Delayed-interval BNT162b2 mRNA COVID-19 vaccination enhances humoral immunity and induces robust T cell responses.

Delayed dosing intervals are a strategy to immunize a greater proportion of the population. In an observational study, we compared humoral and cellular responses in health care workers receiving two doses of BNT162b2 (Pfizer-BioNTech) vaccine at standard (3- to 6-week) and delayed (8- to 16-week) intervals. In the delayed-interval group, anti-receptor-binding domain antibody titers were significantly enhanced compared to the standard-interval group. The 50% plaque reduction neutralization test (PRNT50) and PRNT90 titers against wild-type (ancestral) severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and Alpha, Beta and Delta variants were higher in the delayed-interval group. Spike-specific polyfunctional CD4+ and CD8+ T cells expressing interferon-γ and interleukin-2 were comparable between the two groups. Here, we show that the strategy of delaying second doses of mRNA vaccination may lead to enhanced humoral immune responses, including improved virus neutralization against wild-type and variant SARS-CoV-2 viruses. This finding has potentially important implications as vaccine implementation continues across a greater proportion of the global population.

Longitudinal outcomes of COVID-19 in solid organ transplant recipients from 2020 to 2023.

Data regarding coronavirus disease 2019 (COVID-19) outcomes in solid organ transplant recipients (SOTr) across severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) waves, including the impact of different measures, are lacking. This cohort study, conducted from March 2020 to May 2023 in Toronto, Canada, aimed to analyze COVID-19 outcomes in 1975 SOTr across various SARS-CoV-2 waves and assess the impact of preventive and treatment measures. The primary outcome was severe COVID-19, defined as requiring supplemental oxygen, with secondary outcomes including hospitalization, length of stay, intensive care unit (ICU) admission, and 30-day and 1-year all-cause mortality. SARS-CoV-2 waves were categorized as Wildtype/Alpha/Delta (318 cases, 16.1%), Omicron BA.1 (268, 26.2%), Omicron BA.2 (268, 13.6%), Omicron BA.5 (561, 28.4%), Omicron BQ.1.1 (188, 9.5%), and Omicron XBB.1.5 (123, 6.2%). Severe COVID-19 rate was highest during the Wildtype/Alpha/Delta wave (44.6%), and lower in Omicron waves (5.7%-16.1%). Lung transplantation was associated with severe COVID-19 (OR: 4.62, 95% CI: 2.71-7.89), along with rituximab treatment (OR: 4.24, 95% CI: 1.04-17.3), long-term corticosteroid use (OR: 3.11, 95% CI: 1.46-6.62), older age (OR: 1.51, 95% CI: 1.30-1.76), chronic lung disease (OR: 2.11, 95% CI: 1.36-3.30), chronic kidney disease (OR: 2.18, 95% CI: 1.17-4.07), and diabetes (OR: 1.97, 95% CI: 1.37-2.83). Early treatment and ≥3 vaccine doses were associated with reduced severity (OR: 0.29, 95% CI: 0.19-0.46, and 0.35, 95% CI: 0.21-0.60, respectively). Tixagevimab/cilgavimab and bivalent boosters did not show a significant impact. The study concludes that COVID-19 severity decreased across different variants in SOTr. Lung transplantation was associated with worse outcomes and may benefit more from preventive and early therapeutic interventions.

Association between cytomegalovirus viremia and long-term outcomes in lung transplant recipients.

