Letermovir for Prevention of Cytomegalovirus Reactivation in Haploidentical and Mismatched Adult Donor Allogeneic Hematopoietic Cell Transplantation with Post-Transplantation Cyclophosphamide for Graft-versus-Host Disease Prophylaxis

Viral infection after hematopoietic stem cell transplantation

PURPOSE OF REVIEW

Viral infections are important complications after allogeneic hematopoietic stem cell transplantation. New infections develop such as SARS-CoV-2 with the potential for severe consequences. In this review, newly published information regarding management of viral infections is discussed.

RECENT FINDINGS

Letermovir and maribavir are antiviral agents that have positively impacted the management of cytomegalovirus infections. These should today be included in treatment algorithms. The first antiviral cellular therapy for anti-CD20 refractory EBV-associated lymphoproliferative disease is now licensed and available. Vaccination as well as introduction of antiviral agents, mAbs and possibly the development of different viral strains have reduced mortality in COVID-19 in this patient population. Well designed studies have shown the improved immunogenicity of high-dose influenza vaccines. There is still an unmet medical need for patients infected with human metapneumovirus and parainfluenza viruses.

SUMMARY

Although improvements in patient management for several important posttransplantation viral infections have been reported, an unmet medical need still exists for other viruses occurring in this high-risk population.

Impact of Primary Letermovir Prophylaxis Versus Preemptive Antiviral Therapy for Cytomegalovirus on Economic and Clinical Outcomes after Hematopoietic Cell Transplantation

Preemptive therapy (PET) historically has been the primary strategy to reduce early-onset cytomegalovirus (CMV) reactivation after allogeneic hematopoietic cell transplantation (HCT) but is associated with antiviral-associated toxicities and increases in healthcare resource utilization and cost. Despite its high cost, letermovir (LTV) prophylaxis has largely supplanted PET due to its effectiveness and tolerability. Direct comparisons between LTV and PET approaches on economic and clinical outcomes after allogeneic HCT remain limited. Objective: To compare total cost of care (inpatient and outpatient) between LTV prophylaxis and PET through day+180 after allogeneic HCT. Adult allogeneic CMV seropositive (R+) HCT recipients who initiated LTV <30 days after HCT between 01/01/18 and 12/31/18 were matched 1:1 to allogeneic CMV R+ HCT recipients between 01/01/15 and 12/31/17 (PET cohort). Patients were grouped into high-risk (HR) or standard-risk (SR) for CMV to compare the LTV and PET cohorts. Direct costs for each patient's index HCT admission and all subsequent inpatient and outpatient care through day+180 after HCT were determined and converted into 2021 US dollars and then to Medicare proportional dollars (MPD). A secondary analysis using 2019 average wholesale price was conducted to specifically evaluate anti-CMV medication costs. There were a total of 176 patients with 54 HR CMV pairs and 34 SR CMV pairs. No differences in survival between LTV and PET for both HR and SR CMV groups were observed. The rate of clinically significant CMV infection decreased for both HR CMV (11/54, 20.4% versus 38/54, 70.4%, P < .001) and SR CMV (1/34, 2.9% versus 12/34, 35.3%, P < .001) patients who were given LTV prophylaxis with corresponding reductions in val(ganciclovir) and foscarnet (HR CMV only) use. Among HR CMV patients, LTV prophylaxis was associated with reductions in CMV-related readmissions (3/54, 5.6% versus 18/54, 33.3%, P < .001) and outpatient visits within the first 100 days after HCT (20 versus 25, P = .002), and a decreased median total cost of care ($36,018 versus $75,525, P < .001) in MPD was observed. For SR CMV patients on LTV, a significant reduction in the median inpatient cost ($15,668 versus $27,818, P < .001) was found, but this finding was offset by a higher median outpatient cost ($26,145 versus $20,307, P = .030) that was not CMV-driven. LTV prophylaxis is highly effective in reducing clinically significant CMV reactivations for both HR and SR HCT recipients. In this study, LTV prophylaxis was associated with a decreased total cost of care for HR CMV patients through day+180. Specifically, reductions in CMV-related readmissions, exposure to CMV-directed antiviral agents, and outpatient visits in the first 100 days after HCT were observed. SR CMV patients receiving LTV prophylaxis benefited by having a reduced inpatient cost of care due to lowered room and pharmacy costs.

