Gene Therapy

Gene Therapy

1. Definition, scope & conceptual framing

• Gene therapy is a therapeutic modality in which genetic material (DNA or RNA) is introduced into a patient's cells to treat or prevent disease — by replacing a faulty or missing gene, silencing an over-active gene, or directly editing a defective gene — rather than delivering a conventional small-molecule or protein drug (R&D 10e Ch.5, pp.27–43).
• The driving rationale: gene therapy offers, in principle, a radical (potentially one-time) cure for the literally thousands of rare monogenic disorders (e.g. cystic fibrosis, the haemoglobinopathies) that conventional pharmacotherapy can only palliate; many common malignant, neurodegenerative and infectious diseases also have a large genetic component amenable to this approach (R&D 10e Ch.5, p.27).
• Gene therapy is conceptually distinct from, but pipeline-adjacent to, the other "biopharmaceuticals" in R&D Ch.5 — protein/peptide therapeutics, monoclonal antibodies, and RNA (oligonucleotide) drugs — which share the theme of large, biologically-manufactured molecules but do not alter the host genome (R&D 10e Ch.5, pp.1–27). Recombinant protein drugs and general drug discovery fall outside gene therapy proper and are touched on below only where they border it.
• A philosophically unresolved question flagged by R&D: "Is a gene a 'drug'? Is a virus a 'drug'? Is a GM stem cell a 'drug'?" A gene has no inherent pharmacodynamic or pharmacokinetic properties of its own; most of the toxicity and adverse effects of gene therapy arise from the vector or carrier, not the gene. The conventional dose–response logic also breaks down — how does one assess the optimal dose of a "drug" that is self-replicating? (R&D 10e Ch.5, p.43).
• Indian definition (ICMR–DBT 2019): a Gene Therapy Product (GTP) is "a biological substance or therapeutic molecule which could modify the genome, or the extra-genomic DNA or RNA segments (mitochondrial and episomal)" (ICMR–DBT National Guidelines for GTP, 2019) [CDSCO/ICMR].
• KDT lists antisense oligonucleotides and gene therapy as among the principal experimental approaches in new drug development, alongside biotechnology/recombinant-DNA products (human insulin, growth hormone, interferon, monoclonal/chimeric antibodies) — i.e. it frames gene therapy as a frontier modality emerging from the biotechnology revolution (KDT 8e Ch.5, p.~64 [biotechnology subsection]).

Historical milestones (orientation)

• 1944 — Avery and colleagues demonstrate the theoretical feasibility of gene transfer, showing a virulence factor (later identified as DNA) could be transferred between pneumococcal strains — before DNA was even recognised as the genetic material (R&D 10e Ch.5, p.27).
• The molecular-biology revolution of the 1980s turned the prospect of replacing faulty/missing genes from a distant dream into an achievable goal (R&D 10e Ch.5, p.27).
• The field had a "shaky beginning" but has now achieved notable successes; despite only a handful of approvals, some experts estimate the sector will be worth US$10–20 billion by 2028 (R&D 10e Ch.5, p.27).