Active immunotherapy with Flt3-ligand mobilized peripheral blood dendritic cells loaded with carcinoembryonic antigen peptide in patients with metastatic malignancies

Background: Dendritic cells (DC) loaded with tumor antigens induce immune responses in some cancer patients. However, the most commonly used method for obtaining clinical grade DC requires in vitro generation over 7 days in media containing cytokine, increasing the complexity and cost of the cellular vaccine product. The cytokine Flt3-ligand (FL) increases peripheral blood DC numbers in humans permitting an alternative approach to obtaining an adequate number of clinical grade DCs. We sought to evaluate the safety and immunogenicity of immunizations with FL-mobilized DC loaded with the tumor antigen CEA. Methods: Patients with CEA-expressing cancers received FL 20 μg/kg/d SQ x 10 d and were then leukapheresed to obtain peripheral blood mononuclear cells enriched for DC (FL-DC). After maturation overnight, FL-DC were coadministered (1 × 10⁷ cells) as a combined ID and SQ injection with a class I peptide fragment of CEA, hepatitis B core antigen, tetanus toxoid or KLH protein every 3 weeks for four immunizations. Results: We found that FL and FL-DC immunizations were well tolerated. Following FL, the CD11c+CD14- DC population within the PBMC increased (1.5 ± 1.4% to 8.5 ± 4.2%). After overnight maturation, 10 to 20% of these DC expressed the maturation marker CD80. Antigen-specific DTH reactivity was observed at injection sites in all but 1 patient. Antigen specific immune responses were detected in the peripheral blood of 4 of 6 patients by intracellular cytokine staining, ELISPOT, proliferation, or tetramer analysis. Among the 6 patients who completed the immunizations, there was 1 with stable disease and 5 with progressive disease. Immunization with mobilized dendritic cells loaded with tumor antigens appears feasible and induces low levels of immune response.