Haploidentical HSCT in the Treatment of Pediatric Hematological Disorders

Allogeneic hematopoietic stem cell transplantation has become a treatment option for otherwise non-curative conditions, both malignant and benign, affecting children and adults. Nevertheless, the latest research has been focusing extensively on transplantation from related and unrelated haploidentical donors, suitable for patients requiring emergent hematopoietic stem cell transplantation (HSCT) in the absence of an HLA-matched donor. Haploidentical HSCT (haplo-HSCT) can be an effective treatment for non-malignant pediatric disorders, such as primary immunodeficiencies or hemoglobinopathies, by enabling a much quicker selection of the appropriate donor for virtually all patients, low incidence of graft-versus-host disease (GVHD), and transplant-related mortality (TRM). Moreover, the outcomes of haplo-HSCT among children with hematological malignancies have improved radically. The most demanding tasks for clinicians are minimizing T-cell-mediated alloreactivity as well as early GVHD prevention. As a result, several T-cell depletion approaches, such as ex vivo T-cell depletion (TCD), and T-cell replete approaches, such as a combination of anti-thymocyte globulin (ATG), post-transplantation cyclophosphamide (PTCy), cyclosporine/tacrolimus, mycophenolate mofetil, or methotrexate, have been taken up. As more research is needed to establish the most beneficial form of therapy, haplo-HSCT is currently considered an alternative donor strategy for pediatric and adult patients with complications like viral and bacterial infections, invasive fungal disease, and GVHD.

Real-World Challenges of Haplo-Identical Hematopoietic Stem Cell Transplant in a Developing Country: A Single Center Experience

Hematopoietic stem cell transplant (HSCT) is potentially, the sole curative option for many malignant and non-malignant hematological disorders. Finding a human leukocyte antigen (HLA) compatible donor remains one of the limiting factors, hampering the utilization of HSCT. However, the introduction of post-transplant cyclophosphamide (PTCy) has improved the outcomes of haploidentical transplants making it a suitable option for patients lacking HLA-compatible donors. We collected data from 44 patients who underwent haplo-identical allogeneic stem cell transplants at the Armed Forces Bone Marrow Transplant Center/National Institute of Blood and Marrow Transplant (AFBMTC/NIBMT) from the year 2015 to 2022. The diseases were divided into three categories, i.e., bone marrow failure (BMF) syndromes, hematological malignancies (HM) and miscellaneous (Misc) groups. Median age at transplant was 18 (01-39) years. Transplant indications included aplastic anemia (AA) in 21 (47.7%) cases, 15 (34.1%) HM, and eight (18.2%) cases falling in the Misc groups. A maximum number of graft failures occurred in the BMF group; primary graft failure in 07 (33.3%) cases and secondary graft failure in four (19%) cases, (p-value < 0.05). Acute graft versus host disease (aGVHD) grade II-IV occurred in nine (20.5%) cases while chronic graft versus host disease (cGVHD) occurred in 10 (22.7%) cases. Cytomegalovirus (CMV) reactivation was seen in 31 (70.5%) cases. Maximum CMV reactivation was seen in HM group 13 (86.6%) cases, (p-value < 0.05) as compared to BMF (71.4%) and Misc groups (37.5%). Post-transplant cyclophosphamide (PTCy) based regimens, early neutrophil engraftment, and patients with GVHD had better survival outcomes (p-value < 0.05) overall survival (OS), and relapse-free survival (RFS). and GVHD-free relapse-free survival (GFRS) were significantly better in cases with early neutrophil engraftment. OS of the study cohort was 50% while disease-free survival (DFS) and GFRS were 45.5% and 36.4%, respectively.

Differential clinical impact of letermovir prophylaxis according to graft sources: a KSGCT multicenter retrospective analysis

ABSTRACT

Clinically significant cytomegalovirus infection (csCMVi) is frequently observed after allogeneic hematopoietic stem cell transplantation (HSCT) and prophylaxis with letermovir is commonly adopted. However, the clinical benefit of letermovir prophylaxis according to graft sources has not been sufficiently elucidated. We retrospectively analyzed 2194 recipients of HSCT who were CMV-seropositive (236 with letermovir prophylaxis and 1958 without prophylaxis against CMV). csCMVi was significantly less frequent in patients with letermovir prophylaxis than in those without (23.7% vs 58.7% at 100 days after HSCT, P < .001) and the same trend was seen when recipients of bone marrow (BM), peripheral blood stem cell (PBSC), or cord blood (CB) transplantation were separately analyzed. In recipients of BM, nonrelapse mortality (NRM) was significantly lower in the letermovir group at 6 months after HSCT (5.0% vs 14.9%, P = .018), and the same trend was observed in recipients of PBSCs (14.7% vs 24.8%, P = .062); however, there was no statistical significance at 1 year (BM, 21.1% vs 30.4%, P = .67; PBSCs, 21.2% vs 30.4%, P = .096). In contrast, NRM was comparable between recipients of CB with and without letermovir prophylaxis throughout the clinical course (6 months, 23.6% vs 24.3%, P =.92; 1 year, 29.3% vs 31.0%, P = .77), which was confirmed by multivariate analyses. In conclusion, the impact of letermovir prophylaxis on NRM and csCMVi should be separately considered according to graft sources.

