Immunological memory is the ability of the immune system, upon re-encounter with the same antigen, to respond with greater speed and intensity and constitutes the basis for vaccination. Regarding CD8+ T-cells, the memory compartment has been divided in different subsets of memory cells: Central Memory CD8+ T cells (CD45RO+CD62L+; Tcm) and Effector Memory CD8+ T cells (CD45RO+CD62L- ; Tem). In cancer immunotherapy, studies performed on animal models showed that Tcm tumor-reactive CD8+ T cells, as compared to effector memory T cells, confer superior antitumor immunity leading to better outcome.. In the last decades has been clarified that CD4+T cells help, during CD8+ T cells memory differentiation, is mainly mediated by the CD40L expression on their surface upon activation and consecutive triggering of CD40 expressed by antigen presenting cells and activated CD8+ T cells.

Recombinant vaccinia virus (rVV) is one of the most immunogenic viral vectors enabling specific targeting and modulation of anti-tumor immune responses. We previously demonstrated that infection of antigen presenting cells (APCs) , with a non-replicating rVV encoding human CD40L (rVV-CD40L) was leading to an efficient licensing of APC, as demonstrated by increased expression of surface ligand/receptors (MHC I/II, CD80 and CD86),Th1 and homeostatic cytokines (IL-12, TNFa, IL-7 and IL-15). Using sorted naive CD8+ Tcells (CD45RA+CD62L+) primed with infected allogeneic CD14+ we observed that activated cells had an increased central memory phenotype (CD45RO+ CD62L+) with rVV40L infection as compared to culture primed with wild type virus infected CD14+ cells or treated with soluble 40 Ligand recombinant protein (s40L). The majority of Tcm express even the a-chain of IL-7 receptor (IL-7Ra) which has been reported to be express on “Bona Fide” memory cells and is associated with an increased cells survival. In an autologous system targeting a tumor antigen response, we demonstrated how CD14+rVV40L, as compared controls or soluble 40L stimulation, strongly promote the expansion of MelanA/Mart-1 specific CD8+ characterized with a Tcm phenotype and expression of IL-7Ra. Functional characterization of these tumor specific CD8+ demonstrated higher levels of IFN-g and IL-2. Studies performed in murine models have shown that, upon activation, CD8+ T cells can also express the CD40 receptor and therefore become directly sensitive to CD40L activation. However,in our hands, induction and characterization of CD40 receptor, on human CD8+ T cells remained negative.

Overall, these data are confirming the potent anti-tumor capacities of recombinant vaccinia viruses expressing CD40L notably via CD40 driven APC licensing which promotes an effective generation of antigen specific CD8+ T cells with a memory phenotype. These in-vitro observations validate the strong clinical potential of our recombinant vaccinia virus constructs co-expressing CD40L for cancer immunotherapies.

Citation Format: Emanuele Trella, Evangelos Panoupolos, Swantje Heidtmann, Nermin Raafat, Giulio Cesare Spagnoli, Paul Zajac. Improved generation of central memory CD8+ T cells with CD40L expressing recombinant vaccinia virus. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2883. doi:10.1158/1538-7445.AM2014-2883