Adenoviral-transduced dendritic cells are susceptible to suppression by T regulatory cells and promote interleukin 17 production.

Dendritic cell (DC) vaccines offer a robust platform for the development of cancer vaccines, but their effectiveness is thought to be limited by T regulatory cells (Tregs). Recombinant adenoviruses (RAdV) have been used successfully to engineer tumor antigen expression in DCs, but the impact of virus transduction on susceptibility to suppression by Tregs is unknown. We investigated the functional consequences of exposure to adenovirus on interactions between human monocyte-derived DCs and Tregs. Since the development of Tregs is linked to that of pro-inflammatory Th17 cells, the role of Th17 cells and IL-17-producing Tregs in the context of DC-based immunotherapies was also investigated. We found that Tregs potently suppressed the co-stimulatory capacity of RAdV-transduced DCs, regardless of whether the DCs were maturated by inflammatory cytokines or by exposure to Th1 or Th17 cells. Furthermore, exposure of Tregs to RAdV-exposed DCs increased IL-17 production and suppressive capacity, and correlated with enhanced secretion of IL-1ß and IL-6 by DCs. The findings that DCs exposed to RAdV are suppressed by Tregs, promote Treg plasticity, and enhance Treg suppression indicates that strategies to limit Tregs will be required to enhance the efficacy of such DC-based immunotherapies.

Recombinant vesicular stomatitis virus transduction of dendritic cells enhances their ability to prime innate and adaptive antitumor immunity.

Dendritic cell (DC)-based vaccines are a promising strategy for tumor immunotherapy due to their ability to activate both antigen-specific T-cell immunity and innate immune effector components, including natural killer (NK) cells. However, the optimal mode of antigen delivery and DC activation remains to be determined. Using M protein mutant vesicular stomatitis virus (DeltaM51-VSV) as a gene-delivery vector, we demonstrate that a high level of transgene expression could be achieved in approximately 70% of DCs without affecting cell viability. Furthermore, DeltaM51-VSV infection activated DCs to produce proinflammatory cytokines (interleukin-12, tumor necrosis factor-alpha, and interferon (IFN)alpha/beta), and to display a mature phenotype (CD40(high)CD86(high) major histocompatibility complex (MHC II)(high)). When delivered to mice bearing 10-day-old lung metastatic tumors, DCs infected with DeltaM51-VSV encoding a tumor-associated antigen mediated significant control of tumor growth by engaging both NK and CD8(+) T cells. Importantly, depletion of NK cells completely abrogated tumor destruction, indicating that NK cells play a critical role for this DC vaccine-induced therapeutic outcome. Our findings identify DeltaM51-VSV as both an efficient gene-delivery vector and a maturation agent allowing DC vaccines to overcome immunosuppression in the tumor-bearing host.