Preemptive antiviral therapy in lung transplantation from hepatitis C donors results in a rapid and sustained virologic response.

Objective: The study objective was to assess the safety and efficacy of a preemptive direct-acting antiviral therapy in lung transplants from hepatitis C virus donors to uninfected recipients. Methods: This study is a prospective, open-label, nonrandomized, pilot trial. Recipients of hepatitis C virus nucleic acid test positive donor lungs underwent preemptive direct-acting antiviral therapy with glecaprevir 300 mg/pibrentasvir 120 mg for 8 weeks from January 1, 2019, to December 31, 2020. Recipients of nucleic acid test positive lungs were compared with recipients of lungs from nucleic acid test negative donors. Primary end points were Kaplan-Meier survival and sustained virologic response. Secondary outcomes included primary graft dysfunction, rejection, and infection. Results: Fifty-nine lung transplantations were included: 16 nucleic acid test positive and 43 nucleic acid test negative. Twelve nucleic acid test positive recipients (75%) developed hepatitis C virus viremia. Median time to clearance was 7 days. All nucleic acid test positive patients had undetectable hepatitis C virus RNA by week 3, and all alive patients (n = 15) remained negative during follow-up with 100% sustained virologic response at 12 months. One nucleic acid test positive patient died of primary graft dysfunction and multiorgan failure. Three of 43 nucleic acid test negative patients (7%) had hepatitis C virus antibody positive donors. None of them developed hepatitis C virus viremia. One-year survival was 94% for nucleic acid test positive recipients and 91% for nucleic acid test negative recipients. There was no difference in primary graft dysfunction, rejection, or infection. One-year survival for nucleic acid test positive recipients was similar to a historical cohort of the Scientific Registry of Transplant Recipients (89%). Conclusions: Recipients of hepatitis C virus nucleic acid test positive lungs have similar survival as recipients of nucleic acid test negative lungs. Preemptive direct-acting antiviral therapy results in rapid viral clearance and sustained virologic response at 12 months. Preemptive direct-acting antiviral may partially prevent hepatitis C virus transmission.

Anti-fibrotic therapy and lung transplant outcomes in patients with idiopathic pulmonary fibrosis.

BACKGROUND: It is unclear whether continuing anti-fibrotic therapy until the time of lung transplant increases the risk of complications in patients with idiopathic pulmonary fibrosis. OBJECTIVES: To investigate whether the time between discontinuation of anti-fibrotic therapy and lung transplant in patients with idiopathic pulmonary fibrosis affects the risk of complications. METHODS: We assessed intra-operative and post-transplant complications among patients with idiopathic pulmonary fibrosis who underwent lung transplant and had been treated with nintedanib or pirfenidone continuously for ⩾ 90 days at listing. Patients were grouped according to whether they had a shorter (⩽ 5 medication half-lives) or longer (> 5 medication half-lives) time between discontinuation of anti-fibrotic medication and transplant. Five half-lives corresponded to 2 days for nintedanib and 1 day for pirfenidone. RESULTS: Among patients taking nintedanib (n = 107) or pirfenidone (n = 190), 211 (71.0%) had discontinued anti-fibrotic therapy ⩽ 5 medication half-lives before transplant. Anastomotic and sternal dehiscence occurred only in this group (anastomotic: 11 patients [5.2%], p = 0.031 vs patients with longer time between discontinuation of anti-fibrotic medication and transplant; sternal: 12 patients [5.7%], p = 0.024). No differences were observed in surgical wound dehiscence, length of hospital stay, or survival to discharge between groups with a shorter versus longer time between discontinuation of anti-fibrotic therapy and transplant. CONCLUSION: Anastomotic and sternal dehiscence only occurred in patients with idiopathic pulmonary fibrosis who discontinued anti-fibrotic therapy < 5 medication half-lives before transplant. The frequency of other intra-operative and post-transplant complications did not appear to differ depending on when anti-fibrotic therapy was discontinued. REGISTRATION: clinicaltrials.gov NCT04316780: https://clinicaltrials.gov/ct2/show/NCT04316780.

