Background: Dendritic cell (DC) vaccines can induce antitumor immune responses in patients with malignant diseases, while the most suitable DC culture conditions have not been established yet. In this study we compared monocyte derived human DC from conventional cultures containing GM-CSF and IL-4/TNF-alpha (IL-4/TNF-DC) with DC generated by the novel protocol using GM-CSF and IFN-alpha (IFN-DC).
Methods: To characterise the molecular differences of both DC preparations, gene expression profiling was performed using Affymetrix microarrays. The data were conformed on a protein level by immunophenotyping, and functional tests for T cell stimulation, migration and cytolytic activity were performed.
Results: Both methods resulted in CD11c+ CD86+ HLA-DR+ cells with a typical DC morphology that could efficiently stimulate T cells. But gene expression profiling revealed two distinct DC populations. Whereas IL-4/TNF-DC showed a higher expression of genes envolved in phagocytosis IFN-DC had higher RNA levels for markers of DC maturity and migration to the lymph nodes like DCLAMP, CCR7 and CD49d. This different orientation of both DC populations was confined by a 2.3 fold greater migration in transwell experiments (p = 0.01). Most interestingly, IFN-DC also showed higher RNA levels for markers of NK cells such as TRAIL, granzymes, KLRs and other NK cell receptors. On a protein level, intracytoplasmatic TRAIL and granzyme B were observed in 90% of IFN-DC. This translated into a cytolytic activity against K562 cells with a median specific lysis of 26% at high effector cell numbers as determined by propidium iodide uptake, whereas IL-4/TNF-DC did not induce any tumor cell lysis (p = 0.006). Thus, IFN-DC combined characteristics of mature DC and natural killer cells.
Conclusion: Our results suggest that IFN-DC not only stimulate adaptive but also mediate innate antitumor immune responses. Therefore, IFN-DC should be evaluated in clinical vaccination trials. In particular, this could be relevant for patients with diseases responsive to a treatment with IFN-alpha such as Non-Hodgkin lymphoma or chronic myeloid leukemia.