How do we expand the lung donor pool?

PURPOSE OF REVIEW: Lung transplantation activity continues to be limited by the availability of timely quality donor lungs. It is apparent though that progress has been made. The steady evolution of clinical practice, combined with painstaking scientific discovery and innovation are described. RECENT FINDINGS: There have been successful studies reporting innovations in the wider use and broader consideration of donation after circulatory death donor lungs, including an increasing number of transplants from each of the controlled, uncontrolled and medically assisted dying donor descriptive categories. Donors beyond age 70 years are providing better than expected long-term outcomes. Hepatitis C PCR positive donor lungs can be safely used if treated postoperatively with appropriate antivirals. Donor lung perfusion at a constant 10 degrees appears capable of significantly improving donor logistics and ex-vivo lung perfusion offers the potential of an ever-increasing number of novel donor management roles. Bioartificial and xenografts remain distant possibilities only at present. SUMMARY: Donor lungs have proved to be surprisingly robust and combined with clinical, scientific and engineering innovations, the realizable lung donor pool is proving to be larger than previously thought.

COVID-19 infection is mild and has minimal impact on lung function in well vaccinated and widely treated lung transplant recipients.

BACKGROUND: COVID-19 has become a common infection affecting lung transplant recipients (LTR), who are at high risk for poor outcomes. Outcomes early in the pandemic were poor, but since the rollout of vaccination and novel COVID-19 treatments, outcomes of LTR have not been well described. Our aim was to evaluate the effect of COVID-19 on the clinical course and lung function trajectory in an Australian cohort of LTR. METHODS: Data were retrospectively collected from LTR with confirmed COVID-19 managed at Alfred Health, between August 2020 and December 2022. Baseline demographics, COVID-19 disease details (including severity) and spirometry pre- and postinfection have been analyzed. RESULTS: A total of 279 LTR were included. The cohort was comorbid, but well vaccinated, with 275/279 (98.6%) having ≥2 COVID-19 vaccines at symptom onset. Severe disease occurred in only 17 cases (6%) and overall mortality was very low (4%). Prompt treatment with antivirals, particularly remdesevir (OR 0.18, 95% CI 0.04-0.81, p = 0.02) and vaccination (OR 0.24, CI 0.08-0.81, p = 0.01), was protective. There was not a clinically significant drop in lung function post-COVID-19 with the median absolute decline in forced expiratory volume (FEV1) being 40 ml (IQR 5-120 ml, p < 0.001), with a decline of >10% occurring in only 42 patients (17%). After multivariate adjustment, only rejection before COVID-19 was significantly associated with FEV1 decline afterward (OR 3.74, 1.12-11.86, p = 0.03). CONCLUSIONS: In our highly COVID-19 vaccinated, promptly treated LTR, the majority of COVID-19 infections were mild and did not result in a clinically significant decline in lung function.

Comparison of human leukocyte antigen immunologic risk stratification methods in lung transplantation.

Outcomes after lung transplantation (LTx) remain poor, despite advances in sequencing technology and development of algorithms defining immunologic compatibility. Presently, there is no consensus regarding the best approach to define human leukocyte antigen (HLA) compatibility in LTx. In this study, we compared 5 different HLA compatibility tools in a high-resolution HLA-typed, clinically characterized cohort, to determine which approach predicts outcomes after LTx. In this retrospective single-center study, 277 donor-recipient transplant pairs were HLA-typed using next generation sequencing. HLA compatibility was defined using HLAMatchmaker, HLA epitope mismatch algorithm (HLA-EMMA), predicted indirectly recognizable HLA epitopes (PIRCHE), electrostatic mismatch score (EMS), and amino acid mismatches (AAMMs). Associations with HLA mismatching and survival, chronic lung allograft dysfunction (CLAD), and anti-HLA donor-specific antibody (DSA) were calculated using adjusted Cox proportional modeling. Lower HLA class II mismatching was associated with improved survival as defined by HLAMatchmaker (P < .01), HLA-EMMA (P < .05), PIRCHE (P < .05), EMS (P < .001), and AAMM (P < .01). All approaches demonstrated that HLA-DRB1345 matching was associated with freedom from restrictive allograft syndrome and HLA-DQ matching with reduced DSA development. Reducing the level of HLA mismatching, in T cell or B cell epitopes, electrostatic differences, or amino acid, can improve outcomes after LTx and potentially guide immunosuppression strategies.

