#vaccine mechanism

Vaccine

mRNA vaccines work by:

Messenger RNA vaccines represent nucleic acid platform delivering synthetic mRNA encoding pathogen antigen directly to host cytoplasm where host ribosomal machinery translates it transiently. Manufacturing involves in vitro transcription using T7 RNA polymerase from linearized plasmid DNA template encoding spike protein, incorporation of modified nucleoside N1 methylpseudouridine replacing uridine reducing TLR7 mediated inflammation and increasing translation half-life, addition of 5' cap 7-methylguanosine via vaccinia capping enzyme and 2'O-methylation, and 3' polyadenine tail 100 nt for stability. mRNA encapsulated in lipid nanoparticles LNP composed of ionizable lipid ALC-0315 or SM-102 protonated at low pH encapsulating RNA, helper lipid DSPC forming bilayer, cholesterol fluidity, and PEGylated lipid reducing aggregation and prolonging circulation. Upon intramuscular injection LNPs fuse with cell membrane or endocytosed, ionizable lipid becomes cationic at endosomal low pH disrupting endosome releasing mRNA to cytosol. Ribosomes translate antigen protein undergoing post translational modifications, secreted or membrane anchored, processed for MHC I and II presentation inducing neutralizing IgG and CD4 Th1 and CD8 cytotoxic memory. mRNA degraded within days by RNases no integration risk enabling rapid design.

Ref: Pardi et al. Nat Rev Drug Discov 2018 mRNA mechanism; Polack NEJM mRNA; CDC mRNA work.

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Vaccine

Vaccines primarily work by:

Vaccines function primarily by inducing immunological memory mimicking natural infection without causing severe pathology. Upon antigen administration intramuscularly or mucosally, local dendritic cells and macrophages sense danger signals via pattern recognition receptors TLR, NLR, STING. Activated dendritic cells pick up antigen, mature upregulating CCR7, migrate to draining lymph node T cell zone presenting peptides on MHC class II to naive CD4 T cells and via cross presentation on MHC I to CD8 cells. T follicular helper cells provide IL-21 and CD40L signals to B cells in germinal centers driving proliferation, somatic hypermutation of immunoglobulin variable genes mediated by AID, affinity maturation, class switch recombination to IgG and IgA isotypes, generation of long lived plasma cells homing to bone marrow secreting high affinity antibodies years, and memory B cells expressing surface Ig capable of rapid differentiation upon rechallenge. Memory CD4 and CD8 T cells persist as central memory and tissue resident populations secreting IFN gamma, IL-2. Upon natural exposure, anamnestic response within 2-3 days neutralizes pathogen preventing disease. Adjuvants enhance this process.

Ref: Pollard Bijker Nat Rev Immunol 2021 Vaccine memory; Janeway Immunobiology 9th ed Ch 12.

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Immunological Applications

DNA vaccines work by:

DNA vaccination concept bypasses conventional protein purification manufacturing by delivering genetic blueprint encoding protective antigen allowing host cells to synthesize immunogen in situ mimicking viral infection while noninfectious. Plasmid vector engineered with strong eukaryotic promoter typically human cytomegalovirus immediate early enhancer promoter driving high transcription, chimeric intron improving mRNA stability and export, Kozak consensus GCCACCATGG for efficient translation initiation, antigen coding sequence codon optimized for human usage bias replacing rare codons to increase expression tenfold, and bovine growth hormone polyadenylation signal specifying cleavage and poly-A adding 200 adenines. After intramuscular injection with needle or gene gun gold particles, myocytes and keratinocytes internalize negatively charged plasmid via macropinocytosis, plasmid enters nucleus through nuclear pore complex during mitosis when nuclear envelope breaks down or via active import mediated by importin. This mechanistic insight supports diagnostic and therapeutic applications while reinforcing core immunological and cell biology principles taught in advanced curricula. This mechanistic detail underpins practical applications in diagnostics, vaccine design, and biopharmaceutical manufacturing.

Ref: Ulmer et al Science 1993 DNA vaccine CMV promoter MHC I II; NIH Vaccine plasmid CpG TLR9 adjuvant mechanism.

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Immunological Applications

DNA vaccines work by:

DNA vaccines third-generation platform delivering plasmid DNA encoding microbial antigen rather live attenuated organism purified protein circumventing biosafety level concerns anti-vector immunity. Plasmid constructed E. coli DH5 alpha containing bacterial origin ColE1 antibiotic resistance beta-lactamase ampicillin selection strong eukaryotic expression cassette CMV immediate early enhancer promoter high constitutive transcription Pol II chimeric intron A human beta-globin improving mRNA stability splicing removing premature terminator target gene viral spike bacterial protective antigen tumor neoantigen optimized human codon usage removing rare codons increasing translation bovine GH polyA terminating transcription adding polyA tail aiding nuclear export. Additional unmethylated CpG immunostimulatory motifs GTCGTT enriched activating TLR9 plasmacytoid dendritic MyD88 IRF7 type I interferon alpha endogenous adjuvant stimulating Th1. Intramuscular injection 1 mg plasmid saline followed electroporation needle electrodes 100V 50ms pulses increasing myocyte membrane permeability transient pores enhancing uptake 100-fold plasmid enters nucleus nucleopore remains episomal circular monomer not integrating

Ref: Wolff et al Science 1990 DNA Plasmid Expression Landmark; NIH NIAID DNA Vaccine Mechanism Overview Summary; Nature Reviews Immunology DNA Vaccines Principles 2021 Adjuvant.

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