Capsular polysaccharides of encapsulated bacterial pathogens such as Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenza, and Salmonella enterica serovar Typhi are the primary antigenic components involved in protective immunity. Purified polysaccharides of these bacteria, however, are T-independent antigens, that elicit poor antibody responses in children under the age of 2 and do not elicit a ‘memory’, or anamnestic immune response. Polysaccharide antigens can be covalently linked (conjugated) to a protein carrier, and converted to T-dependent antigens, capable of eliciting robust and anamnestic immune responses. However, the manufacture of polysaccharide-protein conjugate vaccines is a complex and expensive process, requiring each polysaccharide to be conjugated to a carrier protein in individual chemical reactions. The manufacture process for conjugate vaccines is further complicated by the diversity of capsule composition and structure, which often necessitates different conjugation chemistries and the need to produce multivalent vaccines that contain many different capsular polysaccharides.
Protein Capsular Matrix Vaccine (PCMV) technology is an alternative to conjugate vaccine technology, commonly termed a ‘virtual conjugate’. In PCMV technology, the capsular antigens are entrapped in a matrix of crosslinked carrier protein, rather than covalently linked to a carrier protein, as in conjugate technology, making this a ‘single reaction’ chemistry enabling efficient production of multivalent polysaccharide vaccines, resulting in lower cost of goods.