8-K: Krystal Biotech's KB407 Shows Positive CF Lung Delivery

Krystal Biotech announces successful wild-type CFTR delivery and expression in cystic fibrosis patients' lungs from its CORAL-1 study, advancing its mutation-agnostic gene therapy.

Summary

• Krystal Biotech reported a positive interim clinical update from the highest dose cohort (Cohort 3) of its Phase 1 CORAL-1 study evaluating KB407 in patients with cystic fibrosis (CF).
• The study confirmed successful lung delivery and expression of wild-type cystic fibrosis transmembrane conductance regulator (CFTR) protein following inhaled administration of KB407.
• KB407 transduction was confirmed in all six patients who underwent successful bronchoscopies, irrespective of their modulator-status or genetic background.
• The percentage of conducting airway cells transduced in each patient ranged from 29.4% to 42.1%.
• Clear evidence of CFTR protein expression was observed in patients with Class I mutations, who currently lack effective modulator therapies.
• KB407 continued to be well tolerated in the highest dose cohort, with all but one KB407-related adverse event being mild to moderate in severity and transient in nature.
• One serious adverse event (SAE) of asthma exacerbation was reported 24 hours after bronchoscopy, but was deemed procedure-related and not related to KB407 by the independent data monitoring committee, resolving in 5 days.
• The registrational repeat dosing CORAL-3 study design was submitted to the FDA in late December.
• The company anticipates aligning on the CORAL-3 study design with the FDA in 1Q 2026 and expects enrollment to start in 2Q 2026.
• An investor conference call and webcast was scheduled for January 8, 2026, at 4:30 pm ET to discuss the data update and timelines.

Sentiment

Score: 9

Explanation: The interim clinical data for KB407 is overwhelmingly positive, demonstrating a significant scientific and clinical breakthrough in cystic fibrosis gene therapy. The successful delivery and expression of wild-type CFTR protein, particularly in patients with Class I mutations, addresses a major unmet medical need. The high transduction rates, broad distribution, and favorable safety profile, combined with the established redosable HSV-1 platform, position KB407 as a potentially transformative, mutation-agnostic therapy. The clear and accelerated path to a registrational Phase 3 study (CORAL-3) and strong regulatory and foundation engagement further de-risk future development. This validation of the lung platform also has positive implications for Krystal's broader pipeline, and the substantial addressable market indicates significant commercial potential.

Positives

• Successful lung delivery and expression of wild-type CFTR protein in clinically relevant ciliated and secretory cells of CF patients' lungs, marking a significant breakthrough.
• High rates of KB407 transduction, ranging from 29.4% to 42.1% of conducting airway cells, with broad distribution across patient airways.
• Transduction was confirmed irrespective of underlying lung disease, genetic background, or modulator status, underscoring KB407's potential as a mutation-agnostic therapy.
• Demonstrated functionality of its full-length CFTR payload.
• KB407 was well tolerated in the highest dose cohort, with a safety profile consistent with previous cohorts, and mostly mild-to-moderate, transient adverse events.
• No evidence of significant neutralizing antibody response or systemic vector distribution after inhalation.
• Clear evidence of CFTR protein expression in patients with Class I mutations, addressing a critical unmet need for those ineligible for or underserved by current modulators.
• CFTR protein expression for at least 96 hours, indicating potential for weekly or better dosing regimens.
• Advancing to a potentially registrational repeat dosing study (CORAL-3), with the study design already submitted to the FDA.
• Strong engagement with the Cystic Fibrosis Foundation (CFF) Therapeutics Development Network (TDN) to accelerate clinical development.
• Validation of Krystal's lung platform, which further de-risks other inhaled programs like KB408 and KB707, and supports pipeline expansion.
• KB407 is positioned to address a significant market opportunity, estimated at over $2 billion, for modulator-ineligible or refractory CF patients.

Negatives

• One serious adverse event (SAE) of asthma exacerbation was reported, although it was deemed procedure-related and not related to KB407.

Risks

• Uncertainties inherent in the initiation and conduct of clinical trials.
• Regulatory review processes for clinical trials and applications for marketing approvals.
• Whether results from early clinical trials will be indicative of outcomes in later-stage studies.
• Uncertainties regarding the ultimate availability or commercial potential of product candidates.

Future Outlook

KB407 is anticipated to be a transformative, mutation-agnostic therapy for cystic fibrosis patients who are either ineligible for or underserved by currently available modulators. The company plans to advance into the repeat dosing CORAL-3 study with registrational intent, which will evaluate the safety and efficacy of repeat KB407 administration, including regular assessments of lung function by spirometry. Krystal Biotech expects to align on the CORAL-3 study design with the FDA in 1Q 2026 and initiate enrollment in 2Q 2026. This positive data is also expected to further de-risk other inhaled programs, KB408 and KB707, and supports broader pipeline expansion, with multiple blockbuster opportunities under evaluation. KB407 is set on an accelerated path towards addressing a market opportunity exceeding $2 billion.