Utilization of Oil Red O staining for assessing aspiration risk in lung transplant patients: A multidisciplinary prospective study with clinical practice insights.

BACKGROUND: Gastroesophageal reflux disease with microaspiration has been associated with graft dysfunction in lung transplant patients. Identifying patients with aspiration is clinically important because it enables implementation of appropriate interventions like antireflux therapy. Oil Red O (ORO) staining with determination of the lipid-laden macrophage index (LLMI) has been proposed as a noninvasive surrogate marker in the detection of aspiration. The aim of this study was to prospectively evaluate clinical utilization of ORO staining in the assessment of aspiration risk. METHODS: All transbronchial surgical pathology biopsies obtained in lung transplant patients undergoing routine surveillance from August 2020 through November 2021 were included in this study. Clinical team members prospectively ascertained the aspiration risk category (ARC) of each patient both before and after biopsy findings and recorded reasons for change in ARC. RESULTS: A total of 132 transbronchial biopsies with concurrent LLMI were included in the study. LLMI was low in 51 cases (38.6%), including 21 of the 54 cases (38.9%) where aspiration was suggested based on the transbronchial biopsy findings. In total, 19 cases (14.4%) underwent a change in ARC post-biopsy including 10 that were upgraded and nine cases that were downgraded. Transbronchial biopsy findings were noted as the reason for change in ARC in the majority (15/19; 79%) of cases; only a minority (2/19; 10.5%) were due to the LLMI. Notably, 16 cases (12.1%) had a low LLMI with high-risk post-biopsy ARC and nine cases (6.8%) had a high LLMI with low-risk post-biopsy ARC. CONCLUSIONS: This study observed that clinical evaluation for aspiration relied more heavily on transbronchial biopsy findings. Although LLMI may retain clinical utility in some scenarios, reevaluation of the clinical value of ORO testing would be prudent.

The microfluidic artificial lung: Mimicking nature's blood path design to solve the biocompatibility paradox.

The increasing prevalence of chronic lung disease worldwide, combined with the emergence of multiple pandemics arising from respiratory viruses over the past century, highlights the need for safer and efficacious means for providing artificial lung support. Mechanical ventilation is currently used for the vast majority of patients suffering from acute and chronic lung failure, but risks further injury or infection to the patient's already compromised lung function. Extracorporeal membrane oxygenation (ECMO) has emerged as a means of providing direct gas exchange with the blood, but limited access to the technology and the complexity of the blood circuit have prevented the broader expansion of its use. A promising avenue toward simplifying and minimizing complications arising from the blood circuit, microfluidics-based artificial organ support, has emerged over the past decade as an opportunity to overcome many of the fundamental limitations of the current standard for ECMO cartridges, hollow fiber membrane oxygenators. The power of microfluidics technology for this application stems from its ability to recapitulate key aspects of physiological microcirculation, including the small dimensions of blood vessel structures and gas transfer membranes. An even greater advantage of microfluidics, the ability to configure blood flow patterns that mimic the smooth, branching nature of vascular networks, holds the potential to reduce the incidence of clotting and bleeding and to minimize reliance on anticoagulants. Here, we summarize recent progress and address future directions and goals for this potentially transformative approach to artificial lung support.

Factors Related to Survival in Low-Glomerular Filtration Rate Cohorts Undergoing Lung Transplant.

