Key words :

Key words: Age-dependent factors, Opportunistic infection, Renal allograft dysfunction, Transplant serostatus

Introduction
Cytomegalovirus (CMV) infection can present as asymptomatic viremia, viral syndrome with symptoms, and/or with an end organ disease (CMV disease). Infection acquired during seronegative status is termed primary infection, whereas infection diagnosed in recipients with previously confirmed seropositivity is called reactivation.¹ Cytomegalovirus has both short-term and long-term implications on allograft survival. This seems to be true with all types of infection, even asymptomatic viremia, highlighting the need to prevent the occurrence of infection in the first instance.² The most important risk factor for CMV infection is the serostatus of both the donor and the recipient. A seropositive donor kidney transplanted to a recipient who is seronegative (ie, D+/R-) carries the highest risk, followed by transplant to a recipient who is seropositive (regardless donor serostatus, ie, either D+/R+ or D-/R+).^2,3 Observational studies have shown that recipient age may be a risk factor for CMV reactivation if the recipient is seropositive for CMV.⁴

The incidence rate for CMV seropositivity increases with advancing age, and over 90% of people older than 60 years are seropositive for CMV.⁵ The United Kingdom (UK) has an aging population with 18.6% of people aged 65 years and older.⁶ The Southwest region of the UK has similar population demographics with areas having the highest life expectancy in the UK.⁶ This potentially affects the demographics of kidney recipients being considered for kidney transplant. We conducted a retrospective study to investigate the overall incidence of CMV reactivation in kidney transplant recipients who were seropositive for CMV at our center in the Southwest UK. In addition, we sought to ascertain and compare the infection rates in various age ranges and to determine the effect of CMV reactivation on 6-month and 12-month allograft function.

Materials and Methods
A retrospective study was conducted at the Southwest Transplant Center, University Hospitals Plymouth NHS Trust, UK. Kidney transplant recipients seropositive for CMV who received a transplant (regardless of the donor serostatus) during the period from January 2015 to January 2021 were followed up for 12 months after transplant. Demographic variables and other transplant-specific and CMV-specific variables were recorded.

Definition of cytomegalovirus reactivation
Occurrence of CMV viremia was diagnosed as a CMV polymerase chain reaction (PCR) titer >log 3.2 according to local transplant and microbiology guidelines, with or without symptoms suggestive of viral syndrome or tissue invasive disease. The CMV seropositivity in recipients was defined as a positive result for immunoglobin G by enzyme-linked immunosorbent assay as part of the pretransplant workup.

Data collection and statistical analyses
We used SPSS software (version 29) for the statistical analyses. Significance was defined as P < .05. Continuous parametric variables were analyzed with unpaired t tests, and nonparametric data were analyzed with Mann-Whitney U tests. All binary variables were analyzed with the Fisher exact test. Chi-square tests were used if there were several categories. We used binary logistic regression to determine the influence of each variable on CMV reactivation according to univariate analysis.

Results
Ninety-seven kidney transplant recipients with CMV seropositivity were included in our study. Table 1 shows the distribution of these patients according to the 5 age ranges commonly used by the National Health Service Blood and Transplant. Among 97 recipients, 47 (48.5%) were older than 60 years, and 49 (50.5%) developed CMV reactivation within the first 12 months after transplant. Table 2 shows a comparison of variables between recipients who developed CMV reactivation and those who did not develop CMV reactivation. There were 38 recipients aged 65 years and older and 58 younger than 65 years. We observed CMV reactivation in 24 of 38 recipients ≥65 years versus 25 of 59 (42%) patients <65 years (P = .046). Per the National Health Service Blood and Transplant age range guidelines, 30 of 49 recipients (61.2%) who developed CMV reactivation were older than 60 years (P = .026).

Table 3 compares transplant rejection, CMV acquisition time frame, and 6-month and 12-month graft outcomes. Reactivation of CMV occurred in 48 of 49 patients (98%) within 6 months posttransplant (P < .001). The mean 12-month graft function was 37.86 ± 21.54 mL/min in recipients with CMV reactivation versus 50.85 ± 23.18 mL/min in recipients without CMV reactivation (P = .005). Urinary tract infections developed within 3 months of transplant in 18 of 38 recipients (48%) aged ≥65 years compared with only 17 of 59 (28%) recipients aged <65 years (P = .018). Table 4 shows the binary logistic regression analysis results with CMV reactivation as the dependent variable. Recipient age and age ≥65 years were the only variables that predicted CMV reactivation (P = .048).

Discussion
Cytomegalovirus seropositivity increases with age. Almost 48% of our cohort was older than 60 years. In Europe and the United States, approximately 25% of kidney transplant recipients belong to the D+/R- CMV category, whereas 60% of recipients are seropositive (R+) for CMV at the time of transplant.⁷ Poloni and colleagues described accelerated aging and immune dysregulation in healthy, asymptomatic, older adults with CMV seropositivity.⁸ Cytomegalovirus affects peripheral T-cell phenotypes, increases inflammatory-mediated cytokines such as interleukin-6, and plays a role in immune dysregulation as humans age.⁹ Also, CMV is known to exploit the hematopoietic system with complexity that facilitates its initial infection and dissemination, followed by a prolonged period of latency in cells.¹⁰ With these details in perspective, older kidney recipients with CMV seropositivity may have a more at-risk immune system and thus may be at higher risk for reactivation of the virus when exposed to immunosuppression after transplant. Indeed, large population studies have shown a link between CMV seropositivity and cardiovascular mortality.¹¹ This link is thought to be due to the proinflammatory consequence of CMV infection. Aging and inflammation have a combined tandem effect, a phenomenon to which Franceschi and colleagues have assigned the term, inflamm-aging.¹²