Real-Life Data on the Efficacy and Safety of Letermovir for Primary Prophylaxis of Cytomegalovirus in Allogeneic Hematopoietic Stem Cell Recipients: A Single-Center Analysis

Objective

Cytomegalovirus (CMV) reactivation is a life-threatening complication after allogeneic hematopoietic stem cell transplantation (HSCT). Introduction of letermovir (LMV) seems to improve post-transplant outcomes, but delayed-onset CMV reactivation still remains a challenge. In this study, we report on our first experience with LMV prophylaxis in 93 CMV-seropositive adult patients receiving HSCT in our center.

Materials and Methods

We retrospectively analyzed the data of 93 adult CMV-seropositive recipients receiving LMV as CMV prophylaxis after HSCT for hematological malignancies between 2019 and 2023. The starting LMV dose was 480 mg daily, reduced to 240 mg daily for those receiving cyclosporin A co-administration. CMV DNA in the blood was measured by real-time polymerase chain reaction weekly for the first 2 months after transplantation, then every other week until the end of immunosuppressive treatment. LMV was continued to day +100 or to CMV reactivation.

Results

The median recipient age at the time of transplant was 51 (range: 20-71) years. All patients received grafts from peripheral blood, mostly for acute myeloid leukemia (60%). The median time from transplantation to LMV initiation was 3 (range: 0-24) days. While 55% of patients were transplanted from matched related donors, 32% had unrelated donors and 13% underwent haploidentical HSCT. Four patients (4%) had CMV “blips” while on LMV, but the drug was continued and repeated assays were negative. Only 2 patients (2%) experienced CMV reactivation while on LMV, on days 48 and 34 after HSCT, respectively. Seven patients (7%) developed late-onset CMV reactivation after a median of 124 days after HSCT (range: 118-152 days) and they were successfully treated with ganciclovir. CMV disease was not observed. Grade III-IV acute graft-versus-host disease occurred in 6 patients (6%) during LMV treatment. LMV treatment was free of side effects.

Conclusion

LMV prophylaxis was effective in preventing CMV reactivation with a favorable safety profile. CMV reactivation occurred mostly after LMV discontinuation; thus, extending the duration of prophylaxis beyond 100 days could be beneficial.

Human Leukocyte Antigen-Haploidentical Haematopoietic Stem Cell Transplantation Using Post-Transplant Cyclophosphamide for Paediatric Haematological Malignancies

The use of human leukocyte antigen (HLA)-haploidentical haematopoietic stem cell transplantation (HSCT) with post-transplant cyclophosphamide (PTCY), which markedly reduces the risk of graft-versus-host disease, has rapidly increased worldwide, even in children. It was initially developed for post-transplant relapse or non-remission at transplant for patients with high-risk haematologic malignancies. However, this strategy is currently used more frequently for standard-risk, transplant-eligible paediatric haematological malignancies. It has recently been recognised in adults that the transplant outcomes after PTCY-based HLA-haploidentical HSCT are comparable with those achieved after HLA-matched HSCT. Therefore, even in children, parental donors who are HLA-haploidentical donors and cord blood are currently considered the next donor candidates when an HLA-matched related or unrelated donor is unavailable. This review addresses the current status of the use of haplo-HSCT with PTCY for paediatric haematologic malignancies and future directions for donor selection (sex, age, ABO blood type, and HLA disparity), donor source, the dose of infused CD34+ cells, optimal conditioning, the concomitant graft-versus-host disease prophylaxis other than PTCY, and the pharmacokinetic study of CY and CY metabolites. These aspects present key solutions for further improvements in the outcomes of haplo-HSCT with PTCY for paediatric haematological malignancies.

Outcomes of allogeneic hematopoietic cell transplantation under letermovir prophylaxis for cytomegalovirus infection

Cytomegalovirus (CMV) infection is a major infectious complication following allogeneic hematopoietic cell transplantation (allo-HCT). Although letermovir (LMV) prophylaxis dramatically reduces the incidence of early clinically significant CMV (csCMV) infection, it remains unclear whether it has a beneficial effect on nonrelapse mortality (NRM) and overall survival (OS). Herein, we evaluated the impact of LMV prophylaxis on posttransplant outcomes using the registry database of the Japanese Society for Transplantation and Cellular Therapy. Adult patients who underwent allo-HCT between 2017 and 2019 were analyzed (n = 6004). LMV prophylaxis was administered to 1640 patients (LMV group) and it significantly reduced the incidence of csCMV infection compared with those not administered LMV prophylaxis (15.4% vs 54.1%; p < 0.01). However, it did not improve the 1-year NRM (hazard ratio [HR], 0.93; p = 0.40) and OS (HR, 0.96; p = 0.49). In the LMV group, 74 patients had breakthrough csCMV infection and showed inferior NRM (HR, 3.44; p < 0.01) and OS (HR, 1.93; p = 0.02) compared with those without infection. After completing LMV prophylaxis, 252 patients had late csCMV infection and showed inferior NRM (HR, 1.83; p < 0.01) and OS (HR, 1.58; p < 0.01). Our findings suggest that managing breakthrough and late csCMV infections is important for improving long-term outcomes.