BACKGROUND: Historically, a glomerular filtration rate (GFR) of less than 50 mL/min per 1.73 m2 has been considered a contraindication to lung transplantation. Combined or sequential lung-kidney transplantation is an option for those with a GFR less than 30 mL/min per 1.73 m2. Patients with a GFR of 30 to 50 mL/min per 1.73 m2 are provided with no options for transplantation. This study explores factors associated with improved survival in patients who undergo isolated lung transplantation with a GFR of 30 to 50 mL/min per 1.73 m2. METHODS: The United Network for Organ Sharing database was queried for adult patients undergoing primary isolated lung transplantation between January 2007 and March 2018. Regression models were used to identify factors associated with improved survival in lung recipients with a preoperative GFR of 30 to 50 mL/min per 1.73 m2. The propensity score method was used to match highly performing patients (outpatient recipients aged less than 60 years) with a GFR of 30 to 50 mL/min per 1.73 m2 with patients who had a GFR greater than 50 mL/min per 1.73 m2. Kaplan-Meier, Cox, and logistic regression analyses compared outcomes in matched populations. RESULTS: A total of 21,282 lung transplantations were performed during the study period. Compared with patients with a GFR greater than 50 mL/min per 1.73 m2, survival was significantly worse for patients with a GFR of 30 to 50 mL/min per 1.73 m2. Multivariate analysis of patients with a GFR of 30 to 50 mL/min per 1.73 m2 demonstrated outpatient status and age less than 60 years to be predictive of superior survival. After propensity matching, survival of this highly performing subset with a GFR of 30 to 50 mL/min per 1.73 m2 was no different from that of patients with a normal GFR. CONCLUSIONS: Outpatient recipients aged less than 60 years represent an optimal subset of patients with a GFR of 30 to 50 mL/min per 1.73 m2. Lung transplant listing should not be declined based only on a GFR less than 50 mL/min per 1.73 m2.

Pain management and safety profiles after preoperative vs postoperative thoracic epidural insertion for bilateral lung transplantation.

OBJECTIVE: Thoracic epidural analgesia provides effective pain control after lung transplantation; however, the optimal timing of placement is controversial. We sought to compare pain control and pulmonary and epidural morbidity between patients receiving preoperative vs postoperative epidurals. METHODS: Institutional records were reviewed for patients undergoing a bilateral lung transplant via a bilateral anterior thoracotomy with transverse sternotomy incision between January 2014 and January 2017. Pain control was measured using visual analog scale pain scores (0-10). Pulmonary complications included a composite of pneumonia, prolonged intubation, and reintubation/tracheostomy. RESULTS: Among 103 patients, 72 (70%) had an epidural placed preoperatively and 31 (30%) had an epidural placed within 72 hours posttransplant. There were no differences in the rates of cardiopulmonary bypass (3% vs 0%, P = 0.59); however, patients with a preoperative epidural were less likely to be placed on extracorporeal membrane oxygenation intraoperatively (25% vs 52%, P = 0.01). Pain control was similar at 24 hours (1.2 vs 1.7, P = 0.05); however, patients with a preoperative epidural reported lower pain scores at 48 (1.2 vs 2.1, P = 0.02) and 72 hours posttransplant (0.8 vs 1.7, P = 0.02). There were no differences in primary graft dysfunction (42% vs 56%, P = 0.28), length of mechanical ventilation (19.5 vs 24 hours, P = 0.18), or adverse pulmonary events (33% vs 52%, P = 0.12). No adverse events including epidural hematoma, paralysis, or infection resulted from epidural placement. CONCLUSION: Preoperative thoracic epidural placement provides improved analgesia without increased morbidity following lung transplantation.

Lung Transplantation From Donation After Circulatory Death: United States and Single-Center Experience.

