Title: T cell responses induced by bacterial toxin fusion proteins
Description: CD8 + T cells are essential for protective immunity against many intracellular pathogens; therefore stimulation of this population of cells is an important goal of vaccination. Our laboratory has previously shown that a detoxified derivative of anthrax lethal toxin (LT) can deliver heterologous CD8 + T cell epitopes to the cytosolic MHC class I processing and presentation pathway of host cells and that immunization of mice with these LT-antigen fusion proteins leads to the stimulation of antigen-specific CD8 + T cells. I have expanded upon these early studies to gain a more thorough understanding of the types of effector and memory T cells stimulated by toxin-based delivery systems, and how properties of the immunization affect the quality and quantity of the ensuing T cell response. I demonstrated that memory CD8 + T cells stimulated by the LT-based system produce IFNγ, display in vivo cytotoxic activity, and are a mixture of effector memory (CD62L low ) and central memory (CD62L high ) T cells. Their transition to memory appears to be quite rapid based on the analysis of the phenotypic marker CD127 and the effectiveness of an early booster immunization (which also preferentially expanded the CD62L low pool).

I also showed that a single LT fusion protein could co-deliver antigen to both the MHC class II and MHC class I pathways, resulting in the induction of antigen-specific CD4 + and antigen-specific CD8 + T cells in the same mouse. Furthermore, I generated another toxin-based delivery system using detoxified diphtheria toxin (DT). In combination with transgenic mice that express the DT receptor specifically in dendritic cells (DC), this system allowed for targeted delivery of CD8 + T cell antigens to DC. I demonstrated that DT-mediated delivery of antigen to DC is sufficient to stimulate antigen-specific CD8 + T cells, and induces a more robust T cell response than widespread delivery of the same antigen by the LT-based system. Cumulatively, these results further our understanding of how CD8 + and CD4 + T cells respond to toxin-delivered antigen. Increased knowledge of the requirements for stimulating and maintaining antigen-specific T cells provides a framework for successful vaccine development against those diseases that require cellular immunity.