Silencing the Virus Within: William Brandler’s Bid to Turn “Jumping Genes” Into Precision Medicines

William Brandler was 12 or 13 when he learned that the genome is not as fixed as it looks.

He read the biography of his great-aunt, Barbara McClintock, the pioneering geneticist whose studies of maize revealed that genetic elements could move within a genome. Her once-radical discovery of what became popularly known as “jumping genes” ultimately earned her the 1983 Nobel Prize in Physiology or Medicine.

Today, he is the Founder and CEO of L1 Therapeutics, Inc., a San Diego biotechnology company founded in 2026. Its mission is to develop precision small-molecule therapies that suppress LINE-1, a class of mobile, virus-like DNA that is normally kept quiet but can reactivate in disease.

“I had a vision for my career to help translate McClintock’s discoveries about the genome into technologies or medicines that can benefit people,” Brandler says.

A Virus-Like Mechanism Hidden in Our DNA

LINE-1 is best understood as biological copy-and-paste code embedded inside the human genome.

LINE-1, or L1, accounts for roughly 17% of human DNA. The genome contains approximately 500,000 copies, although only around 80 to 100 retain the machinery needed to make new insertions. Unlike a conventional gene, an active LINE-1 element can create an RNA copy of itself, convert that RNA back into DNA and insert the new copy elsewhere in the genome. Researchers call that process retrotransposition. 

The phrase “virus within” is a metaphor, not a diagnosis. LINE-1 is not a contagious infection; it is inherited DNA that uses some virus-like molecular machinery. In healthy adult tissue, cellular defenses generally keep it suppressed. In certain diseased or stressed cells, however, those controls can weaken.

When that happens, LINE-1 activity may create insertions, DNA breaks or larger genomic rearrangements. LINE-1-derived DNA also appears foreign to the cell, provoking an innate immune response and inflammation.

This combination of genomic instability and inflammatory signaling is what makes LINE-1 scientifically compelling. Its relative silence in healthy tissue also raises the possibility of targeting diseased cells more selectively. But possibility is not proof, and Brandler is careful about the distinction.

Driver, Biomarker or Both?

The central scientific question is not whether LINE-1 can be detected in disease. It is whether suppressing it will meaningfully alter a patient’s outcome. When asked whether LINE-1 is a driver of disease or merely a marker of cellular stress, Brandler’s response was,

“The answer is that it is both, depending on the circumstances. For example, in cancer we know that it is marker of late stage disease. We also know that treatments such chemotherapy and radiotherapy induce LINE-1. Furthermore, LINE-1 directly causes mutations that can promote tumor progression and spread. It is an ongoing process that can both contribute to disease and be a marker of it”

For L1 Therapeutics, the company’s primary focus is on determining where LINE-1 is active, when it contributes causally to disease and which patients are most likely to benefit from inhibition.

First, Make the Biology Visible

Brandler’s precision-medicine strategy begins with a principle borrowed directly from McClintock.

“You first have to see the ‘jumping genes’ for yourself,” he says. “She did it using a microscope. We’re going to do it using single-cell whole-genome sequencing.”

Examining genomes one cell at a time could allow L1 Therapeutics to identify how LINE-1 is actively moving, and to compare its relative importance across multiple diseases.

Alongside that strategy, the company has released open-source software designed to detect retrotransposon insertions in DNA sequencing data. L1 Therapeutics reports that it can identify candidate events in short-read data that earlier analyses missed. However, the tool is still a prototype. 

Why Open Source—and Where AI Fits

Publishing software openly may appear counterintuitive for a company that eventually needs defensible intellectual property. Brandler sees it differently.

“There is some risk putting it out there,” he says, “but execution speed and strategy are far more important. Software companies in Silicon Valley have proven this”

Open source can invite scrutiny, feedback and scientific collaboration. L1 Therapeutics has not publicly disclosed the details of its therapeutic intellectual-property strategy, but its long-term advantage will ultimately depend on far more than code: disease selection, proprietary biological insight, rigorous validation, drug development and the speed and quality of execution.

