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TTV quantification predicts infection after kidney transplantation and might be a potential tool to tailor immunosuppressive drug therapy.

In lung transplant patients undergoing immunosuppression, more than one human cytomegalovirus (HCMV) genotype may emerge during follow-up, and this could be critical for the outcome of HCMV infection. Up to now, many cases of infection with multiple HCMV genotypes were probably overlooked due to the limitations of the current genotyping approaches. We have now analyzed mixed-genotype infections in 17 clinical samples from 9 lung transplant patients using the highly sensitive ultradeep-pyrosequencing (UDPS) technology. UDPS genotyping was performed at three variable HCMV genes, coding for glycoprotein N (gN), glycoprotein O (gO), and UL139. Simultaneous analysis of a mean of 10,430 sequence reads per amplicon allowed the relative amounts of distinct genotypes in the samples to be determined down to 0.1% to 1% abundance. Complex mixtures of up to six different HCMV genotypes per sample were observed. In all samples, no more than two major genotypes accounted for at least 88% of the HCMV DNA load, and these were often accompanied by up to four low-abundance genotypes at frequencies of 0.1% to 8.6%. No evidence for the emergence of new genotypes or sequence changes over time was observed. However, analysis of different samples withdrawn from the same patients at different time points revealed that the relative levels of replication of the individual HCMV genotypes changed within a mixed-genotype population upon reemergence of the virus. Our data show for the first time that, similar to what has been hypothesized for the murine model, HCMV reactivation in humans seems to occur stochastically.Human cytomegalovirus (HCMV) is the most important viral pathogen affecting patients after solid organ transplantation (12,18,29). Lung transplant recipients have an especially high risk of acquiring severe and sometimes fatal HCMV infections, which are also associated directly or indirectly with graft rejection and bronchiolitis obliterans syndrome (6, 53).Human cytomegalovirus is a double-stranded DNA virus with a genome size of about 236 kb that is predicted to contain 165 protein-coding genes (9). Although most of the HCMV genome is highly conserved among the various HCMV strains, a subset of genes exhibits a high degree of variability, as has been shown by genome-wide sequence analysis as well as by examination of individual genes. A high level of genetic heterogeneity usually occurs in a limited number of distinct genotypes (9, 32, 33). Among the most variable genes are the viral envelope glycoprotein N (gN) and gO genes and the gene encoding the predicted membrane glycoprotein UL139. Sequence analysis of highly polymorphic regions within these three genes allows the discrimination of seven distinct gN genotypes (30, 31) and eight distinct gO and UL139 genotypes (3,24,35,45). The existence of such a large number of distinct genotypes provides a useful tool for investigating HCMV population diversity within a host.Reinfection with different HCMV strains is possible in the human host, and several strains can accumulate during...

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BackgroundThe human Torque Teno virus (TTV) causes persistent viremia in most immunocompetent individuals. Elevated TTV levels are observed after solid organ transplantation and are related to the extent of immunosuppression especially during the phase of maintenance immunosuppression. However, the extent to which the TTV increase in the early phase post-transplantation is associated with the patient’s immunosuppressive state is unclear.ObjectivesIn this study, we assessed the TTV increase dynamics in detail during the first three months after lung transplantation under a defined immunosuppressive regimen and in relation to the pre-transplant TTV level.Study DesignForty-six lung transplant recipients (LTRs) were included in this prospective longitudinal study. All received alemtuzumab induction combined with tacrolimus and corticosteroids immunosuppressive therapy. Plasma TTV DNA was monitored before transplantation and regularly within the first three months post-transplantation (n = 320 samples; mean sampling interval: 12.2 days).ResultsIn 43/46 LTRs (93%), TTV DNA was detectable before transplantation (median 4.4 log10 copies/mL; range: 2.0–6.4). All 46 LTRs showed a TTV increase post-transplantation, which followed a sigmoidal-shaped curve before the median peak level of 9.4 log10 copies/mL (range: 7.6–10.7) was reached at a median of day 67 (range: 41–92). The individual TTV DNA doubling times (range: 1.4–20.1 days) significantly correlated with the pre-transplant TTV levels calculated over 30 or 60 days post-transplantation (r = 0.61, 0.54, respectively; both P < 0.001), but did not correlate with the mean tacrolimus blood levels. Pre-transplant TTV levels were not associated with time and level of the patients’ post-transplant TTV peak load.ConclusionThe TTV level may be used to mirror the state of immunosuppression only after the patients’ initial peak TTV level is reached.