Although cytomegalovirus (CMV) viremia/DNAemia has been associated with reduced survival after lung transplantation, its association with chronic lung allograft dysfunction (CLAD) and its phenotypes is unclear. We hypothesized that, in a modern era of CMV prophylaxis, CMV DNAemia would still remain associated with death, but also represent a risk factor for CLAD and specifically restrictive allograft syndrome (RAS)/mixed phenotype. This was a single-center retrospective cohort study of all consecutive adult, first, bilateral-/single-lung transplants done between 2010-2016, consisting of 668 patients. Risks for death/retransplantation, CLAD, or RAS/mixed, were assessed by adjusted cause-specific Cox proportional-hazards models. CMV viral load (VL) was primarily modeled as a categorical variable: undetectable, detectable to 999, 1000 to 9999, and ≥10 000 IU/mL. In multivariable models, CMV VL was significantly associated with death/retransplantation (≥10 000 IU/mL: HR = 2.65 [1.78-3.94]; P < .01), but was not associated with CLAD, whereas CMV serostatus mismatch was (D+R-: HR = 2.04 [1.30-3.21]; P < .01). CMV VL was not associated with RAS/mixed in univariable analysis. Secondary analyses with a 7-level categorical or 4-level ordinal CMV VL confirmed similar results. In conclusion, CMV DNAemia is a significant risk factor for death/retransplantation, but not for CLAD or RAS/mixed. CMV serostatus mismatch may have an impact on CLAD through a pathway independent of DNAemia.

Impact of machine perfusion on transplant infectious diseases: New challenges and opportunities.

Preservation techniques that maintain the viability of an organ graft between retrieval from the donor and implantation into the recipient remain a critical aspect of solid organ transplantation. While traditionally preservation is accomplished with static cold storage, advances in ex vivo dynamic machine perfusion, both hypothermic and normothermic, have allowed for prolongation of organ viability and recovery of marginal organs effectively increasing the usable donor pool. However, the use of these novel machine perfusion technologies likely exposes the recipient to additional infectious risk either through clonal expansion of pathogens derived during organ recovery or de novo exogenous acquisition of pathogens while the organ remains on the machine perfusion circuit. There is a paucity of high-quality studies that have attempted to quantify infection risk, although it appears that prolonging the time on the machine perfusion circuit and normothermic parameters increases the risk of infection. Conversely, the use of ex vivo machine perfusion unlocks new opportunities to detect and treat donor-derived infections before implantation into the recipient. This review seeks to reveal how the use of ex vivo machine perfusion strategies may augment the risk of infection in the organ recipient as well as outline ways that this technology could be leveraged to enhance our ability to manage donor-derived infections.

Omicron BA.4/5 Neutralization and T-Cell Responses in Organ Transplant Recipients After Booster Messenger RNA Vaccine: A Multicenter Cohort Study.

BACKGROUND: In solid organ transplant (SOT) recipients, the primary vaccination series against Coronavirus Disease 2019 is 3 doses followed by boosters. We determined whether a fourth dose booster induced Omicron BA.4/5 neutralizing antibodies (nAbs) and T cells in a large multicenter cohort study. METHODS: Serum was collected 4-6 weeks post-third and post-fourth doses of messenger RNA vaccine in 222 SOT recipients. nAbs were measured using a pseudovirus neutralization assay that targeted the Omicron BA.4/5 spike protein. A subset underwent T-cell testing. RESULTS: The median age of the cohort was 63 years (interquartile range [IQR], 50-68) with 61.7% men. BA.4/5 nAb detection increased from 26.6% (59 of 222) post-third dose to 53.6% (119 of 222) post-fourth dose (P < .0001). In patients with breakthrough infection prior to the fourth dose (n = 27), nAbs were detected in 77.8% and median nAb titers were significantly higher compared with those with 4 vaccine doses alone (P < .0001). Factors associated with a low BA.4/5 neutralization response after the fourth dose were older age (odds ratio [OR], 0.96; 95% confidence interval [CI], .94-.99), mycophenolate use (OR, 0.39; 95% CI, .20-.77) and prednisone use (OR, 0.34; 95% CI, .18-.63), and vaccine type (OR, 0.72; 95% CI, .51-.99), while breakthrough infection prior to the fourth dose (OR, 3.6; 95% CI, 1.3-9.9) was associated with a greater nAb response. Polyfunctional BA.4/5-specific CD4+ T cells significantly increased after 4 doses and were identified in 76.9% of patients at a median frequency of 213/106 cells (IQR, 98-650). CONCLUSIONS: In summary, a booster significantly increases BA.4/5-specific neutralization and polyfunctional CD4+ T-cell responses, suggesting protection from severe disease even with new Omicron variants. However, SOT recipients who are older and on mycophenolate and prednisone need additional preventative strategies.

