Method for modifying genes

1. A method of modulating the level of expression of a mammalian gene in a cell, wherein the mammalian gene is expressed or is capable of being expressed in the cell, wherein the cell is one which expresses a microRNA (miRNA) or is capable of expressing the miRNA, the method comprising the steps of:

(a) producing five or more nucleic acid molecules, each said nucleic acid molecule independently comprising a reporter gene and a different modified heterologous miRNA response element (MRE) in the 3′ untranslated region (3′-UTR) of the reporter gene,

wherein the nucleotide sequence of the reporter gene in each of the nucleic acid molecules is the same,

wherein the nucleotide sequences of the different modified heterologous MREs have 1, 2, 3, 4 or 5 nucleotide changes with respect to an MRE which is perfectly complementary to the full length of the miRNA, and

wherein each said modified heterologous MRE binds the miRNA at a different affinity;

(b) determining the expression level of the reporter gene of each said nucleic acid molecule in the presence of the miRNA, wherein the expression level of the reporter gene of each said nucleic acid molecule is different and wherein the expression level of the reporter gene is distributed across an entire range of from 5% to 90% of an un-silenced control;

(c) selecting a modified heterologous MRE from the nucleic acid molecules which resulted in or lead to a desired defined reduction of the level of expression of the reporter gene; and

(d) inserting the selected modified heterologous MRE into the 3′-UTR of the mammalian gene.

2. A method of treating cancer cells in a subject, wherein the cancer cells have the potential of being detected by the immune system, the method comprising the steps of:

(a) producing five or more nucleic acid molecules, each said nucleic acid molecule independently comprising a reporter gene and a different modified heterologous MRE in the 3′-UTR of the reporter gene,

wherein the nucleotide sequence of the reporter gene in each of the nucleic acid molecules is the same,

wherein the nucleotide sequences of the different modified heterologous MREs have 1, 2, 3, 4 or 5 nucleotide changes with respect to an MRE which is perfectly complementary to the full length of an miRNA which is differentially upregulated in activated T-cells,

wherein each said modified heterologous MRE binds the miRNA at a different affinity;

(b) determining the expression level of the reporter gene of each said nucleic acid molecule in the presence of the miRNA, wherein the expression level of the reporter gene of each said nucleic acid molecule is different and wherein the expression level of the reporter gene is distributed across an entire range of from 5% to 90% of an un-silenced control;

(c) selecting a modified heterologous MRE from the nucleic acid molecules which resulted in or lead to a desired defined reduction of the level of expression of the reporter gene;

(d) in the genome of a T-cell which has been obtained from the subject, inserting the nucleotide sequence of the selected modified heterologous MRE in the 3′-UTR of a gene which encodes an immune checkpoint polypeptide thus producing a modified T-cell;

and

(e) introducing the modified T-cell into the subject;

wherein the modified T-cell, when activated by contact with the cancer cells, is not negatively regulated by the cancer cells, and wherein the modified T-cell promotes the destruction or rejection of the cancer cells.

3. The method of claim 1 , wherein the mammalian gene codes for a transcription factor, chromatin protein, oncogene, receptor, kinase, proto-oncogene or DNA binding protein.

4. The method of claim 1 , wherein the miRNA is one which is differentially-expressed in a human disease.

5. The method of claim 1 , wherein the selected modified heterologous MRE is positioned in a MRE-desert in the 3′-UTR of the mammalian gene.

6. The method of claim 1 , wherein the mammalian gene is selected from the group consisting of MYB, PD-1, LAG-3, TIM-3, BTLA, CTLA-4, HBA1, HBA2 and BCL-2.

7. The method of claim 1 , wherein the miRNA is selected from the group consisting of miR-17, miR-19, miR-21, miR-155, miR-196b, miR-92, miR-126 and miR-148a.

8. The method of claim 1 , wherein the mammalian gene encodes an immune checkpoint polypeptide.

9. The method of claim 1 , wherein step (a) comprises producing ten or more of the nucleic acid molecules.

10. The method of claim 1 , wherein step (a) comprises producing fifteen or more of the nucleic acid molecules.

11. The method of claim 1 , wherein step (a) comprises producing twenty or more of the nucleic acid molecules.

12. The method of claim 2 , wherein step (a) comprises producing ten or more of the nucleic acid molecules.

13. The method of claim 2 , wherein step (a) comprises producing fifteen or more of the nucleic acid molecules.

14. The method of claim 2 , wherein step (a) comprises producing twenty or more of the nucleic acid molecules.