The Endothelial Cell Dysfunction and Outcome Project for Hematological Neoplasms

Functional heterogeneity is a hallmark of the endothelial cell system. The hypothetical functional definition of ECs as input-output devices emphasizes their role as direct responders to a variety of challenges such as blood pressure, temperature, pH and oxygen pressure, and serum factors. Maintaining homeostasis of tissue perfusion is an important function of ECs that are continuously exposed to stimuli provided by the alternative complement pathway, coagulation factors, cytokines, activated platelets, leukocytes, and occasional infectious agents. Due to their distribution over space and time, hardly two ECs will be exposed to the same set of input signals 8. Moreover, stochastic or inheritable heterogeneous DNA methylation patterns add to the functional variability of seemingly "homogeneous" mature EC populations. Therefore, tissue-specific stress responses of ECs can explain that even during systemic EC dysfunction (e.g. due to calcineurin inhibitors, viruses, TBI etc.), microangiopathy develops locally in individual patients. This functional heterogeneity has to be considered in all attempts to define clinical diagnostic criteria for endothelial complications after hematological anti-neoplastic therapy including alloSCT and CART infusions.

Over the last years, our group has developed the concepts of "endothelial vulnerability" and "endothelial cell dysfunction" that pre-exist before alloSCT and CART infusions and at initial diagnosis of patients with hematological disorders, e.g. myelodysplastic syndromes, but also in COVID-19 patients. We have defined and validated novel and pre-existing endothelial vulnerability markers (e.g. single nucleotide polymorphisms in THBD (Thrombomodulin) and CD40 Ligand; serum levels of Angiopoietin-2, serum nitrates, asymmetric dimethyl-arginine (ADMA), testosterone deficiency, interleukin-18), and markers of endothelial cell dysfunction or damage (e.g. suppressor of tumorigenicity (ST)-2, interleukin-18, insulin-like growth factor 1 (IGF1), CXCL8), and we have established their role as prognostic markers for treatment-related mortality and for a variety of allo- and CART-specific endothelial complications.

The heterogeneity of EC explains why global one-for-all markers were not found within the group of endothelial-derived and endothelial-specific prognostic factors. We therefore developed the Endothelial activation and stress index, EASIX, as a marker that represents the response of the organism to endothelial dysfunction. EASIX represents an interplay of the basic laboratory parameters (LDH*creatinine/platelets) observed at onset of the most severe endothelial complication after alloSCT, i.e. transplant-associated thrombotic microangiopathy (TAM). EASIX correlated with endothelial serum markers such as IL18, ANG2 and IGF1 and predicted outcome in a variety of clinical settings including COVID-19. However, the exact relationship of EASIX to endothelial cell biology requires further clarification. We hypothesize that reduced endothelial glycocalyx thickness will permit direct interactions of leukocytes and platelets with endothelial cells, resulting in cellular activation (increased LDH), loss of platelets due to activation and microembolism, and ensuing kidney damage.

Thus, key areas of interest are:

• Comprehensive collection and intercorrelation of endothelial parameters before, during and after new lines of therapy including in vivo microscopy, ECHO cardiography, EASIX, body weight, endothelial serum markers including, but not restricted to, ST2, ANG2, IL18, IL8, sCD141, Hyaluronan, Syndecan-1, CXCL9, Leptin, Adiponectin, Testosterone, and others.
• Correlation of EASIX with glycocalyx thickness and capillary flow measured by in vivo microscopy of the capillary bed.
• Systematic collection of clinical data on known endothelial complications, including, but not restricted to, sepsis, septic shock, macrophage activation syndrome, veno-occlusive disease / sinusoidal obstruction syndrome (SOS/VOD), thrombotic microangiopathy, idiopathic pneumonia syndromes (IPS), paraneoplastic syndromes, engraftment syndrome, persistent intestinal inflammation, cachexia, and others.
• Systematic collection and evaluation of comprehensive biological specimens and information from patients with hematological neoplasms, including data on the genomic, transcriptomic, epigenomic and proteomic "landscapes" as well as expression of surface antigens of hematological disease subtypes, to identify novel prognostic and predictive endothelial parameters as well as entry points for targeted therapeutic interventions that protect the endothelium.
• Multivariable prediction analyses of endothelial parameters on outcome and endothelial complications.

The above challenges are ideally met by a registry study with a sufficient population size to answer relevant questions in rare therapy-related complications and rare cancer entities.

The aim is to set up a registry study that covers systematic and comprehensive clinical data acquisition, and longitudinal banking of serum, blood cells and bone marrow samples of patients with hematological diseases, with focus on in vivo microscopy, EASIX, and serum endothelial markers.

This resource will spur patient-oriented investigations into relationships between endothelial, clinical and tumor-biological parameters in hematological neoplasms and lay the groundwork for novel, supportive treatment approaches protecting the endothelial system in poorly understood and difficult-to-treat subsets.

As a first prospective analysis, we will answer the question if EASIX and serum endothelial biomarkers correlate with sublingual glycocalyx thickness, and if these parameters combine to predict outcome after anti-neoplastic therapy including alloSCT and CART.