Table 2.

Overall conference summary recommendations and questions for further study

Fundamental/basic

For studies evaluating putative engraftment of any type of cell, including endogenous lung progenitor cells and/or iPSC-derived lung cells, as either lung epithelial, interstitial, and pulmonary vascular cells, advanced histologic imaging techniques (e.g., confocal microscopy, deconvolution microscopy, electron microscopy, laser capture dissection, etc.) must be used to avoid being misled by inadequate photomicroscopy and immunohistochemical approaches. Imaging techniques must be used in combination with appropriate statistical and other quantitative analyses of functional cell engraftment to allow for an unbiased assessment of engraftment efficiency.

Continue to elucidate mechanisms of potential recruitment, mobilization, and homing of circulating or therapeutically administered cells to lung epithelial, interstitial, and pulmonary vascular compartments for purposes of either engraftment or of immunomodulation.

Continue to encourage new research to elucidate molecular programs for development of lung cell phenotypes. Incorporate technological advances including single cell sorting and analyses, CRISPR/Caspase, and advanced microarray approaches.

Continue to refine the nomenclature used in study of endogenous and exogenous lung stem and progenitor cells.

Comparatively identify and study endogenous stem/progenitor cell populations between different lung compartments and between species.

Identify additional cell surface markers that characterize lung cell populations for use in visualization and sorting techniques.

Increase focus on study of endogenous pulmonary vascular and interstitial progenitor populations.

Continue to develop robust and consistent methodologies for the study of endogenous lung stem and progenitor cell populations. This includes exploration of different lung injury models that provide individually novel and grouped complementary data.

Develop more sophisticated tools to identify, mimic, and study ex vivo the relevant microenvironments (niches) for study of endogenous lung progenitor/stem cells.

Continue to develop functional outcome assessments for endogenous progenitor/stem cells.

Elucidate how endogenous lung stem and progenitor cells are regulated in normal development and in diseases.

Identify and characterize putative lung cancer stem cells and regulatory mechanisms guiding their behavior.

Continue to elucidate mechanisms by which embryonic and induced pluripotent stem cells develop into lung cells/tissue.

Comparative assessments of different ESC and iPSC differentiation protocols. Should protocols be standardized?

Devise better definitions of “lung in a dish” studies. Is expression of a few phenotypic genes enough? What functional assays are currently available and how can these be expanded?

Continue to develop disease-specific populations of ESCs and iPSCs, for example for cystic fibrosis and alpha-1 antitrypsin deficiency, with the recognition that no strategy has yet been devised to overcome the propensity of ESCs and iPSCs to produce tumors. Expand use of these cell populations for drug screening and as tools for probing basic disease-specific molecular and cellular pathophysiology.

Continue to develop approaches for ex vivo engineered trachea and large airways for clinical use in both pediatric and adult patients. Increase focus on producing biologically epithelialized and otherwise functional scaffolds. Increase studies on the underlying biology of engineered tracheal scaffolds.

Continue to explore lung tissue bioengineering approaches, such as artificial matrices, 3D culture systems, 3D bioprinting, and other novel approaches, for generating lung ex vivo and in vivo from stem cells, including systems that facilitate vascular development.

Develop standards for potential clinical use of ex vivo engineered trachea and lung.

What is the optimal environment for growing and/or maintaining lungs ex vivo? Develop advanced bioreactor systems for doing this. Evaluate effect of environmental influences, including oxygen tension, and mechanical forces, including stretch and compression pressure, on development of lung from stem and progenitor cells.

Incorporate studies of pulmonary nervous and lymphatic structure and function in ex vivo lung bioengineering.

Strong focus must be placed on understanding immunomodulatory and other mechanisms of cell therapy approaches in different specific preclinical lung disease models.

Improved preclinical models of lung diseases are necessary.

Disseminate information about and encourage use of existing core services, facilities, and web links.

Actively foster interinstitutional, multidisciplinary research collaborations and consortiums as well as clinical/basic partnerships. Include a program of education on lung diseases and stem cell biology. A partial list includes NHLBI Production Assistance for Cellular Therapies (PACT), NCRR stem cell facilities, GMP Vector Cores, small animal mechanics, and computed tomography scanner facilities at several pulmonary centers.

Translational/clinical

Support high-quality translational studies focused on cell-based therapy for human lung diseases. Preclinical models will provide proof of concept; however, these must be relevant to the corresponding human lung disease. Disease-specific models, including large animal models where feasible, should be used and/or developed for lung diseases.

Basic/translational/preclinical studies should include rigorous comparisons of different cell preparations with respect to both outcome and toxicological/safety endpoints. For example, it remains unclear which MSC or EPC preparation (species and tissue source, laboratory source, processing, route of administration, dosing, vehicle, etc.) is optimal for clinical trials in different lung diseases

Incorporate rigorous techniques to unambiguously identify outcome measures in cell therapy studies. Preclinical models require clinically relevant functional outcome measures (e.g., pulmonary physiology/mechanics, electrophysiology, and other techniques).

Continue to expand well-designed and appropriately regulated clinical investigations of cell-based therapies for pulmonary diseases and critical illnesses. This includes full consideration of ethical issues involved, particularly which patients should be initially studied.

Develop uniform criteria for outcome measures and clinical assessments in cell therapy trials and in patients who receive engineered tracheal implantations or lung implantations when applicable.

Provide increased clinical support for cell therapy trials in lung diseases. This includes infrastructure, use of NIH resources such as the PACT program, and the NCRR/NIH Center for Preparation and Distribution of Adult Stem Cells (MSCs; http://medicine.tamhsc.edu/irm/msc-distribution.html), coordination among multiple centers, and registry approaches to coordinate smaller clinical investigations.

Clinical trials must include evaluations of potential mechanisms, and this should include mechanistic studies as well as assessments of functional and safety outcomes. Trials should include, whenever feasible, collection of biologic materials such as lung tissue, bronchoalveolar lavage fluid, blood, etc. for investigation of mechanisms as well as for toxicology and other safety endpoints. Correlations between in vitro potency and in vivo actions of the cells being used should be incorporated whenever possible.

Creation of an international registry to encompass clinical and biological outcomes from all cell therapy–based and ex vivo trachea and lung bioengineering trials.

Partner with existing networks, such as ARDSNet or ACRC, nonprofit respiratory disease foundations, and/or industry as appropriate to maximize the scientific and clinical aspects of clinical investigations.

Integrate with other ongoing or planned clinical trials in other disciplines in which relevant pulmonary information may be obtained. For example, inclusion of pulmonary function testing in trials of MSCs in graft vs. host disease will provide novel and invaluable information about potential MSC effects on development and the clinical course of bronchiolitis obliterans.

Work with industry to have access to information from relevant clinical trials

All relevant investigators should take a strong stand against stem cell medical tourism and be familiar with the resources available to patients, caregivers, and all involved health care professionals on the websites of respiratory disease and patient advocacy groups as well those of the leading stem cell societies, the International Society for Cellular Therapy (ISCT), and the International Society for Stem Cell Research (ISSCR).

Definition of abbreviations: 3D = three-dimensional; ACRC = Asthma Clinical Research Centers; CRISPR = clustered regularly interspaced short palindromic repeats; EPC = endothelial progenitor cells; ESC = embryonic stem cells; GMP = good manufacturing practice; iPSC = induced pluripotent stem cell; MSC = mesenchymal stromal cells; NCRR = National Center for Research Resources; NIH = National Institutes of Health.