Efficacy of LCMV-based cancer immunotherapies is unleashed by intratumoral injections of polyI:C.

BACKGROUND: Lymphocytic choriomeningitis virus (LCMV) belongs to the Arenavirus family known for inducing strong cytotoxic T-cell responses in both mice and humans. LCMV has been engineered for the development of cancer immunotherapies, currently undergoing evaluation in phase I/II clinical trials. Initial findings have demonstrated safety and an exceptional ability to activate and expand tumor-specific T lymphocytes. Combination strategies to maximize the antitumor effectiveness of LCMV-based immunotherapies are being explored. METHODS: We assessed the antitumor therapeutic effects of intratumoral administration of polyinosinic:polycytidylic acid (poly(I:C)) and systemic vaccination using an LCMV-vector expressing non-oncogenic versions of the E6 and E7 antigens of human papillomavirus 16 (artLCMV-E7E6) in a bilateral model engrafting TC-1/A9 cells. This cell line, derived from the parental TC-1, exhibits low MHC class I expression and is highly immune-resistant. The mechanisms underlying the combination's efficacy were investigated through bulk RNA-seq, flow cytometry analyses of the tumor microenvironment, selective depletions using antibodies and clodronate liposomes, Batf3 deficient mice, and in vivo bioluminescence experiments. Finally, we assessed the antitumor effectiveness of the combination of artLCMV-E7E6 with BO-112, a GMP-grade poly(I:C) formulated in polyethyleneimine, currently under evaluation in clinical trials. RESULTS: Intratumoral injection of poly(I:C) enhanced the antitumor efficacy of artLCMV-E7E6 in both injected and non-injected tumor lesions. The combined treatment resulted in a significant delay in tumor growth and often complete eradication of several tumor lesions, leading to significantly improved survival compared with monotherapies. While intratumoral administration of poly(I:C) did not impact LCMV vector biodistribution or transgene expression, it significantly modified leucocyte infiltrates within the tumor microenvironment and amplified systemic efficacy through proinflammatory cytokines/chemokines such as CCL3, CCL5, CXCL10, TNF, IFNα, and IL12p70. Upregulation of MHC on tumor cells and a reconfiguration of the gene expression programs related to tumor vasculature, leucocyte migration, and the activation profile of tumor-infiltrating CD8+ T lymphocytes were observed. Indeed, the antitumor effect relied on the functions of CD8+ T lymphocytes and macrophages. The synergistic efficacy of the combination was further confirmed when BO-112 was included. CONCLUSION: Intratumoral injection of poly(I:C) sensitizes MHClow tumors to the antitumor effects of artLCMV-E7E6, resulting in a potent therapeutic synergy.

CD8+ T Cells Mediate Lethal Lung Pathology in the Absence of PD-L1 and Type I Interferon Signalling following LCMV Infection.

CD8+ T cells are critical to the adaptive immune response against viral pathogens. However, overwhelming antigen exposure can result in their exhaustion, characterised by reduced effector function, failure to clear virus, and the upregulation of inhibitory receptors, including programmed cell death 1 (PD-1). However, exhausted T cell responses can be "re-invigorated" by inhibiting PD-1 or the primary ligand of PD-1: PD-L1. Further, the absence of the type I interferon receptor IFNAR1 also results in T cell exhaustion and virus persistence in lymphocytic choriomeningitis virus Armstrong (LCMV-Arm)-infected mice. In this study, utilizing single- and double-knockout mice, we aimed to determine whether ablation of PD-1 could restore T cell functionality in the absence of IFNAR1 signalling in LCMV-Arm-infected mice. Surprisingly, this did not re-invigorate the T cell response and instead, it converted chronic LCMV-Arm infection into a lethal disease characterized by severe lung inflammation with an infiltration of neutrophils and T cells. Depletion of CD8+ T cells, but not neutrophils, rescued mice from lethal disease, demonstrating that IFNAR1 is required to prevent T cell exhaustion and virus persistence in LCMV-Arm infection, and in the absence of IFNAR1, PD-L1 is required for survival. This reveals an important interplay between IFNAR1 and PD-L1 with implications for therapeutics targeting these pathways.

