Association of human cytomegalovirus DNAaemia and specific granzyme B responses in lung transplant recipients

In lung transplant recipients (LTRs), human cytomegalovirus (HCMV) DNAaemia could be associated with HCMV disease and reduced allograft survival. In the present study we analysed whether or not HCMV‐specific granzyme B (Grz‐B) responses indicating CD8⁺ T cell cytotoxicity exert an impact on HCMV DNAaemia and relate to specific interferon (IFN)‐γ secretion. HCMV‐specific Grz‐B responses were quantitated by enzyme‐linked immunosorbent assay (ELISA) in 70 samples from 39 HCMV seropositive LTRs who were prospectively investigated for HCMV DNA plasma levels and IFN‐γ kinetics using a standardized CD8⁺ T cell assay (QuantiFERON®‐CMV assay). In all LTRs who were protected from HCMV DNAaemia by early and persistent IFN‐γ responses, Grz‐B responses were also detected. In LTRs who developed episodes of HCMV DNAaemia, the Grz‐B responses which were detected prior to viral DNA detection differed significantly in patients who experienced episodes with high (exceeding 1000 copies/ml) and low plasma DNA levels (P = 0·0290, Fisher's exact test). Furthermore, the extent of Grz‐B release prior to viral DNAaemia correlated statistically with the detected levels of IFN‐γ (P < 0·0001, Spearman's rank test). Of note, simultaneous detection of Grz‐B and IFN‐γ secretion was associated significantly with protection from high HCMV DNA plasma levels during the subsequent follow‐up (P = 0·0057, Fisher's exact test), and this association was stronger than for IFN‐γ detection alone. We conclude that, in addition to IFN‐γ responses, Grz‐B secretion by CD8⁺ T cells is essential to control HCMV replication and a simultaneous measurement of IFN‐γ and Grz‐B could contribute to the immune monitoring of LTRs.     

Strong and sustained effector function of memory‐ versus naïve‐derived T cells upon T‐cell receptor RNA transfer: Implications for cellular therapy

Current protocols used to select CMV‐specific T cells for adoptive immunotherapy focus on virus‐specific memory T cells from seropositive donors. However, this strategy is not feasible in patients undergoing allogeneic haematopoietic stem‐cell transplantation (HSCT) from CMV‐seronegative donors. Here, we redirected T cells of CMV‐seronegative donors with a human genetically engineered TCR recognizing an HLA‐A*0201‐binding peptide epitope of CMVpp65. To facilitate clinical translation of this approach, we used a non‐viral expression system based on in vitro transcribed RNA and electroporation. Although memory and naïve‐derived T‐cell subsets were both efficiently transfected by TCR‐RNA, memory‐derived T cells showed much stronger levels of HLA‐A*0201‐restricted cytolytic activity to CMV‐infected fibroblasts and maintained acquired function for 5–10 days. In addition to redirection of CD8⁺ cytotoxic T cells, TCR‐RNA transfection was capable of redirecting CD4⁺ T cells into potent Ag‐specific Th cells that efficiently triggered maturation of DCs. Our data suggest that memory rather than naïve‐derived T cells are the preferred subset for transient TCR expression by RNA electroporation, providing more efficient and sustained virus‐specific CD4⁺ and CD8⁺ T‐cell function. CMV TCR‐RNA may represent a suitable therapeutic ‘off‐the‐shelf’ reagent to be used in severe CMV infections of HSCT patients when endogenous CMV‐specific T‐cell immunity is insufficient.     

Systemic varicella zoster virus reactive effector memory T‐cells impaired in the elderly and in kidney transplant recipients

