A randomized, phase 2 study of ASP0113, a DNA-based vaccine, for the prevention of CMV in CMV-seronegative kidney transplant recipients receiving a kidney from a CMV-seropositive donor

Cytomegalovirus Treatment in Solid Organ Transplantation: An Update on Current Approaches

OBJECTIVE

The article reviews the safety and efficacy of treatments for cytomegalovirus (CMV) in solid organ transplantation.

DATA SOURCES

A literature review was conducted in PubMed, MEDLINE, and Clinicaltrials.gov from database inception through January 2024, using terms CMV, therapy, and solid organ transplantation.

STUDY SELECTION AND DATA EXTRACTION

Clinical trials, meta-analyses, cohort studies, case reports, and guidelines were included. Letters to the editor, reviews, and commentaries were excluded.

DATA SYNTHESIS

After abstract screening and full-text review of 728 citations for eligibility, 53 were included. Valganciclovir and intravenous ganciclovir are drugs of choice for CMV management and, until recently, the availability of alternative options has been restricted due to toxicity. For instance, foscarnet and cidofovir serve as second-line agents due to potential bone marrow and renal toxicity. In patients with refractory or resistant CMV, maribavir, a novel oral agent, has proven efficacy and a lower adverse effect profile. However, in refractory or resistant CMV, foscarnet and cidofovir are preferred in invasive disease (CMV gastritis, CMV retinitis, and CMV encephalitis), high viral loads, and inability to tolerate oral preparations.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

Consensus guidelines have not been revised since approval of novel antivirals in solid organ transplantation. Valganciclovir and ganciclovir remain drugs of choice for initial CMV therapy. Foscarnet, cidofovir, and maribavir are treatments for refractory or resistant-CMV.

CONCLUSIONS

Selection of CMV antiviral treatment should be determined by patient-specific factors, including severity of illness, resistant or refractory disease, dose-limiting adverse effects, and the preferred route of administration.

Patient years lost due to cytomegalovirus serostatus mismatching in the scientific registry of transplant recipients

Background

The cytomegalovirus (CMV) mismatch rate in deceased donor kidney transplant (DDKT) recipients in the US remains above 40%. Since CMV mismatching is common in DDKT recipients, the cumulative effects may be significant in the context of overall patient and graft survival. Our primary objective was to describe the short- and long-term risks associated with high-risk CMV donor positive/recipient negative (D+/R-) mismatching among DDKT recipients with the explicit goal of deriving a mathematical mismatching penalty.

Methods

We conducted a retrospective, secondary analysis of the Scientific Registry of Transplant Recipients (SRTR) database using donor-matched DDKT recipient pairs (N=105,608) transplanted between 2011-2022. All-cause mortality and graft failure hazard ratios were calculated from one year to ten years post-DDKT. All-cause graft failure included death events. Survival curves were calculated using the Kaplan-Meier estimation at 10 years post-DDKT and extrapolated to 20 years to provide the average graft days lost (aGDL) and average patient days lost (aPDL) due to CMV D+/R- serostatus mismatching. We also performed an age-based stratification analysis to compare the relative risk of CMV D+ mismatching by age.

Results

Among 31,518 CMV D+/R- recipients, at 1 year post-DDKT, the relative risk of death increased by 29% (p<0.001), and graft failure increased by 17% (p<0.001) as compared to matched CMV D+/R+ group (N=31,518). Age stratification demonstrated a significant increase in the risk associated with CMV mismatching in patients 40 years of age and greater. The aGDL per patient due to mismatching was 125 days and the aPDL per patient was 100 days.

Conclusion

The risks of CMV D+/R- mismatching are seen both at 1 year post-DDKT period and accumulated throughout the lifespan of the patient, with the average CMV D+/R- recipient losing more than three months of post-DDKT survival time. CMV D+/R- mismatching poses a more significant risk and a greater health burden than previously reported, thus obviating the need for better preventive strategies including CMV serodirected organ allocation to prolong lifespans and graft survival in high-risk patients.

Updates in Cytomegalovirus Prevention and Treatment in Solid Organ Transplantation

The authors summarize recent updates in the prevention and management of cytomegalovirus (CMV) in solid organ transplant (SOT) recipients with a focus on CMV seronegative recipients of organs from seropositive donors (CMV D+/R-) who are at highest risk of CMV infection and disease. They discuss advantages of preemptive therapy for CMV disease prevention in CMV D+/R- liver transplant recipients, letermovir for CMV prophylaxis, and updates in the development of monoclonal antibodies and vaccines as immune-based preventative strategies. They review the roles of maribavir and virus-specific T cells for management of resistant or refractory CMV infection in SOT recipients.

Immunization of Solid Organ Transplant Candidates and Recipients: A 2022 Update

Immunizations are a relatively safe and cost-effective intervention to prevent morbidity and mortality associated with vaccine preventable infection (VPIs). As such, immunizations are a critical part of the care of pre and posttransplant patients and should be prioritized. New tools are needed to continue to disseminate and implement the most up-to-date vaccine recommendations for the SOT population. These tools will help both primary care providers and multi-disciplinary transplant team members taking care of transplant patients to stay abreast of evidence-based best practices regarding the immunization of the SOT patient.

Increasing Proportion of High-risk Cytomegalovirus Donor-positive/Recipient-negative Serostatus in Solid Organ Transplant Recipients

BACKGROUND

Cytomegalovirus (CMV) donor-positive/recipient-negative (D+R-) serostatus is independently associated with worse allograft and patient survival across solid organ transplant (SOT) types. We characterized trends in CMV D+R- serostatus among adult SOT recipients performed in the United States.

