---
title: "The State of HSV Gene-Therapy Development: Fred Hutch's Meganuclease Program and the Broader Herpes-Cure Pipeline"
kind: "Research"
topic: "Drugs & public health"
date: "2026-09-01"
url: "https://canopticon.com/p/the-state-of-hsv-gene-therapy-development-fred-hutch-s-meganuclease-pr"
author: "Chris Telford"
license: "CC BY 4.0"
---

# The State of HSV Gene-Therapy Development: Fred Hutch's Meganuclease Program and the Broader Herpes-Cure Pipeline

## TL;DR
- **The Fred Hutch/Jerome-lab HSV meganuclease program remains preclinical (pre-IND) as of mid-2026 — no IND has been filed and no human trial has begun.** It is now housed in a Fred Hutch spinout, Caladan Therapeutics, Inc., and a realistic IND-to-approval path is roughly 8–12+ years away. No large-pharma licensee has been announced.
- **In animal models the therapy is impressive but not yet a true cure**: ~90% elimination of latent HSV-1 in orofacial mouse models and up to 97% in genital mouse models, but only ~30% in guinea pigs (a more human-like recurrence model), with dose-dependent hepatotoxicity and subtle neuronal injury as the main safety flags.
- **For patients seeking relief sooner, the nearer-term winners are antivirals** — Assembly Bio/Gilead's long-acting helicase-primase inhibitors (ABI-5366, ABI-1179) and AiCuris's pritelivir (Phase 3 met endpoint; FDA Priority Review granted) are years ahead of any gene-editing cure. The vaccine field contracted sharply in late 2025: Moderna discontinued its mRNA-1608 therapeutic vaccine and GSK's candidate failed its Phase 2 efficacy endpoint.

## Key Findings

**1. Fred Hutch program status.** Drs. Keith Jerome and Martine Aubert have published three landmark works (Nature Communications 2020, bioRxiv preprint 2022, Nature Communications May 2024). The program is in late preclinical / pre-IND work. The 2024 paper simplified the approach to a single AAV9 vector carrying a single dual-cutting meganuclease under a neuron-specific promoter. A Fred Hutch spinout, **Caladan Therapeutics, Inc.** (co-founded by Jerome and Aubert, both equity holders; established Nov 2021, publicly disclosed ~2024), now holds the commercial pathway; the lab plus the company won an NIH STTR grant. The underlying meganuclease sequences originated with Cellectis (France). No IND has been filed.

**2. Delivery, dose, efficacy, safety.** Delivery is systemic intravenous AAV (retro-orbital in mice), with the team showing that local injection into the fluid around affected nerves reduces the required dose ~5-fold. The original optimized regimen used a triple-serotype combination (AAV9 + AAV-Dj/8 + AAV-Rh10) delivering two meganucleases (m5+m8) at a total of 3×10¹² vg/mouse; the 2024 streamlined version uses a single AAV9 serotype, single meganuclease, and neuron-specific promoter. Efficacy: ≥90% latent HSV reduction (orofacial), up to 97% (genital, dorsal root ganglia), with significant reduction in viral shedding frequency and amount. In guinea pigs (natural recurrence model), latent HSV was reduced >30%, with fewer recurrences and 50% lower severity. Safety: hepatotoxicity at high doses and "subtle histological evidence of neuronal injury without observable neurological signs or deficits"; the neuron-specific promoter and dose reduction improved tolerability. Trigeminal-ganglia reductions (~41–48%) were notably lower than superior-cervical-ganglia reductions (~90–95%) — a delivery/completeness limitation.

**3. Competing gene-editing programs.** Yes — several. Excision BioTherapeutics (EBT-104, CRISPR/Cas9 targeting ICP0+ICP27 for HSV-1 keratitis, preclinical; >99.99% viral DNA reduction in Vero cells and near-elimination of shedding — 11 of 12 animals — in a rabbit keratitis model). BDGene/Shanghai (BD111, CRISPR/Cas9 mRNA delivered by a lentivirus-like particle via corneal injection for HSV-1 stromal keratitis) is the first gene-editing herpes therapy actually in humans (Phase 1, NCT06474416 and NCT04560790, in China). Academic CRISPR programs exist at Harvard and Temple. CRISPR approaches dominate the competitor field; notably, Jerome's group specifically found meganucleases outperformed CRISPR/Cas9 for editing *latent* HSV.

