Congenital and acquired platelet disorders: current dilemmas and treatment strategies

Characterization of all small RNAs in and comparisons across cultured megakaryocytes and platelets of healthy individuals and COVID-19 patients

BACKGROUND

The small noncoding RNAs (sncRNAs) in megakaryocytes (MKs) and platelets are not well characterized. Neither is the impact of SARS-CoV-2 infection on the sncRNAs of platelets.

OBJECTIVES

To investigate the sorting of MK sncRNAs into platelets, and the differences in the platelet sncRNAomes of healthy donors (HDs) and COVID-19 patients.

METHODS

We comprehensively profiled sncRNAs from MKs cultured from cord blood-derived CD34+ cells, platelets from HDs, and platelets from patients with moderate and severe SARS-CoV-2 infection. We also comprehensively profiled Argonaute (AGO)-bound sncRNAs from the cultured MKs.

RESULTS

We characterized the sncRNAs in MKs and platelets and can account for ∼95% of all sequenced reads. We found that MKs primarily comprise microRNA isoforms (isomiRs), tRNA-derived fragments (tRFs), rRNA-derived fragments (rRFs), and Y RNA-derived fragments (yRFs) in comparable abundances. The platelets of HDs showed a skewed distribution by comparison: 56.7% of all sncRNAs are yRFs, 34.4% are isomiRs, and <2.0% are tRFs and rRFs. Most isomiRs in MKs and platelets are either noncanonical, nontemplated, or both. When comparing MKs and platelets from HDs, we found numerous isomiRs, tRFs, rRFs, and yRFs showing opposite enrichments or depletions, including molecules from the same parental miRNA arm, tRNA, rRNA, or Y RNA. The sncRNAome of platelets from patients with COVID-19 is skewed compared to that of HDs with only 19.8% of all sncRNAs now being yRFs, isomiRs increasing to 63.6%, and tRFs and rRFs more than tripling their presence to 6.1%.

CONCLUSION

The sncRNAomes of MKs and platelets are very rich and more complex than it has been believed. The evidence suggests complex mechanisms that sort MK sncRNAs into platelets. SARS-CoV-2 infection acutely alters the contents of platelets by changing the relative proportions of their sncRNAs.

Current Status of Platelet Transfusion in Pediatric Patients

Outside the neonatal period, most platelets that are transfused to pediatric patients are given to those who are thrombocytopenic secondary to malignancy and associated therapy and/or hematopoietic progenitor cell transplant, or to those with significant bleeding associated with surgery, especially cardiac surgery. Indications for platelet transfusion, doses, and other practices for children largely mimic adult platelet transfusion protocols because there are few pediatric-specific studies in this area. Pediatric platelet transfusion practices would benefit from focused pediatric research. The appropriate indications and doses for platelet transfusions in oncology, hematopoietic progenitor cell transplant, and cardiac surgery patients need to be determined.

Megakaryocyte- and megakaryocyte precursor-related gene therapies

Hematopoietic stem cells (HSCs) can be safely collected from the body, genetically modified, and re-infused into a patient with the goal to express the transgene product for an individual's lifetime. Hematologic defects that can be corrected with an allogeneic bone marrow transplant can theoretically also be treated with gene replacement therapy. Because some genetic disorders affect distinct cell lineages, researchers are utilizing HSC gene transfer techniques using lineage-specific endogenous gene promoters to confine transgene expression to individual cell types (eg, ITGA2B for inherited platelet defects). HSCs appear to be an ideal target for platelet gene therapy because they can differentiate into megakaryocytes which are capable of forming several thousand anucleate platelets that circulate within blood vessels to establish hemostasis by repairing vascular injury. Platelets play an essential role in other biological processes (immune response, angiogenesis) as well as diseased states (atherosclerosis, cancer, thrombosis). Thus, recent advances in genetic manipulation of megakaryocytes could lead to new and improved therapies for treating a variety of disorders. In summary, genetic manipulation of megakaryocytes has progressed to the point where clinically relevant strategies are being developed for human trials for genetic disorders affecting platelets. Nevertheless, challenges still need to be overcome to perfect this field; therefore, strategies to increase the safety and benefit of megakaryocyte gene therapy will be discussed.

