Practical Applications of Immunology: Vaccines and Monoclonal Antibodies

Practical Applications of Immunology

Vaccines: Historical Development and Principles

Vaccines are a cornerstone of immunology, providing protection against infectious diseases by stimulating the immune system. The concept originated with variolation and was advanced by Jenner and Pasteur.

• Variolation: Early method using material from smallpox scabs to induce immunity (1400s–1700s).

• Vaccination: Jenner used cowpox to prevent smallpox (1798); Pasteur coined the term 'vaccination' (vacca = cow).

• Vaccine: Suspension of organisms or their fractions that induce immunity.

Principles of Vaccination:

• Provokes a primary immune response, leading to antibody and memory cell formation.

• Enables a rapid, intense secondary response upon re-exposure.

• Herd immunity: Immunity in most of the population reduces outbreaks.

Types of Vaccines and Their Characteristics

Vaccines are classified based on their composition and method of action. Each type has distinct advantages and limitations.

• Attenuated Vaccines: Weakened pathogens, closely mimic natural infection, confer lifelong immunity, not suitable for immunocompromised patients, risk of reversion to virulence.

• Inactivated Vaccines: Whole microbes killed or inactivated, safer, require booster doses, induce mainly humoral immunity.

• Subunit Vaccines: Use antigenic fragments; includes recombinant vaccines (produced by genetic modification), toxoids (inactivated toxins), virus-like particle (VLP) vaccines, polysaccharide vaccines, and conjugated vaccines.

• Nucleic Acid Vaccines: DNA or mRNA vaccines direct synthesis of protein antigens, stimulating both humoral and cellular immunity.

• Recombinant Vector Vaccines: Avirulent viruses or bacteria genetically modified to deliver DNA coding for antigens.

CDC-Recommended Vaccines to Prevent Bacterial and Viral Diseases

The CDC recommends various vaccines to prevent bacterial and viral diseases. These recommendations are based on age, risk factors, and disease prevalence.

Bacterial Diseases

Disease(s)	Vaccine	Recommendation	Booster
H. Influenzae type b meningitis	Polysaccharide from H. influenzae type b	Children 2-18 months	None recommended
Meningococcal A C W Y meningitis	Purified polysaccharide from Neisseria meningitides	Age 11–12 years	At 16 years and for outbreak settings
Meningococcal B meningitis	Purified polysaccharide from Neisseria meningitidis	Substantial risk; college freshmen in dorms	After 1 year; every 2–3 years if risk remains
Pneumococcal pneumonia	Polysaccharide from Streptococcus pneumoniae	Adults with chronic diseases, people over 65, children 2–18 months	None if first dose ≥24 months
Tetanus, diphtheria, pertussis	DTaP, Tdap, Td	Children 2–18 months, 4–6 years; single dose for 11–12 years and adults	Tdap or Td every 10 years

Viral Diseases

Disease(s)	Vaccine	Recommendation	Booster
Chickenpox (varicella)	Attenuated virus	Infants aged 12 months	Duration unknown
COVID-19	mRNA	Two dose series, ages vary	Recommended
Dengue	Attenuated recombinant virus	Age 9–16 years in endemic areas	None recommended
Hepatitis A	Inactivated virus	Children at age 1 year; risk groups	Protection ~10 years
Hepatitis B	Virus antigen in yeast cells	Infants, children, risk groups	Protection ≥7 years; boosters uncertain
Human Papillomavirus	Virus antigen in yeast/insect cells	Children ages 11–12	Duration ≥5 years
Influenza	Injected/inactivated or nasal/attenuated virus	Everyone over 6 months	Annual
Measles	Attenuated virus	Infants aged 15 months; adults if exposed	As needed
Mumps	Attenuated virus	Infants aged 15 months; adults if exposed	As needed
Poliomyelitis	Inactivated virus	Children; adults as risk warrants	Duration unknown
Rabies	Inactivated virus	Field biologists, veterinarians, exposed individuals	Every 2 years
Rotavirus	Attenuated virus	Oral, infants up to 8 months	None recommended
Rubella	Attenuated virus	Infants aged 15 months; females of childbearing age	As needed
Smallpox	Attenuated vaccinia virus	Military, health care personnel	Protection 3–5 years
Zoster (shingles)	Virus antigen in mammalian cells	Adults over 50; immunocompromised over 19	None recommended