METHODS

Donor (D) and recipient (R) CMV serostatus and demographic factors were obtained from the Scientific Registry of Transplant Recipients for persons ≥18 y undergoing a first SOT between January 1, 2000, and December 31, 2020. The proportions of D+R- SOTs over time were assessed using Chi square for trend and modeled through 2040. Factors associated with D/R seropositivity were assessed using logistic models.

RESULTS

Among 472 549 SOTs, the average proportion of D+R- SOTs increased significantly among kidney, liver, heart, and lung between 2000 to 2009 and 2010 to 2020: 18.0% to 18.3% ( P  = 0.034), 19.4% to 21.8% ( P  < 0.001), 22.2% to 25.5% ( P  < 0.001), and 23.6% to 27.0% ( P  < 0.001), respectively. The increased proportion over time resulted from a disproportionate increase in R- (34.9% to 37.0% for all organ types, P  < 0.001) and a smaller corresponding change in D+ (60.8% to 60.3%, P  < 0.001).

CONCLUSIONS

The proportion of high-risk CMV D+R- SOTs increased significantly across all organs and is projected to continue to increase. These findings inform population-level strategies to mitigate the negative impact of CMV D+R- in SOT.

DNA and mRNA Vaccines for Chronic Viral Infections and Cancer: Rationale, Mechanisms, and Progress

Interest in the capabilities of nucleic acid vaccines, (DNA and mRNA vaccines) for both prophylactic and therapeutic uses have greatly increased following the successful deployment of two mRNA and, on a more limited scale, one DNA vaccine for COVID-19. In addition to targeting other pathogens for prophylactic vaccines, efforts are also being made towards using them for therapies for chronic infections and cancer. An examination of past and current successes for such therapies using other technologies with an emphasis on the immunological mechanisms will be provided followed by an assessment of the relevant characteristics of DNA and mRNA vaccines to predict their utility for therapies for chronic viral infections and cancer. Efforts and progress for these targets will be described.

Natural killer cell infusion for cytomegalovirus infection in pediatric patients with Wiskott-Aldrich syndrome following cord blood transplantation: A case report and literature review

NK cells have important functions in resisting cytomegalovirus infection, as they proliferate after viral infection and have certain immunological memory. Here, we report infusion of haploid donor-derived natural killer cells to treat two pediatric patients with Wiskott-Aldrich syndrome (WAS) who were infected with cytomegalovirus after cord blood transplantation (CBT), which successfully cleared the viral infection in both patients.

Lessons from Acquired Natural Immunity and Clinical Trials to Inform Next-Generation Human Cytomegalovirus Vaccine Development

Human cytomegalovirus (HCMV) infection, the most common cause of congenital disease globally, affecting an estimated 1 million newborns annually, can result in lifelong sequelae in infants, such as sensorineural hearing loss and brain damage. HCMV infection also leads to a significant disease burden in immunocompromised individuals. Hence, an effective HCMV vaccine is urgently needed to prevent infection and HCMV-associated diseases. Unfortunately, despite more than five decades of vaccine development, no successful HCMV vaccine is available. This review summarizes what we have learned from acquired natural immunity, including innate and adaptive immunity; the successes and failures of HCMV vaccine human clinical trials; the progress in related animal models; and the analysis of protective immune responses during natural infection and vaccination settings. Finally, we propose novel vaccine strategies that will harness the knowledge of protective immunity and employ new technology and vaccine concepts to inform next-generation HCMV vaccine development.

Deciphering the Potential Coding of Human Cytomegalovirus: New Predicted Transmembrane Proteome

CMV is a major cause of morbidity and mortality in immunocompromised individuals that will benefit from the availability of a vaccine. Despite the efforts made during the last decade, no CMV vaccine is available. An ideal CMV vaccine should elicit a broad immune response against multiple viral antigens including proteins involved in virus-cell interaction and entry. However, the therapeutic use of neutralizing antibodies targeting glycoproteins involved in viral entry achieved only partial protection against infection. In this scenario, a better understanding of the CMV proteome potentially involved in viral entry may provide novel candidates to include in new potential vaccine design. In this study, we aimed to explore the CMV genome to identify proteins with putative transmembrane domains to identify new potential viral envelope proteins. We have performed in silico analysis using the genome sequences of nine different CMV strains to predict the transmembrane domains of the encoded proteins. We have identified 77 proteins with transmembrane domains, 39 of which were present in all the strains and were highly conserved. Among the core proteins, 17 of them such as UL10, UL139 or US33A have no ascribed function and may be good candidates for further mechanistic studies.

