复发难治性白血病是临床难题，白血病干细胞(LSC)是其复发的根源。CD3-CD19双特异性抗体（CD3-CD19 BiTE）治疗B系肿瘤的临床试验结果良好，但重复应用易耐药，可能与鼠源性BiTE易诱发人抗鼠抗体（HAMA）有关。课题组前期研究发现，自制新单抗3A4（CD45RA）能识别几乎100%复发的AML细胞和近90％的AML-LSC，3A4识别抗原可能是良好的免疫治疗新靶点，但国际上尚无有关该靶点的研究报道，更无CD45RA-CD3 BiTE抗体相关的研究。本项目拟采用一系列细胞及分子生物学方法构建鼠源性和人源化双特异性小分子（55kDa）和高分子(105kDa) 3A4-CD3 BiTE抗体基因并优化结构后在CHO细胞中表达，鉴定其生物学特性及体内外靶向杀伤AML及其LSC的作用及机制，为进一步开发该新颖抗体药物制剂提供实验依据，具有重要的科学意义和潜在的临床应用前景。

Relapsed/refractory acute leukemia is a serious clinical problem and leukemia stem cell (LSC) is believed to be the cause of relapse. CD3-CD19 bispecific T cell engager (BiTE) has being demonstrated very promising treatment outcomes for patients with r/r B lineage malignancies, however, early relapses occurs frequently after BiTE treatment, which may be caused by the induction of the human anti-mouse immunoglobulin antibody (HAMA). Our previous studies have showed that 3A4, a novel murine IgG1k antibody (designated as CD45RA by HLDA-7) was generated in our laboratory. This antibody can recognize almost all relapsed AML cells and about 90% of AML-LSC but not react with clinically important normal cell components which may offer a potential therapeutic target for those patients. However, no data regarding CD45RA or CD45RA-CD3 BiTE as targeting activity have yet been reported in the world. This project will focus on the genetic design, optimization and expression of mouse and humanized 3A4-CD3 BiTE antibody in Chinese hamster ovary (CHO) cells and the targeting activity and its mechanism of this BiTE antibody will be studied systemically using a series of cellular and moleculobiological approaches and mouse model, which is of great scientific significance and clinical application potential in the near future.