| Cell-cell interactions play an important role in the development of multicellular tissue structures,maintaining cellular homeostasis,and realizing biological functions.In the field of cancer immunotherapy,the realization of complex biological functions is mainly reflected in the immune response.For example,natural killer cells bind to specific ligands of cancer cells through activating and inhibitory receptors on the cell membrane surface,thereby killing cancer cells.This cellular communication based on ligand-receptor interactions is widespread in multicellular organisms and provides a favorable target for regulating cell-cell interactions.However,the complexity and heterogeneity of biological systems have brought great challenges to the study of cellular interactions.For example,most cancer-associated membrane proteins are expressed not only on cancer cells but also at low levels on normal cells,making conventional cell recognition strategies less specific.Therefore,the development of molecular tools with high specificity,strong programmability,and good biocompatibility is of great significance for regulating cell-cell interactions and developing new methods for disease diagnosis and treatment.Aptamer is a kind of functional nucleic acid with target recognition ability.It has the advantages of low immunogenicity,easy synthesis,flexible and controllable design and is widely used in many fields such as biosensing and disease diagnosis and treatment.In recent years,aptamer has been modified on the cell membrane surface by cell surface engineering,which provides a new way for the study of cellcell interactions.However,how to use functional nucleic acids to achieve precise regulation of cellular interactions remains a challenging scientific issue.Tumor tissue usually has the characteristics of insufficient blood perfusion,uncontrolled proliferation and abnormal metabolism,which make it have different physicochemical properties from normal tissue,such as hypoxia,low p H and high ATP content.Based on the above special properties,the development of molecular tools responsive to the microenvironment is expected to realize cell-cell interactions under specific conditions.In conclusion,based on the target recognition ability of aptamers and the p Hresponsive properties of triple helix DNA,a p H-responsive DNA nanoplatform was constructed to regulate cell-cell interactions.At the same time,we modified it on NK cells,giving the cells the ability to selectively recognize and kill cancer cells under the acidic conditions of the tumor microenvironment,providing new ideas for precise immunotherapy of tumors.In the second chapter,we synthesized p H-responsive triple helix aptamer probes.By optimizing the sequence of aptamer and triple helix structure,the probe sequence with the best response effect and ability to identify target cells was obtained.Characterization by circular dichroism spectroscopy and fluorescence resonance energy transfer method confirmed that the probe sequence can self-assemble to form triple helix structure under acidic conditions.This indicates that the triple helix aptamer probe has p H-responsive conformational switching ability and can selectively identify target cells.In the third chapter,we constructed a DNA nanoplatform with the ability of cell system application through the assembly of triple helix aptamer probes and DNA tetrahedron.CEM cells modified with this nanoplatform could recognize K562 cells under acidic conditions of p H 6.5,thereby shortening the intercellular distance.However,under physiological conditions of p H 7.5,there was no obvious recognition effect and the interaction was weakened,which proved that the platform could be used to precisely regulate cell-cell interactions.And by exploring the effect of cell ratio on the interaction effect,it was found that the optimal effect was obtained when the ratio of anchor cells to target cells was 1:1.In the fourth chapter,we applied the triple-helix DNA nanoplatform to enhance the specific recognition ability of NK cells.The DNA nanoplatforms have cell versatility and can be successfully modified on the surface of NK-92 MI cells with anchorage stability.And the modified NK-92 MI cells can effectively enhance the ability of cell-cell interactions,and can enhance the killing ability of K562 cells in an acidic environment that mimics the tumor microenvironment.This indicates that the triple helix DNA nanoplatform can effectively enhance the killing specificity of NK cells by regulating cell-cell interactions under specific p H conditions,and has the potential to be applied in the field of cancer therapy. |
