Comparing Neoantigen Cancer Vaccines and Immune Checkpoint Therapy Unveils an Effective Vaccine and Anti-TREM2 Macrophage-Targeting Dual Therapy [CD45]

The goal of therapeutic cancer vaccines and immune checkpoint therapy (ICT) is to eliminate cancer by expanding and/or sustaining T cells with anti-tumor capabilities. Here, we compared effective therapeutic tumor-specific mutant neoantigen (NeoAg) synthetic long peptide (SLP) cancer vaccines with anti-CTLA-4 and/or anti-PD-1 ICT in preclinical models. Effective NeoAg SLP vaccines and ICT required both CD8 and CD4 T cells. Both NeoAg SLP vaccines and ICT induce expansion of intratumoral NeoAg-specific CD8 T cells, though the degree of expansion and acquisition of effector activity was much more substantial following NeoAg SLP vaccination. Further, we found that NeoAg SLP vaccines are particularly adept at inducing proliferating and stem-like NeoAg-specific CD8 T cells. While NeoAg SLP vaccines and anti-PD-1 affected the CD4 T cell compartment, it was to less of an extent than observed with anti-CTLA-4, which notably induced ICOS+Bhlhe40+ Th1-like CD4 T cells. Although effective NeoAg SLP vaccines or ICT expanded intratumoral M1-like iNOS+ macrophages, NeoAg SLP vaccines maintained, rather than suppressed as observed with ICT, M2-like CX3CR1+CD206+ macrophages expressing the TREM2 receptor. While combining NeoAg SLP vaccination with ICT induced superior efficacy compared to either therapy in isolation, we also assessed a novel combination of NeoAg SLP vaccination and anti-TREM2, demonstrating enhanced efficacy of this combination associated with a decrease in intratumoral CX3CR1+CD206+ macrophages and promotion of IFN-g+ NeoAgspecific CD8 T cells. These findings highlight the utility of combining NeoAg SLP vaccines with ICT, as well as novel combinatorial therapy targeting the myeloid compartment via TREM2 blockade to enhance NeoAg SLP vaccine efficacy. Overall design: Droplet-based 5' end massively parallel single-cell RNA sequencing was performed by encapsulating sorted live intratumoral CD45+ cells into droplets and preparing libraries using Chromium Single Cell 5' Reagent Kits following the manufacturer's protocol (10x Genomics). The generated scRNAseq libraries were sequenced using a NovaSeq 6000 Sequencing System (Illumina).