Understanding Colon Inflammation from Cancer Immunotherapy Through Molecular Pathways
Summary
Checkpoint blockade with antibodies specific for the PD-1 and CTLA-4 inhibitory receptors can induce durable responses in a wide range of human cancers. However, the immunological mechanisms responsible for severe inflammatory side effects remain poorly understood. They report a comprehensive single-cell analysis of immune cell populations in colitis, a common and severe side effect of checkpoint blockade. They observed a striking accumulation of CD8 T cells with highly cytotoxic and proliferative states and no evidence of regulatory T cell depletion. T cell receptor (TCR) sequence analysis demonstrated that a substantial fraction of colitis-associated CD8 T cells originated from tissue-resident populations, explaining the frequently early onset of colitis symptoms following treatment initiation. Their analysis also identified cytokines, chemokines, and surface receptors that could serve as therapeutic targets for colitis and potentially other inflammatory side effects of checkpoint blockade.
Fig.1 Graphical abstract. (Luoma, 2020)
Research Criteria
They identified possible mechanisms by which tumor immunotherapy triggers side effects of the enteritis response by comparing single cell sequencing data from normal subjects and melanoma patients immunized with CTLA-4 and PD-1 inhibitors. This was accomplished by comparing data from normal subjects with data from melanoma patients.
Sample Type
Normal control population (Control), colonic mucosa of patients with melanoma and immunotherapy without triggering intestinal inflammatory response (+CPI no colitis), and patients with an induced intestinal inflammatory response (+CPI colitis), CD45+ monocytes and CD3+ T cells enriched by flow cytometric sorting.
Fig.2 Experimental design. (Luoma, 2020)
Result—Cell Type Comparison Statistics Based on scRNA-Seq Data
In this study, a total of 51,652 immune cells were obtained by sorting CD45+ cells. By analyzing CD45+ immune cells in all samples, it was discovered that the Control and +CPI no colitis groups had very similar transcriptome profiles, whereas the +CPI colitis group had a significant T cell and myeloid cell (Myeloid cell) enrichment. This finding suggests a strong correlation between changes in the composition of specific immune cells.
Fig.3 Cell type comparison statistics. (Luoma, 2020)
Result—T Cell Differentiation Origin Analysis Based on scTCR-Seq Data
TCR-based data analysis revealed that 94.2% of expanded TCRs in cluster 8 (cycling cells) were shared with cluster 7 (cytotoxic effector cells) in +CPI colitis patients, indicating a dynamic link between these two colitis-associated CD8+ T cell states. In colitis patients, a large proportion of clonally expanded TCRs from Trm T cell clusters (1-3) were shared with colitis-associated clusters 7 and 8, indicating that there is a clear dynamic transition between these two cell types and that a significant proportion of enteritis-associated virulent and proliferative T cells originate from tissues tissue-resident memory T cells (Trm).
Fig.4 Colon-related changes in the cytotoxicity and proliferation program of CD8+ T cells. (Luoma, 2020)
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Reference
- Luoma, A.M.; et al. Molecular pathways of colon inflammation induced by cancer immunotherapy. Cell. 2020, 182(3): 655-671.e22.
