BASIC AND TRANSLATIONAL RESEARCH IN INTRACEREBRAL HEMORRHAGE: LIMITATIONS, PRIORITIES AND RECOMMENDATIONS

Introduction

Hemorrhagic stroke remains a major cause of mortality and permanent disability. There are unmet needs for effective therapies to improve outcomes after hemorrhagic stroke, in particular intracerebral hemorrhage (ICH). Modeled after the Stroke Therapy Academic Industry Roundtable (STAIR) meetings^{1, 2}, the first HEmorrhagic stroke acAdemia inDuStry (HEADS) roundtable was convened in May 2017. The meeting focused on ICH. Participants were asked to define unmet needs and challenges in the field. They were then divided into two working subgroups, basic and clinical research, and tasked with the development of recommendations and benchmark standards to improve the process of researching, developing, and refining therapies for ICH. Emerging recommendations for preclinical and translational research are presented in the current report. Recommendations for clinical research and trial design are discussed in a companion article. Preclinical research into ICH is focused on three broad goals: elucidating the mechanisms causing ICH; determining the local and systemic pathways that underlie ICH-induced brain injury, self-defense, and repair; developing preclinical therapies that can translate to the clinic to limit ICH occurrence and expansion, reduce injury severity, and improve repair and functional recovery. Aims of this part of the HEADS roundtable discussion were to: 1) highlight limitations in such preclinical research and, thereby, develop priorities for future research and 2) outline recommendations for more effective clinical translation of preclinical research. While the STAIR guidelines^{1, 2} for preclinical ischemic stroke research have application to hemorrhagic stroke, the outlined discussion particularly focused on identifying specific needs in the ICH field.

Preclinical modeling of ICH

Preclinical research on ICH has mostly focused on reducing ICH-induced brain injury rather than preventing hemorrhage. There are relatively few preclinical models of spontaneous ICH to test hemorrhage prevention strategies and new models are critical (Table 1), particularly for the more common risk factors of ICH (hypertension and anticoagulant use). Additionally, modeling modifiable and non-modifiable risk factors for ICH occurrence (e.g. alcoholism, sympathomimetic drug use, aging) is required for greater understanding of ICH prevention. Areas for advances in modeling for particular etiologies are highlighted below:

Table 1.

Priorities for Preclinical Research: Spontaneous ICH

• Develop models of spontaneous ICH with more consistent ICH occurrence and/or clinically equivalent hematoma sizes.

• Compare vascular pathophysiology in models of spontaneous ICH and human ICH.

• Understand the impact of comorbidities on spontaneous ICH.

• Determine the pathophysiological signaling underlying genetic causes of ICH and whether they intersect with sporadic causes.

• Develop methods to rapidly detect the occurrence of spontaneous ICH in animals.

Hypertension

Hypertension is the primary risk factor for ICH, but relatively few models of hypertension-related spontaneous ICH exist³. There is a critical need for models that provide understanding of translatable pathophysiologic mechanisms. How well these models reflect human hypertension-induced ICH is important. If the increased blood pressure is the sole cause of the ICH, these models may be extremely useful. However, if the etiology of hypertension impacts bleeding/brain injury and is not reflective of human disease, these models may be inadequate. Thus, careful comparison across multiple relevant spontaneous ICH models is useful, and creation of new models to address this should be sought.

Cerebral amyloid angiopathy (CAA)

There are genetic mouse models of Alzheimer’s disease and CAA, but few reports of ICH^{3, 4}. Models present with sporadic microhemorrhages that increase in number with age. However, microhemorrhages may not occur in all animals, are infrequent in animals that do hemorrhage, vary in location and do not induce obvious neurological deficits. These all pose problems for using the models to test therapeutic agents. It may be possible to impose a second ‘stress’ to enhance either size or frequency of the hemorrhages (e.g. hypertension⁵ or anticoagulants) and this deserves further investigation.

Interestingly, there are reports of naturally occurring CAA and microhemorrhages in aged larger animals³. However, the utility of these models for more than natural history studies is doubtful given the infrequency and size of hemorrhage, and high cost. Developments in producing transgenic Alzheimer’s disease models in larger animals may be of use⁶.

