The infectious hepatitis B virus represents 42 nm spherical double-shelled particles. However, analysis of blood from hepatitis B virus carriers revealed the presence of smaller 22 nm particles consisting of a viral envelope surface protein. These particles are highly immunogenic and have been used in the design of hepatitis B virus vaccine produced in yeast. Upon expression in yeast, these proteins form virus-like particles that are used for parenteral immunization. Therefore, the DNA fragment encoding hepatitis B virus surface antigen was introduced into Agrobacterium tumerifacience LBA4404 and used to obtain transgenic lupin (Lupinus luteus L.) and lettuce (Lactuca sativa L.) cv. Burpee Bibb expressing envelope surface protein. Mice that were fed the transgenic lupin tissue developed significant levels of hepatitis B virus-specific antibodies. Human volunteers, fed with transgenic lettuce plants expressing hepatitis B virus surface antigen, developed specific serum-IgG response to plant produced protein.

Efficient immunization against hepatitis B virus (HBV) and other pathogens with plant-based oral vaccines requires appropriate plant expressors and the optimization of vaccine compositions and administration protocols. Previous immunization studies were mainly based on a combination of the injection of a small surface antigen of HBV (S-HBsAg) and the feeding with raw tissue containing the antigen, supplemented with an adjuvant, and coming from plants conferring resistance to kanamycin. The objective of this study was to develop a prototype oral vaccine formula suitable for human immunization. Herbicide-resistant lettuce was engineered, stably expressing through progeny generation micrograms of S-HBsAg per g of fresh weight and formed into virus-like particles (VLPs). Lyophilized tissue containing a relatively low, 100-ng VLP-assembled antigen dose, administered only orally to mice with a long, 60-day interval between prime and boost immunizations and without exogenous adjuvant, elicited mucosal and systemic humoral anti-HBs responses at the nominally protective level. Lyophilized tissue was converted into tablets, which preserved S-HBsAg content for at least one year of room temperature storage. The results of the study provide indications on immunization methodology using a durable, efficacious, and convenient plant-derived prototype oral vaccine against hepatitis B.

Quantitative trait loci for yield, yield components and seed protein content were investigated on the basis of experiments performed with two populations of pea (Pisum sativum L.) lines derived from linked crosses between lines Wt11238, Wt3557 and Wt10245 with contrasting characteristics. The yield-related traits were defined as components giving the grain yield in a multiplicative way. The aim was to clarify the genetic architecture of the relation between seed yield, its components and protein content, with a possible inclusion of the role of epistasis in this explanation. To take full advantage of the availability of the two populations, additive QTL effects and both types of epistasis were analysed: the QTL by genetic background interaction and the first-order QTL-QTL interaction. The two hybrid populations differed with respect to the prevailing gene action, which in the Wt11238 9 Wt3557 progeny was mainly additive, while in the Wt10245 9 Wt11238 progeny mainly epistatic. Some loci with previously reported, large, repeatable, but contradictory effects on yield and protein content were confirmed. New loci with alleles coming from the protein-rich Wt11238 line, positive for yield components, were identified. It was found that the first order QTL-QTL interaction events were more frequent for the loci showing the QTL by genetic background interaction.