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Evaluation of live attenuated Streptococcus pneumoniae vaccine strains on the epithelial response to colonisation using a human challenge model

Weight, C, Guerra-Assuncao, J.A., Ramos-Sevillano, E, Blizzard, Anne, Venturini, C, Ferreira, Daniela ORCID:, Brown, J and Heyderman, Robert (2020) 'Evaluation of live attenuated Streptococcus pneumoniae vaccine strains on the epithelial response to colonisation using a human challenge model' in International Congress on Infectious Diseases 2020, Kuala Lumpur, Malaysia, 10-13th September.

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Background: Streptococcus pneumoniae frequently colonises
the human nasopharynx but causes over 500,000 deaths each year
from Pneumonia, Sepsis and Meningitis. Nasopharyngeal carriage
is required for transmission and is a pre-requisite for disease.
The conjugate polysaccharide vaccines have proven effective in
decreasing disease. However, replacement of vaccine serotypes
with non-vaccine types in carriage threatens the future of the vaccines’
Using an Experimental Human Pneumococcal Challenge model
(EHPC) and epithelial cell culture models, we have previously
shown that pneumococcal colonisation involves both direct epithelial
association and micro-invasion, inducing innate immunity and
clearance without overt disease. Repeated challenge in the EHPC
with the same strain decreases subsequent carriage efficiency and
diminishes transmission potential and/or progression to disease,
suggesting active mucosal immunity in the nasopharynx.

Methods and materials: We have generated live attenuated
strains of 6B S. pneumoniae (AS1 and AS2) that have double virulence
deletions and cannot revert to cause disease. Here, we have
explored the hypothesis that despite their attenuation in a mouse
model of disease, these attenuated strains retain their ability to
invade the epithelium and induce epithelial-derived innate immunity
in humans.
Colonisation were measured by confocal microscopy and microbiology
density by CFU counts. Epithelial activation was measured
by flow cytometry, ELISA and RNAseq.

Results: We found that both mutants colonised the human
nasopharynx and formed epithelial associations with microinvasion
in the EHPC model. In vitro, both mutants adhered, invaded
and transmigrated across the epithelium 4-fold less than wild type.
However, both mutants still resulted in secretion of IL-8, IL-6 and
ICAM-1 secretion and barrier integrity was maintained. PCA analyses
revealed that epithelial transcriptomic responses between wild
type and the mutants generally overlapped, indicating overall similar
stimulation of signaling pathways following exposure.

Conclusion: The results reveal that attenuation of these pneumococcal
strains has not led to loss of their ability to elicit amucosal
immune/inflammatory response. This approach provides an exciting
new pipeline for the development and testing of novel vaccines.
The application of these attenuated strains in the EHPC also has the
potential to provide important new knowledge on the mechanisms
behind bacterial clearance, transmission and disease progression
during colonisation.

Item Type: Conference or Workshop Item (Paper)
Subjects: QS Anatomy > Histology > QS 532.5.E7 Epithelium
QW Microbiology and Immunology > Bacteria > QW 142 Gram-positive bacteria (General)
WC Communicable Diseases > Infection. Bacterial Infections > Bacterial Infections > WC 202 Pneumonia (General or not elsewhere classified)
WC Communicable Diseases > Infection. Bacterial Infections > Bacterial Infections > WC 217 Pneumococcal infections
Faculty: Department: Clinical Sciences & International Health > Clinical Sciences Department
Depositing User: Julie Franco
Date Deposited: 13 Apr 2021 11:55
Last Modified: 17 Aug 2022 08:59


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