Other genetic mutations

There have been advances in identifying genes that underlie some human ICH, such as familial cerebral cavernous malformations (CCM)⁷ and mutant mice are being used to identify potential therapeutic targets to prevent ICH⁸. There is a need for further clinical work to identify relevant genetic mutations underlying ICH, such as studies by the International Stroke Genetics Consortium and others. This can guide preclinical models through reverse translation. A fuller understanding of how genetic mutations cause ICH may not only develop preventive strategies for those specific etiologies but also, potentially, targets for limiting ICH in the general population; e.g. by identifying common pathways.

Anticoagulants

Preclinical studies on anticoagulant-induced ICH have focused on exacerbating collagenase-induced hemorrhage⁹. This model has advantages, but the underlying mechanism, collagenase-induced extracellular matrix degradation, and the vessels affected, differ from human ICH. There is a need to examine the effects of anticoagulants on ICH occurrence and size in preclinical models of spontaneous ICH.

Assessing spontaneous ICH

A concern with models of spontaneous ICH, irrespective of etiology, is identifying hemorrhage onset. Serial imaging allows assessment before and after ICH and behavioral testing may identify animals with ICH. However, limitations on imaging/testing frequency prevent knowing the exact time of ictus. The time frame of hemorrhaging can be shortened (e.g. salt-feeding in SHRSP¹⁰) but such interventions may not reflect most human ICH. Strategies identifying ICH occurrence (e.g. kinematics with alarms) would be of enormous use.

Models of spontaneous ICH also have variability in hematoma volume and location. In patients, hematoma volume is highly correlated with outcome. While spontaneous ICH models might be postulated to better reflect human disease, greater animal numbers will likely be required for experiments to be adequately powered.

Modeling ICH-induced brain injury and repair – areas for focus

ICH has both primary (physical disruption, increased intracranial pressure (ICP)) and secondary (e.g. clot-derived cytotoxic factors, neuroinflammation^11–13) injury components followed by a period of repair. The therapeutic time window for modulating brain repair may be longer than for preventing ICH-induced brain injury¹⁴.

Much has been learnt about ICH-induced brain injury and repair using preclinical in vivo and in vitro models. The most commonly used in vivo ICH models involve intracerebral collagenase injection to induce bleeding or blood injection to mimic a hematoma¹². In vitro modeling has focused on cell exposure to potential clot-derived neurotoxic factors (e.g. thrombin, iron, hemoglobin¹³). While our understanding of ICH in preclinical models has increased and translation of these findings into clinical ICH studies is ongoing, there are still major areas for future progress (Table 2).

Table 2.

Priorities for Preclinical Research: ICH-induced injury and repair

Understudied areas of ICH-induced injury and repair Effect of co-morbidities on ICH prevention, injury and repair. Effect of ICH on oligodendrocyte survival and repair and axonal biology. Impact of ICH location on distinct impairments. Model other outcomes in animals (vision, motor, sensory and cognition) relevant to humans. Hematoma/erythrocyte lysis and clearance as a therapeutic target. Systemic changes and brain/body bidirectional communication Leveraging adaptive responses and diminishing maladaptive responses following ICH.

Model and technique development and utilization Modeling increased ICP: morbidity and mortality in ICH. Models/methods for hematoma integrity, resolution, and expansion. Modeling microhemorrhage. Systems neuroscience of ICH. In vitro models to study pathogenesis and repair. Creation of pluralistic preclinical networks to leverage distinct core competencies in ICH.

Species differences

Unlike human ICH, mortality is low, neurological consequences are modest, and recovery is often rapid in current ICH preclinical models. This raises the issue of whether there may be species differences in mechanisms of brain injury/recovery after ICH and highlights several research priorities.

Increased use of endoscopic catheters to evacuate ICH gives access to hematoma and perihematomal tissue as well as the opportunity to collect CSF and plasma. These human samples can be of great use to compare to preclinical models (e.g. injury pathway activation/potential biomarkers) and for reverse translation (identifying human pathways and examining their occurrence in preclinical models). Studies that leverage ‘omics’ to examine peripheral and central changes in patients and preclinical models will facilitate species comparisons. A repository for such human samples and autopsy brains along with clinical data would greatly aid the field. In addition, such comparisons could aid in the validation of humanized rodent models for ICH studies.

In addition, use of advanced neuroimaging would allow direct quantitative comparison of the same important parameters (e.g. edema volume, hematomal and perihematomal iron, blood clearance, neuroinflammation, neuronal connectivity, hydrocephalus, brain atrophy) in human and animal ICH. Another potential approach to gain greater understanding of human ICH using preclinical models is the use of humanized mice. For example, the effect of different human apolipoprotein-E genotypes (APOE3 and APOE4) on ICH-induced brain injury has been examined by knocking in these genes into mice¹⁵.

