Non-overt disseminated intravascular coagulation in patients during treatment with antithymocyte globulin for unrelated allogeneic hematopoietic stem cell transplantation

Immunothrombosis and the molecular control of tissue factor by pyroptosis: prospects for new anticoagulants

The interplay between innate immunity and coagulation after infection or injury, termed immunothrombosis, is the primary cause of disseminated intravascular coagulation (DIC), a condition that occurs in sepsis. Thrombosis associated with DIC is the leading cause of death worldwide. Interest in immunothrombosis has grown because of COVID-19, the respiratory disease caused by SARS-CoV-2, which has been termed a syndrome of dysregulated immunothrombosis. As the relatively new field of immunothrombosis expands at a rapid pace, the focus of academic and pharmacological research has shifted from generating treatments targeted at the traditional 'waterfall' model of coagulation to therapies better directed towards immune components that drive coagulopathies. Immunothrombosis can be initiated in macrophages by cleavage of the non-canonical inflammasome which contains caspase-11. This leads to release of tissue factor (TF), a membrane glycoprotein receptor that forms a high-affinity complex with coagulation factor VII/VIIa to proteolytically activate factors IX to IXa and X to Xa, generating thrombin and leading to fibrin formation and platelet activation. The mechanism involves the post-translational activation of TF, termed decryption, and release of decrypted TF via caspase-11-mediated pyroptosis. During aberrant immunothrombosis, decryption of TF leads to thromboinflammation, sepsis, and DIC. Therefore, developing therapies to target pyroptosis have emerged as an attractive concept to counteract dysregulated immunothrombosis. In this review, we detail the three mechanisms of TF control: concurrent induction of TF, caspase-11, and NLRP3 (signal 1); TF decryption, which increases its procoagulant activity (signal 2); and accelerated release of TF into the intravascular space via pyroptosis (signal 3). In this way, decryption of TF is analogous to the two signals of NLRP3 inflammasome activation, whereby induction of pro-IL-1β and NLRP3 (signal 1) is followed by activation of NLRP3 (signal 2). We describe in detail TF decryption, which involves pathogen-induced alterations in the composition of the plasma membrane and modification of key cysteines on TF, particularly at the location of the critical, allosterically regulated disulfide bond of TF in its 219-residue extracellular domain. In addition, we speculate towards the importance of identifying new therapeutics to block immunothrombotic triggering of TF, which can involve inhibition of pyroptosis to limit TF release, or the direct targeting of TF decryption using cysteine-modifying therapeutics.

Anti-thymocyte globulin-induced hyperbilirubinemia in patients with myelofibrosis undergoing allogeneic hematopoietic cell transplantation

Allogeneic hematopoietic cell transplantation (allo-HCT) remains the only curative treatment option for myelofibrosis (MF) despite the emergence of novel targeted therapies. To reduce graft rejection and graft-versus-host disease (GvHD), current allo-HCT protocols often include in vivo T lymphocyte depletion using polyclonal anti-thymocyte globulin (ATG). Shortly after ATG administration, an immediate inflammatory response with fever, chills, and laboratory alterations such as cytopenias, elevation of serum C-reactive protein, bilirubin, and transaminases can develop. Here, we explore whether MF patients, who commonly exhibit extramedullary hematopoiesis in the liver, might be particularly susceptible to ATG-induced liver toxicity. To test this hypothesis, we analyzed 130 control and 94 MF patients from three transplant centers treated with or without ATG during the allo-HCT conditioning regimen. Indeed, hyperbilirubinemia was found in nearly every MF patient treated with ATG (MF-ATG 54/60 = 90 %) as compared to non-ATG treated MF (MF-noATG 15/34 = 44.1 %, p < 0.001) and respectively ATG-treated non-MF patients of the control group (control-ATG, 43/77 = 56 %, p < 0.001). In contrast, transaminases were only inconsistently elevated. Hyperbilirubinemia was in most cases self-limiting and not predictive of increased incidence of non-relapse mortality, hepatic sinusoidal obstruction syndrome (SOS) or liver GvHD. In sum, awareness of this stereotypic bilirubin elevation in MF patients treated with ATG provides a relatively benign explanation for hyperbilirubinemia occurring in these patients during the early transplant. However, attention to drug levels of biliary excreted drugs is warranted, since altered bile flow may influence their clearance and enhance toxicity (e.g., busulfan, antifungal agents).

