There is growing evidence that a variety of tumors including breast cancer may be driven by a small subset of cancer stem/progenitor cells that exhibit chemotherapeutic resistance and cause tumor relapse. The eradication of this small subset of cells might improve therapeutic outcome. However, it is unknown whether breast cancer stem/progenitor cells are susceptible to T-cell mediated immunotherapy. We used defined serum-free conditions to establish primary neupos BCSC lines. Spontaneous breast tumors arising in neu-N transgenic mice were passaged in vivo to generate progressor lines and tumors were harvested and prepared as a single cell suspension. Paired aliquots of tumor cells were cultured in either serum-free medium supplemented with EGF and bFGF to derive BCSC sub-lines, or alternatively in standard serum-containing medium to generate mouse mammary carcinoma (MMC) sub-lines. The BCSC cells display morphologic characteristics of breast cancer stem/progenitor cells, such as non-attached growth in spheroid colonies, and high expression of CD44. We vaccinated neu-N transgenic mice with 2×107 irradiated MMC10-BCSC or its paired cell line MMC10-AD and harvested vaccine-draining lymph nodes 9 days later. Antigen-primed CD62Llow cells were isolated using MACS beads and CD62LlowCD4+ or CD62LlowCD8+ T cells were additionally purified and stimulated with anti-CD3/IL-2/IL-7 for two stimulation cycles. Adoptive transfer of 3×107 CD62Llow CD4+ cells from MMC10-BCSC-draining LNs effectively eradicated pulmonary metastases (p<0.001). By contrast, 3×107 CD62Llow CD4+ T cells from MMC10-AD-draining LNs was sub-therapeutic (p>0.05 vs. control). In an independent experiment, adoptive transfer of 3×107 CD8+ T cells sensitized by MMC10-BCSCs mediated the regression of established MMC10 pulmonary metastasis (p<0.001), whereas 6×107 CD8+ cells primed by MMC10-AD was ineffective. More importantly, adoptive transfer of 4 × 107 in vitro-activated CD8+ cells combined with 2×107 CD4+ cells derived from LNs draining MMC10-BCSCs are effective against the parental MMC10 line as well as an independently derived neupos line MMC-1. Also, transfer of either 3×107 CD4+ or CD8+ T cells from LNs draining MMC10-BCSCs effectively mediated regression of established 3-day neupos MMC4 pulmonary metastasis. In conclusion, irradiated whole tumor cell vaccines derived from neupos BCSCs can prime T-cells in neu-tolerant hosts. Although this immune response is insufficient to prevent progressive tumor growth, highly activated effector function and large numbers of CD4+ and CD8+ T cells can be generated through in vitro activation with anti-CD3/IL-2/IL-7 stimulation. Either CD4+ or CD8+ T cells are cross-protective against other neu-positive tumor metastases indicating that this approach provides MHC class I and II immune responses.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1929.