Gene Therapy in Cancer

From viral vectors to CRISPR genome editing — how gene therapy approaches are transforming oncology and hematology

Key Points

What Is Gene Therapy?

Gene therapy is the deliberate alteration of the genetic material within cells to prevent, treat, or cure disease. In contrast to drugs that interact with existing proteins, gene therapy intervenes at the nucleic acid level — adding a functional gene copy, disabling a harmful gene, correcting a mutation, or instructing cells to produce a therapeutic protein they could not previously produce. In oncology, gene therapy encompasses a remarkably broad spectrum of approaches: 1. **Ex vivo cell engineering:** Removing a patient's cells, genetically modifying them outside the body, and reinfusing…

Viral Vector Delivery Systems

The central technical challenge of gene therapy is delivering genetic cargo into target cells efficiently, safely, and specifically. Viral vectors — engineered viruses stripped of their disease-causing genes but retaining their cellular entry and gene-delivery machinery — are the dominant delivery platform. Each vector type has distinct properties that make it suitable for specific applications. **Lentiviral vectors (LVs):** Derived from HIV-1 (replication-incompetent); among the most important vectors for ex vivo gene therapy and CAR T manufacturing. Key properties: - Integrate stably into…

Non-Viral Delivery and RNA-Based Approaches

Although viral vectors dominate current clinical gene therapy, non-viral delivery platforms offer important advantages — particularly for nucleic acid drugs (mRNA, siRNA, ASOs) and CRISPR ribonucleoprotein (RNP) delivery. **Lipid nanoparticles (LNPs):** The most clinically advanced non-viral delivery system, validated by the COVID-19 mRNA vaccines (Pfizer-BioNTech, Moderna). LNPs encapsulate nucleic acids in a lipid bilayer that protects the cargo from nuclease degradation, enables cellular uptake through endocytosis, and releases the payload intracellularly. In cancer gene therapy and…

CRISPR-Cas9 Genome Editing in Cancer

CRISPR-Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats / CRISPR-associated protein 9) represents a fundamental advance in precision genome editing that has transformed biology research and is now entering clinical applications. The 2020 Nobel Prize in Chemistry was awarded to Jennifer Doudna and Emmanuelle Charpentier for its development. **Mechanism:** The CRISPR-Cas9 system uses a single guide RNA (sgRNA) to direct the Cas9 nuclease to a specific sequence in the genome (determined by 20-nucleotide complementarity). Cas9 creates a double-strand break (DSB) at that location.…

Oncolytic Virotherapy

Oncolytic viruses (OVs) are naturally occurring or engineered viruses that preferentially infect, replicate within, and lyse tumor cells — exploiting the same defects in anti-viral signaling pathways (innate immunity, type I interferon response, RAS pathway activation) that cancers use to survive. Tumor lysis releases tumor-associated antigens and danger signals (DAMPs), triggering an anti-tumor immune response that can attack distant metastases — the "abscopal effect" of OV therapy. **Talimogene laherparepvec (T-VEC; Imlygic — Amgen):** The only FDA-approved oncolytic virus therapy (2015…

TCR-T Cell Therapy (T Cell Receptor Therapy)

TCR-T cell therapy is closely related to CAR T but uses a different receptor architecture. Instead of a synthetic chimeric antigen receptor that binds surface proteins, TCR-T cells are engineered to express a T cell receptor that recognizes intracellular tumor-derived peptides presented by HLA molecules on the cell surface — the natural pathway of T-cell antigen recognition. **Advantages over CAR T:** - **Intracellular target access:** TCRs recognize peptides from any intracellular protein (transcription factors, mutant oncoproteins, viral proteins) — CAR T is limited to surface antigens,…

Gene Therapy for Non-Malignant Hematologic Diseases

Some of the most compelling clinical successes in gene therapy have come not in cancer, but in treating non-malignant hematologic diseases that previously required allogeneic bone marrow transplantation for cure — and the advances in these diseases directly enable cancer gene therapy by validating the platform, manufacturing processes, and safety profile of gene-modified HSC therapy. **Sickle Cell Disease (SCD):** *Casgevy (exagamglogene autotemcel; exa-cel) — Vertex Pharmaceuticals / CRISPR Therapeutics:* FDA-approved December 8, 2023 for SCD (≥12 years) and transfusion-dependent…

Challenges, Costs, and the Future of Gene Therapy

Gene therapy occupies a unique position in medicine — extraordinary therapeutic potential paired with extraordinary manufacturing complexity, cost, and access barriers. Understanding these challenges is essential for clinicians counseling patients and for policymakers shaping healthcare systems. **Manufacturing complexity and scalability:** Autologous gene therapy products require individualized manufacturing for each patient — a fundamentally different paradigm from mass-produced drugs. Each product lot must pass extensive quality control (sterility, potency, identity, purity, vector copy…