The Development of Therapeutics for the Treatment and Prevention of CMV Disease in the Transplant Population: A Regulatory Perspective

What's New: Updates on Cytomegalovirus in Solid Organ Transplantation

Cytomegalovirus (CMV) is one of the most common infections occurring after solid organ transplantation. This high burden of disease, which incurs sizeable morbidity, may be worsening with the proportion of high-risk D+/R- solid organ transplantation recipients increasing in some regions globally. Cohort studies continue to support either universal prophylaxis or preemptive therapy as effective prevention strategies. Letermovir prophylaxis was noninferior to valganciclovir in adult high-risk D+/R- kidney transplant recipients with fewer drug-related adverse events in a recent clinical trial and has now been approved for such use in some regions. Maribavir preemptive therapy failed to demonstrate noninferiority when compared with valganciclovir in hematopoietic stem cell transplant recipients but looked promising for safety. Donor matching could be useful in prevention CMV disease with a survival advantage demonstrated in seronegative recipients waiting up to 30 mo for a seronegative kidney. Immune-guided prophylaxis resulted in fewer CMV infection episodes in lung transplant recipients when compared with fixed-duration prophylaxis in a recent clinical trial. For treatment of refractory or resistant CMV infection, maribavir was more efficacious and better tolerated when compared with investigator-initiated therapy in its registration trial for this condition. Further research regarding best treatment and prophylaxis of resistant or refractory CMV infection is needed to reflect best clinical practice choices. Optimal use of immune globulin or CMV-specific T cells for prevention or treatment of CMV disease remains undefined. Standardized definitions for the design of CMV clinical trials have been developed. In this review, we highlight recent updates in the field from data published since 2018.

Shaping the future of antiviral Treatment: Spotlight on Nucleobase-Containing drugs and their revolutionary impact

Nucleobases serve as essential molecular frameworks present in both natural and synthetic compounds that exhibit notable antiviral activity. Through molecular modifications, novel nucleobase-containing drugs (NCDs) have been developed, exhibiting enhanced antiviral activity against a wide range of viruses, including the recently emerged SARS‑CoV‑2. This article provides a detailed examination of the significant advancements in NCDs from 2015 till current, encompassing various aspects concerning their mechanisms of action, pharmacology and antiviral properties. Additionally, the article discusses antiviral prodrugs relevant to the scope of this review. It fills in the knowledge gap by examining the structure-activity relationship and trend of NCDs as therapeutics against a diverse range of viral diseases, either as approved drugs, clinical candidates or as early-stage development prospects. Moreover, the article highlights on the status of this field of study and addresses the prevailing limitations encountered.

Inhibition of Cytomegalovirus by Pentacta pygmaea Fucosylated Chondroitin Sulfate Depends on Its Molecular Weight

Many viruses attach to host cells by first interacting with cell surface proteoglycans containing heparan sulfate (HS) glycosaminoglycan chains and then by engaging with specific receptor, resulting in virus entry. In this project, HS–virus interactions were targeted by a new fucosylated chondroitin sulfate from the sea cucumber Pentacta pygmaea (PpFucCS) in order to block human cytomegalovirus (HCMV) entry into cells. Human foreskin fibroblasts were infected with HCMV in the presence of PpFucCS and its low molecular weight (LMW) fractions and the virus yield at five days post-infection was assessed. The virus attachment and entry into the cells were visualized by labeling the purified virus particles with a self-quenching fluorophore octadecyl rhodamine B (R18). The native PpFucCS exhibited potent inhibitory activity against HCMV specifically blocking virus entry into the cell and the inhibitory activities of the LMW PpFucCS derivatives were proportional to their chain lengths. PpFucCS and the derived oligosaccharides did not exhibit any significant cytotoxicity; moreover, they protected the infected cells from virus-induced lytic cell death. In conclusion, PpFucCS inhibits the entry of HCMV into cells and the high MW of this carbohydrate is a key structural element to achieve the maximal anti-viral effect. This new marine sulfated glycan can be developed into a potential prophylactic and therapeutic antiviral agent against HCMV infection.

Investigation into the use of gamma irradiated Cytodex-1 microcarriers to produce a human cytomegalovirus (HCMV) vaccine candidate in epithelial cells

V160 is a viral vaccine candidate against human cytomegalovirus (HCMV) that is manufactured using Adult Retinal Pigment Epithelial cells (ARPE-19) grown on Cytodex-1 microcarriers. The microcarriers are generally hydrated, washed, and autoclaved prior to use, which can be limiting at large production scales. To minimize microcarrier preparation and sterilization, the use of gamma irradiated Cytodex-1 was investigated. Similar ARPE-19 cell growth was observed on heat-sterilized and gamma irradiated Cytodex-1; however, significantly reduced virus production was observed in cultures exposed to gamma irradiated Cytodex-1. Additional experiments suggest that infection inhibition is not exclusive to ARPE-19 but is most directly linked to HCMV V160, as evidenced by similar inhibition of V160 with Vero cells and no inhibition of Measles virus with either cell type. These observations suggest a putative impact on HCMV infection from the presence of extractable(s)/leachable(s) in the gamma irradiated microcarriers. Thorough aseptic rinsing of gamma irradiated Cytodex-1 prior to use can mitigate this impact and enable comparable process performance to heat-sterilized Cytodex-1. Though not fully a "ready-to-use" product for the HCMV V160 production process, utilization of Cytodex-1 microcarriers was possible without requiring heat sterilization, suggesting a potential path forward for large scale production of V160.

