Spatial proteomic analysis of a lung cancer model reveals regulatory T cells attenuate KRAS-G12C inhibitor-induced immune responses

We recently showed that lung tumor specific KRAS-G12C inhibition causes remodelling of the tumor immune microenvironment from cold to hot. As a result, KRAS-G12C inhibition is able to synergise with anti-PD-1 treatment, but only in tumor models that were already moderately responsive to immune checkpoint blockade at baseline. To investigate mechanisms that restrain immunotherapy sensitivity in non-responsive tumors, we used multiplex imaging mass cytometry to explore spatial patterns in the tumor microenvironment of the highly immune evasive KRAS mutant murine Lewis Lung Cancer model. Clustering of close neighbour information per cell allowed characterisation of spatial patterns or ‘communities’ in the tissue. We identified a community harbouring features of localised T-cell activation, where CD4 ⁺ and CD8 ⁺ T cells and dendritic cells were gathered together. KRAS-G12C inhibition led to increased expression of PD-1 on T cells, CXCL9 expression by dendritic cells, together with increased proliferation and potential cytotoxicity of CD8 ⁺ T cells, indicating an effector response. However, we also observed a high incidence of regulatory T cells (Tregs) within this community, which had frequent contact with effector T cells, suggesting that Tregs may be able to dampen anti-tumoral immune responses following KRAS-G12C inhibition. Similar communities were detected in human lung adenocarcinoma clinical samples. Depleting Tregs in vivo with anti-CTLA-4 antibody rescued the anti-tumor immune response and led to enhanced tumor control in combination with anti-PD-1 and KRAS-G12C inhibitor. We therefore propose use of KRAS-G12C inhibitor in combination with Treg depletion as a therapeutic opportunity that increases anti-tumoral immune responses and initiates tumor regression.