Association of Donor and Recipient Cytomegalovirus Serostatus on Graft and Patient Survival in Liver Transplant Recipients

Among solid organ transplant recipients, donor cytomegalovirus (CMV) seropositive (D+) and recipient seronegative (R-) status are associated with an increased risk of graft loss and mortality after kidney or lung transplantation. Whether a similar relationship exists among liver transplant recipients (LTR) is unknown. We assessed graft loss and mortality among adult LTRs from January 1, 2010, to March 14, 2020, in the Organ Procurement and Transplantation Network database. We used multivariable mixed Cox proportional hazards regression to analyze the association of donor and recipient CMV serostatus group with graft loss and mortality, with donor seronegative (D-) and recipient seronegative (R-) as the reference group. Among 54,078 LTRs, the proportion of D-R-, D- and recipient seropositive (R+), D+R-, and D+R+ was 13.4%, 22.5%, 22%, and 42%, respectively. By unadjusted Kaplan-Meier survival curve estimates, survival by the end of follow-up was 73.3%, 73.5%, 70.1%, and 69.7%, among the D-R-, D-R+, D+R-, and D+R+ groups, respectively. By multivariable Cox regression, the CMV D+R- serogroup, but not other serogroups, was independently associated with increased risks of graft loss (adjusted hazard ratio [aHR], 1.13; 95% confidence interval [CI], 1.05-1.22) and mortality (aHR, 1.13; 95% CI, 1.05-1.22). The magnitude of the association of the CMV D+R- serostatus group with mortality was similar when the Cox regression analysis was restricted to the first year after transplant and beyond the first year after transplant: aHR, 1.13 (95% CI, 1.01-1.27) and aHR, 1.13 (95% CI, 1.02-1.25), respectively. Even in an era of CMV preventive strategies, CMV D+R- serogroup status remains independently associated with increased graft loss and mortality in adult LTRs. Factors in addition to direct CMV-associated short-term mortality are likely, and studies to define the underlying mechanism(s) are warranted.

Update on cytomegalovirus in transplant recipients: new agents, prophylaxis, and cell-mediated immunity

PURPOSE OF REVIEW

This review is an overview of recent advances in diagnostics, therapies, and prevention strategies for cytomegalovirus (CMV), focusing on solid-organ transplant and hematopoietic stem cell transplant recipients.

RECENT FINDINGS

A randomized trial of prophylaxis vs preemptive therapy in donor-seropositive, recipient-seronegative liver transplant recipients found significantly less CMV disease in the preemptive group. Maribavir has shown promise for the treatment of resistant/refractory CMV and for uncomplicated CMV DNAemia. A post hoc mortality analysis, as well as emerging reports of real-world and off-label use, have expanded the spectrum of clinical experience with letermovir. The first interventional trials using CMV cell-mediated immune assays have been published and showed promising results for delineating antiviral strategies. New data from additional interventional trials are expected soon.

SUMMARY

The past 1-2 years have seen major developments in the area of CMV management in transplant recipients. Expanding diagnostic and therapeutic capabilities provide a foundation for optimizing strategies in the future, to reduce morbidity and mortality from CMV.

Development of a Vaccine against Human Cytomegalovirus: Advances, Barriers, and Implications for the Clinical Practice

Human cytomegalovirus (hCMV) is one of the most common causes of congenital infection in the post-rubella era, representing a major public health concern. Although most cases are asymptomatic in the neonatal period, congenital CMV (cCMV) disease can result in permanent impairment of cognitive development and represents the leading cause of non-genetic sensorineural hearing loss. Moreover, even if hCMV mostly causes asymptomatic or pauci-symptomatic infections in immunocompetent hosts, it may lead to severe and life-threatening disease in immunocompromised patients. Since immunity reduces the severity of disease, in the last years, the development of an effective and safe hCMV vaccine has been of great interest to pharmacologic researchers. Both hCMV live vaccines-e.g., live-attenuated, chimeric, viral-based-and non-living ones-subunit, RNA-based, virus-like particles, plasmid-based DNA-have been investigated. Encouraging data are emerging from clinical trials, but a hCMV vaccine has not been licensed yet. Major difficulties in the development of a satisfactory vaccine include hCMV's capacity to evade the immune response, unclear immune correlates for protection, low number of available animal models, and insufficient general awareness. Moreover, there is a need to determine which may be the best target populations for vaccine administration. The aim of the present paper is to examine the status of hCMV vaccines undergoing clinical trials and understand barriers limiting their development.

A trimeric capable gB CMV vaccine provides limited protection against a highly cell associated and epithelial tropic strain of cytomegalovirus in guinea pigs

Multiple strains of human cytomegalovirus (HCMV) can cause congenital cytomegalovirus (cCMV) by primary or secondary infection. The viral gB glycoprotein is a leading vaccine candidate, essential for infection of all cell-types, and immunodominant antibody target. Guinea pig cytomegalovirus (GPCMV) is the only small animal model for cCMV. Various gB vaccines have shown efficacy but studies have utilized truncated gB and protection against prototype strain 22122 with preferential tropism to fibroblasts despite encoding a gH-based pentamer complex for non-fibroblast infection. A highly cell-associated novel strain of GPCMV (TAMYC) with 99 % identity in gB sequence to 22122 exhibited preferred tropism to epithelial cells. An adenovirus vaccine encoding full-length gB (AdgB) was highly immunogenic and partially protected against 22122 strain challenge in vaccinated animals but not when challenged with TAMYC strain. GPCMV studies with AdgB vaccine sera on numerous cell-types demonstrated impaired neutralization (NA₅₀) compared to fibroblasts. GPCMV-convalescent sera including pentamer complex antibodies increased virus neutralization on non-fibroblasts and anti-gB depletion from GPCMV-convalescent sera had minimal impact on epithelial cell neutralization. GPCMV(PC+) 22122-convalescent animals challenged with TAMYC exhibited higher protection compared to AdgB vaccine. Overall, results suggest that antibody response to both gB and PC are important components of a GPCMV vaccine.

