Cancer cells recapitulate many behaviors of pluripotent embryonic cells such as unlimited proliferation, the capacity to self renew and to migrate. Previously, a search for new embryonic genes also expressed in cancer identified Embryo-Cancer Sequence A (ECSA), also named Developmental Pluripotency Associated-2 (DPPA2). ECSA/DPPA2 has been shown to be expressed in human pre-implantation embryos and primordial germ cells (PGCs) but is rapidly down regulated upon differentiation. ECSA/DPPA2 transcripts in normal tissues are limited to testis, placenta, bone marrow and thymus but expressed in a variety of tumors including colorectal cancers and melanoma but most notably in Non-Small Cell Lung Cancers (NSCLC). Transcripts for a panel of Cancer Testis antigens (CTAs) investigated in the same NSCLC tissues, demonstrated enrichment of CTAs in ECSA/DPPA2 positive tumors. IHC demonstrated nuclear localization for ECSA/DPPA2 in subpopulations of basally located cells consistent with cells occupying a 'stem-cell niche'. Antibodies to ECSA/DPPA2 protein were detected in the sera of patients with NSCLC, but not in healthy controls. The restricted expression in normal tissues, expression in tumors with co-expression of CTAs and spontaneous immunogenicity, indicate that ECSA/DPPA2 is a promising target for antigen specific immunotherapy in NSCLC. This project will define ECS-A/DPPA2 further in human lung cancer. In particular, it will focus on defining lung cancer stem cell surface markers to enable sorting and purification of these cells.