Modulation of Natural Killer cell response by human cytomegalovirus

The Natural Killer (NK) cell activating receptor DNAM-1 (CD226) is stimulated through recognition of CD112 (nectin-2) and CD155 (nectin-like molecule 5; PVR) on target cells. HCMV UL141 elicits protection from NK-cells by down-regulating CD155 from the cell surface and sequestering it in the ER (Tomasec, 2005). Here, HCMV UL141 was shown to be involved in the down-regulation of CD112. Interestingly, UL141 appeared necessary but not sufficient to modulate CD112 expression. This thesis therefore focused on a hypothesis whereby UL141 was acting with one or more additional HCMV genes to target CD112 for degradation. This project was the first to utilise an entire recombinant adenovirus (RAd) library expressing individual HCMV ORFs (RAd-HCMV-ORF library) to screen for function. The RAd-HCMV-ORF library clearly provided an extremely powerful tool for the screening of HCMV gene function as results were highly repeatable and robust. The co-infection of RAd-UL141 and RAd-US2 resulted in a single, clear, positive hit in the final screening process. This hit was further verified by immunoblot where CD112 appeared to be down-regulated in cells infected with both RAd-UL141 and RAd-US2, compared to controls. While a Hela-US2 cell line which stably expressed US2 also down-regulated CD112 when infected with RAd-UL141. A RCMVΔUS1-11 virus was constructed, which failed to down-regulate CD112 from the cell surface of RCMVΔSU1-11 infected cells. The addition of proteasome inhibitors was able to partially restore CD112 expression in HCMV infected cells (Prod'homme et al., 2010). It therefore appeared that US2 and UL141 act to degrade CD112 via the proteasome during HCMV infection. CD112 downregulation may have the potential to prevent DNAM-1:CD112 interaction between HCMV infected targets and effector cells of the immune system, providing another facet to HCMV’s ability to avoid the human immune response