When Sanjana Dayal, PhD, and her colleagues met for their weekly “Blood Club” on March 12, 2020, they kickstarted a branch of research that would captivate them for years to come. The club, which discusses all things related to benign hematology, was already seeing the budding effects of the COVID-19 pandemic that would quickly become center of the global stage.

“That day, our team was discussing if we should open a clinical trial at our center, and I immediately jumped in requesting for a blood draw to observe biomarkers and mechanisms of blood clot formation in COVID-19,” Dayal said. “We were interested because 40% of hospitalized [COVID] patients at the time were suspected to have excessive blood clots.”

From the beginning of the COVID-19 pandemic, infected patients had been found to have elevated levels of extracellular histones in plasma. Histones are DNA-bound structural proteins involved in some transcription and repair processes; elevated plasma levels of H3Cit histones in COVID-19, specifically, are associated with disease severity.

Dayal and others hypothesized that platelet activation triggered by these histones might be contributing to increased thrombin generation and thrombosis. They hoped to test this possibility by evaluating the potential of circulating extracellular histones to enhance platelet adhesion and thrombin generation and generate platelet-derived extracellular vesicles (PEVs) that would potentiate thrombin generation in plasma and enhance thrombotic susceptibility in vivo in mice. Higher susceptibility to thrombosis in plasma with elevated histone levels would suggest a link, exposing an underlying mechanism of COVID and opening the door to understanding potential treatment options in cases with this added risk.

The clinical trial, once reviewed and approved by the Institutional Review Board, proposed comparing blood samples taken from an early clinical trial of patients hospitalized with SARS-CoV-2 and a control group of healthy subjects in order to measure the procoagulant and prothrombotic potential of circulating extracellular histones and EVs.

Initially supported by two pilot grants, first from the Division of Hematology, Oncology, and Blood & Marrow Transplantation and then by the Carver College of Medicine, Dayal says the promising early data generation allowed the team to submit an R01 proposal that was funded in 2022 February by the NIH’s National Institute of Allergy and Infectious Disease (NIAID). Steven Lentz, MD, PhD, is a Co-PI on this grant with Dayal.

Dayal credits her team’s skills and the tools available to them for the continued success of the project. “Alicia Eustes was involved in shaping up the project and designed and performed most of the experiments. Dr. Lentz and Dr. Usha Perepu were actively recruiting patients and participated in data discussion and interpretation, and I basically conceived the idea and directed the project,” she noted. “This project was not possible without a critical reagent (histone-neutralizing RNA aptamer) that was donated to us by Dr. Francis J. Jr. Miller, a former cardiologist at the University of Iowa. The aptamer [a molecule that can selectively bind to a target – histones, in this case] was developed during his time at Iowa, and my lab participated in its testing that was published in Nature Communication in 2019. We fully utilized the power of this newly developed aptamer during the pandemic.”

With this support, the team recently published Extracellular histones: a unifying mechanism driving platelet-dependent extracellular vesicle release and thrombus formation in COVID-19. The paper concludes that elevated histone and EV levels do have implications for prothrombotic behavior, and that histone-targeting treatment strategies may be a beneficial next step for patients who are at risk of clots and their subsequent detrimental effects.

Of their future plans, Dayal said, “The ongoing study is following up with patients who were initially hospitalized for COVID-19, and the plan is to collect samples up to three years, to determine the time course of changes in prothrombotic factors. There were several parallel mechanisms suggested for blood clot formation in these patients; our study showed a unifying mechanism via which histones expelled in the blood is a major driver of excessive blood clotting. Future studies can focus on therapeutic approaches to target histones.”

In addition to monitoring the long-term outcomes in these patients, Dayal is also collaborating with Alpana Garg, MD, and Alejandro Comellas, MD—who established the Post-COVID-19 Clinic at UI Health Care—on another project, tracking people who contracted only mild SARS-CoV-2 virus but continue to have symptoms of persistent pain, lethargy, headache, brain fog, and other symptoms.

Dayal and her colleagues believe the impact of this research is incredibly promising, as it enhances understanding of COVID-19 pathology but also suggests novel therapeutic strategies that could improve patient outcomes after thrombotic events and inform groundbreaking preventative treatments. The combined efforts of these scientists and clinicians make managing the residual effects of the pandemic more achievable.