Tumor cell lysate-pulsed human dendritic cells induce a T-cell response against pancreatic carcinoma cells: an in vitro model for the assessment of tumor vaccines

Dendritic cells (DCs) are potent antigen-presenting cells and play a pivota l role in T cell-mediated immunity. DCs have been shown to induce strong an titumor immune responses in vitro and in vivo, and their efficacy is being investigated in clinical trials. Compared with vaccination strategies direc ted against a single tumor antigen, tumor-cell lysate as the source of anti gen offers the potential advantage of inducing a broad T-cell response agai nst multiple known, as well as unknown, tumor-associated antigens expressed by the individual tumor. We used pancreatic carcinoma cell lines to develo p an in vitro model for monitoring T-cell responses induced by lysate-pulse d DCs. Monocyte-derived DCs of HLA-A2(+) donors were pulsed with lysate gen erated from the HLA-A2(+) pancreatic carcinoma cell line Panc-1. In some ex periments, the immunogenic protein keyhole limpet hemocyanin (KLH) was adde d to the lysate. Subsequently, the antigen-loaded DCs were activated with t umor necrosis factor-alpha and prostaglandin E-2. Autologous mononuclear ce lls were cocultured with DCs in the presence of low-dose interleukin (IL)-2 and IL-7 and were restimulated weekly with new DCs. High levels of IL-12 a nd IFN-T could be detected in the supernatants, indicating a T-helper type 1-type immune response. This cytokine profile was associated with the expre ssion of the activation marker CD69 on both T helper and CTLs and with an a ntigen-induced proliferative T-cell response. After 4 weeks, CTL-mediated c ytotoxicity was assessed. Tumor cell lysis was specific for Panc-1 tumor ce lls and was MHC class I-restricted. Cytokine secretion, CD69 expression of T cells, and antigen-induced T-cell proliferation correlated with the cytot oxic activity and were more pronounced when KLH was added to the lysate. Th is is the first study to show that T cells specific for pancreatic carcinom a cells can be generated in vitro by lysate-pulsed DCs and that the T-cell response can be enhanced by KLH. This in vitro model can be applied to comp are different strategies in the development of DC-based tumor vaccines.