In situ Activation of Dendritic Cells (DC) with Imiquimod for Cancer Immunotherapy

Proc Amer Assoc Cancer Res, Volume 47, 2006 3997 The concept that active immunotherapy with antigen-loaded dendritic cells (DC) may have therapeutic promise in oncology is well established. Induction of potent immune response in cancer patients requires an activation step - termed maturation - that turns DC into potent antigen presenting cells. However, the appropriate conditions for ex-vivo maturation remain largely unknown. The objective of this study was to develop a more effective vaccination platform for human immunotherapy trials by maturing DC in vivo through injection of DC into dermal sites conditioned with the immunomodulator Imiquimod (Aldara®). In order to assess the biological response to Imiquimod treatment, skin biopsies from prostate cancer patients were analyzed for secretion of cytokines, including RANTES, MIG, MCP-1, MIP-1α, MIP-1β, IL-1β, IL-8, IL-6, TNF-α, IL-10, IL-12, IFN-α, and PGE-2. Furthermore, immunohistochemistry was performed on Imiquimod-treated skin using mAbs against CD3, CD4, CD11b, CD11c, CD14, CD15, CD56, CD68, and CD123. TLR expression by DC was assessed by RT-PCR and Imiquimod-mediated activation of DC was determined by assessing upregulation of maturation markers (CD80, CD83, CD25, and CCR-7) and by functional assays, including primary allogeneic mixed lymphocyte reactions (MLR) and DC migration assays. Topical application of Imiquimod led to increases in levels of the chemokines RANTES and MCP-1 in human skin biopsies with peak levels after the second administration, while expression of other cytokines known to facilitate DC maturation (TNF- α, MIP-1α, IL-1β, IL-6, IFN- α and PGE2) was not altered. Immunohistochemical analyses revealed activation of skin residing Langerhans cells after Imiquimod treatment. Activation was mediated by TLR-8 and not TLR-7. Imiquimod had no direct effects on maturation of monocyte-derived DC, however, incubation of DC with supernatant derived from Imiquimod-treated Langerhans cells greatly enhanced expression of maturation markers CD80 and CD83 as well as the immunostimulatory properties of monocyte-derived DC, as evidenced by allogeneic MLRs. Furthermore, DC acquired migratory properties as shown by in vitro migration towards MIP-3β gradients and imaging of DC migration in prostate cancer patients. In summery, injection of immature DC into Imiquimod-conditioned skin may represent a superior method of maturing monocyte-derived DC for immunotherapy. Based on these results, a phase I/II clinical trial is ongoing at our institution to assess the immunological and clinical efficacy of in situ-activated DC in patients with metastatic prostate cancer. Results of this ongoing clinical trial will be presented.