Immune Responses to SARS-CoV-2 in Solid Organ Transplant Recipients

PURPOSE OF REVIEW

Coronavirus disease 2019 (COVID-19) is caused by a complex interplay between severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) dynamics and host immune responses. Hosts with altered immunity, including solid organ transplant recipients, may be at increased risk of complications and death due to COVID-19. A synthesis of the available data on immune responses to SARS-CoV-2 infection is needed to inform therapeutic and preventative strategies in this special population.

RECENT FINDINGS

Few studies have directly compared immune responses to SARS-CoV-2 between transplant recipients and the general population. Like non-transplant patients, transplant recipients mount an exuberant inflammatory response following initial SARS-CoV2 infection, with IL-6 levels correlating with disease severity in some, but not all studies. Transplant recipients display anti-SARS-CoV-2 antibodies and activated B cells in a time frame and magnitude similar to non-transplant patients-limited data suggest these antibodies can be detected within 15 days of symptom onset and may be durable for several months. CD4+ and CD8+ T lymphopenia, a hallmark of COVID-19, is more profound in transplant recipients, but SARS-CoV-2-reactive T cells can be detected among patients with both mild and severe disease.

SUMMARY

The limited available data indicate that immune responses to SARS-CoV-2 are similar between transplant recipients and the general population, but no studies have been sufficiently comprehensive to understand nuances between organ types or level of immunosuppression to meaningfully inform individualized therapeutic decisions. The ongoing pandemic provides an opportunity to generate higher-quality data to support rational treatment and vaccination strategies in this population.

A randomised, placebo-controlled phase 3 study to evaluate the efficacy and safety of ASP0113, a DNA-based CMV vaccine, in seropositive allogeneic haematopoietic cell transplant recipients

BACKGROUND

Cytomegalovirus (CMV) is a complication of allogeneic haematopoietic cell transplantation (allo-HCT). ASP0113, a DNA-based vaccine, contains two plasmids encoding human CMV glycoprotein B and phosphoprotein 65 (pp65). We assessed ASP0113 in CMV-seropositive allo-HCT recipients.

METHODS

In this phase 3, randomised, placebo-controlled study, CMV-seropositive allo-HCT recipients were randomly assigned (1:1) via interactive response technology to receive five injections of 1 mL of 5 mg/mL ASP0113 or placebo. The pharmacist and designated staff were unblinded. Masked syringes maintained the blind for patients and study personnel. Efficacy and safety analyses included patients who received ≥1 dose of ASP0113/placebo. The primary efficacy endpoint was the proportion of allo-HCT recipients with composite all-cause mortality and adjudicated CMV end-organ disease (EOD) by 1 year post-transplant. ClinicalTrials.gov: NCT01877655 (not recruiting).

FINDINGS

Patients were recruited between Sept 11, 2013 and Sept 21, 2016. Overall, 501 patients received ≥1 dose of ASP0113 (n = 246) or placebo (n = 255). The proportion of patients with composite all-cause mortality and adjudicated CMV EOD by 1 year post-transplant was 35.4% (n = 87) with ASP0113 and 30•2% (n = 77) with placebo (odds ratio 1.27; 95% confidence interval: 0.87 to 1.85; p = 0.205). Incidence of injection site-related treatment-emergent adverse events (TEAEs) was higher with ASP0113 than placebo. Overall incidence and severity of other TEAEs was similar between groups. T-cell response to pp65 increased over time and was greater with placebo than ASP0113 (p = 0.027).

INTERPRETATION

ASP0113 did not reduce overall mortality or CMV EOD by 1 year post-transplant. Safety findings were similar between groups.

FUNDING

Astellas Pharma Global Development, Inc .

Human cytomegalovirus infection: A considerable issue following allogeneic hematopoietic stem cell transplantation

Cytomegalovirus (CMV) is an opportunistic virus, whereby recipients are most susceptible following allogeneic hematopoietic stem cell transplantation (allo-HSCT). With the development of novel immunosuppressive agents and antiviral drugs, accompanied with the widespread application of prophylaxis and preemptive treatment, significant developments have been made in transplant recipients with human (H)CMV infection. However, HCMV remains an important cause of short- and long-term morbidity and mortality in transplant recipients. The present review summarizes the molecular mechanism and risk factors of HCMV reactivation following allo-HSCT, the diagnosis of CMV infection following allo-HSCT, prophylaxis and treatment of HCMV infection, and future perspectives. All relevant literature were retrieved from PubMed and have been reviewed.

The Status of Vaccine Development Against the Human Cytomegalovirus

Numerous candidate vaccines against cytomegalovirus (CMV) infection and disease are in development. Whereas the previous article [1] provides background and opinions about the issues relating to vaccination, this article provides specifics about the vaccines in active development, as reported at a National Institutes of Health-sponsored meeting in Bethesda on September 4-6, 2018. Here, vaccine developers provide synopses of their candidate vaccines to immunize women to protect against congenital CMV disease and to prevent the consequences of CMV disease in recipients of transplanted organs or hematopoietic stem calls. The projects are presented here roughly in the descending order of their stage of development in the opinion of the first author.

