Porcine xenografts lacking swine leukocyte antigen (SLA) class I are thought to be protected from human T cell responses. We have previously shown that SLA class I deficiency can be achieved in pigs by CRISPR/Cas9-mediated deletion of β2 -microglobulin (B2M). Here, we characterized another line of genetically modified pigs in which targeting of the B2M locus did not result in complete absence of B2M and SLA class I but rather in significantly reduced expression levels of both molecules. Residual SLA class I was functionally inert, because no proper differentiation of the CD8+ T cell subset was observed in B2Mlow pigs. Cells from B2Mlow pigs were less capable in triggering proliferation of human peripheral blood mononuclear cells in vitro, which was mainly due to the nonresponsiveness of CD8+ T cells. Nevertheless, cytotoxic effector cells developing from unaffected cell populations (eg, CD4+ T cells, natural killer cells) lysed targets from both SLA class I+ wildtype and SLA class Ilow pigs with similar efficiency. These data indicate that the absence of SLA class I is an effective approach to prevent the activation of human CD8+ T cells during the induction phase of an anti-xenograft response. However, cytotoxic activity of cells during the effector phase cannot be controlled by this approach.

中文翻译：

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三重（GGTA1、CMAH、B2M）修饰的猪表达 SLA Ilow 表型-对免疫状态和对人体免疫反应的易感性的影响。

缺乏猪白细胞抗原 (SLA) I 类的猪异种移植物被认为不受人类 T 细胞反应的影响。我们之前已经表明，通过 CRISPR/Cas9 介导的 β2-微球蛋白 (B2M) 缺失可以在猪身上实现 SLA I 类缺陷。在这里，我们描述了另一条转基因猪的特征，其中 B2M 基因座的靶向不会导致 B2M 和 SLA I 类完全缺失，而是两种分子的表达水平显着降低。残留的 SLA I 类在功能上是惰性的，因为在 B2Mlow 猪中没有观察到 CD8+ T 细胞亚群的适当分化。来自 B2Mlow 猪的细胞在体外触发人外周血单核细胞增殖的能力较弱，这主要是由于 CD8+ T 细胞的无反应性。尽管如此，从未受影响的细胞群（例如，CD4+ T 细胞、自然杀伤细胞）发展而来的细胞毒性效应细胞以相似的效率裂解来自 SLA I+ 类野生型和 SLA Ilow 类猪的靶标。这些数据表明，在抗异种移植反应的诱导阶段，不存在 I 类 SLA 是防止人 CD8+ T 细胞激活的有效方法。然而，这种方法无法控制效应阶段细胞的细胞毒活性。