Short-course early outpatient remdesivir prevents severe disease due to COVID-19 in organ transplant recipients during the omicron BA.2 wave.

Solid organ transplant recipients (SOTr) remain at risk of severe COVID-19. Several previous early therapies are no longer effective against new circulating variants. We performed a prospective cohort study in outpatient adult SOTr during the omicron BA.2 wave (April-May 2022), to determine the effectiveness of 3 doses of remdesivir given within 7 days of symptoms onset. Patients were followed for at least 30 days. The primary outcome was hospitalization. Of 210 SOTr that had COVID-19, we included 192. The median age was 54.5 years and 61.5% were men. The most common transplants were kidney (41.7%), lung (19.3%), liver (18.8%), and heart (6.3%). Most patients (90.1%) had previously received ≥3 COVID-19 vaccine doses. Fifteen (7.8%) were hospitalized, 5(2.6%) required supplemental oxygen, 3(1.6%) ICU admission, and 2(1%) mechanical ventilation with 2(1%) deaths. Age, the number of comorbidities, prednisone chronic treatment, and lung transplant were risk factors for hospitalization. Early remdesivir significantly decreased the hospitalization rate: adjusted hazard ratio 0.12 (95% CI: 0.03-0.57). The adjusted number needed to treat to prevent one hospitalization was 15.2 (95% CI: 13.6-31.4). No patient that received early remdesivir needed ICU admission or died. In a cohort of SOTr with COVID-19 infection, administration of 3-dose early remdesivir independently reduced the disease severity.

Into the unknown: The end of the coronavirus disease 2019 public health emergency in the United States and potential impacts on organ transplant recipients.

The public health emergency for coronavirus disease 2019 ended on April 11, 2023, 1 month earlier than its planned termination. The hasty cessation of emergency measures may negatively impact the care of solid organ transplant recipients and other immunosuppressed hosts. Accelerated pathways for drug and vaccine approvals, research funding, and insurance coverage for medical therapies and diagnostic testing are likely to be affected. Health care disparities that characterized the early pandemic may again be intensified. It is imperative that the transplant community promptly anticipate the impact of these changes and prepare accordingly to avoid disruptions in care for the most vulnerable patients.

Impact of Omicron BA.1 infection on BA.4/5 immunity in transplant recipients.

Mutations in the spike protein of SARS-CoV-2 have allowed Omicron subvariants to escape neutralizing antibodies. The degree to which this occurs in transplant recipients is poorly understood. We measured BA.4/5 cross-neutralizing responses in 75 mostly vaccinated transplant recipients who recovered from BA.1 infection. Sera were collected at 1 and 6 months post-BA.1 infection, and a lentivirus pseudovirus neutralization assay was performed using spike constructs corresponding to BA.1 and BA.4/5. Uninfected immunized transplant recipients and health care worker controls were used for comparison. Following BA.1 infection, the proportion of transplant recipients with neutralizing antibody responses was 88.0% (66/75) against BA.1 and 69.3% (52/75) against BA.4/5 (P = .005). The neutralization level against BA.4/5 was approximately 17-fold lower than that against BA.1 (IQR 10.6- to 45.1-fold lower, P < .0001). BA.4/5 responses declined over time and by ≥0.5 log10 (approximately 3-fold) in almost half of the patients by 6 months. BA.4/5-neutralizing antibody titers in transplant recipients with breakthrough BA.1 infection were similar to those in immunized health care workers but significantly lower than those in uninfected triple-vaccinated transplant recipients. These results provide evidence that transplant recipients are at ongoing risk for BA.4/5 infection despite vaccination and prior Omicron strain infection, and additional mitigation strategies may be required to prevent severe disease in this cohort.

