Cryopreserved dendritic cells for intratumoral immunotherapy do not require re-culture prior to human vaccination.

Dendritic cell (DC) immunotherapy for cancer has shown great promise so far. The ability to deliver dendritic cells directly into tumours where they are capable of acquiring tumour antigens prior to stimulating specific T cell responses has been demonstrated both in animal models and human patients. Clinical grade DCs can be grown from peripheral blood monocytes in the absence of foetal calf serum (FCS) and cryopreserved to generate plentiful identical aliquots thus avoiding repeated venesection. However, the approach is still limited by the necessity to return thawed DCs to culture prior to injection. It would be more advantageous to directly inject the DCs whilst still in the freezing medium and thus prevent the need for further manipulation. Whilst several reports have shown that cryopreserved DCs can survive for over 72 h when returned to culture, there is no information regarding the longevity of cells maintained in the freezing medium after thawing. In this report we have shown that DCs may remain in freezing medium for up to 1 h without affecting their survival, phenotype or function. This period of time is sufficient to allow for any delays incurred between the preparation of the DCs and time taken to be administered within a standard clinical setting. This study demonstrates that clinical grade DCs can be cryopreserved and thawed whilst retaining the ability to acquire exogenous antigenic material required for intratumoural immunotherapy. The survival of these cells within the freezing medium without the requirement for re-culture expands their availability for administration directly to the tumours of patients in non-specialist centres that do not have the appropriate facilities for DC re-culture.