Cytomegalovirus Immunity Assays Predict Viremia but not Replication Within the Lung Allograft.

Cytomegalovirus (CMV) infection causes significant morbidity and mortality in lung transplant recipients. Current guidelines use pretransplant donor and recipient CMV serostatus to predict the risk of subsequent CMV replication and length of antiviral prophylaxis. Immunological monitoring may better inform the risk of CMV infection in patients, thereby allowing for improved tailoring of antiviral prophylaxis. In this study, we compared 2 commercially available assays, the QuantiFERON-CMV (QFN-CMV) and T-Track-CMV (enzyme-linked immunosorbent spot assay), to predict the risk of CMV disease in lung transplant recipients. Methods: We performed CMV immunity assays on 32 lung transplant recipients at risk of CMV disease as defined by serostatus (CMV-seropositive recipients, n = 26; or CMV-seronegative lung transplant recipient receiving a CMV-seropositive donor organ, n = 6). QFN-CMV and T-Track were performed on peripheral blood mononuclear cells, and episodes of CMV replication in both serum and bronchoalveolar lavage were found to be correlated to the CMV immune assays. The predictive ability of the assays was determined using Kaplan-Meier curves. Results: There was a degree of concordance between tests, with 44% of recipients positive for both tests and 28% negative for both tests; however, test results were discordant in 28% of cases. A negative result in either the QFN-CMV (P < 0.01) or T-Track (P < 0.05) assays was obtained in a significantly higher number of recipients who experienced CMV replication in the blood. Using these assays together gave higher predictability of CMV replication, with only 1 recipient experiencing CMV replication in the blood who obtained a positive test result for both assays. Neither assay was able to predict recipients who experienced CMV replication in the lung allograft. Conclusions: Our study demonstrates that CMV immunity assays can predict viremia; however, the lack of association with allograft infection suggests that CMV-specific T-cell immunity in the circulation is not associated with the control of CMV replication within the transplanted lung allograft.

Determining Clinical Thresholds for Donor HLA Eplet Compatibility to Predict Best Outcomes Following Lung Transplantation.

Currently, the assessment of immunological risk in lung transplantation (LTx) does not completely consider HLA compatibility at the molecular level. We have previously demonstrated the association of HLA eplets in predicting chronic lung allograft dysfunction following LTx; however, the associations between HLA eplet mismatch (epMM) loads and overall survival are unknown. Methods: In this retrospective, single-center study, 277 LTx donor-recipient pairs were high resolution HLA typed and analyzed for HLA epMMs using HLAMatchmaker (version 3.1). LTx pairs were also assessed for the presence of the previously described risk epitope mismatches DQ2-DQA1*05 and DQ7-DQA1*05. Results: HLA class I epMMs were not associated with deleterious outcomes; however, lower HLA class II (≤19), DQA1 (≤2), and combined HLA class I and II (≤29) epMM demonstrated an association with increased time to chronic lung allograft dysfunction and improved overall survival. The presence of a risk epitope mismatch was not associated with worse clinical outcomes. Conclusions: HLA epMM can risk-stratify LTx recipients and potentially guide donor-recipient matching and immunosuppression strategies.

A prediction model to determine the untapped lung donor pool outside of the DonateLife network in Victoria.