Non-myeloablative conditioning with busulfan before hematopoietic stem cell transplantation leads to phenotypic correction of murine Bernard-Soulier syndrome

BACKGROUND

Bernard-Soulier syndrome (BSS) is an inherited bleeding disorder characterized by macrothrombocytopenia. Platelet transfusion is used for the management of bleeding, but repeated transfusion often results in alloimmunization. We have recently shown phenotypic correction of murine BSS (GPIbα(null) ) using lethal radiation conditioning followed by hematopoietic lentivirus-mediated gene transfer.

OBJECTIVES

For application of gene therapy to treatment of human patients, it is important to minimize treatment-related side effects. The objective of this study is to model a clinically relevant non-myeloablative hematopoietic stem cell (HSC) transplantation strategy.

METHODS

Using transplantation of bone marrow (BM) HSCs from transgenic mice that express hGPIbα (hGPIbα(tg+/+) ), we sought to (i) determine the percentage of hGPIbα(tg+/+) HSCs required for therapeutic benefit, (ii) evaluate the efficacy of non-myeloablative conditioning using busulfan, and (iii) test the ability of anti-thymocyte globulin (ATG) to prevent/reduce undesirable immune responses.

RESULTS

Transplantation of 10-20% hGPIbα(tg+/+) BM HSCs mixed with GPIbα(null) BM HSCs into irradiated GPIbα(null) mice was sufficient to correct bleeding time (n = 5). Transplantation of hGPIbα(tg+/+) BM HSCs into busulfan-conditioned GPIbα(null) mice corrected bleeding time in 21 of 27 recipients. Antibody response to hGPIbα and immune-mediated thrombocytopenia was documented in eight of 27 recipients, suggesting immunogenicity of hGPIbα in busulfan-conditioned GPIbα(null) mice. However, these antibodies disappeared without treatment within 30 weeks after transplantation. A combination of busulfan plus ATG conditioning successfully prevented antibody development and significantly increased therapeutic engraftment.

CONCLUSION

A conditioning regimen of busulfan in combination with ATG could potentially be used in non-myeloablative autologous gene therapy in human BSS.

The caspase-3 inhibitor (peptide Z-DEVD-FMK) affects the survival and function of platelets in platelet concentrate during storage

Background

Although apoptosis occurs in nucleated cells, studies show that this event also occurs in some anucleated cells such as platelets. During storage of platelets, the viability of platelets decreased, storage lesions were observed, and cells underwent apoptosis. We investigated the effects of caspase-3 inhibitor on the survival and function of platelets after different periods of storage.

Methods

Platelet concentrates were obtained from the Iranian Blood Transfusion Organization in plastic blood bags. Caspase-3 inhibitor (Z-DEVD-FMK) was added to the bags. These bags along with control bags to which no inhibitor was added were stored in a shaking incubator at 22℃ for 7 days. The effects of Z-DEVD-FMK on the functionality of platelets were analyzed by assessing their ability to bind to von Willebrand factor (vWF) and to aggregate in the presence of arachidonic acid and ristocetin. Cell survival was surveyed by MTT assay.

Results

At day 4 of storage, ristocetin-induced platelet aggregation was significantly higher in the inhibitor-treated (test) than in control samples; the difference was not significant at day 7. There was no significant difference in arachidonic acid-induced platelet aggregation between test and control samples. However, at day 7 of storage, the binding of platelets to vWF was significantly higher in test than in control samples. The MTT assay revealed significantly higher viability in test than in control samples at both days of study.

Conclusion

Treatment of platelets with caspase-3 inhibitor could increase their functionality and survival.

