gms | German Medical Science

Objective: 5-ALA-based photodynamic therapy (PDT) can improve clinical outcome in patients suffering from recurrent glioblastoma and causes long-sustaining responses. Due to the limited penetration (Δeff=3mm) of the laser light in the brain tissue, however, additional mechanisms have to be involved in the elimination of more distant infiltrating tumor cells. To determine whether an immunological component plays a role, the impact of ALA/PDT on the afferent phase of adaptive immunity was studied.

Methods: Human glioma spheroids (U373, A172 cells) were treated with ALA/PDT, labelled with the fluorescent dye CFSE and co-cultured with immature dendritic cells (DC) to determine uptake of tumor material by the DC. To study maturation of DC, immature DC were co-cultured with spheroid-conditioned medium, and maturation was monitored by flow-cytometry.

Results: Immature dendritic cells co-cultured with tumor spheroids revealed uptake of tumor material, which was localized perinuclearly in the DC. Flow cytometric evaluation demonstrated a significantly enhanced uptake of material derived from ALA/PDT treated spheroids compared to control spheroids (16.8±5.3% vs. 1.9±.0.8% CFSE+ DC; p≤0,05). At the same time, spheroids caused maturation of DC, as indicated by up-regulation of the mature DC-associated surface molecule CD83. The mean CD83 expression of DC matured in the presence of spheroid-conditioned medium was 42.9±8.7% (p≤0,001) compared to 2.9±2.2% in control cultures. Thus, spheroids induced a similar level of maturation as the potent maturation stimulus TNFα (55.2±21.8% CD83+ DC).

Conclusions: ALA/PDT treatment of glioma-spheroids promotes the two initial steps of the afferent phase of adaptive immunity. This suggests that ALA/PDT therapy may contribute to the induction of anti-tumoral immune responses in glioma patients.