While there are major advantages to studying ICH in multiple species, it should be realized that there are difficulties. These include expense, relative lack of behavioral tests in some species, and development of many biochemical assays and reagents only in rodents.

White matter changes

The relative amount of white matter differs in humans and animals. White matter damage, including demyelination, axonal injury, and Wallerian degeneration is an important component of human ICH-induced injury/recovery and this remains understudied in preclinical models. Such studies, particularly in large animals with significant white matter, needs to be prioritized. MRI-based tractography may be an important tool for assessing white matter injury and recovery, allowing translation/reverse translation to similar human studies.

Co-morbidities

Most ICH patients have multiple co-morbidities, which may affect brain injury and recovery after ICH. The recovery of neurological deficits is slowed in aged animals¹⁶. However, the effect of co-morbidities (e.g. hypertension, diabetes and hyperlipidemia) on injury and recovery after ICH is still an understudied area of preclinical research and should be prioritized. In particular, greater use of aged animals is important. Age impacts ICH occurrence and outcome. Currently, nearly all preclinical work is done in relatively young rodents.

In vivo model development

In current models, it is imperative to determine how well they replicate injury in spontaneous ICH. It is also important to determine the impact of different absolute hematoma volumes across species. Currently, modeling is typically based upon inducing an ICH where the volume is a similar % of brain weight to human. However, some injury and therapeutic parameters may not scale with volume (e.g. with hematoma radius). It is unknown how this impacts therapeutic targets or time windows.

A determinant of outcomes in ICH patients is increased ICP. Acute, but relatively short-lived, increases in ICP have been recorded in pig ICH¹⁷ but they do not reach the levels observed in patients. Having an ICH model generating high, sustained ICP values and/or obstructive hydrocephalus could be translationally important.

Clinically, hematoma expansion is thought to contribute to ICH-induced injury¹⁸. While collagenase-induced hematomas expand with time, the underlying mechanism (continued extracellular matrix degradation in many vessel types) likely differs from human hematoma expansion. Alternative preclinical models of hematoma expansion, specifically involving arterioles/small arteries, should be a priority.

In humans, cerebral microbleeds are common, particularly in the aging population¹⁹. How to preclinically model microbleeds is uncertain. As noted above, some genetic models have microhemorrhages. Others have used lasers to rupture vessels causing very small bleeds²⁰. There are questions over scaling for such studies; should the animal hematoma be the same size as a human microbleed; should it be scaled for brain size; does total volume of microhemorrhage need to be related between human and animal brain, and, finally, how to appropriately incorporate predominant brain location of hemorrhages? These decisions may depend on the research questions being addressed.

One advantage of ICH models is that they can be titrated to produce different hematoma volumes. While volume clearly affected the efficacy of minimally invasive evacuation²¹, the preclinical use of different hematoma volumes to inform clinical trials has not been examined, e.g. does efficacy vary with hematoma volume? Demonstrating efficacy in specific hematoma volumes preclinically may help define translational parameters for human trials. Replicating clinical hematoma volume variability within preclinical trials may help assess whether therapeutic efficacy is sufficient to overcome lesion variability.

The outcome of human ICH is impacted by location. Although hindbrain models have been described²², most preclinical models have focused on cerebral cortex or caudate/putamen hemorrhage. While location almost certainly impacts rehabilitation potential and recovery, whether it affects injury mechanisms merits further investigation. Some locations are prone to cause intraventricular hemorrhage, a poor prognosis factor for patients with ICH.

Emerging endpoints

Most preclinical studies examining neurological deficits and recovery have focused on sensorimotor function. Clinically, there is increased interest in neurocognitive decline after ICH²³ and more preclinical studies focused on cognition after ICH are warranted. Furthermore, tests of behavioral/functional performance need to be relevant to tests performed in humans in order to be of translational value; blinding, randomization, and adequately powered studies are essential to minimize experimental bias.

Biomarkers/surrogate measures (e.g. imaging, inflammatory and other injury markers) may be of great use for assessing ICH-induced injury and target engagement. However, a greater understanding of the importance of these measures is needed. Advances in validated neuroimaging platforms and translation/reverse translation of biochemical markers could be useful.

