Cryopreservation of immature monocyte-derived dendritic cells results in enhanced cell maturation but reduced endocytic activity and efficiency of adenoviral transduction.

To date, phase I/II dendritic cell (DC)-based cancer vaccine trials have required repeated venesection or leukapheresis to generate the DCs. Previous studies have suggested that DCs may be cryopreserved and revived for clinical use as sequential immunisations. We have developed a method of cryopreserving monocyte-derived DCs, reviving the cells with minimal loss, and have performed immunophenotypic and functional comparisons of freeze-thawed DCs with their fresh counterparts. We found that the freeze-thawing process itself is efficient in terms of DC recovery, results in semimaturation and reduced endocytic activity, but does not impair the capacity of the DCs to achieve full maturation. Revived cells also showed enhanced allostimulatory activity and antigen-specific responses. After freeze-thawing, DCs produced lower levels of IL-12 p40 and IL-12 p70 on maturation compared to fresh DCs with little change in concentration over 72 h. Genetic modification of DCs by adenoviral transduction was possible after cryopreservation albeit at a lower efficiency of gene transfer than with fresh cells. We conclude that cryopreservation of DCs for clinical immunotherapy is feasible. Modification of cells by pulsing or genetic transfer should take place prior to cryopreservation as the freeze-thawing process itself leads to increased maturation, reduction in endocytic activity but enhanced allostimulatory activity and antigen-specific responses.