Fred Hutch / Caladan HSV gene editing

Researchers at Fred Hutch and the associated company Caladan Therapeutics are developing a potentially curative HSV gene-editing approach that uses AAV vectors to deliver HSV-specific meganucleases to infected nerve cells.

The strongest public evidence is still from HSV-1 mouse studies. Those studies reported large reductions in latent viral DNA and less experimentally induced shedding, but also identified dose-related liver toxicity and subtle neuronal injury in some settings. No human candidate or trial was identified through September 1, 2026.

Meganucleases are engineered enzymes that cut selected DNA sequences. In this program, adeno-associated virus vectors carry the enzymes into peripheral neurons so they can damage essential HSV DNA and reduce the latent viral reservoir.

The program is sometimes described generically as CRISPR gene editing, but its lead published animal strategy uses meganucleases. The public studies tested several enzyme combinations, AAV serotypes, promoters, and doses; no final human-ready product or product code was disclosed.

The goal is to move beyond temporary suppression by directly reducing latent HSV DNA in ganglia. A separate NIH-funded Caladan/Fred Hutch project aimed to adapt the platform to HSV-2 by selecting a lead HSV-2 meganuclease and testing activity and safety in a guinea-pig model.

A 2020 mouse study established that optimized dual-meganuclease delivery could reduce latent HSV-1 DNA in multiple ganglia more effectively than several single-site approaches. A 2024 study extended the work to genital and orofacial HSV-1 infection models and measured induced peripheral shedding as well as latent viral load.

Fred Hutch said in March 2025 that the team was working through preclinical studies needed before testing in human volunteers. The identified NIH small-business project ended on July 31, 2026. No newer direct source established that the wider program stopped or continued after that funding period.

In the 2024 paper, some dual-meganuclease and triple-AAV experiments reduced latent HSV-1 DNA by 90% or more in mouse ganglia, with a reported reduction up to about 97% in one genital-infection model. Results varied by ganglion, dose, vector configuration, and experiment, and residual viral DNA remained.

Across combined mouse experiments using a drug to induce HSV-1 reactivation, treated animals were less likely to have detectable peripheral shedding than controls. Individual experiments were small and often did not reach statistical significance; the combined analysis reported an odds ratio of 0.41 with p=0.010.

At high AAV/meganuclease doses, about 10% of treated animals showed clinical signs consistent with liver toxicity, and histology showed subtle neuronal injury in some settings. Lower doses, a neuron-specific promoter, and simplified vector configurations improved observed tolerability while retaining animal activity.

This is a potentially curative preclinical program because it targets latent viral DNA rather than only active replication. That category does not mean a cure has been demonstrated: partial reservoir reduction in mice is not proof of a sterilizing or functional cure in people.

The shedding result is also animal evidence. It does not show prevention of recurrences or transmission between people, and the safety findings make dose, distribution, off-target activity, and neuronal tolerability central development questions.

The public evidence supports a preclinical stage. Because the named HSV-2 award had ended shortly before September 1, 2026, and no newer direct progress or discontinuation statement was identified, the wider program's current operating status is unclear rather than confirmed active or abandoned.

A credible next update would identify the HSV-2 lead and executed animal results, a finalized delivery configuration, safety and biodistribution evidence, follow-on funding, or a registered first-in-human study. None had been confirmed as of September 1, 2026.