Chronic viral infection impairs immune memory to a different pathogen.

Chronic viral infections cause T cell dysfunction in both animal models and human clinical settings, thereby affecting the ability of the host immune system to clear viral pathogens and develop proper virus-specific immune memory. However, the impact of chronic viral infections on the host's immune memory to other pathogens has not been well described. In this study, we immunized mice with recombinant Listeria monocytogenes expressing OVA (Lm-OVA) to generate immunity to Lm and allow analysis of OVA-specific memory T (Tm) cells. We then infected these mice with lymphocytic choriomeningitis virus (LCMV) strain Cl-13 which establishes a chronic infection. We found that chronically infected mice were unable to protect against Listeria re-challenge. OVA-specific Tm cells showed a progressive loss in total numbers and in their ability to produce effector cytokines in the context of chronic LCMV infection. Unlike virus-specific T cells, OVA-specific Tm cells from chronically infected mice did not up-regulate the expression of inhibitory receptors, a hallmark feature of exhaustion in virus-specific T cells. Finally, OVA-specific Tm cells failed to mount a robust recall response after bacteria re-challenge both in the chronically infected and adoptively transferred naïve hosts. These results show that previously established bacteria-specific Tm cells become functionally impaired in the setting of an unrelated bystander chronic viral infection, which may contribute to poor immunity against other pathogens in the host with chronic viral infection.

Universal recording of immune cell interactions in vivo.

Immune cells rely on transient physical interactions with other immune and non-immune populations to regulate their function1. To study these 'kiss-and-run' interactions directly in vivo, we previously developed LIPSTIC (labelling immune partnerships by SorTagging intercellular contacts)2, an approach that uses enzymatic transfer of a labelled substrate between the molecular partners CD40L and CD40 to label interacting cells. Reliance on this pathway limited the use of LIPSTIC to measuring interactions between CD4+ T helper cells and antigen-presenting cells, however. Here we report the development of a universal version of LIPSTIC (uLIPSTIC), which can record physical interactions both among immune cells and between immune and non-immune populations irrespective of the receptors and ligands involved. We show that uLIPSTIC can be used, among other things, to monitor the priming of CD8+ T cells by dendritic cells, reveal the steady-state cellular partners of regulatory T cells and identify germinal centre-resident T follicular helper cells on the basis of their ability to interact cognately with germinal centre B cells. By coupling uLIPSTIC with single-cell transcriptomics, we build a catalogue of the immune populations that physically interact with intestinal epithelial cells at the steady state and profile the evolution of the interactome of lymphocytic choriomeningitis virus-specific CD8+ T cells in multiple organs following systemic infection. Thus, uLIPSTIC provides a broadly useful technology for measuring and understanding cell-cell interactions across multiple biological systems.

High-Affinity-Mediated Viral Entry Triggers Innate Affinity Escape Resulting in Type I IFN Resistance and Impaired T Cell Immunity.

Increased receptor binding affinity may allow viruses to escape from Ab-mediated inhibition. However, how high-affinity receptor binding affects innate immune escape and T cell function is poorly understood. In this study, we used the lymphocytic choriomeningitis virus (LCMV) murine infection model system to create a mutated LCMV exhibiting higher affinity for the entry receptor α-dystroglycan (LCMV-GPH155Y). We show that high-affinity receptor binding results in increased viral entry, which is associated with type I IFN (IFN-I) resistance, whereas initial innate immune activation was not impaired during high-affinity virus infection in mice. Consequently, IFN-I resistance led to defective antiviral T cell immunity, reduced type II IFN, and prolonged viral replication in this murine model system. Taken together, we show that high-affinity receptor binding of viruses can trigger innate affinity escape including resistance to IFN-I resulting in prolonged viral replication.