Mechanism of Platelet Activation and Hypercoagulability by Antithymocyte Globulins (ATG)

T cell depletion with antithymocyte globulins (ATG) can be complicated by thrombopenia and hypercoagulability. The underlying mechanism is still unclear. We found that binding of ATG to platelets caused platelet aggregation, α-granule release, membrane phosphatidylserine exposure and the rapid release of procoagulant platelet microvesicles (MV). Platelet activation and MV release were complement-dependent and required membrane insertion of C5b-8 but not stable lytic pore formation by C5b-9. ATG also activated platelets via binding to the low-affinity Fc gamma receptor FcγRII. However, only complement inhibition but not blockade of FcγRII prevented MV release and subsequent thrombin activation in plasma. In 19 hematopoietic stem cell and kidney transplant patients, ATG treatment resulted in thrombopenia and increased plasma levels of d-dimer and thrombin-antithrombin complexes. Flow cytometric analysis of complement fragments on platelet MV in patient plasma confirmed dose-dependent complement activation by ATG. However, the rapid rise in MV numbers observed in vitro was not seen during ATG treatment. In vitro experiments suggested that this was due to adherence of C3b-tagged MV to red blood cells via complement receptor CR1. These data suggest a clinically relevant link between complement activation and thrombin generation and offer a potential mechanism underlying ATG-induced hypercoagulability.

Ocular manifestations of idiopathic aplastic anemia: retrospective study and literature review

Aplastic anemia (AA) is a rare disease with few reports on its ophthalmic manifestations. The ocular findings are described in a retrospective consecutive series of 719 AA Korean patients followed at the Hematology Clinic of The Catholic University of Korea. Out of a total of 719 patients, 269 patients had eye examinations, 156 patients had retinal evaluation, and 37 (23.7%) had retinal findings. These 37 patients had unilateral retinal hemorrhage in seven and bilateral retinal hemorrhage in 30 with mean hemoglobin of 6.6 g/dL (range 2.7–12.6 g/dL) and platelet counts of 18.8×10⁹/L (range 4–157×10⁹/L); central retinal vein occlusion-like picture occurred in nine patients and these had similar rheology to the rest of the subjects; optic disc edema, cotton-wool spots, macular edema, and dry eyes occurred in two, three, five, and three patients, respectively. In this Korean series of 141 subjects with AA, systemic bleeding occurred in 24.8% of subjects, retinal hemorrhage in 37% of subjects, and any bleeding site (eye or elsewhere) occurred in 47.5% of subjects with AA. A literature review (1958–2010) of 200 AA cases revealed retinal hemorrhages in 56%, subhyaloid or vitreous hemorrhage in 9%, peripheral retinal vasculopathy in 5.5%, and cotton-wool spots, Sjögren’s syndrome, or optic disc edema in 4% each. The prevalence of retinopathy among series of AA patients varied from 20% to 28.3%, which is consistent with the Korean series of 24.8%. Management of AA patients needs to involve multiple specialties, including hematologists, ophthalmologists, and infectious disease specialists.

Antithymocyte antibody-induced coagulopathy in renal transplant recipients

BACKGROUND

Antithymocyte antibody (ATA) remains the most commonly used induction immunosuppressive agent in renal transplantation (RT). To date, few case reports of ATA-induced coagulopathy exist.

METHODS

We performed a single-center, retrospective analysis of renal transplant recipients (RTRs) who underwent RT followed by ATA therapy between 2007 and 2011. The protocol used for deceased donor and unrelated living donor recipient immunosuppression was Thymoglobulin (TMG), methylprednisolone, Cellcept, Prograf, and Rapamune. In related living donor recipients, Simulect (SIM) was substituted for TMG. The international normalized ratio (INR) was routinely checked on days 0 and 2, and thereafter at the discretion of the surgeon. RTRs were transfused packed red blood cells (PRBCs) or fresh frozen plasma (FFP) at the discretion of the surgeon.

