Extended Data Fig. 6: Histopathological and molecular analysis, and response to immunotherapy in MSI gastric cancer EPO-GEMMs.
From: Somatic mouse models of gastric cancer reveal genotype-specific features of metastatic disease
(a) Immunoblot of MSH2 and actin (loading control) in MSI or MSS gastric cancer cell lines (n = 3 lines each, derived from independent mice). (b) Most of the MSI tumor was typically diffuse (bar = 1 mm). Representative image of n = 3 mice. (c) Higher magnification of an MSI tumor with tightly cohesive neoplastic cells and scant extracellular matrix. There were abundant foci of apoptotic and necrotic cells (arrows) (bar = 250 µm). Representative image of n = 3 mice. (d) A region of diffuse phenotype in an MSI tumor composed of sheets of tumor cells (arrows) and minimal stroma (arrowheads) (bar = 200 µm). Representative image of n = 3 mice. (e) In rare areas, MSI tumors formed primitive glandular-like structures (arrows) (bar = 200 µm). (f-g) MSI tumors had numerous mitotic figures (arrows) and apoptotic cells (arrowhead) (bar = 50 µm). Representative images of n = 3 mice. (h) Whole-exome sequencing analysis of insertions (INS) or deletions (DEL) in either MYC-p53−/− or MYC-p53−/−-Msh2−/− gastric tumors (n = 3 independent mice each). The center horizontal line denotes the median (50th percentile) value; box extends from the 25th to the 75th percentile of each group′s distribution of values. The whiskers mark the 5th and 95th percentiles. (i) Representative immunohistochemistry staining of intratumoral regions of MYC-p53−/− (MSS) or MYC-p53−/−-Msh2−/− (MSI) gastric EPO-GEMM tumors for CD8. Quantification to the right (n = 3 independent mice each). Data are presented as mean values +/− s.e.m. (j) Number of CD3+, CD4+ and CD8+ T cells (left) or CD11c+ cells (right) in MSI gastric tumors after treatment of mice with antibodies targeting CTLA-4 or IgG control (n = 7 independent mice each). Statistical analysis by two-tailed Mann–Whitney U-test. Data are presented as mean values +/− s.e.m. (k) Kaplan–Meier survival curves of C57BL/6 gastric cancer EPO-GEMMs of MYC-p53−/−-Msh2−/− genotype (n = 8 mice IgG-treated, 4 mice α-PD-1-treated) after antibody-mediated blockade of PD-1 (RMP1-14, 200 µg) (solid line) or IgG control (dashed line). Treatment was initiated (day 0) after tumor formation was confirmed by abdominal palpation. Statistical analysis by one-sided log-rank test; ns = not significant (P > 0.05).
