Inhaled Gene Therapy for Lung Cancer: KB707 and the Next Frontier of Localized Immunotherapy
Gene therapy has traditionally been delivered intravenously or injected directly into tumors. A new investigational approach, however, is challenging that paradigm by delivering genetic therapies directly into the lungs through inhalation.
KB707, an inhaled gene therapy currently in clinical development for advanced lung cancer, represents one of the most unconventional immunotherapy strategies now entering human trials. Instead of administering immune-stimulating drugs systemically, the therapy aims to turn lung cells themselves into localized producers of potent immune cytokines.
If successful, the strategy could redefine how immunotherapies are delivered to lung tumors and establish a new class of localized immunogene therapies.
A New Strategy: Turning Lung Cells into Cytokine Factories
KB707 is designed to deliver two powerful immune-activating cytokines—interleukin-2 (IL-2) and interleukin-12 (IL-12)—directly into the lung tumor microenvironment. The therapy uses a modified herpes simplex virus type-1 (HSV-1) vector engineered to carry genes encoding these cytokines (Krystal Biotech, 2025a).
Importantly, the vector used in the inhaled therapy program is replication-defective and non-integrating, meaning it cannot replicate within the body or integrate into host DNA. Instead, it functions as a gene delivery vehicle that enables temporary cytokine expression in transduced cells.
The biological rationale for this approach is rooted in decades of cytokine immunotherapy research.
IL-2 and IL-12 are well known for their ability to stimulate strong anti-tumor immune responses. IL-2 promotes the expansion and activation of cytotoxic T cells and natural killer cells, while IL-12 enhances Th1-type immune responses and induces interferon-gamma production (Nguyen et al., 2020).
However, systemic administration of these cytokines has historically been limited by severe toxicity.
High-dose IL-2 therapy, once used for melanoma and renal cell carcinoma, can cause life-threatening complications such as capillary leak syndrome and requires intensive inpatient monitoring (Dutcher et al., 2014). Similarly, early clinical trials of systemic IL-12 demonstrated potent immune activation but also severe inflammatory toxicity and treatment-related deaths (Atkins et al., 1997; Leonard et al., 1997).
The KB707 strategy attempts to solve this problem by localizing cytokine expression within lung tumors, thereby maximizing anti-tumor immune activation while minimizing systemic exposure.
Why Deliver Gene Therapy Through Inhalation?
Unlike conventional gene therapies, KB707 is administered through nebulized inhalation, allowing viral vectors to be deposited directly within the lungs (National Cancer Institute, n.d.).
This approach offers several theoretical advantages:
• Direct delivery to lung tumors
• Higher local drug concentrations within the tumor microenvironment
• Reduced systemic toxicity
• Repeat dosing potential
• Outpatient administration
The lungs represent a unique therapeutic target because they are accessible through the airway system. Aerosol delivery allows therapeutic particles to reach distal lung tissue when particle sizes fall within the 1–5 µm respirable range (Pleasants & Hess, 2018).
However, inhaled gene therapy also presents significant biological and engineering challenges. Mucus barriers and mucociliary clearance can remove particles before they reach target cells, limiting gene transfer efficiency (Duncan et al., 2016).
Additionally, aerosolization itself can damage biological vectors. Shear stress during nebulization may reduce viral infectivity or degrade nucleic acid payloads, meaning device selection and formulation design become critical determinants of therapeutic performance (Ruzycki et al., 2023).
Early Clinical Signals from the KYANITE-1 Trial
KB707 is currently being evaluated in the KYANITE-1 clinical trial, a Phase 1/2 open-label study investigating inhaled KB707 as both a monotherapy and in combination with other treatments in patients with advanced cancers affecting the lungs (National Cancer Institute, n.d.).
The trial includes dose-escalation and expansion cohorts exploring doses of 10⁸ and 10⁹ plaque-forming units (PFU) administered weekly for three weeks followed by dosing every three weeks.
Early clinical data from heavily pre-treated non-small cell lung cancer (NSCLC) patients has shown encouraging activity.
In an early efficacy-evaluable subset:
-
Objective response rate (ORR): 27 %
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Disease control rate (DCR): 73 %
When analyzing lung lesions specifically, the response rate appeared higher, with an ORR of 36 %, including a complete response in at least one patient (Krystal Biotech, 2024).