BACKGROUND: Lung transplants from donation after circulatory death (DCD) have been scarcely used in the United States. Concerns about the warm ischemic injury, resource mal-utilization due to the uncertain timing of death, and public scrutiny may be some factors involved. METHODS: Survival for recipients of a donation after brain death (DBD) versus DCD was analyzed by using the United Network for Organ Sharing and our institutional database. A propensity-matching and Cox regression analysis was performed for 25 characteristics. Primary graft dysfunction metrics were compared. RESULTS: A total of 389 of 20,905 lung transplantations (2%) were performed by using DCDs in the United States, and 15 of 128 (12%) at our institution. Five and 10-year survival for DBDs was 55% and 30% and 59% and 33% for DCDs, respectively. Propensity-matched analysis of 311 DBD/DCD pairs did not demonstrate any difference in survival. On Cox regression, DCD was not associated with impaired survival. Male sex, Karnofsky class greater than 50, double lung transplantation, and transplantation year were predictors of improved survival. Age, creatinine, pulmonary fibrosis, retransplantation, extracorporeal membrane oxygenation, allocation score, and donor age were predictors of worse survival. Primary graft dysfunction at time 0 was worse for recipients of DCDs (p = 0.005) but equivalent at 24, 48, and 72 hours. CONCLUSIONS: DCD lung transplants remain underused in the United States. Nevertheless, survival is similar to DBD. Primary graft dysfunction metrics for DCDs are worse than DBDs on intensive care arrival but improved subsequently.

Single- Versus Double-Lung Transplantation in Pulmonary Fibrosis: Impact of Age and Pulmonary Hypertension.

BACKGROUND: Double-lung transplantation (DLT) has better long-term outcomes compared with single-lung transplantation (SLT) in pulmonary fibrosis. However, controversy persists about whether older patients or patients with high lung allocation scores would benefit from DLT. Moreover, the degree of pulmonary hypertension in which SLT should be avoided is unknown. METHODS: A retrospective analysis using the United Network for Organ Sharing database was performed in all recipients of lung transplants for pulmonary fibrosis. Kaplan-Meier survival for SLT versus DLT was compared and stratified by age, allocation score, and mean pulmonary artery pressure. Cox regression and propensity-matching analyses were performed. RESULTS: Between 1987 and 2015; 9,191 of 29,779 lung transplants were performed in pulmonary fibrosis. Ten-year survival rates were 55% for DLT and 32% for SLT (p < 0.001). When stratified by age, DLT recipients had improved survival at all age cutoffs, except age ≥70 years. In addition, DLT recipients had improved survival across all lung allocation scores (<45, ≥45, ≥60, ≥75) and all pulmonary artery pressure categories (<25, ≥25, ≥30, ≥40 mm Hg). Among DLT recipients, pulmonary artery pressure and allocation score did not affect survival. Among SLT recipients, a pressure ≥25 mm Hg did not influence survival. Conversely, patients with a pressure ≥30 mm Hg and an allocation score ≥45 had decreased survival. On Cox regression and on propensity matching, DLT had improved survival compared with SLT. CONCLUSIONS: In pulmonary fibrosis, DLT has improved survival compared with SLT and should be considered the procedure of choice in patients younger than 70 years of age. SLT in patients with mean pulmonary artery pressure ≥30 mm Hg and an allocation score ≥45 should be discouraged.

Clinical management and outcomes of patients with Hermansky-Pudlak syndrome pulmonary fibrosis evaluated for lung transplantation.

Pulmonary fibrosis is a progressive, fatal manifestation of Hermansky-Pudlak syndrome (HPS). Some patients with advanced HPS pulmonary fibrosis undergo lung transplantation despite their disease-associated bleeding tendency; others die while awaiting donor organs. The objective of this study is to determine the clinical management and outcomes of a cohort with advanced HPS pulmonary fibrosis who were evaluated for lung transplantation. Six patients with HPS-1 pulmonary fibrosis were evaluated at the National Institutes of Health Clinical Center and one of two regional lung transplant centers. Their median age was 41.5 years pre-transplant. Three of six patients died without receiving a lung transplant. One of these was referred with end-stage pulmonary fibrosis and died before a donor organ became available, and donor organs were not identified for two other patients sensitized from prior blood product transfusions. Three of six patients received bilateral lung transplants; they did not have a history of excessive bleeding. One patient received peri-operative desmopressin, one was transfused with intra-operative platelets, and one received extracorporeal membrane oxygenation and intra-operative prothrombin complex concentrate, platelet transfusion, and desmopressin. One transplant recipient experienced acute rejection that responded to pulsed steroids. No evidence of chronic lung allograft dysfunction or recurrence of HPS pulmonary fibrosis was detected up to 6 years post-transplant in these three lung transplant recipients. In conclusion, lung transplantation and extracorporeal membrane oxygenation are viable options for patients with HPS pulmonary fibrosis. Alloimmunization in HPS patients is an important and potentially preventable barrier to lung transplantation; interventions to limit alloimmunization should be implemented in HPS patients at risk of pulmonary fibrosis to optimize their candidacy for future lung transplants.

