Abstract
Background. Human cytomegalovirus (HCMV) is a ubiquitous viral infection of worldwide distribution. This virus is the most significant infectious cause of congenital disease, an important opportunist in the immunocompromised hosts, such as allogeneic hematopoietic stem cells transplantation (allo-HSCT) recipients (Mokarski E.S.,2013). If seropositive recipient develops HCMV infection after allo-HSCT, it is usually unknown whether it is a reactivation of endogenous HCMV or a reinfection by a new exogenous HCMV strain. The impact of genetic diversity of HCMV on its pathogenesis has not been well evaluated by now. However, the emerging data indicate a possible correlation: the viral load and the course of the infection were different in AIDS patients with different HCMV genotypes (Renzette, 2015). The estimation of a possible link between viral genotype and probability of HCMV infection occurrence is relevant. Very little data on difference in HCMV genotypes within one patient before and after allo-HSCT is available.
The aim. The aim of this study was the identification of difference in HCMV UL139 gene sequences before and after the allo-HSCT.
Materials and Methods. Patients: 13 allo-HSCT recipients (5 ALL, 3 AML, 3 CML, 1 AA, 1 lymphoma of the mantle) were enrolled in the study, male/female 6/7; median age was 27 (22-49) years. Patients' blood samples were collected within 6 month before and 6 month after transplantation and tested for the HCMV DNA by PCR. Positive samples were sequenced by Sanger inside the UL139 (putative membrane gp gene) region for genotyping. Sequences within one patient before and after transplantation were compared by BLAST (Basic Local Alignment Search Tool) software.
Results and discussion. Sequencing was successfully completed only in samples of 7 patients (pts), probably due to low concentration of the viral DNA in the samples or other technical issues. The comparison of sequences showed (see table) that 3 out of 7 pts had reactivation of endogenous virus, because sequences exhibited 100% match. Another 2 out of 7 patients' sequences showed about 88% match. This indicates change in genotype to phylogenetically closest one. The rest 2 pts did not show any similarity in sequences at all which definitely points to reinfection after allo-HSCT. Data obtained are similar to a recent study by Zawilinska (Zawilinska B, 2016), which appeals that reinfection occurs slightly more often than reactivation. Data analys showed that reactivation was detected in patients with AML, reinfection in patients with ALL. Average period before reactivation occurrence was 27 days and before reinfection occurrence - 111 days. Statistical reliability cannot be obtained due to patients' number paucity. The genotyping of patients' HCMV by comparison of sequences with known genotypes of the UL139 gene from GenBank® revealed that before transplantation HCMV genotype in 3 patients had a strong resemblance to genotype 2, another 2 patients had genotype close to the genotype 5, and 1 patient had genotype 1. After transplantation genotype 2 became dominant and was identified in 6 out of 7 patients (see table).
Conclusions. The conducted study shows that HCMV infection after allo-HSCT may be the result of both reactivation of endogenous virus and reinfection by exogenous strain. Reactivation was detected in patients with AML only, reinfection - in patients with ALL only. Reactivation developed earlier than reinfection (27 days versus 111 days). The chosen method allowed us to detect several mononucleotide substitutions in sequences, what can be useful in cases when no evident change of genotype happened after allo-HSCT. There are several possible explanations of the occurrence of reinfection: possible transmission from the outer environment or reactivation of a minor genotype if 2 or more HCMV genotypes originally had taken place. Further studies are required for more reliable conclusions.
No relevant conflicts of interest to declare.
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