Lung transplantation is limited by a lack of suitable lung donors. In Australia, the national donation organisation (DonateLife) has taken a major role in optimising organ donor identification. However, the potential outside the DonateLife network hospitals remains uncertain. We aimed to create a prediction model for lung donation within the DonateLife network and estimate the untapped lung donors outside of the DonateLife network. We reviewed all deaths in the state of Victoria's intensive care units using a prospectively collected population-based intensive care unit database linked to organ donation records. A logistic regression model derived using patient-level data was developed to characterise the lung donors within DonateLife network hospitals. Consequently, we estimated the expected number of lung donors in Victorian hospitals outside the DonateLife network and compared the actual number. Between 2014 and 2018, 291 lung donations occurred from 8043 intensive care unit deaths in DonateLife hospitals, while only three lung donations occurred from 1373 ICU deaths in non-DonateLife hospitals. Age, sex, postoperative admission, sepsis, neurological disease, trauma, chronic respiratory disease, lung oxygenation and serum creatinine were factors independently associated with lung donation. A highly discriminatory prediction model with area under the receiver operator characteristic curve of 0.91 was developed and accurately estimated the number of lung donors. Applying the model to non-DonateLife hospital data predicted only an additional five lung donors. This prediction model revealed few additional lung donor opportunities outside the DonateLife network, and the necessity of alternative and novel strategies for lung donation. A donor prediction model could provide a useful benchmarking tool to explore organ donation potential across different jurisdictions, hospitals and transplanting centres.

An Intention-to-treat View of Lung Transplantation for Interstitial Lung Disease: Successful Strategies to Minimize Waiting List and Posttransplant Mortality.

BACKGROUND: Access to lung transplantation (LTx) and rates of waiting list and posttransplant mortality for patients with interstitial lung disease (ILD) remain problematic. We evaluated the outcomes of ILD patients listed for LTx at our institution. METHODS: Between 2012 and 2018, adult patients with ILD were listed and transplanted from a donor-pool that included extended criteria and donation after circulatory-determined death donors. Patients were categorized as experiencing 1 of 4 competing events: transplant, waitlist death, delisting, or alive on waitlist. Multivariable competing risk regression analysis was performed to determine predictors of waitlist death/delisting. Posttransplant survival was analyzed using Kaplan-Meier methods. RESULTS: Among 187 patients listed, 82% (153 of 187) underwent LTx (median time-to-transplant, 2.0 mo), whereas 16% (30 of 187) died or were delisted (median time-to-event, 1.6 mo). At 90 d, 6 mo, and 12 mo after listing, 51%, 63%, and 78% of patients had been transplanted, whereas 10%, 14%, and 16% had died or were delisted. Multivariable predictors of waitlist death/delisting were: blood group O compared to A (subdistribution hazard ratio [SHR]: 6.43, P < 0.001), shorter height (per 1 cm, SHR: 1.11, P < 0.001), hospitalization at listing (SHR: 3.98, P = 0.002), and reduced 6-min-walk test distance (per 50 m, SHR: 1.28, P = 0.001). Among LTx recipients, 24% (36 of 153) underwent single LTx. Donor lungs were 58% (88 of 153) extended-criteria, inclusive of 24% (37 of 153) circulatory-determined death. Ninety-day and 1-, 3-, and 5-y retransplant free survival were 97% ± 1%, 92% ± 2%, 81% ± 4%, and 69% ± 6%. CONCLUSIONS: Patients with ILD require a rapid transit to LTx after listing. Despite this, the vast majority of ILD patients in this study reached LTx with excellent early and midterm outcomes.

Mitral Valve Regurgitation After Lung Transplantation: Aetiology, Management and Outcome.

