Reinfection of cytomegalovirus in renal transplantation

Prevalence and Impact of Cytomegalovirus Primary Infection and Reactivation on Graft Function in Post-Renal Transplant Recipients

Introduction Cytomegalovirus (CMV) is often associated with mortality and significant morbidity following renal transplantation leading to graft rejection or dysfunction. Primary CMV infection refers to the first detection of the virus in a person who has no prior evidence of CMV exposure before transplantation. CMV has a unique property called latency. After the initial infection, CMV can enter a dormant state within the body, residing in myeloid cells without causing active disease. CMV reactivation is likely when a latent CMV infection switches to a lytic phase of replication, which can be detected using IgG avidity ELISA. Aims and objectives This study aims to assess the prevalence of primary CMV infection and reactivation in renal transplant recipients, evaluate the impact of CMV infection on graft function following transplantation, and identify the risk factors and comorbidities associated with CMV-related graft rejection. Methodology During the study period from March 2020 to November 2021, blood samples were collected from 46 CMV-positive (by PCR) renal transplant recipients, and serum was separated and stored. IgG avidity ELISA test was performed, which served as a valuable tool to differentiate primary infection from reactivation due to difference in binding strength where low binding strength (low avidity<30%) indicated primary infection and high binding strength (high avidity>40%) indicated reactivation. All these patients were followed up to study the impact of CMV on graft functions. Results The age-wise distribution of patients shows a maximum number of cases under 40 years. The gender distribution of cases shows a higher preponderance of males (76%) compared to females (24%). The clinical presentation showed CMV syndrome as the most common (50%), followed by CMV colitis (37%), CMV nephritis (9%), CMV pneumonitis, CMV esophagitis, and CMV duodenitis, each comprising 2%. After performing the IgG avidity test, CMV infection with maximum cases of reactivation (87%) followed by primary infection (13%) was observed. The investigations related to renal dysfunction such as serum creatinine showed >3 mg/dL (85% of cases), 2.1-3 mg/dL (4.33% of cases), 1.6-2 mg/dL (2% of cases), 1-1.5 mg/dL (4.33% of cases) in decreasing order. Normal urea values are seen in 9% of cases followed by the range between 24 and 55 mg/dL in 67% and >100% in 24% of cases. The graft rejection based on the biopsy report showed that acute cellular rejection (ACR) (72%) was higher followed by antibody-mediated rejection (ABMR) with 15% and then ACR + ABMR with 4%. No rejection was found in 9% of cases. Renal dysfunction showed a higher preponderance to chronic graft dysfunction (67%) followed by acute graft dysfunction (24%) and stable graft function among 9% of cases. A comparison of graft dysfunction in primary infection/reactivation was assessed, and it was found that acute graft dysfunction was more common in primary infection. In the case of reactivation, chronic graft dysfunction was more common. Conclusion This study focuses on the microbiological dimensions and the critical role of CMV antibody screening. It underscores the necessity of vigilant monitoring and prophylactic antiviral therapy to reduce CMV infection risks and enhance patient outcomes. It also highlights the use of IgG avidity testing to differentiate between primary infection and reactivation, facilitating timely and effective interventions to prevent graft dysfunction and rejection.

Long-Term Evolution of the Adaptive NKG2C+ NK Cell Response to Cytomegalovirus Infection in Kidney Transplantation: An Insight on the Diversity of Host-Pathogen Interaction

Human CMV infection is frequent in kidney transplant recipients (KTR). Pretransplant Ag-specific T cells and adaptive NKG2C⁺ NK cells associate with reduced incidence of infection in CMV⁺ KTR. Expansions of adaptive NKG2C⁺ NK cells were reported in posttransplant CMV-infected KTR. To further explore this issue, NKG2C⁺ NK, CD8⁺, and TcRγδ T cells were analyzed pretransplant and at different time points posttransplant for ≥24 mo in a cohort of CMV⁺ KTR (n = 112), stratified according to CMV viremia detection. In cryopreserved samples from a subgroup (n = 49), adaptive NKG2C⁺ NK cell markers and T cell subsets were compared after a longer follow-up (median, 56 mo), assessing the frequencies of CMV-specific T cells and viremia at the last time point. Increased proportions of NKG2C⁺ NK, CD8⁺, and TcRγδ T cells were detected along posttransplant evolution in viremia(+) KTR. However, the individual magnitude and kinetics of the NKG2C⁺ NK response was variable and only exceptionally detected among viremia(-) KTR, presumably reflecting subclinical viral replication events. NKG2C⁺ expansions were independent of KLRC2 zygosity and associated with higher viral loads at diagnosis; no relation with other clinical parameters was perceived. Increased proportions of adaptive NKG2C⁺ NK cells (CD57⁺, ILT2⁺, FcεRIγ^-) were observed after resolution of viremia long-term posttransplant, coinciding with increased CD8⁺ and Vδ2^- γδ T cells; at that stage CMV-specific T cells were comparable to viremia(-) cases. These data suggest that adaptive NKG2C⁺ NK cells participate with T cells to restore CMV replication control, although their relative contribution cannot be discerned.

