Dendritic cells engineered to express the Flt3 ligand stimulate type I immune response, and induce enhanced cytoxic T and natural killer cell cytotoxicities and antitumor immunity

Abstract Background Tumor antigen presentation by dendritic cells (DCs) to T cells in lymphoid organs is crucial for induction of antitumor immune responses. Fms‐like tyrosine kinase 3 ligand (Flt3L) is a regulator of hematopoietic cell development. Methods To investigate the potential effect of Flt3L transgene expression on DC‐based cancer vaccines, we constructed a recombinant adenovirus AdVFlt3L expressing Flt3L, transfected DCs with AdVFlt3L, and investigated the efficacy of antitumor immunity by vaccination of DC Flt3L engineered to express Flt3L transgene. Results Our data demonstrated that AdVFlt3L transfection up‐regulated the expression of cytokine IL‐1β and chemokines MIP‐1α, MIP‐1β, IP‐10, MCP‐1 and MIP‐2, and stimulated DC Flt3L cell proliferation in vitro and migration toward regional lymph nodes in vivo . Our data also demonstrated that vaccination of Mut1 ‐pulsed DC Flt3L cells was able to stimulate (i) a type 1 immune response comprising CD4 + Th1 and CD8 + Tc1 activation and (ii) around 2‐ and 3‐fold enhanced tumor‐specific cytotoxic T lymphocyte (CTL) and non‐specific NK responses ( p < 0.05) than vaccination with similarly pulsed control virus‐transfected and untransfected DCs, respectively. More importantly, vaccination of Mut1 ‐pulsed DC Flt3L cells induced enhanced antitumor immunity in vivo , even against poorly immunogenic 3LL tumor cells. Vaccinations of Mut1 ‐pulsed DCs, DC pLpA and DC Flt3L all protected mice from challenge of low dose (0.5 × 10 5 ) tumor cells. However, only vaccination of the last one was able to protect 63% (6/8) mice from challenge of high dose (3 × 10 5 ) 3LL tumor cells ( p < 0.01). Conclusions DCs engineered to secrete Flt3L may offer a new strategy in DC‐based cancer vaccines. Copyright © 2003 John Wiley & Sons, Ltd.