**4. Clinical/regulatory pathway.** A neurotropic AAV gene therapy follows the FDA biologics/gene-therapy route (IND → Phase 1 dose-escalation → Phase 2/3 → BLA). Precedents exist for AAV approvals: Zolgensma (AAV9-SMN1, IV, ~$2.125M) for SMA; Luxturna (AAV2, subretinal, $850K total / $425K per eye) for RPE65 retinal dystrophy; Kebilidi/eladocagene exuparvovec (AAV2, the first FDA-approved direct-to-brain AAV, Nov 13, 2024) for AADC deficiency; and Lenmeldy/Libmeldy (~$4.25M US) for MLD. However, **no AAV therapy has yet been approved for a latent/persistent viral infection** — an HSV gene-editing cure would be first-in-class, raising the regulatory bar. Realistic IND-to-approval timeline: roughly 8–12+ years.

**5. Treatment procedure.** Intended as a one-time treatment. The route in animals is IV systemic; the team is exploring local peri-neural injection to cut the dose. Reaching all latent reservoirs simultaneously (trigeminal, dorsal-root, sacral, autonomic ganglia) is the central scientific challenge — single-cell RNA-sequencing showed AAV and HSV are non-randomly distributed across neuronal subsets, so complete elimination is hard. Because ~90% is not 100%, residual latent genomes could in principle reactivate; re-infection from a new exposure also remains possible. Anesthesia/hospitalization needs would depend on route (outpatient IV infusion vs. image-guided ganglia injection).

**6. Costs/insurance.** No price exists (not approved). By analogy to AAV one-time therapies: Zolgensma ~$2.1M, Luxturna ~$850K, Lenmeldy/Libmeldy ~$2.8–4.25M. A herpes therapy faces a fundamentally different commercial calculus: per the WHO Herpes simplex virus fact sheet, "In 2020 (last available estimates), 3.8 billion people under the age of 50, or 64% of the global population, had HSV-1 infection," and HSV-2 affects 520 million aged 15–49 (13%). At that population scale, a rare-disease million-dollar price is implausible for a mass indication; the Fred Hutch team explicitly emphasizes affordability and dose reduction. Cost-benefit versus lifetime valacyclovir suppression (a cheap generic) would be a key payer hurdle. Insurance/Medicare coverage would hinge on a defined high-need indication (e.g., frequently recurrent or antiviral-refractory disease) and likely outcomes-based contracting.

**7. Patient population.** The likely first indication is frequently recurrent symptomatic genital HSV-2 (high unmet need, measurable endpoints such as shedding rate and lesion rate), or a narrow severe niche (e.g., refractory disease). The unmet need is large and the addressable market enormous, but pricing and safety constraints make patient selection critical. Asymptomatic seropositive individuals and post-herpetic neuralgia patients are less likely first targets.

**8. Competing cure/suppression approaches.** mRNA therapeutic vaccines: Moderna's mRNA-1608 completed Phase 1/2 (NCT06033261, completed April 2025) and showed safety and "a trend of improvement," but per Moderna's Nov 20, 2025 Analyst Day 8-K (SEC), "The Company's herpes simplex virus (HSV) clinical development program will not advance to Phase 3." BioNTech's BNT163 (prophylactic, Phase 1, NCT05432583) remains ongoing and is now, per Fierce Biotech, "the only active HSV injection in big biopharma development" after GSK's recombinant protein vaccine GSK3943104 "failed to hit the primary efficacy endpoint of reducing episodes of recurrent genital herpes in the phase 2 portion" (announced Sept 2025). Long-acting antivirals: Assembly Bio/Gilead's ABI-5366 and ABI-1179 (Phase 1b; Phase 2 planned mid-2026; Gilead exercised its license option Dec 22, 2025); AiCuris's pritelivir (Phase 3 PRIOH-1 met its endpoint). These antivirals compete on convenience and suppression but do **not** eliminate latent virus — so a true gene-therapy cure would still be differentiated. Therapeutic vaccines beyond GEN-003 (Genocea, discontinued 2017): Rational Vaccines' 0ΔNLS/RVx-201, largely earlier-stage.

