Tumor cell lysate-pulsed dendritic cells induce a T cell response against colon cancer in vitro and in vivo

To investigate whether tumor cell lysate-pulsed (TP) dendritic cells (DCs) induce cytotoxic T lymphocyte (CTL) activity against colon cancer in vitro and in vivo. Hematopoietic progenitor cells were magnetically isolated from BALB/c mice bone marrow cells. These cells were cultured with cytokines GM-CSF, IL-4, and TNFα to induce their maturation. They were analyzed by morphological observation and phenotype analysis. DCs were pulsed with tumor cell lysate obtained by rapid freezing and thawing at a 1:3 DC:tumor cell ratio. CTL activity and interferon gamma (IFNγ) secretion was evaluated ex vivo. In order to determine whether or not vaccination with CT26 TP DCs induce the therapeutic potential in the established colon tumor model, CT26 colon tumor cells were implanted subcutaneously (s.c.) in the midflank of naïve BALB/c mice. Tumor-bearing mice were injected with vaccination with CT26 TP DCs on days 3 and 10. Tumor growth was assessed every 2–3 days. Finally, CTL activity and IFNγ secretion were evaluated in immunized mice. Hematopoietic progenitor cells from mice bone marrow cells cultured with cytokines for 8 days showed the character of typical mature DCs. Morphologically, these cells were large with oval or irregularly shaped nuclei and with many small dendrites. Phenotypically, FACS analysis showed that they expressed high levels of MHC II, CD11b, CD80, and CD86 antigen, and were negative for CD8α. However, immature DCs cultured with cytokines for 5 days did not have typical DCs phenotypic markers. Ex vivo primed T cells with CT26 TP DCs were able to induce effective CTL activity against CT26 tumor cells, but not B16 tumor cells (E:T = 100:1, 60.36 ± 7.11% specific lysis in CT26 group vs. 17.36 ± 4.10% specific lysis in B16 group), and produced higher levels of IFNγ when stimulated with CT26 tumor cells but not when stimulated with B16 tumor cells (1210.33 ± 72.15 pg/ml in CT26 group vs. 182.25 ± 25.51 pg/ml in B16 group, P < 0.01). Vaccination with CT26 TP DCs could induce anti-tumor immunity against CT26 colon tumor in murine therapeutic models (tumor volume on day 19: CT26 TP DCs 342 ± 55 mm³ vs. the other control groups, P < 0.05). In addition, all splenic CD3⁺ T cells obtained from mice vaccinated with CT26 TP DCs produced high levels of IFNγ and shown specific cytotoxic activity against CT26 tumor cells, but no cytotoxic activity when stimulated with B16 tumor cells. Tumor cell lysate-pulsed DCs can induce tumor-specific CTL activity against colon cancer in vitro and in vivo.