A novel combination of vidutolimod, an experimental TLR9-targeting agent, and nivolumab, a PD-1 checkpoint inhibitor, has shown promising results in treating stage III cutaneous melanoma. A recent phase II clinical trial published in Cancer Cell indicates that presurgical treatment with this combination led to tumor control in a significant proportion of patients, suggesting a potential new approach to improve outcomes in this high-risk population.
Study Design and Key Findings
The single-arm phase II trial involved 31 patients with high-risk, resectable stage III cutaneous melanoma. Patients received seven injections of vidutolimod directly into their tumors, along with three rounds of intravenous nivolumab before surgery. Post-surgery, the combined treatment continued every four weeks for a year.
The results showed that 55% of patients experienced tumor control, defined as having less than 10% viable tumor cells remaining after presurgical therapy. This level of response has been previously correlated with improved long-term survival. In the responding patients, the 2-year recurrence-free survival rate was 88%, and the metastasis-free survival rate reached 94%.
Immunological Insights
Researchers compared tumor and blood samples from high-responding patients with those who responded less favorably. They observed an enrichment of plasmacytoid dendritic cells and myeloid cells in the former group. These cells play critical roles in augmenting T cell-mediated tumor elimination and modulating immune responses, respectively. Notably, this enrichment was not typically seen with nivolumab monotherapy, indicating that vidutolimod uniquely stimulated antitumor immunity.
Mass spectrometry analysis revealed elevated levels of key immune-related proteins in most patients treated with the combination, suggesting that distinct signatures of TLR9 activation underlie the drugs' activity. Furthermore, analysis of the gut microbiome showed that patients with the greatest tumor shrinkage had higher levels of Gram-negative bacteria, a finding not typically associated with anti-PD-1 therapy response.
Expert Commentary
"This is the first and only clinical trial so far to test the novel combination of nivolumab and the experimental drug vidutolimod in the neoadjuvant setting. It’s exciting that we saw a response rate of 55%, which is on par with currently approved immunotherapy combinations," said lead study author Dr. Diwakar Davar, Associate Professor at the University of Pittsburgh School of Medicine and the UPMC Hillman Cancer Center.
Dr. Davar also emphasized the importance of identifying pharmacodynamic parameters for TLR9 agonists: "Prior to this work, we did not have a pharmacodynamic parameter for TLR9 agonists and other innate agonists, so identifying a protein signature associated with TLR9 administration was a key finding."
Senior study author Dr. Hassane Zarour, Professor at the University of Pittsburgh School of Medicine and the UPMC Hillman Cancer Center, commented on the microbiome findings: "Our data suggest that the mechanisms by which the gut microbiome modulates responses to cancer immunotherapy may differ depending on the specific therapy. Such novel findings highlight the complexity and context dependency of the gut microbiome’s effects in cancer immunotherapy and have prompted ongoing studies to confirm this observation."
Implications for Melanoma Treatment
The study suggests that the combination of vidutolimod and nivolumab could offer a valuable neoadjuvant treatment option for patients with stage III cutaneous melanoma. The observed response rates and survival outcomes warrant further investigation in larger, randomized trials. The identification of a potential pharmacodynamic marker for TLR9 activation could also aid in the development and monitoring of future TLR9-targeted therapies.
