History of Vaccines

History of Vaccines
Leading cause of death in human population
INFECTION
Most important contributions to public health in last 100 yrs
SANITATION
VACCINATION
Earliest contributions
JENNER – smallpox vaccine
PASTEUR – rabies vaccine
Greatest Triumphs
Global eradication of smallpox (1980)
Future global eradication of polio
History
Although early in history the basis of disease was not known, the presence of a life-long immunity to disease was understood as early as the 4th century.
The first documentation of “immunization” was the process of variolation – the removal of pus from smallpox lesions and the subsequent scratching of an uninfected person in the 10th century in India
In 1796, Edward Jenner observed that milk maids exposed to cowpox (vaccinia virus) did not acquire smallpox – he predicted that deliberately infecting an individual with vaccinia would protect against smallpox (variola virus) – Sarah Nelmes donated fluid from her cowpox-infected hands, which was inoculated into James Phipps – produced a lesion similar to cowpox – later challenged James Phipps with fluid from a smallpox lesion, but no subsequent smallpox developed – this was the first recorded incidence of “vaccination”.
Jenner would be imprisoned for this type of experiment today, but the James Phipps vaccination led to the development of the smallpox vaccine and the eradication of naturally occurring infections worldwide.
Immune mechanisms to eliminate virus or virus-infected cells
Humoral & cell-mediated immune responses important for antiviral immunity
Must eliminate both virus & virus-infected cells
Failure to resolve infection leads to;
Persistent infection
Late Complications
Humoral immune response acts primarily on extracellular virions/bacteria
Cell-mediated immune responses (T cells) target virus-infected cells
Primary and Secondary Antibody
Responses
Virus-specific T Cell Responses ~
CD4 and CD8 T Cells
Antiviral CD8+ and CD4+ T-cell responses.   The three phases of the T-cell immune response (expansion, contraction and memory) are indicated. Antigen-specific T cells clonally expand during the first phase in the presence of antigen. Soon after the virus is cleared, the contraction phase ensues and the number of antigen-specific T cells decreases due to apoptosis. After the contraction phase, the number of virus-specific T cells stabilizes and can be maintained for great lengths of time (the memory phase). Note that, typically, the magnitude of the CD4+ T-cell response is lower than that of the CD8+ T-cell response, and the contraction phase can be less pronounced than that of CD8+ T cells. The number of memory CD4+ T cells might decline slowly over time.
Humoral Immune Response
Not all immunogens elicit protective immunity
Best targets usually viral attachment proteins
Capsid proteins of non-enveloped viruses
Envelope glycoproteins of enveloped viruses
Antibody may neutralize free virus particles
Antibody binds virus particles
Blocks binding to cell-surface receptors
Destabilizes virus particles
Antibody opsonizes free virus particles
Antibody binds virus particles
Promotes uptake & clearance by macrophages (Fc receptors)
Antibody prevents spread of extracellular virus to other cells
Most important in viremic infections
Antiviral antibodies can impact viral infection in multiple ways.
The antiviral activities of antibodies.   a | Activities against free virus (an enveloped virus is shown). Neutralizing antibodies probably act primarily by binding to the envelope protein (Env) at the surface of the virus and blocking infection (neutralization). They can also trigger effector systems that can lead to viral clearance, as discussed in the text. b | Activities against infected cells. These activities can be mediated by both neutralizing and non-neutralizing antibodies. Neutralizing antibodies bind to the same proteins on infected cells as on free virus. Non-neutralizing antibodies bind to viral proteins that are expressed on infected cells but not, to a significant degree, on free virus particles. Examples include altered forms of Env protein and certain non-structural (NS) proteins, such as NS1 of dengue virus. The binding of neutralizing and/or non-neutralizing antibodies to infected cells can lead to clearance of such cells or the inhibition of virus propagation as shown.
Targets for Antiviral Antibodies
Cancer Vaccines
Tumors can be destroyed by cytotoxic T cells or antibody-dependent cytotoxic mechanisms if the immune system can identify the tumor as “nonself”
This is difficult with uninfected cells since the immune response is generally tolerized toward “self” antigens
However, some tumor-specific antigens are expressed by cancer cells either in a unique context or are antigens that were expressed prior to but not after the tolerization process. This is generally because tumor cells are less differentiated than normal cells.
In addition, tolerance can be broken by especially immunogenic vaccines
The “holy grail” of tumor vaccines is an antigen that is expressed only by the tumor cells, to which the host is not tolerized
Gene Therapy Vaccines: Introduction of nucleic acids
Subdivided into groups:

