Thrombotic Thrombocytopenic Purpura (TTP)–An Ultra-Rare Life-Threatening Classic Hematology Disorder
Thrombotic thrombocytopenic purpura (TTP) is a rare thrombotic microangiopathy characterized by microangiopathic hemolytic anemia, severe thrombocytopenia, and organ ischemia linked to disseminated microvascular platelet-rich thrombi. It is specifically related to a severe deficiency in ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeats, member 13), the specific von Willebrand factor-cleaving protease. There are two main types of TTP – inherited TTP and acquired TTP.
The first acute episode of TTP can be observed during adulthood, with a predominant anti-ADAMTS13 autoimmune etiology. TTP begins as soon as childhood, with frequent inherited forms in rare cases. TTP is approximately 2-fold more frequent in women, and its outcome is characterized by a relapsing tendency. It is a rare disease that affects approximately only 4 to 11 cases per 100,000 population in the United States. The average annual incidence of TTP is observed to be around 14.89 per 100,000 hospitalizations with an Annual Percent Change (APC) of 0.99 which is statistically not significant.
Currently, the first line of therapy for acute TTP is based on daily therapeutic plasma exchange supplying deficient ADAMTS13 with or without steroids. Additional immune modulators that target ADAMTS13 autoantibodies are based on steroids and the humanized anti-CD20 monoclonal antibody rituximab. The treatment approach is highly effective in inducing clinical remission in approximately 80–90% of affected patients and is associated with the long-term survival of approximately 90%. Recently, The US Food and Drug Administration has approved Cablivi (caplacizumab-yhdp) injection, the first therapy specifically indicated, in combination with plasma exchange and immunosuppressive therapy, for the treatment of adult patients with acquired thrombotic thrombocytopenic purpura (aTTP). It is the first targeted treatment that inhibits the formation of blood clots and provides a new treatment option for patients that may reduce recurrences.
The key players involved in the development of the therapeutics of TTP include Shire and Omeros. SHP655 (Shire) has been granted with Fast Track Designation by the US Food and Drug Administration for the treatment of acute episodes of hereditary thrombotic thrombocytopenic purpura (hTTP) in patients with a constitutional deficiency of the von Willebrand factor-cleaving (VWF) protease ADAMTS13.
The primary approach of removing or suppressing the production of autoantibodies to ADAMTS13 resulted in a large decrease in mortality rates among patients with acquired TTP. While newer immunosuppressive drugs, such as rituximab and bortezomib, have improved disease outcomes, none of these has provided definitive cures. The novel approaches targeting UL-vWF multimers and the ADAMTS13 enzyme hold significant promise. A multifaceted approach simultaneously involving suppressing ADAMTS13 autoantibodies, repleting ADAMTS13 enzymes, and decreasing vWF agglutination to platelets may ultimately be the most effective treatment strategy to induce remission and prevent relapses.
Shire has received Fast Track Designation by the US Food and Drug Administration (FDA) for recombinant ADAMTS13 (SHP655 – historically known as BAX930) for the treatment of acute episodes of hereditary thrombotic thrombocytopenic purpura (hTTP) in patients with a constitutional deficiency of the von Willebrand factor-cleaving (VWF) protease ADAMTS13.