Study Notes on TLR4 Agonist and Immune Response Profiles in Pertussis Vaccines

Immunology Study Notes: TLR4 Agonist BECC438b and Immune Response Profiles from Vaccines

Author Information

  • Authors: Megan A. DeJong, M. Allison Wolf, Graham J. Bitzer, Jesse M. Hall, Nicholas A. Fitzgerald, Gage M. Pyles, Annalisa B. Huckaby, Jonathan E. Petty, Katherine Lee, Mariette Barbier, Justin R. Bevere, Robert K. Ernst, F. Heath Damron
  • Affiliations: West Virginia University, University of Maryland School of Dentistry

Abstract

  • The protection from acellular pertussis vaccines (aP vaccines) decreases over time, leading to the need for improved formulations.
  • Various methods to improve vaccine efficiency include using different adjuvants and administration routes.
  • Intramuscular (IM) vaccination provides a strong systemic immune response; however, intranasal (IN) vaccination is intended to create a local immune response, similar to natural infection.
  • Current aP vaccines incorporate alum as an adjuvant, but antibody levels decline over time.
  • BECC438b: A novel TLR4 agonist incorporated into both formulation routes to test against mortality in a murine challenge model.
  • Results show that DTaP + BECC438b significantly reduced bacterial burden in the lung and trachea compared to controls.
  • IN vaccination induces a Th1 immune response, contrasting the Th2 response seen with IM vaccination.
  • RNA sequencing analysis indicated similar pathway activation as seen in natural infection, highlighting the effects of BECC438b on immune responses.

Keywords

  • Bordetella pertussis, whooping cough, DTaP, vaccines, Th1 immune response, TLR4 agonist, mucosal immunity, leukocytosis, bacterial challenge

Background

  • Despite nearly eradicating pertussis in the 1950s, the U.S. has seen cyclic surges in cases due to:
    • Use of acellular pertussis vaccines (DTaP/Tdap) which are associated with a Th2 dominant immune response.
    • The absence of pertactin (PRN) antigen in many strains of B. pertussis.
    • Waning immunity leading to asymptomatic infections.
  • Whole-cell pertussis vaccines (DTP/wP) provide better, long-lasting protection via Th1-polarized immune responses but are linked to adverse effects.

Adjuvants in Vaccination

  • Acellular Vaccines use alum as an adjuvant, which skews toward the Th2 response, advancing antibody production but limiting cell-mediated immunity needed for clearing B. pertussis.
  • There is ongoing research to integrate Th1-polarizing adjuvants such as TLR ligands into aP vaccines to mitigate these issues.
  • Lipid A Mimetics: Highly studied for Th1 response induction via TLR4.

Design and Synthesis of BECC438b

  • BECC438b is a bisphosphorylated lipid A derivative of Yersinia pestis engineered to induce balanced Th1/Th2 immune responses.
  • BECC438b improves efficacy in preclinical vaccine models across various pathogens including B. pertussis and SARS-CoV-2.

Study Methods

Vaccine Formulation

  • GSK Infanrix formulation used at 1/40th human dose (12.5 µL/vaccine) combined with BECC438b (50 µg/dose) for mouse vaccination, leading to both humoral and cellular immune responses.

Vaccine Administration

  • IM group: 50 µL administered in the right thigh.
  • IN group: 25 µL delivered into each nostril under anesthesia.
  • Mice challenged with B. pertussis strain UT25Sm1 (genome sequenced) and evaluated for CFUs.

Results

Intranasal vs. Intramuscular Administration

  • IN DTaP + BECC438b demonstrated superior protection against bacterial load in the nasal cavity and lung as compared to control groups.
  • IM vaccination maintained low tonsil counts, confirming the impact of administration route on immune activation and pathway expression post-challenge.

Immune Response Evaluation

  • Th1/Th2 Polarization: Analysis of IgG isotypes post-challenge showcased a shift in Th1 dominance correlated with IN administration of DTaP + BECC438b.
  • Significant elevations in IgA and IgG levels, particularly anti-PT antibodies, were observed in the IN group.

Cytokine Production and Inflammation

  • Post-challenge, cytokine profiles and histological analyses reflected increased inflammation mediated by BECC438b, suggesting a heightened anti-pathogen defense mechanism.
  • Increased recruitment of lymphocytes and plasma cells indicated that BECC438b supports a Th1 inflammatory profile.

RNA Sequencing

  • Comparative analysis of transcriptomic data derived from lung tissues showed differential gene expression profiles between IM and IN administered groups, highlighting distinct pathways activated by BECC438b.
  • GO term analysis indicated pathways primarily tied to immune activation were significantly more robust in mice receiving DTaP + BECC438b.

Discussion

  • The study provides evidence that switching from IM to IN administration of DTaP could enhance mucosal immunity while also suggesting potential synergies with novel adjuvants like BECC438b in a pertussis vaccine context.
  • In the long term, BECC438b presents a viable candidate for improving aP vaccine formulations, emphasizing the need to further explore its use against respiratory pathogens in future research.

Conclusion

  • Intranasal vaccination may confer protective immunity similar to natural infection, with BECC438b enhancing the immune response, offering insights for future vaccine development against pertussis and possibly other respiratory diseases.

Acknowledgments

  • Acknowledgment of key contributors and funding sources for the study.

Ethical Considerations

  • Research conducted in accordance with NIH Guidelines and approved by the West Virginia University Animal Care and Use Committee.

Additional Files

  • Supplementary figures and references outlining the comprehensive details of the study.