## Details

### Fred Hutch / Jerome lab: scientific trajectory
The Jerome lab's foundational 2020 paper (Aubert et al., *Nature Communications*, DOI 10.1038/s41467-020-17936-5) showed that AAV-delivered meganucleases — but not CRISPR/Cas9 — eliminated >90% of latent HSV from superior cervical ganglia in mice, using a triple AAV serotype combination (AAV9, AAV-Dj/8, AAV-Rh10) delivering two meganucleases (m5+m8). The 2024 paper (Aubert et al., *Nature Communications*, DOI 10.1038/s41467-024-47940-y) reported ≥90% elimination in orofacial models and up to 97% in genital models, plus significant reductions in viral shedding frequency and amount, and critically simplified the regimen to a single AAV9 serotype + single meganuclease targeting a duplicated region of the HSV genome under a neuron-specific promoter, reducing hepatotoxicity and neuronal injury.

Aubert's mechanistic explanation: "We are using a meganuclease enzyme that cuts in two different places in the herpes virus's DNA. These cuts damage the virus so much that it can't repair itself. Then the body's own repair systems recognize the damaged DNA as foreign and get rid of it." Jerome's framing: "Herpes is very sneaky. It hides out among nerve cells and then reawakens and causes painful skin blisters... Our aim is to cure people of this infection, so that they don't have to live with the worry of outbreaks or of transmitting it to another person." On the streamlined approach: "Our streamlined gene editing approach is effective at eliminating the herpes virus and has less side effects to the liver and nerves... This suggests that the therapy will be safer for people and easier to make, since it has fewer ingredients."

### Status and timeline reality-check
The timeline has repeatedly slipped. In 2020–2022, the team hoped for a Phase 1 "before the end of 2023." In 2020 they said HSV-2 work would take "at least 3 years to move toward clinical trials." As of March 2025, Jerome said: "Hopefully, we'll take that into a human trial reasonably soon" — and the team is still "working through the preclinical studies needed prior to testing the strategy in human volunteers." Jerome's standing line is: "We're collaborating with numerous partners as we approach clinical trials so we align with federal regulators to ensure safety and effectiveness of the gene therapy."

The commercial vehicle is **Caladan Therapeutics, Inc.** Per a Fred Hutch donor update attributed to Jerome: "the business development group at Fred Hutch Cancer Center has worked with our team and external collaborators to establish a company called Caladan Therapeutics... Having a company structure helps us protect the intellectual property of the HSV gene therapy as it continues to develop and will support our work with federal regulators as we progress toward clinical implementation." The conflict-of-interest disclosures in the 2024 Nature Communications paper confirm "K.R.J. is a founder and holds equity in Caladan Therapeutics" and "M.A. holds equity in Caladan Therapeutics." Jerome is also a paid advisor/equity holder in Excision Biosciences (a separate CRISPR-based effort). No Big Pharma licensing deal has been announced — the "numerous partners" language refers to Caladan and regulatory/manufacturing collaborators, not a major commercial partner.

Funding is a mix of NIH grants (R01AI132599; an earlier R21AI117519; and an NIH STTR award jointly to the lab and Caladan providing, per Jerome, "modest funding for two years"), the Caladan Foundation (a long-standing philanthropic funder, distinct from the for-profit Caladan Therapeutics), named donors (Kenneth Hill Foundation, Krieger Family Trust, Tiny Foundation), and individual donors (over 2,000 cited in 2024). The public "Heroes Against Herpes" Fred Hutch fundraiser had raised approximately $1.3M toward a $1.5M goal. Patents (e.g., PCT/US2022/013757) are held by Fred Hutch.

### Guinea pig caveat (important)
The much lower efficacy in guinea pigs (>30% latent reduction, versus 90–97% in mice) is the single most important caveat. Guinea pigs experience natural recurrence (more human-like than mice), so the gap between mouse and guinea pig data should temper expectations for human efficacy. NIH was expanding independent guinea pig testing at its own facilities starting October 2023 to reproduce the results.

