Further removal of factor v related antigen from bovine thrombin by utilizing a membrane-filtration step

Delayed spontaneous remission of acquired factor V inhibitor refractory to immunosuppressive therapy with pregnancy-associated improvement

Introduction: Acquired factor V inhibitor (AFVI) is a rare autoimmune bleeding disorder. The treatment of AFVI is challenging, and patients often require both bleeding control and inhibitor eradication. Methods: We conducted a retrospective analysis of the medical records of a 35-year-old Caucasian woman who presented with severe AFVI-induced bleeding and subsequent immunosuppressive therapy. Results: To provide haemostasis, rFVIIa was given with good efficacy. The patient was treated with various combinations of immunosuppressive regimens over the course of 2.5 years, including plasmapheresis plus immunoglobulins, dexamethasone + rituximab, cyclophosphamide + dexamethasone + rituximab + cyclosporine, cyclosporin + sirolimus + cyclophosphamide + dexamethasone, bortezomib + sirolimus + methylprednisolone, and sirolimus + mycophenolate mofetil. Although these treatment modalities resulted in intermittent partial reversals of AFVI over 2.5 years, eventually the inhibitor became therapy-resistant. However, following the discontinuation of all immunosuppressive therapy, the patient experienced a partial spontaneous remission, which was followed by a pregnancy. During the pregnancy, the FV activity increased to 54% and the coagulation parameters returned to normal levels. The patient underwent Caesarean section without any bleeding complications and delivered a healthy child. Discussion: The use of an activated bypassing agent for bleeding control is effective in patients with severe AFVI. The presented case is unique because the treatment regimens included multiple combinations of immunosuppressive agents. This demonstrates that AFVI patients may undergo spontaneous remission even after multiple courses of ineffective immunosuppressive protocols. Additionally, pregnancy-associated improvement of AFVI is an important finding that warrants further investigation.

Cross-Reactivity of Various Thrombin Products With Anti-Rabbit Antibodies to Bovine, Human, and Recombinant Thrombin

JMI-thrombin is used as topical hemostatic agent. While earlier clinically available JMI were reported to produce immunologic responses upon repeated exposure, the improved JMI, Recothrom?, and Evithrom? are claimed to be less immunogenic. Recothrom, despite its reduced immunogenic nature, upon repeated administration may result in the generation of antibodies (Abs) and that may cross react with bovine and human thrombin. Therefore, groups of rabbits were challenged repeatedly with Recothrom, Evithrom, and JMI over a 9-month period. Pre-immune blood and antiserum were collected from each rabbit on different time point. To determine their relative cross reactivity, JMI, Recothrom, and Evithrom were evaluated by western blotting using the rabbit IgG fractions. The results suggest that anti-Recothrom Abs cross-react with Evithrom and JMI in a time dependent fashion. Anti-JMI Abs did not cross-react with Recothrom, and Evithrom. Also, anti-Evithrom did not show any cross-reactivity with Recothrom and JMI at any time.

Immune Responses Associated With Perioperative Exposure and Reexposure to Topical Bovine Thrombin Do Not Impair Hemostasis

Topical bovine thrombin has been associated with immune responses and anecdotal reports of coagulopathy. This open-label study assessed the impact on clinical hemostasis of human antibodies to bovine thrombin (aBT) or factor V/Va (aBV/Va) in response to topical bovine thrombin (THROMBIN-JMI) in patients both with and without preexisting anti-bovine antibodies. Noninferiority analysis assessed primary endpoint for mean shift from baseline activated partial thromboplastin time (aPTT) at 48 hours postsurgery; secondary endpoints included changes from baseline antibodies/titers and coagulation parameters through 8 weeks postsurgery. A total of 550 patients underwent surgery with THROMBIN-JMI utilized at investigator’s discretion. Adjusted mean aPTT change in (+)aBT/(+)THROMBIN-JMI cohort was greater than (-)aBT/(-)THROMBIN-JMI cohort; 4.67-second upper confidence bound exceeded 4.5-second margin (based on assumed mean aPTT of 30 seconds) and noninferiority was not met. Post hoc analysis indicated noninferiority would have been met had noninferiority margin been set prior at relative 15% of actual baseline aPTT. Antibodies/titers were unchanged by THROMBIN-JMI exposure 48 hours postsurgery and unrelated to postsurgical changes in coagulation. Thus, THROMBIN-JMI exposure in patients with/without preexisting aBT or aBV/Va does not alter hemostasis.

