Two Injection Sites Outperformed Single-Site Delivery for Melanoma Peptide Vaccine

Clinical Summary: 

• Design/Population: This multicenter, randomized phase 2 trial evaluated a vaccine composed of 12 class I major histocompatibility complex–restricted melanoma peptides, administered with or without granulocyte–macrophage colony-stimulating factor (GM-CSF) and at either 1 or 2 injection sites, in patients with resected high-risk melanoma.
• Key Outcomes: Vaccination at 2 sites was associated with significantly improved recurrence-free survival compared with vaccination at 1 site. No significant differences in recurrence-free survival or overall survival were observed with the addition of GM-CSF.
• Clinical Relevance: The long-term findings challenge the use of GM-CSF as a local adjuvant for melanoma peptide vaccination and suggest that administering a vaccine at multiple sites may improve clinical outcomes by engaging a broader locoregional immune response.

Results from a phase 2 study demonstrated that administering a 12-peptide melanoma vaccine at 2 injection sites significantly improved recurrence-free survival (RFS) compared with vaccination at a single site among patients with resected high-risk melanoma. 

In this multicenter study, 121 patients were randomized to receive a vaccine composed of 12 class I major histocompatibility complex–restricted melanoma peptides at 1 injection site with or without granulocyte–macrophage colony-stimulating factor (GM-CSF), the vaccine alone at 2 sites, or the vaccine with GM-CSF at 2 sites.

The study was originally powered to compare immunogenicity according to GM-CSF use and the number of vaccine injection sites. For the long-term analysis, investigators evaluated RFS and overall survival (OS) according to these predefined vaccine groups. 

After a median follow-up of 5.6 years, no significant differences in RFS or OS were observed between patients who received GM-CSF and those who received the peptide vaccine without the adjuvant. However, patients vaccinated at 2 sites experienced a significant improvement in RFS compared with those vaccinated at 1 site. Two-site vaccination was associated with a 41% reduction in the risk of recurrence or death (hazard ratio [HR], 0.59; 95% confidence interval [CI], 0.38 to 0.93; P = .02).

Two-site vaccination was also associated with a numerical improvement in OS, although the difference did not reach statistical significance. The risk of death was reduced by 36% among patients vaccinated at 2 sites compared with 1 site (HR, 0.64; 95% CI, 0.39 to 1.06; P = .08).

In a landmark multivariable analysis adjusting for CD8-positive T-cell response and other prognostic factors, vaccination at 2 sites remained the only significant predictor of RFS. Two-site vaccination was associated with a 45% reduction in the risk of recurrence or death (HR, 0.55; 95% CI, 0.34 to 0.88; P = .01). 

As study authors concluded, “future work to characterize the locoregional immune response to cancer vaccination at the injection site and vaccine-draining lymph nodes is warranted.” 

Source: 

Ninmer EK, Zhu H, Sarkar A, et al. Impact of GM-CSF and two-site vaccination on clinical outcomes after multipeptide vaccination for melanoma: Long-term analysis of a randomized phase II trial. Clin Cancer Res. Published online: June 15, 2026. doi: 10.1158/1078-0432.CCR-25-4606