Larson All Vaccines

What is the general purpose of vaccines?

To generate an immune response in the absence of a pathogen (or with a less pathogenic microbe)

Vaccines reduce risk of _____

Disease-associated complications and hospitalizations

What happens in the immune system when a vaccine is administered?

• Dendritic cells collect vaccine antigens and adjuvants

• Dendritic cells migrate to lymph nodes

• Antigens are presented to CD4 and CD8 T cells

• CD8 T cell activation results in CD8 effector T cells and CD8 memory T cells

• T cell help from activated CD4 T cells leads to:

  • additional activation of CD8 T cells

  • proliferation of antigen specific B cells

  • maturation of the antibody response

  • plasma cell differentiation and antibody production

  • proliferation of memory B cells

The immune memory after vaccination for a pathogen with a long incubation time (like Hepatitis B) is _____

sufficient

the antibodies will reach the necessary protective level without a booster vaccine

The immune memory after vaccination for a pathogen with a short incubation time (like Influenza B) is _____

not sufficient

rapidly invasive pathogens require boosters to produce a sufficient response

Live attenuated vaccines

Live pathogens that have been weakened or inactivated

Attenuation

Reduces virulence while maintaining immunogenicity

Rational attenuation

Inactivates or removes virulence genes by targeted mutations or gene deletion (typical for viruses)

Killed whole organism vaccines

Whole organism killed by physical or chemical means

Toxoid vaccines

modified bacterial exotoxins

How do toxoid vaccines work?

Antibodies directed at toxoid neutralize exotoxins before they reach the target cell

Why are antibodies effective at neutralizing exotoxins?

Antibodies recognize linear epitopes AND conformation epitopes

This includes secondary, tertiary, and quaternary protein structure, as well as glycosylated proteins

Subunit vaccines

Antigenic molecules or critical epitopes necessary for protection against infection

Whole cell vaccines contain nonantigenic molecules that can cause rare systemic and frequent local adverse effects

Purified protein, recombinant protein, polysaccharide, peptide

Virus-like particle vaccines

Particles constructed of viral proteins that structurally mimic the native virus but lack the viral genome

Nonenveloped VLPs or Enveloped VLPs

Outer membrane vesicle vaccines

Contain gram negative bacterial outer membrane and antigen

Polysaccharide and protein-polysaccharide conjugate vaccines

Need to be conjugated to proteins to elicit T cell dependent responses and generation of immune memory

Viral vectored vaccines

Recombinant virus (replicating or not) with altered genomes to express the target pathogen antigen

Nucleic acid vaccines

Consist of either DNA or RNA encoding the target antigen

Subcutaneous or intramuscular injection of vaccines

• Stimulates systemic immunity in the spleen, lymph nodes, and peripheral blood

• Interrupts person-to-person transmission

• Prevents the spread to crucial organs

Mucosal administration of vaccines

Antigen-stimulated lymphocytes from initial site travel to other mucosal surfaces conferring immunity at multiple mucosal sites

Passive protection

Use of specific neutralizing antibodies purified from immune donors to prevent the transmission of various viruses

Main point of herd immunity

For vaccine coverage above the threshold for herd immunity, infection cannot spread in the population and susceptible individuals are indirectly protected by vaccinated individuals

MMR vaccine

Live attenuated vaccine for measles, mumps, and rubella

(Other options include measles alone or in combination with mumps or rubella)

How many types of influenza affect humans?

Three types: A, B, C

Type A Influenza

Subtypes determined by hemagglutinin (HA) and neuraminidase (NA)

Type B Influenza

Two lineages:

• B/Yamagata

• B/Victoria

Type C Influenza

Rarely reported as a cause of human illness

Not associated with epidemic disease

How do influenza viruses enter cells?

Attaches and penetrates respiratory epithelial cells in trachea and bronchi

Enters through sialic acid receptors

After influenza enters a cell, replication results in _____

Destruction of host cells

• Regeneration of epithelium takes 3-4 weeks

• Viremia (presence in blood) is rare

Engagement of receptors by influenza leads to _____

• Activation of IRF3, IRF7, and NF-kappaB

• Transcription factors

• Production of IFNs

• Transcription of interferon-stimulated genes

How are CD8 T cells involved in influenza?

Use cytotoxic granules and FasL-mediated apoptosis to eliminate infected cells

How are CD4 T cells involved in influenza?

Trigger B cell activation and promote antibody production to neutralize virus

_____ is important for early recovery from severe influenza

Rapid and prominent CD8 CTL recall

What type of transmission is important for Influenza A virus?

Zoonotic Transmission (Primarily wild aquatic birds)

Reassortment

Swap gene segments to generate a new virus

Which influenza virus is capable of reassortment?

Influenza A virus

Antigenic Shift

Intermixing of RNA from two viruses to make a new virus

Antigenic Drift

Accumulation of mutations over time

Can flu vaccines give you the flu?

No

• IIVs (Inactivated Influenza Vaccines) are inactivated virus, so the virus is “dead”

• Recombinant vaccines include only the Hemagglutinin protein

What does WHO/CDC try to predict about influenza?

