Type I-polarized BRAF-pulsed dendritic cells induce antigen-specific CD8+ T cells that impact BRAF-mutant murine melanoma

Existing therapies targeting the mutated BRAF oncodriver (BRAF(V600E)) successfully treat melanoma but are susceptible to resistance. This study assessed the potential of a dendritic cell-based BRAF(V600E) vaccine for the treatment of BRAF(V600E)-mutant melanoma. Type 1-polarized dendritic cells (DC1) pulsed with affinity-modified BRAF(V600E) peptide were administered to C57Bl/6 mice both before (prevention) and twice weekly after (treatment) the development of established tumor with B16 melanoma transfected to express BRAF(V600E) (B16(V600E)). The efficacy of the BRAF(V600E)-pulsed DC1 vaccine was corroborated in a novel transplantable BRAF(V600E)-mutant murine melanoma model (BRAF(V600E/+); PTEN-/-; CDK2NA(-/-)). Three-dimensional tumor measurements and survival were determined. Induction of BRAF(V600E)-specific CD8(+) T-cell responses after brief in-vitro sensitization was assessed by interferon-gamma enzyme-linked immunosorbent assay and/or enzyme-linked immunospot. Mice receiving BRAF(V600E)-pulsed DC1 vaccines before B16(V600E) tumor challenge demonstrated increased tumor-doubling times (P < 0.001) and improved survival (P=0.0186) compared with those that received ovalbumin (control)-pulsed DC1 vaccines. In mice bearing established B16(V600E) tumors (mean 32 mm(3)), BRAF-pulsed DC1 vaccines delayed tumor growth (P < 0.001) and improved survival (P=0.0008), compared with untreated mice. Likewise, in mice bearing BRAF(V600E/+); PTEN-/-; CDK2NA(-/-) tumors, compared with controls, BRAF-DC1 vaccination recapitulated these effects by delaying tumor growth (P < 0.001) and improving survival (P=0.002). Vaccination elicited specific CD8(+) T-cell recognition of BRAF(V600E)-pulsed antigen-presenting cells (P < 0.05), as well as BRAF(V600E)-expressing cancer cells (P < 0.001), measured by interferon-gamma release in vitro. BRAF(V600E)-pulsed DC1 vaccines induce oncogene-specific CD8(+) T-cell immune responses that impact tumor growth and survival in preclinical models of BRAF(V600E)-mutant melanoma. Exploration of BRAF(V600E)-targeted vaccines, in combination with BRAF-targeted therapies and checkpoint inhibitors, is warranted.