The impact of cytomegalovirus serology for 7-year graft survival in cadaveric kidney transplantation--the Newcastle experience

Murine cytomegalovirus promotes renal allograft inflammation via Th1/17 cells and IL-17A

Human cytomegalovirus (HCMV) infection is associated with renal allograft failure. Allograft damage in animal models is accelerated by CMV-induced T helper 17 (Th17) cell infiltrates. However, the mechanisms whereby CMV promotes Th17 cell-mediated pathological organ inflammation are uncharacterized. Here we demonstrate that murine CMV (MCMV)-induced intragraft Th17 cells have a Th1/17 phenotype co-expressing IFN-γ and/or TNF-α, but only a minority of these cells are MCMV specific. Instead, MCMV promotes intragraft expression of CCL20 and CXCL10, which are associated with recruitment of CCR6⁺ CXCR3⁺ Th17 cells. MCMV also enhances Th17 cell infiltrates after ischemia-reperfusion injury, independent of allogeneic responses. Pharmacologic inhibition of the Th17 cell signature cytokine, IL-17A, ameliorates MCMV-associated allograft damage without increasing intragraft viral loads or reducing MCMV-specific Th1 cell infiltrates. Clinically, HCMV DNAemia is associated with higher serum IL-17A among renal transplant patients with acute rejection, linking HCMV reactivation with Th17 cell cytokine expression. In summary, CMV promotes allograft damage via cytokine-mediated Th1/17 cell recruitment, which may be pharmacologically targeted to mitigate graft injury while preserving antiviral T cell immunity.

Human cytomegalovirus infection: A considerable issue following allogeneic hematopoietic stem cell transplantation

Cytomegalovirus (CMV) is an opportunistic virus, whereby recipients are most susceptible following allogeneic hematopoietic stem cell transplantation (allo-HSCT). With the development of novel immunosuppressive agents and antiviral drugs, accompanied with the widespread application of prophylaxis and preemptive treatment, significant developments have been made in transplant recipients with human (H)CMV infection. However, HCMV remains an important cause of short- and long-term morbidity and mortality in transplant recipients. The present review summarizes the molecular mechanism and risk factors of HCMV reactivation following allo-HSCT, the diagnosis of CMV infection following allo-HSCT, prophylaxis and treatment of HCMV infection, and future perspectives. All relevant literature were retrieved from PubMed and have been reviewed.

NK cell and Th17 responses are differentially induced in murine cytomegalovirus infected renal allografts and vary according to recipient virus dose and strain

Human cytomegalovirus (HCMV) donor positive (D+) serostatus with acute rejection is associated with renal allograft loss, but the impact of recipient positive (R+) serostatus is unclear. In an allogeneic renal transplant model, antiviral natural killer (NK) and CD8+ T cell memory responses in murine CMV (MCMV) D+/R+ transplants were compared to D-/R- and D+/R- transplants, with recipient infection varied by MCMV dose and strain. D+/R- transplants had high primary antiviral cytolytic (interferon-γ+) and cytotoxic (granzyme B+) NK responses, whereas NK memory responses were lower in D+/R+ recipients receiving a high primary MCMV dose. Despite MCMV immunity, D+/R+ recipients receiving a low MCMV dose showed primary-like high cytolytic and cytotoxic NK responses. D+/R+ transplants infected with different D/R strains had low cytolytic NK responses but high cytotoxic NK responses. NK memory also induced a novel TNF-α+ NK response among high-dose virus recipients. MCMV+ transplants had greater Th17 responses than MCMV-uninfected transplants and Th17 inhibition ameliorated graft injury. All MCMV+ recipients had similar CD8+ T cell responses. In sum, NK and Th17 responses, but not CD8+ T cells, varied according to conditions of primary recipient infection. This variability could contribute to variable graft outcomes in HCMV D+/R+ renal transplantation.

Ganciclovir prophylaxis improves late murine cytomegalovirus-induced renal allograft damage

BACKGROUND

Human cytomegalovirus (CMV) infection is associated with inferior survival in renal transplant patients, and ganciclovir (GCV) prophylaxis is associated with improved survival. In a murine CMV (MCMV) renal transplantation model, ganciclovir prophylaxis improved innate infiltrates and allograft damage during the period of prophylaxis. In this study, late effects were examined after the discontinuation of prophylaxis.

METHODS

MCMV D+/R- and D-/R- allogeneic transplants were performed with cyclosporine immunosuppression. One D+/R- cohort received ganciclovir prophylaxis for 14 days after transplantation followed by 28 days without ganciclovir. At 42 days after transplantation, grafts were analyzed for histologic tissue damage and immune infiltrates. Another D+/R- cohort was treated with anti-NK1.1 antibodies for 14 days after transplantation and compared with animals without natural killer (NK) cell depletion.

RESULTS

At day 42, MCMV-infected transplants had higher damage scores (15.6±0.6) compared with uninfected transplants (8.3±0.9; P<0.01), which improved in ganciclovir-treated allografts (9.5±1.4). MCMV-infected grafts contained greater frequencies of NK cell and myeloid infiltrates compared with uninfected grafts (P<0.05), which decreased in the ganciclovir-treated grafts. NK cell depletion improved allograft histology of MCMV-infected grafts.

