Role of T Regulatory Cell Suppression in Autoimmunity and Cancer

我们对Tregs的研究表明，肿瘤坏死因子通过作用于Tregs最高表达的TNFR2受体，意外地导致Tregs在小鼠和人类体内的增殖扩张和功能激活。鉴于众所周知的肿瘤坏死因子的促炎作用，我们的数据显示，肿瘤坏死因子以更延迟的方式也可以下调免疫反应，这是相当令人惊讶的。此外，肿瘤坏死因子和IL-2联合作用可上调Tregs表面TNFR2、4-1BB和OX-40受体的表达。因此，肿瘤坏死因子通过诱导3个TNFRSF受体家族成员来增强其对Tregs的刺激作用。肿瘤坏死因子与肿瘤坏死因子受体2的相互作用也稳定了炎症部位的CD4+FOXP3+T调节细胞表型。对肿瘤坏死因子这些意想不到的影响的一种澄清是基于我们的数据，即通过激活T效应细胞也诱导它们表达更多的TNFR2，并对Tregs的抑制作用变得更具抵抗力。因此，激活的炎症细胞可以战胜Tregs的抑制作用。然而，随着炎症在愈合的伤口或非炎症的肿瘤中消退，Treg占上风。约50%的肿瘤浸润性T细胞(TIL)发育成Tregs并表达TNFR2。它们被肿瘤来源的肿瘤坏死因子激活，比周围淋巴组织中的Tregs具有更强的免疫抑制作用。抑制Tregs导致更有效的宿主抗肿瘤反应，并减少肿瘤生长。我们假设TNFR2可以被Tregs的“检查点抑制物”靶向。通过用中和抗TNFR2抗体(抑制Tregs)和CpG(TLR9配体)促进细胞免疫来治疗携带小CT26结肠癌的小鼠，验证了这一假设。这导致80%的小鼠没有肿瘤，并选择性地抵抗随后的CT26肿瘤挑战。这些接受治疗的小鼠通过产生IFNGamma而不是Treg TIL细胞对其肿瘤进行了相当大的渗透，并减少了脾和肿瘤中免疫抑制MDSC的数量。这些发现表明，这种疗法使小鼠表现出相当大的抗肿瘤免疫力。发现更有效的TNFR2拮抗剂应该会产生更有效的检查点抑制。这一想法促使我们与Dimiter Dimitrov博士和他的同事合作，他们设计了高亲和力的抗人抗TNFR2抗体的生产。ADCC对表达TNFR2的人细胞有细胞毒作用，而对小鼠细胞无细胞毒作用。该抗体可能能够耗尽高度激活的人类Tregs和TJeff细胞。虽然我们可以证明该抗体在体外与NK细胞一起具有强大的抗TNFR2作用，但由于它只对人TNFR2具有活性，所以我们不能在体外或体内评估其对小鼠细胞的作用。因此，我们必须与一个临床小组合作，他们将有兴趣在患者身上测试它，以确定它是否作为一种有效的检查点样抑制物发挥作用。虽然一些公司已经表示了兴趣，但到目前为止还没有一家公司批准了这种抗体。我们目前正在研究上调TNFR2表达Tregs的试剂的作用效果和作用机制，以确定抑制自身免疫状况的治疗方法。

Our studies of Tregs have revealed that TNF by acting on the TNFR2 receptor, which is most highly expressed by Tregs, unexpectedly results in the proliferative expansion and functional activation of Tregs both in mice and in man. In view of the well-known proinflammatory effects of TNF, our data showing that TNF in a more delayed manner can also down-regulate immune responses, is rather surprising. Furthermore, TNF together with IL-2 up-regulates the cell surface expression of TNFR2 and also of 4-1BB and OX-40 receptors on Tregs. Thus, TNF amplifies its stimulatory effect on Tregs by inducing 3 TNFRSF receptor family members. TNF interactions with TNFR2 also stabilizes the CD4+FOXP3+ T regulatory cell phenotype at inflammatory sites. One clarification of these unexpected effects of TNF is based on our data showing that TNF by activating Teffector cells also induce them to express more TNFR2 and to become more resistant to the suppressive effects of Tregs. Thus, activated inflammatory cells can prevail over the suppressive effects of Tregs. However, as inflammation subsides in healing wounds or in non-inflamed tumors, Tregs prevail. About 50% tumor infiltrating T cells (TIL's) develop into Tregs and express TNFR2. They are activated by tumor-derived TNF to be even more immunosuppressive than Tregs in peripheral lymphoid tissues. Suppression of Tregs results in more effective host antitumor responses and reduces tumor growth. We hypothesize that TNFR2 can be targeted by "checkpoint inhibitors" of Tregs. This hypothesis was tested by treating mice bearing small CT26 colon tumors with neutralizing anti-TNFR2 antibodies, which suppresses Tregs, and CpG, a TLR9 ligand, to promote cell mediated immunity. This resulted in 80% of the mice becoming tumor free and selectively resisting a subsequent CT26 tumor challenge. These treated mice developed considerable infiltration of their tumors by IFNgamma producing rather than Treg TIL cells and also reduced the numbers of immunosuppressive MDSC in their spleens and tumors. These finding suggest that this therapy enabled the mice to exhibit considerable antitumor immunity. Identification of more potent antagonists of TNFR2 should yield even more effective checkpoint inhibition. This idea motivated us to collaborate with Dr. Dimiter Dimitrov and his colleagues who engineered the production of high affinity anti-human anti-TNFR2 antibodies. These antibodies are cytotoxic by ADCC for human, but not mouse cells expressing TNFR2. The antibody may be able to deplete both highly activated human Tregs and Teff cells. Although we can show this antibody together with NK cells has potent anti-TNFR2 effects in vitro, we can not evaluate its effects on mouse cells in vitro or in vivo because it is active only against human TNFR2. We therefore have to collaborate with a clinical group that would be interested in testing it in patients to determine if it acts as a potent checkpoint-like inhibitor. Although a number of companies have expressed an interest, none have licensed this antibody as yet. We are currently investigating the effect and mechanism of action of reagents that upregulate TNFR2 expressing Tregs to identify therapeutic approaches to inhibiting autoimmune conditions.