Hemocytes facilitate interclonal cooperation-induced tumor malignancy by hijacking the innate immune system in Drosophila

Tumor heterogeneity, a hallmark of cancer, frequently leads to treatment failure and relapse. However, the intricate communication between various cell types within the tumor microenvironment and their roles in tumor progression in vivo remain poorly understood. Here we establish a novel tumor heterogeneity model in the Drosophila larval eye disc epithelium and dissect the in vivo mechanisms by combining sophisticated genetics with single-cell RNA sequencing. We found that mutation of the tricellular junction protein M6 in cells surrounding RasV12 benign tumors promotes their malignant transformation. Mechanistically, early RasV12//M6-/- tumors secrete Pvf1, which activates the Pvr receptor on hemocytes, facilitating their recruitment to the tumor site. These tumor-associated hemocytes secrete the Spätzle (Spz) ligand to activate the Toll receptor within the RasV12 tumors. This enhanced activation of the Toll pathway synergizes with RasV12 to promote malignant transformation through the JNK-Hippo signaling cascade. In summary, our study elucidates the complex interplay between genetically distinct oncogenic cells and between tumors and hemocytes, highlighting how hemocytes exploit the ancient innate immune system to coordinate tumor heterogeneity and drive tumor progression.