Neutralization of SARS-CoV-2 Variants in Transplant Recipients After Two and Three Doses of mRNA-1273 Vaccine : Secondary Analysis of a Randomized Trial.

BACKGROUND: COVID-19 is more severe in transplant recipients. Variants of concern have supplanted wild-type virus. In transplant recipients, data are limited on 2-dose or 3-dose vaccine immunogenicity against variant viruses. OBJECTIVE: To assess neutralizing antibody responses against SARS-CoV-2 variants in transplant recipients after 2 and 3 vaccine doses. DESIGN: Secondary analysis of a randomized, double-blind, controlled trial of a third dose of mRNA-1273 vaccine versus placebo. (ClinicalTrials.gov: NCT04885907). SETTING: Single-center transplant program. PATIENTS: Organ transplant recipients. INTERVENTION: Third dose of mRNA-1273 vaccine versus placebo. MEASUREMENTS: Sera were analyzed for neutralization against wild-type virus and the Alpha, Beta, and Delta variants using a surrogate virus neutralization assay and a spike-pseudotyped lentivirus assay. RESULTS: A total of 117 transplant recipients were analyzed (60 in the mRNA-1273 group and 57 in the placebo group). Sera were obtained before and 4 to 6 weeks after the third dose. After 2 doses, the proportion of patients with positive neutralization for all 3 variants was small compared with wild-type virus. After the third dose of mRNA-1273 vaccine, the proportion with a positive neutralization response versus placebo was improved for all 3 variants as measured by both assays. Based on the pseudovirus neutralization assay against the Delta variant, 33 of 60 (55%) patients were positive in the mRNA-1273 group versus 10 of 57 (18%) in the placebo group (difference, 37 [95% CI, 19 to 53] percentage points). The differences were 36 (CI, 17 to 51) percentage points for the Alpha variant and 31 (CI, 15 to 46) percentage points for the Beta variant. In the mRNA-1273 group, lower neutralization values were observed for variants compared with wild-type virus, especially the Beta variant. LIMITATIONS: There is no clear correlate of protection for neutralizing antibody. This was a secondary analysis. CONCLUSION: In organ transplant recipients, a third dose of mRNA vaccine increases neutralizing antibody response against SARS-CoV-2 variants compared with placebo. PRIMARY FUNDING SOURCE: Ajmera Transplant Centre.

Respiratory viral infections including COVID-19 in solid organ transplantation.

PURPOSE OF REVIEW: Respiratory viral infections are prevalent and contribute to significant morbidity and mortality among solid organ transplant (SOT) recipients. We review updates from literature on respiratory viruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), in the SOT recipient. RECENT FINDINGS: With the wider availability and use of molecular diagnostic tests, our understanding of the epidemiology and impact of respiratory viruses in the SOT population continues to expand. While considerable attention has been given to the coronavirus disease 2019 (COVID-19) pandemic, the advances in prevention and treatment strategies of SARS-CoV-2 offered valuable insights into the development of new therapeutic options for managing other respiratory viruses in both the general and SOT population. SUMMARY: Respiratory viruses can present with a diverse range of symptoms in SOT recipients, with potentially associated acute rejection and chronic lung allograft dysfunction in lung transplant recipients. The epidemiology, clinical presentations, diagnostic approaches, and treatment and preventive strategies for clinically significant RNA and DNA respiratory viruses in SOT recipients are reviewed. This review also covers novel antivirals, immunologic therapies, and vaccines in development for various community-acquired respiratory viruses.

Impact of Vaccination and Early Monoclonal Antibody Therapy on Coronavirus Disease 2019 Outcomes in Organ Transplant Recipients During the Omicron Wave.

