Practice question

Subunit vaccines consist of specific antigenic components derived from pathogen rather than whole organism, representing purified or recombinant fractions capable of eliciting protective immunity. Components include capsular polysaccharides, detoxified toxins, recombinant surface proteins, virus-like particles formed by self assembly. Hepatitis B vaccine contains recombinant HBsAg 22 nm particles produced in Saccharomyces cerevisiae yeast after cloning S gene under alcohol oxidase promoter; human papillomavirus vaccine contains L1 protein VLPs from yeast or insect cells; influenza subunit vaccines contain purified hemagglutinin and neuraminidase after detergent treatment splitting virions; acellular pertussis contains pertussis toxin genetically mutated PT-9K/129G, filamentous hemagglutinin, pertactin and fimbriae 2/3. Advantages include precisely defined composition, inability to cause infection, reduced reactogenicity removing lipopolysaccharide, lower risk in immunocompromised hosts. Limitations include poor innate immunogenicity requiring adjuvants MF59 oil-in-water, AS01 containing QS21 saponin and MPL, aluminum to enhance Dendritic cell recruitment. Many polysaccharides T-independent requiring conjugation to carrier proteins tetanus or CRM197 converting to T-dependent response inducing germinal center memory, crucial for infant vaccines against Haemophilus and pneumococcus.