RESULTS

During the study period, 257 RTs were performed at our institution. The following 18 RTR were excluded: simultaneous kidney and pancreas transplant recipients (4), RTRs on warfarin at the time of admission (2), RTRs who received OKT3 (2), and RTRs with INR ≥ 1.2 at the time of admission (10). Of the remaining 239 RTR, 208 (87%) underwent TMG induction therapy; 31 RTR (13%) underwent SIM induction therapy. The mean INR peaked in both groups on day 4 but was higher in TMG recipients (TMG 1.35, SIM 1.20). FFP was transfused in 65 TMG (31%) and 3 SIM (10%) recipients (P = .01); PRBCs were transfused in 88 TMG (44%) and 6 SIM (19%) recipients (P = .02). No patients returned to the operating room for bleeding complications within 7 days of RT. Patient age, gender, ethnicity, and diabetes status were not statistically significant factors in the development of coagulopathy.

CONCLUSION

TMG administration is associated with coagulopathy. Using an INR screening protocol and an aggressive transfusion protocol, bleeding complications associated with coagulopathy can be avoided in this higher-risk group.

Management of bleeding in the terminally ill patient

Clinically significant bleeding occurs in approximately 6%-10% of patients in the palliative-care setting. Bleeding can range from persistent and small in quantity (but enough to interfere with a patient's quality of life), to catastrophic bleeding that ultimately leads to the rapid demise of the patient. Uncontrolled bleeding can be very distressing for staff, patients and families. Advanced planning is necessary in all bleeding circumstances. This session will review the types of cancer associated with bleeding, as well as management options for these situations. Emphasis will be placed on aspects of communication with families.

Rapid activation of monocyte tissue factor by antithymocyte globulin is dependent on complement and protein disulfide isomerase

Lymphocyte depletion with antithymocyte globulin (ATG) can be complicated by systemic coagulation activation. We found that ATG activated tissue factor procoagulant activity (TF PCA) on monocytic cells more potently than other stimuli that decrypt TF, including cell disruption, TF pathway inhibitor inhibition, and calcium ionophore treatment. Induction of TF PCA by ATG was dependent on lipid raft integrity and complement activation. We showed that ATG-mediated TF activation required complement activation until assembly of the C5b-7 membrane insertion complex, but not lytic pore formation by the membrane attack complex C5b-9. Consistently, induction of TF PCA by ATG did not require maximal phosphatidylserine membrane exposure and was not correlated with the magnitude of complement-induced lytic cell injury. Blockade of free thiols, an inhibitory monoclonal antibody to protein disulfide isomerase (PDI), and the small-molecule PDI antagonist quercetin-3-rutinoside prevented ATG-mediated TF activation, and C5 complement activation resulted in oxidation of cell surface PDI. This rapid and potent mechanism of cellular TF activation represents a novel connection between the complement system and cell surface PDI-mediated thiol-disulfide exchange. Delineation of this clinically relevant mechanism of activation of the extrinsic coagulation pathway during immunosuppressive therapy with ATG may have broader implications for vascular thrombosis associated with inflammatory disorders.

P-selectin glycoprotein ligand-1 positive microparticles in allogeneic stem cell transplantation of hematologic malignancies

