Objective To investigate the effects of syncytial formation induced by severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)spike protein(SARS-2-S)on the proliferation and migration of human lung adenocarcinoma A549 cells and mouse melanoma B16 cells in vitro.Methods Plasmids expressing human angiotensin-converting enzyme 2(hACE2)and SARS-2-S were constructed and respectively co-transfected with lentiviral packaging plasmids into HEK-293FT cells before the lentiviral supernatant was collected and infected with A549 cells which were screened by puromycin to obtain the A549 cells respectively that were stably transfected with hACE2(A549-A)and SARS-2-S(A549-S).The protein expression of A549-A and A549-S cells was verified by Western blotting.A549-A and A549-S cells were co-cultured before their syncytia were observed by fluorescence microscopy.Conditioned media(syncytial supernatant and non-syncytial supernatant)was collected to culture A549 cells,ovalbumin(OVA)-gene-modified B16 cells(B16-OVA),and B16-F10 cells in vitro.The CCK-8 assay and colony formation assay were used to assess the proliferation capacity of tumor cells,while the wound healing assay was employed to evaluate the migration capacity of tumor cells.Results Stable A549 cell lines expressing hACE2 and SARS-2-S were constructed.The SARS-2-S-induced syncytial formation system was established after co-culture of A549-A and A549-S cells.Both syncytial and non-syncytial supernatants significantly promoted the proliferation and migration of A549,B16-OVA,and B16-F10 cells in vitro,especially the syncytial supernatant.Conclusion SARS-2-S-induced syncytial formation promotes the proliferation and migration properties of A549 and B16 cells in vitro.