Duthaler Rudolf O, Ernst Beat, Fischer Reto, Katopodis Andreas G, Kinzy Willy, Marterer Wolfgang, Oehrlein Reinhold, Streiff Markus B, Thoma Gebhard
Novartis Institutes of Biomedical Research (NIBR), Novartis Pharma AG, PO. Box, CH-4002 Basel.
Chimia (Aarau). 2010;64(1-2):23-8. doi: 10.2533/chimia.2010.23.
Pig-to-human xenotransplantation of islet cells or of vascularized organs would offer a welcome treatment alternative for the ever-increasing number of patients with end-stage organ failure who are waiting for a suitable allograph. The main hurdle are preexisting antibodies, most of which are specific for 'Linear-B', carbohydrate epitopes terminated by the unbranched Gal-alpha(1,3)Gal disaccharide. These antibodies are responsible for the 'hyper-acute rejection' of the xenograft by complement mediated hemorrhage. For depletion of such antibodies we have developed an artificial injectable antigen, a glycopolymer (GAS914) with a charge neutral poly-lysine backbone (degree of polymerization n = 1000) and 25% of its side chains coupled to Linear-B-trisaccharide. With an average molecular weight of 400 to 500 kD, presenting 250 trisaccharide epitopes per molecule, this multivalent array binds anti-alphaGal antibodies with at least three orders of magnitude higher avidity on a per-saccharide basis than the monomeric epitope. In vivo experiments with non-human primates documented that rather low doses--1 to 5 mg/kg of GAS914 injected i.v.--efficiently reduce the load of anti-Linear-B antibodies quickly by at least 80%. This treatment can be repeated without any sensitization to GAS914. Interestingly, although the antibody levels start raising 12 h after injection, they do not reach pretreatment levels. The polymer is degraded and excreted within hours, with a minute fraction remaining in lymphoid tissue of anti-alphaGal producing animals only, probably binding to and inhibiting antibody-producing B-cells. The results of pig-to-non-human primate xenotransplantations established GAS914 as a relevant therapeutic option for pig-to-human transplantations as well. The synthesis of GAS914 was successfully scaled up to kg amounts needed for first clinical studies. Key was the use of galactosyl transferases and UDP-galactose for the synthesis of the trisaccharide.
胰岛细胞或血管化器官的猪到人的异种移植，对于越来越多等待合适同种异体移植的终末期器官衰竭患者而言，将提供一种受欢迎的治疗选择。主要障碍是预先存在的抗体，其中大多数针对“线性-B”，即由无分支的半乳糖-α(1,3)半乳糖二糖终止的碳水化合物表位。这些抗体通过补体介导的出血导致异种移植物的“超急性排斥”。为了清除此类抗体，我们开发了一种人工可注射抗原，一种具有电荷中性聚赖氨酸主链（聚合度n = 1000）且其25%的侧链与线性-B-三糖偶联的糖聚合物（GAS914）。平均分子量为400至500 kD，每个分子呈现250个三糖表位，这种多价阵列以每个糖为基础结合抗αGal抗体的亲和力比单体表位至少高三个数量级。用非人类灵长类动物进行的体内实验证明，相当低的剂量——静脉注射1至5 mg/kg的GAS914——能迅速有效地将抗线性-B抗体的负荷至少降低80%。这种治疗可以重复进行，且不会对GAS914产生任何致敏作用。有趣的是，尽管抗体水平在注射后12小时开始上升，但它们并未达到预处理水平。聚合物在数小时内降解并排出，只有极少量残留在仅产生抗αGal的动物的淋巴组织中，可能与产生抗体的B细胞结合并抑制其产生。猪到非人类灵长类动物的异种移植结果也确立了GAS914作为猪到人类移植的一种相关治疗选择。GAS914的合成已成功扩大规模至首次临床研究所需的千克量。关键在于使用半乳糖基转移酶和UDP-半乳糖来合成三糖。