Central tolerance shapes the neutralizing B cell repertoire against a persisting virus in its natural host.

Viral mimicry of host cell structures has been postulated to curtail the B cell receptor (BCR) repertoire against persisting viruses through tolerance mechanisms. This concept awaits, however, experimental testing in a setting of natural virus-host relationship. We engineered mouse models expressing a monoclonal BCR specific for the envelope glycoprotein of lymphocytic choriomeningitis virus (LCMV), a naturally persisting mouse pathogen. When the heavy chain of the LCMV-neutralizing antibody KL25 was paired with its unmutated ancestor light chain, most B cells underwent receptor editing, a behavior reminiscent of autoreactive clones. In contrast, monoclonal B cells expressing the same heavy chain in conjunction with the hypermutated KL25 light chain did not undergo receptor editing but exhibited low levels of surface IgM, suggesting that light chain hypermutation had lessened KL25 autoreactivity. Upon viral challenge, these IgMlow cells were not anergic but up-regulated IgM, participated in germinal center reactions, produced antiviral antibodies, and underwent immunoglobulin class switch as well as further affinity maturation. These studies on a persisting virus in its natural host species suggest that central tolerance mechanisms prune the protective antiviral B cell repertoire.

Draining Lymph Node Metastasis Model for Assessing the Dynamics of Antigen-Specific CD8+ T Cells During Tumorigenesis.

Tumor antigen-specific CD8+ T cells from draining lymph nodes gain an accumulating importance in mounting anti-tumor immune response during tumorigenesis. However, in many cases, cancer cells form metastatic loci in lymph nodes before further metastasizing to distant organs. To what extent the local and systematic CD8+ T cell responses were influenced by LN metastasis remains obscure. To this end, we set up a murine LN metastasis model combined with a B16F10-GP melanoma cell line expressing the surrogate neoantigen derived from lymphocytic choriomeningitis virus (LCMV), glycoprotein (GP), and P14 transgenic mice harboring T cell receptors (TCRs) specific to GP-derived peptide GP33-41 presented by the class I major histocompatibility complex (MHC) molecule H-2Db. This protocol enables the study of antigen-specific CD8+ T cell responses during LN metastasis. In this protocol, C57BL/6J mice were subcutaneously implanted with B16F10-GP cells, followed by adoptive transfer with naive P14 cells. When the subcutaneous tumor grew to approximately 5 mm in diameter, the primary tumor was excised, and B16F10-GP cells were directly injected into the tumor draining lymph node (TdLN). Then, the dynamics of CD8+ T cells were monitored during the process of LN metastasis. Collectively, this model has provided an approach to precisely investigate the antigen-specific CD8+ T cell immune responses during LN metastasis.

Single-cell RNA sequencing reveals the dynamics and heterogeneity of lymph node immune cells during acute and chronic viral infections.

Introduction: The host immune response determines the differential outcome of acute or chronic viral infections. The comprehensive comparison of lymphoid tissue immune cells at the single-cell level between acute and chronic viral infections is largely insufficient. Methods: To explore the landscape of immune responses to acute and chronic viral infections, single-cell RNA sequencing(scRNA-seq), scTCR-seq and scBCR-seq were utilized to evaluate the longitudinal dynamics and heterogeneity of lymph node CD45+ immune cells in mouse models of acute (LCMV Armstrong) and chronic (LCMV clone 13) viral infections. Results: In contrast with acute viral infection, chronic viral infection distinctly induced more robust NK cells and plasma cells at the early stage (Day 4 post-infection) and acute stage (Day 8 post-infection), respectively. Moreover, chronic viral infection exerted decreased but aberrantly activated plasmacytoid dendritic cells (pDCs) at the acute phase. Simultaneously, there were significantly increased IgA+ plasma cells (MALT B cells) but differential usage of B-cell receptors in chronic infection. In terms of T-cell responses, Gzma-high effector-like CD8+ T cells were significantly induced at the early stage in chronic infection, which showed temporally reversed gene expression throughout viral infection and the differential usage of the most dominant TCR clonotype. Chronic infection also induced more robust CD4+ T cell responses, including follicular helper T cells (Tfh) and regulatory T cells (Treg). In addition, chronic infection compromised the TCR diversity in both CD8+ and CD4+ T cells. Discussion: In conclusion, gene expression and TCR/BCR immune repertoire profiling at the single-cell level in this study provide new insights into the dynamic and differential immune responses to acute and chronic viral infections.