These findings were observed in patients who had already received multiple prior lines of therapy, including immune checkpoint inhibitors.
Although the dataset remains small and early-stage, the results suggest that localized cytokine expression may meaningfully stimulate immune responses within lung tumors.
Combination Therapy Strategy
While early trials are evaluating KB707 as a monotherapy, the broader development strategy focuses on combining the therapy with existing cancer treatments.
Two key combinations are currently being explored:
Checkpoint inhibitors
KB707 is being studied alongside pembrolizumab to determine whether localized cytokine expression can enhance immune checkpoint responses and overcome resistance to PD-1 blockade.
Chemotherapy
Combination regimens with docetaxel are also under investigation, potentially positioning KB707 as an immune-activating therapy used alongside standard second-line treatments (Krystal Biotech, 2025b).
If successful, inhaled cytokine gene delivery could function as an immune-priming platform that enhances the effectiveness of established therapies.
Safety and Tolerability
Early safety data from the KYANITE-1 trial suggests that inhaled KB707 has been generally well tolerated.
Reported treatment-related adverse events have included:
• chills
• cytokine release syndrome
• fatigue
• influenza-like illness
• dyspnea
• fever
Most events were Grade 1 or Grade 2, and no Grade 4 or Grade 5 treatment-related adverse events were reported in the monotherapy population at the time of analysis (Krystal Biotech, 2025b).
These findings are consistent with the hypothesis that localized cytokine production may reduce the systemic toxicity historically associated with IL-2 and IL-12 therapy.
However, larger datasets and combination therapy cohorts will be necessary to fully characterize long-term safety.
Regulatory Momentum
KB707 has also gained regulatory attention.
The therapy received FDA Fast Track designation in 2024 for the treatment of solid tumors affecting the lungs that are refractory to standard therapies (Krystal Biotech, 2024).
In February 2026, the U.S. Food and Drug Administration granted the therapy Regenerative Medicine Advanced Therapy (RMAT) designation for advanced or metastatic non-small cell lung cancer (Krystal Biotech, 2026).
RMAT designation is intended to accelerate the development of regenerative medicine therapies that show early evidence of addressing serious unmet medical needs (FDA, 2025a).
The designation allows increased interaction with regulators and potential eligibility for expedited approval pathways.
Technical Challenges Ahead
Despite promising early results, several key scientific and operational challenges remain.
Aerosol delivery consistencyEnsuring consistent viral delivery across patients is technically complex. Differences in lung anatomy, airway obstruction, and breathing patterns may influence deposition efficiency.
Anti-vector immunityBecause HSV-1 is a common human virus, many patients already have antibodies against it. Pre-existing immunity could theoretically reduce gene transfer efficiency with repeated dosing.
Systemic disease controlBecause the therapy is delivered locally to the lungs, it remains unclear whether it can meaningfully control metastatic disease outside the lungs.
Biosafety and viral sheddingRegulatory agencies require careful monitoring of viral shedding and potential transmission risks when viral gene therapies are used (FDA, 2019).
These factors introduce additional operational requirements for clinical trial sites.
The Long Road to Inhaled Gene Therapy
Although KB707 has been described as the first inhaled gene therapy for cancer to gain major regulatory momentum, the concept itself has existed for decades.
Earlier studies explored aerosol gene therapy approaches for lung diseases and cancer, including aerosolized p53 gene delivery. However, many of these programs struggled due to inefficient gene transfer and biological barriers within the lung (Zarogouldis et al., 2012).
Advances in viral vector engineering, aerosol delivery technologies, and immunotherapy biology may now allow these early ideas to be revisited with greater success.
The Future of Localized Immunotherapy
If inhaled gene therapy proves effective, it could represent an entirely new category of cancer treatment.
Rather than administering drugs systemically, therapies like KB707 attempt to engineer localized immune activation directly within the tumor microenvironment.
For lung cancer—still the leading cause of cancer death worldwide—such an approach could provide new treatment options for patients whose disease has progressed after standard therapies.
The coming years of clinical trials will determine whether inhaled gene therapy can translate early promise into durable clinical benefit.
References
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