Objective: To assess the feasibility and efficiency of eliciting leukemia-specific T cell responses in acute myeloid leukemia patients in complete remission (AML-CR) in vitro by dendritic cells (DC) pulsed with the leukemia cells total RNA.
Methods: The immature DCs were generated from the adherent bone marrow mononuclear cell in vitro in the presence of combined cytokines (GM-CSF 100 ng/ml, IL-4 500 U/ml), and pulsed with total RNA isolated from autologous leukemic cells by cationic lipid 1,2-dioleoyloxy-3-trimethyl ammonium propane (DOTAP) at day 5 of culture. Then the cells were incubated for another 24 h in a medium containing 10 ng/ml of TNF-alpha for maturation of DC. After the total 7 days culture, the cells were harvested as the mRNA-DC and the expression of mature DC markers were determined by FACS. The proliferative capacity of T cell activated by mRNA-DC was determined by MTT assay. Meanwhile, the mRNA-DC was co-cultured with T lymphocytes at a ratio of 1:3 for 7 days. The activated T lymphocytes were harvested, the secretion of IFN-gamma was determined by ELISPOT assay, and the cytotoxicity was analyzed in vitro by LDH release assay.
Results: After culture, the BMMNC from 14 AML-CR patients developed morphologic and phenotypic characteristics of mature DC. At a stimulator/reactor ratio of 1:16, auto-T lymphocytes primed with mRNA-DC exhibited significant proliferative activity compared with T lymphocyte primed with non-pulsed DC [(36.84 +/- 5.68)% vs (12.20 +/- 3.16)%, (P < 0.05)]. An expansion of mRNA reacted T cell secreting IFN-gamma could be observed on ELISPOT assay. At an effector/target ratio of 20:1, the auto-T lymphocytes primed with mRNA-DC exhibited significant killing activity to auto-AML cells (45.46 +/- 6.34 )% as compared with that stimulated by IL-2 alone (13.26 +/- 2.28)% or primed by non-pulsed DC (12.32 +/- 1.32)% (P < 0.05).
Conclusion: Immunization with DC-leukemia cell RNA vaccines may be a simple, rapid and potent approach to elicitation of T cell-mediated anti-leukemia immunity.