Releasing the concept of HLA-allele specific peptide anchors in viral infections: A non-canonical naturally presented human cytomegalovirus-derived HLA-A*24:02 restricted peptide drives exquisite immunogenicity

Engineered HCMV-infected APCs enable the identification of new immunodominant HLA-restricted epitopes of anti-HCMV T-cell immunity

Complications due to HCMV infection or reactivation remain a challenging clinical problem in immunocompromised patients, mainly due to insufficient or absent T-cell functionality. Knowledge of viral targets is crucial to improve monitoring of high-risk patients and optimise antiviral T-cell therapy. To expand the epitope spectrum, genetically-engineered dendritic cells (DCs) and fibroblasts were designed to secrete soluble (s)HLA-A*11:01 and infected with an HCMV mutant lacking immune evasion molecules (US2-6 + 11). More than 700 HLA-A*11:01-restricted epitopes, including more than 50 epitopes derived from a broad range of HCMV open-reading-frames (ORFs) were identified by mass spectrometry and screened for HLA-A*11:01-binding using established prediction tools. The immunogenicity of the 24 highest scoring new candidates was evaluated in vitro in healthy HLA-A*11:01+/HCMV+ donors. Thus, four subdominant epitopes and one immunodominant epitope, derived from the anti-apoptotic protein UL36 and ORFL101C (A11SAL), were identified. Their HLA-A*11:01 complex stability was verified in vitro. In depth analyses revealed highly proliferative and cytotoxic memory T-cell responses against A11SAL, with T-cell responses comparable to the immunodominant HLA-A*02:01-restricted HCMVpp65NLV epitope. A11SAL-specific T cells were also detectable in vivo in immunosuppressed transplant patients and shown to be effective in an in vitro HCMV-infection model, suggesting their crucial role in inhibiting viral replication and improvement of patient's outcome. The developed in vitro pipeline is the first to utilise genetically-engineered DCs to identify naturally presented immunodominant HCMV-derived epitopes. It therefore offers advantages over in silico predictions, is transferable to other HLA alleles, and will significantly expand the repertoire of viral targets to improve therapeutic options.

Battle between Host Immune Cellular Responses and HCMV Immune Evasion

Human cytomegalovirus (HCMV) is ubiquitously prevalent. HCMV infection is typically asymptomatic and controlled by the immune system in healthy individuals, yet HCMV can be severely pathogenic for the fetus during pregnancy and in immunocompromised persons, such as transplant recipients or HIV infected patients. HCMV has co-evolved with the hosts, developed strategies to hide from immune effector cells and to successfully survive in the human organism. One strategy for evading or delaying the immune response is maintenance of the viral genome to establish the phase of latency. Furthermore, HCMV immune evasion involves the downregulation of human leukocyte antigens (HLA)-Ia molecules to hide infected cells from T-cell recognition. HCMV expresses several proteins that are described for downregulation of the HLA class I pathway via various mechanisms. Here, we review the wide range of immune evasion mechanisms of HCMV. Understanding the mechanisms of HCMV immune evasion will contribute to the development of new customized therapeutic strategies against the virus.

Releasing the concept of HLA-allele specific peptide anchors in viral infections: A non-canonical naturally presented human cytomegalovirus-derived HLA-A*24:02 restricted peptide drives exquisite immunogenicity

T‐cell receptors possess the unique ability to survey and respond to their permanently modified ligands, self HLA‐I molecules bound to non‐self peptides of various origin. This highly specific immune function is impaired following hematopoietic stem cell transplantation (HSCT) for a timespan of several months needed for the maturation of T‐cells. Especially, the progression of HCMV disease in immunocompromised patients induces life‐threatening situations. Therefore, the need for a new immune system that delivers vital and potent CD8+ T‐cells carrying TCRs that recognize even one human cytomegalovirus (HCMV) peptide/HLA molecule and clear the viral infection long term becomes obvious. The transcription and translation of HCMV proteins in the lytic cycle is a precisely regulated cascade of processes, therefore, it is a highly sensitive challenge to adjust the exact time point of HCMV‐peptide recruitment over self‐peptides. We utilized soluble HLA technology in HCMV‐infected fibroblasts and sequenced naturally sHLA‐A*24:02 presented HCMV‐derived peptides. One peptide of 14 AAs length derived from the IE2 antigen induced the strongest T‐cell responses; this peptide can be detected with a low ranking score in general peptide prediction databanks. These results highlight the need for elaborate and HLA‐allele specific peptide selection.