Assessment of human cytomegalovirus (HCMV)- specific memory T and B-cell responses as predictors of HCMV infection after kidney transplantion

Abstract

Despite the outstanding progress made in the understanding of the immune response against viral pathogens as well as on the care-management of transplant patients since the beginning of organ transplantation, hCMV infection still represents a major adverse complication among solid organ and hematopoietic cell transplant patients directly threatening both allograft and patient survival.

While the advent of new and more potent anti-viral therapies used either as anti-viral treatments during active infection or as part of a preventive strategy, has lead to a significant reduction of the incidence of hCMV infection and its related complications, the occurrence of viral infection after transplantation is still considered as a rather unpredictable event. Certainly, this is the reflection of the considerably poor clinical monitoring of the viral immune susceptibility of each individual, which is merely based on the serological immune status combination between recipient and donor IgGantibody levels in sera and the direct assessment of the virus itself replicating in peripheral blood.

The work constituting this doctoral thesis, researches further into how assessing hCMV-specific memory T and B-cell subsets, using a highly sensitive technique such as the ELiSPOT assay, which allows an accurate enumeration of antigen-specific immune responses at the single cell level, may help to better identify cellular and humoral immunized patients against the hCMV and thus, ultimately helping identifying kidney allograft recipients at high risk of hCMV infection after kidney transplantation. Importantly, an accurate and reliable knowledge of the immune-protection level against hCMV of transplant patients would allow individualization for anti-viral decision-making, thus personalizing this therapy.

To date, an important body of evidence has been generated within the transplant scientific community, demonstrating the key role of the adaptive immunity, and particularly the cellular immune response in preventing, controlling and restricting viral replication. In contrast to previous reported data, in which have analyzed different types of organ transplant patients, receiving distinct type of anti-viral therapies and have fundamentally focused on the post-transplant setting, we here focused for the first time on the evaluation of hCMV-specific memory T and B cells against different immunogenic hCMV antigens prior to kidney transplantation in very clean and homogenous cohorts of kidney transplant recipients. In the first part of this thesis, it is shown that high frequencies of hCMV-specific T-cell responses, particularly against the IE-1 dominant hCMV antigen, may significantly improve the current serological identification of those kidney allograft recipients at high-risk for hCMV infection. Importantly, this approach was capable to discriminate such patients before transplantation with high sensitivity, regardless the type of preventive anti-viral strategy used based on the classical risk factors for the estimation of CMV risk after transplantation. Furthermore, the high negative predictive value of the test highlights the usefulness of such diagnostic tool among the kidney transplant population.

In the second part of this study, we provide further insight about the cross-talk between the humoral and cellular memory adaptive immune response against hCMV, by monitoring baseline hCMV-specific memory T and B-cell responses, which significantly increases the capacity to discriminate "true" immunized kidney transplant recipients against hCMV as compared to current evaluation of hCMV-specific antibody titers in the sera.

Our study points to the direction that monitoring IE-1 hCMV-specific T-cell frequencies before transplantation would help transplant physicians on the one hand to better discriminate patients with no need of hCMV prophylactic treatment from those in whom prophylaxis should preferentially be indicated and on the other, to better predict those patients in whom prophylaxis treatment could safely be discontinued.

El treball que constitueix aquesta tesi doctoral, investiga més a fons com avaluar cèl·lules T IB de memòria CMVh específiques, utilitzant una tècnica altament sensible, com l'assaig ELISPOT, que permet una enumeració precisa de respostes immunes antigen específiques a nivell individual cel·lular, pot ajudar a identificar millor els pacients cel.lulars i humorals immunitzat contra la CMVh i, per tant, en última instància, ajudar a la identificació de receptors d'al·loempelts renals amb alt risc d'infecció per CMVh després del trasplantament renal. És important destacar que un coneixement exacte i fiable del nivell de protecció immunitària contra CMVh dels pacients trasplantats permetria individualització per a la presa de decisions anti-viral, personalitzant així aquesta teràpia.

A la primera part d'aquesta tesi, es demostra que les altes freqüències de les respostes de cèl·lules T CMVh específics, en particular contra l'antigen CMVh dominant IE-l, pot millorar significativament l'actual identificació serològica dels receptors de al·loempelts renals d'alt risc per infecció per CMVh. És important destacar que aquest enfocament era capaç de discriminar aquests pacients abans del trasplantament amb una alta sensibilitat, sense importar el tipus d'estratègia antiviral preventiva utilitzada està basada en els factors de risc clàssics per a l'estimació del risc de CMV després del trasplantament. D'altra banda, l'alt valor predictiu negatiu de la prova posa de manifest la utilitat d'aquesta eina de diagnòstic entre la població trasplantament de ronyó.

Ala segona part d'aquest estudi, es proporcionarà més informació sobre la diafonia entre la resposta immune adaptativa memòria humoral i cel·lular contra de HCMV, mitjançant el control de la memòria T i de cèl·lules 8 respostes HCMV específics de la línia de base, el que augmenta significativament la capacitat de discriminar "veritable" immunitzat receptors de trasplantament renal en contra CMVh en comparació amb l'avaluació actual dels títols d'anticossos CMVh específics en els sèrums.

En els punts d'estudi a l'adreça que el monitoratge-l IE freqüències de cèl.lules T específiques de CMVh abans del trasplantament seria ajudar els metges de trasplantament, per una banda per discriminar millor els pacients sense necessitat de CMVh tractament profilàctic d'aquells a qui la profilaxi preferentment s'han d'indicar i en l'altra, per predir millor els pacients en els quals amb seguretat podria interrompre la profilaxi tractament.