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Stable Surface Display Engineering for Oral and Mucosal Vaccine Delivery Strains

Oral/mucosal vaccines often fail not because antigens are not expressed, but because they are not stably exposed on the bacterial surface throughout passaging and gastrointestinal transit. Creative Biolabs provides an end-to-end engineering workflow—from anchor selection and vector/integration design to surface localization validation (Flow/IF/Western) and stability profiling under passaging & GI-like stresses—with quantitative readouts and actionable recommendations to move your candidate toward in vivo studies.

Overcoming Antigen Delivery Bottlenecks in Live Biotherapeutic Products

The primary bottleneck in utilizing lactic acid bacteria and other probiotics as mucosal vaccine vectors is not merely achieving protein expression, but ensuring the stable, accessible surface display of the target antigen. Unstable anchoring leads to antigen shedding in the gastrointestinal tract, significantly diluting the localized immune response. Our engineering platform is meticulously designed to resolve this pain point, transforming promising genetic concepts into robust, validation-ready vaccine delivery strains capable of maintaining antigen integrity in harsh physiological environments.

Comprehensive Surface Display Engineering Services

We construct highly efficient cell surface display systems tailored to your specific live biotherapeutic strain and antigen characteristics, providing actionable data at every step.

Anchor Protein Selection & Vector Construction

Proper anchor selection is critical for maximizing surface density and structural presentation. We screen and integrate optimal anchoring motifs—including covalent anchors (e.g., LPXTG motifs interacting with sortase A) and non-covalent binding domains (e.g., LysM domains, S-layer proteins). Furthermore, we construct robust expression vectors utilizing highly efficient constitutive or inducible promoters (such as the nisin-controlled expression system, NICE) and perform precise chromosomal integration to eliminate the need for antibiotic resistance markers during downstream scale-up.

Expression & Display Validation

Displaying a protein is only half the challenge; proving it is strictly localized to the surface is the other. Our multi-tiered validation approach provides orthogonal evidence for surface localization. We deploy Flow Cytometry to quantitatively measure the percentage of cells successfully displaying the antigen. We complement this with Immunofluorescence (IF) microscopy for direct visual confirmation of spatial localization, and perform cell fractionation followed by Western Blot to definitively differentiate cell-wall associated proteins from cytosolic remnants.

Genetic & Environmental Stability Testing

A vaccine strain must remain functionally consistent. We evaluate the genetic stability of the engineered display cassette across multiple generations (in vitro passaging). Additionally, we rigorously expose the recombinant strain to stress testing—including Simulated Gastric Fluid (SGF), Simulated Intestinal Fluid (SIF), and varying bile salt concentrations—to assess whether the displayed antigen maintains integrity against premature proteolytic degradation during host transit.

Exploratory In Vitro Immune Screening (Optional)

To bridge the gap between engineering and therapeutic efficacy, we provide early-stage functional validation. By employing co-culture assays with specific antigen-presenting cells (e.g., dendritic cells, macrophages) or specialized epithelial models, we track cell activation markers and conduct comprehensive cytokine profiling (such as IL-10, IL-12, and TNF-alpha). These in vitro readouts offer early evidence of mucosal immune stimulation potential.

Note: These assays are intended for early screening and mechanism-oriented insights and do not replace in vivo immunogenicity/efficacy studies.

Standardized Deliverables for Vaccine Strain Engineering

Every project concludes with comprehensive documentation, validated strains, and reproducible datasets designed for smooth regulatory and manufacturing transitions.

Project Phase Specific Deliverable Methodology / Format
Phase 1: Design & Construction Engineered Expression Vectors & Plasmids
Transformed/Integrated Host Strains 		Purified plasmids, glycerol stocks of strains, full sequencing reports confirming in-frame integration.
Phase 2: Display Validation Surface Expression Quantification
Localization Confirmation 		Surface display efficiency (% antigen-positive cells, MFI shift), Localization confidence (whole-cell vs. permeabilized staining, cell wall fraction enrichment via WB), High-resolution IF imaging.
Phase 3: Stability & Stress Generational Stability Report
Gastrointestinal Survival Curves 		Genetic stability: cassette retention and expression drift (MFI trends) for up to 50 generations (project-dependent). Stress stability: SGF/SIF exposure pre/post display % and survival (CFU).
Phase 4: Exploratory Immune Screening In vitro Screening Data In vitro co-culture assay reports, multiplex cytokine expression panels, raw analytical data.

Streamlined Workflow for Recombinant Delivery Strains

1

Consultation & Design

Determine target antigen characteristics, select host strain, and identify optimal surface anchor systems.