Choice of Study Populations for Vaccines

The natural history of cytomegalovirus (CMV) infection is complex. Individuals may experience primary infection, reactivation of latent infection, or reinfection with a new strain despite natural immunity. The ability of this virus to continue to replicate despite substantial immune responses is attributable to the many immune evasion genes encoded within its genome. Given this complex natural history and immunology, the design of clinical trials of CMV vaccines may require components not usually found in trials of vaccines designed to protect against viruses that cause only acute infections. In this article, we focus on specific aspects of clinical trial design that could be adopted to address the complexities of CMV infections. We consider women of childbearing age, toddlers, recipients of solid organ transplantation, and stem cell transplant patients, emphasizing the parallels between women and solid organ transplantation that could allow vaccines to be developed in parallel in both these patient groups. We emphasize the potential for studies of passive immunity to inform the selection of immunogens as candidates for active immunization and vice versa. We also illustrate how application of whole-genomic sequencing could document whether vaccines protect against reactivation or reinfection of CMV or both.

Progress and Challenges in the Prevention, Diagnosis, and Management of Cytomegalovirus Infection in Transplantation

Hosts with compromised or naive immune systems, such as individuals living with HIV/AIDS, transplant recipients, and fetuses, are at the highest risk for complications from cytomegalovirus (CMV) infection. Despite substantial progress in prevention, diagnostics, and treatment, CMV continues to negatively impact both solid-organ transplant (SOT) and hematologic cell transplant (HCT) recipients. In this article, we summarize important developments in the field over the past 10 years and highlight new approaches and remaining challenges to the optimal control of CMV infection and disease in transplant settings.

Cytomegalovirus after kidney transplantation in 2020: moving towards personalized prevention

Cytomegalovirus (CMV)-related complications after kidney transplantation remain a substantial challenge. Rather than applying one preventive strategy to all at-risk patients, we can now adapt our strategy at the individual patient level. Antiviral prophylaxis or a strict pre-emptive strategy may be optimal for patients at the highest risk for CMV, while patients at lower risk may benefit particularly from pre-emptive monitoring and the administration of therapy only if needed. CMV-specific T-cell assays may be useful for further refining the pre-transplant determination of CMV risk, and for guiding decisions about antiviral therapy need or duration. An immunosuppressive regimen including a mammalian target of rapamycin inhibitor reduces CMV risk and may thus be an attractive option in some patients. New antiviral agents may further expand our therapeutic arsenal in the near future, and the prospects of CMV vaccination and adoptive T-cell therapy appear to be on the horizon.

Human Cytomegalovirus Primary Infection and Reactivation: Insights From Virion-Carried Molecules

Human cytomegalovirus (HCMV), a ubiquitous beta-herpesvirus, is able to establish lifelong latency after initial infection. Periodical reactivation occurs after immunosuppression, remaining a major cause of death in immunocompromised patients. HCMV has to reach a structural and functional balance with the host at its earliest entry. Virion-carried mediators are considered to play pivotal roles in viral adaptation into a new cellular environment upon entry. Additionally, one clear difference between primary infection and reactivation is the idea that virion-packaged factors are already formed such that those molecules can be used swiftly by the virus. In contrast, virion-carried mediators have to be transcribed and translated; thus, they are not readily available during reactivation. Hence, understanding virion-carried molecules helps to elucidate HCMV reactivation. In this article, the impact of virion-packaged molecules on viral structure, biological behavior, and viral life cycle will be reviewed.

Role of Neutralizing Antibodies in CMV Infection: Implications for New Therapeutic Approaches

Cytomegalovirus (CMV) infection elicits a potent immune response that includes the stimulation of antibodies with neutralizing activity. Recent studies have focused on elucidating the role of neutralizing antibodies in protecting against CMV infection and disease and characterizing viral antigens against which neutralizing antibodies are directed. Here, we provide a synthesis of recent data regarding the role of neutralizing antibodies in protection against CMV infection/disease. We consider the role of humoral immunity in the context of the global CMV-specific immune response, and the implications that recent findings have for vaccine and antibody-based therapy design.

New treatments for cytomegalovirus in transplant patients

PURPOSE OF REVIEW

The purpose of this review is to highlight novel advances in prophylaxis against and treatment of CMV in kidney transplant recipients. Current options include intravenous ganciclovir and oral valganciclovir, but use of these agents is limited by side effects, such as myelosuppression as well as evolving resistance in CMV strains.

RECENT FINDINGS

Advances in the field include novel drugs that have shown promise in preliminary studies and are now being tested in large-scale clinical trials. Moreover, there is a developing focus in enhancing host immune responses to better protect against viral infection using anti-CMV vaccines. Studying host immune responses to CMV has also led to improved monitoring strategies, such as the QuantiFERON assay, which will allow for improved risk stratification and targeted therapies in transplant recipients.

SUMMARY

In summary, although options for prophylaxis and treatment against CMV have been somewhat limited to date, a number of new strategies are currently under development with several drugs in phase 3 trials. Therefore, the landscape of CMV management in kidney transplant recipients will be changing significantly in the coming years with the ultimate goal of safer and more effective therapies to combat CMV.

A Randomized Dose-Escalating Phase I Trial of a Replication-Deficient Lymphocytic Choriomeningitis Virus Vector-Based Vaccine Against Human Cytomegalovirus

BACKGROUND

A vaccine (HB-101) consisting of 2 nonreplicating lymphocytic choriomeningitis virus (LCMV) vectors expressing the human cytomegalovirus antigens glycoprotein B (gB) and the 65-kD phosphoprotein (pp65), respectively, is in development to prevent cytomegalovirus infection.

METHODS

HB-101 was tested in cytomegalovirus-naive, healthy adults in a randomized, double-blind, placebo-controlled, dose-escalation Phase I trial. Fifty-four subjects received low, medium, or high dose of HB-101 or placebo by intramuscular administration at Month 0, 1, and 3. Safety and immunogenicity were the respective primary and secondary endpoints. Subjects were followed for 12 months after the initial immunization.

