Why viruses matter in modern medicine

For most of human history, viruses were feared as invisible enemies. They are tiny packets of RNA or DNA designed to invade cells and replicate. However, biology reveals a surprising twist. Nearly 8% of the human genome comes from ancient viruses. Over time, evolution repurposed these viral remnants into tools that support pregnancy and immune defense. Today, scientists are applying the same principle to modern medicine.

How AAV launched the first wave of gene therapy

One of the first breakthroughs came from adeno-associated viruses (AAV). Research in the 1960s showed that AAV could safely transport engineered genes into human cells. As a result, they became early delivery vehicles for gene therapy. However, AAV rarely integrate into human DNA. Because of this, their use has been most effective in slow-dividing tissues such as the liver, muscle, and eye.

How HIV became a lentiviral vector for gene delivery

The next major leap came from HIV research. In the 1990s, scientists learned how to remove HIV’s harmful genes. Then, they rebuilt the virus into a safe delivery system known as a lentiviral vector. Unlike AAV, lentiviral vectors integrate therapeutic genes directly into DNA. Therefore, they are especially useful for diseases involving rapidly dividing cells, including cancer.

For a clear, non-technical overview of HIV progression, see: Stages of HIV infection (HIVinfo/NIH) .

How lentiviral vectors enabled CAR-T cancer therapy

This innovation reshaped oncology. In 2017, Novartis’s Kymriah became the first FDA-approved therapy using lentiviral vectors. Specifically, the treatment reprograms a patient’s immune cells to recognize and destroy leukemia cells. As a result, many patients gained effective treatment options where few existed before.

Ex vivo vs. in vivo gene therapy: what’s changing

Since then, lentiviral vectors have powered therapies for sickle-cell disease and beta-thalassemia. Most of these treatments are ex vivo. That means cells are removed, modified in specialized facilities, and returned to the patient. However, this process is slow and expensive. In many cases, production takes months and costs can exceed $1 million per dose.

Why in vivo lentiviral therapy could expand access

To address this challenge, researchers are advancing in vivo gene therapy. Instead of removing cells, lentiviral vectors deliver genetic instructions directly inside the body. As a result, treatment timelines shrink and manufacturing complexity drops. Importantly, this approach could expand access beyond elite medical centers.

In 2025, Umoja Biopharma treated leukemia and lymphoma patients using an in vivo lentiviral therapy. Notably, the treatment reprogrammed T cells without extraction or chemotherapy preparation. Therefore, hospitals without advanced cell-manufacturing infrastructure could offer cutting-edge care. Meanwhile, companies such as AstraZeneca and AbbVie are pursuing similar strategies.

What pricing and manufacturing mean for the future of gene therapy

Cost remains a critical issue. Currently approved in vivo AAV therapies often carry seven-figure prices. For example, Zolgensma launched at $2.1 million per dose. However, lentiviral in vivo therapies may scale more efficiently. In fact, a single manufacturing run could treat tens of thousands of patients. By contrast, AAV production typically treats fewer than ten.

What policymakers and investors should watch next

This shift could redefine gene therapy. Instead of boutique medicine, it may become standard care for cancer, cardiovascular disease, and autoimmune conditions. Consequently, policymakers and investors must prepare for rapid expansion. At the same time, viral-vector manufacturing capacity is emerging as a competitive bottleneck.

Investment is already accelerating. The global cell and gene-therapy market is projected to exceed $100 billion by 2034. Meanwhile, pharmaceutical leaders such as Novartis, AbbVie, and Johnson & Johnson are securing partnerships and acquisitions. Early leaders, therefore, will be companies that scale production while lowering costs.

Ethics and oversight: balancing innovation with safeguards

Still, innovation brings responsibility. Technologies capable of curing genetic disease could also be misused. For this reason, regulators must balance progress with ethical safeguards. Clear standards, transparent oversight, and fair pricing will be essential to public trust.

The bottom line: turning a deadly virus into a life-saving tool

Ultimately, viral vectors may define 21st-century medicine. If the 20th century belonged to antibiotics and chemotherapy, this era may belong to genetic precision. In the end, it is a powerful reminder that even humanity’s smallest adversaries can become its greatest medical allies.