Can CRISPR End Influenza's Hold?

During the Pandemic Research Alliance Symposium in October, an intriguing proposal was put forward by Wei Zhao for an audience of virologists from across China, Australia, and Singapore.

CRISPR, primarily known for providing revolutionary treatments for rare genetic conditions by correcting or deleting faulty genes, is being reconsidered for a new purpose by Zhao and his associates at Melbourne's Peter Doherty Institute for Infection and Immunity.

Their innovative vision sees CRISPR as a potential powerhouse against influenza viruses, whether seasonal outbreaks or new, concerning strains from birds and other animals that could spark future pandemics.

CRISPR’s ability to edit genetic blueprints opens doors for diverse applications. While the Cas9 enzyme is famed for DNA cutting, leader researchers, like Zhao, are delving into Cas13, an enzyme adept at slicing RNA, the primary component of the flu’s genetic material.

“Cas13 specializes in targeting RNA-based viruses for deactivation,” Zhao illuminated.

Though Cas9 and Cas13 enzymes aren't naturally occurring in human bodies, these proteins are common in certain bacteria and archaea, where they combat viral invaders. Zhao and his team are working hard to adapt these natural defense mechanisms for human protection.

A Two-Tiered Defense Mechanism

Initially conceptualized as a novel antiviral for Covid-19, the plan is to use lipid nanoparticles within a nasal spray or injection to transport molecular directives to cells infected by the flu in the respiratory system. This approach is sequential: introducing an mRNA that tells cells to manufacture Cas13 and employing guide RNA to drive Cas13 to the influenza RNA for destruction.

“By slicing the viral RNA, Cas13 impairs the flu's replication process, halting the infection genetically,” explains Sharon Lewin, project leader from the Peter Doherty Institute.

The technology primarily aims to lessen short-term infections, but Zhao imagines it also serving as a preemptive strike during harsh flu seasons. “Think of it as preloading your respiratory tract cells with this defense, akin to soldiers readying for battle,” he describes.

Cas13’s appeal lies in its ability to be programmed to assault conserved regions within flu’s genetic framework—segments critical to all flu strains—unlike traditional antivirals like Tamiflu that only address specific flu versions.

Challenges and Considerations

CRISPR-Cas13 is among the pioneering tools leading the charge against flu, but it isn’t the solitary contender. Alternative drugs targeting genetic constants in flu or amplifying the body’s immune signaling, known as interferons, are under exploration as well.

Annually, influenza A results in 12,000 to 52,000 American deaths, underscoring the critical need for improved solutions. Nonetheless, Nicholas Heaton of Duke University warns of obstacles like immune responses to bacterial proteins and potential off-target effects of CRISPR treatments.

Preliminary safety evaluations have utilized Harvard’s Wyss Institute’s “lung-on-a-chip,” a model replicating human air sacs, to assess if Cas13 can combat severe flu strains effectively without unintended reactions.

Donald Ingber, Wyss Institute's founding director, reported successful trials, with Cas13-fortified cells resisting multiple flu variants without adverse effects. “Not only did viral replication drop, but cells released fewer inflammation-causing molecules,” Ingber shared.

Future Prospects and Alternative Approaches

Despite promising results, delivery methods for getting lipid nanoparticles to deep lung cells remain a complex challenge. Heaton further highlights the evolutionary risk where targeting viral components might prompt unforeseen mutations.

Explorations are ongoing into using CRISPR to modify human genes to increase flu resistance. Heaton considers adjusting genes that the virus exploits to penetrate cells as a defensive strategy.

Experiments have isolated the SLC35A1 gene as a flu vulnerability, a gene pivotal for signaling pathways influenza uses to access our cells. This discovery opens pathways for treatments that inhibit this gene's function to potentially block all flu types.

Heaton reflects on whether strategic, temporary suppression of such genes could thwart influenza without side effects. “Could we tolerate inhibiting such a gene in specific areas without adverse consequences? It’s speculative, yet promising in these early stages.”