Abstract: Objective To investigate the blockade effects of soluble PD-1 (sPD-1) expressed in vivo on B7-H1/PD-1 signal transduction,and inhibitory effect in pulmonary metastasis of melanoma with combination of Hsp70-B16 antigen peptides in mice.Methods The pulmonary metastasis model of melanoma was established in mice.Immunohistochemical staining and flow cytometry were utilized to detect the expression of PD-1 and B7-H1 respectively in pulmonary metastasis loci.Four days after the inoculation of tumor cells,forty murine models of pulmonary metastasis were randomly divided to be immunized with normal sodium (group A),empty vector pcDNA3.1 (group B),PDlA plasmid (group C) respectively via tail vein injection,subcutaneous injection of Hsp70-B16 antigen peptides (group D) or with the combination of intravenous PDlA plasmid and subcutaneous Hsp70-B 16 antigen peptides (group E).The local infiltration with lymphocytes in pulmonary metastasis loci was observed and a series of immunological parameters were assessed 17 days after the inoculation of tumor cells.Results The melanoma pulmonary metastasis model was successfully established.There were a lot of PD-1 positive cells in these loci,and B7-H1 molecule was massively expressed on the surface of B16 cells in metastasis loci.The pulmonary metastasis was inhibited in the mice of group E,and the inhibition rate was 95%,higher than that in other groups (53%,76%,9% in group C,D,B,respectively).The quantity of CD8⁺ T cells in pulmonary metastasis loci,cytotoxicity of spleen lymphocytes to tumor cells,and serum concentration of IL-2 and IFN-γwere all significantly elevated in the mice of group E as compared with those of other groups (all P<0.01).Conclusions The expressed sPD-1 in vivo can block the signal transduction between B7-H1 and PD-1,and inhibit the metastasis of melanoma in mice.Also,the combined Hsp70-B16 peptides could enhance the effect of sPD-1.

Key words: Melanoma,experimental, Gene therapy, HSP70 heat-shock proteins, sPD-1