Cryopreservation of primary human monocytes does not negatively affect their functionality or their ability to be labelled with radionuclides: basis for molecular imaging and cell therapy.

Background: Circulating white blood cells crucially contribute to maintenance and repair of solid organs. Therefore, certain cell populations such as monocytes are attractive targets for use in molecular imaging and cell imaging, e.g. after labelling with radionuclides, as well as for cell therapies. However, the preparation of monocytes may require freezing and thawing to preserve cells for timely and standardised applications. Additional modifications of these cells such as radioisotope labelling are necessary prior to their application in vivo. We therefore tested the hypothesis whether cryopreservation of freshly isolated circulating human monocytes affects their functional phenotype or their suitability for radionuclide labelling.

Results: CD14+CD16- monocytes were isolated from human peripheral blood. They were either directly used for cellular assays and labelling or frozen down using cryoprotectants. In the latter case, cells were thawed prior to further use and analysed for survival, chemotactic responses to various growth factors and adhesion on endothelial cells. In addition, both fresh and cryopreserved monocytes were labelled with radiotracers followed by assessment of survival and chemotactic responses. In all functional assays performed, cryopreserved monocytes did not significantly differ from freshly isolated monocytes with regard to their functionality. Cryopreservation did not affect cell survival. There was no effect on the chemotactic response of monocytes towards different growth factors. Likewise, adhesion properties remained unchanged following cryopreservation. Moreover, the labelling efficiency was similar for freshly isolated and cryopreserved monocytes. Labelling did not negatively affect monocyte survival and function.

Conclusions: Our data indicate that cryopreservation of freshly isolated human primary monocytes is feasible and does not negatively affect their functionality when used for labelling and functional assessment.