By analyzing the ligands corresponding to chemokine target genes expressed in immune cells, we found that the chemotactic response of immune cells was mediated by the expression of NRG1 and HMGB1 ligands on Tum_1 tumor cells, which interacted with the CXCL1 target on APOE+ macrophages (Figure 5k). The gene discussed is APOE; the disease is neoplasm.