Abstract 757: Transfection of dendritic cells with IL-21 mRNA gives rise to CD8+ effector T cells with a higher proliferation rate and increased cytotoxic capacity
Authors: Turksma Annelies W. , Bontkes Hetty J. , Ruizendaal Janneke J. , van den Heuvel Heleen , Scholten Kirsten B.J. , Leemans C Rene , Meijer Chris J.L.M. , Hooijberg Erik 
Published: June 2012

Abstract
Interleukin -21, mainly produced by activated CD4+ T cells, has been shown to play a central role in the differentiation and proliferation of B and T cells. Here, we investigated the utility of IL-21 to generate high numbers of functional CD8+ effector T cells for the immunotherapy of cancer. To this end, we made use of IL-21 mRNA transfected dendritic cells (DCs) to prime and activate CD8+ T cells recognizing the melanoma antigen Mart-1. Expansion rates and functional avidity were assessed.
mRNA was transcribed in vitro from pGEM encoding eGFP/2A/IL-21 or IL-21. IL-21 transfection of cytokine-matured DCs was performed, which did not alter the expression of co-stimulatory markers (CD40, CD80, CD83 and CD86). Translation of the mRNA and secretion of the IL-21 protein were confirmed by ELISA. Initially, CD28+ T cell bulks were stimulated with allogeneic DCs transfected with IL-21 or eGFP (i.e. negative control) mRNA. The T cells primed in the presence of IL-21 showed a higher proliferation rate and cytotoxic capacity (by Granzyme B expression) than controls. Subsequently, IL-21 mRNA was co-transfected with mRNA encoding a MART-1 minigene, consisting of four copies of the MART-126L-35 immunodominant epitope preceded by a Ubiquitin sequence, into mature DCs. These DCs were used for the priming of isolated autologous CD8β+ T cells. After two rounds of stimulation, a slight, but not significant, increase in the frequencies of HLA-A2-tetramer binding T cells was observed for the MART-126L-35 epitope in comparison to control cultures with MoDCs transfected with the Ubi-MART-1 minigene mRNA without IL-21 mRNA. Of note, these specifically primed tetramer+ T cells displayed an equivalent functional avidity by IFNγ release as compared to their counterparts in control cultures, but did express significantly higher levels of Granzyme-B (P=0.05), indicative of a higher cytotoxic capacity. To assess the effects of IL-21 stimulation on effector-memory T cells, we made use of an established MART-126L-35 specific T cell clone. In multiple parallel cultures, significantly increased proliferation rates and Granzyme-B expression levels were observed when the T cells were stimulated by MoDCs co-transfected with both Ubi-MART-1 and IL-21 mRNA, as compared to Ubi-MART-1 mRNA only.
We conclude that the inclusion of IL-21 in active vaccination approaches, such as mRNA-based DC vaccines, or indeed in adoptive T cell therapies, may increase their efficacy through the accelerated expansion of anti-tumor CD8+ effector T cells with increased cytolytic potential.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 757. doi:10.1158/1538-7445.AM2011-757