The result led researchers to call for a future study comparing the regimen against a suitable control group.
“We were very excited to see the ability of intratumoral vidutolimod to augment T-cell infiltrate. (Pathologic) response was associated with a dense infiltrate of CD8 T cells. We were also able to demonstrate for what I think may be the first time, that intratumoral CpG resulted in clear evidence of CD303+ plasmacytoid dendritic cells [pDCs],” said Diwakar Davar, MD, assistant professor of medicine at the University of Pittsburgh, during a presentation of the results at the annual meeting of the Society for Immunotherapy of Cancer. He noted that pDCs represent a very rare cell population, less than 0.4% of circulating peripheral blood mononuclear cells, and tend to be found in lymph nodes.
The current standard of care for stage 3 melanoma is up-front surgery followed by adjuvant therapy – anti–PD-1 therapy for patients with wild-type or BRAF-mutant cancers, and targeted therapy with BRAF/MEK inhibitors in patients with BRAF mutations. However, preclinical studies suggest that neoadjuvant immunotherapy could lead to a stronger antitumor T-cell response than adjuvant immunotherapy.
Vidutolimod targets the toll-like receptor 9 (TLR-9) endosomal receptor found in B cells and pDC cells. The formulation is a virus-like particle (VLP) that contains unmethylated cytosine guanine–rich oligonucleotides (CpG ODN). Bacterial and viral genomes tend to be enriched in CpG ODN, and this acts as a TLR-9 agonist. TLR-9 activation in turn triggers an interferon response, and this may help overcome PD-1 blockade resistance in metastatic melanoma.
The researchers conducted a nonrandomized, open-label trial that included 30 patients with stage 3 melanoma (14 women; median age, 61 years). Patients received neoadjuvant nivolumab and vidutolimod for 8 weeks, then were evaluated for surgery. Patients continued both drugs in the adjuvant setting for 48 weeks. 47% experienced complete pathologic response, 10% a major pathologic response, and 10% a partial pathologic response.
Analysis of resected samples revealed clear evidence of an immune response, Dr. Davar said during a press conference held in advance of the meeting. “Pathologic response was associated with compelling evidence of immune activation both peripherally and within the tumor, with clear evidence of pDC infiltrate and pDC activation – something that has not previously been seen in human specimens.”
The study regimen appeared safe, with no dose-limiting toxicities or grade 4 or 5 adverse events. He noted that the regimen is now being tested in the phase 2 ECOG-ACRIN trial.
The results are “very exciting,” said Pamela Ohashi, PhD, who commented on the study during the press conference. The virus-like nature of vidutolimod may be an important element of the therapy. “I think scientifically we would have predicted that the VLP carrying the CPG would be very good at activating the CD8 cells, which in fact is what you’re seeing. So I think it’s very exciting and has lots of potential for future combinations,” said Dr. Ohashi, who is director of the tumor immunotherapy program at the Princess Margaret Cancer Centre, Toronto.
The study was funded by Checkmate Pharmaceuticals. Dr. Davar has financial relationships with Checkmate Pharmaceuticals and Regeneron, which has acquired Checkmate Pharmaceuticals.