NON-LIVING VACCINES (inactivated/subunit/killed) – Don’t infect but contain nucleic acids (adjuvant effects)
LIVE VACCINES – Modified virus or bacterium or replicating vector expressing heterologous immunogen
DNA VACCINES – Plasmid DNA injected, expresses immunogen
ADJUVANTS – Nucleic acid-based vectors that non-specifically stimulate host responses to co-administered immunogen
Non-Living Virus Vaccines
No risk of infection by viral agent
Generally safe, except in people with allergic reactions
Large amount of antigen elicits protective antibody response
Produced in several ways:
Chemical inactivation (e.g., formalin) of virus
Heat inactivation of virus
Purification of components or subunits of viral agent from infected cells
Typically administered with ADJUVANT
Boosts immunogenicity
Influences type of response (TH1 versus TH2, secretory IgA)
Used when wild-type virus:
Cannot be attenuated
Causes recurrent infection
Has oncogenic potential
Live Virus Vaccines
Preparations of viruses limited in ability to cause disease
AVIRULENT – does not cause human disease (often other species)
ATTENUATED – deliberately manipulated to become benign
Immunization resembles natural infection
Progresses through normal host response
Humoral, cellular & memory immune responses develop
Immunity generally long-lived
BUT, can revert to virulent form in host
May still be poorly immunogenic
May still be dangerous in immunocompromised individuals
Pregnant women
Infants
Immunosuppressed (chemotherapy, HIV etc.)
Live Virus Vaccines
Live virus vaccines are attenuated because:
They are mutants of wild-type virus
They are related viruses with non-human host that share epitopes
They are genetically-engineered to lack virulence properties
Attenuated mutant viruses include:
HOST RANGE MUTANTS: Grown in embryonated eggs or tissue culture cells
TEMPERATURE-SENSITIVE MUTANTS: Grown at non-physiological temperatures
IMMUNE-SENSITIVE MUTANTS: Grown away from selective pressures of host immune response
TROPISM-ALTERED MUTANTS: Replicate at benign site, but not target organ (e.g. Sabin polio vaccine in GI tract but not CNS)
Live-attenuated virus vaccines licensed for measles, mumps, rubella, VZV, yellow fever & polio
Blind Passage: Most live attenuated virus and bacterial vaccines
Live Versus Non-Living Vaccines
The Future of Vaccines
Molecular biology now applied to vaccine design
New live vaccines genetically engineered to inactivate/delete virulence genes
Replaces random attenuation by cell culture passage
Many new types of vaccines now being developed:
SUBUNIT VACCINES (not technically gene therapy)
HYBRID VIRUS VACCINES
REPLICON VACCINES
DNA VACCINES
Subunit Protein Vaccines
Genes for immunogenic proteins cloned into bacterial & eukaryotic expression vectors which produce protein in vitro:
Identifying appropriate subunit or peptide immunogen to elicit protective antibody & ideally CTL
Present antigen in correct conformation
Examples include:
HBV surface antigen (in use)
HIV gp120
Influenza virus hemagglutinin
Papillomavirus virus-like particles (VLP; in use)
With viruses, single proteins can make particles that bud from cells (VLP) that can use class I and class II pathways
Hybrid Virus & Replicon Vaccines
Genes from infectious agents that cannot be attenuated inserted into “safe” viruses:
CHIMERIC VIRUSES: Combined genomes from related virulent & attenuated viruses
YFV 17D-based vaccines for dengue, West Nile & Japanese encephalitis virus
VIRUS VECTORS: Attenuated virus engineered to express immunogenic gene from pathogenic virus
Canarypox, retrovirus & alphavirus vectors
Replicons - virus particles capable of only one round of infection
Essential gene(s) deleted from genome
Added back in trans to make virus particles in cell culture
Chimeric RNA virus (Acambis “Chimeravax”)
cDNA clone of 17D Yellow fever virus vaccine with C, prM and E of Dengue, Japanese encephalitis or West Nile virus substituted
Viral Immunogens
26S
Structural
Genomic
Foreign protein
26S
Non-structural
RNA virus vector expressing heterologous immunogen
More like natural infection but possibility for virulence
Alphaviruses
26S
Genomic
Immunogen
Non-structural
Alphavirus replicon expressing heterologous immunogen (limits potential for virulence)
26S
E3/E2/E1
Alphavirus Replicon Vectors
26S
Genomic
Non-structural
26S
E3/E2/E1
Immunogen
Alphaviruses natrually target dendritic cells (APCs)
DNA Vaccines
Great potential for immunization against infectious agents requiring T cell & antibody responses
Gene of protein eliciting immune response cloned into eukaryotic expression vector
Naked DNA injected into muscle or skin
DNA taken up by cells & gene expressed
Protein produced and presented to immune system
Very easy to design & produce
Extremely safe, no possibility of reversion to virulence
Have many similar drawbacks to other non-living vaccines (limited immunogenicity, require adjuvants)
However, bacterial DNA (plasmid amplified in bacteria) is a natural adjuvant for Toll-like receptor 9, an innate immunity stimulating molecule
Plasmid contains general eukaryotic promoter (e.g., cytomegalovirus promoter in pcDNA3.1) that is transcribed in most mammalian cells
Immunogen determines route of presentation e.g., class I (cytoplasmic) vs. class II (secreted)
Clinical trials for plasmid-based cancer vaccines
Gene Therapy Adjuvants
Adjuvant can be protein delivered with live or killed vaccine

