Photodynamic therapy induces interleukin secretion from dendritic cells

Dendritic cells (DC) pulsed with tumor-derived peptides, proteins, genes, or lysates have been studied as therapeutic cancer vaccines. However, the overall therapeutic efficacy of this approach has been limited, indicating a need to either enhance its potency or combine it with other treatment modalities. Photodynamic therapy (PDT) process consists of injecting a photosensitizer, which selectively accumulates at the lesion site, followed by local illumination of the tumor with a laser of the appropriate wavelength to activate the specific drug. PDT has the potential to create an environment at the tumor site that favors both tumor antigen loading and activation of DCs, key requirements for induction of antitumor immunity. Here, we report that PDT can induce IL-1 and IL-6 and reduce TNF-alpha expression from DCs. This finding has potentially broad clinical implications since these changes are mechanistically involved in the observed effects of PDT on host immune responses. Not all tumors are amenable to PDT, either because of size or location, and one could conceive of an adjuvant use for PDT vaccines in conjunction with other cancer modalities that do not enhance the host antitumor immune response.