A protein subunit vaccine elicits a balanced immune response that protects against Pseudomonas pulmonary infection

Abstract

The opportunistic pathogen Pseudomonas aeruginosa (Pa) causes severe nosocomial infections, especially in immunocompromised individuals and the elderly. Increasing drug resistance, the absence of a licensed vaccine and increased hospitalizations due to SARS-CoV-2 have made Pa a major healthcare risk. To address this, we formulated a candidate subunit vaccine against Pa (L-PaF), by fusing the type III secretion system tip and translocator proteins with LTA1 in an oil-in-water emulsion (ME). This was mixed with the TLR4 agonist (BECC438b). Lung mRNA sequencing showed that the formulation activates genes from multiple immunological pathways eliciting a protective Th1-Th17 response following IN immunization. Following infection, however, the immunized mice showed an adaptive response while the PBS-vaccinated mice experienced rapid onset of an inflammatory response. The latter displayed a hypoxic lung environment with high bacterial burden. Finally, the importance of IL-17 and immunoglobulins were demonstrated using knockout mice. These findings suggest a need for a balanced humoral and cellular response to prevent the onset of Pa infection and that our formulation could elicit such a response.

Development of a nano-emulsion based multivalent protein subunit vaccine against Pseudomonas aeruginosa

“…Humans with CF have high levels of IL-17 in their sputum and their airway submucosa is more prone to be infiltrated with Th17 lymphocytes ( 22 , 23 ). Although this sounds alarming for a vaccine that partly depends on the Th17 response as a component of its efficacy, we have tested our vaccine in CF rats and the results are promising ( 8 – 10 , 24 ). Nevertheless, at this time, we do not have results that can confer a precise protective mechanism for our vaccine in these rats against acute Pa infection.…”

“…Previously, we demonstrated the importance of having a systemic humoral response, and a local lung response, to mount an effective anti-Pa immune response ( 10 ). The presence of serum IgG and IgA against PcrV and PopB of the Pa T3SA confirms the presence of a systemic immune response in the immunized mice.…”

“…L-PaF, BECC438b, and ME were prepared as previously described ( 9 , 10 ). The sequence for the C-terminus of ExlA (residues 1361-1651) was cloned into pET-15b to be expressed with an N-terminal histidine tag (HT).…”

“…The animals (n = 10) in these groups were immunized as follows: (a) PBS; (b) ExlA + dmLT; (c) ExlA + L-PaF + BECC/ME; (d) L-PaF + BECC/ME; (e) ExlA alone; (f) L-PaF; (g) PaF ± dmLT. For ExlA, dose escalation was conducted, while the doses for L-PaF, ME, and BECC438b were previously optimized ( 8 – 10 ). Mice were bled on days 0 and 56 post first immunization.…”

“…The total read counts were subjected to data processing and differential expression analyses using iDEP ( 17 ). Cutoff values for positive counts were set as described before ( 10 ). Briefly, at least 0.5 counts/million (CPM) reads were considered and transformed into log 2 (CPM) by EdgeR.…”