IL-6-engineered DC stimulate efficient antitumor immunity via enhanced and prolonged T cell cytotoxicity and survival

Abstract

Dendritic cells (DCs) modified by some immunomodulatory genes can stimulate a strong antitumor immunity and improve the treatment of tumor cells on the condition that the sources of tumor-associated antigens (TAAs) are available. IL-6, a pleotropic cytokine, has been found to inhibit CD4+25+ regulatory T (Treg)-cell-mediated immune suppression and decrease activation-induced cell death (AICD) without interfering the process of T-cell activation. To enhance DC-based cancer vaccine, we engineered DCs to express transgene IL-6.

We constructed a fiber-modified recombinant adenovirus vector AdVIL-6 expressing IL-6, infected DCs with AdVIL-6, and then investigated the efficacy of antitumor immunity induced by vaccination with DCs engineered to express IL-6 transgene. We demonstrated that DCs infected with the recombinant adenovirus AdVIL-6 induced DC maturation by up-regulation of the expression of MHC class ‡U (Iab), CD40, CD54 and CD80 expression. We also demonstrated that vaccination of OVA-pulsed AdVIL-6-infected DCs (DCOVA/AdVIL-6) was able to stimulate a stronger OVA-specific effector CD8+ cytotoxic T lymphocyte (CTL) response than vaccination with the control virus AdVpLpA-infected DCs (DCOVA/AdVpLpA). More importantly, vaccination of mice with DCOVA/AdVpLpA could protect 100% mice from intravenous (i.v.) challenge of a low dose (0.5 ~105 cells per mouse, 8/8 mice protected) of OVA-expressing BL6-10OVA tumor cells, but only 63% mice from i.v. challenge of a high dose (1 ~105 cells per mouse, 5/8 mice protected) of BL6-10OVA tumor cells. However, vaccination of DCOVA/AdVIL-6 induced an augmented antitumor immunity in vivo by complete protection of mice (8/8) from challenge of both low and high doses of BL6-10OVA tumor cells.

To study the immune mechanism underlying the result of IL-6 engineered-DC vaccine, we generated the DCOVA/AdVIL-6-activated OTI CD8+ T cells and DCOVA/AdVpLpA-activated OTI CD8+ T cells. We demonstrated that DCOVA/AdVIL-6-activated CD8+ T cells displayed a higher level of CD62L, FasL and perforin than DCOVA/AdVpLpA-activated CD8+ T cells. DCOVA/AdVIL-6-activated CD8+ T cells had a prolonged T cell survival after they were transferred into C57BL/6 mice. Furthermore, the results of the animal study showed that 100% of mice bearing OVA-expressing EG7 tumors (8mm in diameter, 8 mice per group) were tumor-free after they were i.v. treated with DCOVA/AdVIL-6-activated CD8+ T cells (2 ~106 cells per mouse). However, the control DCOVA/AdVpLpA-activated CD8+ T cells failed in eradication of EG7 tumors in all 8/8 mice.

Taken together, Adenovirus-mediated IL-6 transgene engineered DC vaccine stimulates efficient CD8+ T cell responses and antitumor immunity via enhanced T cell cytotoxicity and prolonged T cell survival. DCs engineered to express IL-6 by adenovirus-mediated IL-6 gene transfer may offer a new strategy in production of DC cancer vaccines.