Lymphocytic choriomeningitis arenavirus requires cellular COPI and AP-4 complexes for efficient virion production.

Lymphocytic choriomeningitis virus (LCMV) is a bisegmented negative-sense RNA virus classified within the Arenaviridae family of the Bunyavirales order. LCMV is associated with fatal disease in immunocompromized populations, and as the prototypical arenavirus, acts as a model for the many serious human pathogens within this group. Here, we examined the dependence of LCMV multiplication on cellular trafficking components using a recombinant LCMV expressing enhanced green fluorescent protein in conjunction with a curated siRNA library. The screen revealed a requirement for subunits of both the coat protein 1 (COPI) coatomer and adapter protein 4 (AP-4) complexes. By rescuing a recombinant LCMV harboring a FLAG-tagged glycoprotein (GP-1) envelope spike (rLCMV-GP1-FLAG), we showed infection resulted in marked co-localization of individual COPI and AP-4 components with both LCMV nucleoprotein (NP) and GP-1, consistent with their involvement in viral processes. To further investigate the role of both COPI and AP-4 complexes during LCMV infection, we utilized the ARF-I inhibitor brefeldin A (BFA) that prevents complex formation. Within a single 12-h cycle of virus multiplication, BFA pre-treatment caused no significant change in LCMV-specific RNA synthesis, alongside no significant change in LCMV NP expression, as measured by BFA time-of-addition experiments. In contrast, BFA addition resulted in a significant drop in released virus titers, approaching 50-fold over the same 12-h period, rising to over 600-fold over 24 h. Taken together, these findings suggest COPI and AP-4 complexes are important host cell factors required for the formation and release of infectious LCMV. IMPORTANCE: Arenaviruses are rodent-borne, segmented, negative-sense RNA viruses, with several members responsible for fatal human disease, with the prototypic member lymphocytic choriomeningitis virus (LCMV) being under-recognised as a pathogen capable of inflicting neurological infections with fatal outcome. A detailed understanding of how arenaviruses subvert host cell processes to complete their multiplication cycle is incomplete. Here, using a combination of gene ablation and pharmacological inhibition techniques, we showed that host cellular COPI and AP-4 complexes, with native roles in cellular vesicular transport, were required for efficient LCMV growth. We further showed these complexes acted on late stages of the multiplication cycle, post-gene expression, with a significant impact on infectious virus egress. Collectively, our findings improve the understanding of arenaviruses host-pathogen interactions and reveal critical cellular trafficking pathways required during infection.

Activation of protein kinase receptor (PKR) plays a pro-viral role in mammarenavirus-infected cells.