RESULTS

Vaccination was associated with transient mild to moderate adverse events. HB-101 administration induced dose-dependent gB- and pp65-specific cellular responses, dominated by pp65-specific CD8 T cells, a high fraction of which were polyfunctional. Two administrations were sufficient to elicit dose-dependent gB-binding and cytomegalovirus-neutralizing antibodies (Abs). Cytomegalovirus-specific immune responses were boosted after each administration. Only 1 of 42 vaccine recipients mounted a transient LCMV vector-neutralizing Ab response.

CONCLUSIONS

HB-101 was well tolerated and induced cytomegalovirus-specific polyfunctional CD8 T-cell and neutralizing Ab responses in the majority of subjects. Lack of vector-neutralizing Ab responses should facilitate booster vaccinations. These results justify further clinical evaluation of this vaccine candidate.

Moving Past Ganciclovir and Foscarnet: Advances in CMV Therapy

PURPOSE OF REVIEW

CMV DNA polymerase inhibitors such as ganciclovir and foscarnet have dramatically reduced the burden of CMV infection in the HCT recipient. However, their use is often limited by toxicities and resistance. Agents with novel mechanisms and favorable toxicity profiles are critically needed. We review recent developments in CMV antivirals and immune-based approaches to mitigating CMV infection.

RECENT FINDINGS

Letermovir, an inhibitor of the CMV terminase complex, was approved in 2017 for primary CMV prophylaxis in adult seropositive allogeneic HCT recipients. Maribavir, an inhibitor of the CMV UL97 kinase, is currently in two phase 3 treatment studies. Adoptive immunotherapy using third-party T cells has proven safe and effective in preliminary studies. Vaccine development continues, with several promising candidates currently under study. No longer limited to DNA polymerase inhibitors, the prevention and treatment of CMV infections in the HCT recipient is a rapidly evolving field which should translate into improvements in CMV-related outcomes.

Pharmacokinetics and Immunogenicity of ASP0113 in CMV-Seronegative Dialysis Patients and CMV-Seronegative and -Seropositive Healthy Subjects

Cytomegalovirus (CMV) infection causes significant morbidity and mortality in immunocompromised transplant patients. ASP0113, a first-in-class DNA vaccine containing plasmids encoding CMV phosphoprotein 65 and glycoprotein B (gB), was evaluated in a phase 1b, subject-blinded study in CMV-seropositive (n = 13) and CMV-seronegative (n = 12) healthy and CMV-seronegative dialysis subjects (n = 12) randomized to ASP0113 or placebo. End points included pharmacokinetics, anti-gB antibody levels, phosphoprotein 65-specific T-cell responses measured by ex vivo enzyme-linked immune absorbent spot (ELISpot) assay and 10-day cultured ELISpot and Stat T-cell activation assays, and safety. ASP0113 concentrations peaked at 2-10 and 24-48 hours; the pharmacokinetics were similar across groups. No group demonstrated significant anti-gB antibody responses. T-cell responder rates in the cultured ELISpot assay were 8/12 (66.7%, 95%CI 35% to 90%) and 4/12 (33.3%, 95%CI 10% to 65%) in CMV-seronegative healthy subjects and dialysis patients, respectively, whereas ex vivo ELISpot assay response rates were 4/11 (36.4%, 95%CI 11% to 69%) and 0/12, respectively. Responses peaked at week 27, with lower magnitude observed in CMV-seronegative dialysis patients versus CMV-seronegative healthy subjects. No serious adverse events occurred; the most common adverse event in ASP0113-vaccinated patients was injection-site pain (64.9%). Some CMV-seronegative healthy subjects and dialysis patients had T-cell responses; no humoral responses were detected.

Cytomegalovirus Infection in Solid Organ and Hematopoietic Cell Transplantation: State of the Evidence

This review focuses on recent advances in the field of cytomegalovirus (CMV). The 2 main strategies for CMV prevention are prophylaxis and preemptive therapy. Prophylaxis effectively prevents CMV infection after solid organ transplantation (SOT) but is associated with high rates of neutropenia and delayed-onset postprophylaxis disease. In contrast, preemptive therapy has the advantage of leading to lower rates of CMV disease and robust humoral and T-cell responses. It is widely used in hematopoietic cell transplant recipients but is infrequently utilized after SOT due to logistical considerations, though these may be overcome by novel methods to monitor CMV viremia using self-testing platforms. We review recent developments in CMV immune monitoring, vaccination, and monoclonal antibodies, all of which have the potential to become part of integrated strategies that rely on viral load monitoring and immune responses. We discuss novel therapeutic options for drug-resistant or refractory CMV infection, including maribavir, letermovir, and adoptive T-cell transfer. We also explore the role of donor factors in transmitting CMV after SOT. Finally, we propose a framework with which to approach CMV prevention in the foreseeable future.

Scientific and Regulatory Considerations for Efficacy Studies of Cytomegalovirus Vaccines

The considerable public health burden due to cytomegalovirus (CMV) supports current interest in vaccine development. Clinical studies intended to support regulatory action should be designed to demonstrate substantial evidence of effectiveness. However, design and conduct of clinical endpoint studies may be hampered by low incidence of disease, especially for congenital CMV. Discussion and experience from other vaccines directed against congenital disease (including rubella and Zika) may be instructive. This article summarizes current scientific and US regulatory considerations related to design of studies of vaccines intended to prevent congenital CMV and complications of CMV in transplantation, as discussed at the 2018 workshop entitled "Cytomegalovirus Infection: Advancing Strategies for Prevention and Treatment."

