Department of Biochemical and Cellular Pharmacology, Genentech Inc, 1 DNA Way, South San Francisco, CA, 94080, USA.
Cancer Immunology, Genentech Inc, 1 DNA Way, South San Francisco, CA, 94080, USA.
J Immunother Cancer. 2019 Aug 6;7(1):207. doi: 10.1186/s40425-019-0687-9.
One of the mechanisms by which tumors evade immune surveillance is through shedding of the major histocompatibility complex (MHC) class I chain-related protein A and B (MICA/B) from their cell surface. MICA/B are ligands for the activating receptor NKG2D on NK and CD8 T cells. This shedding reduces cell surface levels of MICA/B and impairs NKG2D recognition. Shed MICA/B can also mask NKG2D receptor and is thought to induce NKG2D internalization, further compromising immune surveillance by NK cells.
We isolated human primary NK cells from normal donors and tested the suppressive activity of soluble recombinant MICA in vitro. Utilizing a panel of novel anti-MICA antibodies, we further examined the stimulatory activities of anti-MICA antibodies that reversed the suppressive effects of soluble MICA.
We show that suppressive effects of soluble MICA (sMICA) on NK cell cytolytic activity was not due to the down-regulation of cell surface NKG2D. In the presence of an α3 domain-specific MICA antibody, which did not obstruct NKG2D binding, sMICA-mediated NK cell suppression was completely reversed. Reversal of NK cell inhibition by sMICA was mediated by immune complex formation that agonized NKG2D signaling. Furthermore, this restorative activity was dependent on antibody Fc effector function as the introduction of Fc mutations to abrogate Fc receptor binding failed to reverse sMICA-mediated NK cell suppression. Furthermore, MICA immune complexes preformed with an α3 domain-specific antibody (containing a wild-type Fc) induced IFN-γ and TNF-α secretion by NK cells in the absence of cancer cells, whereas MICA immune complexes preformed with the Fc effectorless antibody failed to induce IFN-γ and TNF-α secretion. Finally, we demonstrated that MICA immune complexes formed with the α3 domain-specific antibody activates NKG2D on NK cells leading to the release of IFN-γ.
Our results demonstrate that an α3 domain-specific MICA antibody can circumvent sMICA-mediated suppression of NK cell cytolytic activity. Moreover, our data suggest that MICA immune complexes formed with α3-specific antibodies can activate NKG2D receptor and restore NK cell function in a Fc-dependent manner. The clinical utility of α3 domain-specific MICA/B antibodies may hold great promise as a new strategy for cancer immunotherapy.
肿瘤逃避免疫监视的机制之一是通过从细胞表面脱落主要组织相容性复合体（MHC）I 类链相关蛋白 A 和 B（MICA/B）。MICA/B 是 NK 和 CD8 T 细胞上激活受体 NKG2D 的配体。这种脱落降低了细胞表面 MICA/B 的水平，并损害了 NKG2D 的识别。脱落的 MICA/B 还可以掩盖 NKG2D 受体，并被认为诱导 NKG2D 内化，从而进一步损害 NK 细胞的免疫监视。
我们从正常供体中分离出人类原代 NK 细胞，并在体外测试了可溶性重组 MICA 的抑制活性。利用一系列新型抗 MICA 抗体，我们进一步研究了逆转可溶性 MICA 抑制作用的抗 MICA 抗体的刺激活性。
我们表明，可溶性 MICA（sMICA）对 NK 细胞细胞毒性活性的抑制作用不是由于细胞表面 NKG2D 的下调所致。在存在不阻碍 NKG2D 结合的α3 结构域特异性 MICA 抗体的情况下，sMICA 介导的 NK 细胞抑制作用完全逆转。sMICA 介导的 NK 细胞抑制的逆转是通过免疫复合物形成介导的，该复合物激动了 NKG2D 信号。此外，这种恢复活性依赖于抗体 Fc 效应子功能，因为引入 Fc 突变以消除 Fc 受体结合未能逆转 sMICA 介导的 NK 细胞抑制。此外，与含有野生型 Fc 的α3 结构域特异性抗体形成的 MICA 免疫复合物在没有癌细胞的情况下诱导 NK 细胞分泌 IFN-γ和 TNF-α，而与无 Fc 效应子的抗体形成的 MICA 免疫复合物则不能诱导 IFN-γ和 TNF-α的分泌。最后，我们证明与α3 结构域特异性抗体形成的 MICA 免疫复合物激活了 NK 细胞上的 NKG2D，导致 IFN-γ的释放。
我们的结果表明，α3 结构域特异性 MICA 抗体可以规避 sMICA 介导的 NK 细胞细胞毒性活性的抑制。此外，我们的数据表明，与α3 特异性抗体形成的 MICA 免疫复合物可以以 Fc 依赖性方式激活 NKG2D 受体并恢复 NK 细胞功能。α3 结构域特异性 MICA/B 抗体的临床应用可能具有很大的潜力，成为癌症免疫治疗的一种新策略。