Safety and Efficacy of Thrombin-JMI: A Multidisciplinary Expert Group Consensus

Background: The use of bovine thrombin has been an effective approach to aiding hemostasis during surgery for over 60 years. Its use has a reported association with the development of antibodies to coagulation factors with limited evidence to the clinical significance. Methods: The Collaborative Delphi survey methodology was used to develop a consensus on specified topic areas from a panel of 12 surgeons/scientists who have had experience with topical thrombins; it consisted of 2 rounds of a Web-based survey and a final live discussion. Results: Some key issues that reached consensus included: bovine, human plasma-derived and recombinant human thrombin are equally effective hemostatic agents with similar adverse event rates, and immunogenicity to a topical protein rarely translate into adverse events. Conclusions: Although a risk of immunogenicity is associated with all topical thrombins, no conclusive clinical evidence is available that these antibodies have any significant effect on short- and long-term clinical consequences.

Cross-reactivity of rabbit anti-bovine prothrombin/thrombin IgGs with bovine factor V/Va-related antigens

The purpose of this study was to determine whether rabbit anti-bovine prothrombin/thrombin immunoglobulin Gs (IgGs) would cross-react with bovine factor V/Va-related antigens. Bovine prothrombin, crude thrombin, as well as 2 purified versions of thrombin, that is, thrombin 4A (the previous version of Thrombin-JMI marketed prior to 2008) and 4B (the currently marketed version of Thrombin-JMI), were administrated to individual groups of rabbits on days 0, 21, 42, 91, 123, and 151 using standard immunologic methods. Blood was drawn from each rabbit on days 30, 50, 105, 137, and 165 and the pooled antisera from individual groups were purified to obtain the IgGs using protein G affinity columns. By probing bovine factor V/Va samples, the possible cross-reactivity of each IgG collected at different time points (from day 30 to day 165) was explored using Western blotting techniques. The results indicated that rabbit anti-bovine prothrombin and crude thrombin IgGs could cross-react strongly with bovine factor V/Va in an immunization time-dependent manner. However, antibodies generated in thrombin 4A-treated rabbits presented much weaker cross-reactivity with bovine factor V/Va. Furthermore, no cross-reactivity with bovine factor V/Va-related antigens was observed when the anti-bovine thrombin 4B IgG collected at any time point was used. The results suggest that thrombin 4B preparation contains the least bovine factor V/Va contaminants among the bovine prothrombin/thrombin preparations studied and the amount of bovine factor V/Va contaminants in bovine thrombin 4B is too small to elicit the generation of antibodies against bovine factor V/Va in rabbits.

Cross-reactivity of rabbit anti-bovine thrombin IgGs with human alpha-thrombin and a recombinant version of human thrombin (Recothrom)

It has been reported that patients exposed to topical bovine thrombin preparations may develop antibodies against bovine thrombin, factr V or various other proteins found in these preparations. Such antibodies can cross-react with human endogenous coagulation proteins and may lead to alterations in the coagulation laboratory parameters, hypersensitivity reactions, and severe bleeding or thrombosis. The underlying mechanisms for the coagulopathy are not fully understood yet. To better understand the cross-reactivity of anti-bovine thrombin antibodies with human corresponding coagulation proteins, bovine crude thrombin, and its purified versions, thrombin 4A (the old version of Thrombin-JMI before year 2008) and thrombin 4B (the current version of Thrombin-JMI on market), were used to generate relevant anti-bovine thrombin immunoglobulin G (IgGs) in rabbits. Using Western blotting, the cross-reactivity of each IgG with human alpha-thrombin and a recombinant version of human thrombin (Recothrom) was investigated. The results indicated that no cross-reactivity with either human alpha-thrombin or Recothrom was observed with both anti-bovine crude thrombin IgGs and thrombin 4B IgGs. However, anti-bovine thrombin 4A IgGs showed apparent cross-reactivity with human alpha-thrombin and Recothrom in a protein amount-dependent manner. Furthermore, the results revealed that the cross-reactivity of anti-bovine thrombin 4A IgGs with human alpha-thrombin and Recothrom was immunization time-dependent. The minimum concentration of 4A IgG required to exhibit cross-reactivity with human alpha-thrombin and Recothrom varied considerably among individual rabbits. These results indicate that rabbit anti-bovine thrombin IgGs can cross-react with human alpha-thrombin and Recothrom, suggesting that human antibodies against bovine thrombin may also cross-react with human recombinant thrombin. Thus, the patients who were previously exposed to bovine thrombin may also develop antibodies which can cross-react with human recombinant thrombin.