The direct and indirect consequences of cytomegalovirus infection and potential benefits of vaccination

Active infection with cytomegalovirus (CMV) occurs in patients who are immunocompromised and may produce the high viral loads required to cause end-organ disease. Such patients have complex medical histories and many experienced physicians have speculated that CMV may, additionally, contribute to adverse clinical outcomes. In 1989, Dr Bob Rubin coined the term "indirect effects" to describe this potential relationship between virus and patient. Examples include accelerated atherosclerosis in patients after heart transplant or with underlying HIV infection, the number of days patients require ventilation after admission to intensive care units, the development of immunosenescence in the elderly and mortality in many groups of patients, including the general population. It is difficult to distinguish between CMV acting as causal contributor to such diverse pathology or simply having a benign bystander effect. However, recruitment of patients into placebo-controlled randomised trials of antiviral drugs with activity against CMV offers such a potential. This article describes the studies that have been conducted to date and emphasises that mortality after stem cell transplant (not attributed to CMV end-organ disease) has recently become the first proven indirect effect of CMV now that letermovir has significantly reduced non-relapse deaths. The implications for CMV vaccines are then discussed. Vaccines are already predicted to be highly cost-effective if they can reduce CMV end-organ disease. Health planners should now consider that cost effectiveness is likely to be enhanced further through reduction of the indirect effects of CMV. A prototype scheme for assessing this possibility is provided in order to stimulate discussion within the field. This article forms part of an online symposium on the prevention and therapy of DNA virus infections, dedicated to the memory of Mark Prichard.

Dynamic Changes in Natural Killer Cell Subset Frequencies in the Absence of Cytomegalovirus Infection

Individuals lacking functional natural killer (NK) cells suffer severe, recurrent infections with cytomegalovirus (CMV), highlighting the critical role of NK cells in antiviral defense. Therefore, ongoing attempts to develop an efficacious vaccine to prevent CMV infection should potentially aim to elicit NK-cell antiviral responses as an accessory to conventional T- and B-cell based approaches. In this regard, CMV infection provokes marked phenotypic and functional differentiation of the NK-cell compartment, including development of adaptive NK cells that exhibit enhanced antiviral activity. We examined longitudinal blood samples collected from 40 CMV-seronegative adolescents to ascertain whether a CMV glycoprotein B (gB) vaccine in the absence of CMV infection can stimulate differentiation or expansion of CMV-associated subsets of NK cells. Study participants uniformly lacked the CMV-dependent NKG2C⁺ subset of NK cells, suggesting that an adjuvanted CMV gB vaccine alone is an inadequate stimulus for sustained expansion of these cells. In contrast, we observed unexpected dynamic fluctuations in the frequency of NK cells lacking FcRγ, EAT-2, and SYK, which were independent of vaccination or CMV infection. Whereas, FcRγ^neg NK cells in CMV infection are reported to express increased levels of the maturation marker CD57, the FcRγ^neg NK cells observed in our CMV-negative vaccine cohort express less CD57 than their FcRγ⁺ counterparts. The FcRγ^neg NK cells in CMV-negative individuals were also functionally distinct from this subset in CMV infection, exhibiting comparable IFN-γ production and degranulation as FcRγ⁺ NK cells in response to cytokine or antibody-dependent stimuli. These results suggest that frequencies of some NK cell subsets may increase in response to unknown environmental or inflammatory cues distinct from that which occurs after CMV infection. Greater understanding of the nature of the signals driving CMV-independent accumulation of these subsets should permit development of mechanisms to facilitate vaccine-driven expansion of CMV-reactive NK cells.

Revisiting Role of Vaccinations in Donors, Transplant Recipients, Immunocompromised Hosts, Travelers, and Household Contacts of Stem Cell Transplant Recipients

Vaccination is an effective strategy to prevent infections in immunocompromised hematopoietic stem cell transplant recipients. Pretransplant vaccination of influenza, pneumococcus, Haemophilus influenza type b, diphtheria, tetanus, and hepatitis B, both in donors and transplant recipients, produces high antibody titers in patients compared with recipient vaccination only. Because transplant recipients are immunocompromised, live vaccines should be avoided with few exceptions. Transplant recipients should get inactive vaccinations when possible to prevent infection. This includes vaccination against influenza, pneumococcus, H. influenza type b, diphtheria, tetanus, pertussis, meningococcus, measles, mumps, rubella, polio, hepatitis A, human papillomavirus, and hepatitis B. Close contacts of transplant recipients can safely get vaccinations (inactive and few live vaccines) as per their need and schedule. Transplant recipients who wish to travel may need to get vaccinated against endemic diseases that are prevalent in such areas. There is paucity of data on the role of vaccinations for patients receiving novel immunotherapy such as bispecific antibodies and chimeric antigen receptor T cells despite data on prolonged B cell depletion and higher risk of opportunistic infections.