Disseminated Ureaplasma infection as a cause of fatal hyperammonemia in humans.

Hyperammonemia syndrome is a fatal complication affecting immunosuppressed patients. Frequently refractory to treatment, it is characterized by progressive elevations in serum ammonia of unknown etiology, ultimately leading to cerebral edema and death. In mammals, ammonia produced during amino acid metabolism is primarily cleared through the hepatic production of urea, which is eliminated in the kidney. Ureaplasma species, commensals of the urogenital tract, are Mollicutes dependent on urea hydrolysis to ammonia and carbon dioxide for energy production. We hypothesized that systemic infection with Ureaplasma species might pose a unique challenge to human ammonia metabolism by liberating free ammonia resulting in the hyperammonemia syndrome. We used polymerase chain reaction, specialized culture, and molecular resistance profiling to identify systemic Ureaplasma infection in lung transplant recipients with hyperammonemia syndrome, but did not detect it in any lung transplant recipients with normal ammonia concentrations. Administration of Ureaplasma-directed antimicrobials to patients with hyperammonemia syndrome resulted in biochemical and clinical resolution of the disorder. Relapse in one patient was accompanied by recurrent Ureaplasma bacteremia with antimicrobial resistance. Our results provide evidence supporting a causal relationship between Ureaplasma infection and hyperammonemia, suggesting a need to test for this organism and provide empiric antimicrobial treatment while awaiting microbiological confirmation.

Bilateral lung transplantation in a patient with humoral immune deficiency: a case report with review of the literature.

Humoral immune deficiencies have been associated with noninfectious disease complications including autoimmune cytopenias and pulmonary disease. Herein we present a patient who underwent splenectomy for autoimmune cytopenias and subsequently was diagnosed with humoral immune deficiency in the context of recurrent infections. Immunoglobulin analysis prior to initiation of intravenous immunoglobulin (IVIG) therapy was notable for low age-matched serum levels of IgA (11 mg/dL), IgG2 (14 mg/L), and IgG4 (5 mg/L) with a preserved total level of IgG. Flow cytometry was remarkable for B cell maturation arrest at the IgM+/IgD+ stage. Selective screening for known primary immune deficiency-causing genetic defects was negative. The disease course was uniquely complicated by the development of pulmonary arteriovenous malformations (AVMs), ultimately requiring bilateral lung transplantation in 2012. This is a patient with humoral immune deficiency that became apparent only after splenectomy, which argues for routine immunologic evaluation prior to vaccination and splenectomy. Lung transplantation is a rare therapeutic endpoint and to our knowledge has never before been described in a patient with humoral immune deficiency for the indication of pulmonary AVMs.

Comprehensive evaluation of lung allograft function in infants after lung and heart-lung transplantation.