Varicella zoster virus (VZV) infections cause varicella and subsequently herpes zoster upon reactivation. Immune‐compromised individuals and the elderly are at high risk of developing herpes zoster due to waning of VZV‐specific T‐cell immunity. In the present study, a novel functional T‐cell assay was developed to test the correlation between age and VZV‐specific T‐cell responses in peripheral blood from healthy individuals. Secondly, VZV‐specific T‐cell responses from renal transplant recipients were compared with healthy individuals. Monocytes were differentiated into mature monocyte‐derived dendritic cells (moDCs) and were infected with VZV. T‐cells were co‐cultured with autologous moDCs infected with VZV and subjected to flowcytometric analysis to identify the phenotype (i.e., naïve [NA: CCR7⁺CD45RO^?], central [CM: CCR7⁺CD45RO⁺] and effector memory [EM: CCR7^?CD45RO⁺] T‐cells) and the frequency of VZV‐reactive T‐cell subsets by intra‐cellular IFN‐γ flowcytometry. In contrast to NA and CM T‐cells, the frequency of VZV‐reactive CD4 and CD8 EM T‐cells was inversely correlated with age (P = 0.0007 and P = 0.01). No difference was found in the percentage of VZV‐reactive CD4 NA, CM and EM T‐cells between transplant recipients and controls. However, the percentage of VZV‐reactive CD8 EM T‐cells was significantly lower in transplant recipients compared to controls (P = 0.02). In conclusion, moDCs infected with VZV are efficient antigen presenting cells applicable to enumerate and characterize the phenotype and differentiation status of the systemic VZV‐specific T‐cell response ex‐vivo. The data suggest that VZV‐reactive EM T‐cells are impaired in the elderly and renal transplant recipients. J. Med. Virol. 84:2018–2025, 2012. © 2012 Wiley Periodicals, Inc.     

NK cells generate memory‐type responses to human cytomegalovirus‐infected fibroblasts

Natural killer (NK) cells are cytotoxic lymphocytes that selectively respond against abnormal cells. Human cytomegalovirus (HCMV) infection causes expansion of NKG2C⁺CD57⁺ NK cells in vivo and NKG2C⁺ NK cells proliferate when cultured with HCMV‐infected cells. This raises the possibility of an NK‐cell subset selectively responding against a specific pathogen and accruing memory. To test this possibility, we compared proliferation, natural cytotoxicity and interferon‐γ (IFN‐γ) production of NK cells from HCMV‐seropositive and HCMV‐seronegative individuals co‐cultured with HCMV‐infected or uninfected MRC‐5 cells. There was no significant difference in proliferation of NK cells from HCMV‐seropositive or seronegative individuals against uninfected MRC‐5 cells, but significantly more NK cells from the HCMV‐seropositive group proliferated in response to HCMV‐infected MRC‐5 cells. Natural cytotoxicity of NK cells against K562 cells increased following co‐culture with HCMV‐infected versus uninfected MRC‐5 only for the HCMV‐seropositive group. After co‐culture with HCMV‐infected MRC‐5 cells, proliferating NK cells from HCMV‐seropositive donors selectively produced IFN‐γ when re‐exposed to HCMV‐infected MRC‐5 cells. Both NKG2C⁺ and NKG2C^? NK cells proliferated in co‐culture with HCMV‐infected MRC‐5 cells, with the fraction of proliferating NKG2C⁺ NK cells directly correlating with the circulating NKG2C⁺ fraction. These data illustrate an at least partly NKG2C‐independent human NK‐cell memory‐type response against HCMV.     

Cytomegalovirus drives Vδ2neg γδ T cell inflation in many healthy virus carriers with increasing age

Cytomegalovirus (CMV) usually causes lifelong asymptomatic infection, but over time can distort immune profiles. Recent reports describe selective expansion of Vδ2^neg γδ T cells in healthy and immunocompromised CMV carriers. Having shown previously that virus‐specific CD8⁺ and CD4⁺ T cell responses are increased significantly in elderly CMV carriers, probably driven by chronic stimulation, we hypothesized that Vδ2^neg γδ T cells may also be expanded with age. Our results show that Vδ2^neg γδ T cells are increased significantly in CMV‐seropositive healthy individuals compared to CMV‐seronegative controls in all age groups. The differences were most significant in older age groups (P < 0·0001). Furthermore, while Vδ2^neg γδ T‐ cells comprise both naive and memory cells in CMV‐seronegative donors, highly differentiated effector memory cells are the dominant phenotype in CMV carriers, with naive cells reduced significantly in numbers in CMV‐seropositive elderly. Although phenotypically resembling conventional CMV‐specific T cells, Vδ2^neg γδ T cells do not correlate with changes in magnitude of CMV‐specific CD4⁺ or CD8⁺ T cell frequencies within those individuals, and do not possess ex‐vivo immediate effector function as shown by CMV‐specific CD4⁺ and CD8⁺ T cells. However, after short‐term culture, Vδ2^neg γδ T cells demonstrate effector T cell functions, suggesting additional requirements for activation. In summary, Vδ2^neg γδ T cells are expanded in many older CMV carriers, demonstrating a further level of lymphocyte subset skewing by CMV in healthy individuals. As others have reported shared reactivity of Vδ2^neg γδ T cells towards tumour cells, the composition of γδ T cell subsets may also have implications for risk of developing cancer in elderly people.     