Patterns of CMV infection after letermovir withdrawal in recipients of posttransplant cyclophosphamide-based transplant

Reactivation of latent cytomegalovirus (CMV) is increased in recipients of allogeneic hematopoietic cell transplantation (allo-HCT) with seropositive CMV using posttransplant cyclophosphamide (PT-Cy)-based graft-versus-host disease (GVHD) prophylaxis. Letermovir, a novel DNA terminase complex inhibitor, reduces the incidence of clinically significant CMV infection (csCMVi) in this population; however, parameters that predict csCMVi after letermovir withdrawal are not well described. Here, we examined clinical and immunological parameters in 294 recipients of PT-Cy-based allo-HCT, including 157 patients with CMV, of whom 80 completed letermovir prophylaxis without csCMVi and subsequently stopped letermovir. In this population, the median duration of letermovir exposure was 203 days (interquartile range [IQR], 160-250 days). After letermovir withdrawal, the 90-day cumulative incidence of csCMVi was 23.0% (95% confidence interval, 14.3-32.8). There were no episodes of CMV end-organ disease. Hypogammaglobulinemia before letermovir discontinuation was predictive of csCMVi (hazard ratio, 0.33; 95% confidence interval, 0.12-0.93; P = .03), whereas T-cell and B-cell reconstitution before letermovir withdrawal were not predictive of csCMVi. Higher numbers of natural killer cells were found before letermovir withdrawal in patients who experienced csCMVi (median, 202 vs 160; P = .03). In recipients with seropositive CMV, CD3+CD4-CD8+ T-cell reconstitution was faster in patients with CMV regardless of letermovir exposure. Taken together, these data suggest that csCMVi after letermovir withdrawal was frequent in patients treated with PT-Cy, despite prolonged exposure. Strategies to boost CMV-specific adaptive immunity in patients with persistent hypogammaglobulinemia is a logical pathway to reduce csCMVi after letermovir withdrawal.

Dynamics of polyclonal immuno-reconstitution after allogeneic transplant with post-transplant cyclophosphamide and letermovir

Cytomegalovirus (CMV) reactivations are strong stimulators of immune-reconstitution (IR) in hematopoietic stem cell transplantation (HSCT) recipients. Herein, we analyzed 317 CMV-seropositive consecutive patients (n = 109 letermovir, LTV; n = 208 no-LTV), undergoing HSCT with post-transplant cyclophosphamide (PTCy) and calcineurin inhibitor- (CNI) free graft-versus-host-disease (GvHD) prophylaxis. At day+90, median CD19+/mm3 was higher in LTV-cohort: 5.5 [0;439] versus 2 [0;294], p = 0.008; median CD3+/mm3 counts were lower in LTV-cohort, with no differences in CD4+, CD8+ and NK-cells. At day+180 median CD3+, CD4+ and CD8+/mm3 values were comparable between groups. Higher CD19+/mm3 counts were observed in LTV-cohort: 62 [0; 2983] versus 42 [0; 863]. Significantly higher median NK/mm3 values were seen in LTV-cohort: 225.5 [0;763] versus 163.5 [0;1181], p = 0.0003. The impact of LTV on B-cell IR at 3 months and NK-cell levels at 6 months was retained in multivariate analysis (p < 0.01), whereas the effect on T-cells was not confirmed. Moreover, we confirmed a significant reduction of clinically-relevant CMV, and moderate-to- severe chronic GvHD in LTV-cohort. Overall, in our study the use of LTV was associated with a slight improvement of B-cell and NK-cells reconstitution, with only minor impact on T-cell subsets, giving new insights on polyclonal IR for HSCT recipients in the LTV era.

Effectiveness of letermovir for cytomegalovirus prophylaxis in allogeneic hematopoietic stem cell transplant recipients: A global systematic review

OBJECTIVE(S)

Letermovir (LET), a novel antiviral, has largely supplanted more traditional preemptive therapy (PET) for cytomegalovirus (CMV) prophylaxis in allogeneic hematopoietic stem cell transplant (allo-HCT) patients. Use of LET demonstrated efficacy against placebo in phase III randomized controlled trials, but is considerably more expensive than PET. This review aimed to evaluate the real-world effectiveness of LET in preventing clinically significant CMV infection (csCMVi) for allo-HCT recipients and related outcomes.

DESIGN

A systematic literature review was performed using an a priori protocol using PubMed, Scopus, and ClinicalTrials.gov from January 2010 to October 2021.

SETTING AND PARTICIPANTS

Studies were included if they met the following criteria: LET compared with PET, CMV-related outcomes, patients aged 18 years or older, and English language-only articles. Descriptive statistics were used to summarize study characteristics and outcomes.

OUTCOME MEASURES

CMV viremia, csCMVi, CMV end-organ disease, graft-versus-host-disease, all-cause mortality.

