The prevention and treatment of cytomegalovirus infection in haematopoietic stem cell transplantation

Differential Reactivation of Cytomegalovirus and Epstein-Barr Virus in Patients with B Cell Lymphoma

Although cytomegalovirus (CMV) and Epstein-Barr virus (EBV) are considered latent viruses, their reactivation occurs in immunosuppressed conditions. We previously reported that CMV and EBV are reactivated in patients receiving immunosuppressive therapy and/or chemotherapy. This retrospective, single-center study aimed to determine the frequency of viral reactivation and clinical characteristics of patients with B cell lymphoma (B-ML) receiving chemotherapy. Twenty-four patients (mean age 73 years, range 40-87 years; male-to-female ratio, 15:9) with diffuse large B cell lymphoma (n = 15), follicular lymphoma (n = 8), or mantle cell lymphoma (n = 1) were enrolled. Serum CMV and EBV DNA levels were analyzed using quantitative real-time polymerase chain reaction in patients with B-ML receiving chemotherapy. We determined the cumulative reactivation of each virus and analyzed the relationship between viral reactivation and clinical characteristics. Three patients experienced relapse or refractory (R/R) disease and the others had de novo lymphomas. The frequencies of CMV and EBV reactivations were 54.2% and 37.5%, respectively. CMV reactivation occurred significantly earlier during chemotherapy courses in R/R patients than in de novo patients (p = 0.0038), while EBV reactivation was frequently found before treatment. Baseline serum levels of soluble interleukin-2 receptor were higher (4318.0 vs. 981.1 U/mL, p = 0.010) and hemoglobin levels were lower (11.1 vs. 13.0 g/dL, p = 0.0038) in patients with EBV reactivation than in those without reactivation. These findings were not observed in patients with CMV reactivation. CMV reactivation was associated with iatrogenic immunosuppression, whereas EBV reactivation was related to immunosuppression by lymphoma, indicating that the mechanisms of these viral reactivations differed.

New therapies for human cytomegalovirus infections

The recent approval of letermovir marks a new era of therapy for human cytomegalovirus (HCMV) infections, particularly for the prevention of HCMV disease in hematopoietic stem cell transplant recipients. For almost 30 years ganciclovir has been the therapy of choice for these infections and by today's standards this drug exhibits only modest antiviral activity that is often insufficient to completely suppress viral replication, and drives the selection of drug-resistant variants that continue to replicate and contribute to disease. While ganciclovir remains the therapy of choice, additional drugs that inhibit novel molecular targets, such as letermovir, will be required as highly effective combination therapies are developed not only for the treatment of immunocompromised hosts, but also for congenitally infected infants. Sustained efforts, largely in the biotech industry and academia, have identified additional highly active lead compounds that have progressed into clinical studies with varying levels of success and at least two have the potential to be approved in the near future. Some of the new drugs in the pipeline inhibit new molecular targets, remain effective against isolates that have developed resistance to existing therapies, and promise to augment existing therapeutic regimens. Here, we will describe some of the unique features of HCMV biology and discuss their effect on therapeutic needs. Existing drugs will also be discussed and some of the more promising candidates will be reviewed with an emphasis on those progressing through clinical studies. The in vitro and in vivo antiviral activity, spectrum of antiviral activity, and mechanism of action of new compounds will be reviewed to provide an update on potential new therapies for HCMV infections that have progressed significantly in recent years.

Cyclophilin A as a target in the treatment of cytomegalovirus infections

BACKGROUND

Viruses are obligate parasites that depend on the cellular machinery of the host to regenerate and manufacture their proteins. Most antiviral drugs on the market today target viral proteins. However, the more recent strategies involve targeting the host cell proteins or pathways that mediate viral replication. This new approach would be effective for most viruses while minimizing drug resistance and toxicity.

METHODS

Cytomegalovirus replication, latency, and immune response are mediated by the intermediate early protein 2, the main protein that determines the effectiveness of drugs in cytomegalovirus inhibition. This review explains how intermediate early protein 2 can modify the action of cyclosporin A, an immunosuppressive, and antiviral drug. It also links all the pathways mediated by cyclosporin A, cytomegalovirus replication, and its encoded proteins.

RESULTS

Intermediate early protein 2 can influence the cellular cyclophilin A pathway, affecting cyclosporin A as a mediator of viral replication or anti-cytomegalovirus drug.

