GTKO/hCD55基因工程猪到人异种移植CDC技术的探讨

Exploration of complement-dependent cytotoxicity technology for GTKO/hCD55 genetically engineered pig-to-human xenotransplantation

目的探讨和比较人CD55(hCD55)转基因猪外周血单个核细胞(PBMC)表面表达的hCD55对兔补体和人补体依赖的细胞毒(CDC)的抑制效果。方法选择来自同一品系的3头α1, 3-半乳糖转移酶基因敲除猪(GTKO)。其中两头猪转入了hCD55基因。根据三头猪PBMC表面hCD55表达水平, 分为GTKO、hCD55低表达(GTKO/hCD55Low)和hCD55高表达(GTKO/hCD55High)猪。将3头猪的PBMC分别与灭活补体的混合人血清(20例份)孵育后, 流式细胞仪检测兔补体或人补体依赖的细胞毒以及猪PBMC的抗体(IgM和IgG)结合水平。结果 3头猪PBMC与人血清异种抗体的结合无明显差异。兔补体和人补体对GTKO猪PBMC的细胞毒均较高, 分别为98.97%±0.50%和82.73%±3.20%。与GTKO组相比, 低表达hCD55对兔补体依赖的细胞毒无明显抑制作用(97.07%±2.25%比98.9%±0.50%, P=0.2267), 而高表达hCD55对兔补体依赖的细胞毒有轻度的抑制作用(81.70%±5.86%比98.9%±0.50%, P=0.0355)。不同的是, 低表达hCD55对人补体依赖的细胞毒有显著的抑制作用(23.83%±3.53%比82.73%±3.20%, P<0.0001);高表达hCD55对人补体依赖的细胞毒较低表达hCD55有进一步抑制作用(2.79%±0.45%比82.73%±3.20%, P=0.009), 使之达到阴性对照组水平。低表达或高表达hCD55对人补体介导CDC的抑制作用均优于对兔补体介导CDC的抑制作用。结论相较于传统使用兔补体的CDC技术, 使用商品化标准人补体的CDC技术评价GTKO/hCD55基因工程猪细胞表面hCD55对受者补体激活的调节作用具有明显优势。本研究对在异种移植走向临床后, 建立能有效评估hCD55功能的CDC实验体系提供了实验依据。

Objective To compare the inhibitory effect of human CD55(hCD55)expressed on porcine peripheral blood mononuclear cells(PBMC)on rabbit complement-and human complement-dependent cytotoxicity(CDC).Methods Threeα1,3-galactosyltransferase gene knockout(GTKO)pigs from the same strain were selected.Two were transferred with hCD55 gene.According to the expression level of hCD55,the animals were divided into three groups of GTKO,GTKO/hCD55Low(low-expression of hCD55)and GTKO/hCD55High(high-expression of hCD55).After PBMC from these pigs were incubated with complement-inactivated pooled human serum(20 cases),rabbit complement-or human complement-dependent cytotoxicity and binding of antibodies(IgM/G)to pig PBMC were detected by flow cytometry.Results No significant difference existed in binding of human serum xenoreactive antibodies to PBMC from three groups.The cytotoxicity to GTKO pig PBMC mediated by rabbit complement or human complement were 98.97%±0.50%and 82.73%±3.20%respectively.Both values were quite high.Compared with GTKO group,a low expression of hCD55 had no significant inhibitory effect on rabbit complement-dependent cytotoxicity(97.07%±2.25%vs.98.9%±0.50%,P=0.2267)while a high expression of hCD55 exerted a mild inhibitory effect on rabbit complement-dependent cytotoxicity(81.70%±5.86%vs.98.9%±0.50%,P=0.0355).Differently,a low expression of hCD55 had a potent inhibitory effect on human complement-dependent cytotoxicity(23.83%±3.53%vs.82.73%±3.20%,P<0.0001).Compared with hCD55 low-expression group,a high expression of hCD55 had a further inhibitory effect on human complement-dependent cytotoxicity(2.79%±0.45%vs.82.73%±3.20%,P=0.009),attaining the level of negative control group.The inhibitory effect of low/high expression of hCD55 on human complement-mediated CDC was significantly better than that on rabbit complement-mediated CDC.Conclusions Compared with traditional CDC counterpart using rabbit complement,modified CDC technology of commercial standard human complement is recommended for evaluating the regulatory effect of hCD55 expressed on cell surface from GTKO/hCD55 genetically engineered pigs.It thus provides experimental rationales for establishing a novel CDC experimental system of effectively evaluate the function of hCD55 after xenotransplantation.