Gene Therapy

Introduction & rationale

• Gene therapy introduces genetic material (DNA/RNA) into a patient's cells to treat or prevent disease — by replacing a faulty/missing gene, silencing an over-active gene, or directly editing a defective gene — rather than delivering a conventional small-molecule or protein drug.
• Rationale — offers, in principle, a radical (potentially one-time) cure for the thousands of rare monogenic disorders (cystic fibrosis, the haemoglobinopathies) that conventional pharmacotherapy can only palliate; many cancers and neurodegenerative/infectious diseases also have a genetic component amenable to the approach.
• Conceptual challenge — "Is a gene a 'drug'? Is a virus a 'drug'?" — a gene has no intrinsic PK/PD; most toxicity arises from the vector, not the gene, and conventional dose–response logic breaks down because a gene "drug" is self-replicating.
• 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)."
• Milestone framing — feasibility of gene transfer was shown by Avery (1944); the 1980s molecular-biology revolution made gene replacement achievable. After a "shaky beginning," the sector is now projected at US$10–20 billion by 2028.