Abstract Antibodies against cancer targets are routinely used for facilitating early detection of disease, for diagnosing and predicting disease severity, and for guiding and monitoring therapeutic treatment. Ten of the 11 FDA-approved cancer therapeutic monoclonal antibodies (MAbs) target membrane proteins, and membrane proteins comprise >30% of existing cancer biomarkers. MAbs that recognize conformation-dependent epitopes on membrane proteins are usually the most valuable type of antibody because they can bind to critical structures of the receptor that can be exploited for its detection or inhibition. However, the development of conformational MAbs against membrane proteins is especially challenging because these proteins require a lipid environment to maintain their native structure, can be difficult to purify, and are usually poorly represented by peptide immunogens. To overcome these limitations, we have developed a novel technology, the ‘Lipoparticle’, which incorporates high concentrations (10-100 fold greater than cells or membrane preparations) of properly folded and oriented membrane proteins onto the surface of virus-like particles (VLPs). Here, we have used Lipoparticles as immunogens to generate monoclonal antibodies against two important membrane protein targets: the GPCR CXCR4, associated with tumor metastasis, and the ion channel Hv1, implicated in B cell activation. Lipoparticles containing each target were used to immunize mice, eliciting sera with strong and specific immunoreactivity. Screening of >900 hybridomas using Lipoparticles resulted in the identification of CXCR4-specific MAbs validated for reactivity against surface expressed antigen by immunofluorescence. Epitope mapping and functional studies demonstrate that each MAb binds a conformational-dependent epitope on the second extracellular loop capable of inhibiting ligand-dependent signaling in vitro. Similar studies are currently ongoing to isolate MAbs against the Hv1 ion channel, with strong sera responses against Hv1 detected in immunized mice. Our data highlight the utility of Lipoparticles for generating MAbs and screening hybridomas to isolate antibodies against challenging cancer membrane protein targets. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4635. doi:1538-7445.AM2012-4635