For gene therapy, adjuvant can be delivered by a vector:
Virus
Replicon
Bacterium
Plasmid

Or, adjuvant can be the nucleic acid itself delivered with another vaccine (usually killed vaccine)

Adjuvant protein and/or nucleic acid is utilized to increase the response of host cells such that immunization with vaccine resembles or is more stimulating than natural agent infection. Examples:
Mip3-alpha – chemokine attracting immature dendritic cells
IFN-gamma – cytokine skewing towards TH1 immunity
IL-12 – cytokine promoting TH1 and mucosal antibody
CpG DNA – elicits cytokine response like pathogen
Virus RNA – elicits cytokine response like pathogen
CD86 - co-stimulatory molecule can be supplied, required for naïve T cell activation
Ubiquitin – proteasome targeting molecule, enhances Ag processing
Adjuvants
26S
Genomic
Cytokine (e.g.,IFN-g, IL-12)
Non-structural
Alphavirus replicon expressing adjuvant
26S
E3/E2/E1
Virus Vaccines Licensed in U.S.

Hepatitis B virus Parenteral, recombinant protein
Measles Parenteral, live, booster 4-6 yrs
Mumps Parenteral, live, booster 4-6 yrs
Poliovirus Parenteral, killed
Rubella Parenteral, live
Varicella Parenteral, live
Universal childhood vaccines
Influenza A & B virus Elderly Parenteral, annual, killed
Hepatitis A virus Travelers Parenteral, killed
Japanese encephalitis virus Travelers Parenteral, killed
Yellow fever virus Travelers Parenteral, live
Rabies High-risk Prophylactic & therapeutic , killed
Smallpox High-risk Intradermal, live
Rotavirus Children Live, cow virus
Human Papilloma virus (3 dose) Females Intramuscular, Recombinant Virus-Like Particle (no DNA)
Virus Vaccines Licensed in U.S.
Bacteria as vaccines/vectors

Killed/Subunit – DTaP , anthrax, meningococcal meningitis,
Live attenuated – Mycobacterium bovis cow bacterium (BCG), Salmonella typhimurium Ty21a, CVD, Vibrio cholera 103-HgR
Expression of heterologous antigen – S. typhimurium, Listeria monocytogenes, Bacillus anthracis
Plasmid delivery – Shigella sp., Listeria sp. Some intracellular bacteria target dendritic cells and can deliver plasmids to the APCs
Advantages: can give orally for mucosal immunity, sometimes long term antigen expression
Disadvantages: much more complex than viruses, attenuation mechanisms less well understood and may have unexpected long term consequences for vaccinees