BACKGROUND: Limited data exist on methods to evaluate allograft function in infant recipients of lung and heart-lung transplants. At our institution, we developed a procedural protocol in coordination with pediatric anesthesia where infants were sedated to perform infant pulmonary function testing, computed tomography imaging of the chest, and flexible fiberoptic bronchoscopy with transbronchial biopsies. METHODS: A retrospective review was performed of children aged younger than 1 year who underwent lung or heart-lung transplantation at our institution to assess the effect of this procedural protocol in the evaluation of infant lung allografts. RESULTS: Since 2005, 5 infants have undergone thoracic transplantation (3 heart-lung, 2 lung). At time of transplant, the mean ± standard deviation age was 7.2 ± 2.8 months (range, 3-11 months). Of 24 procedural sessions performed to evaluate lung allografts, 83% (20 of 24) were considered surveillance where the patients were completely asymptomatic. Of the surveillance procedures, 80% were performed as an outpatient, whereas 20% were done as inpatients during the lung or heart-lung transplant post-operative period before discharge home. Sedation was performed with propofol alone (23 of 24) or in addition to ketamine (1 of 24) infusion; mean sedation time was 141 ± 39 minutes (range, 70-214) minutes. Of the 16 outpatient procedures, patients were discharged after 14 (88%) on the same day, and after 2 (12%) were admitted for observation, with 1 being due to transportation issues and the other due to fever during the observation period. CONCLUSIONS: A comprehensive procedural protocol to evaluate allograft function in infant lung and heart-lung transplant recipients was performed safely as an outpatient.

Surveillance transbronchial biopsies in infant lung and heart-lung transplant recipients.

There are limited published data on surveillance TBB for the identification of allograft rejection in infants after lung or heart-lung transplantation. We performed a retrospective review of children under one yr of age who underwent lung or heart-lung transplant at our institution. Since 2005, four infants were transplanted (three heart-lung and one lung). The mean age (±s.d.) at the time of transplant was 5.5 ± 2.4 (range 3-8) months. A total of 16 surveillance TBB procedures were completed in both inpatient and outpatient settings, with a range of 3-7 performed per patient. A minimum of five acceptable tissue pieces with expanded alveoli were obtained in 81% (13/16) of TBB procedures and a minimum of three pieces in 88% (14/16). There was no evidence of acute allograft rejection in 88% (14/16) of TBB procedures. One TBB procedure yielded two tissue specimens demonstrating A2 acute allograft rejection. One TBB procedure failed to yield tissue with sufficient alveoli. Additionally, B-grade assessment identified B0 in 50% (8/16), B1R in 12% (2/16), and BX (ungradeable or insufficient sample) in 38% (6/16) of biopsy procedures, respectively. In conclusion, TBB may be safely performed as an inpatient and outpatient procedure in infant lung and heart-lung transplant recipients and may provide adequate tissue for detecting acute allograft rejection and small airway inflammation.

Aggressive coronary artery vasculopathy after combined heart-lung transplantation.

Combined heart-lung transplantation remains as a treatment option for patients with cardiopulmonary failure. There is speculation that lung grafts protect the heart from developing graft vasculopathy after combined heart-lung transplantation. This protective mechanism is more likely, at best, a delay in the onset of coronary artery vasculopathy. We present our experiences in two cases of an aggressive form of cardiac allograft vasculopathy after combined heart-lung transplantation that resulted in the death of both patients.

Late thrombus formation on the Helex septal occluder after double-lung transplant.

Percutaneous device closure in patients with an atrial septal defect (ASD) or patent foramen ovale (PFO) has gained popularity because of the short learning curve, cosmetic advantage and relative safety compared with surgery. Device complications may include device embolism, erosion, pericardial tamponade or thrombus formation, and most complications occur early. Herein we describe the previously unreported finding of a late thrombus on a Helex device after PFO closure in a patient with cystic fibrosis and double-lung transplantation.

Variability in immunization guidelines in children before and after lung transplantation.