Which strains will dominate each year

• Surveillance of people, wild bird populations, farms

• Sample from over 100 different sites worldwide → map movement of the virus

Influenza Vaccine Effectiveness Network

• Measure how the vaccine performs under real-world conditions

• Enroll patients ≥ 6 months old seeking medical care for an acute respiratory infection with cough within 7 days of symptom onset

• Test for influenza and group by vaccine status

Cross-protection in influenza

• Antibodies against one strain of influenza may offer cross-protection against related strains

• One antibody could neutralize multiple strains, at least to some extent (overlapping HA or NA)

Benefit of cross-protection in influenza vaccines

Even if there is a mismatch between the vaccine and circulating strains, the vaccine will often confer some degree of protection

What is the difference between positive-sense and negative-sense RNA viruses?

• Positive sense

  • RNA can act as mRNA → translate into protein

• Negative sense

  • RNA requires conversion to positive sense before translation

Characteristics of SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2)

• Highly pathogenic

• Enveloped, positive sense, single stranded, non-segmented RNA virus

How does SARS-CoV-2 enter cells?

• By binding angiotensin converting enzyme 2 (ACE2) receptor through spike protein (S)

• Endocytosis

Acute Respiratory Distress Syndrome (ARDS)

• Clinical feature of COVID-19 that can be fatal

• Monocytes and neutrophils are attracted to damage and promote inflammation and coagulation

  • Neutrophils, activated by platelets, release NETs and promote formation of microthrombi

Result of Acute Respiratory Distress Syndrome (ARDS)

Focal pattern of highly inflamed and flooded lung tissue, impairing oxygen exchange and leading to hypoxia

What was the overall goal of the Dan et al. COVID study?

To understand immune memory responses to SARS-CoV-2

What were the four types of immune memory examined in the Dan et al. COVID study?

• Antibodies

• Memory B cells

• CD4+ T cells

• CD8+ T cells

What does durability mean in the context of immune memory?

The length of time immune memory is measured after infection

Why is IgA important in the context of SARS-CoV-2 infection?

It is associated with humoral immunity at mucosal surfaces like the airway and lung, major sites of SARS-CoV-2

What functions do circulating T follicular helper (cTfh) cells serve as it relates to B cells?

• Provide B cell help

• Support SARS-CoV-2-specific antibody generation

• Long-lived humoral immunity

CCR6+ SARS-CoV-2-specific cTfH (circulating T follicular helper) cells increase over time. What is the function of CCR6? What might be happening to cTfh cells that express CCR6?

CCR6 is a chemokine receptor that mediates cell migration into tissue (especially mucosal tissue like lung and airway)

The increase in CCR6+ cTfh may indicate that these cells are migrating into tissues and providing support of local humoral immune responses

Immune memory to SARS-CoV-2 is heterogenous, which means _____

Different individuals have different patterns of immune memory

What percentage of patients retained immune memory ~6 months after infection?

95% of patients had at least 3 out of 5 immune memory responses at 6-8 months

Is durable immunity possible against secondary COVID-19 disease?

Yes (longer studies are needed to determine how long)

How do mRNA vaccines elicit an immune response?

1. Intramuscular immunization

2. mRNA/antigen uptake by APCs

3. Trafficking to lymph nodes

4. Priming of T lymphocytes

5. CD4 and CD8 T cell activation

6. Germinal center reaction

   • Produces MBCs (Memory B Cells) and LLPCs (Long-Lived Plasma Cells)

Janssen COVID Vaccine

Viral vector vaccine

A replication defective adenovirus that carries the gene for the SARS-CoV-2 spike protein

• Cannot replicate or cause infection

How does boosting (for COVID vaccine) work if it doesn’t match the new variants?

• Greater levels of and cross reactivity from neutralizing antibodies

• T cells are holding up really well against variants

• Leads to affinity maturation, which makes broader and more efficient antibodies

What is the “prototype pathogen” approach in the context of COVID vaccine development?

• Coronaviruses were known to have outbreak potential

• Some labs studied SARS and MERS in anticipation of a new coronavirus

• Developed and tested the mRNA platform before COVID19

What does it mean that mRNA vaccines are “plug and play”?

• Can modify for new strains

• Fast and easy to produce

• No infectious virus

How was the COVID vaccine developed so fast?

Overlap in early clinical trials phases and manufacturing

Safety benchmarks were NOT lowered by the FDA

What two diseases are caused by VZV?

• Chicken pox (varicella)

• Shingles (zoster)

Viral Latency

The virus is present in a cell but is not replicating

Pathogenesis of VZV

Widely distributed vesicular rash due to viral spread to lymph nodes and transport of virus from blood to skin through infected T cells

How does the presentation of VZV differ from measles and rubella?

The skin rash begins on the torso (centripetal distribution) and progresses outward to the arms, legs, and head

What effect does VZV infection have on T cells?

Enhances homing to skin

• VZV infected CD4 T cells express skin homing proteins, such as cutaneous leukocyte antigen (CLA) and CCR4

Once in the skin, VZV triggers _____

Innate immune response

• Type 1 IFNs - IFNα

• PML (Promyelocytic leukemia protein)

PML (promyelocytic leukemia protein)

Forms intranuclear cages to trap new virions

How does VZV establish latency?

