Purpose: The poor response of breast cancer to immune checkpoint blockade might result from low immunogenicity and the immune-suppressive tumor microenvironment. We hypothesized that in situ tumor vaccination via radiation therapy (RT) and suppression of immune tolerance via phosphoinositide 3-kinase δ (PI3Kδ) inhibition would enhance the efficacy of immune checkpoint blockade.
Methods And Materials: 4T1 murine breast cancer cells were grown in both immune-competent and -deficient BALB/c mice, and tumors were irradiated with 24 Gy in 3 fractions.