Antigen binding fragment and single-chain antibody targeting CD70 and application of antigen binding fragment and single-chain antibody

The invention belongs to the technical field of cellular immune engineering, and particularly relates to a fully humanized CD70-targeting antigen binding fragment and a single-chain antibody and application thereof. The amino acid sequence of the antigen binding fragment and the amino acid sequence of the light chain variable region of the single-chain antibody are shown as any one of Sequence NO.1-7; the amino acid sequence of the heavy chain variable region is as shown in any one of Sequence NO.8 to Sequence NO.10. The single-chain antibody provided by the invention is good in affinity performance, can be combined with CD70 positive cells in flow cytometry, can be specifically combined with CD70 antigens in molecular interaction research, is a natural fully humanized antibody source, has a sequence completely coming from a human antibody gene pool, and has the advantages that compared with a mouse antibody, a chimeric antibody and a humanized antibody, the affinity performance of the antibody is greatly imp