Relative purity of different bovine thrombin preparations

The aim of this study was to compare the relative purity of bovine crude thrombin and its purified forms, namely, thrombin 4A and thrombin 4B (the products of King Pharma, Middleton, Wisconsin) by virtue of the detection of bovine prothrombin-related antigens in these preparations. Bovine prothrombin was administered intravenously to 3 individual rabbits on days 0, 21, 42, 91, 123, and 151 using standard immunologic method. Blood was drawn from each rabbit on days 30, 50, 105, 137, and 165, and the pooled antisera from 3 rabbits were purified to isolate immunoglobulin G (IgG) using protein G affinity columns. Using Western blotting method, serially diluted bovine crude thrombin, thrombin 4A, and 4B preparations were probed using the prothrombin IgGs obtained from each time point to explore prothrombin-related antigens in these preparations. The results revealed that compared with the prothrombin IgG collected on day 30, the IgGs collected on days 50 to 165 showed a time-dependent increase in their ability to detect the prothrombin-related antigens in 3 bovine thrombin preparations studied. The lowest amount of crude thrombin, thrombin 4A, and 4B preparations that prothrombin IgG could detect was 0.125, 10, and 20 U, respectively. The rank order of the number of immunoreactive bands detectable in 3 bovine thrombin preparations probed by the prothrombin IgGs collected from any given time point was always the same: crude thrombin > thrombin 4A > thrombin 4B. The results indicate that thrombin 4B preparation contains the least amount of antigens detectable by prothrombin IgG, suggesting that relatively thrombin 4B represents the most purified thrombin preparation among the 3 thrombin preparations studied.

Safety of topical thrombins: the ongoing debate

Until recently, only bovine-derived thrombin was available for use as a stand-alone topical hemostat or as a component of other hemostatic devices. Concerns over a number of case reports of immune-mediated coagulopathies associated with the use of bovine-derived thrombin resulted in a United States Food and Drug Administration warning letter being issued in 1996 and the later addition of a boxed warning ("Black Box Warning") to all bovine-derived thrombin products. Since 2007, both a human-pooled plasma thrombin product and a recombinant thrombin have entered the market.

With the addition of these two products to the topical thrombin class, a unique situation has developed in which only a single member (bovine-derived thrombin) within the class carries the Food and Drug Administration's strongest cautionary language about possible adverse events related to an agent's use. Neither the human-pooled plasma thrombin nor the recombinant thrombin products have a boxed warning; although, the human-pooled plasma product does include a precaution/warning about infectious agent transmission - a warning common to products derived from human sources. This report will address this unique situation and the impact, clinical and non-clinical, that thrombin choice may have. Since alternatives are now available, institutions may need to revisit their formulary choice of thrombin preparation, taking into consideration the potential risks associated with bovine-derived products.

Topical thrombins: benefits and risks

Whether from surgical misadventure, inherent patient factors, or iatrogenic causes, postoperative bleeding can be a consequence of any surgical procedure. There are many methods and products available to assist in managing or preventing bleeding. For each method, there may be specific benefits and indications, but they may also carry some degree of risk. Topical thrombin is used extensively in many surgical specialties, especially in the cardiovascular and neurosurgical arenas where other hemostatic modalities may not be appropriate choices. As a class, topical thrombins are generally a safe and effective method for achieving intraoperative hemostasis; however, some members of the class carry associated risks with their use. For example, the United States Food and Drug Administration required the addition of a black-box warning to the prescribing information of bovine-derived thrombin, the oldest member of the class, due to concerns of immune-mediated coagulopathies developing after use. In addition, human thrombin derived from pooled plasma has its own, if theoretical, risk of transmitting infections due to viral or prion agents. We address the topical thrombin class and review each product in the context of the current literature.

Building an immune-mediated coagulopathy consensus: early recognition and evaluation to enhance post-surgical patient safety

Topical hemostats, fibrin sealants, and surgical adhesives are regularly used in a variety of surgical procedures involving multiple disciplines. Generally, these adjuncts to surgical hemostasis are valuable means for improving wound visualization, reducing blood loss or adding tissue adherence; however, some of these agents are responsible for under-recognized adverse reactions and outcomes. Bovine thrombin, for example, is a topical hemostat with a long history of clinical application that is widely used alone or in combination with other hemostatic agents. Hematologists and coagulation experts are aware that these agents can lead to development of an immune-mediated coagulopathy (IMC). A paucity of data on the incidence of IMC contributes to under-recognition and leaves many surgeons unaware that this clinical entity, originating from normal immune responses to foreign antigen exposure, requires enhanced post-operative vigilance and judicious clinical judgment to achieve best outcomes.