Our results show that CMV reactivation was more common in older kidney recipients. These results are comparable to a similar study by Hemmersbach-Miller and colleagues, who described a 71.4% incidence of CMV reactivation in patients older than 65 years versus 44.4% for patients between 40 and 60 years of age, with a suggestion to consider universal prophylaxis in this patient cohort.⁴ Our results support these previously published results. Given this perspective, there is an argument to offer universal CMV prophylaxis to older kidney recipients with CMV seropositivity. Given the myriad harmful effects of CMV on the human body, as well as recent studies showing that even low-level viremia in the absence of CMV disease is associated with increased mortality in kidney transplant recipients, the best course of action appears to be prevention of CMV at the earliest possible stage.¹³ However, such action must be balanced against the (1) the financial cost of universal prophylaxis, (2) complications such as bone suppression and neutropenia, which are not infrequent with valganciclovir therapy, and (3) polypharmacy concerns.

Cytomegalovirus infection is common during the first 6 months after transplant. This is when the burden of immunosuppression is commonly highest. In a study of the natural history of CMV before the era of effective CMV prevention in 477 kidney transplant recipients, active CMV infection occurred within 3 months of transplant in 69% of D+/R- recipients and 67% of R+ recipients, and CMV disease occurred in 56% of D+/R- recipients and 20% of R+ recipients.¹⁴ Other known risk factors for the occurrence of CMV infection include the use of lymphocyte-depleting agents such as anti-thymocyte globulin for induction or maintenance immunosuppression, use of mycophenolate therapy, and use of high-dose corticosteroids to treat rejection episodes.^15-17 However, we found no significant difference in CMV reactivation rates in patients for whom lymphocyte-depleting agents were used for induction or treatment of rejection. We observed a similar trend with the use of high-dose corticosteroids for the treatment of rejection episodes.

We also observed a higher incidence of urinary tract infections in recipients older than 65 years. This reinforces the discussion with regard to older recipients being more prone to infections possibly due to a weaker immune system. This perspective provides support for early weaning of immunosuppression, particularly in older recipients, although this must be balanced against the risk of allograft rejection.

We observed that 12-month graft function was significantly lower in patients who developed CMV reactivation. Cytomegalovirus is well known to affect renal allografts and cause allograft dysfunction and loss.^2,3,14 There is a direct cytopathic effect of CMV on allografts, as well as indirect effects due to CMV disease in other organs that can lead to allograft dysfunction.¹⁸ Cytomegalovirus also upregulates allograft human leukocyte antigens which can promote acute allograft rejection.^19,20 We did not find a statistically significant difference in rejection rates for recipients who developed CMV reactivation versus those who did not. However, this lack of a significant effect may be due to a relatively smaller sample size.

Proper treatment of CMV infection is imperative to ensure early resolution of infection and prevention of drug resistance. Treatment is guided by symptoms, end organ involvement resolution (if present), and viral load monitoring with a quantitative nucleic acid amplification test, which is also used for surveillance testing and diagnosis of viremia/DNAemia. Available treatment options include oral and intravenous antiviral medications.²¹ Oral valganciclovir and intravenous ganciclovir treatment are associated with similar long-term outcomes in solid-organ transplant recipients with CMV syndrome and tissue-invasive CMV disease.²² Typically, intravenous therapy is preferred for tissue-invasive disease. Treatment should continue until results of viral polymerase chain reaction prove negative for 2 sequential weeks for 2 samples. Some clinicians have also given a so-called secondary prophylaxis for a few months after disease eradication to prevent recurrent infections, although present guidelines do not advocate this approach.²¹ Reduction or cessation of the antimetabolite immunosuppressant is a common practice during treatment of infection, and immunosuppressant reintroduction is usually at a lower dose after the infection has been completely treated. For recurrent infections, the immunosuppressant regimen may be stopped completely.²¹ Reduction in immunosuppression is described as an essential component for treatment of CMV, in the absence of allograft rejection.²³ In addition, dual (versus triple) immunosuppression therapy and lower blood concentrations of calcineurin inhibitors are significantly associated with eradication of CMV DNA at 21 days.²³ Reduction in antiviral dosing in the setting of persistent CMV DNAemia at day 21 is associated with a significant risk of drug resistance. Hence, valganciclovir treatment is recommended to continue until CMV DNAemia falls below a specific threshold and all clinical signs of CMV disease have resolved.^21,24

Our work has some limitations. It was performed in a single center and was a retrospective observational study with a relatively small sample size. However, our study does identify CMV reactivation as an important problem in older kidney recipients, and we have provided directions for future research and interventions. Our study is particularly relevant given the age demographics of patients being referred for transplant, an increasing proportion of whom are now presenting at older than 60 years of age.

Conclusions

We found a significantly higher incidence of CMV reactivation in seropositive kidney transplant recipients aged 65 years and older. Infections were acquired within the first 3 to 6 months after transplant. Twelve-month allograft function was significantly inferior in recipients with CMV reactivation. The risk of CMV seropositivity increases with age, and with an increasing number of older recipients seeking transplant, our results suggest that kidney recipients with CMV seropositivity should be considered for universal prophylaxis to prevent the occurrence of CMV reactivation and its harmful effects on allograft function and patient health. Multicenter trials focusing on this intervention in older kidney recipients will be invaluable in generating more robust evidence.

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