High-quality CMV-specific CD4+ memory is enriched in the lung allograft and is associated with mucosal viral control

Innate and adaptive effector immune drivers of cytomegalovirus disease in lung transplantation: a double-edged sword

Up to 90% of the global population has been infected with cytomegalovirus (CMV), a herpesvirus that remains latent for the lifetime of the host and drives immune dysregulation. CMV is a critical risk factor for poor outcomes after solid organ transplant, though lung transplant recipients (LTR) carry the highest risk of CMV infection, and CMV-associated comorbidities compared to recipients of other solid organ transplants. Despite potent antivirals, CMV remains a significant driver of chronic lung allograft dysfunction (CLAD), re-transplantation, and death. Moreover, the extended utilization of CMV antiviral prophylaxis is not without adverse effects, often necessitating treatment discontinuation. Thus, there is a critical need to understand the immune response to CMV after lung transplantation. This review identifies key elements of each arm of the CMV immune response and highlights implications for lung allograft tolerance and injury. Specific attention is paid to cellular subsets of adaptive and innate immune cells that are important in the lung during CMV infection and reactivation. The concept of heterologous immune responses is reviewed in depth, including how they form and how they may drive tissue- and allograft-specific immunity. Other important objectives of this review are to detail the emerging role of NK cells in CMV-related outcomes, in addition to discussing perturbations in CMV immune function stemming from pre-existing lung disease. Finally, this review identifies potential mechanisms whereby CMV-directed treatments may alter the cellular immune response within the allograft.

CD4+ T-Cell Dysfunction in Severe COVID-19 Disease Is Tumor Necrosis Factor-α/Tumor Necrosis Factor Receptor 1-Dependent

Rationale: Lymphopenia is common in severe coronavirus disease (COVID-19), yet the immune mechanisms are poorly understood. As inflammatory cytokines are increased in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, we hypothesized a role in contributing to reduced T-cell numbers. Objectives: We sought to characterize the functional SARS-CoV-2 T-cell responses in patients with severe versus recovered, mild COVID-19 to determine whether differences were detectable. Methods: Using flow cytometry and single-cell RNA sequence analyses, we assessed SARS-CoV-2-specific responses in our cohort. Measurements and Main Results: In 148 patients with severe COVID-19, we found lymphopenia was associated with worse survival. CD4⁺ lymphopenia predominated, with lower CD4⁺/CD8⁺ ratios in severe COVID-19 compared with patients with mild disease (P < 0.0001). In severe disease, immunodominant CD4⁺ T-cell responses to Spike-1 (S1) produced increased in vitro TNF-α (tumor necrosis factor-α) but demonstrated impaired S1-specific proliferation and increased susceptibility to activation-induced cell death after antigen exposure. CD4⁺TNF-α⁺ T-cell responses inversely correlated with absolute CD4⁺ counts from patients with severe COVID-19 (n = 76; R = -0.797; P < 0.0001). In vitro TNF-α blockade, including infliximab or anti-TNF receptor 1 antibodies, strikingly rescued S1-specific CD4⁺ T-cell proliferation and abrogated S1-specific activation-induced cell death in peripheral blood mononuclear cells from patients with severe COVID-19 (P < 0.001). Single-cell RNA sequencing demonstrated marked downregulation of type-1 cytokines and NFκB signaling in S1-stimulated CD4⁺ cells with infliximab treatment. We also evaluated BAL and lung explant CD4⁺ T cells recovered from patients with severe COVID-19 and observed that lung T cells produced higher TNF-α compared with peripheral blood mononuclear cells. Conclusions: Together, our findings show CD4⁺ dysfunction in severe COVID-19 is TNF-α/TNF receptor 1-dependent through immune mechanisms that may contribute to lymphopenia. TNF-α blockade may be beneficial in severe COVID-19.

Association of CMV-specific T-cell immunity and risk of CMV infection in lung transplant recipients

BACKGROUND

Protecting against CMV infection and maintaining CMV in latent state are largely provided by CMV-specific T-cells in lung transplant recipients. The aim of the study was to assess whether a specific T-cell response is associated with the risk for CMV infection in seronegative patients who are at high risk for delayed CMV infection.

METHODS

All CMV-seronegative recipients (R-) from CMV-seropositive donors (D+) between January 2018 and April 2019 were included and retrospectively screened for CMV infection before and after assessment of CMV-specific cell-mediated immunity.

