Oncogenic PIK3CA mutations shape an immunoregulatory microenvironment in mosaic overgrowth disorders

Abstract PIK3CA-related overgrowth spectrum (PROS) comprises a group of rare genetic disorders caused by de novo, mosaic, post-zygotic gain-of-function mutations in the PIK3CA gene. These mutations arise during embryogenesis, affect multiple organ systems, and result in heterogeneous clinical phenotypes. We previously showed that primary cells derived from a PROS mouse model exhibit a metabolic shift towards aerobic glycolysis (a Warburg-like effect), accompanied by altered secretion of metabolites. Here, we observed that this metabolic reprogramming was associated with the upregulation of key transcription factors, including c-Myc and HIF-1α. PIK3CA hyperactivation induces a distinct microenvironment marked by metabolic dysregulation, extracellular matrix remodelling, increased cellular proliferation, elevated γH2AX levels and enhanced macrophage infiltration, hallmarks commonly associated with increased lactate production. To further examine immune infiltration dynamics, we used a mouse model expressing a constitutively active PIK3CA mutation selectively in adipose tissue (AdipoCreER), a tissue frequently affected in PROS. Single-cell transcriptomics and flow cytometry profiling revealed that macrophages adopt an immunomodulatory phenotype, with increased infiltration of TREM2+ and Lyve1hiMHCIIlo macrophages, along with myeloid-derived suppressor cells, and a concurrent reduction in T-cell populations. These immune alterations parallel those observed in tumour microenvironments and may contribute to tissue overgrowth and impaired immune surveillance. Multiplex immunofluorescence analysis of tissue samples from individuals with PROS confirmed these findings, underscoring the translational relevance of the mouse model. Together, our results demonstrate that PIK3CA mutations in PROS profoundly remodel the tissue microenvironment and reprogram macrophage function in a manner reminiscent of tumour biology.