BACKGROUND: Solid organ transplant (SOT) recipients are at high risk for complications from coronavirus disease 2019 (COVID-19) and vaccine breakthrough infections are common. We determined the effectiveness of ≥3 doses of mRNA vaccine and early monoclonal antibody therapy in reducing disease severity against the Omicron (B.1.1.529) variant. METHODS: Prospective cohort study of consecutive SOT recipients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection referred to our transplant center who were followed for at least 30 days. The primary outcome was supplemental oxygen requirement. Effectiveness of sotrovimab and ≥3 vaccine doses was estimated using adjusted risk ratios (RR). RESULTS: Three hundred adult organ transplant recipients were included. Seventy-one patients (24.1%) were hospitalized, 44 (14.9%) required supplemental oxygen, 19 (6.5%) were admitted to the intensive care unit (ICU), 15 (5.1%) required mechanical ventilation (MV), and 13 (4.4%) died. On multivariate analysis, age and multiple comorbidities were risk factors for oxygen requirement. Both receipt of ≥3 vaccine doses prior to SARS-CoV-2 infection and receipt of sotrovimab in the first 7 days of symptom onset was associated with a reduction in the need for supplemental oxygen (RR 0.30 [95% confidence interval {CI}: .17 to .54] and RR 0.24 (95% CI: .1 to .59), respectively]. For sotrovimab, the number needed to treat (NNT) to prevent one patient requiring oxygen was 6.64 (95% CI: 4.56-13.66). Both sotrovimab use and having received ≥3 vaccine doses were also associated with a shorter hospitalization length of stay. CONCLUSIONS: In a cohort of SOT recipients with Omicron variant COVID-19 infection, prior receipt of ≥3 mRNA vaccine doses and early monoclonal antibody therapy were independently associated with significantly reduced disease severity.

Maribavir for Refractory Cytomegalovirus Infections With or Without Resistance Post-Transplant: Results From a Phase 3 Randomized Clinical Trial.

BACKGROUND: Therapies for refractory cytomegalovirus infections (with or without resistance [R/R]) in transplant recipients are limited by toxicities. Maribavir has multimodal anti-cytomegalovirus activity through the inhibition of UL97 protein kinase. METHODS: In this phase 3, open-label study, hematopoietic-cell and solid-organ transplant recipients with R/R cytomegalovirus were randomized 2:1 to maribavir 400 mg twice daily or investigator-assigned therapy (IAT; valganciclovir/ganciclovir, foscarnet, or cidofovir) for 8 weeks, with 12 weeks of follow-up. The primary endpoint was confirmed cytomegalovirus clearance at end of week 8. The key secondary endpoint was achievement of cytomegalovirus clearance and symptom control at end of week 8, maintained through week 16. RESULTS: 352 patients were randomized (235 maribavir; 117 IAT). Significantly more patients in the maribavir versus IAT group achieved the primary endpoint (55.7% vs 23.9%; adjusted difference [95% confidence interval (CI)]: 32.8% [22.80-42.74]; P < .001) and key secondary endpoint (18.7% vs 10.3%; adjusted difference [95% CI]: 9.5% [2.02-16.88]; P = .01). Rates of treatment-emergent adverse events (TEAEs) were similar between groups (maribavir, 97.4%; IAT, 91.4%). Maribavir was associated with less acute kidney injury versus foscarnet (8.5% vs 21.3%) and neutropenia versus valganciclovir/ganciclovir (9.4% vs 33.9%). Fewer patients discontinued treatment due to TEAEs with maribavir (13.2%) than IAT (31.9%). One patient per group had fatal treatment-related TEAEs. CONCLUSIONS: Maribavir was superior to IAT for cytomegalovirus viremia clearance and viremia clearance plus symptom control maintained post-therapy in transplant recipients with R/R cytomegalovirus. Maribavir had fewer treatment discontinuations due to TEAEs than IAT. Clinical Trials Registration. NCT02931539 (SOLSTICE).