CONCLUSION

Cyclosporin A has a dual function in cytomegalovirus pathogenesis. It has the immunosuppressive effect that establishes virus replication through the inhibition of T-cell function. It also has an anti-cytomegalovirus effect mediated by intermediate early protein 2. Both of these functions involve cyclophilin A pathway.

Immune Reconstitution after Allogeneic Hematopoietic Stem Cell Transplantation

The timely reconstitution and regain of function of a donor-derived immune system is of utmost importance for the recovery and long-term survival of patients after allogeneic hematopoietic stem cell transplantation (HSCT). Of note, new developments such as umbilical cord blood or haploidentical grafts were associated with prolonged immunodeficiency due to delayed immune reconstitution, raising the need for better understanding and enhancing the process of immune reconstitution and finding strategies to further optimize these transplant procedures. Immune reconstitution post-HSCT occurs in several phases, innate immunity being the first to regain function. The slow T cell reconstitution is regarded as primarily responsible for deleterious infections with latent viruses or fungi, occurrence of graft-versus-host disease, and relapse. Here we aim to summarize the major steps of the adaptive immune reconstitution and will discuss the importance of immune balance in patients after HSCT.

The immune response to cytomegalovirus in allogeneic hematopoietic stem cell transplant recipients

Approximately, up to 70 % of the human population is infected with cytomegalovirus (CMV) that persists for life in a latent state. In healthy people, CMV reactivation induces the expansion of CMV-specific T cells up to 10 % of the entire T cell repertoire. On the contrary, CMV infection is a major opportunistic viral pathogen that remains a leading cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation. Due to the delayed CMV-specific immune recovery, the incidence of CMV reactivation during post-transplant period is very high. Several methods are currently available for the monitoring of CMV-specific responses that help in clinical monitoring. In this review, essential aspects in the immune recovery against CMV are discussed to improve the better understanding of the immune system relying on CMV infection and, thereby, helping the avoidance of CMV disease or reactivation following hematopoietic stem cell transplantation with severe consequences for the transplanted patients.

Selection and recombinant phenotyping of a novel CMX001 and cidofovir resistance mutation in human cytomegalovirus

CMX001 is an orally available lipid acyclic nucleotide phosphonate that delivers high intracellular levels of cidofovir (CDV)-diphosphate and exhibits enhanced in vitro antiviral activity against a wide range of double-stranded DNA viruses, including cytomegalovirus (CMV). Mutations in the DNA polymerase of CMV that impart resistance to CDV also render the virus resistant to CMX001. Here, we report a novel resistance mutation that arose under the selective pressure of CMX001. The wild-type CMV strain AD169 was propagated in human foreskin fibroblasts under increasing concentrations of CMX001 over 10 months, and the resulting strain (named CMX001(R)) was less susceptible to CDV and CMX001 in a plaque reduction assay. Genotypic analysis of virus strain CMX001(R) via conventional sequencing of the genes encoding the CMV DNA polymerase (UL54) and UL97 kinase (UL97) demonstrated one mutation that changed the wild-type aspartate to glutamate at position 542 in UL54. A recombinant virus with this novel D542E mutation was generated via bacterial artificial chromosome-mediated marker transfer experiments. Subsequent phenotypic resistance analysis of the D542E mutant demonstrated reductions in susceptibility of greater than 10-fold to CMX001 and CDV, but no resistance to foscarnet (FOS) or ganciclovir (GCV). Analysis of replicative fitness showed that both strain CMX001(R) and the D542E mutant viruses demonstrated a smaller plaque phenotype and slower replication kinetics than their respective parent viruses. These data describe the first resistance mutation generated under the selective pressure of CMX001 and suggest that CMX001 may have a unique resistance profile associated with reduced viral replication and maintenance of sensitivity to FOS and GCV.