Human cytomegalovirus (HCMV)‐specific T cell but not neutralizing or IgG binding antibody responses to glycoprotein complexes gB,gHgLgO, and pUL128L correlate with protection against high HCMV viral load reactivation in solid‐organ transplant recipients

Immune correlates of protection against human cytomegalovirus (HCMV) infection are still debated. This study aimed to investigate which arm of the immune response plays a major role in protection against HCMV infection in kidney transplant recipients (n = 40) and heart transplant recipients (n = 12). Overall, patients were divided into 2 groups: one including 37 patients with low viral load (LVL), and the other including 15 patients with high viral load (HVL). All LVL patients resolved the infection spontaneously, whereas HVL patients were all treated with one or more courses of antivirals. In HVL patients, viral DNAemia, which was more than 100 times higher than LVL, appeared and peaked at significantly earlier times, but disappeared much later than in LVL patients. During a 1‐year follow‐up, all LVL patients had levels of HCMV‐specific CD4⁺ (and CD8⁺) T cells significantly higher than HVL patients. On the contrary, titers of neutralizing antibodies and enzyme‐linked immunosorbent assay‐IgG antibodies to gB, gHgLgO, and pentamer gHgLpUL128L were overlapping in the 2 patient groups. In conclusion, while a valid HCMV‐specific T‐cell response was detected in more than 90% of LVL patients, >90% of HVL patients lacked an adequate T‐cell response. Antibody responses did not appear to be associated directly or indirectly with protection.     

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.     

Cytomegalovirus‐seropositivity has a profound influence on the magnitude of major lymphoid subsets within healthy individuals

Cytomegalovirus (CMV) infects most individuals and elicits a strong CMV‐specific immune response. We have studied the influence of CMV‐seropositivity on the size of lymphoid subsets in healthy donors and demonstrate that the virus substantially modulates the peripheral lymphoid pool. CD8⁺ T cell numbers are increased in all CMV‐seropositive individuals because of a striking 60% increment in the CD8⁺ T cell memory pool. The CD45RA⁺ resting memory pool is doubled after CMV infection and increases further with age. The magnitude of the naïve CD8⁺ T cell pool is dramatically reduced in CMV‐seropositive individuals at all ages, and this accelerates the physiological decline by approximately 40 years. The number of CD4⁺ effector memory T cells is increased in CMV‐seropositive individuals and is differentially accommodated by a reduction in the number of naïve and central memory CD4⁺ T cells in young and elderly donors respectively. CMV‐seropositivity also increases the total number of B cells in older donors and suppresses the number of CD5⁺ B cells. These data reveal that CMV has a profound influence on the immune system of all healthy individuals and add to growing concern regarding the clinical and immunomodulatory significance of CMV infection in healthy donors.     

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.     

Biphasic role of 4‐1BB in the regulation of mouse cytomegalovirus‐specific CD8+ T cells

The initial requirement for the emergence of CMV‐specific CD8⁺ T cells is poorly understood. Mice deficient in the cosignaling TNF superfamily member, 4‐1BB, surprisingly developed exaggerated early CD8⁺ T‐cell responses to mouse CMV (MCMV). CD8⁺ T cells directed against acute MCMV epitopes were enhanced, demonstrating that 4‐1BB naturally antagonizes these primary populations. Paradoxically, 4‐1BB‐deficient mice displayed reduced accumulation of memory CD8⁺ T cells that expand during chronic/latent infection. Importantly, the canonical TNF‐related ligand, 4‐1BBL, promoted the accumulation of these memory CD8⁺ T cells, whereas suppression of acute CD8⁺ T cells was independent of 4‐1BBL. These data highlight the dual nature of the 4‐1BB/4‐1BBL system in mediating both stimulatory and inhibitory cosignaling activities during the generation of anti‐MCMV immunity.     