Lung transplant candidates and recipients are at high risk of infections from vaccine-preventable diseases. However, well-established guidelines neither exist for pre- and post-transplant vaccination nor do monitoring guidelines for pediatric lung transplant recipients. To ascertain the current vaccination and monitoring practices of pediatric lung transplant centers, a self-administered questionnaire was distributed to the 18 pediatric lung transplant centers within the International Pediatric Lung Transplant Collaborative in April 2006. Sixteen of 18 centers (89%) surveyed responded. Pretransplant, national vaccination guidelines are followed. Eleven centers reported following standardized vaccination guidelines post-transplant. Vaccines were more commonly provided by the primary-care physician pretransplant (69%) rather than post-transplant (38%). Post-transplant, 50% of the centers recommend live vaccines for household contacts but not for the transplant recipient. Pretransplant monitoring of response to prior vaccination was performed inconsistently except for varicella (88%). Only 44% of the transplant centers measure for response to vaccination post-transplant, mostly hepatitis B. Current vaccination practices of pediatric lung transplant centers are heterogeneous. The lung transplant community would be well served by studies designed to evaluate the efficacy of vaccinations in this population.

ICP22 is required for wild-type composition and infectivity of herpes simplex virus type 1 virions.

The immediate-early regulatory protein ICP22 is required for efficient replication of herpes simplex virus type 1 in some cell types (permissive) but not in others (restrictive). In mice infected via the ocular route, the pathogenesis of an ICP22- virus, 22/n199, was altered relative to that of wild-type virus. Specifically, tear film titers of 22/n199-infected mice were significantly reduced at 3 h postinfection relative to those of mice infected with wild-type virus. Further, 22/n199 virus titers were below the level of detection in trigeminal ganglia (TG) during the first 9 days postinfection. On day 30 postinfection, TG from 22/n199-infected mice contained reduced viral genome loads and exhibited reduced expression of latency-associated transcripts and reduced reactivation efficiency relative to TG from wild-type virus-infected mice. Notably, the first detectable alteration in the pathogenesis of 22/n199 in these tests occurred in the eye prior to the onset of nascent virus production. Thus, ICP22- virions appeared to be degraded, cleared, or adsorbed more rapidly than wild-type virions, implying potential differences in the composition of the two virion types. Analysis of the protein composition of purified extracellular virions indicated that ICP22 is not a virion component and that 22/n199 virions sediment at a reduced density relative to wild-type virions. Although similar to wild-type virions morphologically, 22/n199 virions contain reduced amounts of two gamma2 late proteins, US11 and gC, and increased amounts of two immediate-early proteins, ICP0 and ICP4, as well as protein species not detected in wild-type virions. Although ICP22- viruses replicate to near-wild-type levels in permissive cells, the virions produced in these cells are biochemically and physically different from wild-type virions. These virion-specific differences in ICP22- viruses add a new level of complexity to the functional analysis of this immediate-early viral regulatory protein.

The products of the herpes simplex virus type 1 immediate-early US1/US1.5 genes downregulate levels of S-phase-specific cyclins and facilitate virus replication in S-phase Vero cells.

Herpes simplex virus type 1 ICP22-/U(S)1.5- mutants initiate viral gene expression in all cells; however, in most cell types, the replication process stalls due to an inability to express gamma2 late proteins. Although the function of ICP22/U(S)1.5 has not been established, it has been suggested that these proteins activate, induce, or repress the activity of cellular proteins during infection. In this study, we hypothesized that cell cycle-associated proteins are targets of ICP22/U(S)1.5. For this purpose, we first isolated and characterized an ICP22-/U(S)1.5- mutant virus, 22/n199. Like other ICP22-/U(S)1.5- mutants, 22/n199 replicates in a cell-type-specific manner and fails to induce efficient gamma2 late gene expression in restrictive cells. Although synchronization of restrictive human embryonic lung cells in each phase of the cell cycle did not overcome the growth restrictions of 22/n199, synchronization of permissive Vero cells in S phase rendered them less able to support 22/n199 plaque formation and replication. Consistent with this finding, expression of cellular S-phase cyclins was altered in an ICP22/U(S)1.5-dependent manner specifically when S-phase Vero cells were infected. Collectively, these observations support the notion that ICP22/U(S)1.5 deregulates the cell cycle upon infection of S-phase permissive cells by altering expression of key cell cycle regulatory proteins either directly or indirectly.