Pretransplant adaptive NKG2C+ NK cells protect against cytomegalovirus infection in kidney transplant recipients

Cytomegalovirus (CMV) infection constitutes a complication for kidney transplant recipients (KTR) and CMV-specific T cells reduce the risk of viral replication in seropositive patients. CMV promotes the adaptive differentiation and expansion of an NK cell subset, hallmarked by expression of the CD94/NKG2C receptor with additional characteristic features. We previously reported an association of pretransplant NKG2C+ NK cells with a reduced incidence of CMV infection. We have strengthened the analysis in cryopreserved peripheral blood mononuclear cells from an enlarged KTR cohort (n = 145) with homogeneous immunosuppression, excluding cases at low risk of infection (ie, CMV D-R-) or receiving antiviral prophylaxis. Moreover, adaptive NKG2C+ NK cell-associated markers (ie, NKG2A, CD57, Immunoglobulin-like transcript 2 [LIR1 or LILRB1], FcεRI γ chain, and Prolymphocytic Leukemia Zinc Finger transcription factor) as well as T lymphocyte subsets were assessed by multicolor flow cytometry. The relation of NKG2C+ NK cells with T cells specific for CMV antigens was analyzed in pretransplant patients (n = 29) and healthy controls (n = 28). Multivariate Cox regression and Kaplan-Meier analyses supported that NKG2C+ NK cells bearing adaptive markers were specifically associated with a reduced incidence of posttransplant symptomatic CMV infection; no correlation between NKG2C+ NK cells and CMV-specific T cells was observed. These results support that adaptive NKG2C+ NK cells contribute to control CMV infection in KTR.

Dual Role of Natural Killer Cells on Graft Rejection and Control of Cytomegalovirus Infection in Renal Transplantation

Allograft rejection constitutes a major complication of solid organ transplantation requiring prophylactic/therapeutic immunosuppression, which increases susceptibility of patients to infections and cancer. Beyond the pivotal role of alloantigen-specific T cells and antibodies in the pathogenesis of rejection, natural killer (NK) cells may display alloreactive potential in case of mismatch between recipient inhibitory killer-cell immunoglobulin-like receptors (KIRs) and graft HLA class I molecules. Several studies have addressed the impact of this variable in kidney transplant with conflicting conclusions; yet, increasing evidence supports that alloantibody-mediated NK cell activation via FcγRIIIA (CD16) contributes to rejection. On the other hand, human cytomegalovirus (HCMV) infection constitutes a risk factor directly associated with the rate of graft loss and reduced host survival. The levels of HCMV-specific CD8⁺ T cells have been reported to predict the risk of posttransplant infection, and KIR-B haplotypes containing activating KIR genes have been related with protection. HCMV infection promotes to a variable extent an adaptive differentiation and expansion of a subset of mature NK cells, which display the CD94/NKG2C-activating receptor. Evidence supporting that adaptive NKG2C⁺ NK cells may contribute to control the viral infection in kidney transplant recipients has been recently obtained. The dual role of NK cells in the interrelation of HCMV infection with rejection deserves attention. Further phenotypic, functional, and genetic analyses of NK cells may provide additional insights on the pathogenesis of solid organ transplant complications, leading to the development of biomarkers with potential clinical value.

Modulation of cellular signaling by herpesvirus-encoded G protein-coupled receptors

Human herpesviruses (HHVs) are widespread infectious pathogens that have been associated with proliferative and inflammatory diseases. During viral evolution, HHVs have pirated genes encoding viral G protein-coupled receptors (vGPCRs), which are expressed on infected host cells. These vGPCRs show highest homology to human chemokine receptors, which play a key role in the immune system. Importantly, vGPCRs have acquired unique properties such as constitutive activity and the ability to bind a broad range of human chemokines. This allows vGPCRs to hijack human proteins and modulate cellular signaling for the benefit of the virus, ultimately resulting in immune evasion and viral dissemination to establish a widespread and lifelong infection. Knowledge on the mechanisms by which herpesviruses reprogram cellular signaling might provide insight in the contribution of vGPCRs to viral survival and herpesvirus-associated pathologies.