In vitro models

Most in vitro models of ICH focus on identifying the effects of clot-derived neurotoxic factors on single cell types. ICH affects multiple cell types within the brain and alters cell-cell communication as well as inducing cytotoxicity. In vitro ICH research should utilize emerging techniques including primary adult microglial and astrocyte cultures, inducible pluripotent stem cells, single cell isolation from brain slices and cell phenotyping after flow cytometry.

Emerging targets and opportunities

Hematoma changes after ICH

Most attention has focused on the effects of ICH on perihematomal tissue and the brain as a whole. Attention should also be directed to changes within the hematoma that may impact clot resolution and release of potential neurotoxic factors, important therapeutic targets. Access to the hematoma cavity, through minimally invasive surgery, provides a critical opportunity for such studies.

For white matter repair, the hematoma forms a physical barrier precluding neuronal connectivity and generating a neurotoxic, pro-inflammatory environment. Removing this barrier by clot evacuation or accelerating hematoma resolution (which may take months in humans) may aid in improving brain repair.

Brain/body communication

ICH has multiple systemic effects including alterations in the coagulation cascade, changes in blood pressure and sympathetic activation, disturbances in ion homeostasis, and alterations in the peripheral immune system. Further, cerebrovascular events can impact other organ function (e.g. spleen, liver, heart, bone marrow), which indirectly could affect brain pathological and reparative processes. In addition to brain-to-body communication, there may be important effects of body-to-brain communication impacting ICH outcome (e.g. the gut microbiome). More work is needed on brain/body bidirectional communication in ICH.

Protective pathways and repair mechanisms induced by ICH

While most preclinical research has focused on identifying pathways that lead to brain injury, ICH also induces neuroprotective pathways (e.g. iron-handling proteins upregulation²⁴). Inducing these protective pathways therapeutically can reduce ICH-induced brain injury²⁵. It is important to understand potential interactions between pro-survival and pro-death pathways. Does pharmacologically inhibiting an injury pathway also prevent induction of endogenous neuroprotection?

As well as cell protection, multiple reparative mechanisms occur after stroke, including inflammation, axonal sprouting, synaptogenesis, neurogenesis, oligodendrogenesis and angiogenesis²⁶. The brain shows plasticity in response to injury. Changes may be ipsi- and/or contralateral to the ICH. Determining their relative importance (and which should be targeted therapeutically) is complex. Technologies such as two photon microscopy, intrinsic optical signal imaging, and functional MRI combined with electrophysiology, as well as more standard histochemistry and tract tracing, may provide insights.

As most evident in ICH-induced inflammation¹¹, pathways may be involved in both inducing brain injury and repair. One possible way of separating these effects is timing. This does, though, stress the importance of comparisons of pathway activation between human and preclinical models²⁷.

Multi-modality (or dual therapy)

Preclinical models should be used to test multimodality or combination therapeutics for reducing ICH-induced injury. For example, clot evacuation with a putative neuroprotectant or restorative therapy to start physical therapy/rehabilitation earlier.

Statistics

As preclinical modeling increases in complexity to more accurately reflect human disease, statistical handling of preclinical data may need to follow suit. Use of factorial design may be one such innovation²⁸. In experiments with two or more factors of interest allowed to vary within, factorial design analyzes each factors’ effect on the outcome of interest, as well as effects of the interaction between factors on outcomes. Preclinical modeling is an excellent venue for this type of experimental design as experiments are controlled for many of the other relevant variables, which is often impossible in human disease. Another statistical approach being used in clinical trials is adaptive design²⁹ where the allocation of patients to particular treatment groups varies during the course of a trial based on incoming data. Adaptive design may be beneficial in preclinical studies by reducing the number of animals needed and lowering cost³⁰.

Developing preclinical therapies that translate to the clinic

As outlined in the previous section, there are concerns with current preclinical ICH models over how well they replicate human ICH and there is room for advance. However, such models can be used to identify injury and protective pathways that occur in a particular model and whether those pathways occur across models/species. They should also form the basis of clinical studies to examine whether those pathways also occur in human ICH through use of biomarkers. Greater access to human samples through current minimally invasive clinical trials will aid in this. In addition, as human ICH is very heterogeneous in terms of size, location and induced injury, it is important to examine whether particular injury and protective pathways occur across a spectrum of models as it will inform clinical trials. However, it should be noted that no preclinical model will fully replicate the absolute hematoma sizes found in human ICH. Figure 1 illustrates potential pathways to inform the design and conduct of clinical trials in ICH.

Figure 1. Pathways to translation.

