Bromelain-stimulated DC revealed an upregulation of surface maturation markers, as well as an increased secretion of IL-12p70. When DC were stimulated with a combination of bromelain and the cytokine
cocktail, an even more mature phenotype was detected. The T cell stimulatory capacity was, however, not changed. When PGE2 was removed from the cytokine cocktail, DC showed a less mature phenotype and lower ability to stimulate T cells. Addition of bromelain to this modified cytokine cocktail did not restore the DC maturation. We conclude that maturing DC with bromelain in vitro does not improve the FDA approved Drug Library functional quality of DC aimed to be used in cancer immunotherapy. Generation of DC. Monocyte-derived DC were generated from MG-132 purchase buffy coat preparations obtained from healthy blood donors at the Blood Bank, Haukeland University Hospital, Bergen, Norway, as described previously [24]. In short, peripheral blood mononuclear cells (PBMC) were isolated by density gradient centrifugation before the monocytes were purified by plastic adherence. To generate immature DC, these cells were then cultured
for 6 days in RP10 medium (RPMI 1640 (Cambrex Bioscience, Verviers, Belgium) with 10% FCS (PAA, Pasching, Austria), 100 units/ml penicillin and 100 μg/ml streptomycin (Sigma-Aldrich, St Louis, MO, USA), with IL-4 (20 ng/ml; ImmunoTools, Friesoythe, Germany) and GM-CSF (100 ng/ml; ImmunoTools). The cytokines were replenished every 2–3 days. In initial experiments, different amounts of bromelain (100, 50, 25, 10 and 5 μg/ml; CPC W. Mühlbauer, Hamburg, Germany) were tested to analyse the effect of bromelain on DC and to determine the most suitable concentration. The maturation stimulus was given for 24 h, and cells were compared with immature DC. DC stimulated with the Jonuleit cytokine cocktail consisting of IL-1β (10 ng/ml), IL-6 (1000 U/ml),
TNF-α (10 ng/ml; all from ImmunoTools) Interleukin-2 receptor and PGE2 (1 μg/ml; Sigma-Aldrich) were used as a control. We next analysed the effect of combining bromelain with the cytokine cocktail. Included in this set-up were DC populations stimulated with the cytokine cocktail with less (¼) PGE2 (250 ng/ml) or without PGE2, both alone and in combination with bromelain. During harvesting of the generated DC populations, aliquots of conditioned medium were collected and stored at −20 °C. An automated CASY cell counter (Innovatis, Ueticon am See, Switzerland) was used to determine the amount of cells, cell size and viability. Immunostaining. The phenotypes of the generated cell populations were analysed using flow cytometry. The cells were stained for 10 min at room temperature with titrated amounts of antibodies in FACS buffer (PBS + 0.5% BSA) before washing and immediately analysed on a FACS Canto I cytometer (BD Biosciences, Heidelberg, Germany).