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. 2017 Dec 27;12(12):e0190312.
doi: 10.1371/journal.pone.0190312. eCollection 2017.

Protein-protein conjugate nanoparticles for malaria antigen delivery and enhanced immunogenicity

Puthupparampil V Scaria  1 , Beth Chen  1 , Christopher G Rowe  1 , David S Jones  1 , Emma Barnafo  1 , Elizabeth R Fischer  2 , Charles Anderson  1 , Nicholas J MacDonald  1 , Lynn Lambert  1 , Kelly M Rausch  1 , David L Narum  1 , Patrick E Duffy  1
Affiliations

Protein-protein conjugate nanoparticles for malaria antigen delivery and enhanced immunogenicity

Puthupparampil V Scaria et al. PLoS One. .

Abstract

Chemical conjugation of polysaccharide to carrier proteins has been a successful strategy to generate potent vaccines against bacterial pathogens. We developed a similar approach for poorly immunogenic malaria protein antigens. Our lead candidates in clinical trials are the malaria transmission blocking vaccine antigens, Pfs25 and Pfs230D1, individually conjugated to the carrier protein Exoprotein A (EPA) through thioether chemistry. These conjugates form nanoparticles that show enhanced immunogenicity compared to unconjugated antigens. In this study, we examined the broad applicability of this technology as a vaccine development platform, by comparing the immunogenicity of conjugates prepared by four different chemistries using different malaria antigens (PfCSP, Pfs25 and Pfs230D1), and carriers such as EPA, TT and CRM197. Several conjugates were synthesized using thioether, amide, ADH and glutaraldehyde chemistries, characterized for average molecular weight and molecular weight distribution, and evaluated in mice for humoral immunogenicity. Conjugates made with the different chemistries, or with different carriers, showed no significant difference in immunogenicity towards the conjugated antigens. Since particle size can influence immunogenicity, we tested conjugates with different average size in the range of 16-73 nm diameter, and observed greater immunogenicity of smaller particles, with significant differences between 16 and 73 nm particles. These results demonstrate the multiple options with respect to carriers and chemistries that are available for protein-protein conjugate vaccine development.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Anti-CSP antibody titer of EPA conjugates of PfCSP synthesized by thioether (TE), Amide (Am) and Glutaraldehyde (GA) conjugation chemistry.
Mice were immunized with conjugates formulated in saline or Alhydrogel. Sera were analyzed on Day 42 after vaccination on Day 0 and 28. Dose: 0.5 μg/mouse.
Fig 2
Fig 2. Anti-CSP antibody titer of EPA conjugates of PfCSP synthesized by thioether (TE) and Adipic acid Dihydrazide (ADH) conjugation chemistry.
Mice were immunized with conjugates formulated in saline or Alhydrogel. Sera were analyzed on Day 42 after vaccination on Day 0 and 28. Dose: 0.5 μg/mouse.
Fig 3
Fig 3. Anti-Pfs25 or Pfs230D1 antibody titer of EPA conjugates of Pfs25 and Pfs230D1 synthesized by thioether (TE) and Amide (Am) conjugation chemistry.
Mice were immunized with conjugates formulated in saline or Alhydrogel. Sera were analyzed on Day 42 after vaccination on Day 0 and 28. Dose: 0.5 μg/mouse.
Fig 4
Fig 4. Anti-Pfs25 antibody titer of EPA, TT or CRM conjugates of Pfs25 synthesized by thioether (TE) chemistry formulated in either Alhydrogel (AH) or AdjuPhos (AP).
Immune sera were collected from Day 42 after two vaccinations were analyzed. Dose: 0.5 μg/mouse.
Fig 5
Fig 5. Anti-Pfs25 antibody titer of EPA conjugates of Pfs25 with varying average molecular weight and particle size, synthesized by thioether (TE) chemistry, formulated in either saline or Alhydrogel (AH).
Immune sera collected on Day 42 (left panel) or 70 (right panel) were analyzed by ELISA. Vaccinations on Days 0 and 28. Doses: 0.5 μg or 0.1 μg/mouse/injection as indicated.
Fig 6
Fig 6
Transmission electron microscopy (A) and scanning electron microscopy images of Pfs25-EPA conjugate. Scale bars, A: 200 nm, B: 1.0 um.
See this image and copyright information in PMC

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