(A) Prostate tissue from SKO (n = 3; 18,622 cells), TKO (n = 6; 19,485 cells), and TKO-Nicd1 (n = 4; 19,253 cells) GEMMs or TKO (TKO.TrPl, n = 2; 11,918 cells) and TKO-Nicd1 (TKO-Nicd1.TrPl, n = 2; 11,691 cells) transplant tumors were analyzed by scRNA-Seq, and the cells were clustered by transcriptional profile. The clusters are color coded on the basis of cell type as determined by the expression of cell-type–specific gene expression markers. UMAP, uniform manifold approximation and projection; prolif., proliferating. (B) The cell-type clusters are displayed for each genotype to compare relative cell-type composition of the samples. (C) Normalized expression of IFN/inflammatory (Ifitm1, Ckap4) and MHC genes (B2m, H2-K1) in neoplastic cells from TKO and TKO-Nicd1 GEMMs was determined by scRNA-Seq (Supplemental Figure 15D). Wilcox tests were used to assess differences between genotypes, and the P values are shown. (D) The proportion of immune cell subtypes detected within TKO and TKO-Nicd1 prostate tissue was calculated from scRNA-Seq data. A 2-tailed t test was used to assess the differences observed, the P values are shown. (E) Volcano plots depicting genes differentially expressed between NE and non-NE lineages developing in fNICD2-#1 transplant tumors. MHC-I genes (HLA-A, -B, -E, and -F) and B2M are highlighted, showing upregulation in non-NE cells. (F) A fNICD2-#1 transplant tumor section immunostained for HLA-ABC demonstrates upregulation at the protein level in cells with a non-NE lineage phenotype. Scale bar: 100 μm. (G) GSEA was performed using the spatial transcriptomics data in the luminal lineage, and type I IFN responses were identified. (H) Schematic of Notch signaling in NEPC. Notch signaling suppresses NE differentiation, drives non-NE lineage differentiation, and influences the immune microenvironment. Mon, monocytes; Mac, macrophages.