Blood Advances Talks

Big data are used in the pursuit of precision medicine in the general population. Applying these tools to patients with sickle cell disease (SCD) is essential for ensuring that they receive the most appropriate customized therapy for their disease. For these tools to be applied, there must be a large number of willing, fully phenotyped participants in collaborative registries. Working collaboratively to respond to unmet clinical needs and the lack of a large multisite registry, SCD providers at multiple sites developed The Globin Regional Data and Discovery (GRNDaD) registry. The specific goals of GRNDaD are to (1) prospectively obtain high-quality curated data on the evolving population affected by SCD; (2) improve adherence to guideline-based care; (3) provide a platform for ongoing quality improvement across sites; (4) allow for real-time investigation of therapies, and collaborate broadly to address research questions using GRNDaD as a shared platform. GRNDaD’s current strength lies in the generous participation of people living with SCD, collaborative investigators, and the opportunity to conduct quality improvement activities across a large number of sites. GRNDaD will serve as the data collection tool for the Health Resources and Services Administration Sickle Cell Treatment Demonstration Program and for the newly established National Alliance for Sickle Cell Centers (https://www.sicklecellcenters.org/). GRNDaD is a robust collaborative registry that providers and researchers will use to identify genetic markers that will help predict outcomes and lead to a better understanding of the natural history of SCD in the modern era of novel therapies.

Sickle cell disease (SCD) is an inherited blood condition resulting from abnormal hemoglobin production. It is one of the most common genetic diseases in the world. The clinical manifestations are variable and range from recurrent acute and debilitating painful crises to life-threatening pulmonary, cardiovascular, renal, and neurologic complications. The only curative treatment of SCD at this time is bone marrow transplantation (also called hematopoietic stem cell transplantation) using healthy blood stem cells from an unaffected brother or sister or from an unrelated donor if one can be identified who is a match in tissue typing. Unfortunately, only a minority of patients with sickle cell has such a donor available. The use of autologous hematopoietic stem cells and alternative types of genetic modifications is currently under study in clinical research trials for this disease. The approaches include the use of viral vectors to express globin genes that are modified to prevent sickle hemoglobin polymerization or to express interfering RNAs to “flip the switch” in adult red cells from adult β-sickle hemoglobin to fetal hemoglobin using a physiologic switch, and several gene editing approaches with the goal of inducing fetal hemoglobin or correcting/modifying the actual sickle mutation. In this audio review, we will discuss these different approaches and review the current progress of curative therapy for SCD using gene therapy.

The prospect of a clinical strategy using an adeno-associated virus (AAV) vector for expression of therapeutic levels of factor VIII (FVIII) has been highly desirable. This was initially anticipated by promising data from clinical studies on AAV5-FVIII in men with severe hemophilia A. However, long-term follow-up showed a unique efficacy concern on the sustainability and durability derived from a continuous decline in the FVIII transgene levels starting 1 year after vector injection through year 5. Additional follow-up of early-phase studies and outcomes of an ongoing phase 3 study will likely provide evidence on the feasibility of this approach. Here, the potential underlying mechanisms of the FVIII declining levels, together with the revision of several unique early and late onset findings, are discussed. The lack of long-term preclinical studies in large animal models prevents the firm conclusion that FVIII levels decline was unexpected. It is possible that the combination of vector manufacturing platform and dose, accompanied with ectopic expression of supraphysiologic levels of FVIII at short-term follow-up, may all contribute to the sustainability and durability of the transgene levels. Notably, vector readministration to further improve the FVIII levels is not feasible at this time. Thus, the need of a one-and-done AAV strategy to achieve sustain FVIII levels of expression is sine qua non to impact favorably the disease phenotype.

The availability of novel nonfactor therapeutics is revolutionizing the management of hemophilia in individuals with inhibitory antibodies, as well as making prophylaxis more convenient even in the absence of inhibitors. Unfortunately, the use of these products has been associated with thrombotic events that are not typically seen with factor replacement. These are primarily seen when a patient on a nonfactor therapy experiences breakthrough bleeding and concomitantly receives another hemostatic agent. This video addresses thrombotic complication in 3 nonfactor products: (1) emicizumab, a bispecific antibody that mimics the cofactor activity of factor VIII; (2) fitusiran, an small interfering RNA that knocks down synthesis of antithrombin; and (3) concizumab, an antibody that blocks inhibition of factor Xa by tissue factor pathway inhibitor. The latter 2 agents were developed on the premise that hemostasis in hemophilia could be “rebalanced” by reducing the levels of anticoagulant activity to compensate for the defect in procoagulant activity. Each of these approaches increases peak levels of thrombin achieved in assays on plasma from treated subjects and reduces bleeding rates in individuals with or without inhibitors. However, we do not yet have a good mechanistic model for precisely how these approaches affect hemostasis in vivo. It is not only the total amount of active thrombin produced that determines the effectiveness of hemostasis but also how thrombin generation is regulated. Therefore, it is currently difficult to predict how these new agents will interact with other perturbations or therapeutic manipulations of the coagulation system.

Amy Shapiro discusses the recent approval of concizumab for the treatment of patients with hemophilia. This novel subcutaneous homeostatic rebalancing agent has proven to be useful for the treatment of patients with hemophilia A and B, and we hope you find this talk to be useful to understand it.

TA-TMA: state of the art for diagnosis and treatment by Blood Advances Talks