Noncytotoxic Lytic Granule–Mediated CD8 ⁺ T Cell Inhibition of HSV-1 Reactivation from Neuronal Latency

Abstract

Reactivation of herpes simplex virus type 1 from neuronal latency is a common and potentially devastating cause of disease worldwide. CD8 + T cells can completely inhibit HSV reactivation in mice, with IFN-γ affording a portion of this protection. Here, we found that CD8 + T cell lytic granules are also required for the maintenance of neuronal latency both in vivo and in ex vivo ganglia cultures, and that their directed release to the junction with neurons in latently infected ganglia did not induce neuronal apoptosis. We describe a non-lethal mechanism of viral inactivation in which the lytic granule component, granzyme B, degrades the herpes simplex virus type 1 immediate early protein, ICP4, which is essential for further viral gene expression.Several lines of evidence support a role for CD8 + T cells in controlling herpes simplex virus type 1 (HSV-1) latency. CD8 + T cells, many expressing granzyme B (GrB), are found juxtaposed to HSV-1 latently infected sensory neurons of both humans (1-4) and mice (5-8). In C57BL/6 mice, CD8 + T cells specific for the immunodominant HSV-1 glycoprotein B 498-505 epitope (gB-CD8) polarize their T cell receptor (TCR) to junctions with neurons in situ forming apparent immunologic synapses (9). Murine gB-CD8 can block HSV-1 reactivation from latency in vivo and in ex vivo ganglia cultures in an MHC-dependent manner (9-11). Because HSV-1 establishes latency solely within ganglionic neurons (12,13), we hypothesize that some latently infected neurons directly present viral antigens to HSV-specific * This manuscript has been accepted for publication in Science. This version has not undergone final editing. Please refer to the complete version of record at http://www.sciencemag.org/. The manuscript may not be reproduced or used in any manner that does not fall within the fair use provisions of the Copyright Act without the prior, written permission of AAAS. Published version available at

CXCL10/CXCR3-Dependent Mobilization of Herpes Simplex Virus-Specific CD8 + T EM and CD8 + T RM Cells within Infected Tissues Allows Efficient Protection against Recurrent Herpesvirus Infection and Disease

“…Results from many mouse models of herpesvirus infection and immunity have yielded tremendous insights into the protective and immunopathological mechanisms during primary acute infection (46)(47)(48)(49)(50)(51)(52). However, the extrapolation of results from mouse primary herpetic disease to human recurrent herpetic diseases, such as recurrent herpetic stromal keratitis (rHSK), is yet to be proven.…”

Granzyme M targets host cell hnRNP K that is essential for human cytomegalovirus replication

“…This model is compatible with the recent finding that antigen-specific CD8 þ T cells recognize HSV-1 latently infected ganglion cells, release GrB towards these cells, and inhibit HSV-1 reactivation without inducing cell death. 13 Materials and Methods Subjects. Two healthy HCMV-seropositive volunteers (HLA-B7 þ , HLA-B8 þ , and/or HLA-A2 þ ) and two HCMV-seronegative renal transplant recipients who received a kidney from an HCMV-seropositive donor (HLA-B8 þ and HLA-A2 þ ) were included in this study.…”

“…11 Although all five human granzymes are able to induce cell death, evidence is emerging that granzymes also use noncytotoxic strategies to control virus replication. [12][13][14][15][16][17] In mice, GrM has been shown to be important for murine cytomegalovirus (MCMV) clearance. 18 We have recently discovered that human GrM can efficiently inhibit HCMV replication in vitro in the absence of host cell death.…”

Granzymes in cancer and immunity

“…In addition, both granzyme H and granzyme B have been shown to limit viral replication by directly targeting viral proteins for proteolytic degradation, which suggests a noncytotoxic role for granzymes in protecting against infection. [88][89][90][91] Thus, a new paradigm for granzyme action is beginning to emerge in which granzymes released or actively secreted into the extracellular space may promote cytokine activation/ secretion, either directly or indirectly, thereby amplifying immune responses to infected or transformed cells (Figure 1). …”