Abstract 2853: Monoclonal antibodies derived in neuN mice following successful T cell therapy of spontaneous breast tumors are specific for tumor progenitor cells.

Abstract

Abstract There is considerable interest in developing approaches to specifically target tumor progenitor cells. Our previous results demonstrated that adoptive transfer of CD4+ and CD8+ T cells primed with a breast cancer progenitor vaccine inhibited the progression of spontaneous primary tumors in neuN mice. Interestingly, post-treatment serum but not pre-treatment serum was reactive with surface molecules on the vaccine cells. This indicates that the transferred T cells resulted in uptake of tumor antigens and stimulation of host B cells. To characterize the antigenic targets, we generated hybridomas from spleen cells derived from treated mice. Three candidate clones which were strongly reactive with a neu-negative variant tumor line were subjected to two rounds of limiting dilution cloning. The mAb prepared from hybridoma #1 (IgG1) and hybridoma #2 (IgG2b) were each reactive against two independent tumor lines derived from spontaneous breast tumors in neuN mice (C2D1 and MMC5) when these cells were maintained in serum-free culture medium as tumorspheres. There was no reactivity against the same tumor cell lines when cultured as adherent monolayers in serum-containing medium nor was there reactivity against 3T3 adherent or tumorsphere cultures. Our previous analysis of tumorsphere cultures of C2D1 and MMC5 indicated that they express a panel of markers associated with tumor progenitor cells and have markedly enhanced per-cell tumorigenicity. Two of these antibodies have been purified by protein G or Protein A columns and retain binding to C2D1-tumorsphere cells, but not to C2D1 adherent cells. Importantly, these two antibodies can also bind to cultured 4T1-tumorsphere cells, an additional breast cancer cell line arising initially in BALB/c mice. These studies will allow us to identity corresponding antigens and determine expression on a broader array of spontaneous breast carcinomas in neuN mice. The epitopes recognized by these mAbs, which are expressed on progenitor cells from multiple tumor lines, might have importance as an immunotherapy target. Citation Format: Li-Xin Wang, Mona Patel, Michael Berk, Gregory E. Plautz. Monoclonal antibodies derived in neuN mice following successful T cell therapy of spontaneous breast tumors are specific for tumor progenitor cells. [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 2853. doi:10.1158/1538-7445.AM2013-2853