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Pathologists at The University of Texas Medical School at Houston have developed a chemically modified protein that may help people with a hard-to-treat form of a genetic bleeding disorder known as Hemophilia A. The discovery and the results of pre-clinical tests appear in the May 2008 issue of the Journal of Biological Chemistry.
Planque, S., Escobar, M.A., Nishiyama, Y., and Paul, S. A protease resistant factor VIII analog for blockade of inhibitory antibodies. 52nd ASH Annual Meeting and Exposition, December 4-7, 2010, Orlando, Florida. Abstract
Planque, S., Escobar, M.A., Smith, K.C., Taguchi, H., Nishiyama, Y., Donnachie, E., Pratt, K.P., and Paul, S. Covalent inactivation of factor VIII antibodies from hemophilia A patients by an electrophilic FVIII analog. J Biol Chem. 2008 May 2;283(18):11876-86. Abstract
Smith, K.C., Planque, S.A., Nishiyama, Y., Escobar, M.A., and Paul, S. A covalent reactive antigen analog to Factor VIII reduces antibody production in memory B cells after re-stimulation with FVIII. 21st Congress of the International Society on Thrombosis and Haemostasis. July 6–12, 2007; Geneva, Switzerland. Abstract 3141. J Throm Haemos. 5 (Suppl. 2) #O-M-063.
Smith, K.C., Planque, S., Nishiyama, Y., Taguchi, H., Escobar, M., and Paul, S. Pretreatment of CD138- B Lymphocytes with a covalent reactive antigen analog to factor VIII reduces antibody production in response to FVIII. Immunology 2007; 94th Annual Meeting. The American Association of Immunologists, May 18-22, 2007; Miami, FL. Abstract 675. Published in J Immunol 178:88.14; Apr 2007. Poster presentation Abstract
With a shortage of the blood-clotting protein Factor VIII (FVIII), people with Hemophilia A typically receive injections of FVIII derived from plasma or produced synthetically to control potentially life-threatening episodes of bleeding. Unfortunately as many as 1 in 3 people with Hemophilia A produce inhibitor antibodies, which attack the externally-administered FVIII and negate its blood-clotting benefits.
To combat this problem, scientists in the laboratory of Sudhir Paul, Ph.D., at The University of Texas Medical School at Houston, developed a chemically modified version of FVIII which during laboratory tests neutralized these inhibitor antibodies, thus paving the way for the correction of the blood-coagulating process. The modification is called electrophilic FVIII analog (E-FVIII).
Working on a potential treatment for people with intractable hemophilia from left to right are: Keri Smith, PhD; Sudhir Paul, PhD; Hiroaki Taguchi, PhD; Yasuhiro Nishiyama, PhD; and Stephanie Planque, PhD.
“It’s a two-step process,’’ said Paul, the senior author. “The E-FVIII permanently inactivates the antibodies that inhibit blood clotting in 20 to 30 percent of patients receiving Factor VIII replacement therapy. Once the antibodies are cleared, additional FVIII can be injected.” The study involved blood donated by eight people with FVIII-resistant Hemophilia A.
Today, people with FVIII-resistant Hemophilia A have limited treatment options, said co-author Keri Smith, Ph.D., an assistant professor of pathology and laboratory medicine at the UT Medical School at Houston. Those options include bypass therapy or multiple FVIII injections. Both are prohibitively expensive and often ineffective to meet emergency blood-clotting needs.
E-FVIII might provide a more economically feasible method of treating inhibitor antibodies, Smith said.
There is no cure for Hemophilia A, and it primarily affects males. About one of every 7,000 males born in the United States has this condition. A person with hemophilia bleeds longer than a person without hemophilia.
Stephanie Planque, who is lead author and is working towards her Ph.D. degree, helped conceive the chemical inactivation principle behind the study. The modified FVIII analog was produced by pathology faculty Hiroaki Taguchi, Ph.D., and Yasuhiro Nishiyama, Ph.D., using newly developed synthesis methods. Miguel Escobar, M.D., of the department of pediatrics and internal medicine at the UT Medical School at Houston and the Gulf States Hemophilia and Thrombophilia Center, led the clinical aspects of the work, and Kathleen Pratt, Ph.D., at the Puget Sound Blood Center and Division of Hematology, University of Washington, Seattle, contributed a genetically-produced protein that helped the study reach its conclusions.
According to Paul, the next step involves clinical trials. “E-FVIII is a first generation reagent. Future genetic and chemical manipulations may help develop improved E-FVIII analogs,” Paul wrote in the paper.
Work was supported by the Hemophilia Associations of New York and Georgia and the National Institutes of Health. The study is titled “Covalent Inactivation of Factor VIII Antibodies from Hemophilia A Patients by an Electrophilic FVIII Analog.”
Covalent Tolerance Induction to Factor VIII
Recent studies indicate the universal presence in antibody (Ab) combining sites of nucleophiles that can bind electrophilic antigens covalently guided by traditional noncovalent recognition of antigenic epitopes. In this proposal, we will synthesize various Factor VIII (FVIII) analogs containing electrophilic groups, designated covalently reactive analogs (FVIII-CRAs). Whole FVIII, individual FVIII domains and certain synthetic FVIII peptides will be employed as the source material for preparing the FVIII-CRAs. We will screen the FVIII-CRAs for specific and irreversible binding to immunoglobulins expressed as components of the B cell receptors (BCRs) on the surface of anti-FVIII Ab producing B cells from hemophilia A patients. Previous studies have suggested that BCR saturation induces B cell tolerance. According to the laws of mass action, the irreversible reaction of a CRA is predicted to result in facile BCR saturation. Therefore, we hypothesize that covalent BCR engagement by an FVIII-CRA will induce tolerance more efficiently than the noncovalently binding FVIII counterpart. This will be tested by FVIII-CRA treatment of peripheral blood mononuclear cells from patients with high titer anti-FVIII Abs. Basal and FVIII-challenge induced anti-FVIII Ab producing cells will be quantified using in vivo and in vitro experimental systems for tolerance induction. Immunodeficient mice reconstituted with lymphocytes from the hemophilia patients will be employed for the in vivo studies. Limited studies of B cell death and signal transduction following FVIII-CRA treatment are also included to help lay the foundation for using CRAs as tolerogens. If our hypothesis is valid, we expect these studies to identify candidate compounds capable of efficiently inducing FVIII-specific tolerance without compromising the immune responses to other antigens. (PI: Sudhir Paul)