Many viruses, including mammarenaviruses, have evolved mechanisms to counteract different components of the host cell innate immunity, which is required to facilitate robust virus multiplication. The double-stranded RNA (dsRNA) sensor protein kinase receptor (PKR) pathway plays a critical role in the cell anti-viral response. Whether PKR can restrict the multiplication of the Old World mammarenavirus lymphocytic choriomeningitis virus (LCMV) and the mechanisms by which LCMV may counteract the anti-viral functions of PKR have not yet been investigated. Here we present evidence that LCMV infection results in very limited levels of PKR activation, but LCMV multiplication is enhanced in the absence of PKR. In contrast, infection with a recombinant LCMV with a mutation affecting the 3'-5' exonuclease (ExoN) activity of the viral nucleoprotein resulted in robust PKR activation in the absence of detectable levels of dsRNA, which was associated with severely restricted virus multiplication that was alleviated in the absence of PKR. However, pharmacological inhibition of PKR activation resulted in reduced levels of LCMV multiplication. These findings uncovered a complex role of the PKR pathway in LCMV-infected cells involving both pro- and anti-viral activities.IMPORTANCEAs with many other viruses, the prototypic Old World mammarenavirus LCMV can interfere with the host cell innate immune response to infection, which includes the dsRNA sensor PKR pathway. A detailed understanding of LCMV-PKR interactions can provide novel insights about mammarenavirus-host cell interactions and facilitate the development of effective anti-viral strategies against human pathogenic mammarenaviruses. In the present work, we present evidence that LCMV multiplication is enhanced in PKR-deficient cells, but pharmacological inhibition of PKR activation unexpectedly resulted in severely restricted propagation of LCMV. Likewise, we document a robust PKR activation in LCMV-infected cells in the absence of detectable levels of dsRNA. Our findings have revealed a complex role of the PKR pathway during LCMV infection and uncovered the activation of PKR as a druggable target for the development of anti-viral drugs against human pathogenic mammarenaviruses.

Serological and molecular screening of arenaviruses in suspected tick-borne encephalitis cases in Finland.

Lymphocytic choriomeningitis virus (LCMV) is one of the arenaviruses infecting humans. LCMV infections have been reported worldwide in humans with varying levels of severity. To detect arenavirus RNA and LCMV-reactive antibodies in different geographical regions of Finland, we screened human serum and cerebrospinal fluid (CSF) samples, taken from suspected tick-borne encephalitis (TBE) cases, using reverse transcriptase polymerase chain reaction (RT-PCR) and immunofluorescence assay (IFA). No arenavirus nucleic acids were detected, and the overall LCMV seroprevalence was 4.5%. No seroconversions were detected in paired serum samples. The highest seroprevalence (5.2%) was detected among individuals of age group III (40-59 years), followed by age group I (under-20-year-olds, 4.9%), while the lowest seroprevalence (3.8%) was found in age group IV (60 years or older). A lower LCMV seroprevalence in older age groups may suggest waning of immunity over time. The observation of a higher seroprevalence in the younger age group and the decreasing population size of the main reservoir host, the house mouse, may suggest exposure to another LCMV-like virus in Finland.

Lymphocytic Choriomeningitis Virus Lineage V in Wood Mice, Germany.

We identified a novel lineage of lymphocytic choriomeningitis virus, tentatively named lineage V, in wood mice (Apodemus sylvaticus) from Germany. Wood mouse-derived lymphocytic choriomeningitis virus can be found across a substantially greater range than previously thought. Increased surveillance is needed to determine its geographic range and zoonotic potential.

Neonatal CD8+ T Cells Resist Exhaustion during Chronic Infection.

Chronic viral infections, such as HIV and hepatitis C virus, represent a major public health problem. Although it is well understood that neonates and adults respond differently to chronic viral infections, the underlying mechanisms remain unknown. In this study, we transferred neonatal and adult CD8+ T cells into a mouse model of chronic infection (lymphocytic choriomeningitis virus clone 13) and dissected out the key cell-intrinsic differences that alter their ability to protect the host. Interestingly, we found that neonatal CD8+ T cells preferentially became effector cells early in chronic infection compared with adult CD8+ T cells and expressed higher levels of genes associated with cell migration and effector cell differentiation. During the chronic phase of infection, the neonatal cells retained more immune functionality and expressed lower levels of surface markers and genes related to exhaustion. Because the neonatal cells protect from viral replication early in chronic infection, the altered differentiation trajectories of neonatal and adult CD8+ T cells is functionally significant. Together, our work demonstrates how cell-intrinsic differences between neonatal and adult CD8+ T cells influence key cell fate decisions during chronic infection.

