Selection and Characterization of Single-Stranded DNA Aptamers Binding Human B-Cell Surface Protein CD20 by Cell-SELEX.

The B-lymphocyte antigen (CD20) is a suitable target for single-stranded (ss) nucleic acid oligomer (aptamers). The aim of study was selection and characterization of a ssDNA aptamer against CD20 using Cell-Systematic Evolution of Ligands by Exponential Enrichment (Cell-SELEX). The cDNA clone of CD20 (pcDNA-CD20) was transfected to human embryonic kidney (HEK293T) cells. Ten rounds of Cell-SELEX was performed on recombinant HEK-CD20 cells. The final eluted ssDNA pool was amplified and ligated in T/A vector for cloning. The plasmids of positive clones were extracted, sequenced and the secondary structures of the aptamers predicted using DNAMAN® software. The sequencing results revealed 10 different types; three of them had the highest thermodynamic stability, named AP-1, AP-2 and AP-3. The AP-1 aptamer was the most thermodynamically stable one (ΔGAP-1 = -10.87 kcal/mol) with the highest binding affinity to CD20 (96.91 ± 4.5 nM). Since, the CD20 is a suitable target for recognition of B-Cell. The selected aptamers could be comparable to antibodies with many advantages. The AP-1, AP-2 and AP-3 could be candidate instead of antibodies for diagnostic and therapeutic applications in immune deficiency, autoimmune diseases, leukemia and lymphoma.