Bleeding diathesis and hemophilias

Patients with hemophilia and other congenital bleeding disorders are at risk for development of central nervous system (CNS) hemorrhage and can present with acute or chronic neurologic symptoms. These disorders are generally caused by qualitative or quantitative deficiency of components of hemostasis such as coagulation proteins, von Willebrand factor, or platelets. Rapid diagnosis and specific medical management such as coagulation factor replacement therapy are mandatory to minimize the morbidity and mortality of CNS bleeding. Therefore, the objective of this chapter is to introduce neurologists to the physiology of hemostasis and to provide an overview of the clinical presentation, and management of inherited bleeding disorders that can potentially present with CNS bleeding. Since hemophilia is the most common bleeding disorder encountered in clinical practice, more emphasis is placed on management of hemophilia. Additionally, neurologic manifestations related to the bleeding diathesis in patients with hemophilia are elaborated.

Coagulopathies in the PICU: DIC and liver disease

Bleeding in patients in pediatric intensive care units is associated with an increased risk of mortality. Fortunately, most patients with an abnormal coagulation profile do not bleed because this is generally secondary to liver disease or dietary-induced vitamin K deficiency. When the laboratory markers of coagulopathy are the result of disseminated intravascular coagulation, bleeding is common and the risk of mortality extreme. Although interventions directed toward correcting the abnormal coagulation test results are generally initiated, they are also generally either not warranted or not fully successful.

Correction of murine Bernard-Soulier syndrome by lentivirus-mediated gene therapy

Bernard-Soulier syndrome (BSS) is an inherited bleeding disorder caused by a defect in the platelet glycoprotein (GP) Ib-IX-V complex. The main treatment for BSS is platelet transfusion but it is often limited to severe bleeding episodes or surgical interventions due to the risk of alloimmunization. We have previously reported successful expression of human GPIbα (hGPIbα) in human megakaryocytes using a lentiviral vector (LV) encoding human GP1BA under control of the platelet-specific integrin αIIb promoter (2bIbα). In this study, we examined the efficacy of this strategy for the gene therapy of BSS using GPIbα(null) as a murine model of BSS. GPIbα(null) hematopoietic stem cells (HSC) transduced with 2bIbα LV were transplanted into lethally irradiated GPIbα(null) littermates. Therapeutic levels of hGPIbα expression were achieved that corrected the tail bleeding time and improved the macrothrombocytopenia. Sequential bone marrow (BM) transplants showed sustained expression of hGPIbα with similar phenotypic correction. Antibody response to hGPIbα was documented in 1 of 17 total recipient mice but was tolerated without any further treatment. These results demonstrate that lentivirus-mediated gene transfer can provide sustained phenotypic correction of murine BSS, indicating that this approach may be a promising strategy for gene therapy of BSS patients.

Effect of Recombinant Activated Factor VII in Critical Bleeding: Clinical Experience of a Single Center

Recombinant activated factor VII (rFVIIa) has been successfully used ‘‘off-label’’ in patients with refractory life-threatening hemorrhage. Intravenous rFVIIa was given to 31 patients unresponsive to standard therapy with blood products and surgical reexploration, who were bleeding due to trauma, surgery, organ transplantation, liver cirrhosis, ruptured uterus. We recorded their coagulation and hematologic profiles, acid-base balance, blood loss, number of red blood cells (RBC), plasma and platelet transfusions, complications, and survival. rFVIIa (mean dose 132.2 ± 56.3 μg/kg) effectively contained the hemorrhage in 28/31 (90.3%) cases, with a mean reduction in blood loss from 12.4 ± 10.2 to 2.7 ± 2.2 L (P < .0001). The need for RBC, platelet, and plasma transfusion decreased significantly after rFVIIa, with a consequent significant improvement in clotting of test hematocrit, pH, and bicarbonates. Four patients had adverse events potentially related to rFVIIa. The survival rates after 1 and 30 days were 48.4% and 29.1%, respectively.

