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

Reconstitution of antiviral CD8 T cells is essential for controlling cytomegalovirus (CMV) infection after bone marrow transplantation. Accordingly, polyclonal CD8 T cells derived from BALB/c mice infected with murine CMV protect immunocompromised adoptive transfer recipients against CMV disease. The protective population comprises CD8 T cells with T-cell receptors (TCRs) specific for defined and for as-yet-unknown viral epitopes, as well as a majority of nonprotective cells with unrelated specificities. Defined epitopes include IE1/m123 and m164, which are immunodominant in terms of the magnitude of the CD8 T-cell response, and a panel of subordinate epitopes (m04, m18, M45, M83, and M84). While cytolytic T-lymphocyte lines (CTLLs) were shown to be protective regardless of the immunodominance of the respective epitope, the individual contributions of in vivo resident epitope-specific CD8 T cells to the antiviral control awaited investigation. The IE1 peptide 168-YPHFMPTNL-176 is generated from the immediate-early protein 1 (IE1) (pp89/76) of murine CMV and is presented by the major histocompatibility complex class I (MHC-I) molecule L(d). To quantitate its contribution to the protective potential of a CD8-T memory (CD8-T(M)) cell population, IE1-TCR(+) and IE1-TCR(−) CD8-T(M) cells were purified by epitope-specific cell sorting with IE1 peptide-loaded MHC-immunoglobulin G1 dimers as ligands of cognate TCRs. Of relevance for clinical approaches to an adoptive cellular immunotherapy, sorted IE1 epitope-specific CD8-T(M) cells were found to be exceedingly protective upon adoptive transfer. Compared with CTLLs specific for the same epitope and of comparable avidity and TCR β-chain variable region (Vβ)-defined polyclonality, sorted CD8-T(M) cells proved to be superior by more than 2 orders of magnitude

The Immune Evasion Paradox: Immunoevasins of Murine Cytomegalovirus Enhance Priming of CD8 T Cells by Preventing Negative Feedback Regulation▿

Cytomegaloviruses express glycoproteins that interfere with antigen presentation to CD8 T cells. Although the molecular modes of action of these “immunoevasins” differ between cytomegalovirus species, the convergent biological outcome is an inhibition of the recognition of infected cells. In murine cytomegalovirus, m152/gp40 retains peptide-loaded major histocompatibility complex class I molecules in a cis-Golgi compartment, m06/gp48 mediates their vesicular sorting for lysosomal degradation, and m04/gp34, although not an immunoevasin in its own right, appears to assist in the concerted action of all three molecules. Using the Ld-restricted IE1 epitope YPHFMPTNL in the BALB/c mouse model as a paradigm, we provide here an explanation for the paradox that immunoevasins enhance CD8 T-cell priming although they inhibit peptide presentation in infected cells. Adaptive immune responses are initiated in the regional lymph node (RLN) draining the site of pathogen exposure. In particular for antigens that are not virion components, the magnitude of viral gene expression providing the antigens is likely a critical parameter in priming efficacy. We have therefore focused on the events in the RLN and have related priming to intranodal viral gene expression. We show that immunoevasins enhance priming by downmodulating an early CD8 T-cell-mediated “negative feedback” control of the infection in the cortical region of the RLN, thus supporting the model that immunoevasins improve antigen supply for indirect priming by uninfected antigen-presenting cells. As an important consequence, these findings predict that deletion of immunoevasin genes in a replicative vaccine virus is not a favorable option but may, rather, be counterproductive

Subdominant CD8 T-Cell Epitopes Account for Protection against Cytomegalovirus Independent of Immunodomination▿ †

Cytomegalovirus (CMV) infection continues to be a complication in recipients of hematopoietic stem cell transplantation (HSCT). Preexisting donor immunity is recognized as a favorable prognostic factor for the reconstitution of protective antiviral immunity mediated primarily by CD8 T cells. Furthermore, adoptive transfer of CMV-specific memory CD8 T (CD8-TM) cells is a therapeutic option for preventing CMV disease in HSCT recipients. Given the different CMV infection histories of donor and recipient, a problem may arise from an antigenic mismatch between the CMV variant that has primed donor immunity and the CMV variant acquired by the recipient. Here, we have used the BALB/c mouse model of CMV infection in the immunocompromised host to evaluate the importance of donor-recipient CMV matching in immundominant epitopes (IDEs). For this, we generated the murine CMV (mCMV) recombinant virus mCMV-ΔIDE, in which the two memory repertoire IDEs, the IE1-derived peptide 168-YPHFMPTNL-176 presented by the major histocompatibility complex class I (MHC-I) molecule Ld and the m164-derived peptide 257-AGPPRYSRI-265 presented by the MHC-I molecule Dd, are both functionally deleted. Upon adoptive transfer, polyclonal donor CD8-TM cells primed by mCMV-ΔIDE and the corresponding revertant virus mCMV-revΔIDE controlled infection of immunocompromised recipients with comparable efficacy and regardless of whether or not IDEs were presented in the recipients. Importantly, CD8-TM cells primed under conditions of immunodomination by IDEs protected recipients in which IDEs were absent. This shows that protection does not depend on compensatory expansion of non-IDE-specific CD8-TM cells liberated from immunodomination by the deletion of IDEs. We conclude that protection is, rather, based on the collective antiviral potential of non-IDEs independent of the presence or absence of IDE-mediated immunodomination

Biodistribution and PET Imaging of Labeled Bispecific T Cell-Engaging Antibody Targeting EpCAM

AMG 110, a bispecific T cell engager (BITE) antibody construct, induces T cell-mediated cancer cell death by cross-linking epithelial cell adhesion molecule (EpCAM) on tumor cells with a cluster of differentiation 3 epsilon (CD3 epsilon) on T cells. We labeled AMG 110 with Zr-89 or near infrared fluorescent dye (IRDye) 800CW to study its tumor targeting and tissue distribution. Methods: Biodistribution and tumor uptake of Zr-89-AMG 110 was studied up to 6 d after intravenous administration to nude BALB/c mice bearing high EpCAM-expressing HT-29 colorectal cancer xenografts. Tumor uptake of Zr-89-AMG 110 was compared with uptake in head and neck squamous cell cancer FaDu (intermediate EpCAM) and promyelocytic leukemia HL60 (EpCAM-negative) xenografts. Intratumoral distribution in HT-29 tumors was studied using 800CW-AMG 110. Results: Tumor uptake of Zr-89-AMG 110 can be clearly visualized using small-animal PET imaging up to 72 h after injection. The highest tumor uptake of Zr-89-AMG 110 at the 40-mu g dose level was observed at 6 and 24 h (respectively, 5.35 +/- 0.22 and 5.30 +/- 0.20 percentage injected dose per gram; n = 3 and 4). Tumor uptake of Zr-89-AMG 110 was EpCAM-specific and correlated with EpCAM expression. 800CW-AMG 110 accumulated at the tumor cell surface in viable EpCAM-expressing tumor tissue. Conclusion: PET and fluorescent imaging provided real-time information about AMG 110 distribution and tumor uptake in vivo. Our data support using Zr-89 and IRDye 800CW to evaluate tumor and tissue uptake kinetics of bispecific T cell engager antibody constructs in preclinical and clinical settings