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

Abstract

&lt;div&gt;Abstract&lt;p&gt;&lt;b&gt;Purpose:&lt;/b&gt; 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.&lt;/p&gt;&lt;p&gt;&lt;b&gt;Experimental Design:&lt;/b&gt; 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.&lt;/p&gt;&lt;p&gt;&lt;b&gt;Results:&lt;/b&gt; The magnitude (&lt;i&gt;P&lt;/i&gt; &lt; 0.001) and incidence (&lt;i&gt;P&lt;/i&gt; &lt; 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&lt;sup&gt;high&lt;/sup&gt;; &lt;i&gt;P&lt;/i&gt; &lt; 0.001) not TgMMTV-neu (luminal/neu/stem cell&lt;sup&gt;low&lt;/sup&gt;; &lt;i&gt;P&lt;/i&gt; = 0.859) murine models. Vaccination increased type I T cells in the tumor (&lt;i&gt;P&lt;/i&gt; = 0.001) and decreased cells expressing the stem cell marker, Sca-1, compared with controls (&lt;i&gt;P&lt;/i&gt; = 0.004).&lt;/p&gt;&lt;p&gt;&lt;b&gt;Conclusions:&lt;/b&gt; 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. &lt;i&gt;Clin Cancer Res; 23(13); 3396–404. ©2016 AACR&lt;/i&gt;.&lt;/p&gt;&lt;/div&gt;