Detection of an Immunogenic HERV-E Envelope with Selective Expression in Clear Cell Kidney Cancer

Abstract

VHL-deficient clear cell renal cell carcinomas (ccRCC), the most common form of kidney cancer, express transcripts derived from the novel human endogenous retrovirus HERV-E (named CT-RCC HERV-E). In this study, we define a transcript encoding the entire envelope gene of HERV-E as expressed selectively in ccRCC tumors, as distinct from normal kidney tissues or other tumor types. Sequence analysis of this envelope transcript revealed long open reading frames encoding putative surface and transmembrane envelope proteins. Retroviral envelopes are known to be capable of eliciting immunity in humans. Accordingly, we found that HLA-A*0201-restricted peptides predicted to be products of the CT-RCC HERV-E envelope transcript-stimulated CD8(+) T cells, which could recognize HLA-A*0201-positive HERV-E-expressing kidney tumor cells. Overall, our results offer evidence of unique HERV-E envelope peptides presented on the surface of ccRCC cells, offering potentially useful tumor-restricted targets for T-cell-based immunotherapy of kidney cancer. Cancer Res; 76(8); 2177-85. ©2016 AACR.

Conflict of interest statement

No potential conflicts of interest were disclosed.

©2016 American Association for Cancer Research.

Figures

Figure 1

Expression of CT-RCC HERV-E envelope transcripts in different cancer cell lines. A, RT-PCR showing expression of three CT-RCC HERV-E transcripts including the Env in the majority of ccRCC cell lines. B, RT-PCR showing lack of expression of the CT-RCC-Env in multiple cancer cell lines other than ccRCC. C, Northern blot analysis of HERV-E env mRNA expression in ccRCC cell lines using a CT-RCC-Env-specific probe. An approximately 3 Kb band was identified in three ccRCC cell lines that were positive for env expression by RT-PCR (ccRCC lines # 2, 4, and 10) but not in three other ccRCC cell lines (ccRCC lines # 5, 6, and 8) that did not express the CT-RCC HERV-E env by RT-PCR. M, RNA marker.

Figure 2

Schematic representation of CT-RCC HERV-E provirus and its three known transcripts. A, A shared 375 bp common region originating from the 5’LTR is spliced into three unique regions of the HERV-E genome. Location of splice donor (SD) and splice acceptor (SA1 and SA2) sites are shown. B, Amino acid sequences predicted to be translated from the common region and envelope ORFs. The ITAM motif is bolded. Motifs RBD, PRR, and CXXC shown in their respective order are underlined. Stop codons are indicated by asterisks (*). SU, the surface protein. TM, the transmembrane protein. CR, common region.

Figure 3

CT-RCC HERV-E envelope derived peptides stimulate peptide specific CD8+ T cells that recognize HERV-E expressing ccRCC cells. Flow cytometry data are shown for CTL bulk cultures stimulated two times with the HERV-E-env peptides: A, CR1, B, SU1, and C, TM1. Axis X, numeration of healthy donors. Axis γ, the percentage of IFNγ positive CD8+ T cells following pulsing with control peptide MART-1 (green), pulsing with corresponding HERV-E env-derived peptide (blue), or after co-culturing with HERV-E+/HLA-A*0201- negative ccRCC line (grey), HLA-A*0201+/HERV-E-negative ccRCC line (black), and HLA-A*0201+/HERV-E+ ccRCC line (red). Yellow bars show the percentage of IFNγ positive CD8+ T cells alone.