Processing of Two Latent Membrane Protein 1 MHC Class I Epitopes Requires Tripeptidyl Peptidase II Involvement

Abstract

The EBV Ag latent membrane protein 1 (LMP1) has been described as a potential target for T cell immunotherapy in EBV-related malignancies. However, only a few CD8+ T cell epitopes are known, and the benefit of LMP1-specific T cell immunotherapy has not yet been proven. In this work, we studied the processing of the two LMP1 HLA-A02-restricted epitopes, YLLEMLRWL and YLQQNWWTL. We found that target cells endogenously expressing the native LMP1 are not recognized by CTLs specific for these epitopes because the N-terminal part of LMP1 limits the efficiency of epitope generation. We further observed that the proteasome is not required for the generation of both epitopes and that the YLLEMLRWL epitope seems to be destroyed by the proteasome, because blocking of proteasomal activities enhanced specific CTL activation. Activation of LMP1-specific CTLs could be significantly reduced after inhibition of the tripeptidyl peptidase II, suggesting a role for this peptidase in the processing of both epitopes. Taken together, our results demonstrate that the MHC class I-restricted LMP1 epitopes studied in this work are two of very few epitopes known to date to be processed proteasome independently by tripeptidyl peptidase II.

The Efficiency of Human Cytomegalovirus pp65495–503 CD8+ T Cell Epitope Generation Is Determined by the Balanced Activities of Cytosolic and Endoplasmic Reticulum-Resident Peptidases

“…Our results indicate that similar to LAP, TPPII also negatively affects pp65 [495][496][497][498][499][500][501][502][503] epitope generation as demonstrated by enhanced pp65 epitope presentation after TPPII knockdown. In contrast, previous observations by Diekmann et al (30) revealed no effect of TPPII on pp65 processing in EBV-transformed B LCLs. An explanation for the observed discrepancy might be the analysis of different cell lines since LCLs primarily contain immunoproteasomes, thereby providing enhanced amounts of proteasomal cleavage products that may compensate for the negative effects of TPPII (see also Fig.…”

“…1). Overall, the role of TPPII in Ag processing is discussed controversially, indicating limitation of the peptide pool on the one hand (31) and epitope enhancing effects on the other hand (30,(32)(33)(34).…”

Generation of a multipathogen-specific T-cell product for adoptive immunotherapy based on activation-dependent expression of CD154

“…24 In brief, 5 ϫ 10 5 partially matched LCLs pulsed with 0.5 g/mL of the AdV hexon protein peptide pool, 0.5 g/mL of the EBV LMP2 peptide pool, or mismatched or CMV pp65-transduced LCLs were used as target cells and pulsed with 100 Ci Na 2 …”

EBV-induced post transplant lymphoproliferative disorders: a persisting challenge in allogeneic hematopoetic SCT

“…19 In the latency period following primary EBV infection, these proteins are exposed to the immune system initiating a T-cell-based immune response later having a crucial role in immunosurveillance of the virus. Many of these cytotoxic T-cell responses target EBNA-3 protein 16 or LMP-2 protein 20 representing potential targets for cellular-based therapies. A key feature of EBV is its potency to induce malignancy in infected B cells.…”