A National Cancer Institute-sponsored phase 2 clinical trial evaluating inhaled recombinant human IL-15 as an adjuvant immunotherapy for canine osteosarcoma has been terminated early due to unexpectedly poor outcomes, raising important questions about combining immunotherapy with conventional cancer treatments.
The multicenter Comparative Oncology Trials Consortium (COTC) study, designated NCI-COTC030, was designed to test whether two weeks of inhaled IL-15 therapy following amputation and prior to chemotherapy could improve outcomes in dogs with localized limb osteosarcoma. Researchers hypothesized the treatment would reduce metastatic failure rates from a historical baseline of 40% to 20%.
Trial Design and Unexpected Results
The study planned to enroll 40 dogs with 80% statistical power using a two-sided alpha of 0.05. However, the trial was halted for futility when interim analyses revealed that both disease-free survival and overall survival were statistically inferior in the intent-to-treat population compared to well-validated historical control cohorts.
This outcome was particularly surprising given previous research showing that inhaled IL-15 was associated with anti-tumor responses in dogs with metastatic osteosarcoma and melanoma. The current study represented the first attempt to evaluate this immunotherapy approach in the adjuvant setting for localized disease eligible for curative treatment.
Immune System Impact Analysis
Comprehensive immune correlative assays provided insights into the unexpected results. Cytotoxicity assays of peripheral blood mononuclear cells (PBMCs) showed significant decreases after both surgery and chemotherapy, with an overall decrease from the start to end of therapy of -18.2±16.1% (P<0.001).
Notably, some dogs demonstrated positive fold changes in PBMC cytotoxicity, which correlated significantly with improved survival outcomes (P=0.004, r=0.62). This finding suggests that maintaining or enhancing immune function during treatment may be crucial for therapeutic success.
Inflammatory Response Patterns
Analysis of plasma cytokine concentrations revealed marked variability with no significant differences between disease-free and metastatic-failure patients. However, inflammatory cytokines such as IL-6 showed absolute increases following both amputation and chemotherapy, and these increases correlated with decreases in cytotoxicity.
This pattern suggests that the inflammatory response triggered by surgery and chemotherapy may counteract the intended immunostimulatory effects of IL-15 therapy, potentially explaining the disappointing clinical outcomes.
Molecular and Cellular Insights
Tumor sequencing data from the study reproduced immune signatures previously observed in both human and canine osteosarcoma cohorts, validating the translational relevance of the canine model. Single-cell sequencing of PBMCs revealed that gene expression profiles of natural killer (NK) cells and T cells were significantly different between subjects with short versus long disease-free intervals.
These molecular findings provide mechanistic insights into the immune dysfunction observed in the study and may inform future immunotherapy development strategies.
Clinical Implications
The study's findings have significant implications for the development of immunotherapy strategies that combine with conventional treatments like surgery and chemotherapy. The results suggest that the timing and sequencing of immunotherapy relative to other cancer treatments may be critical for success.
The research team concluded that inhaled recombinant human IL-15 combined with amputation and chemotherapy is associated with worse outcomes in dogs with osteosarcoma, and that correlative assays suggest significant immunological effects of amputation and chemotherapy on immune responses that may interfere with immunotherapy efficacy.