rFVIIa and a new enhanced rFVIIa-analogue, NN1731, reduce bleeding in clopidogrel-treated and in thrombocytopenic rats

BACKGROUND

The pharmacological effect of rFVIIa occurs at the surface of activated platelets by enhancing thrombin generation at the site of vascular damage. It is therefore important to study the effects of rFVIIa in platelet-related bleeding situations. We examined the effect of rFVIIa and an rFVIIa-analogue, NN1731, on clopidogrel-induced and thrombocytopenic bleeding in rats.

METHODS AND RESULTS

Clopidogrel [10 mg kg(-1); per oral (p.o.)] severely inhibited platelet aggregation and increased blood loss after tail-transection four hours after administration. Treatment with rFVIIa (5, 10, 20 mg kg(-1)) or NN1731 (1, 5, 10 mg kg(-1)), administered five minutes after induction of bleeding, reduced blood loss significantly and dose-dependently. NN1731 had an increased hemostatic potential compared with rFVIIa, reducing blood loss to the control level, whereas this was not even achieved with the highest dose of rFVIIa. Antibody-induced thrombocytopenia reduced platelet numbers by more than 90% and increased the blood loss after tail-transection. Treatment with 10 and 20 mg kg(-1) rFVIIa significantly reduced blood loss, whereas 10 mg kg(-1) NN1731 reduced the bleeding to control levels.

CONCLUSIONS

The hemostatic effect of rFVIIa and NN1731 was demonstrated in thrombocytopenic and clopidogrel-treated rats, showing efficacy in situations with decreased platelet number or functionality. Our findings are consistent with the hypothesis that rFVIIa/NN1731 contribute to hemostasis by thrombin generation even in situations with platelet disorders. Furthermore, NN1731 demonstrated a higher hemostatic potential than rFVIIa.

Successful treatment of canine hemophilia by continuous expression of canine FVIIa

Continuous expression of activated factor VII (FVIIa) via gene transfer is a potential therapeutic approach for hemophilia patients with or without inhibitory antibodies to human factor VIII (FVIII) or IX (FIX). Here, we investigate whether gene transfer of an engineered canine FVIIa (cFVIIa) transgene can affect hemostasis in a canine model of hemophilia, a good predictor of efficacy of hemophilia treatments. Purified recombinant cFVIIa exhibited 12-fold higher tissue factor-dependent activity than purified recombinant zymogen cFVII. Subsequently, we generated a serotype 8 recombinant adeno-associated viral vector expressing cFVIIa from a liver-specific promoter. Vector delivery via the portal vein in hemophilia A and B dogs was well tolerated, and long-term expression of cFVIIa resulted in a shortening of the prothrombin time, partial correction of the whole blood clotting time and thromboelastography parameters, and a complete absence of spontaneous bleeding episodes. No evidence of hepatotoxicity, thrombotic complications, or inhibitory immune response was found. These data provide the first evidence for in vivo efficacy and safety of continuously expressed FVIIa as a FVIII/FIX-bypassing agent in a large animal model of hemophilia, avoiding the risk of inhibitor formation associated with bolus FVIII or FIX infusion.

Platelet storage lesion: a new understanding from a proteomic perspective

Platelet storage and availability for the purposes of transfusion are currently restricted by a markedly short shelf life of 5 to 7 days owing to an increased risk of bacterial growth and storage-related deterioration called the platelet storage lesion. Because most bacteria grow to confluence within 5 days during storage at room temperature, there is little increased risk of bacterial overgrowth with testing in place, and the only remaining issue is the quality of platelets during the extended storage. Although the manifestations of the storage lesion have been well studied using a variety of in vitro measures, the precise biochemical pathways involved in the initiation and progression of this process have yet to be identified. Proteomics has emerged as a powerful tool to identify and monitor changes during platelet storage and, in combination with biochemical and physiologic studies, facilitates the development of a sophisticated mechanistic view. In this review, we summarize recent experimental work that has led to a detailed overview of protein changes linked to platelet functions and signaling pathways, providing potential targets for inhibitors to ameliorate the storage lesion.