RESULTS

Thirty-one of the 50 patients (62%) developed early-onset CMV infection. Lower absolute neutrophil counts were significantly associated with early-onset CMV infection. Antiviral prophylaxis was ceased after 137.2 ± 42.8 days. CMV-CMI were measured at a median of 5.5 months after LTx. 19 patients experienced early and late-onset CMV infection after prophylaxis withdrawal within 15 months post transplantation. Positive CMV-CMI was significantly associated with lower risk of late-onset CMV infection after transplantation in logistic and cox-regression analysis (OR=0.05, p = .01; OR=2,369, p = .026).

CONCLUSION

D+/R- lung transplant recipients are at high risk of developing early and late-onset CMV infection. Measurement of CMV-CMI soon after transplantation might further define the CMV infection prediction risk in LTx recipients being at high risk for CMV viremia.

Screening and identification of key regulatory connections and immune cell infiltration characteristics for lung transplant rejection using mucosal biopsies

This study aimed to explore key regulatory connections underlying lung transplant rejection. The differentially expressed genes (DEGs) between rejection and stable lung transplantation (LTx) samples were screened using R package limma, followed by functional enrichment analysis and protein-protein interaction network construction. Subsequently, a global triple network, including miRNAs, mRNAs, and transcription factors (TFs), was constructed. Furthermore, immune cell infiltration characteristics were analyzed to investigate the molecular immunology of lung transplant rejection. Finally, potential drug-target interactions were generated. In brief, 739 DEGs were found between rejection and stable LTx samples. PTPRC, IL-6, ITGAM, CD86, TLR8, TYROBP, CXCL10, ITGB2, and CCR5 were defined as hub genes. Eight TFs, including STAT1, SPIB, NFKB1, SPI1, STAT5A, RUNX1, VENTX, and BATF, and five miRNAs, including miR-335-5p, miR-26b-5p, miR-124-3p, miR-1-3p, and miR-155-5p, were involved in regulating hub genes. The immune cell infiltration analysis revealed higher proportions of activated memory CD4 T cells, follicular helper T cells, γδ T cells, monocytes, M1 and M2 macrophages, and eosinophils in rejection samples, besides lower proportions of resting memory CD4 T cells, regulatory T cells, activated NK cells, M0 macrophages, and resting mast cells. This study provided a comprehensive perspective of the molecular co-regulatory network underlying lung transplant rejection.

Local heroes or villains: tissue-resident memory T cells in human health and disease

Tissue-resident memory T (T_RM) cells are increasingly associated with the outcomes of health and disease. T_RM cells can mediate local immune protection against infections and cancer, which has led to interest in T_RM cells as targets for vaccination and immunotherapies. However, these cells have also been implicated in mediating detrimental pro-inflammatory responses in autoimmune skin diseases such as psoriasis, alopecia areata, and vitiligo. Here, we summarize the biology of T_RM cells established in animal models and in translational human studies. We review the beneficial effects of T_RM cells in mediating protective responses against infection and cancer and the adverse role of T_RM cells in driving pathology in autoimmunity. A further understanding of the breadth and mechanisms of T_RM cell activity is essential for the safe design of strategies that manipulate T_RM cells, such that protective responses can be enhanced without unwanted tissue damage, and pathogenic T_RM cells can be eliminated without losing local immunity.

Early KLRG1+ but Not CD57+CD8+ T Cells in Primary Cytomegalovirus Infection Predict Effector Function and Viral Control

CMV remains an important opportunistic pathogen in high-risk lung transplant recipients. We characterized the phenotype and function of CD8⁺ T cells from acute/primary into chronic CMV infection in 23 (donor+/recipient-; D+R-) lung transplant recipients and found rapid induction of both KLRG1⁺ and/or CD57⁺ CMV-specific CD8⁺ T cells with unexpected coexpression of CD27. These cells demonstrated maturation from an acute effector T cell (T_AEFF) to an effector memory T cell (T_EM) phenotype with progressive enrichment of KLRG1⁺CD57⁺CD27^- cells into memory. CMV-specific KLRG1⁺ T_AEFF were capable of in vitro proliferation that diminished upon acquisition of CD57, whereas only KLRG1⁺ expression correlated with T-bet expression and effector function. In contrast to blood T_AEFF, lung mucosal T_AEFF demonstrated reduced KLRG1/T-bet expression but similar CD57 levels. Additionally, increased KLRG1⁺T_AEFF were associated with early immune viral control following primary infection. To our knowledge, our findings provide new insights into the roles of KLRG1 and CD57 expression in human T cells, forming the basis for a refined model of CD8⁺ T cell differentiation during CMV infection.