BACKGROUND: Problematic mitral regurgitation (MR) may develop following lung transplantation (LTx). There is limited information on the management of MR in LTx patients, as such we sought to evaluate our centre's experience. METHODS: From 2000 to 2019, 1,054 patients underwent LTx at our centre (896 bilateral, 158 single). We identified patients in whom significant MR developed at any point post-LTx. The aetiology of MR, management and outcome were retrospectively analysed. RESULTS: Eight (8) patients developed severe MR post-LTx, six following bilateral LTx and two following single LTx. Lung transplantation indications included interstitial lung disease (n=5), chronic obstructive pulmonary disease (n=2) and pulmonary arterial hypertension (n=1). Severe MR occurred intraoperatively (n=1), postoperative day 1 (n=1) with the remaining six cases between 80 and 263 days post-LTx. The aetiology was noted to be due to severe left ventricular dysfunction following unmasking of a chronically pulmonary hypertension-related under-preloaded left ventricle in one case, and in the remaining seven patients causes included myxomatous degeneration, ischaemic MR, and functional MR due to annular dilatation. In the patient with intraoperative severe MR, the MR became mild with veno-arterial extracorporeal membrane oxygenation (VA-ECMO) and in the remaining seven patients a variety of procedures were used, including mitral valve repair, valve replacement and transcatheter edge-to-edge mitral valve repair. All patients survived the mitral procedure. Two (2) deaths occurred at 12.9 years (stroke) and 5 years (cancer) from mitral valve surgery. CONCLUSIONS: Development of significant mitral valve regurgitation is a rare but morbid complication after lung transplantation. This may represent the progressive natural history of pre-existing degenerative mitral valve disease and rarely, early after transplantation may be related to changes in ventricular geometry. Management of severe MR can follow the same management approach as in the non-transplant community, with the expectation of similarly good results.

Evaluation of Quantiferon®-Monitor as a biomarker of immunosuppression and predictor of infection in lung transplant recipients.

BACKGROUND: Optimizing immunosuppression in lung transplant recipients (LTR) is crucially important in minimizing the risk of infection and rejection. Quantiferon®-Monitor (QFM) is a candidate immune function biomarker which has not yet been rigorously evaluated in the lung transplant setting. The aim of this prospective cohort study was to explore relationships between QFM results, immunosuppression, and infection/rejection in LTR. METHODS: QFM, which measures interferon-γ after stimulation with innate and adaptive immune antigens, was tested before and at 2, 6, 12, 24 and 52 weeks post-transplant. Immunosuppression relationships were assessed with linear mixed effects models. Clinical outcomes were analyzed based on the preceding QFM result. RESULTS: Eighty LTR were included. Median pre-transplant QFM levels were 171 IU/mL (IQR 45-461), decreasing to 3 IU/mL (IQR 1-8) at 2 weeks post-transplant then progressively recovering toward baseline with time from transplant. Prednisolone was strongly inversely associated with QFM level (0.1 mg/kg dose increase correlating with 88 IU/mL QFM decrease, 95% CI 61-114, P < .001). Patients with QFM values <10 and <60 IU/mL were more likely to develop a serious opportunistic infection between 3 and 6 months (HR 6.38, 95% CI 1.37-29.66, P = .02) and 6-12 months (HR 3.25, 95% CI 1.11-9.49, P = .03) post-transplant, respectively. CONCLUSIONS: QFM values declined significantly post-transplant, with patients recovering at different rates. Prednisolone dose significantly impacted QFM results. Low levels were associated with infection beyond 3 months post-transplant, suggesting that QFM may be able to identify overly immunosuppressed patients who could be targeted for dose reduction. Larger prospective studies are needed to further evaluate this promising assay.

Cytomegalovirus replication is associated with enrichment of distinct γδ T cell subsets following lung transplantation: A novel therapeutic approach?

BACKGROUND: Anti-viral treatments to control cytomegalovirus (CMV) after lung transplantation (LTx) are associated with toxicity and anti-viral resistance. Cellular immunotherapy with virus-specific cytotoxic T cells has yielded promising results but requires donor/recipient matching. γδ T cells are involved in anti-viral immunity and can recognize antigens independently of major histocompatibility complex molecules and may not require the same level of matching. We assessed the phenotype of circulating γδ T cells after LTx to identify the candidate populations for CMV immunotherapy. METHODS: Peripheral blood mononuclear cells were isolated from lung transplant recipients before transplantation and at routine bronchoscopies after LTx. Patients were stratified by risk of CMV disease into moderate risk (recipient CMV seropositive, n = 15) or high risk (HR) (recipient CMV seronegative/donor CMV seropositive, n = 10). CMV replication was classified as polymerase chain reaction positive (>150 copies/ml) in blood and/or bronchoalveolar lavage within the first 18 months. The phenotype of γδ T cells was assessed by multicolor flow cytometry, and T-cell receptor (TCR) sequences were determined by deep sequencing. RESULTS: In HR lung transplant recipients with CMV replication, we observed striking phenotypic changes in γδ T cells, marked by an increase in the proportion of effector Vδ1+ γδ T cells expressing the activating natural killer cell receptor NKG2C. Moreover, we observed a remarkable increase in TCR diversity. CONCLUSIONS: NKG2C+ Vδ1+ γδ T cells were associated with CMV replication and may indicate their potential to control infection. As such, we propose that they could be a potential target for cellular therapy against CMV.

