The lacto-series gangliosides 3'-isoLM1 and 3',6'-isoLD1 have been identified as tumor-associated antigens whose formation is initiated by the Lc3-synthase. Until now, high-affinity IgG monoclonal antibodies (mAbs) against 3'-isoLM1 and 3'.6'-isoLD1. which are highly expressed in gliomas, have not been developed, although mAbs against lacto-series gangliosides are powerful tools for functional Studies We previously produced the Lc3-synthase gene beta 3Gn-T5 knockout mice. In this Study, we immunized beta 3Gn-T5 knockout mice with 3'-isoLM1/3',6'-isoLD1 and produced the anti-3'-isoLM1/3',6'-isoLD1 mAb GMab-1, of the IgG3 subclass, which should be useful for functional analysis of lacto-series gangliosides and for antibody-based therapy of gliomas. (c) 2009 Elsevier Inc All rights reserved