RESULTS

A total of 233 abstracts were screened, with 30 included in this review. Randomized trials demonstrated efficacy of LET prophylaxis in preventing csCMVi. Observational studies demonstrated varying degrees of effectiveness of LET prophylaxis compared with use of PET alone. All studies with a comparator group resulted in lower rates of csCMVi for patients using LET. Included studies varied widely by CMV viral load threshold cutoff and CMV test units, limiting synthesis of results owing to high heterogeneity.

CONCLUSION

LET reduces risk of csCMVi, but lack of standardized clinical definitions on how to evaluate csCMVi and related outcomes largely prevent synthesis of results. Clinicians must consider this limitation in the context of evaluating the effectiveness of LET to other antiviral therapies, especially for patients at risk of late-onset CMV. Future studies should focus on prospective data collection through registries and concordance of diagnostic definitions to mitigate study heterogeneity.

How I prevent viral reactivation in high-risk patients

Preventing viral infections at an early stage is a key strategy for successfully improving transplant outcomes. Preemptive therapy and prophylaxis with antiviral agents have been successfully used to prevent clinically significant viral infections in hematopoietic cell transplant recipients. Major progress has been made over the past decades in preventing viral infections through a better understanding of the biology and risk factors, as well as the introduction of novel antiviral agents and advances in immunotherapy. High-quality evidence exists for the effective prevention of herpes simplex virus, varicella-zoster virus, and cytomegalovirus infection and disease. Few data are available on the effective prevention of human herpesvirus 6, Epstein-Barr virus, adenovirus, and BK virus infections. To highlight the spectrum of clinical practice, here we review high-risk situations that we handle with a high degree of uniformity and cases that feature differences in approaches, reflecting distinct hematopoietic cell transplant practices, such as ex vivo T-cell depletion.

Cytomegalovirus breakthrough and resistance during letermovir prophylaxis

Letermovir is a relatively new antiviral for prophylaxis against cytomegalovirus (CMV) after allogeneic hematopoietic cell transplantation (HCT). CMV-seropositive HCT recipients who received letermovir prophylaxis from 2018 to 2020 at our center were evaluated for letermovir resistance and breakthrough CMV reactivation. Two-hundred twenty-six letermovir recipients were identified and 7/15 (47%) with CMV DNAemia ≥200 IU/mL were successfully genotyped for UL56 resistance. A single C325Y resistance mutation was identified in an umbilical cord blood recipient. Ninety-five (42%), 43 (19%), and 15 (7%) patients had breakthrough CMV at any level, ≥150 IU/mL, and ≥500 IU/mL, respectively. Risk factors for breakthrough CMV reactivation at each viral threshold were examined. Cumulative steroid exposure was the strongest risk factor for CMV at all evaluated viral thresholds. Graft-versus-host disease prophylaxis with post-transplantation cyclophosphamide (aHR 2.34, 95% CI 1.28-4.28, p = 0.001) or calcineurin inhibitors plus mycophenolate (aHR 2.24, 95% CI 1.30-3.86, p = 0.004) were also associated with an increased risk of CMV reactivation at any level. De novo letermovir resistance is rare and can be successfully treated using other antivirals. Letermovir effectively prevents clinically significant CMV, however, subclinical CMV reactivation occurs frequently at our center.

Real world experience: Examining outcomes using letermovir for CMV prophylaxis in high-risk allogeneic hematopoietic stem cell patients in the setting of using T-cell depletion as GVHD prophylaxis

BACKGROUND

Cytomegalovirus (CMV) infection significantly impacts the morbidity and mortality of patients undergoing allogeneic hematopoietic stem cell transplant (HSCT). Despite monitoring and pharmacologic prophylaxis with drugs such as valganciclovir or ganciclovir, rates of early CMV reactivation have continually persisted, contributing to increased rates of morbidity and mortality in allogeneic-HSCT patients. This study evaluates the outcomes of letermovir in preventing CMV reactivation and CMV-related complications in HSCT recipients with initiation of therapy at +21 days in high-risk patients.

METHODS

We retrospectively analyzed adult patients at University of Southern California (USC) Norris Cancer Hospital who received allogeneic-HSCT from 2018 to 2020 with subsequent serial CMV monitoring and treatment. CMV reactivation was determined in patients if they had clinically significant serum CMV viremia (viremia requiring treatment) or organ involvement by day+100. Primary endpoint assessed was day+100 rates of CMV reactivation. Secondary end-points included 1-year OS, 1-year RFS, and incidence of GVHD. Descriptive statistics were used to compare characteristics between groups used in this study, with a significance level of α = 0.05.

RESULTS

Between 2018 and 2020, 116 adult HSCT recipients were reviewed. 51% were male and 49% were female; donor sources consisted of 27% match related donor (MRD) 28% match-unrelated donor (MUD), and 45% haploidentical donor. Of the 116 patients, 92 were identified as high-risk for CMV reactivation. 71 patients received letermovir prophylaxis, and 21 patients received no prophylaxis. In high-risk patients, after adjusting for GVHD status and transplant type, patients that received letermovir had no statistically significant difference of having D + 100 CMV reactivation compared to patients that did not receive letermovir. 1.02 (95% CI: 0.35, 3.20) (p = 0.97). Moreover, there were no statistically significant difference observed between letermovir treatment and 1-year OS, 1-year RFS, and incidence of GVHD.

