Practice question

Viral vector vaccines deliver genes encoding pathogen antigens using harmless viruses engineered to be replication deficient as transportation vehicles. Concept employs vector virus lacking pathogenic genes but retaining ability to infect mammalian cells, deliver DNA into nucleus, transcribe transgene using host polymerase, translate antigen intracellularly mimicking natural infection. Vector backbone commonly human adenovirus serotypes 5 and 26, chimpanzee adenovirus ChAdOx1, canarypox ALVAC, modified vaccinia Ankara MVA, vesicular stomatitis virus VSV, adeno associated virus. Deletion of E1 locus renders adenovirus unable to replicate except in complementing HEK293 cells, E3 deletion increases packaging capacity to 7-8 kb insert. Upon intramuscular injection vector transduces myocytes and dendritic cells, antigen peptides presented on MHC I to CD8 T cells and secreted antigen captured for MHC II to CD4, generating strong humoral and cellular immunity without need exogenous adjuvant because vector components trigger innate sensors TLR9 detecting dsDNA, cGAS STING. Pre-existing immunity to human adenovirus can impair efficacy, mitigated using rare serotypes or chimpanzee vectors low seroprevalence. Platform proved successful for Ebola Ad26 ZEBOV, COVID-19 AstraZeneca and Janssen vaccines demonstrating rapid adaptability.