Prospective, Randomized Study for Predicting Human Cytomegalovirus (hCMV) Infection Based on Baseline hCMV Specific T-cell Response in Kidney Transplant

Human cytomegalovirus (hCMV) is the most common opportunistic pathogen in the first months after solid organ transplantation. Traditionally, hCMV infection in renal transplant patients is indirectly associated with an increased risk of acute rejection, chronic graft dysfunction, graft loss and even increased patient mortality.

The susceptibility of developing hCMV infection is essentially determined by the immune status of the donor and the receptor with regards to the virus, whereby seronegative recipients (IgG) receiving a graft from a seropositive donor (IgG +) are the group of patients with a particularly high risk for developing hCMV infection and disease. In fact, without the administration of a preventative therapy for hCMV, 60 to 70% of this population at risk have an infection (presence of virus in the blood) and up to approximately 20% will develop associated systemic disease (viral invasion of tissues ). Interestingly, the incidence of hCMV infection in patients who are seropositive for the HIV virus and receive a graft is about 20%, increasing to 30% if given cell depletion therapies with polyclonal antibodies administered after transplantation.

There are currently two treatment options to prevent infection by hCMV; One is prophylactic, whereby the antiviral therapy is administered orally for about 90 to 100 days after transplantation in all patients considered at risk (donor IgG+, recipient IgG-) and the second is pre-emptive therapy, in which the presence of virus in the peripheral blood is monitored periodically after transplantation until it appears (at present by polymerase chain reaction (PCR) detection of viral nucleic acids),thus triggering the need for intensive antiviral therapy. When compared with no pharmacological intervention, both therapeutic strategies have demonstrated a significant reduction in the development of hCMV and other herpes virus type diseases, and even a decrease in the incidence of acute graft rejection. However, there are few prospective randomized studies comparing the effectiveness of these two therapeutic alternatives. Recently, a German group prospectively compared the efficacy of prophylactic oral ganciclovir versus intravenous ganciclovir therapy in a group of 148 patients receiving high serological risk renal transplants for hCMV. Interestingly, the group that received prophylactic oral therapy had a higher graft survival at 4 years of follow up (uncensored for death) than the group receiving ganciclovir, suggesting that, despite the administration of intensive intravenous therapy at the time of detection of the virus in the blood, the potential deleterious effect of the virus on the organs during the initial asymptomatic period could explain the benefits of prophylactic therapy from the beginning.

These results have important implications, both clinical and socioeconomic, as they seem to imply the need for systemic prophylaxis to prevent the development of viral infection in all patients currently considered at risk (R -/D +). Moreover, another interesting study which compared primary prophylaxis with oral valganciclovir versus early therapy prevention (pre-emptive therapy) in a large group of kidney transplant recipients with different serologic donor / recipient combinations, showed significantly higher rates of viremia and CMV disease in patients receiving treatment with an incidence of serological CMV infection of up to 53% in serological R + / R + combinations. In this sense, the latest international consensus guidelines indicate that both types of therapy (early and prophylactic) are acceptable, with a degree of moderately high evidence, for groups of seropositive patients receiving a graft from a seropositive donor. The investigator unit has adopted a pre-emptive protocol for the last two years, systematically monitoring viral replication in R + / D + pairs, except in those patients receiving immunosuppressive therapy with Thymoglobulin to whom the investigator assigns a prophylactic treatment with oral valganciclovir for 3 months.This change was introduced 2 years ago before which a prophylactic treatment was given to all R + / R + patients. This change has not led to improved results in terms of prevention of cytomegalic infection.

All such discrepancies among study results examining the efficacy of various therapeutic strategies preventing hCMV could be explained by the poor diagnostic capabilities currently available to identify those patients truly at high risk of developing cytomegalic infection. This is illustrated by the fact that hCMV infection reappears in some patients (15-20%) after transplantation even though they are seropositive (R+) and that, while the majority of patients receiving prophylactic treatment never develop cytomegalic infection after its discontinuation, a small percentage (10-15%) still does, and that, even though 70-80% of seronegative (R-) patients receiving a seropositive graft (R+) will develop post-transplant hCMV infection unless they receive prophylactic treatment, approximately 20-30% never will. All of this leads to important therapeutic contradictions in this field such as that, even though the majority of seropositive recipients will not develop hCMV infection, all of them will still receive an intense and costly monitoring for viremia, and that, although a large majority of patients receiving prophylactic treatment will not develop infection upon treatment discontinuation, continuing such prophylactic antiviral treatment is being proposed across the clinical transplantation community, suggesting that immune surveillance of the risk of developing a post-transplant hCMV infection is currently very poor in clinical practice. It is well established that memory/effector T-cells play a pivotal role in controlling general viral replication and survival, particularly for hCMV. Even though it has been reported that cytotoxic CD8+ T-cells can be activated by a myriad of immunogenic hCMV viral proteins, the predominant and most robust response is directed at the immediate early antigen-1 (IE-1) and phosphoprotein 65 (pp65), which is thought to play a critical role in controlling hCMV replication. Recently published studies suggest that such cellular response is even important for the control and prevention of infection after transplantation.

All such publications, however, refer to the post-transplantation period while patients are under the effects of chronic immunosuppressive therapy and evaluate the T-cell response using assays hardly applicable to routine clinical practice. Even though available, such assays are not used in routine clinical practice to evaluate the hCMV-specific immune response.

One of the most precise functional assays to assess both memory cell and humoral responses under evaluation is the interferon-γ ELISPOT assay. This assay measures antigen-specific memory response frequency by individual cells as they become stimulated.

Recent work in transplantation has established that the detection of highly alloreactive circulating donor-specific T-cells by ELISPOT offers prognostic value when assessing the risk of acute rejection or chronic post-transplant graft dysfunction. Likewise, ELISPOT has been shown to be able to detect highly reactive hCMV-specific T-cells associated with a lower risk of viral infection with both sensitivity and specificity.

The investigator group has recently published that low frequency rates of specific hCMV (IE-1) T-cells before transplantation identify renal transplant recipients at a higher risk of post-transplant hCMV infection with precision, regardless of the therapeutic strategy adopted against hCMV. Remarkably, the same results were observed in patients receiving induction therapy with polyclonal antibodies (Thymoglobuline ®). The investigator thus believes that such an assay approach would allow to identify with precision those patients at risk of developing an infection regardless of their hCMV serology status.