Abstract
BackgroundYeast cells represent an established bioreactor to produce recombinant proteins for subunit vaccine development. In addition, delivery of vaccine antigens directly within heat-inactivated yeast cells is attractive due to the adjuvancy provided by the yeast cell. In this study, Pichia pastoris yeast lysates carrying the nucleoprotein (N) from the measles vaccine virus were evaluated as a novel subunit vaccine platform to deliver the circumsporozoite surface antigen (CS) of Plasmodium. When expressed in Pichia pastoris yeast, the N protein auto-assembles into highly multimeric ribonucleoparticles (RNPs). The CS antigen from Plasmodium berghei (PbCS) was expressed in Pichia pastoris yeast in fusion with N, generating recombinant PbCS-carrying RNPs in the cytoplasm of yeast cells.ResultsWhen evaluated in mice after 3–5 weekly subcutaneous injections, yeast lysates containing N-PbCS RNPs elicited strong anti-PbCS humoral responses, which were PbCS-dose dependent and reached a plateau by the pre-challenge time point. Protective efficacy of yeast lysates was dose-dependent, although anti-PbCS antibody titers were not predictive of protection. Multimerization of PbCS on RNPs was essential for providing benefit against infection, as immunization with monomeric PbCS delivered in yeast lysates was not protective. Three weekly injections with N-PbCS yeast lysates in combination with alum adjuvant produced sterile protection in two out of six mice, and significantly reduced parasitaemia in the other individuals from the same group. This parasitaemia decrease was of the same extent as in mice immunized with non-adjuvanted N-PbCS yeast lysates, providing evidence that the yeast lysate formulation did not require accessory adjuvants for eliciting efficient parasitaemia reduction.ConclusionsThis study demonstrates that yeast lysates are an attractive auto-adjuvant and efficient platform for delivering multimeric PbCS on measles N-based RNPs. By combining yeast lysates that carry RNPs with a large panel of Plasmodium antigens, this technology could be applied to developing a multivalent vaccine against malaria.
Highlights
Yeast cells represent an established bioreactor to produce recombinant proteins for subunit vaccine development
Yeast lysates of Pichia pastoris expressing N‐PbCS RNPs are immunogenic In our previous work, we showed that whole recombinant Pichia pastoris yeast expressing N-PbCS RNPs elicited significant reduction of parasitaemia and decreased clinical damages associated with a highly stringent P. berghei infection in C57Bl/6 mice [6]
Yeast lysates were evaluated as a platform for delivery of antigens multimerized by means of the measles virus nucleoprotein (N)
Summary
Yeast cells represent an established bioreactor to produce recombinant proteins for subunit vaccine development. Pichia pastoris yeast lysates carrying the nucleoprotein (N) from the measles vaccine virus were evaluated as a novel subunit vaccine platform to deliver the circumsporozoite surface antigen (CS) of Plasmodium. A novel subunit vaccine platform based on antigen delivery within heat-inactivated Pichia pastoris yeasts was developed [6]. The measles virus N protein has a remarkable capacity to auto-assemble around local cytoplasmic RNA molecules in multiple expression systems (mammalian [12], bacterial [13], insect [14] or yeast [15] cells) and to generate helical, highly stable and multimeric ribonucleoparticles (RNPs), which resemble the RNP of MV [16]. To take advantage of such intrinsic properties, N-based RNPs the authors used to multimerize antigens of choice and deliver such antigen-carrying RNPs within whole heat-inactivated yeast [6]
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