Comparison of the effects of antibody-coated liposomes, IVIG, and anti-RBC immunotherapy in a murine model of passive chronic immune thrombocytopenia

Abstract

IntroductionImmune thrombocytopenia (ITP) is classified as an autoimmune disease in which antibody-coated platelets are phagocytosed by macrophages in the reticuloendothelial system (RES) through Fc␥ receptor-mediated or complement-mediated pathways. 1 There are about 33 000 new cases of ITP diagnosed in the United States each year. [2][3][4] Platelets play an important role in blood homeostasis and vascular repair; consequently, thrombocytopenic patients are at risk for the development of purpura, petechiae, or even life-threatening bleeding such as intracranial hemorrhage. Corticosteroids, splenectomy, intravenous immunoglobulin (IVIG), anti-D immunotherapy, and plasmapheresis have been used to acutely increase platelet counts in the treatment of ITP. 2-4 However, the above therapies are associated with troubling side effects and high cost. In addition, some ITP patients do not respond to any of the existing therapies; therefore, there is substantial need for the development of new strategies to treat this disease.In 1981, Imbach et al 5 reported the therapeutic efficacy of high-dose IVIG in ITP patients. Later, Salama et al 6 proposed that IVIG contained anti-red blood cell (anti-RBC) antibodies, which led to the opsonization of RBCs in vivo following IVIG administration. Additionally, Salama et al 6 hypothesized that antibodyopsonized RBCs competed for binding to Fc␥ receptors, effectively inhibiting the Fc␥ receptor-mediated elimination of platelets in ITP patients. Consistent with this hypothesis, anti-D, a polyclonal antibody preparation against the D antigens on the RBC, has been used to treat Rh ϩ ITP successfully. 2,7,8 Although anti-D has been Food and Drug Administration (FDA)-approved to treat ITP, this therapy is rarely associated with intravascular hemolysis, leading to severe anemia and, in very rare cases, death. 9,10 Additionally, anti-D has not demonstrated efficacy in D-negative patients or in splenectomized patients. 7,8 We have proposed that antibody-coated liposomes may be used in place of anti-D to compete for pathways for platelet elimination in ITP. 11 Previous work has shown that antibody-coated liposomes increased platelet counts in a rat model of acute passive ITP. 11 A murine model of chronic passive ITP, which may be more similar to human ITP, was developed here. The effects of antibody-coated liposomes were examined and compared with effects observed following treatment with IVIG or treatment with an anti-RBC monoclonal antibody (TER119). Our data showed that antibodycoated liposomes, IVIG, and TER119 increased platelet counts in this model. Antibody-coated liposomes achieved effects at a much lower immunoglobulin dose than that required for IVIG and, in contrast with TER119, antibody-coated liposomes achieved an increase in platelet counts without altering RBC counts. Materials and methods MiceFemale Balb/c mice (20 g) were obtained from Harlan (Bar Harbor, ME). Mice were kept under a natural light/dark cycle, maintained at 22 Ϯ 4°C, and fed with standard diet and water ad libitu...

Fc receptors in immune thrombocytopenias: a target for immunomodulation?

“…As early as 1964, Brambell hypothesized that there existed a process to recycle IgG, later shown to involve the neonatal FcR, FcRn. This FcR is unique among FcRs in that it is a heterodimer consisting of an MHC-1-related glycoprotein bound to a β2 microglobulin protein and has been studied as a therapeutic target to prevent the recycling of autoantibodies in autoimmune disease and, in doing so, shorten autoantibody half-lives (14,15). Importantly, FcRn also mediates transplacental passage of maternal IgG into the fetus (16,17).…”

Pharmacokinetic/Pharmacodynamic Modeling of IVIG Effects in a Murine Model of Immune Thrombocytopenia

“…The detailed description of the experiments work associated with this study has been described elsewhere 10. All animal experiments were approved by the Institutional Animal Use and Care Committee of the University at Buffalo.…”

“…Recently, Deng and Balthasar10 developed a mouse model of sustained ITP, where thrombocytopenia was induced in mice by continuous infusion of an anti‐platelet antibody, MWReg30. Severe thrombocytopenia was observed within 4 days from the start of the MWReg30 infusion, and PLT counts were found to remain at relatively constant values from 4 to 7 days after initiation of the infusion (i.e., approximating a condition of “steady‐state” thrombocytopenia).…”

The role of Fcγ receptors in murine autoimmune thrombocytopenia

“…Several platelet-specific monoclonal antibodies or polyclonal sera specific for mouse platelets can be used to induce ITP [29,[36][37][38][39][40][41]. One common antibody is the CD41-specific rat IgG1 clone MWReg30.…”