The basis of a therapeutic approach is identifying an injury/protective/restorative pathway in either ICH patients or preclinical models (1). Validating that the pathway occurs in patients as well as preclinical models is crucial. Sometimes pathway identification has directly led to clinical trials; e.g. hematoma expansion and blood pressure regulation or factor VIIa (2). Sometimes, the clinical trial has been based on data from other forms of brain injury (e.g. add-ons to ischemia trials). So far, there has been no positive clinical trial for ICH. Another approach (3) has been to identify and develop potential therapeutic approaches in preclinical models and then use that data to clinical trial (4). A concern is the multiple failures of ischemic stroke trials using that approach (although few ICH clinical trials have been based on preclinical studies). Those concerns led to the STAIR criteria and the guidelines proposed for ICH preclinical research in Table 3 (5). It is hoped that such guidelines will help inform which approaches should proceed to clinical trial and inform such trials (6). It is important in early phase clinical trials that there is evidence of ‘target engagement’ for the proposed therapy for progression (7).

Preclinical models can also be used to test the efficacy of potential therapeutics/procedures with the knowledge that the importance of injury/protective pathways as well the delivery of therapy may differ between the preclinical model and humans. Preclinical models can also provide important information on the pharmacokinetics/pharmacodynamics of potential therapeutics as well as potential toxicity.

There are important considerations in deciding whether or not to take an agent/procedure forward from preclinical testing in ICH models to clinical trial as discussed below. Successful translation will require multidisciplinary expertise (e.g. basic scientists, clinical trialists, neuroimaging specialists, neurosurgeons, rehabilitation specialists). Clinically relevant outcome measures are important in preclinical modeling while understanding the inherent limitations of such models. Conversely, the potential impact of a target or outcome measure in a model (and its limitations) must be communicated to those translating it to clinical trials. Early collaboration across the translational pipeline will likely yield more robust preclinical modeling and clinical trial design. The presence of an early commercialization plan is also extremely important for taking a therapy into clinical trial. It impacts industrial participation and early consideration of how a potential therapeutic ultimately reaches the marketplace may guide preclinical testing, translation, and clinical trial design.

Currently, as in clinical trials, neurological deficits are the primary outcome measure to indicate preclinical efficacy. However, having additional biomarkers/surrogate measures (e.g. imaging, inflammatory markers, brain edema and atrophy), especially as these surrogates pertain to a specific therapy target engagement, can be of great use for comparison across species and into clinical trial. The agent/approach should have an appropriate safety window and should not increase bleeding at the therapeutic dose.

Preclinical studies should adhere to ARRIVE and RIGOR guidelines. It is important that results be replicated across laboratories. Replication experiments should be standardized, blinded, and randomized. In other forms of brain injury, consortia have been established to perform studies^{31, 32}. Consortia have employed the same or diverse models, which have advantages and disadvantages, and have highlighted the inhomogeneity of effects between laboratories and models. Although not essential for progression to clinical trial, therapeutics that are at least not detrimental in cerebral ischemia models have a major advantage. They might not require imaging to determine whether a stroke is hemorrhagic or ischemic. Developing collaborations between laboratories to leverage different core competencies would also aid the field.

It is essential that studies be performed in aged animals before clinical trials. In humans, there are conflicting data on whether ICH incidence/outcome differs between males and females³³, but injury pathways may differ between sexes altering therapeutic efficacy. Thus, it is recommended that preclinical trials examine both males and females. Similarly, it would be preferable to test therapeutics in hypertensive and CAA animals that spontaneously develop ICH.

For advancement to clinical trials, it is important that potential therapies be performed in at least two species (preferably not two rodents) as there may be species differences in therapeutic response. While testing in a large animal model may not always be absolutely necessary (depending on therapeutic target), such testing has advantages; e.g. more white matter, greater hematoma volume, longer hematoma resolution and inflammation, potential combination therapy with clot evacuation, more opportunities for neuroimaging. Studies in large animals may also give important information on scaling (therapeutic time windows and dosing). The expertise needed for such models and cost stresses the importance of forming preclinical networks and establishing stringent criteria to determine which therapies go forward to such models.

Examining multiple ICH models serves to show the robustness of therapeutic approaches and increases the probability of successful translation. Given the considerable genetic, co-morbidity and drug regimen heterogeneity in humans, only the most robust therapies are likely to succeed. Potential therapeutics should have a realistic time window for administration based on purported mechanism of action and feasibility of clinical use. Because not all ICH patients access care acutely, studies should not only test immediate or hyperacute administration of therapies.