CONCLUSION

Patients in the high-risk letermovir group had outcomes that were comparable to the lower risk "non-letermovir" group. There was no significant difference in CMV D + 100 reactivation between high-risk patients who did not receive letermovir compared to the patients who did. While other studies have shown that early initiation of letermovir may be associated with improved outcomes, our study shows that the use of letermovir with initiation at 21 days may not necessarily translate to improved secondary outcomes such as overall survival. Further prospective studies evaluating the time of initiating therapy and outcomes are needed.

Cytomegalovirus Therapy: Role of Letermovir in Prophylaxis and Treatment in Transplant Recipients

Cytomegalovirus (CMV) is a common viral pathogen in the transplant population and is associated with significant morbidity and mortality. CMV prevention is paramount; however, selecting the best preventive strategy depends on many factors including donor-recipient CMV serostatus, transplant-specific risks, antiviral toxicities and cost. Novel CMV therapeutics such as letermovir (LTV) are desperately needed to optimize CMV management. Uniquely among CMV antiviral therapies, LTV inhibits the viral terminase complex in the CMV DNA synthesis pathway and disrupts viral genome packaging. Further, it lacks side effects frequently associated with other CMV antiviral therapies and evades common mechanisms of resistance. LTV is approved by the US Food and Drug Administration for CMV prevention in adult CMV-seropositive hematopoietic cell transplant recipients but is increasingly applied off-label for prophylaxis and treatment. This review summarizes important concepts of CMV management in transplantation, with a specific focus on LTV pharmacology and clinical experience to date alongside future prospects for its application.

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.

Comparison of outcomes for HLA-matched sibling and haplo-identical donors in Myelodysplastic syndromes: report from the chronic malignancies working party of EBMT

Myelodysplastic syndromes (MDS) are the second common indication for an Allo-HCT. We compared the outcomes of 1414 matched sibling (MSD) with 415 haplo-identical donors (HD) transplanted with post-transplant cyclophosphamide (PTCy) as GVHD prophylaxis between 2014 and 2017. The median age at transplant with MSD was 58 and 61 years for HD. The median time to neutrophil engraftment was longer for HD being 20 vs 16 days for MSD (p < 0.001). Two-year overall survival (OS) and PFS (progression free survival) with MSD were significantly better at 58% compared with 50%, p ≤ 0.001, and 51% vs 47%, p = 0.029, with a HD. Relapse at 2 years was lower with a HD 23% than with MSD 29% (p = 0.016). Non relapse mortality (NRM) was higher with HD in the first 6 months post-transplant [HR 2.59 (1.5–4.48) p < 0.001] and was also higher at 2 years being 30% for HD and 20% for MSD, p ≤ 0.001. The incidence of acute GVHD grade II-IV and III–IV at 100 days was comparable for MSD and HD, however, chronic GVHD at 2 years was significantly higher with MSD being 44% vs 32% for HD (p < 0.001). After multivariable analysis, OS and primary graft failure were significantly worse for HD particularly before 6 months [HR 1.93(1.24–3.0)], and HR [3.5(1.5–8.1)]. The median age of HD 37 (IQR 30–47) years was significantly lower than sibling donors 56 (IQR 49–62 years) p < 0.001. However, there was no effect on NRM, relapse or PFS. This data set suggests that a MSD donor remains the preferred choice in MDS over a haplo donor. Transplants with haploidentical donors result in satisfactory long-term outcome, justifying it’s use when no better donor is available.

Letermovir vs. high-dose valacyclovir for cytomegalovirus prophylaxis following haploidentical or mismatched unrelated donor allogeneic hematopoietic cell transplantation receiving post-transplant cyclophosphamide

Patients undergoing haploidentical or mismatched unrelated donor (haplo/MMUD) allogeneic hematopoietic cell transplantation (alloHCT) receiving post-transplant cyclophosphamide (PTCy) are at high risk of cytomegalovirus (CMV) infection. Experience with letermovir (LET) in this population is limited. This single center retrospective cohort study compared CMV and transplant outcomes between LET and a historical control with high-dose valacyclovir (HDV) prophylaxis in adults undergoing haplo/MMUD alloHCT. Thirty-eight CMV seropositive patients were included, 19 in each arm. LET reduced the incidence of CMV infection (5% vs. 53%, RR 0.01, 95% CI 0.014-0.71, p = .001) and need for CMV treatment by day +100 (5% vs. 37%, RR 0.14, 95% CI 0.18-0.99, p = .017) compared to HDV. Median CMV event-free-survival was improved with LET (not reached vs. 80 days, HR 0.114, 95% CI 0.07-0.61, p = .004). These data support the efficacy of LET in alternative donor transplants.