Cytomegalovirus infection in transplant recipients: newly approved additions to our armamentarium

BACKGROUND

The burden that cytomegalovirus (CMV) portends for haematopoietic and solid-organ transplant recipients cannot be understated. Valganciclovir and ganciclovir have successfully been used for prevention and treatment of CMV infections, although with serious side effects such as leucopenia and some development of resistance. Until recently, available therapies for ganciclovir-resistant CMV have significant toxicities. Although advances have been made in the field, the unmet medical needs for effective and well-tolerated therapies are significant.

OBJECTIVES

This review aims to summarise the current and emerging CMV antiviral drugs and discusses future perspectives in the field.

SOURCES

We searched for relevant articles with pertinent keywords: "Cytomegalovirus OR CMV", "Transplant" and "Antiviral". Articles published after 2019 were given preference. Articles were reviewed by the authors for relevance and impact to the subject of interest.

CONTENT

We outline in this review current advances in prophylaxis of CMV infection with letermovir, breakthrough CMV infections while on or after prophylaxis, the development of resistant and refractory CMV infections, and the newly approved anti-CMV agent, maribavir, in haematopoietic and solid-organ transplant recipients.

IMPLICATIONS

Prevention of CMV infections after transplant has improved greatly over the past few years. Despite major advancements, breakthrough CMV infections and development of refractory and resistant CMV infections remain major complications post transplantation. We highlight emerging therapeutics that tolerably and effectively prevent and treat CMV infections, especially refractory and resistant cases.

The establishment of a cytomegalovirus -specific CD8+ T-cell threshold by kinetic modeling for the prediction of post-hemopoietic stem cell transplant reactivation

The dynamic interaction between the CMV virus and host immune response remains obscure, thus hindering the diagnosis and therapeutic management of patients with HSCT. The current diagnosis of CMV viremia depends on viral load estimation. Medical intervention based on viral load, can be unnecessary or poorly timed for many patients. Here we examined the clinical features and blood samples of patients with HSCT and assessed the CMV reactivation kinetics and corresponding CMV antigen-specific T-cell response in individual patients based on a peptide pool stimulation T-cell assay, which showed that CMV-specific CD8⁺ T cells were more suitable to be a diagnosis indicator for suppressing CMV reactivation. Using ROC analysis, we defined and verified a CMV-specific CD8⁺ T-cell counts threshold (925 cells/10⁶ PBMCs) as an indicator of CMV reactivation post-HSCT, and suggested that use of this threshold would provide more accurate guidance for prompt medication and better management of CMV infection post-HSCT.

Early immune surveillance to predict cytomegalovirus outcomes after allogeneic hematopoietic stem cell transplantation

Background

There is no method of predicting human cytomegalovirus (HCMV) outcomes in allogeneic hematopoietic stem cell transplant recipients clinically, leading in some cases to excessive or insufficient antiviral therapy. We evaluated the early immune response of recipients with disparate HCMV outcomes.

Methods

The HCMV outcomes of recipients were determined by long-term monitoring of HCMV DNA levels posttransplant. HCMV IgG and IgM concentrations at 1 week before and 1 week after transplantation, absolute lymphocyte counts, and HCMV-specific IFN-γ secreting cells at 1 month posttransplant were evaluated based on HCMV outcome.

Results

All recipients were negative for HCMV IgM. Significant differences between recipients with and without HCMV reactivation were observed in pre- and post-transplant HCMV IgG antibody levels, absolute lymphocyte counts, and HCMV-specific IFN-γ secreting cells (P < 0.05). HCMV IgG antibody levels significantly increased after transplantation in recipients with HCMV reactivation (P = 0.032), but not in those without reactivation. Multivariate analysis revealed that except for the absolute lymphocyte count these biomarkers were related to HCMV reactivation, independent of other clinical factors. In time-to-event analyses, lower levels of these biomarkers were associated with an increased 150-day cumulative incidence of HCMV reactivation (log-rank P < 0.05). In recipients with HCMV reactivation, the duration of HCMV DNAemia had negative correlation with HCMV-specific IFN-γ-secreting cells (P = 0.015, r = -0.372). The relationships between the peak HCMV DNA load and absolute lymphocyte count and HCMV-specific IFN-γ-secreting cells followed the same trends (P = 0.026, r = -0.181 and P = 0.010, r = -0.317).

Conclusions

HCMV IgG, absolute lymphocyte count, and HCMV-specific IFN-γ secreting cells represent the humoral and cellular immune response. Early monitoring of these immune markers could enable prediction of HCMV outcomes posttransplant and assessment of the severity of HCMV DNAemia.

Human cytomegalovirus infection among treatment-naive HIV-1 infected patients in Ethiopia

Subclinical human cytomegalovirus (HCMV) replication is associated with immune dysfunction in immuno-suppressed antiretroviral therapy (ART) naive HIV infected individuals. No data is documented in Ethiopia so far concerning HCMV co-infection among HIV infected individuals. Hence, this study was aimed at generating data regarding the prevalence of active HCMV infection among treatment-naive HIV-infected individuals from Ethiopia. For this purpose, we enrolled 97 treatment-naive HIV infected study subjects in Addis Ababa from June to December 2018. ELISA and conventional PCR were performed consecutively to detect HCMV specific IgM antibody and HCMV DNA respectively. Of the 97 study subjects, 12 (12.4%) were positive for anti-CMV IgM antibodies but were not confirmed by PCR. With regard to the PCR positivity, 4/97 (4.1%) samples were positive for HCMV DNA. No statically significant associations were found between the dependent and independent variables. The presence of HCMV DNA in the current study highlights the need for a routine laboratory diagnosis for preventing HCMV disease among HIV-infected individuals early. Besides, the use of anti-CMV therapy for these CMV viremic individuals is also recommended as this can reduce the burden of CMV complications and consecutively prolonging the life of HIV infected individuals.