CONCLUSIONS

MCMV infection exacerbates late renal allograft damage and is associated with NK and myeloid cell infiltrates. Ganciclovir prophylaxis reduces allograft injury and NK cell and myeloid infiltrates even after the cessation of prophylaxis. NK cell depletion in MCMV-infected transplants also improves histology. These results suggest that ganciclovir prophylaxis may have a long-term beneficial effect on CMV-infected renal allografts and suggest a potential role for NK cells in the pathogenesis of CMV-associated allograft injury.

Ganciclovir transiently attenuates murine cytomegalovirus-associated renal allograft inflammation

BACKGROUND

Prophylactic ganciclovir (GCV) is used in high-risk renal transplant patients to prevent acute cytomegalovirus (CMV) disease, but its impact on inflammation within the allograft itself remains undefined.

METHODS

To study the effect of GCV prophylaxis on allograft inflammation, murine CMV (MCMV)-infected allografts were analyzed in a murine donor positive/recipient negative allogeneic renal transplantation model by flow cytometry and immunofluorescent staining.

RESULTS

By flow cytometry, CD45+ leukocyte infiltrates were more abundant in MCMV-infected allografts at 14 days posttransplant compared with uninfected grafts (P<0.01) and decreased in the presence of GCV (P<0.05). CD11c+ dendritic cells, Gr-1+ myeloid cells, CD204+ macrophages, and CD49b+ natural killer cells were reduced in GCV-treated allografts compared with MCMV-infected grafts without GCV treatment (P<0.05). However, GCV failed to reduce these cell types to levels found in MCMV-uninfected allografts. By day 7 after cessation of GCV prophylaxis, dendritic cells, macrophages, and natural killer cells increased in number and became statistically indistinguishable from numbers of cells found in MCMV-infected allografts without GCV. GCV treatment did not affect the numbers of CD4+, CD8+, or CD19+/B220+ lymphocytes infiltrating the allografts. Infiltrates were confirmed histologically by immunofluorescent staining for CD3+ and CD11b+ cells.

CONCLUSIONS

In this model, MCMV-infected allografts developed significantly greater innate and adaptive leukocytic infiltrates compared with uninfected grafts. GCV attenuated the MCMV-associated innate leukocyte infiltrates in infected allografts but not the lymphocytic infiltrates. The attenuated innate response was limited to the period of GCV prophylaxis.

Human cytomegalovirus induces TGF-β1 activation in renal tubular epithelial cells after epithelial-to-mesenchymal transition

Human cytomegalovirus (HCMV) infection is associated epidemiologically with poor outcome of renal allografts due to mechanisms which remain largely undefined. Transforming growth factor-β1 (TGF-β1), a potent fibrogenic cytokine, is more abundant in rejecting renal allografts that are infected with either HCMV or rat CMV as compared to uninfected, rejecting grafts. TGF-β1 induces renal fibrosis via epithelial-to-mesenchymal transition (EMT) of renal epithelial cells, a process by which epithelial cells acquire mesenchymal characteristics and a migratory phenotype, and secrete molecules associated with extracellular matrix deposition and remodeling. We report that human renal tubular epithelial cells infected in vitro with HCMV and exposed to TGF-β1 underwent morphologic and transcriptional changes of EMT, similar to uninfected cells. HCMV infected cells after EMT also activated extracellular latent TGF-β1 via induction of MMP-2. Renal epithelial cells transiently transfected with only the HCMV IE1 or IE2 open reading frames and stimulated to undergo EMT also induced TGF-β1 activation associated with MMP-2 production, suggesting a role for these viral gene products in MMP-2 production. Consistent with the function of these immediate early gene products, the antiviral agents ganciclovir and foscarnet did not inhibit TGF-β1 production after EMT by HCMV infected cells. These results indicate that HCMV infected renal tubular epithelial cells can undergo EMT after exposure to TGF-β1, similar to uninfected renal epithelial cells, but that HCMV infection by inducing active TGF-β1 may potentiate renal fibrosis. Our findings provide in vitro evidence for a pathogenic mechanism that could explain the clinical association between HCMV infection, TGF-β1, and adverse renal allograft outcome.

Human cytomegalovirus (HCMV) is a common virus that establishes lifelong persistence in the host. Although asymptomatic in healthy people, HCMV can reactivate and cause disease in immunosuppressed patients, such as those undergoing kidney transplantation. HCMV infection is associated with inferior renal allograft survival compared to transplants without HCMV infection. HCMV infected allografts also contain higher levels of the fibrogenic cytokine, transforming growth factor-β1 (TGF-β1), compared to uninfected allografts. TGF-β1 is a potent inducer of renal fibrosis and causes epithelial-to-mesenchymal transition (EMT), whereby epithelial cells acquire characteristics of cells of mesenchymal origin and express molecules associated with fibrosis. Our work shows that renal epithelial cells infected in vitro with HCMV can undergo EMT, but that HCMV infected cells produce greater amounts of the fibrogenic molecule TGF-β1, compared to uninfected cells after EMT. We have shown that this effect is likely due to specific HCMV genes (IE1, IE2), and cannot be prevented by administration of antivirals such as ganciclovir or foscarnet. These data suggest that HCMV may contribute to adverse renal allograft outcome by exacerbating TGF-β1 induced renal fibrosis. Understanding such mechanisms will permit the development of treatments that could improve long-term renal allograft survival in HCMV infected patients.