In vitro, co-culture of macrophages with tumor cell supernatants (Fig. 6E) demonstrated upregulation of M2 polarization markers by qRT-PCR (Fig. 6F) and increased M2/M1 ratio by flow cytometry (Fig. 6G), confirming that GDF15 promotes M2 macrophage polarization and infiltration in GBM. The gene discussed is GDF15; the disease is glioblastoma.