Cytomegalovirus vector expressing RAE‐1γ induces enhanced anti‐tumor capacity of murine CD8+ T cells

Designing CD8⁺ T‐cell vaccines, which would provide protection against tumors is still considered a great challenge in immunotherapy. Here we show the robust potential of cytomegalovirus (CMV) vector expressing the NKG2D ligand RAE‐1γ as CD8⁺ T cell‐based vaccine against malignant tumors. Immunization with the CMV vector expressing RAE‐1γ, delayed tumor growth or even provided complete protection against tumor challenge in both prophylactic and therapeutic settings. Moreover, a potent tumor control in mice vaccinated with this vector can be further enhanced by blocking the immune checkpoints TIGIT and PD‐1. CMV vector expressing RAE‐1γ potentiated expansion of KLRG1⁺ CD8⁺ T cells with enhanced effector properties. This vaccination was even more efficient in neonatal mice, resulting in the expansion and long‐term maintenance of epitope‐specific CD8⁺ T cells conferring robust resistance against tumor challenge. Our data show that immunomodulation of CD8⁺ T‐cell responses promoted by herpesvirus expressing a ligand for NKG2D receptor can provide a powerful platform for the prevention and treatment of CD8⁺ T‐cell sensitive tumors.     

Kinetics of cytomegalovirus (CMV) pp65 and IE‐1‐specific IFNγ CD8+ and CD4+ T cells during episodes of viral DNAemia in allogeneic stem cell transplant recipients: Potential implications for the management of active CMV infection

The dynamics of CMV pp65 and IE‐1‐specific IFNγ‐producing CD8⁺ (IFNγ CD8⁺) and CD4⁺ (IFNγ CD4⁺) T cells and CMV DNAemia were assessed in 19 pre‐emptively treated episodes of active CMV infection. Peripheral counts of IFNγ CD8⁺ and IFNγ CD4⁺ T cells inversely correlated with CMV DNAemia levels (P = <0.001 and P = 0.003, respectively). A threshold value of 1.3 cells/µl predicting CMV DNAemia clearance was established for IFNγ CD8⁺ T cells (PPV, 100%; NPV, 93%) and for IFNγ CD4⁺ T cells (PPV, 100%; NPV, 75%). Undetectable T‐cell responses were usually observed at the time of initiation of pre‐emptive therapy. Either a rapid (within 7 days) or a delayed (median 31 days) expansion of both T‐cell populations concomitant with CMV DNAemia clearance was observed in 5 and 8 episodes, respectively. An inconsistent or a lack of expansion of both T‐cell subsets was related to a persistent CMV DNAemia. Robust and maintained CMV‐specific T‐cell responses after CMV DNAemia clearance and cessation of antiviral therapy were associated with a null incidence of relapsing infections at least during the following month. Data obtained in the present study may be helpful in the design of therapeutic strategies for the management of active CMV infections in the allo‐SCT recipient. J. Med. Virol. 82: 1208–1215, 2010. © 2010 Wiley‐Liss, Inc.     

Human herpesvirus 6B immediate‐early I protein contains functional HLA‐A*02, HLA‐A*03, and HLA‐B*07 class I restricted CD8+ T‐cell epitopes

Human herpesvirus 6B (HHV‐6B) is a ubiquitous pathogen with frequent reactivation observed in immunocompromised patients such as BM transplant (BMT) recipients. Adoptive immunotherapy is a promising therapeutic avenue for the treatment of opportunistic infections, including herpesviruses. While T‐cell immunotherapy can successfully control CMV and EBV reactivations in BMT recipients, such therapy is not available for HHV‐6 infections, in part due to a lack of identified protective CD8⁺ T‐cell epitopes. Our goal was to identify CD8⁺ T‐cell viral epitopes derived from the HHV‐6B immediate‐early protein I and presented by common human leukocyte Ag (HLA) class I alleles including HLA‐A*02, HLA‐A*03, and HLA‐B*07. These epitopes were functionally tested for their ability to induce CD8⁺ T‐cell expansion and kill HHV‐6‐infected autologous cells. Cross‐reactivity of specific HHV‐6B‐expanded T cells against HHV‐6A‐infected cells was also confirmed for a conserved epitope presented by HLA‐A*02 molecule. Our findings will help push forward the field of adoptive immunotherapy for the treatment and/or the prevention of HHV‐6 reactivation in BMT recipients.     

