Peptide-loaded dendritic cells prime and activate MHC-class I-restricted T cells more efficiently than protein-loaded cross-presenting DC

Undifferentiated and differentiated dendritic cells (uDC and dDC, respectively), derived from the bone marrow, were studied in vitro and in vivo. Ovalbumin (OVA) and two OVA-derived peptides binding to H-2K^b and I-A^b, respectively, were used. Two IL-2 secreting T cell hybridomas specific for the OVA-derived epitopes were used in the in vitro read-out. The ability to cross-present the H-2K^b binding OVA_257-264-peptide (SIINFEKL) was restricted to dDC, which express CD11c⁺, CD86⁺, and MHC-II⁺. In vitro, the antigenicity of SIINFEKL-loaded DC declined at a slower rate than that of OVA-pulsed DC. Moreover, SIINFEKL-loaded DC were up to 50 times more efficient than DC-pulsed with OVA-protein for generation of an H-2K^b-restricted response. Immunization of mice with SIINFEKL-loaded DC resulted in a much stronger H-2K^b-restricted response than immunization with OVA-pulsed DC. These data might have important implications for the choice of antigen source in the design of DC-based vaccines.