P-selectin and its receptor P-selectin glycoprotein ligand-1 (PSGL-1) mediate adhesion between leukocytes, tumor cells (including leukemias and lymphomas), and platelets, and play an important role in hematopoiesis, T cell activation, and cancer growth and metastasis. As microparticles (MPs) are released from activated or apoptotic cells, there should be significant numbers of circulating PSGL-1-bearing MPs in the blood of patients undergoing allogeneic stem cell transplantation (alloSCT). We enumerated PSGL-1-expressing MPs in plasma samples from 30 consecutive patients with hematologic disorders at different time points during the course of alloSCT by flow cytometry and analyzed their relation to cell counts, patient characteristics, and clinical outcome. Median follow-up time of surviving patients was 1,772 days (range 1272-1981 days). Nineteen patients (63.3%) died, 10 due to progression of disease (33.3%). The PSGL-1 MPs significantly declined during conditioning therapy but increased again after transfusion of donor cells and even more at the time of engraftment. Numbers >250/μL after graft transfusion were associated with a shorter time to engraftment for patients receiving fresh peripheral stem cell grafts (median, 15 vs. 21 days; p = 0.049). Furthermore, low PSGL-1 MP values at those two time points were associated with a higher risk of progress/relapse in univariate analysis (p = 0.008-0.014; hazard ratio [HR] = 15.0-42.0) with cumulative incidences at 5 years of 81.8% versus 28.6% and 85.7% versus 20.0%, respectively. In conclusion, PSGL-1 microparticles show a characteristic course during alloSCT and their possible association with relapse/progress requires further evaluation of the PSGL-1/P-selectin interaction in leukemias and lymphomas.

Decreased activity of soluble thrombomodulin and plasma procoagulant phospholipids in childhood bone marrow transplantation with severe complications

BACKGROUND

Complications of bone marrow transplantation (BMT) are usually considered to be related to the secretion of inflammatory cytokines, which generate membrane microparticles rich in procoagulant phospholipids (PPL) from different cellular origins and release of endothelial proteins such as thrombomodulin (TM). The use of soluble TM quantified by ELISA (TM:Ag) as a marker of endothelial injury is complex in children since it is age-dependent.

MATERIALS AND METHODS

Using a functional assay which quantifies the activity of sTM activity (TMa), we performed a pilot study to analyze the ratio TMa/TM:Ag in a control group of 25 healthy children, 8 children with autologous and 16 children with allogeneic BMT. In this last group, 8 experienced BMT complications. In addition, we used a functional assay which quantifies PPL.

RESULTS

In healthy children the ratio TMa/TM:Ag was independent of age and stable in children with a favorable outcome but significantly (p<0.05) reduced by the use of antithymocyte globulin during the conditioning regimen, and regularly decreased in children with BMT complications. Surprisingly, low plasma PPL levels were associated with a poor outcome.

CONCLUSION

The ratio TMa/TM:Ag could constitute a marker of endothelium injury, and its follow-up could be of interest for an early discrimination of children with high risk of complications during allogeneic BMT. The decrease of PPL could be also another marker of a poor evolution and deserves further investigations.

Early thrombin generation and impaired fibrinolysis after SCT associate with acute GVHD

The evolution of coagulation and fibrinolysis has not been thoroughly evaluated in allogeneic SCT. In this pilot study, we characterized the adaptive mechanisms of coagulation and fibrinolysis during allogeneic SCT and 3-month follow-up and studied possible associations with outcome, including acute GVHD. Thirty patients underwent SCT for a haematological malignancy after myeloablative conditioning. Nineteen patients received the transplant from an HLA-identical sibling and 11 from an unrelated donor. GVHD prophylaxis consisted of CYA and MTX, with methylprednisolone in sibling transplants. Serial coagulation and fibrinolytic activity markers were assessed, including prothrombin fragments 1+2 (F1+2), thrombin time, D-dimer, tissue-type plasminogen-activator (tPA) and plasminogen-activator inhibitor (PAI-1). Early during conditioning therapy, F1+2 and D-dimer increased threefold indicating thrombin generation and fibrin turnover. TPA activity peaked before engraftment, concurring with diminished PAI-1. At 10 days after transplantation shortened thrombin time (<15 s), F1+2 exceeding 0.7 nmol/L and PAI-1 3.0 IU/mL were associated with the development of GVHD. In conclusion, early maladaptation, that is, upregulated thrombin generation and inhibition of fibrinolysis, occurred in one-third of the SCT patients associating with the development of GVHD, a finding suggesting an interplay between coagulation and immunology during SCT.

