Downloaded from www.microbiologyresearch.org by IP: 54.70.40.11 On: Sat, 22 Dec 2018 06:45:38 Naïve T cells are activated by autologous HCMV-infected endothelial cells through NKG2D and can control HCMV transmission in vitro Narmadha Subramanian, 1 Zeguang Wu, 1 Frank Reister, 2 Kerstin Laib Sampaio, 1 Giada Frascaroli, 1,3 Luka Cicin-Sain 4,5,6 and Thomas Mertens 1, * Abstract Apart from classical antigen-presenting cells (APCs) like dendritic cells and macrophages, there are semiprofessional APCs such as endothelial cells (ECs) and Langerhans’ cells. Human cytomegalovirus (HCMV) infects a wide range of cell types including the ECs which are involved in the trafficking and homing of T cells. By investigating the interaction of naïve T cells obtained from HCMV-seronegative umbilical cord blood with autologous HCMV-infected human umbilical vein ECs (HUVECs), we could show that the activation of naïve T cells occurred after 1 day of peripheral blood mononuclear cell (PBMC) exposure to HCMV-infected HUVECs. The percentage of activated T cells increased over time and the activation of naïve T cells was not induced by either autologous uninfected HUVECs or by autologous HCMV-infected fibroblasts. The activation of T cells occurred also when purified T cells were co-cultured with HCMV-infected HUVECs. In addition, in most of the donors only CD8 + T cells were activated, when the purified T cells were exposed to HCMV-infected HUVECs. The activation of naïve T cells was inhibited when the NKG2D receptor was blocked on the surface of T cells and among the different NKG2D ligands, we identified two ligands (ULBP4 and MICA) on HCMV-infected HUVECs which might be the interaction partners of the NKG2D receptor. Using a functional cell culture assay, we could show that these activated naïve T cells specifically inhibited HCMV transmission. Altogether, we identified a novel specific activation mechanism of naïve T cells from the umbilical cord by HCMV-infected autologous HUVECs through interaction with NKG2D. INTRODUCTION Umbilical cord blood (UCB) is used as a source of haemato- poietic stem cells for transplantation having advantages compared with bone marrow stem cells like easy availability, lower risk of transmitting infections and less stringent human leukocyte antigen matching [1, 2]. UCB transplanta- tion is used to treat patients who are affected by many hae- matologic and non-haematologic disorders [3]. Limitations of using UCB are low counts of stem cells and delayed immune reconstitution [4, 5]. Since most of the immune cells are completely naïve in UCB, there is no transfer of protective memory immune cells which are important for controlling viral infections. Viral infections caused by human cytomegalovirus (HCMV), BK virus, respiratory viruses and Epstein–Barr virus are a major problem in UCB transplant recipients due to post- transplant immune deficiency [5, 6]. HCMV, a member of the beta herpesvirus family, is the most common opportunistic pathogen, occurring in 20–60 % of transplant recipients [7, 8]. The improved detection, the antiviral prophylaxis and the pre-emptive therapy can be credited for keeping the HCMV infection under control in transplant recipients [9, 10]. HCMV is also the most often infectious cause leading to con- genital diseases after infection in utero [11, 12]. Methods to control this important infectious problem are open, although different strategies are under investigation [13, 14]. Received 31 August 2017; Accepted 2 November 2017 Author affiliations: 1 Institute of Virology, Ulm University Medical Center, Ulm, Germany; 2 Gynecology and Obstetrics Clinics, Ulm University Hospital, Ulm, Germany; 3 Heinrich Pette Institute, Leibniz Institute for Experimental Virology, Hamburg, Germany; 4 Department of Vaccinology and Applied Microbiology, Helmholtz Centre for Infection Research, Braunschweig, Germany; 5 Institute for Virology, Hannover Medical School, Hannover, Germany; 6 German Centre for Infection Research (DZIF), Location Hannover-Braunschweig, Germany. *Correspondence: Thomas Mertens, thomas.mertens@uniklinik-ulm.de Keywords: HCMV; Naïve T cells; human umbilical vein endothelial cells; human umbilical Wharton’s jelly fibroblasts; activation; control of HCMV transmission; NKG2D. Abbreviations: APC, antigen-presenting cell; EC, endothelial cell; gdT, gamma delta T; HCMV, human cytomegalovirus; HUVEC, human umbilical vein endothelial cell; HUWF, human umbilical Wharton’s jelly fibroblast; IEA, immediate early antigen; IR, infection rate; NKT, natural killer T; PBMC, peripheral blood mononuclear cell; PMA, phorbol myristate acetate; TKA, transmission kinetic assay; UCB, umbilical cord blood. Eight supplementary figures are available with the online version of this article. RESEARCH ARTICLE Subramanian et al., Journal of General Virology 2017;98:3068–3085 DOI 10.1099/jgv.0.000976 000976 ã 2017 The Authors 3068