Vaccine Development and Antibodies

Development of Vaccines and Antibodies

Early Vaccine Development: Edward Jenner and Smallpox

• In the late 18th century, Edward Jenner discovered the first vaccine-like treatment.
• Smallpox was a significant disease at the time, causing widespread infection, illness, and death.
• Jenner observed that milkmaids, who were constantly exposed to cowpox (a related but milder disease affecting cows), seemed immune to smallpox.
• He hypothesized that exposure to cowpox provided immunity against smallpox.
• Jenner extracted material from cowpox sores on cows and injected it into people, which conferred immunity against smallpox.
• The term "vaccine" is derived from the Latin word for cow, "vacca."

Modern Vaccines: Polio Vaccine

• The first modern vaccine was developed in the 20th century against polio by Salk in 1955.
• Polio was a major concern, with President Roosevelt being a notable figure affected by the disease.

Poliovirus Replication

• Poliovirus stores its genetic material as single-stranded mRNA.
• Viruses can store genetic material as plus strand or minus strand Rna.
• The plus strand can be read by ribosomes.
• Minus strand is complementary to the plus strand.
• The enzyme RNA-dependent RNA polymerase is used to create double-stranded RNA from single-stranded RNA.
  • RNA \rightarrow double-stranded RNA RNA dependent RNA polymerase
• Normally, our bodies don't have RNA-dependent RNA polymerase, so the virus needs to encode it.
• The virus replicates by infecting cells, leading to the production of more virus particles.

Salk and Sabin Vaccines

• Salk developed a method to replicate the virus in cell cultures and then kill it with formaldehyde.
• The killed virus was no longer infectious but still triggered an immune response.
• Sabine developed a different approach by attenuating the virus.
• The virus was passaged through multiple cell cultures, selecting for viral replication in culture and reducing its ability to cause disease in humans.
• Attenuated or killed virus vaccines are still the primary methods used today.
• Cell cultures, such as chicken eggs, are commonly used to produce the virus.
• Vaccines have been highly effective in largely eliminating diseases like polio and smallpox.

Vaccine Production Issues and Risks

• In the early days of vaccine production (e.g., in the 1960s), errors occurred where vaccines were not properly inactivated, leading to some individuals contracting the disease from the vaccine itself.
• This caused a fear of vaccines.
• Such production problems have since been largely eliminated.
• A small percentage of the population may still experience negative effects from vaccines.

Mechanism of Vaccine Action and Antibodies

• Blood serum from recovered individuals can prevent plaque formation in cell cultures infected with the virus.
• Plaques are regions of dead cells in a cell culture infected with a virus.
• Serum contains antibodies that prevent the virus from infecting cells.
• During the early COVID-19 pandemic, serum from recovered patients was used to treat infected individuals with mixed results.

Antibodies and Their Function

• Antibodies are proteins that specifically bind to parts of a virus.
• For SARS-CoV-2 (COVID-19), antibodies bind to the spike protein on the virus's surface, preventing it from infecting cells.
• Viruses evolve to evade antibody defenses, requiring the body to create new antibodies.

Antibody Diversity

• The human body can create millions of different antibodies.
• Antibodies are proteins encoded by mRNA sequences, which are encoded by DNA genes.
• Antibodies are produced by B cells.
• A single B cell produces only one type of antibody.
• Multiple myeloma, a type of cancer, demonstrates that a single B cell makes copies of itself, all producing the same antibody.

Antibody Structure: Heavy and Light Chains, Constant and Variable Regions

• An antibody is composed of 4 proteins: two heavy chains and two light chains, forming a Y-shaped structure.
• It has a constant region and a variable region.
• The variable region binds to the antigen (e.g., virus).
• The variable region is encoded by V, D, and J gene segments.

V(D)J Recombination

• The heavy chain is encoded by V, D, J, and C (constant) segments (V, D, J, C).
• To create antibody diversity, there are approximately 300 different V sequences, 25 different D sequences, and 6 different J sequences.
• During B cell maturation, the cell randomly selects one V, one D, and one J segment to create a unique antibody sequence.
• Additional variation is introduced through imprecise joining of these segments and somatic hypermutation, further modifying the sequence to enhance binding to the target.
• V(D)J recombination allows for a vast number of different antibodies to be generated from a limited number of gene building blocks.
• 6 * 25 * 300 is the potential variance.

Southern Blot: Discovering V(D)J Recombination

• Southern blotting is the method used to discover V(D)J recombination.
• The steps include:
  1. Digesting DNA with a restriction enzyme to chop the DNA at specific locations.
  2. Separating the DNA fragments by gel electrophoresis, where smaller fragments move faster and larger fragments move slower.
  3. Transferring the separated DNA to a membrane.
  4. Labeling with a DNA probe to probe for specific sequences (V and C sequences).
• In an immature B cell, the V sequence is longer than the C sequence.
• In a mature B cell, the V and C sequences end up on the same band, indicating that DNA rearrangement has occurred.
• This demonstrates that the DNA is changed as a B cell goes from immature to mature, rearranging its DNA.
• Southern blot method allows to learn about the structure of DNA. Restriction enzymes chop DNA at specific 6-base sequences.
• Gel electrophoresis separates DNA fragments based on size, with smaller fragments moving faster.
• The DNA is transferred to a membrane and labeled with probes for V and C sequences.