Survey of current transplant center practices regarding COVID-19 vaccine mandates in the United States.

An electronic survey canvassing current policies of transplant centers regarding a COVID-19 vaccine mandate for transplant candidates and living donors was distributed to clinicians at US solid organ transplant centers performing transplants from October 14, 2021-November 15, 2021. Responses were received from staff at 141 unique transplant centers. These respondents represented 56.4% of US transplant centers, and responding centers performed 78.5% of kidney transplants and 82.4% of liver transplants in the year prior to survey administration. Only 35.7% of centers reported implementing a vaccine mandate, while 60.7% reported that vaccination was not required. A minority (42%) of responding centers with a vaccine mandate for transplant candidates also mandated vaccination for living organ donors. Centers with a vaccine mandate most frequently cited clinical evidence supporting the efficacy of pre-transplant vaccination (82%) and stewardship obligations to ensure organs were transplanted into the lowest risk patients (64%). Centers without a vaccine mandate cited a variety of reasons including administrative, equity, and legal considerations for their decision. Transplant centers in the United States exhibit significant heterogeneity in COVID-19 vaccination mandate policies for transplant candidates. While all centers encourage vaccination, most centers have not mandated COVID-19 vaccination for candidates and living donors, citing administrative opposition, legal prohibitions, and concern about equity in access to transplants.

Neutralization against Omicron variant in transplant recipients after three doses of mRNA vaccine.

The SARS-CoV-2 virus Omicron variant has now supplanted wild-type virus as the dominant circulating strain globally. Three doses of mRNA COVID-19 vaccine are recommended for transplant recipients as their primary vaccine series. However, the immunogenicity of mRNA vaccines as they specifically relate to the Omicron variant are not well studied. We analyzed Omicron-specific neutralization in transplant recipients after three-doses of mRNA-1273 vaccine. Neutralization was determined using a SARS-CoV-2 spike pseudotyped lentivirus assay with constructs for Omicron and Delta variants. A total of 60 transplant patients (kidney, kidney-pancreas, lung, heart, liver) were analyzed 1 month and 3 months after completion of three doses of mRNA-1273. At 1 month, 11/60 (18.3%) patients had detectable neutralizing antibody responses to Omicron (log10 ID50 of 2.38 [range 1.34-3.57]). At 3 months, 8/51 (15.7%) were positive (median log10 ID50 [1.68; range 1.12-3.61; approximate fivefold reduction over time]). The proportion of positive patients was lower for Omicron versus wild-type, and Omicron vs. Delta (p < .001). No demographic variables were found to be significantly associated with Omicron response. Many patients with a positive anti-RBD response still had undetectable Omicron-specific neutralizing antibody. In conclusion, three doses of mRNA vaccine results in poor neutralizing responses against the Omicron variant in transplant patients.

A consensus conference to define the utility of advanced infectious disease diagnostics in solid organ transplant recipients.

The last decade has seen an explosion of advanced assays for the diagnosis of infectious diseases, yet evidence-based recommendations to inform their optimal use in the care of transplant recipients are lacking. A consensus conference sponsored by the American Society of Transplantation (AST) was convened on December 7, 2021, to define the utility of novel infectious disease diagnostics in organ transplant recipients. The conference represented a collaborative effort by experts in transplant infectious diseases, diagnostic stewardship, and clinical microbiology from centers across North America to evaluate current uses, unmet needs, and future directions for assays in 5 categories including (1) multiplex molecular assays, (2) rapid antimicrobial resistance detection methods, (3) pathogen-specific T-cell reactivity assays, (4) next-generation sequencing assays, and (5) mass spectrometry-based assays. Participants reviewed and appraised available literature, determined assay advantages and limitations, developed best practice guidance largely based on expert opinion for clinical use, and identified areas of future investigation in the setting of transplantation. In addition, attendees emphasized the need for well-designed studies to generate high-quality evidence needed to guide care, identified regulatory and financial barriers, and discussed the role of regulatory agencies in facilitating research and implementation of these assays. Findings and consensus statements are presented.