Donor Lung Referrals for Lung Transplantation: A 'Behind The Scenes' View.

BACKGROUND: Australia's increasing organ donor rate has translated to increased lung donor referrals and subsequent lung transplantation (LTx). The LTx sector attempts to utilise as many organs as possible-but in reality, not all are used. This analysis aims to assess the utility and efficiency of donor lung referrals to the Alfred Hospital. METHODS: All Donatelife Australia donor lung referrals for the year 2017 were analysed retrospectively. RESULTS: From a total of 440 lung referrals, 220 were local from the state of Victoria (population 6.4 million) and 220 from the Rest-of-Australia (ROA). Sixty-eight per cent (68%) of Victorian and 48% of the ROA were via the donation after circulatory death (DCD) pathway. One hundred and two (102) LTx were performed: 32 represent 21% of 149 Victorian and 8% of 106 ROA DCD donors, 70 represent 54% of the Victorian and 24% of the ROA donation after brain death (DBD) donors. Eighty per cent (80%) of all donors aged <35 and 30% >35 years were used or potentially useable. Thirteen per cent (13%) of DCD and 44% of DBD donors aged >65 years were used. Logistical and resource considerations, around the retrieval of older DCD lungs, are a significant issue. At 11.1 LTx per-million-population the Alfred has one of the highest lung donor conversion and LTx activity rates in the world. CONCLUSION: The Australian donor lung pool could still be further extended by focussing effort and logistics on optimising DBD referrals. Additional resources (staff and transport), tighter referral criteria, and the use of extended warm ischaemic time donors could increase particularly DCD recovery rates.

A donor PaO2/FiO2 < 300 mm Hg does not determine graft function or survival after lung transplantation.

BACKGROUND: A donor arterial PO2/FiO2 (P/F ratio) of less than the 300 threshold would frequently result in either exclusion of the donor or placement of the lungs on ex vivo lung perfusion (EVLP). The aim was to investigate the veracity of the P/F ratio threshold of 300 for donor lung acceptability. METHODS: In 93 brain dead lung donors, arterial blood gases were drawn in the intensive care unit (ICU) just before procurement and each of the 4 donor pulmonary veins in the operating room (OR). No donor lungs were rejected for transplantation based on the last ICU or OR P/F ratio, and EVLP was not used. The recipients were followed up 6 and 12 months following transplantation. RESULTS: There were 93 recipients of bilateral lung transplantation. An arterial P/F ratio of < 300 was largely driven by a low P/F ratio in the lower lobes. There were no differences between the recipients receiving donor lungs where the ICU P/F ratio was < 300 compared with ≥ 300 in the time to extubation, grade of primary graft dysfunction, pulmonary function at 6 and 12 months, and 12-month survival. CONCLUSIONS: From this study:(1) If a donor P/F threshold of 300 was adhered to, 36% would have been rejected, and (2) The donor P/F ratio threshold of 300 is excessively conservative and results in the wastage of donor lungs and the application of unnecessary EVLP.

Enrichment of Cytomegalovirus-induced NKG2C+ Natural Killer Cells in the Lung Allograft.