Mechanisms of Nucleic Acid Vaccines

Nucleic acid vaccines represent a modern approach, using DNA or mRNA to direct the synthesis of antigens within host cells, thereby stimulating immunity.

• DNA Vaccines: Injected naked or encapsulated DNA into muscle; DNA is transcribed and translated to produce protein antigen.

• mRNA Vaccines: mRNA enclosed in lipid nanoparticles is injected; directs synthesis of encoded antigen (e.g., COVID-19 spike protein).

Recombinant Vector Vaccines

Recombinant vector vaccines use genetically modified avirulent viruses or bacteria to deliver DNA coding for antigens, stimulating an immune response.

Vaccine Production, Administration, and Safety

Modern vaccine production methods avoid the need for animal hosts, utilizing plants and recombinant technology. Administration routes and adjuvants enhance effectiveness and safety.

• Production: DNA, mRNA, and recombinant vector vaccines do not require animal hosts; plants are potential production systems.

• Adjuvants: Additives (e.g., alum, monophosphoryl lipid A) improve vaccine effectiveness by activating innate immunity.

• Administration: Oral, nasal, skin patch, and combination vaccines increase accessibility and effectiveness.

• Safety: Vaccines are generally safe; rare cases of disease induction (e.g., oral polio vaccine); no evidence linking MMR to autism; mRNA vaccines have outstanding safety records.

Impact of Vaccines on Disease Prevention

Vaccines have dramatically reduced the incidence of infectious diseases, saving millions of lives. However, some diseases persist due to low vaccination rates, need for boosters, and vaccine hesitancy.

• Diphtheria: Before vaccine, >15,000 deaths in 1921; only 14 cases since 1996.

• Measles and Rubella Initiative: Focused on disease elimination.

• Global Polio Eradication Initiative: Polio eliminated in most countries; persists in Afghanistan and Pakistan.

Monoclonal Antibodies: Production and Applications

Hybridoma Technology and Monoclonal Antibodies (Mabs)

Monoclonal antibodies are produced by hybridoma technology, combining a cancerous B cell with a normal antibody-producing B cell. This allows for the production of highly specific, uniform antibodies in large quantities.

• Hybridoma: Fusion of myeloma cell and normal B cell; produces monoclonal antibodies.

• Monoclonal Antibodies: Uniform, highly specific, used in diagnostics and therapy.

• Applications: Diagnostic tools, treatments for multiple sclerosis, Crohn’s disease, psoriasis, cancer, asthma, arthritis, COVID-19.

• Source: Often derived from mouse cells, which may cause side effects.

Summary Table: Types of Vaccines

Type	Example	Key Features
Live Attenuated	Measles, Mumps, Rubella, Oral Polio	Strong, long-lasting immunity; risk for immunocompromised
Inactivated	Influenza, Hepatitis A	Safe, requires boosters
Subunit	Hepatitis B, HPV	Specific antigens, fewer side effects
Toxoid	Diphtheria, Tetanus	Inactivated toxins, induce antitoxin immunity
Conjugated	Haemophilus influenzae type b	Polysaccharide linked to protein, effective in young children
Nucleic Acid	COVID-19 mRNA vaccines	Directs synthesis of antigen, stimulates both humoral and cellular immunity
Recombinant Vector	Ebola vaccine	Uses modified virus/bacteria to deliver antigen gene

Additional info: Modern vaccine development increasingly relies on recombinant and nucleic acid technologies, which allow rapid response to emerging pathogens and improved safety profiles.