METHOD FOR SCREENING DNA APTAMER OF PD-L1 IN VITRO AND APPLICATION THEREOF IN CANCER DIAGNOSIS

摘要

A new method for screening a high-affinity and specific DNA aptamer of a programmed cell death receptor 1-ligand 1 (PD-L1) in vitro, hereinafter referred to as inner encoded-SELEX. An initial random DNA library of the present method comprises two random sequence areas and a fixed area (i.e., inner encoding) located between the two random sequence areas and containing an II type restriction endonuclease recognition site. The library is pre-enriched by using MCP-SELEX; the library and PD-L1 are subjected to homogeneous incubation; and then restriction endonuclease is added. An inner encoded structure of a sequence capable of binding to PD-L1 is broken, thus the sequence is not cut off by the restriction endonuclease, and PCR amplification is preserved. The obtained aptamer has the characteristic that the larger the inner encoding length is, the higher the affinity is, thereby facilitating quickly selecting a high-affinity aptamer. A fluorescently labeled aptamer is successfully used for fluorescence imaging of PD-L1 expression level of tonsil tissue of a normal person and multiple tumor tissue slices, and has performance equivalent to an antibody and excellent application value.