IMMU-64. SEX-SPECIFIC ROLES OF<i>YAP1</i> AND CD276/B7-H3 IN MEDULLOBLASTOMA IMMUNE SUPPRESSION

Abstract The molecular mechanism governing sex disparities in cancer prevalence, progression, and treatment outcomes represents an important yet understudied area of research with significant implications for cancer treatment. Medulloblastoma (MB), the most prevalent pediatric brain malignancy, exhibits a notable sex bias in incidence and survival rates. Males have a higher incidence rate across all age groups and have worse prognoses than their females for age groups over three years old. Here, we report an unanticipated sex-biased role of the oncogene Yap1 in SHH medulloblastoma. Our results reveal that Yap1 deletion significantly prolongs survival in male, but not female mice with SmoM2-driven SHH MB. Employing an integrated multi-omics approach, we demonstrate that YAP1 is required to maintain cancer stem cells simultaneously activating stemness genes (such as Sox2) and repressing differentiation genes (such as Neurod1 and Zic1/2) in both sexes. In contrast, Yap1 plays a more critical role in immune evasion in males than in females. Specifically, YAP1 regulates the expression of the immune checkpoint molecule Cd276/B7-H3, which suppresses cytotoxic T cell function. In males, CD276 blockade or Yap1 deletion in MB cells is enough to reverse T cell suppression effectively. In females, neither CD276 blockade nor Yap1 deletion alone in MB cells can reverse T cell suppression. Furthermore, YAP1’s direct transcriptional target gene signatures, including CD276, predict survival across multiple human cancers in male patients. These findings suggest broader implications of our findings beyond medulloblastoma and indicate a highly conserved mechanism across species. Our study provides compelling evidence for the male-biased efficacy of Yap1 or CD276 inhibitors and presents novel insights into sex-specific mechanisms of cancer immune evasion.