e21534 Background: mRNA vaccines have been shown to stimulate T-cells targeting patient-specific tumor neoantigens. When combined with immune checkpoint inhibitors (ICI) in a randomized Phase II trial, mRNA vaccines demonstrated improvement in recurrence free survival and distant metastasis free survival compared to ICI alone. We retrospectively examined patients (pts) with advanced melanoma treated more than 5 years ago on clinical trials with adjuvant NYESO1 or mRNA vaccine therapies (VT) then ICI upon recurrence and analyzed biomarkers correlating with treatment response. Methods: This retrospective study examined 22 pts with advanced melanoma treated between 2004-2017 with adjuvant vaccine therapies (VT). 10 of the 22 pts subsequently developed recurrent disease and were treated with ICI. We evaluated disease free interval following ICI, sex, age, BRAF status, HLA type, site of primary and metastatic disease, initial vaccine treatment, vaccine toxicities, stage and sites of melanoma recurrence, ICI treatment, response and toxicities, vaccine site flares or cutaneous immune related adverse events (irAEs) following ICI. Results: Of the 22 patients (11 male, 11 female) treated with adjuvant VT, median age at first vaccine was 53 years old. HLA type was known for 11 pts. Stage at initial VT was IIB to IIIC. 14 pts recurred following adjuvant VT. Median time from vaccine initiation to melanoma recurrence was 3.2 years (range 6.5 months to 11 years). 10 pts received ICI for recurrent melanoma, 3 pts received ipilimumab, 2 anti-PD1 monotherapy, 4 ipilimumab and nivolumab, and 1 nivolumab/relatlimab. Stage at first ICI was IIIB to IV M1d. 9 pts experienced cutaneous irAEs. 7 pts experienced local vaccine site flare reactions following ICI treatment. Additionally, 2 pts experienced vitiligo, 2 with dermatologic flares (bullous pemphigoid and psoriatic rash), 2 with generalized rash that resolved with steroid cream. 1 pt did not experience rash, vaccine site flare, nor irAE dermatologic flare. Of the pts who recurred, 2 pts had BRAF V600E mutations, and 1 of these pts experienced vaccine flare, the other did not. 1 pt with a BRAF Q16L mutation did not have vaccine flare. 6 out of 7 BRAF wild type pts who recurred and received ICI experienced a localized vaccine site flare. Median disease-free interval following ICI treatment was 1.5 years (range 3 months to 9 years). All 10 pts are disease-free and off ICI being closely monitored. Conclusions: Evidence of prior localized vaccination “flare” may be a biomarker for a complete immunologic response in pts with metastatic disease treated with immunotherapy. ICI targeting CTLA-4 and/or PD-1 both triggered this localized vaccination site response, suggesting that T cell memory and immunologic activation against melanoma antigens translate into clinical responses.
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