Monitoring survival and function of transfused platelets in Bernard-Soulier syndrome by flow cytometry and a cone and plate(let) analyzer (Impact-R)

BACKGROUND

Bernard-Soulier syndrome (BSS) patients may repeatedly require transfusion of platelets (PLTs). The hemostatic competence of transfused PLTs requires monitoring.

STUDY DESIGN AND METHODS

Flow cytometry and a cone and plate(let) analyzer (Impact-R, DiaMed) were used to monitor survival and function of transfused PLTs in a 7-year-old girl with BSS undergoing surgery. Flow cytometry was applied to differentiate autologous PLTs from transfused PLTs by staining for CD42b. The Impact, which measures PLT adhesion and aggregation in response to high shear stress, was used to evaluate PLT function.

RESULTS

Transfused PLTs were detectable by flow cytometry for 1 week after transfusion. While the patient's PLTs did not respond to high shear stress before transfusion, a normal response was documented by the Impact on the day after transfusion and 1 week thereafter.

CONCLUSION

Transfused PLTs were detectable by flow cytometry, and their functional activity was demonstrated by the Impact.

Proteomics and transfusion medicine: Future perspectives

Limited number of important discoveries have greatly contributed to the progresses achieved in the blood transfusion; ABO histo-blood groups, citrate as anticoagulant, fractionation of plasma proteins, plastic bags and apheresis machines. Three major types of blood products are transfused to patients: red cell concentrates, platelet concentrates and fresh frozen plasma. Several parameters of these products change during storage process and they have been well studied over the years. However, several aspects have completely been ignored; in particular those related to peptide and protein changes. This review presents what has been done using proteomic tools and the potentials of proteomics for transfusion medicine.

Monitoring survival and function of transfused platelets in Glanzmann thrombasthenia by flow cytometry and thrombelastography

Patients with Glanzmann thrombasthenia (GT) may form isoantibodies which induce refractoriness or inhibition of function of transfused platelets. We monitored the survival and function of transfused platelets by flow cytometry and thrombelastography in a patient with GT. Gating on CD42a+ allowed identification of even a few transfused platelets. Only by gating on these CD41+ CD42a+ cells were we able to demonstrate their capability to bind fibrinogen and PAC-1 upon activation. Platelets were rapidly cleared from the circulation as a result of boosted isoantibodies. The contribution of transfused platelets to clot formation was also demonstrated by thrombelastography by blocking their function with abciximab.

Challenges in the Therapeutic Use of a “So-Called” Universal Hemostatic Agent: Recombinant Factor VIIa

Recombinant factor VIIa (rFVIIa) was developed in the early 1990s to provide “bypassing” hemostatic therapy for hemophilia A and B patients with inhibitors. More recently, it has been licensed for use in patients with inherited deficiency of factor VII. Since it was licensed for use in hemophilia with inhibitors in the US, Europe, and other countries for these specific indications, it has been used selectively but in a wide array of clinical settings for uncontrolled hemorrhage in individuals without an inherited bleeding disorder. Many of these uses have been described in the medical literature as case reports or small, uncontrolled series. Several randomized clinical trials (RCT) for these “off-label” medical uses have been published in recent months and will serve as the focus of this review. In particular, a review of an RCT for spontaneous intracranial hemorrhage that has demonstrated clinical efficacy in reducing both mortality and volume of central nervous system hemorrhage will be offered. A brief discussion of hypothesized physiologic mechanisms of supraphysiologic doses of rFVIIa will introduce the clinical discussion of these broad off-label uses. Since rFVIIa is a very expensive therapy, possible strategies for optimizing its use in the these settings will be presented.