BACKGROUND: In lung transplant recipients, immunosuppressive medications result in impaired antiviral immunity and a propensity for cytomegalovirus (CMV) reactivation within the lung allograft. Natural killer (NK) cells play a key role in immunity to CMV, with an increase in the proportion of NK cells expressing activating CD94-NKG2C receptors in the blood being a strong correlate of CMV infection. Whether a similar increase in NKG2C NK cells occurs in lung transplant recipients following CMV reactivation in the allograft and if such cells contribute to viral control remains unclear. METHODS: In this pilot study, we longitudinally assessed the frequency and phenotype of NKG2C NK cells in the blood and bronchoalveolar lavage (BAL) of lung transplant recipients and stratified recipients based on their risk of developing CMV disease. RESULTS: We observed an increase in the proportion of NKG2C NK cells in the blood and BAL of CMV high-risk patients, coincident with both the cessation of antiviral prophylaxis and subsequent detection of actively replicating CMV in the blood and lung allograft. Additionally, these NKG2C NK cells expressed killer-cell immunoglobulin-like receptors distinct from those of other NK subsets and BAL NKG2C NK cells possessed an activated phenotype. Finally, the frequency of NKG2C NK cells in the BAL may be inversely correlated with CMV blood titers. CONCLUSIONS: Monitoring the phenotype of NK cells postlung transplant may be a useful biomarker for monitoring patient levels of CMV immunity.

A Randomized Study of Quantiferon CMV-directed Versus Fixed-duration Valganciclovir Prophylaxis to Reduce Late CMV After Lung Transplantation.

BACKGROUND: We provide the results of the first interventional study of cytomegalovirus (CMV)-specific immune monitoring to direct the length of antiviral prophylaxis in lung transplantation (LTx). METHODS: Patients (n = 118) at risk of CMV infection were randomized 1:2 to either 5 months or variable length valganciclovir prophylaxis (5-11 mo post-LTx), as determined by the QuantiFERON (QFN)-CMV assay. Patients with a negative QFN-CMV assay (< 0.2 IU/mL) received prolonged valganciclovir prophylaxis. RESULTS: The primary endpoint that was the incidence of CMV infection in the lung allograft within 18 months of LTx was significantly reduced in the QFN-CMV directed arm (37% versus 58%, P = 0.03). Secondary endpoints that included blood viremia, acute rejection, and chronic lung allograft dysfunction did not differ between the 2 arms. Of the 80/118 patients who ceased antiviral prophylaxis at 5 months, the incidence of viremia (> 600 copies/mL) within the blood was significantly reduced in patients with a positive QFN-CMV assay compared with those without protective immunity (13% versus 67%, P = 0.0003), as was the incidence of severe viremia (> 10 000 copies/mL) (3% versus 50%, P < 0.001). Ceasing antiviral prophylaxis at 11 months in patients with a negative assay was associated with a 25% incidence of late CMV viremia. CONCLUSIONS: Cytomegalovirus immune monitoring allows an individualized approach to CMV prophylaxis and reduces late CMV infection within the lung allograft.

Donation after Brain Death versus Donation after Circulatory Death: Lung Donor Management Issues.

Lung transplantation (LTx) has traditionally been limited by a lack of suitable donor lungs. With the recognition that lungs are more robust than initially thought, the size of the donor pool of available lungs has increased dramatically in the past decade. Donation after brain death (DBD) and donation after circulatory death (DCD) lungs, both ideal and extended are now routinely utilized. DBD lungs can be damaged. There are important differences in the public's understanding, legal and consent processes, intensive care unit strategies, lung pathophysiology, logistics, and potential-to-actual donor conversion rates between DBD and DCD. Notwithstanding, the short- and long-term outcomes of LTx from any of these DBD versus DCD donor scenarios are now similar, robust, and continue to improve. Large audits suggest there remains a large untapped pool of DCD (but not DBD) lungs that may yet further dramatically increase lung transplant numbers. Donor scoring systems that might predict the donor conversion rates and lung quality, the role of ex vivo lung perfusion as an assessment and lung resuscitation tool, as well as the potential of donor lung quality biomarkers all have immense promise for the clinical field.