An important question for any therapeutic for ICH is drug delivery. Apart from developing blood-brain barrier (BBB) permeable therapeutics, there are also possibilities with intranasal and direct local delivery (intracerebroventricular, intraparenchymal or intra-hematomal) to bypass the BBB. Local delivery may be particularly relevant to cerebral hemorrhage with catheters in place for clot evacuation and CSF drainage. However, this may delay treatment relative to intravenous or oral administration. By whichever route, there should be evidence that agents reach the site of action at appropriate concentrations (e.g. by measuring drug levels, pathway activation or relevant biomarkers). Caution is needed when using collagenase models as the enzyme-induced vascular disruption may enhance brain drug delivery.

If multiple agents/approaches meet the above criteria, direct comparisons between therapeutics may be of importance.

Strengths and shortcomings

This document was prepared by HEADS participants (preclinical and clinical) and addresses issues that they thought were important barriers to ICH research, potential areas for progress and recommendations for translation of preclinical studies to the clinic. This is an ‘opinion piece’ on matters where there is considerable controversy. It is also not exhaustive and it is hoped that future HEADS conferences (and papers) will delve into particular issues in greater depth.

Conclusions

Significant advances in our understanding of ICH have occurred in the past two decades. From preclinical and clinical studies it is clear that ischemic stroke and ICH significantly differ in underlying causes, injury mechanisms¹², and recovery. Questions have been raised about ICH preclinical models and their ‘translatability’. However, only recently are clinical trials being initiated based on ICH preclinical data. Hopefully, the proposed directions and recommendations of the HEADS working group on preclinical research will aid in achieving successful translation (Table 3).

Table 3.

Recommendations for preclinical ICH research

• Need to develop hypertensive and CAA models of spontaneous ICH in which to test therapeutics.

• Use of novel statistical methods (e.g. factorial design and adaptive design) in pre-clinical trials.

• Preclinical exploration of multi-modality therapies.

• The following criteria must be met before deciding whether to take an experimental agent/procedure forward to clinical trial in ICH Efficacy – therapeutic approach should improve neurological deficits. Positive effects on other surrogate measures/biomarkers provide supportive evidence. Safety – therapeutic approach should not increase bleeding risk or hematoma expansion, or diminish propensity for repair. Evidence of safety in cerebral ischemia, while not essential, facilitates clinical translation. Replicability – efficacy demonstrated by at least two independent laboratories. Age, sex, and species – evidence of efficacy in aged, male and female animals in at least two species. Target studied preclinically is conserved in humans. Multiple ICH models – at least two models. While not essential, evidence in large animal models provides important evidence for translation Therapeutic time window – should be realistic for human use. Drug delivery/target engagement – evidence that drug reaches therapeutic target.

APPENDIX: HEADS PARTICIPANTS

Chairs: Magdy Selim¹; Daniel Hanley¹

Working Groups:

Clinical: Joseph Broderick¹ (Chair), Joshua N Goldstein¹, Barbara A Gregson¹, Guido Falcione¹, Nicole R Gonzales¹, Edip Gurol¹, Jocelyn Kersten², Henry Lewkowicz², A David Mendelow¹, Susanne Muehlschlegel¹, Richey Neuman², Yuko Palesch¹, Michael Rosenblum¹, Kevin N Sheth¹, Vineeta Singh¹, Wendy Ziai¹.

Basic: Richard F Keep¹ (Chair), Jaroslaw Aronowski¹, Curtis Genstler², Michael L James¹, Rajiv Ratan¹, Lauren Sansing¹, Anna Youd², Guohua Xi¹, Marietta Zille¹.

Other Participants and Contributors: Craig Anderson¹, Issam Awad¹, Eric Bastings³, Martin Bednar², Alexander L Coon¹, Rebecca Gottesman¹, Bryan Katz², Saima Khan², James Koenig³, Walter Koroshetz³, Shari Ling³, Christopher Loftus³, John Lockhardt², Thomas Louis¹, John Marler³, Claudia Moy³, Carlos Pena³, Charles Pollack¹, Laurel Omert², Monica Shah³, Ashkan Shoamanesh¹, Michael Singer², Thorsten Steiner¹, Michel Torbey¹, Mike Tymianski¹, Ajay Wakhloo¹, Paul Vespa¹, Mario Zuccarello¹, Xiaolin Zheng³.

Representatives from academia¹, Industry², and governmental agencies³.