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

A significant obstacle in the development of cancer vaccines lies in the need to generate immune responses that are strong enough to effectively control the growth and spread of cancerous tumors. In this research, we employed a systematic and repeated screening process in mice, evaluating a set of 22 lipid-based vaccine adjuvants for their ability to stimulate the production of neoantigen-specific CD8⁺ T cell responses. This screening utilized an integrated approach involving peptide-lipid nanoparticles.

Our initial screening identified CL401, an adjuvant that activates both Toll-like receptor 2 and Toll-like receptor 7, abbreviated as TLR2/7. CL401 was found to rapidly induce T cell responses specific to neoantigens and also improved the drainage of the vaccine particles to the lymphatic system and their uptake by immune cells. Subsequent rounds of screening in living mice identified additional adjuvants that targeted other immune pathways: 3D6A-PHAD, which targets TLR4; motolimod, which targets TLR8; and QS-21, which activates the inflammasome.

These adjuvants were found to work together to enhance the secretion of signaling molecules called cytokines in antigen-presenting cells and in the neoantigen-specific CD8⁺ T cells elicited by the vaccine. The simultaneous delivery of these adjuvants along with the tumor-specific antigens resulted in effective immune responses. These responses led to the regression of large, established tumors, showed a synergistic effect when combined with immune checkpoint blockade therapy, and inhibited the formation of lung nodules in a model of experimental metastasis.

Importantly, these effects were achieved without any noticeable signs of toxicity or adverse reactions. Based on these findings, we conclude that a systematic and iterative screening of adjuvants performed in living mice can successfully identify beneficial combinations of adjuvants. These combinations hold significant promise for advancing the field of therapeutic cancer vaccine research.