. Traditionally, LNPs utilize poly(ethylene glycol) (PEG)-lipids to impart colloidal stability and extend circulation time. However, repeated exposure to PEG-lipids can trigger anti-PEG immune responses, leading to accelerated blood clearance and hypersensitivity reactions, thereby limiting their clinical utility. The key research question addressed by Kong et al. is whether microbial rhamnolipids (RLs) can serve as biocompatible, self-adjuvanting alternatives to PEG-lipids in LNPs for mRNA vaccine delivery—improving immunogenicity while minimizing adverse immune responses.

Key Innovation from the Reference Study

The central innovation of the study lies in engineering RL-stabilized LNPs (RL-LNPs) that simultaneously encapsulate mRNA and engage dendritic cells (DCs) via specific receptor targeting. Unlike PEG-lipids, RLs are biosurfactants with amphiphilic structures, enabling nanoparticle stabilization and conferring intrinsic adjuvant properties through pattern recognition receptor (PRR) engagement. This dual role is achieved without synthetic polymer additives, differentiating RL-LNPs from conventional PEG-based or synthetic hybrid delivery systems. The RL-LNPs combine high mRNA encapsulation efficiency with selective lymph node targeting, mediated by interactions with the mannose receptor and DEC205 on DCs, thereby enhancing both delivery and immune activation in one platform.

Methods and Experimental Design Insights

The authors prepared RL-LNP formulations by substituting PEG-lipids with purified microbial rhamnolipids, maintaining other canonical LNP components such as ionizable lipids, phospholipids, and cholesterol. They evaluated encapsulation efficiency using bioluminescent mRNA reporters and assessed physical stability. Cellular uptake was investigated in vitro using dendritic cell lines and primary cells, focusing on receptor-mediated endocytosis pathways. In vivo, mice were administered RL-LNPs intramuscularly, and the biodistribution, expression kinetics, and immunogenicity of the encapsulated mRNA were tracked using reporter gene expression and serological assays. Comparative analyses with size-matched PEG-LNPs were performed to delineate the unique contributions of RLs. Proteomic profiling and western blotting elucidated downstream immune signaling pathways, particularly C-type lectin receptor (CLR)/NF-κB axis activation, to confirm intrinsic adjuvancy.

Core Findings and Why They Matter

RL-LNPs demonstrated several advantages over conventional PEG-LNPs:

• Efficient mRNA Encapsulation: RL-LNPs achieved over 90% encapsulation efficiency, comparable to or exceeding PEG-LNPs, a critical parameter for robust mRNA delivery.
• Enhanced Dendritic Cell Uptake and Lymph Node Targeting: RL-LNPs preferentially engaged the mannose receptor and DEC205 on DCs, resulting in higher accumulation and gene expression in draining lymph nodes after intramuscular injection. This targeting is essential for efficient vaccine priming.
• Potent Adaptive Immune Responses: In immunization experiments, RL-LNPs induced strong Th1-biased humoral and cytotoxic T-cell responses, surpassing PEG-LNPs in both magnitude and quality of immunity. Enhanced neutralizing antibody titers and T-cell activation were observed against model antigens and pseudoviruses.
• Intrinsic Adjuvant Effect: Proteomic and mechanistic analyses confirmed that RLs activate the CLR/NF-κB signaling axis in antigen-presenting cells, acting as pathogen-associated molecular patterns (PAMPs) to amplify immune activation without external adjuvants.
• Reduced Anti-Carrier Immunogenicity and Improved Safety: Unlike PEG-LNPs, RL-LNPs did not elicit anti-PEG antibodies or induce mast cell infiltration upon repeated dosing, mitigating hypersensitivity risks often seen with PEG-lipid carriers. Systemic toxicity and histological analyses indicated a favorable safety profile for RL-LNPs.

Collectively, these results establish RL-LNPs as a promising platform for mRNA delivery, coupling stabilization, targeted delivery, and intrinsic immunostimulation, which are all crucial for effective mRNA vaccine development.

Comparison with Existing Internal Articles

Several internal articles provide complementary perspectives on mRNA delivery and assay optimization. For instance, EZ Cap™ Firefly Luciferase mRNA (5-moUTP) is highlighted for its immune-silent expression profile and stability, facilitating reliable in vitro and in vivo translation efficiency assays. While the reference study by Kong et al. focuses on the delivery vehicle (RL-LNPs), the internal articles underscore the importance of the mRNA cargo design—such as 5-moUTP modifications and Cap1 capping—for minimizing innate immune activation and maximizing protein yield. Additionally, another resource explores how optimized mRNA chemistry, combined with advanced LNP delivery strategies, can further enhance gene expression assays, supporting the synergy between vector and cargo design. The current study's focus on immune activation suppression and targeted delivery complements these insights, suggesting that both delivery system and mRNA format are critical determinants of translational success.

Limitations and Transferability

Despite promising findings, RL-LNPs require further investigation before broad clinical translation. Potential limitations include:

• Biocompatibility Across Species: While RLs are generally recognized as biocompatible, their safety and immunogenicity profiles must be validated in larger animal models and diverse human populations.
• Scalability and Manufacturing: The reproducible synthesis and purification of microbial RLs at industrial scale may present logistical challenges compared to well-established PEG-lipid production.
• Versatility Across mRNA Types: Although the study uses model antigens, the generalizability of RL-LNPs for different mRNA cargos, including therapeutic or self-amplifying mRNAs, remains to be systematically evaluated.
• Long-Term Immunogenicity: The durability of the immune response and potential for chronic immune activation with RL-LNPs are not yet fully understood.

Transferability to other mRNA delivery contexts—such as gene therapy or protein replacement—will depend on further proof that RL-LNPs maintain performance with various mRNA formats and under different dosing regimens.

Protocol Parameters

• mRNA encapsulation: Prepare RL-LNPs using microfluidic mixing, maintaining a final mRNA:lipid ratio as described in the reference study.
• Administration route: Intramuscular injection is recommended for efficient lymph node targeting and immunogenicity assessment.
• Dendritic cell targeting validation: Use in vitro uptake assays with DCs expressing mannose receptor and DEC205; confirm with in vivo imaging or flow cytometry.
• Immunogenicity assessment: Quantify Th1/Th2 responses using ELISA and T-cell assays post-immunization with RL-LNP-mRNA vaccines.
• Repeat dosing safety: Monitor for mast cell infiltration and anti-carrier antibody development after multiple administrations.

Research Support Resources

To support analogous workflows in mRNA delivery and translation efficiency assay development, researchers can utilize EZ Cap™ Firefly Luciferase mRNA (5-moUTP) (SKU R1013). This in vitro transcribed mRNA incorporates 5-methoxyuridine and a Cap1 structure to enhance translation, stability, and reduce innate immune activation, aligning with the goals of immune-silent, high-yield gene expression described in both the reference study and related internal resources. For optimal results, the product should be handled under RNase-free conditions, aliquoted to prevent freeze-thaw cycles, and mixed with suitable transfection reagents prior to delivery into serum-containing media. This tool is suitable for evaluating the performance of novel nanoparticle delivery systems such as RL-LNPs and for benchmarking translation efficiency in cell-based or in vivo bioluminescent reporter gene assays.