Generation of CD4+ and CD8+ T Lymphocyte Responses by Dendritic Cells Armed with PSA/Anti-PSA (Antigen/Antibody) Complexes

Dendritic cells (DC) acquire antigens through a number of cell surface structures including receptors for the Fc portion of immunoglobulins and mannose. Little is known about the effects of antigen uptake via these receptors on antigen processing and presentation. We compared the capacity of DC to generate CD4+ and CD8+ T cell responses after exposure to prostate-specific antigen (PSA) alone, PSA targeted to the mannose receptor (mannosylated PSA (PSA-m)), or PSA targeted to Fc receptors by combining PSA with an anti-PSA antibody (AR47.47). Autologous CD3+ T cells were added to monocyte-derived immature DC that had been cultured with GM-CSF/IL-4 for 4 days, exposed to antigen, and matured with CD40L or TNFα/IFN-α. After several rounds of stimulation, T cell responses were assessed by intracellular IFN-γ production using flow cytometry. Both CD4+ and CD8+ T cell responses were observed after stimulation with DC exposed to the PSA/anti-PSA complexes, whereas CD4+ predominated over CD8+ T cell responses after stimulation with PSA-armed DC or PSA-m. These CD8+ T cells responded when rechallenged with DC pulsed with HLA allele-restricted PSA peptides. These results indicate that PSA and PSA-m are processed primarily through pathways that favor HLA Class II presentation, while the PSA/anti-PSA immune complexes are processed through both Class I and Class II pathways in monocyte-derived DC. These findings have potential applications in designing more effective cancer vaccines for prostate cancer.