Natural killer (NK) cells are part of the innate immunity. They manifest cytotoxic effect against stressed, infected or malignantly transformed cells. The activation of this process is realized through binding of specific surface ligands of harmed cells to activating receptors of NK cells. But tumour cells strive to escape the immune system surveillance. Thus, the reconstitution of the cytotoxic recognition could be an interesting target of tumour immunotherapy.
We have prepared bivalent fusion proteins able to recognize and bind both tumour cell, and NK cell. The fusion proteins consist of VHH nanobody targeting specific tumour cell marker HER2, and of extracellular domain of MICA, a ligand for the activating NK cell receptor NKG2D. Such approach allows two possible designs of the fusion protein: the activating ligand positioned on N‑terminus and the VHH nanobody on C‑terminus of the protein or the inverse arrangement. The in vitro binding studies have revealed that the arrangement plays an important role in the binding capacity of both parts of the fusion protein. The position of MICA on the N‑terminus is favourable for NK activating receptor binding, whereas the position of antiHER2 nanobody on the N-terminus is advantageous for targeting the tumour marker on the cell surface.
The same approach was used for construction of another fusion protein containing B7-H6, a ligand for the activating NK cell receptor ligand NKp30, and its binding capacity was characterized as well. The prepared fusion proteins will be further used with tumour and NK cell lines where their potential to establish the cytotoxic response will be evaluated.
This study was supported by the Czech Science Foundation (18-10687S), the Ministry of Education, Youth and Sports of the Czech Republic (LTC17065 in frame of the COST Action CA15126), and by the Charles University (GAUK 1740318).