Listeria monocytogenes is a bacterial pathogen that enters the cytosol of infected cells. Secreted bacterial proteins are rapidly degraded into peptides in the host cell cytosol by proteasomes, and peptides are transported into the endoplasmic reticulum by TAP, where they are bound by newly synthesized MHC class I molecules.
We have identified several peptides that are bound by the murine H2-Kd molecule and presented to CD8 T cells, and we have used these peptides to characterize in vivo T cell responses to bacterial infection. Several interesting findings from these studies are:
- the magnitude of the T cell response to a peptide does not correlate with peptide prevalence in infected cells;
- the magnitude of a T cell response can be dramatically influenced by the naïve repertoire of T cells present in the uninfected mouse; and
- the kinetics of T cell expansion are not influenced by the severity of duration of bacterial infection.
Current projects in the laboratory focus on understanding the factors that determine the duration and extent of T cell expansion during infection; characterizing innate inflammatory responses to bacterial infection and correlating these with CD8 T cell responses; investigating the roles of chemokines and chemokine receptors in immunity to Listeria monocytogenes infection; and optimizing the adoptive transfer of CD8 T cell-mediated immunity to naïve mice.
To perform these studies, we have generated T cell receptor transgenic mice that are specific for 2 different Listeria monocytogenes-derived H2-Kd restricted epitopes. Our approach is to transfer naïve, Listeria monocytogenes-specific CD8 T cells into recipient mice that lack genes involved in the innate or adaptive immune responses, and characterize their proliferation, trafficking, and development into memory T cells.
As a second approach, if the genetic deletion is likely to be of direct relevance to CD8 T cells, the TCR transgene is bred onto the gene knock-out strain, and mutant T cells are then transferred into normal recipient mice.
We are using this systematic approach to characterize the roles of a range of different chemokine and pattern recognition receptors on the immune response to Listeria monocytogenes infection. Transfer of pathogen-specific T lymphocytes is being used increasingly in clinical settings to help immunocompromised patients fight viral infections. We are using the Listeria monocytogenes model to study and optimize the transfer of immunity from immune mice to naïve mice.
Although protective immunity to Listeria monocytogenes infection is mediated predominantly by CD8 T cells, it has been difficult to adoptively transfer immune CD8 T cells into naïve recipient mice and achieve a high degree of immunity. We are using a variety of methods to optimize in vitro T cell growth and to improve upon the ability of adoptively transferred T cells to confer protective immunity.
Our studies are showing that different combinations of cytokines, different durations of stimulation, and different doses of antigen can dramatically influence the ability of T cells to eliminate virulent bacteria upon transfer into naïve recipients.
