Gene Therapy and Gene Editing Notes

Learning Objectives

  • Define gene therapy and understand its categories and approaches.
  • Understand the history of gene therapy, in terms of both successes and failures.
  • Appreciate the fundamental challenge of providing accurate gene therapy.
  • Explain gene editing and its potential to revolutionize medicine.
  • Illustrate the basic principles of the CRISPR/Cas9 system.
  • Summarize the differences between the two repair systems for dsDNAdsDNA breaks.
  • Acknowledge the ethical concerns surrounding gene therapy.

What is Gene Therapy?

  • Definition: Gene therapy is the modification of genes or genetic pathways to prevent or reduce disease effects (Moss, 2014).
  • How it Works: Traditionally, it involves inserting new, therapeutic genetic material into the patient.

How Gene Therapy Works

  1. Therapeutic Transgene: Start with a therapeutic transgene (DNA).
  2. Viral Vector: Place the transgene into a viral vector (e.g., AAV).
  3. Administration: Administer the gene therapy to the patient.
  4. Targeting: The viral vector reaches the target cell and releases the transgene.
  5. Expression: The therapeutic gene expresses proteins that treat the disease.

Therapeutic Transgene

  • A therapeutic transgene is a manufactured DNA sequence designed for therapeutic effects.
  • Therapeutic Effects Categorization:
    • Genetic mechanisms: Mendelian or multifactorial
    • Molecular pathology
    • Nature of disease: Chronic or acute?
    • Target organ: Is it accessible? What is the physiology of the organ?
    • Safety, efficacy, and dosing: One or multiple doses? Possible side effects?

Vectors in Gene Therapy

  • Definition: A vector packages the therapeutic gene of interest.
  • Advantages:
    • No risk of immune response
    • No mutations in host cells
    • Protects gene from degradation
    • Secures stable transcription upon nucleus entry
    • Facilitates entry into target cells
  • Types:
    • Viral Vectors: Rich in options; vary in size capacity, target specificity, and effect duration.
    • Non-Viral Vectors: Safer but limited; can be plasmids or liposomes.

Gene Delivery Approaches

  1. Direct/in vivo delivery: Injected into the bloodstream or directly into the target organ.
  2. Cell-based/ex vivo delivery: Extract target cells, grow in culture, correct cells, then reinject into the patient.

Targeting Mechanisms

  • Somatic Cell Therapy: Targets body cells; genetic changes confined to the patient.
  • Germline Therapy: Targets gametes; genetic changes can be passed to future generations.

Therapeutic Effect Longevity

  • Therapeutic effects can ideally lead to corrected cells outnumbering uncorrected ones, providing ongoing treatment benefits. However, several challenges exist:
    1. Longevity of Effect: Depends on the vector and genetic stability.
    2. Immunogenicity: Predicting immune responses can be difficult.
    3. Insertional Mutagenesis: Risks include unintended mutations at integration sites.

History of Gene Therapy

  • Conceptualized in the 1970s; applied in humans starting in the 1990s with mixed success stories.
  • Key Events:
    • Living with SCID: Highlighted challenges of severe combined immune deficiency (SCID).
    • First Gene Therapy Failure: Jesse Gelsinger's tragic case due to OTC deficiency in 1999.