Transgenic papaya: a useful platform for oral vaccines.

MAIN CONCLUSION: Transgenic papaya callus lines expressing the components of the S3Pvac vaccine constitute a stable platform to produce an oral vaccine against cysticercosis caused by Taenia solium or T. crassiceps. The development of effective delivery systems to cope with the reduced immunogenicity of new subunit vaccines is a priority in vaccinology. Herein, experimental evidence supporting a papaya-based platform to produce needle-free, recombinant, highly immunogenic vaccines is shown. Papaya (Carica papaya) callus lines were previously engineered by particle bombardment to express the three protective peptides of the S3Pvac anti-cysticercosis vaccine (KETc7, KETc12, KETc1). Calli were propagated in vitro, and a stable integration and expression of the target genes has been maintained, as confirmed by PCR, qRT-PCR, and HPLC. These results point papaya calli as a suitable platform for long-term transgenic expression of the vaccine peptides. The previously demonstrated protective immunogenic efficacy of S3Pvac-papaya orally administered to mice is herein confirmed in a wider dose-range and formulated with different delivery vehicles, adequate for oral vaccination. This protection is accompanied by an increase in anti-S3Pvac antibody titers and a delayed hypersensitivity response against the vaccine. A significant increase in CD4+ and CD8+ lymphocyte proliferation was induced in vitro by each vaccine peptide in mice immunized with the lowest dose of S3Pvac papaya (0.56 ng of the three peptides in 0.1 µg of papaya callus total protein per mouse). In pigs, the obliged intermediate host for Taenia solium, S3Pvac papaya was also immunogenic when orally administered in a two-log dose range. Vaccinated pigs significantly increased anti-vaccine antibodies and mononuclear cell proliferation. Overall, the oral immunogenicity of this stable S3Pvac-papaya vaccine in mice and pigs, not requiring additional adjuvants, supports the interest in papaya callus as a useful platform for plant-based vaccines.

Identification of loci controlling restriction of parasite growth in experimental Taenia crassiceps cysticercosis.

Human neurocysticercosis (NC) caused by Taenia solium is a parasitic disease of the central nervous system that is endemic in many developing countries. In this study, a genetic approach using the murine intraperitoneal cysticercosis caused by the related cestode Taenia crassiceps was employed to identify host factors that regulate the establishment and proliferation of the parasite. A/J mice are permissive to T. crassiceps infection while C57BL/6J mice (B6) are comparatively restrictive, with a 10-fold difference in numbers of peritoneal cysticerci recovered 30 days after infection. The genetic basis of this inter-strain difference was explored using 34 AcB/BcA recombinant congenic strains derived from A/J and B6 progenitors, that were phenotyped for T. crassiceps replication. In agreement with their genetic background, most AcB strains (A/J-derived) were found to be permissive to infection while most BcA strains (B6-derived) were restrictive with the exception of a few discordant strains, together suggesting a possible simple genetic control. Initial haplotype association mapping using >1200 informative SNPs pointed to linkages on chromosomes 2 (proximal) and 6 as controlling parasite replication in the AcB/BcA panel. Additional linkage analysis by genome scan in informative [AcB55xDBA/2]F1 and F2 mice (derived from the discordant AcB55 strain), confirmed the effect of chromosome 2 on parasite replication, and further delineated a major locus (LOD = 4.76, p<0.01; peak marker D2Mit295, 29.7 Mb) that we designate Tccr1 (T. crassiceps cysticercosis restrictive locus 1). Resistance alleles at Tccr1 are derived from AcB55 and are inherited in a dominant fashion. Scrutiny of the minimal genetic interval reveals overlap of Tccr1 with other host resistance loci mapped to this region, most notably the defective Hc/C5 allele which segregates both in the AcB/BcA set and in the AcB55xDBA/2 cross. These results strongly suggest that the complement component 5 (C5) plays a critical role in early protective inflammatory response to infection with T. crassiceps.