Method for obtaining oligonucleotide aptamers and uses thereof

A method for selecting a nucleic acid aptamer specific for a protein selectively expressed on the cell surface of target cells comprising the steps of:

• a) incubating a collection of synthetic nucleic acid oligoribonucleotide oligomers with human tumor derived counterselection control cells, allowing oligomers to bind to them
• b) recovering a first set of unbound nucleic acid oligomers;
• c) incubating the first set of unbound nucleic acid oligomers with human tumor derived target cells, allowing the first set of unbound nucleic acid oligomers to bind to them;
• d) recovering nucleic acid oligomers bound to the cell surface of target cells;
• and
• e) amplifying and sequencing the nucleic acid oligomers bound to the cell surface of target cells;
• wherein the human tumor derived counterselection control cells of step a) are of the same cell type as the human tumor derived target cells of step c) but wherein the step a) cells exhibit a different phenotype with respect to the step c) cells.