Abstract 512: Leukemia-specific immunity in healthy individuals and patients post-transplant targets phosphorylated tumor antigens
Authors: Hugo De La Peña, James E. Turner, Thomas Butler, Richard Buka, Laura Morton, Sarah Penny, David George Millar, Charles F. Craddock, Guy Pratt, Victor H. Engelhard, Donald F. Hunt, Mark Cobbold
Journal: Cancer Research (2012)

Abstract The major antigenic targets of endogenous tumor immunity remain unknown although many minor targets have been identified. At a proteomic level, cancer is considered a disease of deregulated cell signal pathway activation; therefore we investigated whether endogenous anti-tumor immunity targeted phosphorylated protein antigens generated through the transformation process. In previous work we identified phosphorylated peptides differentially expressed on primary leukemia samples: 58 for acute myeloid leukemia (AML) samples and 31 for chronic lymphocytic leukemia (CLL). Many of the identified phosphopeptides were derived from established leukemogenic oncoproteins such as MLL, RUNX1, c-Myc, EP300, CXCR4, SKI, GRK, CD19, CD20, NCOA1, and TLK1 among others and differentially expressed between malignant and healthy counterpart tissue (splenic B cells, bone marrow). Using ELISpot and HLA-phosphopeptide multimers, we screened 10 healthy donors, 17 patients in complete remission with underlying AML and 14 patients with CLL. Healthy donors (HD) exhibited a highly heterogeneous reactivity against this panel of phosphoantigens but all responded to at least 10/57 phosphoantigens tested. Further investigation revealed this immunity resided within the central memory CD8 T cell compartment at the same magnitude of responses as those against influenza and adenovirus. By contrast only 2/12 AML and 5/14 CLL patients demonstrated anti-phosphopeptide immunity compared to 10/10 HDs (≥2&amp;lt; 0.01 for both). In contrast immunity against viral and mitogenic stimuli was similar between patients and HDs. Following allogeneic stem cell transplantation the majority (10/12) AML patients reconstituted anti-phosphopeptide immunity. In some cases dramatic expansions, of similar magnitude to cytomegalovirus responses, were observed approaching 1% of CD8 T cells for a single phosphopeptide epitope. In CLL, none of whom were transplanted, we found that over the study period of 12 months that among the patients with anti-phosphopeptide immunity only 1 of 5 patients required treatment compared to 4 of 9 patients requiring treatment where no anti phosphopeptide responses were seen (≥2=NS). Importantly, ex vivo expanded phosphopeptide specific T cells isolated from both healthy individuals and patients post-transplant were able to kill both HLA-matched primary leukemia samples and AML cell lines in a phosphopeptide-specific manner. These data suggest a prominent role for tumor-associated phosphopeptide antigens in the prevention and control of haematolymphoid disease in man. 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 512. doi:1538-7445.AM2012-512