Early Cytomegalovirus Reactivation Leaves a Specific and Dynamic Imprint on the Reconstituting T Cell Compartment Long-Term after Hematopoietic Stem Cell Transplantation

Human cytomegalovirus (CMV) reactivation frequently occurs during the early phase of immune recovery after allogeneic hematopoietic stem cell transplantation (HSCT). Whereas the recovery of virus-specific immunity in the early phase after HSCT is extensively studied, the impact of CMV on the reconstitution and composition of the T cell compartment long-term after HSCT is unknown. We analyzed T cell reconstitution 1 to 2 years after HSCT in 131 pediatric patients. One year after HSCT, patients with early CMV reactivation (n = 46) had 3-fold higher CD8⁺ T cell numbers (median, 1323 versus 424 cells/μL; P < .0001) compared with patients without CMV reactivation (n = 85). This effect, caused by a major expansion of CD8⁺ effector memory (EM) and end-stage effector (EMRA) T cells, was independent of pretransplantation donor and recipient CMV serostatus and not seen after Epstein-Barr virus or adenovirus reactivations. At 1 and 2 years after HSCT, the absolute numbers of CD8⁺ naive and central memory T cells, as well as CD4⁺ naive, CM, EM, and EMRA T cells, did not differ between patients with or without CMV reactivation. In the second year after HSCT, a significant contraction of the initially expanded CD8⁺ EM and EMRA T cell compartments was observed in patients with early CMV reactivation. In conclusion, CMV reactivation early after pediatric HSCT leaves a specific and dynamic imprint on the size and composition of the CD8⁺ T cell compartment without compromising the reconstitution of CD8⁺ and CD4⁺ naive and central memory T cells pivotal in the response to neo and recall antigens.     

Control of Schistosoma mansoni egg‐induced inflammation by IL‐4‐responsive CD4+CD25−CD103+Foxp3− cells is IL‐10‐dependent

Host protection to helminth infection requires IL‐4 receptor α chain (IL‐4Rα) signalling and the establishment of finely regulated Th2 responses. In the current study, the role of IL‐4Rα‐responsive T cells in Schistosoma mansoni egg‐induced inflammation was investigated. Egg‐induced inflammation in IL‐4Rα‐responsive BALB/c mice was accompanied with Th2‐biased responses, whereas T‐cell‐specific IL‐4Rα‐deficient BALB/c mice (iLck^creIl4ra^?/lox) developed Th1‐biased responses with heightened inflammation. The proportion of Foxp3⁺ Treg in the draining LN of control mice did not correlate with the control of inflammation and was reduced in comparison to T‐cell‐specific IL‐4Rα‐deficient mice. This was due to IL‐4‐mediated inhibition of CD4⁺Foxp3⁺ Treg conversion, demonstrated in adoptively transferred Rag2^?/? mice. Interestingly, reduced footpad swelling in Il4ra^?/lox mice was associated with the induction of IL‐4 and IL‐10‐secreting CD4⁺CD25^?CD103⁺Foxp3^? cells, confirmed in S. mansoni infection studies. Transfer of IL‐4Rα‐responsive CD4⁺CD25^?CD103⁺ cells, but not CD4⁺CD25^high or CD4⁺CD25^?CD103^? cells, controlled inflammation in iLck^creIl4ra^?/lox mice. The control of inflammation depended on IL‐10, as transferred CD4⁺CD25^?CD103⁺ cells from IL‐10‐deficient mice were not able to effectively downregulate inflammation. Together, these results demonstrate that IL‐4 signalling in T cells inhibits Foxp3⁺ Treg in vivo and promotes CD4⁺CD25^?CD103⁺Foxp3^? cells that control S. mansoni egg‐induced inflammation via IL‐10.     