Cytomegalovirus infection in mesenchymal stem cells and their activation could be enhanced by nuclear factor-κB inhibitor pyrrolidinedithiocarbamate in vitro

Because of the central role of the transcription factor nuclear factor (NF)-κB in cell survival and proliferation in many kinds of cancer cells, NF-κB inhibitors may have a potential role in cancer therapy. Currently, many NF-κB inhibitors are used for immunosuppression to treat hematologic malignancy patients after stem cell transplantation (SCT). Human cytomegalovirus (HCMV) infection is one of the most common complications following SCT. Some workers have reported that HCMV infection has a close relationship to NF-κB activation; however, the specific effects of NF-κB inhibitors, such as pyrrolidinedithiocarbamate (PDTC), on infection with and activation of CMV in mesenchymal stem cells (MSCs) remain unknown. In our study, we isolated MSCs from the bone marrows of healthy human donors for infection with 1 tcid(50) of HCMV with or without 1 μmol/L PDTC. After 48 hours of culture in dmem supplemented with 10% (volume per volume) fetal calf serum, we tested MSCs using reverse transcription-polymerase chain reaction (RT-PCR) assays to detect messenger RNA (mRNA) expression of HCMV immediate early (IE) gene and the GAPDH gene. Flow cytometry was used to detect HCMV pp65 antigen-positive cells and transmission electron microscopy (TEM) for intra cellular HCMV particles. We observed that the shape of the MSCs changed in response to infection by 1 TCID(50) of HCMV. MSCs infected by 1 TCID(50) of HCMV in combination with 1 μmol/L of PDTC changed their shapes more profoundly; almost all cells went from a thin elongated profile to a round, thick ball. In contrast, the shape of cells treated with PDTC alone or the HCMV mock-infected elements did not change. The RT-PCR assay showed that there was a bright band corresponding to HCMV IE mRNA in MSCs infected with 1 TCID(50) of HCMV in combination with 1 μmol/L of PDTC, as compared with cells infected by only 1 TCID(50) of HCMV. The HCMV mock-infected MSCs did not express HCMV IE mRNA. Using flow cytometry, we detected more HCMV pp65 antigen-positive cells among MSCs infected with 1 TCID(50) of HCMV in combination with 1 μmol/L of PDTC. HCMV particles were observed by TEM in the nucleus and cytoplasm of MSCs infected with HCMV. There were more HCMV particles in cells infected by HCMV in combination with PDTC. In conclusion, NF-κB activation may affect HCMV infection efficiency of MSCs. An NF-κB inhibitor increased the infection by activation of HCMV in MSCs, thus we should pay close attention to HCMV infection when we prescribe an NF-κB inhibitor in clinical settings.

Antiviral drug resistance of human cytomegalovirus

The study of human cytomegalovirus (HCMV) antiviral drug resistance has enhanced knowledge of the virological targets and the mechanisms of antiviral activity. The currently approved drugs, ganciclovir (GCV), foscarnet (FOS), and cidofovir (CDV), target the viral DNA polymerase. GCV anabolism also requires phosphorylation by the virus-encoded UL97 kinase. GCV resistance mutations have been identified in both genes, while FOS and CDV mutations occur only in the DNA polymerase gene. Confirmation of resistance mutations requires phenotypic analysis; however, phenotypic assays are too time-consuming for diagnostic purposes. Genotypic assays based on sequencing provide more rapid results but are dependent on prior validation by phenotypic methods. Reports from many laboratories have produced an evolving list of confirmed resistance mutations, although differences in interpretation have led to some confusion. Recombinant phenotyping methods performed in a few research laboratories have resolved some of the conflicting results. Treatment options for drug-resistant HCMV infections are complex and have not been subjected to controlled clinical trials, although consensus guidelines have been proposed. This review summarizes the virological and clinical data pertaining to HCMV antiviral drug resistance.

Hematopoietic stem cell transplantation

More than 25,000 hematopoietic stem cell transplantations (HSCTs) are performed each year for the treatment of lymphoma, leukemia, immune-deficiency illnesses, congenital metabolic defects, hemoglobinopathies, and myelodysplastic and myeloproliferative syndromes. Before transplantation, patients receive intensive myeloablative chemoradiotherapy followed by stem cell “rescue.” Autologous HSCT is performed using the patient’s own hematopoietic stem cells, which are harvested before transplantation and reinfused after myeloablation. Allogeneic HSCT uses human leukocyte antigen (HLA)-matched stem cells derived from a donor. Survival after allogeneic transplantation depends on donor–recipient matching, the graft-versus-host response, and the development of a graft versus leukemia effect. This article reviews the biology of stem cells, clinical efficacy of HSCT, transplantation procedures, and potential complications.