A viral inhibitor of peptide transporters for antigen presentation

Abstract

Cytotoxic T lymphocytes lyse target cells after T-cell-receptor-mediated recognition of class I major histocompatibility complex molecules presenting peptides. Antigenic peptides are generated in the cytoplasm by proteasomes and translocated into the lumen of the endoplasmic reticulum (ER) by peptide transporters (TAP). Herpes simplex virus (HSV) expresses a cytoplasmic protein, ICP47, which seems to interfere with such immune surveillance by mediating retention of 'empty' class I molecules in the ER. By expressing ICP47 in HeLa cells under an inducible promoter, we show that ICP47 efficiently inhibits peptide transport across the ER membrane such that nascent class I molecules fail to acquire antigenic peptides. This inhibition was overcome by transfecting murine TAP. Further, we demonstrate that ICP47 colocalizes and physically associates with TAP within the cell. Inhibition of peptide translocation by a viral protein indicates a previously undocumented potential mechanism for viral immune evasion.

Development of herpes simplex virus replication-defective multigene vectors for combination gene therapy applications

“…17,18 The remaining IE gene, ICP47, does not affect transcription but rather has been reported to interfere with a transporter function (TAP) that is responsible for loading MHC class I molecules with antigenic peptides. [19][20][21][22] The rigid temporal cascade of viral gene expression makes the construction of replication incompetent mutants straightforward. Removal of one essential IE gene prevents expression of the later genes in the gene expression cascade, resulting in a mutant incapable of producing progeny viral particles.…”

Herpes simplex virus type-1 amplicon vectors for vaccine generation in acute lymphoblastic leukemia

“…The immune evasion mechanisms of HSV are specifically targeted to antigen-presenting cells and include impairment of MHC class I molecule peptide transport by HSV ICP47 protein as well as downregulation of costimulatory molecules and reduced T-cell stimulatory capacity by HSV vhs protein. 25,26 In vaccine development for hematological malignancies utilizing herpesviral vectors for genetic modification, careful investigation of the consequences of HSV infection is warranted. This is particularly true for the development of vaccination strategies for ALL of B-cell origin, as HSV has been shown to inhibit the capacity of lymphoblastoid B cells to stimulate an antigen-specific immune response.…”

“…One of the immediate early herpesviral proteins, ICP47, is known to impair MHC/antigen complex assembly in the endoplasmatic reticulum. 26,29 In malignant B cells, significant downregulation of MHC class I molecule expression was observed in CLL following gene transfer with helper virus-dependent amplicon vectors. 5 In contrast, MHC class I expression in ALL blasts is only marginally affected by herpesviral protein expression as shown here.…”

“…26 As HSV-1 helper virusdependent but not helper virus-free amplicon vectors have been reported to downregulate MHC class I expression in CLL blasts, 5 both vectors, HSV.CD70 and BAC.CD70, were assessed in comparison at identical vector doses. Of note, in ALL blasts, even with helper virus-dependent vector HSV.CD70 only minor downregulation of MHC class I expression was observed and with helper virus-free vector BAC.CD70 MHC class I expression remained entirely unaffected ( Figure 6), suggesting that ALL cells are not sensitive to HSV-1-mediated MHC class I molecule downregulation.…”

Clinical development directions in oncolytic viral therapy

“…121 OncoVEX GM-CSF (BioVax, Worcester, MA) is a replication-competent HSV (HSV-1) that has been modified with several novel genetic enhancements that make it a potent oncolytic and immunogenic vector. [126][127][128][129][130] The vector contains the coding sequence for human GM-CSF under the control of the human cytomegalovirus immediate early promoter, which has been shown to enhance the immune response. 131 As a safety factor, the gene for TK remains intact preserving sensitivity to clinically effective antiviral agents.…”