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.
Ipilimumab improves survival in patients with advanced melanoma.,The activity and safety of ipilimumab outside of a clinical trial was assessed in an expanded access programme (EAP).,Ipilimumab was available upon physician request for patients aged 16 or over with pretreated stage III (unresectable)/IV melanoma, for whom no other therapeutic option was available.,Patients received ipilimumab 3 mg/kg every 3 weeks for four doses.,Patients with stable disease or an objective response to ipilimumab were eligible for retreatment upon disease progression.,Tumour assessments were conducted at baseline and week 12.,Patients were monitored for adverse events (AEs) within 3 to 4 days of each scheduled visit.,Of 855 patients participating in the EAP in Italy, 833 were evaluable for response.,Of these, 13% had an objective immune response, and the immune-related disease control rate was 34%.,Median progression-free survival and overall survival were 3.7 and 7.2 months, respectively.,Efficacy was independent of BRAF and NRAS mutational status.,Overall, 33% of patients reported an immune-related AE (irAE).,The frequency of irAEs was not associated with response to ipilimumab.,Outside of a clinical trial setting, ipilimumab is a feasible treatment option in patients with pretreated metastatic melanoma, regardless of BRAF and NRAS mutational status.,Data from this large cohort of patients support clinical trial evidence that ipilimumab can induce durable disease control and long-term survival in patients who have failed to respond to prior treatment.