### Competitive landscape detail
- **Antivirals (nearest term):** Per Assembly Biosciences' Aug 8, 2025 release, ABI-5366 (a long-acting HSV helicase-primase inhibitor) produced a "94% reduction in HSV-2 shedding rate and 98% reduction in high viral load shedding rate, both statistically significant... in cohort evaluating 350 mg weekly oral dose compared to placebo over 29-day evaluation period" (p<0.01), exceeding the company's 80–85% target, plus a 94% reduction in genital lesion rate (the 350 mg weekly cohort showed a 97% reduction in *virologically confirmed* genital lesion rate, p<0.05). A monthly-dosing cohort showed a 76% reduction in HSV-2 shedding rate (p<0.01) and an 88% reduction in virologically confirmed genital lesion rate (p=0.01). Companion candidate ABI-1179 (50 mg weekly) showed up to a 91% reduction in confirmed genital lesions. Gilead exercised its combined license option on Dec 22, 2025; Phase 2 is planned for mid-2026. AiCuris's pritelivir met its Phase 3 PRIOH-1 (NCT03073967) primary endpoint — per AiCuris's Oct 16, 2025 release, the trial "met its primary endpoint of superiority (p=0.0047) in lesion healing in patients receiving treatment up to 28 days," increasing to p<0.0001 at 42 days, in refractory HSV in immunocompromised patients; AiCuris planned to file for marketing authorization in 2026.
- **Vaccines:** Moderna's therapeutic mRNA-1608 (Phase 1/2, NCT06033261; LNP encoding gB, gC, gD plus ICP0 and ICP4) showed safety and "a trend of improvement in select clinical endpoints," but was discontinued before Phase 3 (Nov 20, 2025). BioNTech's prophylactic BNT163 (Phase 1, encoding three HSV-2 glycoproteins) is ongoing and is now the only large-biopharma HSV vaccine in active development after GSK's GSK3943104 failed Phase 2.
- **Gene-editing competitors:** BDGene's BD111 (China) is the only gene-editing herpes therapy in humans (Phase 1, corneal intrastromal injection, HSV-1 stromal keratitis; CRISPR/Cas9 mRNA via lentivirus-like particle). Excision's EBT-104 (CRISPR targeting ICP0+ICP27, HSV-1 keratitis) remains preclinical. Both target the localized eye indication rather than systemic latent infection.

## Recommendations
1. **If you are a patient seeking relief in the next 1–3 years, do not wait for gene therapy.** Track Assembly Bio/Gilead's ABI-5366/ABI-1179 (Phase 2 starting mid-2026) and pritelivir (regulatory filing 2026; initially for refractory HSV in immunocompromised patients). These are realistic near-term options that meaningfully improve on valacyclovir, though they suppress rather than cure.
2. **For a true cure, watch Caladan Therapeutics / Fred Hutch for an actual IND filing announcement** — that is the single most important milestone and has not yet occurred. A registered ClinicalTrials.gov Phase 1 entry would be the first concrete signal. The benchmark that would change the outlook: a filed IND plus first-in-human dosing.
3. **Watch the guinea pig / large-animal efficacy data and trigeminal-ganglion delivery.** If efficacy in recurrence-prone large animals approaches the mouse 90%+ figures and toxicity stays low, the program's credibility rises sharply; if it stays near 30%, expectations should be heavily discounted.
4. **For investors/strategists:** the absence of a large-pharma licensee and reliance on donor funding plus an NIH STTR grant signals the program is early and capital-constrained relative to vaccine/antiviral competitors backed by Moderna, BioNTech, Gilead, and AiCuris. The mass-market scale of HSV is both the commercial attraction and the pricing constraint.

## Caveats
- **Speculative vs. confirmed:** All Fred Hutch efficacy figures are from animal models; none are human data. Human efficacy is unknown, and the mouse-to-guinea-pig efficacy drop is a genuine warning sign. "2026/2027 trial start" projections come from advocacy/secondary sources, not Fred Hutch directly — treat as unconfirmed.
- **No approved AAV therapy exists for any latent viral infection**, so regulatory precedent is limited and the path may be slower and harder than for monogenic diseases like SMA or MLD.
- **Pricing is entirely hypothetical** — no HSV gene therapy is approved, and the mass-market nature of HSV makes million-dollar rare-disease pricing analogies poor fits.
- The Caladan Therapeutics details and STTR funding are sourced partly from a Fred Hutch donor communication and a federal awardee database; exact financial terms and the STTR dollar amount are not publicly disclosed.
- Information is current to approximately mid-2026; clinical pipelines (especially antiviral and vaccine programs) move quickly, and corporate decisions (e.g., Moderna's discontinuation, Gilead's option exercise) can shift the landscape within months.