2

Vector Assembly

Synthesize genes, optimize codons for the host, and construct expression plasmids with selected promoters.

3

Strain Engineering

Execute transformation and chromosomal integration, followed by rigorous sequence verification of clones.

4

Validation & Analytics

Conduct Flow Cytometry, Western Blotting, and Immunofluorescence to confirm robust surface display.

5

Functional Delivery

Assess stress survival, evaluate genetic stability, perform exploratory in vitro immunoassays, and deliver final materials.

Scientific Grounding in Surface Display Technologies

Recent advancements highlight the immense potential of Genetically Modified Lactic Acid Bacteria (gmLAB) as vectors for mucosal vaccines. As delineated by Chowdhury et al. (2025), gmLAB can be engineered to express therapeutic antigens in three primary spatial configurations: intracellular accumulation, extracellular secretion, and surface display. Among these, stable surface display is considered highly advantageous for oral and mucosal vaccine delivery formats.

By fusing the target antigen to specific cell wall anchoring motifs—such as the LPXTG covalent sorting signal or non-covalent binding domains like LysM—the antigen remains structurally accessible directly on the bacterial envelope. This specific configuration facilitates direct, sustained interaction with the host mucosal immune system, including antigen-presenting cells such as dendritic cells and M cells situated in the gut-associated lymphoid tissue (GALT).

Consequently, surface-displayed antigens have been reported to elicit more robust secretory IgA (sIgA) responses and enhanced systemic immunity compared to secreted or intracellularly trapped variants. Creative Biolabs leverages these exact biological paradigms. Our surface display engineering services are strategically designed to optimize the anchoring efficiency and spatial presentation of your vaccine candidates, ensuring they replicate the successful expression patterns recognized in cutting-edge mucosal immunology research.

Recombinant protein expression patterns in gmLAB and administration routes. (Creative Biolabs Authorized)
Fig.1 Schematic representation of recombinant protein expression patterns in gmLAB and administration routes. 1,2

Frequently Asked Questions

Surface display physically tethers the therapeutic antigen to the bacterial cell wall, which inherently acts as a potent biological adjuvant. This structural configuration ensures that the antigen and the immunostimulatory signals from the bacteria are delivered simultaneously to antigen-presenting cells (APCs). Furthermore, it prevents the antigen from being rapidly diluted, washed away, or degraded by enzymes in the highly active mucosal environment, a critical challenge commonly faced with freely secreted proteins.

We deploy a rigorous, multi-tiered validation approach. Flow cytometry using fluorescently labeled antibodies specific to your antigen provides robust quantitative data regarding the percentage of the bacterial population actively displaying the protein. We supplement this with Immunofluorescence (IF) microscopy for direct spatial visualization of the surface localization. Finally, controlled cell fractionation followed by Western blot analysis definitively distinguishes cell wall-associated proteins from cytosolic fractions, providing orthogonal evidence for surface localization.

Absolutely. For successful clinical transition and alignment with regulatory expectations/commonly recommended approaches for live biotherapeutics, we highly recommend and routinely execute markerless chromosomal integration of the expression cassettes. This methodology ensures long-term genetic stability of the engineered strain without necessitating continuous antibiotic selection pressure during downstream fermentation, manufacturing scale-up, or ultimate in vivo application.

Our anchor selection is driven by the host strain physiology and the specific structural or conformational requirements of your antigen. Common and highly effective options include covalent anchors, such as the widely validated LPXTG motif (which is cleaved and covalently anchored by host sortase A enzymes), and diverse non-covalent anchors like LysM domains or S-layer proteins. We frequently perform parallel testing of multiple anchor constructs to empirically determine the optimal display efficiency and stability for your specific candidate.

Other Resources

Creative Biolabs' Live Biotherapeutics - Brochure (Creative Biolabs Original)

Creative Biolabs' Live Biotherapeutics - Brochure

Probiotic Strain Products for NGP Research - Brochure (Creative Biolabs Original)

Probiotic Strain Products for NGP Research - Brochure

Custom Small-scale Probiotic Production - Brochure (Creative Biolabs Original)

Custom Small-scale Probiotic Production - Brochure

Live Biotherapeutics - Creative Biolabs - Video (Creative Biolabs Original)

Live Biotherapeutics - Creative Biolabs - Video

References

  1. Chowdhury, Md Rayhan, et al. "Genetically Modified Lactic Acid Bacteria: a Promising Mucosal Delivery Vector for Vaccines." Probiotics and Antimicrobial Proteins (2025): 1-19. https://doi.org/10.1007/s12602-025-10667-3
  2. Distributed under Open Access license CC BY 4.0, without modification.
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