Radiation and dual checkpoint blockade activate non-redundant immune mechanisms in cancer

Abstract

Immune checkpoint inhibitors1 result in impressive clinical responses2–5 but optimal results will require combination with each other6 and other therapies. This raises fundamental questions about mechanisms of non-redundancy and resistance. Here, we report major tumor regressions in a subset of patients with metastatic melanoma treated with an anti-CTLA4 antibody (anti-CTLA4) and radiation (RT) and reproduced this effect in mouse models. Although combined treatment improved responses in irradiated and unirradiated tumors, resistance was common. Unbiased analyses of mice revealed that resistance was due to upregulation of PD-L1 on melanoma cells and associated with T cell exhaustion. Accordingly, optimal response in melanoma and other cancer types requires RT, anti-CTLA4, and anti-PD-L1/PD-1. Anti-CTLA4 predominantly inhibits T regulatory cells (Tregs) to increase the CD8 T cell to Treg (CD8/Treg) ratio. RT enhances the diversity of the T cell receptor (TCR) repertoire of intratumoral T cells. Together, anti-CTLA4 promotes expansion of T cells, while RT shapes the TCR repertoire of the expanded peripheral clones. Addition of PD-L1 blockade reverses T cell exhaustion to mitigate depression in the CD8/Treg ratio and further encourages oligo-clonal T cell expansion. Similar to results from mice, patients on our clinical trial with melanoma showing high PD-L1 did not respond to RT + anti-CTLA4, demonstrated persistent T cell exhaustion, and rapidly progressed. Thus, PD-L1 on melanoma cells allows tumors to escape anti-CTLA4-based therapy, and the combination of RT, anti-CTLA4, and anti-PD-L1 promotes response and immunity through distinct mechanisms.

Mitotic progression following DNA damage enables pattern recognition within micronuclei

“…A similar impact on tumor size with STING loss was noted in abscopal tumors when the contralateral tumor was irradiated directly in the mice (Extended data 6e and 6f). Consistent with a requirement for T cell responses, STING knockout prevented the enrichment of intratumoral CD8 T cells in the abscopal tumor (Fig 4d) 24, 26 . Thus, STING signaling is a critical component of host immune activation that drives regression of distal tumors in RT- and anti-CTLA4 combination therapy.…”

“…Overall survival and flow cytometry for tumor infiltrating CD8+ T-cells was performed as described 25 . For the in situ irradiation experiments of Extended Data 4e and 4f experiments were performed using the Small Animal Radiation Research Platform (SAARP) as previously described 24 .…”

“…This is most often observed in combination with immune checkpoint blockade (i.e. anti-CTLA4 antibody) 22–24 , suggesting that local radiation can be immunomodulatory. We have extensively characterized how irradiation of one tumor along with immune checkpoint blockade can produce T cell-dependent responses in the contralateral unirradiated tumor using the B16 syngeneic murine model of melanoma 24, 25 .…”

Antigen-capturing nanoparticles improve the abscopal effect and cancer immunotherapy

“…Administering radiotherapy with immunotherapy has been shown to improve immune responses and can elicit an “abscopal effect” 2 . Unfortunately, response rates for this strategy remain low 3 . Herein, we report an improved cancer immunotherapy approach that utilizes antigen-capturing nanoparticles (AC-NPs).…”

Long-term outcomes of a phase I study of agonist CD40 antibody and CTLA-4 blockade in patients with metastatic melanoma

“…28 CD8 positive cells were counted in 5 random high powered fields (HPF, 40x) and averaged per sample. PD-L1 staining was scored 0 to 4, as previously described.…”