Haploidentical Hematopoietic Stem Cell Transplant Using Post-transplant Cyclophosphamide: A Single-Center Initial Experience in Vietnam

AIMS AND OBJECTIVES

Haploidentical transplants constitute a potential alternative therapy for patients who urgently need transplantation in the absence of human leukocyte antigen-matched donors. We report a single-center experience regarding the initial results of haploidentical peripheral blood stem cell transplantation (haplo-PBSCT) using post-transplant cyclophosphamide (PTCy) at the HCMC Blood Transfusion Hematology (BTH) Hospital.

METHODS

We conducted a retrospective case series study of 23 patients who underwent haplo-PBSCT using PTCy at the HCMC BTH Hospital between January 2014 and January 2021. The refined disease risk index (DRI) was used to stratify the outcomes. We evaluated the engraftment rate, graft-versus-host disease (GVHD), and complications during haploidentical transplantation. Overall survival (OS), disease-free survival (DFS), and GVHD-free relapse-free survival (GRFS) were assessed.

RESULTS

The majority of the patients in the present study were diagnosed with acute myeloid leukemia. All patients received reduced-intensity conditioning regimens. The engraftment rate was 86.9%. The median times to neutrophil and platelet engraftment were 17 and 31 days, respectively. Two patients (8.7%) reported severe acute GVHD (grade III-IV), while two patients (8.7%) had grade I-II acute GVHD. Three patients experienced limited chronic GVHD of the skin, requiring topical steroids. The most common complication was bloodstream infection (60.9%). Cytomegalovirus reactivation occurred in 19 patients (82.6%) and 17.4% developed hemorrhagic cystitis. The 1-year relapse rate was 32.5%. The cumulative incidence of non-relapse mortality at 1 year was 17.3%. The 1-year OS and DFS rates were 66.3% and 55.7%, respectively. The 1-year GRFS rate was 49.2%. A high/very high DRI score was associated with worse OS after haplo-PBSCT (P=0.038).

CONCLUSION

Haploidentical transplant using PTCy is a feasible therapy for patients without suitably matched donors in Vietnam. Infection after transplantation remains a challenge and requires effective management.

Cytomegalovirus Infections in Children with Primary and Secondary Immune Deficiencies

Cytomegalovirus (CMV) is a human herpes virus that causes significant morbidity and mortality in immunosuppressed children. CMV primary infection causes a clinically mild disease in healthy children, usually in early childhood; the virus then utilises several mechanisms to establish host latency, which allows for periodic reactivation, particularly when the host is immunocompromised. It is this reactivation that is responsible for the significant morbidity and mortality in immunocompromised children. We review CMV infection in the primary immunodeficient host, including early identification of these infants by newborn screening to allow for CMV infection prevention strategies. Furthermore, clinical CMV is discussed in the context of children treated with secondary immunodeficiency, particularly paediatric cancer patients and children undergoing haematopoietic stem cell transplant (HSCT). Treatments for CMV are highlighted and include CMV immunotherapy.

Lower Incidence of Cytomegalovirus Reactivation Following Post-Transplantation Cyclophosphamide HLA-Mismatched Unrelated Donor Transplantation

The use of haploidentical or HLA-mismatched unrelated donors (MMUD) allows allogeneic hematopoietic cell transplantation in individuals without suitable matched donors. Post-transplantation cyclophosphamide (PTCy) is used routinely for prevention of graft-versus-host disease in recipients of haploidentical transplants, and its use has been recently explored in MMUD transplantation. We compared the incidence of cytomegalovirus (CMV) reactivation and rate of lymphocyte recovery between PTCy MMUD and alternative transplantation modalities. Single-center retrospective study of 22 consecutive PTCy MMUD recipients transplanted between April 2017 and January 2019. Patients undergoing anti-thymocyte globulin (ATG) MMUD (n = 37) and PTCy haploidentical transplantation (n = 19) between January 2015 and July 2018 served as historical controls. We assessed the incidence of CMV (any viremia) and clinically significant CMV reactivation (cs-CMVi; defined as CMV disease or CMV viremia leading to preemptive treatment) in these 3 groups. Immune reconstitution was assessed by absolute lymphocyte count (ALC) at days 30, 90, 180, and 360 after transplantation. Statistical analyses included Kaplan-Meier plots with a log-rank test, Kruskal-Wallis test, and Fisher's exact test where appropriate, and logistic regression analyses. For PTCy MMUD, PTCy haploidentical and ATG MMUD groups, the 100-day and 200-day incidence of CMV (any viremia) were 41%, 63%, and 77% (P = .02), and 64%, 68%, and 86% (P = .049), respectively. The rate of cs-CMVi was also lower in PTCy MMUD compared to PTCy haploidentical and ATG MMUD (14% versus 53% and 54% at day 100 [P = .01] and 25% versus 53% and 58% at day 200 [P = .03]). There was a trend toward lower 200-day incidence of cs-CMVi in PTCy MMUD compared to ATG MMUD, even after excluding letermovir-treated patients from the analysis (25% versus 58% [P = .06]). The association between PTCy MMUD and lower risk of cs-CMVi remained significant even after adjusting for letermovir prophylaxis (odds ratio = 0.23, 95% confidence interval, 0.07-0.81 [P = .02]). Day 30 ALC was lower in PTCy MMUD compared to PTCy haploidentical and ATG MMUD (0.14, 0.33, 0.44 × 10⁹/L, respectively [P = .005) but similar across groups at other time points. PTCy MMUD transplantation was associated with lower incidence of CMV events, independent of the use of CMV prophylaxis. Larger studies are needed.