CMV drives the expansion of highly functional memory T cells expressing NK-cell receptors in renal transplant recipients

Cytomegalovirus (CMV) is a common opportunistic infection encountered in renal transplant recipients (RTRs) and may be reactivated without symptoms at any time post-transplant. We describe how active and latent CMV affect T-cell subsets in RTRs who are stable on maintenance therapy. T-cell responses to CMV were assessed in RTRs (n = 54) >2 years post-transplant, and healthy controls (n = 38). Seven RTRs had CMV DNA detectable in plasma. CMV antibody and DNA aligned with increased proportions of CD8⁺ T cells and reduced CD4/CD8 ratios. This paralleled an expansion of effector memory T-cell (T_EM ), terminally differentiated T-cell (T_EMRA ) and CD57⁺ T_EMRA cell populations. Expression of NK-cell receptors, LIR-1 and KLRG1 on CD4⁺ and CD8⁺ CD57⁺ T_EM and T_EMRA cells correlated with elevated interferon-γ and cytotoxic responses to anti-CD3 and increased cytotoxic responses to CMV phosphoprotein (pp) 65 in RTRs who carried CMV DNA. CD8⁺ T cells from all CMV seropositive RTRs responded efficiently to CMV immediate early (IE) -1 peptides. The data show that latent and active CMV infection can alter T-cell subsets in RTRs many years after transplantation, and up-regulate T-cell expression of NK-cell receptors. This may enhance effector responses of CD4⁺ and CD8⁺ T cells against CMV.

Tissue reservoirs of antiviral T cell immunity in persistent human CMV infection

T cell responses to viruses are initiated and maintained in tissue sites; however, knowledge of human antiviral T cells is largely derived from blood. Cytomegalovirus (CMV) persists in most humans, requires T cell immunity to control, yet tissue immune responses remain undefined. Here, we investigated human CMV-specific T cells, virus persistence and CMV-associated T cell homeostasis in blood, lymphoid, mucosal and secretory tissues of 44 CMV seropositive and 28 seronegative donors. CMV-specific T cells were maintained in distinct distribution patterns, highest in blood, bone marrow (BM), or lymph nodes (LN), with the frequency and function in blood distinct from tissues. CMV genomes were detected predominantly in lung and also in spleen, BM, blood and LN. High frequencies of activated CMV-specific T cells were found in blood and BM samples with low virus detection, whereas in lung, CMV-specific T cells were present along with detectable virus. In LNs, CMV-specific T cells exhibited quiescent phenotypes independent of virus. Overall, T cell differentiation was enhanced in sites of viral persistence with age. Together, our results suggest tissue T cell reservoirs for CMV control shaped by both viral and tissue-intrinsic factors, with global effects on homeostasis of tissue T cells over the lifespan.

T cell responses to cytomegalovirus

Human cytomegalovirus (HCMV) establishes a latent infection that generally remains asymptomatic in immune-competent hosts for decades but can cause serious illness in immune-compromised individuals. The long-term control of CMV requires considerable effort from the host immune system and has a lasting impact on the profile of the immune system. One hallmark of CMV infection is the maintenance of large populations of CMV-specific memory CD8(+) T cells - a phenomenon termed memory inflation - and emerging data suggest that memory inflation is associated with impaired immunity in the elderly. In this Review, we discuss the molecular triggers that promote memory inflation, the idea that memory inflation could be considered a natural pathway of T cell maturation that could be harnessed in vaccination, and the broader implications of CMV infection and the T cell responses it elicits.

