Advances in our understanding of human dendritic cells have resolved many important unknowns about the onset of immunity and how dendritic cells could control these responses against cancer. Tumor antigens are poor immunogens by themselves, because they are either self or altered-self antigens. Hence the bar to overcoming tolerance toward cancer-self antigens, while attainable, is quite high. Dendritic cells can circumvent many of these barriers by presenting tumor antigens in association with all the other requisite molecules that elicit immune reactivity. Genetic strategies offer potential advantages in coupling tumor antigens to dendritic cells. Compared with standard peptide-pulsing, multiple epitopes can be expressed by genetically modified dendritic cells, which can be processed and tailored to a variety of MHC alleles. Sustained antigen-presentation is more likely and can be monitored over time. We have generated substantial preclinical data using common viral antigens (influenza, CMV) as models, in lieu of tumor antigens. We have successfully transduced CD34+ progenitors, however, that differentiate into Langerhans- type dendritic cells and express full-length human tyrosinase, an important melanoma antigen. We now propose a human clinical trial in patients with advanced melanoma (stages III-IV). We will compare Langerhans-type dendritic cells genetically modified by retroviral transduction to express full-length human tyrosinase with Langerhans cells pulsed with the HLA-A*0201 -restricted tyrosinase peptide. Safety and toxicity will be assessed in this phase I trial. Additional response assessments include detailed immune monitoring by ELISpot. tetramer reactivity, and flow cytometry-based cytokine secretion assays, comparing post-vaccine responses with pre-treatment baselines. These studies will provide proof of principle for any advantage to sustained presentation of multiple class I and II MHC epitopes over presentation of a single class I MHC peptide to stimulate adaptive tumor-specific immunity. (LAY SUMMARY: Genetic alterations of specialized Langerhans-type dendritic cells will be tested for safety, toxicity, and the stimulation of tumor- specific immunity in patients with advanced stage III-IV melanoma.) ? ? ?
