Immunization against HIF-1α Inhibits the Growth of Basal Mammary Tumors and Targets Mammary Stem Cells In Vivo

Purpose: Triple-negative breast cancer (TNBC) represents a cancer stem cell-enriched phenotype. Hypoxia-inducible factor-1 alpha (HIF-1 alpha) induces the expression of proteins associated with stemness and is highly upregulated in TNBC. We questioned whether HIF-1 alpha was immunogenic and whether vaccination targeting HIF-1 alpha would impact the growth of basal-like mammary tumors in transgenic mice. Experimental Design: We evaluated HIF-1 alpha-specific IgG in sera from controls and patients with breast cancer. Class II epitopes derived from the HIF-1 alpha protein sequence were validated by ELISPOT. To assess therapeutic efficacy, we immunized Tg-MMTVneu and C3(1)Tag mice with HIF-1 alpha Th1-inducing peptides. Stem cells were isolated via magnetic bead separation. Levels of HIF-1 alpha and stem cells in the tumor were quantitated by Western blotting and flow cytometry. Results: The magnitude (P < 0.001) and incidence (P < 0.001) of HIF-1 alpha-specific IgG were elevated in TNBC patients compared with controls. Both breast cancer patients and donors showed evidence of HIF-1 alpha-specific Th1 and Th2 immunity. Three HIF-1 alpha-specific Th1 class II restricted epitopes that were highly homologous between species elicited type I immunity in mice. After HIF-1 alpha vaccination, mammary tumor growth was significantly inhibited in only C3(1) Tag (basal-like/stem cell(high); P < 0.001) not TgMMTV-neu (luminal/neu/stem cell(low); P = 0.859) murine models. Vaccination increased type I T cells in the tumor (P = 0.001) and decreased cells expressing the stem cell marker, Sca-1, compared with controls (P = 0.004). Conclusions: An HIF-1 alpha vaccine may be uniquely effective in limiting tumor growth in TNBC. Inhibiting outgrowth of breast cancer stem cells via active immunization in the adjuvant setting may impact disease recurrence. (C) 2016 AACR.