Utility of Cytomegalovirus Cell-Mediated Immunity Assays in Solid Organ Transplantation.

Cytomegalovirus (CMV) is one of the most important viral complications after solid organ transplantation (SOT). Current preventive and management strategies rely primarily on serologic and viral load testing and remain suboptimal. To address these issues, multiple techniques to measure CMV-specific cell-mediated immunity (CMI) have been developed and evaluated in clinical studies over the past two decades. These assays show significant promise for the personalization of CMV management. For example, CMI assays can be used to help determine the optimal duration of antiviral prophylaxis or whether antiviral therapy is indicated in patients with low levels of CMV reactivation. However, despite numerous studies showing potential utility, these assays are not yet in widespread routine clinical use. Barriers to adoption include variations in test complexity, standardization, and thresholds for positivity and insufficient interventional clinical trials. Here, we provide an updated assessment of commonly available tests and the clinical utility of CMV-specific CMI testing in SOT recipients.

Tacrolimus Impairs Kupffer Cell Capacity to Control Bacteremia: Why Transplant Recipients Are Susceptible to Infection.

BACKGROUND AND AIMS: Kupffer cells (KCs) are the resident intravascular phagocyte population of the liver and critical to the capture and killing of bacteria. Calcineurin/nuclear factor of activated T cells (NFAT) inhibitors (CNIs) such as tacrolimus are used to prevent rejection in solid organ transplant recipients. Although their effect on lymphocytes has been studied extensively, there are limited experimental data about if and how CNIs shape innate immunity, and whether this contributes to the higher rates of infection observed in patients taking CNIs. APPROACH AND RESULTS: Here, we investigated the impact of tacrolimus treatment on innate immunity and, more specifically, on the capability of Kupffer cells (KCs) to fight infections. Retrospective analysis of data of >2,700 liver transplant recipients showed that taking calcineurin inhibitors such as tacrolimus significantly increased the likelihood of Staphylococcus aureus infection. Using a mouse model of acute methicillin-resistant S. aureus (MRSA) bacteremia, most bacteria were sequestered in the liver and we found that bacteria were more likely to disseminate and kill the host in tacrolimus-treated mice. Using imaging, we unveiled the mechanism underlying this observation: the reduced capability of KCs to capture, phagocytose, and destroy bacteria in tacrolimus-treated animals. Furthermore, in a gene expression analysis of infected KCs, the triggering receptor expressed on myeloid cells 1 (TREM1) pathway was the one with the most significant down-regulation after tacrolimus treatment. TREM1 inhibition likewise inhibited KC bacteria capture. TREM1 levels on neutrophils as well as the overall neutrophil response after infection were unaffected by tacrolimus treatment. CONCLUSIONS: Our results indicate that tacrolimus treatment has a significant impact directly on KCs and on TREM1, thereby compromising their capacity to fend off infections.

Characterization and predictive functional profiles on metagenomic 16S rRNA data of liver transplant recipients: A longitudinal study.

Long-term survival after Liver Transplantation (LT) is often compromised by infectious and metabolic complications. We aimed to delineate alterations in intestinal microbiome (IM) over time that could contribute to medical complications compromising long-term survival following LT. Fecal samples from LT recipients were collected at 3 months (3 M) and 6 months (6 M) post-LT. The bacterial DNA was extracted using E.Z.N.A. Stool DNA Kit and 16S rRNA gene sequencing at V4 hypervariable region was performed. DADA2 and Phyloseq was implemented to analyze the taxonomic composition. Differentially abundant taxa were identified by metagenomeSeq and LEfSe. Piphillin, an Inferred functional metagenomic analysis tool was used to study the bacterial functional content. For comparison, healthy samples were extracted from NCBI and analyzed similarly. The taxonomic & functional profiles of LT recipients were validated with metagenomic sequencing data from animals exposed to immunosuppressants using Venny. Our findings provide a new perspective on longitudinal increase in specific IM communities post-LT along with an increase in bacterial genes associated with metabolic and infectious disease.

