Utilizing the transporter associated with antigen processing (TAP) to enhance immune responsiveness to cancers and viruses

by Alimonti, Judie Barbara

For cytotoxic T lymphocytes (CTL) to recognize infecteci, mutated, or cancerous cells, an antigenic peptide mut be presented on the ce11 surface by the major histocompatibility complex 1 (MHC 1). The majonty of peptides bound to MHC 1 anse from the cytosolic degradation of proteins. These peptides are translocated by transporters associated with antigen processing (TAP), into the endoplasmic reticulum (ER) where they bind with MHC class 1 before proceeding to the ce11 surface for recognition by CD8+ T lymphocytes. In TAP deficient cell lines the MHC class 1 surface expression is 1ow resulting in poor recognition by T cells. Therefore TAP is important in the loading of MHC class I with peptide, and this thesis examines TAP's role in antigen processing and presentation ana its eîrecr on CTI mrxiiaied kiiiing. Three aspects are considered: 1) the use of TAP as an adjuvant in vaccines, 2) the involvement of TAP in secreting antigen which sensitizes cells to CTL killing, and 3) restoring TAP in TAP deficient cancer cells to irnprove immune recognition and destruction of the tumour. CTL play an essential role in eliminating viral pathogens, and adjuvants can promote the induction of CD8+ CTL when injected dong with antigenic peptide. The first study demonstrated a 2 4.8 X increase in the frequency of specific CTL when TAP was included in a vaccine contauiing a cytotoxic peptide. Thus TAP can act as an adjuvant to enhance an immune response to a viral cytotoxic epitope. TAP is the major transporter of peptides for MHC class 1 assembly in the ER lumen. The second section in this study shows that there is an aitemative fate for ER lumenal peptides other than binding to MHC class 1. The peptides cm be actively secreted from the ce11 through the constitutive secretory pathway in a TAP dependent rnanner. Furthennore, the secreted peptides can sensitize surrounding cells to be recognized by CTL. This demonsirates that CTL recognition of neighbouring uninfecteci cells presenting viral antigen involves TAP. Some cancer cells, like CMT.64, escape CTL rnediated destruction due to low surface concentration of MHC class 1. CMT.64 cells transfected with TAP restores viral antigen presentation to CTL in vitro. The final section of this thesis explores the role of TAP in restoring antigen presentation and immune recognition of cancer cells Nt vivo. Although TAP functions as a heterodimer (TAPI and 2), re-expression of TAP1 in CMT.64 improved survival of tumour bearing anirnals drarnatically. Furthemore, a Vaccinia Virus containing *I'WI could be usd as a form of cancer Uierapy in CiViT.64 burdened mice. These findings argue that T ce11 recognition of the tumours increases with the addition of TAP. Collectively, the addition of TAP to either wiId type cells, and TAP defrcient cells increased imrnunogenicity. This supports a role for TAI? in the CTL mediateci recognition of both vhses and cancers, and the use of TAP in the development of vaccines, or cancer therapeutics.