Anterior Gradient 2 (AGR2) is a potential anti-tumor target and we previously reported a murine antibody 18A4 with specific binding to AGR2. However, humanization is a must to overcome immunogenicity before considering for clinical use and optimized vectors for mammalian expression are also necessary for following industrialized manufacture. Here, we describe an anti-tumor humanized antibody blocking secreted AGR2 activity. We employed the CDR grafting technique and deimmunization analysis to construct humanized antibody variants of 18A4, and 18A4Hu I was selected as the best humanization candidate, characterized by physical and chemical property comparison. Mouse xenograft study showed that 18A4Hu I could effectively inhibit the xenograft tumor growth, antibody blocking epitope analysis using AGR2 mutants indicated that the inhibition activity of 18A4Hu I is exerted probably through blocking the AGR2 functions which rely on the amino acid sites of E60-H76 and A86-E153. What's more, in this report, we also describe a pHAb-FAST vector system which is specifically designed for humanized antibody mammalian expression vector fast construction. With pHAb-FAST system, expression vector of 18A4Hu I could be quickly constructed only through twice overlapping PCR reactions. To our knowledge, AGR2-targeted 18A4Hu I is a promising humanized anti-tumor drug candidate, and pHAb-FAST system is a useful optimized mammalian expression vector construction tool. Our findings are supposed to accelerate the development of antibody-based cancer therapy. (C) 2016 Elsevier Inc. All rights reserved.