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 affinitymodified 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-. 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 32mm3), 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-. 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.