Letermovir Administration to Prevent Cytomegalovirus Reactivation Is the Potential Risk of Chronic Graft-Versus-Host Disease in Patients Who Received Haploidentical Stem-Cell Transplantation With Post-Transplant Cyclophosphamide

The prevention of chronic graft-versus-host disease (cGVHD) is important for recipients of hematopoietic stem-cell transplantation (HSCT). As one of the etiologies, the relationship between early T-cell recovery and subsequent cGVHD development has been the focus of attention. Recently, letermovir (LTV) was approved for preventing cytomegalovirus (CMV) reactivation in the early transplantation phase. Although CMV affects the immune reconstitution after HSCT, the impacts of LTV to prevent CMV reactivation on early T-cell recovery and cGVHD have not been fully investigated. We aimed to identify early T-cell recovery under LTV at day 30 in 15 and 33 recipients from matched related donors (MRDs) and haploidentical donors with post-transplant cyclophosphamide (PTCy-haplo), respectively. Early increases in the levels of total lymphocytes and HLA-DR⁺ activated T-cells at day 30 were observed under CMV prophylaxis by LTV only in PTCy-haplo recipients and not in MRD recipients. Moreover, PTCy-haplo recipients with LTV showed a significantly higher incidence of cGVHD, but not acute GVHD. Our observations suggest that an early increase in the levels of HLA-DR⁺ activated T-cells may be implicated in the development of cGVHD in patients treated with PTCy who received LTV. Further studies are warranted to validate our results and elucidate the detailed mechanisms of our new insights.

Refractory and Resistant Cytomegalovirus after Hematopoietic Cell Transplant in the Letermovir Primary Prophylaxis Era

BACKGROUND

Cytomegalovirus (CMV) reactivation is one of the most common infectious complications after allogeneic hematopoietic cell transplant (HCT) and may result in significant morbidity and mortality. Primary prophylaxis with letermovir demonstrated a reduction in clinically significant CMV infections (CS-CMVi) in clinical trials of CMV-seropositive HCT recipients. This study aims at exploring the effect of primary letermovir prophylaxis in this population on the incidence and outcomes of refractory or resistant CMV infections.

METHODS

This is a single-center, retrospective cohort study of 537 consecutive CMV-seropositive allogeneic HCT recipients cared for during March 2016 to October 2018. Baseline demographics, HCT characteristics, CMV infections, treatment and mortality data were collected from the electronic medical record. CMV outcomes were defined according to the recently standardized definitions for clinical trials. Characteristics and outcomes were assessed according to receipt of primary letermovir prophylaxis.

RESULTS

Of 537 patients identified, 123 received letermovir for primary prophylaxis during the first 100 days after HCT, and 414 did not. In a multivariate analysis, primary prophylaxis with letermovir was associated with reductions in CS-CMVi (hazard ratio [HR] 0.26, 95% CI 0.16-0.41), CMV end-organ disease (HR 0.23, 95% CI 0.10-0.52), refractory or resistant CMV infection (HR 0.15, 95% CI 0.04-0.52), and non-relapse mortality at week 48 (HR 0.55, 95% CI 0.32-0.93). There was neither resistant CMV nor CMV-related mortality in the primary letermovir prophylaxis group.

CONCLUSIONS

Primary letermovir prophylaxis effectively prevents refractory or resistant CMV infections and decreases non-relapse mortality at week 48, as well as CS-CMVi and CMV disease after allogeneic HCT.

Immune Reconstitution after Haploidentical Donor and Umbilical Cord Blood Allogeneic Hematopoietic Cell Transplantation

Allogeneic hematopoietic cell transplantation (HCT) is the only potentially curative therapy for a variety of hematologic diseases. However, this therapeutic platform is limited by an initial period when patients are profoundly immunocompromised. There is gradual immune recovery over time, that varies by transplant platform. Here, we review immune reconstitution after allogeneic HCT with a specific focus on two alternative donor platforms that have dramatically improved access to allogeneic HCT for patients who lack an HLA-matched related or unrelated donor: haploidentical and umbilical cord blood HCT. Despite challenges, interventions are available to mitigate the risks during the immunocompromised period including antimicrobial prophylaxis, modified immune suppression strategies, graft manipulation, and emerging adoptive cell therapies. Such interventions can improve the potential for long-term overall survival after allogeneic HCT.