Lymphocytic choriomeningitis virus injures the developing brain: effects and mechanisms.

Lymphocytic choriomeningitis virus (LCMV) is a prevalent pathogen, whose natural host and reservoir is the wild mouse. Humans can be infected when they contact the secretions of mice. Most infections of postnatal humans result in mild illness. However, the consequences can be severe when the infection occurs during pregnancy, as the virus crosses the placenta to infect the fetus. LCMV infection of the human fetus can lead to severe neuropathologic effects, including microencephaly, hydrocephalus, focal destructive lesions, and cerebellar hypoplasia. Outcomes among children with congenital LCMV are variable, but most are permanently and severely disabled. The neonatal rat inoculated with LCMV models human prenatal infection. The rat model has demonstrated that effects of LCMV depend on host age at the time of infection. Some effects, including encephalomalacia and neuronal migration disturbances, are immune-mediated and depend on the actions of T-lymphocytes. Other effects, including cerebellar hypoplasia, are virus-mediated and do not depend on T-lymphocytes. Cerebellar neuronal migration disturbances are caused by immune-mediated corruption of Bergmann glia structure. The rat pup inoculated with LCMV is a superb animal model for human congenital infection. All neuropathologic effects observed in human congenital LCMV infection can be recapitulated in the rat model. IMPACT: Lymphocytic choriomeningitis virus (LCMV) is a prevalent human pathogen that can cause serious neurologic birth defects when the infection occurs during pregnancy. The effects of the virus on the developing brain depend strongly on the age of the host at the time of infection. Some of the pathologic effects of LCMV are immune-mediated and are driven by T-lymphocytes, while other pathologic effects are due to the virus itself.

Gene editing of hematopoietic stem cells restores T-cell response in familial hemophagocytic lymphohistiocytosis.

BACKGROUND: Hemophagocytic lymphohistiocytosis (HLH) is a hyperinflammatory disorder characterized by a life-threatening cytokine storm and immunopathology. Familial HLH type 3 (FHL3) accounts for approximately 30% of all inborn HLH cases worldwide. It is caused by mutations in the UNC13D gene that result in impaired degranulation of cytotoxic vesicles and hence compromised T-cell- and natural killer-cell-mediated killing. Current treatment protocols, including allogeneic hematopoietic stem cell (HSC) transplantation, still show high mortality. OBJECTIVE: We sought to develop and evaluate a curative genome editing strategy in the preclinical FHL3 Jinx mouse model. Jinx mice harbor a cryptic splice donor site in Unc13d intron 26 and develop clinical symptoms of human FHL3 upon infection with lymphocytic choriomeningitis virus (LCMV). METHODS: We employed clustered regularly interspaced short palindromic repeats (CRISPR)-Cas technology to delete the disease-causing mutation in HSCs and transplanted Unc13d-edited stem cells into busulfan-conditioned Jinx recipient mice. Safety studies included extensive genotyping and chromosomal aberrations analysis by single targeted linker-mediated PCR sequencing (CAST-Seq)-based off-target analyses. Cure from HLH predisposition was assessed by LCMV infection. RESULTS: Hematopoietic cells isolated from transplanted mice revealed efficient gene editing (>95%), polyclonality of the T-cell receptor repertoire, and neither signs of off-target effects nor leukemogenesis. Unc13d transcription levels of edited and wild-type cells were comparable. While LCMV challenge resulted in acute HLH in Jinx mice transplanted with mock-edited HSCs, Jinx mice grafted with Unc13d-edited cells showed rapid virus clearance and protection from HLH. CONCLUSIONS: Our study demonstrates that transplantation of CRISPR-Cas edited HSCs supports the development of a functional polyclonal T-cell response in the absence of genotoxicity-associated clonal outgrowth.

