Imiquimod combined with dendritic cell vaccine decreases Treg proportion and enhances anti-tumor responses in mice bearing melanoma

Objective: To investigate the therapeutic effect of Toll-like receptor 7( TLR7) agonist imiquimod combined with dendritic cell( DC)-based tumor vaccine on melanoma in mice and the potential mechanism.

Methods: Melanoma-bearing mouse models were established by subcutanous injection of B16-OVA cells into C57 BL /6 mice. DCs were isolated from mouse bone marrow and propagated in culture medium with recombinant mouse granulocyte-macrophage colony-stimulating factor( rm GM-CSF) and recombinant mouse interleukin-4( rm IL-4). DC vaccine( OVA-DC) was prepared by overnight incubation of DCs added with chicken ovalbumin. C57 BL /6 mice were separated into four groups which were treated with PBS,topical imiquimod application,OVA-DC intradermal injection and imiquimod plus OVA-DC,respectively. The tumor size was calculated by digital vernier caliper. Peripheral blood CD4~+FOXP3~+Tregs of the tumor-bearing mice was detected by flow cytometry. The cytotoxicity of splenic lymphocyte against B16-OVA was assessed in vitro by CCK-8 assay.

Results: Compared with the other three groups,B16-OVA-bearing mice treated with imiquimod plus DC vaccine had the smallest tumor volume. The percentage of CD4~+FOXP3~+Tregs decreased significantly in the combined treated mice. The combined treatment enhanced significantly cytotoxicity of splenic lymphocytes against B16-OVA cells.

Conclusion: Imiquimod combined with antigen-pulsed-DC vaccine could reduce CD4~+FOXP3~+Treg proportion and promote anti-tumor effect in mice with melanoma