Eliminating B Cell Precursor Acute Lymphoblastic Leukemia by Targeting the Uniquely Specific Pre-B Cell Receptor

摘要 B细胞前体急性淋巴细胞性白血病(BCP-ALL)是一种由突变的前B细胞引起的恶性肿瘤 儿童白血病最常见，但也可见于成人。虽然对高达90%的患者有效，但目前 针对BCP的化疗和靶向治疗都暂时破坏了BCP的体液(产生抗体)手臂 并引起长期后果的毒性。这项R21拨款提案的目标是 参与关于前B细胞受体(Pre-BCR)作为一种独特的治疗方法的效用的概念性研究 BCP-ALL的治疗靶点。前BCR包括免疫球蛋白(Ig)重链和 代理轻链(SLC)以及信号分子Igα和Igβ。SLC由以下部分组成 两个非共价连接的多肽，VpreB和L5。在正常组织中，Pre-BCR仅在Pre-BCR中表达 但在更成熟的B细胞或任何其他组织中不存在。重要的是，我们的初步数据表明 VpreB和L5在90%的BCP-ALL中表达。因此，我们产生了高亲和力的单抗。 (单抗)VpreB和L5的特异性，发现单抗内化到BCP-ALL细胞中，表达 BCR之前。内化是抗体-药物结合物中抗体成分的重要前提 (ADC)。我们的中心假设是，用VpreB或L5特有的ADC攻击BCP-ALL将消除 白血病细胞，同时保留成熟的体液免疫系统以对抗感染。我们的目标是获得证据- 概念外数据，首先，证实VpreB单抗在几个BCP-ALL细胞系中内化，并允许 选择单一的、最有效地内化铅的单抗(特定目标1)；第二，在蛋白质水平上显示 35例bcp-ALL患者白血病标本中广泛表达Pre-bcr(特异性靶点2)；第三， 证明我们的VpreB ADC能够在体外杀死已建立的和患者来源的BCP-ALL细胞系， 体外和患者来源的异种移植模型(特定目标3)。我们希望这项研究将支持 一种新的BCP-ALL疗法的开发，该疗法将安全地消除白血病细胞，同时节省体液 免疫系统，并最终取代化疗，使患者可以在没有 短期或长期的不利后果。

ABSTRACT B cell precursor acute lymphoblastic leukemia (BCP-ALL), a malignancy that arises from mutant pre-B cells, is the most common childhood leukemia but also occurs in adults. While effective in up to 90% of patients, current chemo- and targeted therapies for BCP-ALL temporarily destroy the humoral (antibody-producing) arm of the immune system and cause toxicities with long term consequences. The goal of this R21 grant proposal is to engage in conceptual research regarding the utility of the pre-B cell receptor (pre-BCR) as a unique therapeutic target for the treatment of BCP-ALL. The pre-BCR comprises an immunoglobulin (Ig) heavy chain and a surrogate light chain (SLC) together with the signaling molecules Ig alpha and Ig beta. The SLC is composed of two noncovalently-linked polypeptides, VpreB and l5. In normal tissues, the pre-BCR is expressed only in pre- B cells but not in more mature B cells nor in any other tissues. Importantly, our preliminary data suggest that VpreB and l5 are expressed in >90% of BCP-ALL. We therefore generated high avidity monoclonal antibodies (mAbs) specific for VpreB and l5 and found that the mAbs are internalized into BCP-ALL cells expressing the pre-BCR. Internalization is an important prerequisite for the antibody component of an antibody-drug conjugate (ADC). Our central hypothesis is that attacking BCP-ALL with an ADC specific for VpreB or l5 will eliminate the leukemia cells while sparing the mature humoral immune system to combat infection. Our goal is to obtain proof- of-concept data that first, confirms internalization of VpreB mAbs in several BCP-ALL cell lines and allows selection of a single, most efficiently internalizing lead mAb (Specific Aim 1); second, show at the protein level the widespread expression of the pre-BCR in 35 BCP-ALL patient leukemia samples (Specific Aim 2); and third, demonstrate the ability of our lead VpreB ADC to kill established and patient-derived BCP-ALL cell lines in vitro, ex vivo, and in a patient-derived xenograft model (Specific Aim 3). We hope that this research will support the development of a new BCP-ALL therapeutic that will safely eliminate leukemia cells while sparing the humoral immune system and ultimately supplanting chemotherapy so that patients can achieve full remission without short- or long-term adverse consequences.