Broncholaveolar lavage to detect cytomegalovirus infection, latency, and reactivation in immune competent hosts

Roughly 1/3rd of immune competent patients will reactivate latent cytomegalovirus (CMV) during critical illness. There are no standard methods to detect reactivation, and some investigators have postulated that presence of DNA in BAL fluid is indicative of viral replication. To test this hypothesis, we used a murine model that allows inclusion of matched healthy controls which is not possible in human studies. BALB/c mice infected with Smith-murine CMV or PBS (mock) had BAL evaluated 7, 14, or 21 days after acute infections, during latency, or during bacterial sepsis. Plaque assay, PCR, and rtPCR were performed on BALs and concomitantly obtained lung tissue. BAL cellular compositions, including tetramer evaluation of CMV-specific T cells were evaluated by flow cytometry. CMV DNA were detected in BAL at all time-points during acute infection, becoming undetectable in all mice during latency, then were detected again during bacterial sepsis, peaking 3 weeks after onset. mCMV specific T-cells were most numerous in BAL after acute viral infections, decreasing to low levels during latency, then fluctuating during bacterial sepsis. Specifically, mCMV-specific T-cells contracted at sepsis onset, expanding 2-4 weeks post-sepsis, presumably in response to increased viral loads at that time point. Altogether, our results support the use of BAL PCR for the diagnosis of CMV replication in immune competent hosts. Additionally, we demonstrate dynamic changes in CMV-specific T cells that occur in BAL during CMV infection and during sepsis induced viral reactivation. J. Med. Virol. 88:1408-1416, 2016. © 2016 Wiley Periodicals, Inc.

IL-12-Dependent Cytomegalovirus-Specific CD4+ T Cell Proliferation, T-bet Induction, and Effector Multifunction during Primary Infection Are Key Determinants for Early Immune Control

CMV remains an important opportunistic pathogen in solid organ and hematopoietic cell transplantation, particularly in lung transplant recipients (LTRs). LTRs mismatched for CMV (donor(+)/recipient(-); D(+)R(-)) are at high risk for active CMV infection and increased mortality; however, the immune correlates of viral control remain incompletely understood. We prospectively studied 27 D(+)R(-) LTRs during primary CMV infection to determine whether acute CD4(+) T cell parameters differentiated the capacity for viral control during early chronic infection. Unexpectedly, the T-box transcription factor, T-bet, was expressed at low levels in CD4(+) compared with CD8(+) T cells during acute primary infection. However, the capacity for in vitro CMV phosphoprotein 65-specific proliferation and CD4(+)T-bet(+) induction differentiated LTR controllers from early viremic relapsers, correlating with granzyme B loading and effector multifunction. Furthermore, impaired CMV-specific proliferative responses from relapsers, along with T-bet, and effector function could be significantly rescued, most effectively with phosphoprotein 65 Ag and combined exogenous IL-2 and IL-12. Acute CD4(+) T cell CMV-specific proliferative and effector responses were highly IL-12-dependent in blocking studies. In addition, we generated monocyte-derived dendritic cells using PBMC obtained during primary infection from relapsers and observed impaired monocyte-derived dendritic cell differentiation, a reduced capacity for IL-12 production, but increased IL-10 production compared with controls, suggesting an APC defect during acute CMV viremia. Taken together, these data show an important role for CMV-specific CD4(+) effector responses in differentiating the capacity of high-risk LTRs to establish durable immune control during early chronic infection and provide evidence for IL-12 as a key factor driving these responses.

Activation-induced cell death drives profound lung CD4(+) T-cell depletion in HIV-associated chronic obstructive pulmonary disease

RATIONALE

As overall survival improves, individuals with HIV infection become susceptible to other chronic diseases, including accelerated chronic obstructive pulmonary disease (COPD).

OBJECTIVES

To determine whether individuals with HIV-associated COPD exhibit dysregulated lung mucosal T-cell immunity compared with control subjects.

METHODS

Using flow cytometry, we evaluated peripheral blood and lung mucosal T-cell immunity in 14 HIV(+)COPD(+), 13 HIV(+)COPD(-), and 7 HIV(-)COPD(+) individuals.