A20 deletion in T cells modulates acute graft‐versus‐host disease in mice

The NF‐κB regulator A20 limits inflammation by providing negative feedback in myeloid cells and B cells. Functional lack of A20 has been linked to several inflammatory and autoimmune diseases. To define how A20 affects the functionality of T effector cells in a highly inflammatory environment, we performed conventional allogeneic hematopoietic stem cell transplantation (allo‐HSCT) with A20‐deficient CD4⁺ and CD8⁺ donor T cells in mice. Severity and mortality of graft‐versus‐host disease (GVHD) after allo‐HSCT was drastically reduced in recipients transplanted with conventional doses of A20‐deficient T cells. Consistently, we found that the A20‐deficient donor T‐cell compartment was strongly diminished at various timepoints after allo‐HSCT. However, proportionally more A20‐deficient donor T cells produced IFN‐γ and systemic inflammation was elevated early after allo‐HSCT. Consequently, increasing the dose of transplanted A20‐deficient T cells reversed the original phenotype and resulted in enhanced GVHD mortality compared to recipients that received A20^+/+ T cells. Still, A20‐deficient T cells, activated either through T cell receptor‐dependent or ‐independent mechanisms, were less viable than control A20^+/+ T cells, highlighting that A20 balances both, T‐cell activation and survival. Thus, our findings suggest that targeting A20 in T cells may allow to modulate T‐cell‐mediated inflammatory diseases like GVHD.     

IFN‐γ‐receptor signaling ameliorates transplant vasculopathy through attenuation of CD8+ T‐cell‐mediated injury of vascular endothelial cells

Occlusive transplant vasculopathy (TV) is the major cause for chronic graft rejection. Since endothelial cells (EC) are the first graft cells encountered by activated host lymphocytes, it is important to delineate the molecular mechanisms that coordinate the interaction of EC with activated T cells. Here, the interaction of CD8⁺ T cells with Ag‐presenting EC in vivo was examined using a transgenic heart transplantation model with β‐galactosidase (β‐gal) expression exclusively in EC (Tie2‐LacZ hearts). We found that priming with β‐gal peptide‐loaded DC failed to generate a strong systemic IFN‐γ response, but elicited pronounced TV in both IFN‐γ receptor (IFNGR)‐competent, and ifngr^?/? Tie2‐LacZ hearts. In contrast, stimulation of EC‐specific CD8⁺ T cells with β‐gal‐recombinant mouse cytomegalovirus (MCMV‐LacZ) in recipients of ifngr^+/+ Tie2‐LacZ hearts did not precipitate significant TV. However, MCMV‐LacZ infection of recipients of ifngr^?/? Tie2‐LacZ hearts led to massive activation of β‐gal‐specific CD8 T cells, and led to development of fulminant TV. Further analyses revealed that the strong systemic IFN‐γ “storm” associated with MCMV infection induced upregulation of programmed death‐1 ligand 1 (PD‐L1) on EC, and subsequent attenuation of programmed death‐1 (PD‐1)‐expressing EC‐specific CD8⁺ T cells. Thus, IFNGR signaling in ECs activates a potent peripheral negative feedback circuit that protects vascularized grafts from occlusive TV.     

Adaptive reconfiguration of the human NK‐cell compartment in response to cytomegalovirus: A different perspective of the host‐pathogen interaction

As discussed in this review, human cytomegalovirus (HCMV) infection in healthy individuals is associated with a variable and persistent increase of NK cells expressing the CD94/NKG2C activating receptor. The expansion of NKG2C⁺ NK cells reported in other infectious diseases is systematically associated with HCMV co‐infection. The functionally mature NKG2C^bright NK‐cell subset expanding in HCMV⁺ individuals displays inhibitory Ig‐like receptors (KIR and LILRB1) specific for self HLA class I, and low levels of NKp46 and NKp30 activating receptors. Such reconfiguration of the NK‐cell compartment appears particularly marked in immunocompromised patients and in children with symptomatic congenital infection, thus suggesting that its magnitude may be inversely related with the efficiency of the T‐cell‐mediated response. This effect of HCMV infection is reminiscent of the pattern of response of murine Ly49H⁺ NK cells against murine CMV (MCMV), and it has been hypothesized that a cognate interaction of the CD94/NKG2C receptor with HCMV‐infected cells may drive the expansion of the corresponding NK‐cell subset. Yet, the precise role of NKG2C⁺ cells in the control of HCMV infection, the molecular mechanisms underlying the NK‐cell compartment redistribution, as well as its putative influence in the response to other pathogens and tumors remain open issues.