An Influenza Virus Hemagglutinin-Based Vaccine Platform Enables the Generation of Epitope Specific Human Cytomegalovirus Antibodies

Human cytomegalovirus (CMV) is a highly prevalent pathogen with ~60%–90% seropositivity in adults. CMV can contribute to organ rejection in transplant recipients and is a major cause of birth defects in newborns. Currently, there are no approved vaccines against CMV. The epitope of a CMV neutralizing monoclonal antibody against a conserved region of the envelope protein gH provided the basis for a new CMV vaccine design. We exploited the influenza A virus as a vaccine platform due to the highly immunogenic head domain of its hemagglutinin envelope protein. Influenza A variants were engineered by reverse genetics to express the epitope of an anti-CMV gH neutralizing antibody that recognizes native gH into the hemagglutinin antigenic Sa site. We determined that the recombinant influenza variants expressing 7, 10, or 13 residues of the anti-gH neutralizing antibody epitope were recognized and neutralized by the anti-gH antibody 10C10. Mice vaccinated with the influenza/CMV chimeric viruses induced CMV-specific antibodies that recognized the native gH protein and inhibited virus infection. In fact, the influenza variants expressing 7–13 gH residues neutralized a CMV infection at ~60% following two immunizations with variants expressing the 13 residue gH peptide produced the highest levels of neutralization. Collectively, our study demonstrates that a variant influenza virus inserted with a gH peptide can generate a humoral response that limits a CMV infection.

Development of novel vaccines against human cytomegalovirus

Congenital human cytomegalovirus (HCMV) infection and HCMV infection of the immunosuppressed patients cause significant morbidity and mortality, and vaccine development against HCMV is a major public health priority. Efforts to develop HCMV vaccines have been ongoing for 50 y, though no HCMV vaccine has been licensed; encouraging and promising results have obtained from both preclinical and clinical trials. HCMV infection induces a wide range of humoral and T cell-mediated immune responses, and both branches of immunity are correlated with protection. In recent years, there have been novel approaches toward the development of HCMV vaccines and demonstrated that vaccine candidates could potentially provide superior protection over natural immunity acquired following HCMV infection. Further, rationally designed HCMV protein antigens that express native conformational epitopes could elicit optimal immune response. HCMV vaccine candidates, using a multi-antigen approach, to maximize the elicited protective immunity will most likely be successful in development of HCMV vaccine.

Cytomegalovirus in solid organ transplant recipients-Guidelines of the American Society of Transplantation Infectious Diseases Community of Practice

Cytomegalovirus (CMV) is one of the most common opportunistic infections that affect the outcome of solid organ transplantation. This updated guideline from the American Society of Transplantation Infectious Diseases Community of Practice provides evidence-based and expert recommendations for screening, diagnosis, prevention, and treatment of CMV in solid organ transplant recipients. CMV serology to detect immunoglobulin G remains as the standard method for pretransplant screening of donors and transplant candidates. Antiviral prophylaxis and preemptive therapy are the mainstays of CMV prevention. The lack of a widely applicable viral load threshold for diagnosis and preemptive therapy is highlighted, as a result of variability of CMV nucleic acid testing, even in the contemporary era when calibrators are standardized. Valganciclovir and intravenous ganciclovir remain as drugs of choice for CMV management. Strategies for managing drug-resistant CMV infection are presented. There is an increasing use of CMV-specific cell-mediated immune assays to stratify the risk of CMV infection after solid organ transplantation, but their role in optimizing CMV prevention and treatment efforts has yet to be demonstrated. Specific issues related to pediatric transplant recipients are discussed.

Vaccinations in kidney transplant recipients: Clearing the muddy waters

Vaccine preventable diseases account for a significant proportion of morbidity and mortality in transplant recipients and cause adverse outcomes to the patient and allograft. Patients should be screened for vaccination history at the time of pre-transplant evaluation and vaccinated at least four weeks prior to transplantation. For non-immune patients, dead-vaccines can be administered starting at six months post-transplant. Live attenuated vaccines are contraindicated after transplant due to concern for infectious complications from the vaccine and every effort should be made to vaccinate prior to transplant. Since transplant recipients are on life-long immunosuppression, these patients may have lower rates of serological conversion, lower mean antibody titers and waning of protective immunity over shorter period as compared to general population. Recommendations regarding booster dose in kidney transplant recipients with sub-optimal serological response are lacking. Travel plans should be part of routine post-transplant assessment and pre-travel vaccines and counseling should be provided. More studies are needed on vaccination schedules, serological response, need for booster doses and safety of live attenuated vaccines in this special population.

A fifty-year odyssey: prospects for a cytomegalovirus vaccine in transplant and congenital infection

INTRODUCTION

It has been almost fifty years since the Towne strain was used by Plotkin and collaborators as the first vaccine candidate for cytomegalovirus (CMV). While that approach showed partial efficacy, there have been a multitude of challenges to improve on the promise of a CMV vaccine. Efforts have been dichotomized into a therapeutic vaccine for patients with CMV-infected allografts, either stem cells or solid organ, and a prophylactic vaccine for congenital infection.

AREAS COVERED

This review will evaluate research prospects for a therapeutic vaccine for transplant recipients that recognizes CMV utilizing primarily T cell responses. Similarly, we will provide an extensive discussion on attempts to develop a vaccine to prevent the manifestations of congenital infection, based on eliciting a humoral anti-CMV protective response. The review will also describe newer developments that have upended the efforts toward such a vaccine through the discovery of a second pathway of CMV infection that utilizes an alternative receptor for entry using a series of antigens that have been determined to be important for prevention of infection.

EXPERT COMMENTARY

There is a concerted effort to unify separate therapeutic and prophylactic vaccine strategies into a single delivery agent that would be effective for both transplant-related and congenital infection.