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Molecular Diagnostics in Lung Transplantation


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Kieran Halloran, MD
University of Alberta
Edmonton, AB, Canada
Kieran.halloran@ualberta.ca



Diagnostics is one of the most significant issues facing the field of lung transplantation. In almost every other domain - donor utilization, bridging, surgical issues - major challenges have been met with meaningful solutions, but the diagnostic toolset available to the transplant clinician has only minimally evolved (1-3). Our ability to accurately and reproducibly recognize histologic T cell mediated rejection (TCMR) in the transbronchial biopsy (TBB) is limited, while the histology of antibody mediated rejection (ABMR) remains almost entirely elusive (4,5). Some of this is related to intrinsic limitations of histology, but this is further complicated by the risks and morbidity of TBB, preventing the sickest patients from being biopsied (6). Perhaps nowhere else in medicine is this diagnostic equipoise as clinically dangerous: the transplant clinician will (and in most cases, must) do something, and that decision often comes down to whether or not to augment the immune suppressive (IS) regimen. Either increasing (in the setting of suspected rejection) or decreasing IS presents serious hazards, and establishing a reliable basis for this decision constitutes an urgent clinical need.

One solution to providing a safer and more informative basis for assessing donor tissue lies in molecular methodology. Our group recently presented the results of a microarray-based molecular diagnostic system in lung transplant recipients (7,8). This system is based on several core principles: biologic processes in tissue can be more accurately and reproducibly assessed by looking at the molecular changes than the histologic changes; that these biologic processes in transplantation - e.g. T cell infiltration and TCMR, antibody binding and ABMR - are tissue agnostic; and that probabilistic assessment is a more realistic way of capturing disease processes than threshold based categorization i.e. present or absent. This system has been developed and validated in kidney transplants, where it can distinguish TCMR, ABMR, and tissue injury better than the combination of histology, DSA and C4d staining (9). Molecular assessment also provides a global view of the injuries and the immunologic events in the transplanted organ, from the initial days dominated by parenchymal injury and TCMR, followed by adaptation and exhaustion of the T cell mediated processes, the emergence of non-adherence related phenotypes, and the long-term dominance of ABMR as a driver of late phenotypes (10).

Our key findings were as follows: high quality RNA is readable in 100% of cases, both in TBB and in mucosal biopsy tissue from the second airway bifurcation (2B-MB); the rejection-associated biologic processes (assayed via "pathogenesis-based transcript sets") show variation across a population of indication biopsies in both TBB and 2B-MB; individual rejection-associated probesets organize and correlate with population variability in an identical fashion to the pattern shown in kidney and heart; and there is little correlation with conventional diagnostics and histology. This last point may initially seem like a failing, but is compatible with the hypothesis: if the "gold-standard" is flawed, then an accurate test demonstrating a relationship with the gold standard is not anticipated. This study establishes the principles but the number of observations remains small and many more biopsies will be required to train the diagnostic equations. The system at this early point in its development cannot assign TCMR or ABMR labels, and cannot be used clinically. Computationally, this form of analysis iteratively improves the strengths of its classifications with each additional biopsy via machine learning. This will require large numbers of biopsies to analyze with accompanying patient data, so our current efforts are directed towards recruitment for a large scale, multicenter diagnostic study. The potential benefits include:

  1. A tissue based assay for TCMR and ABMR
  2. Diagnostic objectivity and reproducibility;
  3. New understanding of the injury response and its relationship to late lung deterioration.
  4. Safer biopsy methods, either a single TB or a mucosal biopsy, reducing risk;
  5. The ability to safely biopsy sick patients;
  6. Accurate delivery of immunosuppression to only those who will benefit, avoiding unnecessary risk for those who do not

As always, the ultimate aim with diagnostics is that, provided with more accurate, reproducible and complete information, the clinician can make more informed decisions, resulting in patients living longer and better lives, and allowing for expanded access to lung transplantation as a treatment. ■

Disclosure Statement: The author has no conflicts of interest to disclose.


References:

  1. Yusen RD, Edwards LB, Kucheryavaya AY, et al. The Registry of the International Society for Heart and Lung Transplantation: Thirty-second Official Adult Lung and Heart-Lung Transplantation Report-2015; Focus Theme: Early Graft Failure. The Journal of Heart and Lung Transplantation. 2015;34(10):1264-1277. doi:10.1016/j.healun.2015.08.014.
  2. Cypel M, Yeung JC, Liu M, et al. Normothermic Ex Vivo Lung Perfusion in Clinical Lung Transplantation. N Engl J Med. 2011;364(15):1431-1440. doi:10.1056/NEJMoa1014597.
  3. Cypel M, Keshavjee S. Extracorporeal Life Support as a Bridge to Lung Transplantation. Clin Chest Med. 2011;32(2):245-251. doi:10.1016/j.ccm.2011.02.005.
  4. Levine DJ, Glanville AR, Aboyoun C, et al. Antibody-mediated rejection of the lung: A consensus report of the International Society for Heart and Lung Transplantation. J Heart Lung Transplant. 2016;35(4):397-406. doi:10.1016/j.healun.2016.01.1223.
  5. Arcasoy SM, Berry G, Marboe CC, et al. Pathologic Interpretation of Transbronchial Biopsy for Acute Rejection of Lung Allograft Is Highly Variable. Am J Transplant. 2011;11(2):320-328. doi:10.1111/j.1600-6143.2010.03382.x.
  6. McWilliams TJ, Williams TJ, Whitford HM, Snell GI. Surveillance Bronchoscopy in Lung Transplant Recipients: Risk versus Benefit. The Journal of Heart and Lung Transplantation. 2008;27(11):1203-1209. doi:10.1016/j.healun.2008.08.004.
  7. Halloran K, Chang J, Ramassar V, et al. Microarray Analysis of Endobronchial Lung Transplant Biopsies_ Detection of T-cell Mediated Inflammation in a Safer Biopsy. HEALUN. 2016;35(Supplement):S155-S156. doi:10.1016/j.healun.2016.01.433.
  8. Halloran K, Chang J, Ramassar V, et al. Microarray Analysis of Transbronchial Biopsies in Lung Transplant Recipients Detects Molecular Changes of T-cell Mediated Inflammation. HEALUN. 2016;35(Supplement):S234-S235. doi:10.1016/j.healun.2016.01.666.
  9. Sellarés J, Reeve J, Loupy A, et al. Molecular diagnosis of antibody-mediated rejection in human kidney transplants. Am J Transplant. 2013;13(4):971-983. doi:10.1111/ajt.12150.
  10. Halloran PF, Reeve JP, Pereira AB, Hidalgo LG, Famulski KS. Antibody-mediated rejection, T cell-mediated rejection, and the injury-repair response: new insights from the Genome Canada studies of kidney transplant biopsies. Kidney Int. 2013;85(2):258-264. doi:10.1038/ki.2013.300.



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