Iterative selection of lipid nanoparticle vaccine adjuvants for rapid elicitation of tumoricidal CD8⁺ T cells

A challenge for cancer vaccines is to elicit immune responses of sufficient magnitude to control malignant tumor growth and spread. In this study, we iteratively screened a panel of 22 lipid-phase vaccine adjuvants in mice for the elicitation of neoantigen-specific CD8⁺ T cell responses, using an integrated peptide-lipid nanoparticle approach. CL401, a dual Toll-like receptor 2/7 (TLR2/7) adjuvant rapidly induced neoantigen-specific T cell responses and improved lymphatic drainage and uptake of the particle. Additional rounds of <i>in vivo</i> screening identified complementary adjuvants which targeted TLR4 (3D6A-PHAD adjuvant), TLR8 (motolimod), and inflammasome (QS-21) pathways and synergized to enhance cytokine secretion in antigen presenting cells and vaccine-elicited neoantigen-specific CD8⁺ T cells. Co-delivery of adjuvants and antigens led to effective immune responses which regressed large established tumors, synergized with immune checkpoint blockade, and inhibited lung nodules in an experimental metastasis model, without overt toxicity or reactogenicity. We conclude that iterative adjuvant screening, performed in mice <i>in vivo</i>, can identify useful adjuvant combinations that hold potential for therapeutic cancer vaccine research.