Immunophysiological Mechanisms in the Biological Therapy of Cancer

癌症免疫治疗新方法的成功开发需要了解早期先天反应元件与随后强大的适应性免疫反应的复杂，相互依赖的活动。我们正在采取几种新的方法，以最大限度地提高宿主的能力，建立一个有效的抗肿瘤反应。这些方法包括通过使用CD 40优化抗原呈递能力，CD 40是一种TNF超家族受体，作为树突细胞的有效触发物，在先天性和适应性反应之间提供关键界面。当与IL-2联合使用时，激动剂CD 40抗体刺激树突状细胞的效力增强，并且激动剂抗CD 40加IL-2的组合显示针对小鼠中转移性肾癌的增强的抗肿瘤活性。由于CD 40存在于各种造血源性细胞、内皮细胞和一些肿瘤本身上，我们还进行了研究，以明确确定CD 40刺激和IL-2的抗肿瘤作用是否主要由CD 40+造血源性细胞介导。我们已经开发了一种方法，其中仅肿瘤细胞表达功能性CD 40;具体而言，我们使用了这样的模型，其中将仅对抗人CD 40有反应的CD 40+人肿瘤植入仅表达小鼠CD 40且对抗人CD 40的施用无反应的SCID小鼠中。这两个模型使我们能够表明肿瘤细胞确实对激动剂CD 40的连接有反应，并且这种反应确实有助于限制肿瘤生长。我们采取的另一种方法集中于这样一个事实，即许多成功的基于精氨酸的疗法完全依赖于宿主产生IFN-γ的能力，然而纯IFN-γ蛋白的施用在小鼠肿瘤模型或人类癌症患者中几乎没有抗肿瘤益处。我们现在已经开发出缺乏功能性IFN-γ受体（IFN-γ R）的小鼠，这使我们能够显示肿瘤生长和转移增加的暴露。目前的研究集中在如何优先刺激IFN-γ宿主反应，同时最大限度地减少IFN-γ触发肿瘤自身免疫逃避活动的能力。此外，靶向破坏肿瘤微环境中的其他事件可能最终揭示将免疫治疗与其他分子靶向策略相结合的新方法。在这方面，我们已经取得了表达载体编码的可溶性形式的VEGF受体（VEGFRs），Flk-1和Flt-1，连接到恒定区的人IgG 1，并将这些质粒传递到Balb/c小鼠通过高效的流体动力学注射，这种策略导致高达0.1mg/ml的适当的基因产物在小鼠血清中，并成功地抑制血管生成在含VEGF的基质胶。Balb/c小鼠肾癌的体内生长也被相同的治疗阻断，特别是用可溶性Flt-1。总的来说，这些类型的互补方法寻求触发宿主可以识别或损害肿瘤生长的几种途径，同时还靶向肿瘤细胞增强其自身存活或抑制抗肿瘤宿主反应的能力。

Successful development of new approaches for the immunotherapy of cancer requires an understanding of complex, interdependent activities of early innate response elements with subsequent powerful adaptive immune responses. We are taking several novel approaches to maximize the host's ability to mount an effective antitumor response. These approaches include optimizing antigen presenting capability through the use of CD40, a TNF superfamily receptor that serves as a potent trigger for dendritic cells which provide a key interface between innate and adaptive responses. The potency of dendritic cell stimulation by agonist CD40 antibodies is enhanced when used in conjunction with IL-2 and the combination of agonist anti-CD40 plus IL-2 shows enhanced antitumor activity against metastatic kidney cancer in mice. Because CD40 is present on various hematopoietic-derived cells, endothelial cells, and some tumors themselves, we have also performed studies to definitively determine if the antitumor effects of CD40 stimulation and IL-2 were primarily mediated by CD40+ hematopoietic-derived cells. We have developed an approach where only tumor cells express functional CD40; specifically we have used models where CD40+ human tumors that respond only to anti-human CD40 were implanted in SCID mice that express only mouse CD40 and do not respond to the administration of the anti-human CD40. These two models have allowed us to show that tumor cells do respond to ligation with agonist CD40 and this response does contribute to limiting tumor growth. Another approach we have taken focuses on the fact that many successful cytokine-based therapies are totally dependent on the ability of the host to produce IFN-gamma, yet the administration of pure IFN-gamma protein has virtually no antitumor benefit in both mouse tumor models or human cancer patients. We have now developed mice lacking a functional IFN-gamma receptor (IFN-gammaR) that have allowed us to show that exposure of tumor growth and increase metastasis. Present studies are focused on how to preferentially stimulate IFN-gamma host responses while minimizing the ability of IFN-gamma to trigger immune-evading activities by the tumor itself. In addition, targeted disruption of other events in the tumor microenvironment may ultimately reveal new approaches for combining immunotherapy with other molecularly targeted strategies. In this regard, we have made expression vectors encoding the soluble forms of the VEGF receptors (VEGFRs), Flk-1 and Flt-1, linked to the constant region of human IgG1, and delivered these plasmids to Balb/c mice by highly efficient hydrodynamic injection, this strategy resulted in up to 0.1mg/ml of the appropriate gene products in mouse serum and successfully inhibited angiogenesis in VEGF-containing matrigel. Growth in vivo of a Balb/c mouse renal cancer was also blocked by the same treatment, particularly with soluble Flt-1. Overall, these types of complementary approaches seek to trigger several pathways through which the host can recognize or impair tumor growth, while also targeting the ability of tumor cells to enhance their own survival or inhibit antitumor host responses.