Abstract 4925: Lymphocyte cytosolic protein 1 (LCP1) is a membrane-associated molecular target in chronic lymphocytic leukemia and is activated in microenvironment signaling.
Authors: Chappell Danielle L. , Dubovsky Jason A. , Andritsos Leslie A. , Flynn Joseph M. , Jones Jeffrey A. , Paulaitis Mike E. , Agrawal Kitty , Byrd John C. , Muthusamy Natarajan 
Published: August 2014

Abstract
Chronic lymphocytic leukemia (CLL) is an incurable accumulation of malignant B-cells in peripheral circulation, which home to supportive leukemic microenvironments. Critical to the pathogenesis of CLL are membrane-associated antigens since they facilitate leukemic cell signaling, microenvironment homing, proliferation, and survival. Targeting these CLL surface molecules is a current focus of CLL therapeutic development. Rituximab, alemtuzumab, and ofatumumab are commonly used antibody-based therapeutics that proved to be effective at targeting CLL membrane associated antigens. Despite enhanced patient survival, targeting of non-obligate antigens ultimately leads to antibody resistance. In addition, off target expression often produces unacceptable toxicity. Immunosurveilance antigens may provide a key to overcome these obstacles. A number of relevant tumor antigens such as p53, EGFR, WT1, BCR-Abl and ROR1 elicit robust autoimmune responses in cancer patients due to high levels of ectopic expression, high relative immunogenicity and obligate oncogenic signaling that forces expression despite autoimmune recognition. In many cases, autoantibody signatures were realized long after identification of the oncologic target antigens; however, the convergence of these two datasets implies that such signatures could be utilized to identify novel targets. To further explore this possibility, we interrogated anti-tumor humoral reactivity specifically directed against autologous CLL membrane antigens. Immunoreactive leads were identified by mass spectrometry. Potential membrane antigens were further confirmed using immunoblot and ELISA. Our analysis revealed Lymphocyte Cytosolic Protein 1 (LCP1), a membrane associated lymphocyte-specific target that is constitutively expressed on CLL and ectopically expressed in various cancers. Confirmatory assays unveiled robust LCP1-specific IgG autoimmune responses in CLL patients despite a profound absence of reactivity to common viral and vaccine antigens. LCP1 plays a critical role in B-cell biology by cross linking f-actin filaments, thereby solidifying cytoskeletal structures and providing a scaffold for CLL-critical signaling pathways such as PKC. Transwell assays confirmed that LCP1 activity contributed to the migration of CLL cells towards CXCL12. We further utilize a novel xenograft model to demonstrate LCP1 involvement in CLL pathogenesis. We have also characterized LCP1 expression within cancer derived exosomes revealing a previously unknown function of this gene. Our data reveals that LCP1 is a novel membrane associated target antigen in CLL with evidence of differential immune response as compared to common vaccine antigens. We also demonstrate that LCP1 plays a role in CLL microenvironment signaling and progression.
Citation Format: Danielle L. Chappell, Jason A. Dubovsky, Leslie A. Andritsos, Joseph M. Flynn, Jeffrey A. Jones, Mike E. Paulaitis, Kitty Agrawal, John C. Byrd, Natarajan Muthusamy. Lymphocyte cytosolic protein 1 (LCP1) is a membrane-associated molecular target in chronic lymphocytic leukemia and is activated in microenvironment signaling. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4925. doi:10.1158/1538-7445.AM2013-4925