Severity of COVID-19 among solid organ transplant recipients in Canada, 2020-2021: a prospective, multicentre cohort study.

BACKGROUND: Severe COVID-19 appears to disproportionately affect people who are immunocompromised, although Canadian data in this context are limited. We sought to determine factors associated with severe COVID-19 outcomes among recipients of organ transplants across Canada. METHODS: We performed a multicentre, prospective cohort study of all recipients of solid organ transplants from 9 transplant programs in Canada who received a diagnosis of COVID-19 from March 2020 to November 2021. Data were analyzed to determine risk factors for oxygen requirement and other metrics of disease severity. We compared outcomes by organ transplant type and examined changes in outcomes over time. We performed a multivariable analysis to determine variables associated with need for supplemental oxygen. RESULTS: A total of 509 patients with solid organ transplants had confirmed COVID-19 during the study period. Risk factors associated with needing (n = 190), compared with not needing (n = 319), supplemental oxygen included age (median 62.6 yr, interquartile range [IQR] 52.5-69.5 yr v. median 55.5 yr, IQR 47.5-66.5; p < 0.001) and number of comorbidities (median 3, IQR 2-3 v. median 2, IQR 1-3; p < 0.001), as well as parameters associated with immunosuppression. Recipients of lung transplants (n = 48) were more likely to have severe disease with a high mortality rate (n = 15, 31.3%) compared with recipients of other organ transplants, including kidney (n = 48, 14.8%), heart (n = 1, 4.4%), liver (n = 9, 11.4%) and kidney-pancreas (n = 3, 12.0%) transplants (p = 0.02). Protective factors against needing supplemental oxygen included having had a liver transplant and receiving azathioprine. Having had 2 doses of SARS-CoV-2 vaccine did not have an appreciable influence on oxygen requirement. Multivariable analysis showed that older age (odds ratio [OR] 1.04, 95% confidence interval [CI] 1.02-1.07) and number of comorbidities (OR 1.63, 95% CI 1.30-2.04), among other factors, were associated with the need for supplemental oxygen. Over time, disease severity did not decline significantly. INTERPRETATION: Despite therapeutic advances and vaccination of recipients of solid organ transplants, evidence of increased severity of COVID-19, in particular among those with lung transplants, supports ongoing public health measures to protect these at-risk people, and early use of COVID-19 therapies for recipients of solid organ transplants.

Severe Acute Respiratory Syndrome Coronavirus 2 Infection Induces Greater T-Cell Responses Compared to Vaccination in Solid Organ Transplant Recipients.

T-cell immunity associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection or vaccination in solid organ transplant recipients (SOTRs) is poorly understood. To address this, we measured T-cell responses in 50 SOTRs with prior SARS-CoV-2 infection. The majority of patients mounted SARS-CoV-2-specific CD4+ T-cell responses against spike (S), nucleocapsid, and membrane proteins; CD8+ T-cell responses were generated to a lesser extent. CD4+ T-cell responses correlated with antibody levels. Severity of disease and mycophenolate dose were moderately associated with lower proportions of antigen-specific T cells. Relative to nontransplant controls, SOTRs had perturbations in both total and antigen-specific T cells, including higher frequencies of total PD-1+ CD4+ T cells. Vaccinated SOTRs (n = 55) mounted significantly lower proportions of S-specific polyfunctional CD4+ T cells after 2 doses, relative to unvaccinated SOTRs with prior coronavirus disease 2019. Together, these results suggest that SOTRs generate robust T-cell responses following natural infection that correlate with disease severity but generate comparatively lower T-cell responses following mRNA vaccination.