Immunosuppressive effects of factor IX products: an in vitro study

Why do inhibitors develop? Principles of and factors influencing the risk for inhibitor development in haemophilia

The formation of inhibitory alloantibodies is, in the postinfectious era, the most severe and costly complication of replacement therapy in patients with haemophilia. The complexity of the immune response to the infused factor becomes more and more obvious as knowledge in the area increases. Antibodies develop as a result of a complex multi-factorial interaction between antigen-presenting cells, T- and B-lymphocytes. Genetic susceptibility of cell surface molecules, such as the major histocompatibility complex, the T-cell receptor and cytokine receptors, as well as various immunomodulatory molecules have a major impact on the outcome. In addition, environmental factors probably influence the risk of inhibitor development. The current concept of inhibitor development is reviewed. A better understanding of the pathophysiological mechanisms involved will facilitate improvement of therapy in the future, and hopefully provide an opportunity to prevent this complication of treatment.

Overview of Inhibitors

Inhibitory antibodies that develop in patients with hemophilia render standard therapy with factor concentrates ineffective. Several factors may influence inhibitor incidence, including genetics, the type of factor concentrate, and environment. A higher incidence of inhibitors in siblings compared to extended relatives, and in African Americans compared to Caucasians, suggests that genetics may play an important role in inhibitor development; however, genetic markers that indicate a predisposition for inhibitor development have yet to be identified. In addition, the appearance of inhibitors in immunologically challenged patients points to the role of the immune response system in the development of inhibitor antibodies, an area that warrants further study. Thus, the medical community faces the difficult task of developing new, improved therapies to combat inhibitors in patients with hemophilia, a task that will require careful consideration of the roles of environmental factors, the immune system, and genetics in inhibitor development.

The effects of inhaled nitric oxide on the levels of cGMP plasma and lung tissue in a canine model of smoke inhalation injury

The effects of inhaled nitric oxide (NO) on pulmonary hypertension and their mechanisms were studied in a canine model of smoke inhalation injury. Twenty-one dogs were randomly divided into three groups: four dogs constituted the normal control group, eight dogs subjected to smoke inhalation followed by O(2) inhalation (FiO(2)=0.45) constituted the injury control group, and nine dogs inhaling a mixture of O(2) and 45ppm nitric oxide after smoke exposure served as the treatment group. The levels of cyclic guanosine monophosphate (cGMP) in arterial plasma of the treatment group were higher than that of the control group at 5, 8, and 12h after smoke exposure, while the levels of cGMP in lung tissue were also significantly higher compared with that of the control group (P<0.01). The levels of cGMP of injury control group were decreased significantly compared with normal controls (P<0.05). Pulmonary vasoconstriction following smoke inhalation was significantly attenuated by inhalation of NO (P<0.05), which exerted no apparent effect on the systemic circulation (P>0.05). Inhalation of NO may lower pulmonary hypertension induced by smoke inhalation injury in dogs. The selective effect of NO on pulmonary circulation may be attributed to an increase in level of cGMP in smooth muscle cells of the lung tissue after inhalation of NO.

Use of recombinant factor IX in subjects with haemophilia B undergoing surgery

Recombinant human FIX (rFIX) was evaluated in 28 subjects, including 26 with mild, moderate, or severe haemophilia B and two haemophilia B carriers undergoing 36 surgical procedures. Preoperative rFIX dose was highly correlated with postinfusion FIX activity, r=0.61, P=0.0158. Peri- and post-operative estimated blood loss was similar to that expected in non-haemophilic individuals, and haemostasis was rated as excellent or good in 34 of 35 (97.1%) of the operative procedures. Transfusions were required in five of 36 (13.9%) procedures, including one liver transplantation, and three knee and one hip arthroplasties. Adverse events occurred in 15 of 28 (53.6%) subjects, but there were no perioperative haemorrhages, thromboembolic events, coagulation activation, viral transmission, or inhibitor formation. A transient low-responding FIX inhibitor developed in one subject preoperatively, but required no change in treatment and resolved 15 months later. Thus, rFIX was found to be safe and effective in achieving haemostasis in subjects with FIX deficiency undergoing surgery.