Immunization against HIF-1α Inhibits the Growth of Basal Mammary Tumors and Targets Mammary Stem Cells <i>In Vivo</i>.

Abstract

<b>Purpose:</b> Triple-negative breast cancer (TNBC) represents a cancer stem cell-enriched phenotype. Hypoxia-inducible factor-1α (HIF-1α) induces the expression of proteins associated with stemness and is highly upregulated in TNBC. We questioned whether HIF-1α was immunogenic and whether vaccination targeting HIF-1α would impact the growth of basal-like mammary tumors in transgenic mice.<b>Experimental Design:</b> We evaluated HIF-1α-specific IgG in sera from controls and patients with breast cancer. Class II epitopes derived from the HIF-1α protein sequence were validated by ELISPOT. To assess therapeutic efficacy, we immunized Tg-MMTVneu and C3(1)Tag mice with HIF-1α Th1-inducing peptides. Stem cells were isolated via magnetic bead separation. Levels of HIF-1α and stem cells in the tumor were quantitated by Western blotting and flow cytometry.<b>Results:</b> The magnitude (<i>P</i> < 0.001) and incidence (<i>P</i> < 0.001) of HIF-1α-specific IgG were elevated in TNBC patients compared with controls. Both breast cancer patients and donors showed evidence of HIF-1α-specific Th1 and Th2 immunity. Three HIF-1α-specific Th1 class II restricted epitopes that were highly homologous between species elicited type I immunity in mice. After HIF-1α vaccination, mammary tumor growth was significantly inhibited in only C3(1)Tag (basal-like/stem cell^high; <i>P</i> < 0.001) not TgMMTV-neu (luminal/neu/stem cell^low; <i>P</i> = 0.859) murine models. Vaccination increased type I T cells in the tumor (<i>P</i> = 0.001) and decreased cells expressing the stem cell marker, Sca-1, compared with controls (<i>P</i> = 0.004).<b>Conclusions:</b> An HIF-1α 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. <i>Clin Cancer Res; 23(13); 3396-404. ©2016 AACR</i>.