‘Exciting’ Results for Cancer Vaccine Plus Pembro in Melanoma

ORLANDO, Florida — The combination of a patient-specific mRNA-based cancer vaccine (mRNA-4157/V940, Moderna) and the immune checkpoint inhibitor pembrolizumab significantly improved recurrence-free survival for patients with high-risk melanoma compared with pembrolizumab alone, according to the latest data from the KEYNOTE-942 trial.

This recurrence-free survival benefit corresponded to a 44% reduced risk of recurrence or death in patients who received the personalized vaccine plus pembrolizumab compared with the immunotherapy alone.

The randomized phase 2b trial is the first to show a positive result for a cancer vaccine in a randomized trial. The results, if confirmed in further studies, hold promise for treating other solid tumors with sensitivity to the programmed death-1 (PD-1) protein, investigators said.

“KEYNOTE-942 is the first randomized study to demonstrate improvement in recurrence-free survival in melanoma, or in any cancer in my view, with an individualized neoantigen vaccine approach,” trial investigator Jeffrey S. Weber, MD, PhD, from the NYU Langone Perlmutter Cancer Center in New York City said during an oral abstract session at the annual meeting of the American Association for Cancer Research.

“I have every confidence that this strategy will be expanded to other histologies that are PD-1 sensitive, such as non-small cell lung cancer, renal cell cancer, hepatocellular cancer, gastroesophageal cancer, et cetera,” Weber said.

Invited discussant Margaret Callahan, MD, PhD, from Memorial Sloan Kettering Cancer Center in New York City, called the results “exciting,” especially in light of previous results in cancer vaccine trials. “Despite hundreds of formulations and dozens of studies, cancer vaccines have been disappointing so far, and have largely failed to have a meaningful impact in oncology,” she said.

A Promising Personalized Vaccine

The mRNA vaccine is individually tailored and encodes up to 34 patient-specific tumor neoantigens. The vaccine also acts as an adjuvant to strengthen the immune response.

“mRNA 4157 is what one would call an individualized neoantigen therapy. It will target an individual patient’s unique tumor mutations, and the revelation over the last 5 to 10 years, is that, for better or worse, virtually all the neoantigens are unique to an individual patient,” Weber said. “There are very, very few true universal neoantigens, or at least universal neoantigens that could have clinical utility.”

The vaccines are developed from tumor biopsy tissues that then undergo whole exome and RNA sequencing to identify single nucleotide variants that are present in the tumor but not in normal tissue.

The findings are then fed into a computer algorithm that identifies potential neoepitope peptides that would bind well to the patient’s human leukocyte antigen (HLA) type and could evoke strong T-cell responses.

“Once they’re chosen, you concatenate the sequences together into a single-strand mRNA vaccine, it’s packaged with nanoparticles to encapsulate it, and there you have your mRNA vaccine,” Weber explained.

In the KEYNOTE-942 trial, the investigators randomly assigned patients with completely resected high-risk cutaneous melanoma on a 2:1 basis to receive mRNA-4157 via intramuscular injection every 3 weeks for a total of nine doses, plus intravenous pembrolizumab every 3 weeks for 18 cycles (107 patients) or pembrolizumab alone (50 patients). Median follow-up was 101 weeks in the combination group and 105 weeks in the pembrolizumab group.

Overall, the 18-month recurrence-free survival rates were 78.6% in the combination arm and 62.2% in the pembrolizumab arm. The recurrence-free survival rates corresponded to a 44% reduced risk of recurrence or death in patients who received the personalized vaccine plus pembrolizumab compared with those who only received pembrolizumab (hazard ratio [HR] for recurrence, 0.561; P =.0266).

Grade 3 or greater adverse events occurred in 25% of patients in the combination group and 18% of patients in the pembrolizumab group. The most common grade 3 event associated with the vaccine was fatigue. No grade 4 adverse events or deaths were associated with the vaccine, and the addition of the vaccine to pembrolizumab did not appear to increase risk for immune-mediated adverse events.

In a subanalysis, Weber and colleagues explored the relationship between tumor mutational burden and recurrence-free survival. Higher tumor mutational burden may mean more neoepitopes to target, which is helpful when developing personalized neoantigen vaccines, explained co-investigator Ryan Sullivan, MD, associate director of the melanoma program at Mass General Cancer Center, Boston, who presented the subanalysis results.

The investigators performed whole exome and whole transcriptome sequencing of baseline tumor biopsy samples to determine the mutational burden of tumors and defined a high mutational burden as 10 or more mutations per megabase.

Overall, in the combination group, patients with a higher tumor mutational burden at baseline showed improved outcomes (HR, 0.642; 95% CI, 0.284 – 1.494), as did patients with a lower tumor mutational burden (HR, 0.586; 95% CI, 0.243 – 1.415).

The authors found the same was true for patients with high vs low tumor inflammation scores (high: HR, 0.576; 95% CI, 0.209 – 1.591 vs low: HR, 0.528; 95% CI, 0.253 – 1.101) and higher PD-L1 expression (PD-L1 positive: HR, 0.485; 95% CI, 0.226 – 1.039 vs PD-L1 negative: HR, 0.162; 95% CI, 0.038 – 0.685).

The hazard ratios crossed 1, which suggest that the combination was similarly effective in all patient subsets, said Sullivan.

Callahan also highlighted that the P value was based on a one-side log-rank test, “a relatively low bar to jump over” and that there were slight imbalances in both PD-1 expression status and tumor mutational burden — both of which favored the vaccine group and may be associated with better recurrence-free survival.

The 16% difference in recurrence-free survival seen with the combination vs pembrolizumab alone, if confirmed in further studies, “is clinically meaningful for high-risk patients,” said Callahan. “The authors are to be congratulated for presenting the first randomized study of a neoantigen vaccine with a clinical efficacy primary endpoint, and this is a trial that incorporates many of the lessons we’ve learned along the years.”

Sullivan also commented on the promising results. “The field of cancer vaccines is a wasteland of failed clinical trials after some initial promising data, so to have something like this where it does appear that this vaccine strategy works is good not only for patients with melanoma but for those people who have dedicated their lives to trying to develop cancer vaccines,” he said in an interview with Medscape Medical News.

KEYNOTE-942 was funded by Moderna with collaboration from Merck. Weber has financial relationships with Merck, Moderna, and other companies. Sullivan has served as a paid consult for Merck and has received research funding from the company. Callahan disclosed a consulting/advisory role with Moderna, Merck, and others.

American Association for Cancer Research (AACR) Annual Meeting 2023: Abstract CT001. Presented April 16, 2023.

Neil Osterweil, an award-winning medical journalist, is a long-standing and frequent contributor to Medscape.

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