Background: Relapsed medulloblastoma (MB) poses a significant therapeutic challenge due to its highly immunosuppressive tumor microenvironment. Immune checkpoint inhibitors (ICIs) have struggled to mitigate this challenge, largely due to low T-cell infiltration and minimal PD-L1 expression. Identifying the mechanisms driving low T-cell infiltration is crucial for developing more effective immunotherapies. Methods: We utilize a syngeneic mouse model to investigate the tumor immune microenvironment of MB and compare our findings to transcriptomic and proteomic data from human MB. Results: Flow cytometry reveals a notable presence of CD45^hi/CD11b^hi macrophage-like and CD45^int/CD11b^int microglia-like tumor-associated macrophages (TAMs), alongside regulatory T-cells (T_regs), expressing high levels of the inhibitory checkpoint molecule VISTA. Compared to sham control mice, the CD45^hi/CD11b^hi compartment significantly expands in tumor-bearing mice and exhibits a myeloid-specific signature composed of VISTA, CD80, PD-L1, CTLA-4, MHCII, CD40, and CD68. These findings are corroborated by proteomic and transcriptomic analyses of human MB samples. Immunohistochemistry highlights an abundance of VISTA-expressing myeloid cells clustering at the tumor–cerebellar border, while T-cells are scarce and express FOXP3. Additionally, tumor cells exhibit immunosuppressive properties, inhibiting CD4 T-cell proliferation in vitro. Identification of VISTA’s binding partner, VSIG8, on tumor cells, and its correlation with increased VISTA expression in human transcriptomic analyses suggests a potential therapeutic target. Conclusions: This study underscores the multifaceted mechanisms of immune evasion in MB and highlights the therapeutic potential of targeting the VISTA–VSIG axis to enhance anti-tumor responses.

BACKGROUND: Prostate cancer (PC) is driven by aberrant signaling of the androgen receptor (AR) or its ligands, and androgen deprivation therapies (ADTs) are a cornerstone of treatment. ADT responsiveness may be associated with germline changes in genes that regulate androgen production, uptake, and conversion (APUC). METHODS: We analyzed whole-exome sequencing (WES) and whole-transcriptome sequencing (WTS) data from prostate tissues (SU2C/PCF, TCGA, GETx). We also interrogated the Caris Precision Oncology Alliance (POA) DNA (592-gene/whole exome) and RNA (whole transcriptome) next-generation sequencing databases. Algorithm for Linking Activity Networks (ALAN) was used to quantify all pairwise gene-to-gene associations. Real-world overall survival was determined from insurance claims data using Kaplan-Meier estimates. RESULTS: Six APUC genes ( HSD3B1 , HSD3B2 , CYP3A43 , CYP11A1 , CYP11B1 , CYP17A1 ) exhibited coalescent gene behavior in a cohort of metastatic tumors ( n = 208). In the Caris POA dataset, the 6 APUC genes (APUC-6) exhibited robust clustering in primary prostate ( n = 4,490) and metastatic ( n = 2,593) biopsies. Surprisingly, tumors with elevated APUC-6 expression had statically lower expression of AR , AR-V7, and AR signaling scores, suggesting ligand-driven disease biology. APUC-6 genes instead associated with the expression of alternative steroid hormone receptors, ESR1/2 and PGR . We used RNA expression of AR or APUC-6 genes to define 2 subgroups of tumors with differential association with hallmark pathways and cell surface targets. CONCLUSIONS: The APUC-6-high/ AR -low tumors represented a subgroup of patients with good clinical outcomes, in contrast with the AR -high or neuroendocrine PCs. Altogether, measuring the aggregate expression of APUC-6 genes in current genomic tests identifies PCs that are ligand (rather than AR) driven and require distinct therapeutic strategies. FUNDING: NCI/NIH 1R37CA288972-01, NCI Cancer Center Support P30 CA077598, DOD W81XWH-22-2-0025, R01 CA249279.

Background/Objectives: Colorectal cancer (CRC) is the second leading cause of cancer-related death in the US. The presence of deficient DNA mismatch repair and microsatellite instability (dMMR/MSI) in CRC is linked to responses to immune checkpoint inhibitors (ICIs). This study investigates the impact of metformin on the tumor microenvironment (TME) and clinical outcomes of patients with dMMR/MSI CRC treated with ICIs, aiming to better understand its potential role in enhancing ICI efficacy. Methods: Of 25,011 CRC patients in Caris database, 47 received both metformin and ICI therapy (Met-ICI group), and 475 patients received ICI therapy alone (ICI group). Samples underwent genomic or transcriptome sequencing at Caris Life Sciences. Immune cell fractions were estimated using quanTIseq. Univariate and multivariate survival analyses were conducted using the Cox proportional model. Results: The TME analysis of CRC patient samples revealed that TMB-High (≥10 mut/Mb) was more prevalent in the “ICI” group compared to the “Met-ICI” group (99.1% vs. 95.6%, p = 0.036). Mutation rates for most genes between the two groups were similar, but CIC gene mutations were more common in the “ICI” group than in the “Met-ICI” group (23.2% vs. 4.8%, p = 0.006). No significant differences were observed in the PD-L1 positivity rate or immune checkpoint gene expression (including IDO1, IFNG, TIM3, and CTLA4). M1 macrophages and neutrophils showed the highest infiltration among immune cells. However, the fractions of infiltrated immune cells were similar between the two cohorts. Univariate and multivariate analyses showed that there was no significant difference in patient survival between “ICI” and “Met-ICI” cohorts. Conclusions: In this retrospective analysis of real-world clinical outcomes, the concurrent use of metformin with ICIs in patients with dMMR/MSI CRC did not reveal an impact on clinical outcomes.