AI has accelerated the engineering layer. According to Brandler, AI assistance helped the company produce a working software prototype in weeks rather than months. But he does not portray the technology as autonomous science. AI took shortcuts, introduced bugs and required experienced human direction.

For Brandler, its deeper importance was entrepreneurial. He had wanted to build a company for some time but was not able to assemble every capability required to begin.

“AI changed all that,” he says.

It reduced the distance between an informed idea and an executable first version. 

The Advantage of Being Both Outsider and Insider

Brandler’s career has prepared him for a company that crosses scientific and technical boundaries. Educated at Cambridge and Oxford, where he earned his doctorate, he has more than a decade of experience across genetics, software and biotechnology. His research includes a 2018 paper in Science examining structural genetic variants associated with autism.

His founder influences, however, extend beyond the laboratory.

His grandfather grew up as a German Jew in Berlin and escaped to Britain with his parents and siblings during the 1930s, although much of the extended family was lost in the Holocaust. After the war, he left Europe and became an entrepreneur in Africa. 

Like his Grandfather, Brandler grew up in different countries. Like his Great Aunt, he studied and worked at elite institutions. That combination gave him what he describes as an outsider-insider perspective: enough distance to question the status quo, but enough institutional fluency to navigate science, technology and business.

That duality may be particularly valuable in biotechnology, where founders must challenge convention without becoming detached from evidence.

Truth-Seeking Before Scale

Brandler is unusually candid about the transition from scientist and engineer to CEO.

“Most of my assumptions have proved to be incorrect,” he says. “Almost every detail of the company strategy has changed. However, the core idea remains the same.”

That philosophy shapes capital allocation. Biotechnology can become difficult and expensive to redirect once a program is committed to a particular indication or development path. L1 Therapeutics therefore intends to begin with focused experiments, perform due diligence and increase investment only as evidence builds conviction.

There are many diseases in which LINE-1 biology may be relevant. Brandler says the company will prioritize programs according to the quality of the science and the probability of success, not simply the size of the initial market or the personal preferences of investors, employees or partners.

“We have to be truth-seeking,” he says, “even though the truth can hurt in the short-term.”

From Tractable Biology to a Medicine

Because both retroviruses such as HIV and LINE-1 rely on reverse transcriptase, some medicines originally designed to block viral replication can also inhibit LINE-1 in laboratory models.

That gives Brandler a starting point. His stated three-to-five-year objective is to obtain clinical-trial readouts from the first patients treated with LINE-1 inhibitors in one disease, then expand into other conditions where the biology supports it. For a pre-seed company, that is a deliberately ambitious target and will depend on successful validation, financing, drug development and regulatory execution.

Clarity as a Leadership Discipline

Asked what one lesson CEOInsider readers should remember, Brandler returns to a principle that applies equally to science and leadership.

“You don’t truly understand something until you can teach it to others,” he says. “Great leaders make complex ideas clear, explain how things work and communicate what success looks like. They lead by example because they live those expectations themselves.”

At L1 Therapeutics, clarity is more than a communication style. It is an operating requirement. A biotechnology CEO must explain unfamiliar biology to investors, define decisive experiments for scientists, communicate uncertainty to partners and remain honest about what any future result could mean for patients.

McClintock’s breakthrough made mobile DNA visible. Brandler’s challenge is to determine when that movement matters—and whether silencing it can change the course of disease.

L1 Therapeutics is still at the beginning. Its thesis may evolve as the evidence arrives. But at this stage, the company’s most credible asset is not certainty. It is precision about what must be learned next—and the willingness to let the data decide.

Company at a Glance

• Company: L1 Therapeutics, Inc.

• Founder and CEO: William Brandler

• Founded: 2026

• Headquarters: San Diego, California

• Stage: Pre-seed; raising capital

• Scientific focus: Precision small-molecule therapeutics targeting LINE-1 biology

• Company website: l1tx.com

• Open-source project: retrotransposon-miner