By infecting sensory nerve bodies in the dorsal root ganglia (spine) and trigeminal ganglia (face)

Where in the body does zoster manifest?

In the dermatome that is innervated by the affected ganglion

What two things are needed to resolve VZV infection?

• Cell mediated immunity (CMI)

• Antibodies

What is needed to prevent reactivation of VZV?

Memory T cells (CD4 and CD8 T cells)

If you have shingles once, can you get it again?

Yes

Rates of recurrent infections are similar to rates of first occurrences

Why is the varicella vaccine given after 12 months?

Maternal antibodies are high the first year of life and will clear out virus

Antibodies against gE (glycoprotein E) are neutralizing, which means _____

Attachment and infection are blocked

What was added to the Shingrix vaccine to improve the immune response to gE (glycoprotein E)?

An adjuvant

What does it mean that HPV is a Naked DNA Virus?

• Non-enveloped

  • Composed of the capsid protein called L1

  • L stands for “late” as in it's a late/structural gene

• L1 spontaneously self-assembles

  • Does not require any other viral proteins to assemble

How does HPV enter the cell?

• Conformational changes in capsid promote association with a secondary receptor on epithelial cells

• Virion internalized by endocytosis

Once inside the cell, viral capsid proteins _____

Hide by inserting into membrane vesicle and are transported to the nucleus

What happens when the host cell infected with HPV divides?

Promyelocytic leukemia (PML) nuclear bodies reform in association with encapsulated virus

• Important for the establishment of infection

• PMLs are usually antiviral, but in this case, they protect the viral DNA

What do E1 and E2 proteins do in the pathogenesis of HPV?

Replicate the HPV genome as extrachromosomal plasmids

What do E5, E6, E7 proteins do in the pathogenesis of HPV?

Promote viral life cycle

• Induce cell cycle re-entry and delay differentiation

• Virion production requires fully differentiated keratinocytes

How does cell-mediated immunity recognize HPV-infected cells?

1. Local activation of APCs

2. Activated APCs migrate to lymph node

3. Antigen presentation by APCs and stimulation of CD8 T cells and B cells by CD4 T cells

4. Recruitment of NK cells and activated APCs into the infected tissue

5. CD8 T cell infiltration and clearance of viral infection

6. Secretion of neutralizing antibodies (nAbs) and neutralizing of viral particles

   • New HPV infection prevented by nAb

What do E6 and E7 proteins do in the oncogenesis of HPV?

Deregulate cell cycle control

• Less well differentiated lower layers of the lesion

• Creates genomic instability (higher frequencies of mutations)

What does the Gardasil 9 vaccine for HPV contain?

• Adjuvant - Aluminum hydroxyphosphate sulfate

  • Most aluminum exposure is through diet and antacids

  • Low doses of aluminum salts can act as adjuvants

  • Stimulates a specific antibody response

• Antigen - Virus-like particles (VLPs)

  • Composed of only one viral protein

  • No genetic material (no DNA)

• Gardasil does NOT contain live virus

Are virus-like particles infectious?

• No, they do not contain any DNA or other proteins

• They are also not oncogenic

What does it mean that virus-like particles are highly immunogenic?

Produce high levels of antibodies and B cell memory

• Some antibodies are crossprotective against other HPV strains that are not seen in the vaccines

Why does the Gardasil 9 HPV vaccine produce a better antibody response than natural infection?

Intramuscular administration allows the virus-like particles to reach the lymphatics and lymph nodes

• Greater antigen presentation and cell mediated immunity in the lymph nodes

Who can’t receive the Gardasil 9 HPV vaccine?

• Someone who had a life-threatening reaction to a prior dose of the vaccine

• Someone who had a life-threatening reaction to yeast

  • Yeast is used to generate virus-like particles

What is the main limitation of the Gardasil HPV vaccine?

The vaccine is prophylactic, so it is effective at preventing HPV prior to exposure

What kind of bacteria is Streptococcus pneumoniae?

Gram-positive facultative anaerobic

What is a distinguishing feature of gram positive bacteria?

Thick layer of peptidoglycans

What is the basis for pathogenicity of Streptococcus pneumoniae?

Surface complex polysaccharides (capsular polysaccharides) (CPS)

What does the bacterial capsule do in Streptococcus pneumoniae?

Aids in immune evasion

• capsule prevents binding of IgG to membrane antigens

What two ways can Streptococcus pneumoniae spread?

• Through respiratory droplets person-to-person

• Autoinoculation in a person carrying S. pneumoniae in their upper respiratory tract

What do capsular polysaccharides (CPS) do in the pathogenesis of Streptococcus pneumoniae?

Allow S. pneumoniae to avoid entrapment by:

• mucus

• opsonophagocytosis

• detection by host receptors

Streptococcus pneumoniae produces a biofilm, which can _____

Hinder drug penetration and contribute to drug resistance

How does Streptococcus pneumoniae enter the bloodstream?

Through epithelial polymeric immunoglobulin receptor (used to translocate antibodies) or, in severe cases, lung injury and severe epithelial damage