Memory T cell inflation in CMV infection

In recent years accumulation of CMV-specific CD8+ memory T cells termed memory inflation has appeared to be one of the most important aspects of cytomegalovirus (CMV) immunobiology. Recent studies indicate that DCs are responsible for the induction of primary CMV-specific CD8+ T cells responses, whereas non-hematopoietic cells in lymph nodes are supposed to drive memory CD8+ T cell inflation. To further test this hypothesis we will utilize a mouse CMV infection model and take advantage of a novel model of memory inflation based on replication-deficient adenovirus (HuAd5). We will investigate CMV and HuAd5 infection of non-hematopoietic stromal cell subsets in the secondary lymphoid tissues. We will also study the capacity of stromal cell subsets infected with CMV or HuAd5 constructs to induce specific T cell responses as well as their involvement in the induction of memory T cell inflation. This project is expected to provide first direct evidence that latently CMV infected non-hematopoietic cells can directly present viral antigens to inflationary CD8+ T cells thereby promoting secondary expansion and migration to the periphery. Understanding the mechanisms of memory inflation and its role in immune protection against viruses could have important implications well beyond CMV persistence, including the development of new vaccines.

A phenomenon named Memory Inflation where certain epitope-specific CD8+ T cell responses were recorded to gradually increase over time resulting in the accumulation of CD8+ T cells with an effector-memory phenotype in blood and tissues has been discovered in murine cytomegalovirus (CMV) infection. This process represents one of the most important aspects of both human and murine CMV immunobiology. The mechanism of memory inflation has been intensively studied but critical aspects are still unknown. Recent studies suggest that non-hematopoietic cells in lymph nodes drive memory CD8+ T cell inflation. We are able to mirror memory inflation very accurately with a novel model of memory inflation based on replication-deficient adenovirus containing LacZ gene (Ad-LacZ) encoding ?-galactosidase (?gal). This model provides a highly controlled and very flexible system to study molecular and cellular requirements of memory inflation. Ad-LacZ immunised mice produce two responses against ?gal epitope - an inflationary D8V, and a non-inflationary I8V response. In our project utilising the Ad-lacZ model we found that non-hematopoietic cells like fibroblastic reticular cells (FRC) and lymphoid endothelial cells (LEC) in secondary lymphoid tissues as well as liver sinusoid endothelial cells (LSEC) in the liver can be infected by Ad both in vitro and in vivo. Ad-lacZ infected FRCs and LECs were able to activate CD8+ T cells recognising inflating D8V epitope, but not CD8+ T cells specific for I8V epitope supporting the hypothesis that these cell-types might be involved in the maintenance of memory inflation. Furthermore, we designed modified Ad-LacZ constructs enable to switch on/off lacZ expression specifically in particular infected cell-types. Analyses using these modified Ad-LacZ constructs are being used to define the non-hematopoietic cell population critical for driving memory inflation. Thus, the results of our project contribute in understanding the mechanisms of memory inflation and its role in immune protection against viruses and might have important implications well beyond CMV persistence, including the development of new vaccines.