Abstract 4100: AMP-peptide vaccination against mutant BRAF epitopes promotes lymph node delivery to generate potent, functional T cell immunity

Abstract

Abstract Background Mutations in BRAF cause ~8% of human cancers[1]. Nonetheless, therapies designed to promote immune responses against mutated BRAF (mBRAF) have led to limited clinical success[2], despite evidence confirming T cell recognition of these mutations[3,4]. The Amphiphile (AMP) platform improves the potency of vaccine immunotherapy by programming the delivery of vaccine components to the lymph nodes where efficient uptake by resident immune cells initiates tumor-targeted immune responses. AMP-modification of vaccine components including peptide antigens and molecular adjuvants results in covalent conjugation to albumin-binding lipids. Upon injection, AMP-vaccines associate with tissue resident albumin which efficiently distributes to draining lymph nodes. This approach was shown to promote activation of polyfunctional, cytotoxic T cells with promising safety, and improved clinical outcomes in a Phase 1 trial of ELI-002, an mKRAS AMP therapeutic vaccine (AMPLIFY-201 NCT04853017). Application of this strategy to prevalent BRAF mutations with ELI-007 offers the potential for improved therapeutic activity in a setting of significant unmet need, as BRAF inhibitors benefit only a fraction of patients, with near universal progression. Methods Following multi-dose immunization of C57BL/6J mice with AMP-modified or soluble comparator vaccines consisting of mBRAF V600E/K peptides and CpG adjuvant, immunological readouts were performed 7 days after dosing. Antigen-specific T cell responses were assessed after ex vivo re-stimulation of cells with mBRAF overlapping peptides. Assays included analysis of antigen-specific T cell frequencies, multiplexed proteomics determining polyfunctionality, and effector function and cytotoxic potential evaluation. Responses were determined in secondary lymphoid tissues (spleen), as well as lung, to which many BRAF driven cancers metastasize. Results AMP-immunization generated robust in vivo immune responses yielding strong T cell activation against mBRAF epitopes. Non-lymph node targeted vaccination using soluble comparators were inactive with no response above mock treated mice. Responses to AMP-vaccination were characterized by the generation of significantly increased frequency of Th1-skewed, polyfunctional T cells (IFNγ, TNFα, IL2) specific to mBRAF V600E and V600K. Induced T cells further exhibited mBRAF-specific cytotoxic function. Conclusions AMP-conjugation enhances efficient delivery directly to the lymph nodes and thus improves the immunogenicity of peptide vaccination. These enhanced immune responses provide an encouraging therapeutic opportunity to treat >90% of BRAF-mutated cancers[5] with the AMP-mBRAF vaccine, ELI-007. Moreover, the AMP-platform technology is simple, rapidly executable, and scalable, promising broad clinical off-the-shelf application for BRAF. Citation Format: Martin P. Steinbuck, Xavier Cabana-Puig, Erica Palmer, Mimi M. Jung, Thomas Williams, Kristen Osaer, Jeff Zhang, Christopher M. Haqq, Peter C. DeMuth. AMP-peptide vaccination against mutant BRAF epitopes promotes lymph node delivery to generate potent, functional T cell immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4100.