Development and Evaluation of Novel Aptamers Specific for Human PD1 Using Hybrid Systematic Evolution of Ligands by Exponential Enrichment Approach

Background Programmed cell death protein 1 (PD1; also known as CD279) is an inhibitory receptor on T lymphocytes interacting with PD1-ligand 1 and PD1-ligand 2 in the synapse of T cells and antigen presenting cells (APC) resulting in the suppression of T cell activity. Systematic evolution of ligands by exponential enrichment (SELEX) is a method for generating aptamers which can bind specifically to the target of interest. PD-1 antagonistic aptamers could introduce an attractive alternative over the antibody-based treatments due to the distinguished advantages of aptamers including small size and efficient tissue penetration, low cost, lack of immunogenicity, and ease of manufacturing. Methods: Here, we developed single-stranded DNA aptamers which bind specifically to the human extracellular domain of PD-1. We performed hybrid SELEX, a combination of targeting of recombinant proteins and cell membrane expressed PD1 to select and identify specific aptamers and for the first time, homology of aptamer sequences selected from protein and cell SELEX pool have been evaluated in this study. Results: C42–aptamer, one of the selected aptamers, could specifically bind to human PD1 with dissociation constant in the nanomolar range. Although the developed aptamer inhibited binding of PD1 to PD-L1 but it was not able to restore the cell proliferation and cytokine production of the CD8+ CD279+ T cells. Conclusion: Further studies are required to assess the therapeutic potential of C42 aptamer and other aptamers developed in this study. The introduced PD1 specific aptamers can be used for specific detection of PD1 in diagnostic assay such as immunohistochemistry and targeted drug delivery to PD+ T cells.