Transmission, seroprevalence, and maternal-fetal impact of lymphocytic choriomeningitis virus.

Congenital infections can have devastating short- and long-term impacts on the developing fetus. Lymphocytic choriomeningitis virus (LCMV) is a zoonotic pathogen of concern that causes a severe congenital syndrome but is under-recognized and under-studied. Herein we review data on the natural animal reservoirs of LCMV, modes of transmission to humans, seroprevalence of LCMV worldwide in both pregnant and non-pregnant individuals, mechanisms of viral dissemination to placenta and fetus, and impact of climate change on viral transmission. We highlight opportunities to enhance awareness of congenital LCMV and provide recommendations for prevention and monitoring among at-risk pregnant people. IMPACT: Key message of the article: LCMV is a zoonotic virus that poses a major threat to maternal-fetal health. Adds to the existing literature: We comprehensively address transmission of LCMV from the natural reservoir to the pregnant individual, placenta, and fetus. Impact: Available data call for enhanced patient and provider awareness about congenital LCMV during pregnancy, as well as a need for efforts to better define the seroprevalence and impact of congenital LCMV worldwide.

A replicating LCMV-based vaccine for the treatment of solid tumors.

Harnessing the immune system to eradicate tumors requires identification and targeting of tumor antigens, including tumor-specific neoantigens and tumor-associated self-antigens. Tumor-associated antigens are subject to existing immune tolerance, which must be overcome by immunotherapies. Despite many novel immunotherapies reaching clinical trials, inducing self-antigen-specific immune responses remains challenging. Here, we systematically investigate viral-vector-based cancer vaccines encoding a tumor-associated self-antigen (TRP2) for the treatment of established melanomas in preclinical mouse models, alone or in combination with adoptive T cell therapy. We reveal that, unlike foreign antigens, tumor-associated antigens require replication of lymphocytic choriomeningitis virus (LCMV)-based vectors to break tolerance and induce effective antigen-specific CD8+ T cell responses. Immunization with a replicating LCMV vector leads to complete tumor rejection when combined with adoptive TRP2-specific T cell transfer. Importantly, immunization with replicating vectors leads to extended antigen persistence in secondary lymphoid organs, resulting in efficient T cell priming, which renders previously "cold" tumors open to immune infiltration and reprograms the tumor microenvironment to "hot." Our findings have important implications for the design of next-generation immunotherapies targeting solid cancers utilizing viral vectors and adoptive cell transfer.

SHP-1 Regulates CD8+ T Cell Effector Function but Plays a Subtle Role with SHP-2 in T Cell Exhaustion Due to a Stage-Specific Nonredundant Functional Relay.

SHP-1 (Src homology region 2 domain-containing phosphatase 1) is a well-known negative regulator of T cells, whereas its close homolog SHP-2 is the long-recognized main signaling mediator of the PD-1 inhibitory pathway. However, recent studies have challenged the requirement of SHP-2 in PD-1 signaling, and follow-up studies further questioned the alternative idea that SHP-1 may replace SHP-2 in its absence. In this study, we systematically investigate the role of SHP-1 alone or jointly with SHP-2 in CD8+ T cells in a series of gene knockout mice. We show that although SHP-1 negatively regulates CD8+ T cell effector function during acute lymphocytic choriomeningitis virus (LCMV) infection, it is dispensable for CD8+ T cell exhaustion during chronic LCMV infection. Moreover, in contrast to the mortality of PD-1 knockout mice upon chronic LCMV infection, mice double deficient for SHP-1 and SHP-2 in CD8+ T cells survived without immunopathology. Importantly, CD8+ T cells lacking both phosphatases still differentiate into exhausted cells and respond to PD-1 blockade. Finally, we found that SHP-1 and SHP-2 suppressed effector CD8+ T cell expansion at the early and late stages, respectively, during chronic LCMV infection.