Human CD8 + T Cell Responses to EBV EBNA1: HLA Class I Presentation of the (Gly-Ala)–Containing Protein Requires Exogenous Processing

Abstract

Epstein-Barr virus (EBV)-induced cytotoxic T lymphocyte (CTL) responses have been detected against many EBV antigens but not the nuclear antigen EBNA1; this has been attributed to the presence of a glycine-alanine repeat (GAr) domain in the protein. Here we describe the isolation of human CD8+ CTL clones recognizing EBNA1-specific peptides in the context of HLA-B35.01 and HLA-A2.03. Using these clones, we show that full-length EBNA1 is not presented when expressed endogenously in target cells, whereas the GAr-deleted form is presented efficiently. However, when supplied as an exogenous antigen, the full-length protein can be presented on HLA class I molecules by a TAP-independent pathway; this may explain how EBNA1-specific CTLs are primed in vivo.

Mini‐review: Regulation of cytotoxic T lymphocyte responses by dendritic cells: peaceful coexistence of cross‐priming and direct priming?

“…Similar observations have been made in many different viral infections, including vaccinia virus [5, 77,78], influenza virus [78] and Epstein-Barr virus (EBV) [79,80] infection. In the case of EBV-induced Burkitt's lymphoma, a glycine-alanine repeat domain in the EBNA1 protein, required to establish viral latency, completely blocks proteasome-dependent MHC class I processing in EBNA1-expressing cells.…”

“…In the case of EBV-induced Burkitt's lymphoma, a glycine-alanine repeat domain in the EBNA1 protein, required to establish viral latency, completely blocks proteasome-dependent MHC class I processing in EBNA1-expressing cells. Nonetheless EBNA1-specific CTL can be readily detected in EBV-infected individuals [79,80]. This can best be explained by crosspresentation and cross-priming.…”

“…This can best be explained by crosspresentation and cross-priming. Indeed DC readily process and present exogenously offered EBNA1 protein in MHC class I molecules [79,80].…”

Creation of immune ‘stealth’ genes for gene therapy through fusion with the Gly-Ala repeat of EBNA-1

“…45 The observation that the GAr does not inhibit priming of CTL is important and consistent with reports describing the presence of EBNA-1-specific CTL in EBV-seropositive individuals. [31][32][33][34][35][36] As antigen presentation by professional APC, most likely DC, is crucial to the initiation of virusspecific CTL responses, the presence of EBNA-1-specific CTL in EBV-positive donors suggests that antigen processing for MHC class I by specialized APC is not hampered by the GAr. In case EBV-specific CTL are induced through the direct route following EBV infection of DC, these observations would indicate that antigen presentation in DC differs intrinsically from presentation by 'nonprofessional' APC.…”

“…Although EBNA-1-specific CTL have been described in infectious mononucleosis patients and healthy carriers, they cannot recognize EBV-infected cells. [31][32][33][34][35][36] The failure to recognize endogenously expressed EBNA-1 has been attributed to the glycine-alanine repeat (GAr) domain in the EBNA-1 sequence that protects EBNA-1 from proteasomal degradation and subsequent presentation in the context of MHC class I. 37,38 This successful immune-evasion strategy points to the unique opportunity to hide cells expressing transgenes from CTLmediated target-cell destruction by incorporation of the GAr sequence into the transgene.…”