Postoperative bleeding may result from issues such as loosened ties or clips or the occurrence of a coagulopathy due to hemodilution, vitamin K deficiency, disseminated intravascular coagulation (DIC) or post-transfusion, post-shock coagulopathic states. Other causes, such as liver disease, may be ruled out by a careful patient history and common pre-operative liver function tests. Less common are coagulopathies secondary to pathologic immune responses. Such coagulopathies include those that may result from inherent patient problems such as patients with an immune dysfunction related to systemic lupus erythrematosus (SLE) or lymphoma that can invoke antibodies against native coagulation factors. Medical interventions may also provoke antibody formation in the form of self-directed anti-coagulation factor antibodies, that result in problematic bleeding; it is these iatrogenic post-operative coagulopathies, including those associated with bovine thrombin exposure and its clinical context, that this panel was convened to address.

The RETACC panel's goal was to attain a logical consensus by reviewing the scientific evidence surrounding IMC and to make recommendations for the clinical recognition, diagnosis and evaluation, and clinical management of these complications. In light of the under-recognition and under-reporting of IMC, and given the associated morbidity, utilization of health care resources, and potential economic impact to hospitals, the panel engaged in a detailed review of peer-reviewed reports of bovine thrombin associated IMC. From that clinical knowledge base, recommendations were developed to guide clinicians in the recognition, diagnosis, and management of this challenging condition.

Comparison of immunogenic potentials of bovine thrombin preparations

Using a membrane filtration step, bovine crude thrombin was purified into thrombin 4A and 4B preparations. The purpose of this study was to determine whether the improved purity of a bovine thrombin preparation can reduce its overall immunogenic potential and lower the risk of development of factor V antibodies. Bovine crude thrombin and its purified versions, thrombin 4A and 4B, were administered to individual groups of rabbits on days 0, 21, 42, 91, 123, and 151 using standard immunologic methods. Blood was drawn from each rabbit on days 30, 50, 105, 137, and 165, and the pooled antisera from individual groups were purified to obtain the Ig Gs using protein G affinity columns. Using Western blotting, the specificity of each immunoglobulin G collected at the first time point (day 30) and last time point (day 165) was determined. The results of Western blotting using the Ig Gs collected on days 30 and 165 were consistent; both demonstrating that thrombin 4B has the least immunogenic potential among the 3 thrombin preparations tested. Compared with the immunoglobulin Gs collected on day 30, the Ig Gs from day 165 did not show obvious difference regarding their ability to detect antigens in bovine thrombin samples. Neither showed cross-reactivity with human coagulation factors nor the recognition of bovine factor Va antigens. These results suggest that despite the presence of a trace amount of bovine factor Va antigen in bovine thrombin preparations, these contaminants failed to elicit the generation of antibodies against factor Va light chain in rabbit.

The unresolved safety concerns of bovine thrombin

A recent review has suggested that bovine thrombin is not associated with an increased risk of bleeding in surgical populations. In spite of extremely limited evidence available, many valuable resources (e.g. safety surveillance and post-marketing programs, case reports) were excluded in reaching this conclusion. While waiting for the adequately powered, controlled clinical trials to address the effects of bovine thrombin on bleeding and thrombotic events, the potential risk cannot be simply ignored. Rather, continued vigilance in the post-surgical setting for bleeding events that may be associated with the development of acquired coagulation factor inhibitors following bovine thrombin administration is warranted.

Reduced Immunogenic Potential of Membrane Filtered Bovine Thrombin Preparations for Hemostatic Application

There is concern that exposure to bovine thrombin can result in the development of antibodies, usually against factor V/Va, which can lead to hemostatic abnormalities. It is thought that purer preparations of bovine thrombin might be less immunogenic. Utilizing newer methods including a membrane filtration step, bovine crude thrombin is further purified into thrombin 4A and 4B preparations which exhibit a higher specific activity and are devoid of some of the protein contaminants. Bovine crude thrombin and its purified versions were administered intravenously to individual groups of rabbits using standard immunologic protocols. Antiserum was drawn from each rabbit and the pooled antisera were purified to obtain the IgGs using protein G affinity columns. The results suggest that the reported purification process, including filtration, resulted in the removal of most of the antigens found in crude thrombin, and that none of these preparations generated any detectable antibodies against bovine factor V related antigens.