Highly Protective In Vivo Function of Cytomegalovirus IE1 Epitope-Specific Memory CD8 T Cells Purified by T-Cell Receptor-Based Cell Sorting

Abstract

Reconstitution of antiviral CD8 T cells is essential for controlling cytomegalovirus (CMV) infectionThe L d -restricted immediate-early 1 (IE1) peptide 168-YPHFMPTNL-176 of murine cytomegalovirus (mCMV) was the first antigenic peptide to be identified for a herpesvirus (50). The IE1 protein derived from open reading frame (ORF) m123, an intranuclear phosphoprotein which exists in molecular species of 89 and 76 kDa (32), is expressed in the IE phase of viral gene expression and performs regulatory and transactivating functions (12,31,39). It is encoded in transcription unit ie1/3 of which mRNAs specifying proteins IE1 (encoded by exons 2, 3, and 4) and IE3 (encoded by exons 2, 3, and 5) are generated by differential splicing (31, 39). The IE1 protein is processed to yield peptide 168-YPHFMPTNL-176 and an Nterminally elongated precursor 166-DMYPHFMPTNL-176 by the constitutive proteasome and, more efficiently, by the immunoproteasome, with only the precursor being translocated into the lumen of the endoplasmic reticulum for major histocompatibility complex class I (MHC-I) loading (36). N-terminal trimming finally leads to the IE1 peptide presented by the MHC-I molecule L d (reviewed in reference 45). Based on the frequency of IE1 epitope-specific CD8 T cells primed during acute infection and on the establishment of long-term IE1-specific memory, the IE1 peptide was classified as one of just two immunodominant MHC-I-restricted antigenic peptides in the H-2 d haplotype (25). Owing to MHC polymorphism, it is evident that immunodominance of peptides and the proteins from which they are derived cannot be extrapolated to other haplotypes in the same animal species. This is all the more true for extrapolation from mCMV to antigenic peptides of human cytomegalovirus (hCMV) presented by HLA molecules. Thus, although an early report by Borysiewicz et al. (4) had indicated the CD8 T-cell immunogenicity of the hCMV IE1 ortholog, the predictive value of the BALB/c mouse model in terms of the role of IE proteins in immunity to CMVs has been debated for a long time, until more recently the IE1 immunogenicity in humans was revisited with unbiased new methodology (10,14,33,34). Most intriguingly, in a comprehensive pangenomic search for antigenic ORFs of hCMV by using overlapping peptides and by covering all major HLA molecules present in the human population, Louis Picker and colleagues identified ORF UL123 encoding the IE1 protein as one of the top three antigen-encoding ORFs of hCMV that are most frequently detected by HLA class I-restricted human CD8 T cells (L. Picker, "T cell recognition of hCMV in natural human infection: pan-genome analysis of immunogenic open reading frames," Instituto Juan March de Estudios e Investigaciones workshop "Immunodominance: the key to understanding and manipulating CD8 ϩ T cell responses

Epitope-specific in vivo protection against cytomegalovirus disease by CD8 T cells in the murine model of preemptive immunotherapy

“…In this work we have asked the question if the protective antiviral effect of CD8 T cells in the preemptive therapy of CMV infection is strictly epitope-specific, involving the recognition of MHC class-I-presented antigenic peptide by [1]. Asterisks mark the individual mice used for the liver histology shown in Fig.…”

“…1a, bottom). It should be noted that all cells also still expressed the co-receptor molecule CD8 (data not shown) [1], which is important for the avidity of target cell recognition.…”

“…Notably, in a preemptive therapy regimen tested in the BALB/c mouse model-a regimen that involves HSCT and adoptive T cell transfer on the day of murine CMV (mCMV) infection of immunocompromised recipients-as few as 400 IE1 epitope-specific, T cell receptor (TCR)-sorted memory CD8 T cells (CD8-T M ) derived from latently infected and thus CMV-immune donors inhibited the infection of the recipients' spleen by 3 log 10 infectious units compared to a ''no therapy'' control group. Moreover, 10 4 of these cells proved to be curative in that they completely prevented viral histopathology and organ disease with no detectable side effect of immunopathology [1] (see also the accompanying review article by Holtappels et al …”

“…Immunotherapy by adoptive transfer of donor-derived CD8 T cells is a promising option to avoid cytomegalovirus disease in immunocompromised recipients of hematopoietic stem cell transplantation (HSCT), both in the murine model [1,2] and upon clinical application [3,4] (see the accompanying review article by Holtappels et al in this issue of MMI). Notably, in a preemptive therapy regimen tested in the BALB/c mouse model-a regimen that involves HSCT and adoptive T cell transfer on the day of murine CMV (mCMV) infection of immunocompromised recipients-as few as 400 IE1 epitope-specific, T cell receptor (TCR)-sorted memory CD8 T cells (CD8-T M ) derived from latently infected and thus CMV-immune donors inhibited the infection of the recipients' spleen by 3 log 10 infectious units compared to a ''no therapy'' control group.…”

Exogenous introduction of an immunodominant peptide from the non-structural IE1 protein of human cytomegalovirus into the MHC class I presentation pathway by recombinant dense bodies

“…Although pp65 by itself appears to be an attractive antigen for the design of a vaccine, other HCMV proteins may also be important and should thus be considered (Reddehase, 2002). One of these, as far as the CTL response is concerned, is the regulatory immediate-early 1 protein (IE1) (Borysiewicz et al, 1988;Bunde et al, 2005;Kern et al, 1999;Lacey et al, 2006;Pahl-Seibert et al, 2005;Simon et al, 2006). However, IE1 is not contained in viral particles.…”