Management Comments

• Jorge Lascano, MD, Professor of Medicine, Associate Director of the Adult Cystic Fibrosis Program, and Director of the Cystic Fibrosis Therapeutics Development Center at the University of Florida, stated: "Molecular confirmation of delivery and expression of unmodified, wild-type CFTR protein in clinically relevant ciliated and secretory cells of the lungs of patients with CF is a tremendous breakthrough and a first for our field."
• Dr. Lascano further commented: "High rates of KB407 transduction and broad distribution across patient airways irrespective of underlying lung disease, genetic background, or modulator status — combined with the redosability of KB407 and demonstrated functionality of its full-length CFTR payload — underscore the transformative potential of KB407 as a mutation-agnostic therapy for the many patients either ineligible for or underserved by currently availably modulators."
• Suma Krishnan, President, Research & Development, Krystal Biotech, Inc., remarked: "Todays update has profound implications for Krystal and for the many CF patients unable to benefit from modulator therapy. With clear evidence of CFTR protein expression in patients with class I mutations and reproducible KB407 transduction across a diverse CF population, we are moving forward with conviction into our repeat dosing study with registrational intent, CORAL-3."
• Ms. Krishnan also added: "We are excited to be working with the Cystic Fibrosis Foundation to accelerate clinical development and potential registrational timelines."

Industry Context

Cystic fibrosis (CF) is a severe inherited disease affecting approximately 40,000 children and adults in the United States and an estimated 105,000 globally. While CFTR modulators have significantly improved outcomes for patients with specific mutations, a substantial portion of CF patients (over 10% are modulator ineligible, plus thousands with suboptimal responses) still lack effective disease-modifying treatment options. This represents a critical unmet medical need. Krystal Biotech's KB407, a gene replacement therapy, offers a mutation-agnostic strategy to target CF, aiming to restore functional CFTR protein regardless of the underlying genetic mutation. This approach seeks to overcome limitations faced by previous inhaled gene therapy efforts, which struggled with delivery efficiency, cargo capacity, immunogenicity, and stability, positioning KB407 as a potential leader in addressing this underserved patient population.

Comparison to Industry Standards

• KB407 is now the first gene therapy to achieve molecular confirmation of wild-type CFTR protein expression in the lungs of cystic fibrosis patients, setting a new benchmark for gene therapy in this field.
• Krystal Biotech's HSV-1 platform, utilized for KB407, is clinically validated and redosable, as evidenced by VYJUVEK, the company's first commercial product. VYJUVEK is the first-ever redosable gene therapy and the first genetic medicine approved in the United States, Europe, and Japan for dystrophic epidermolysis bullosa, providing a strong precedent for KB407's potential redosability and safety profile compared to other gene therapy vectors.
• The company's approach with KB407 aims to overcome historical challenges faced by prior nucleic acid-based therapies for CF, which encountered pitfalls related to delivery through thick and infected airways, degradation of less-stable therapies, cargo limitations for the large CFTR gene, and immunogenicity impacting repeat dosing.

Stakeholder Impact

• **Shareholders**: Highly positive news, validating the company's lung gene therapy platform and opening a significant market opportunity, likely leading to increased investor confidence and potential share price appreciation.
• **Cystic Fibrosis Patients**: Offers substantial hope for a new, mutation-agnostic disease-modifying treatment, especially for those with Class I mutations or who are ineligible for/unresponsive to current modulator therapies, where no effective options currently exist.
• **Employees**: Provides strong validation of their research and development efforts, potentially boosting morale and reinforcing the company's leadership in genetic medicines.
• **Regulatory Authorities (FDA)**: Ongoing engagement and submission of the CORAL-3 study design indicate continued collaboration and a clear regulatory pathway for potential future approval.
• **Cystic Fibrosis Foundation**: Active collaboration with the CFF TDN highlights a shared commitment to accelerating the development of novel CF therapies.

Next Steps

• Host an investor conference call and webcast on January 8, 2026, at 4:30 pm ET to discuss the clinical data updates and timelines.
• Align on the CORAL-3 study design with the FDA in 1Q 2026.
• Start enrollment in the CORAL-3 study in 2Q 2026 (or 1H 2026).
• Provide additional details on the CORAL-3 study design by the time of study initiation.
• Continue working with the Cystic Fibrosis Foundation to accelerate clinical development and potential registrational timelines for KB407.

Key Dates

Recommendation

The interim clinical data for KB407 represents a significant scientific and clinical breakthrough, confirming successful delivery and expression of wild-type CFTR protein in CF patients' lungs, including those with Class I mutations who have no current effective treatment. The high transduction rates, broad distribution, and favorable safety profile, combined with the redosable HSV-1 platform, position KB407 as a potentially transformative, mutation-agnostic therapy. The clear path to a registrational Phase 3 study (CORAL-3) and strong engagement with the FDA and CFF TDN significantly de-risk future development. This validation of the lung platform also has positive implications for Krystal's broader pipeline. The addressable market for modulator-ineligible or refractory CF patients is substantial ($2B+), indicating significant commercial potential. This news is fundamentally positive and suggests strong future growth and value creation for Krystal Biotech.

Keywords

Cystic Fibrosis, CFTR, Gene Therapy, KB407, Krystal Biotech, CORAL-1, CORAL-3, Clinical Trial, Phase 1, Lung Delivery, Genetic Medicine, Rare Disease, Modulator Ineligible, Biotechnology, NASDAQ: KRYS