Hepatotoxicity induced by horse ATG and reversed by rabbit ATG: a case report

BACKGROUND

The use of antilymphocyte agents has improved patient and graft survival in hematopoietic stem cell and solid organ transplantation but has been associated with the development of short-term toxicities as well as long-term complications.

CASE PRESENTATION

We report a young female with Fanconi anemia who received antithymocyte globulin as part of the conditioning regimen prior to her planned allogeneic hematopoietic stem cell transplant at King Faisal Specialist Hospital and Research Centre in Riyadh. She developed sudden and severe hepatotoxicity after receiving the first dose of horse antithymocyte globulin, manifested by marked elevation of serum transaminases and mild elevation of serum bilirubin level. Immediately after withdrawal of the offending agent and shifting to the rabbit form of antithymocyte globulin, the gross liver dysfunction started to subside and the hepatic profile results returned to the pre-transplant levels few weeks later. The patient had her allogeneic hematopoietic stem cell transplant as planned without any further hepatic complications. After having a successful allograft, she was discharged from the stem cell transplant unit. During her follow up at the outpatient clinic, the patient remained very well and no major complication was encountered.

CONCLUSION

Hepatotoxicity related to the utilization of antithymocyte globulin varies considerably in severity and may be transient or long standing. There may be individual or population based susceptibilities to the development of side effects and these adverse reactions may also vary with the choice of the agent used. Encountering adverse effects with one type of antithymocyte agents should not discourage clinicians from shifting to another type in situations where continuation of the drug is vital.

Assessment of the coagulation profile in hemato-oncological patients receiving ATG-based conditioning treatment for allogeneic stem cell transplantation

Antithymocyte globulin (ATG) is increasingly used in pre-allogeneic stem cell transplantation (allo-SCT) conditioning regimens to prevent graft rejection and graft-versus-host disease. However, ATG was also found to be associated with increased incidence of thrombosis during organ transplantation. In the present study, we tested the coagulation status of 21 patients with hematologic malignancies undergoing allo-SCT who received ATG-based (11 patients) or non-ATG-based (10) conditioning treatment. We assessed several thrombophilia markers as well as circulating total and endothelial microparticles (TMP/EMP) and soluble CD40 ligand (CD40L). No significant difference in the mean values of prothrombin time, partial thromboplastin time, fibrinogen, antithrombin, protein C, protein S, thrombin-antithrombin III complex, homocysteine levels, prevalence of genetic thrombophilia markers and levels of EMP, TMP or CD40L was observed between the ATG-treated and ATG-untreated patients, as well as before and after conditioning in each group separately. Platelet counts decreased significantly in ATG-treated patients; however, this decrease was not associated with clinical or laboratory evidence of disseminated intravascular coagulation. No patient developed thromboembolic event or veno-occlusive liver disease. Our results suggest that allo-SCT is not associated with increased hypercoagulability and addition of ATG to conditioning regimen has no significant procoagulant effect.

Bleeding complications after hematopoietic stem cell transplantation

Hemostatic disturbances are common in patients undergoing hematopoietic stem cell transplantation (HSCT), and have a significant impact on morbidity and mortality. Graft-versus-host disease (GvHD), in which the donor's T lymphocytes mount an immune response against the recipient's cells, is a life-threatening condition that correlates strongly with the incidence and severity of bleeding episodes, highlighting the complex interaction between the hemostatic and immunological systems. Patients with GvHD of the gut also exhibit a deficiency of factor XIII (FXIII), further increasing the hemorrhagic risk. Among other risk factors for bleeding complications is use of the purified polyclonal immunoglobulin G (IgG), antithymocyte globulin (ATG). Although frequently used in preparative conditioning regimens, ATG may contribute to leukopenia, platelet reduction, and signs of disseminated intravascular coagulation (DIC). This paper will examine the cause and incidence of bleeding complications in patients undergoing HSCT, the potential contribution of GvHD and ATG to such bleeds, and the close interaction between the hemostatic and immune systems. The role of recombinant FVIIa as a hemostatic agent for the treatment of HSCT-associated hemorrhage will be briefly explored.