MEASUREMENTS AND MAIN RESULTS

HIV(+)COPD(+) individuals demonstrated profound CD4(+) T-cell depletion with reduced CD4/CD8 T-cell ratios in bronchoalveolar lavage-derived lung mononuclear cells, not observed in peripheral blood mononuclear cells, and diminished CD4(+) T cell absolute numbers, compared with control subjects. Furthermore, HIV(+)COPD(+) individuals demonstrated decreased pulmonary HIV-specific and staphylococcal enterotoxin B-reactive CD4(+) memory responses, including loss of multifunctionality, compared with HIV(+)COPD(-) control subjects. In contrast, lung mucosal HIV-specific CD8(+) T-cell responses were preserved. Lung CD4(+) T cells from HIV(+)COPD(+) individuals expressed increased surface Fas death receptor (CD95) and programmed death-1, but similar bronchoalveolar lavage viral loads as control subjects. However, programmed death-1 expression inversely correlated with HIV-specific lung CD4(+)IFN-γ(+) T-cell responses, suggesting functional exhaustion. Moreover, lung CD4(+) T cells from HIV(+)COPD(+) patients demonstrated increased basal and HIV antigen-induced expression of the early apoptosis marker annexin V compared with control subjects, which was significantly attenuated with anti-Fas blockade. Lastly, lung mucosal, but not blood, CD4(+)/CD8(+) ratios from HIV(+) patients significantly correlated with the FEV1, but not in HIV(-)COPD(+) patients.

CONCLUSIONS

Together, our results provide evidence for profound lung mucosal CD4(+) T-cell depletion via a Fas-dependent activation-induced cell death mechanism, along with impaired HIV-specific CD4(+) immunity as immunologic features of HIV-associated COPD.

Phenotypic and functional characterization of cytotoxic T lymphocytes by flow cytometry

Cytotoxic T lymphocytes (CTLs) are important constituents of the adaptive immune system. Development of CTLs are particularly important for bacterial and viral infections, in addition to tumor surveillance. Measuring T cell immune function is important in evaluating host defense, allergy, autoimmunity, transplant rejection, and tumor immunity. In these recent years it has become possible to measure multiple effector functions in a single cell such as cytokine, transcription factors, and cytolytic function. In addition these parameters can be evaluated in conjunction with cellular proliferation. In this chapter we detail these cellular based assays and the methods used to characterize and quantify both phenotype and function of CTL.

Flow cytometry and solid organ transplantation: a perfect match

In the field of transplantation, flow cytometry serves a well-established role in pre-transplant crossmatching and monitoring immune reconstitution following hematopoietic stem cell transplantation. The capabilities of flow cytometers have continuously expanded and this combined with more detailed knowledge of the constituents of the immune system, their function and interaction and newly developed reagents to study these parameters have led to additional utility of flow cytometry-based analyses, particularly in the post-transplant setting. This review discusses the impact of flow cytometry on managing alloantigen reactions, monitoring opportunistic infections and graft rejection and gauging immunosuppression in the context of solid organ transplantation.

Adoptive transfer of cytomegalovirus-specific effector CD4+ T cells provides antiviral protection from murine CMV infection

Cytomegalovirus (CMV) infects a majority of the human population and establishes a life-long persistence. CMV infection is usually asymptomatic but the virus carries pathogenic potential and causes severe disease in immunocompromised individuals. T-cell-mediated immunity plays an essential role in control of CMV infection and adoptive transfer of CMV-specific CD8(+) T cells restores viral immunity in immunosuppressed patients but a role for CD4(+) T cells remains elusive. Here, we analyzed in adoptive transfer studies the features and antiviral functions of virus-specific CD4(+) T cells during primary murine CMV (MCMV) infection. MCMV-specific CD4(+) T cells expanded upon MCMV infection and displayed an effector phenotype and function. Adoptive transfer of in vivo activated MCMV-specific CD4(+) T cells to immune-compromised mice was protective during pathogenic MCMV infection and IFN-γ was a crucial mediator of this protective capacity. Moreover, co-transfer of low doses of both MCMV-specific CD4(+) T cells and CD8(+) T cells synergized in control of lytic viral replication in immune-compromised mice. Our data reveal a pivotal antiviral role for virus-specific CD4(+) T cells in protection from pathogenic CMV infection and provide evidence for their antiviral therapeutic potential.

CD4 T cell responses in latent and chronic viral infections

The spectrum of tasks which is fulfilled by CD4 T cells in the setting of viral infections is large, ranging from support of CD8 T cells and humoral immunity to exertion of direct antiviral effector functions. While our knowledge about the differentiation pathways, plasticity, and memory of CD4 T cell responses upon acute infections or immunizations has significantly increased during the past years, much less is still known about CD4 T cell differentiation and their beneficial or pathological functions during persistent viral infections. In this review we summarize current knowledge about the differentiation, direct or indirect antiviral effector functions, and the regulation of virus-specific CD4 T cells in the setting of persistent latent or active chronic viral infections with a particular emphasis on herpes virus infections for the former and chronic lymphocytic choriomeningitis virus infection for the latter.