Prior CTLA-4 blockade as associated with a hyperactive immunosuppressive signature and limited response to subsequent immunotherapy in melanoma.

2634 Background: Checkpoint blockade achieves durable long term responses in about 30-50% of patients with malignant melanoma (MM). However, a substantial proportion of patients either fail to respond or develop resistance after initial response. As a result, many MM patients undergo multiple sequential immunotherapeutic treatments in an attempt to achieve clinical benefit. However, the effects of repeated rounds of immunotherapy on the immune system remain poorly understood. We herein report that prior anti-CTLA-4 blockade within 12 months of analysis associated with a hyperactive immunosuppressive immune signature involving IL-6, in 24 patients with anti-PD-1 refractory metastatic MM enrolled in a Phase I/II trial. Methods: The patients received continued checkpoint inhibition with an anti-PD-L1 antibody in combination with an immunostimulatory gene therapy based on replication-competent adenovirus targeting the CD40 and 4-1BB pathways (LOKON003, NCT04123470). Using unsupervised clustering, plasma biomarker profiles at baseline and post treatment initiation was evaluated and correlated to clinical parameters. Results: Two plasma protein profiles were identified at baseline among enrolled patients and one of those included immunosuppressive biomarkers. While patients with this hyperactive immunosuppressive signature (n=8) at baseline experienced a median overall survival (mOS) of 4.0 months, patients without this baseline signature (n=15) had a mOS of 28.1 months. The hyperactive immunosuppressive signature was not related to M1 status, sex, age, or number of prior treatments, but prior anti-CTLA-4 treatment within a year of enrollment was more prevalent in patients with this signature. If dividing the patients only based on receiving anti-CTLA-4 therapy within 12 months (n=10) versus later or not at all (n=14), mOS was 5.3 and 30.7 months, respectively. Patients that had received recent anti-CTLA-4 treatment, presented with a plasma protein signature resembling the hyperactive immunosuppressive signature with IL-6 as a central node among the upregulated proteins. Patients who did not receive anti-CTLA-4 blockade during the past 12 months responded to the combination of the immunostimulatory gene therapy and continued checkpoint blockade with upregulation of biomarkers associated with T cell activation and cell killing capacity, which may have supported the better survival outcome in this patient group. Conclusions: The findings highlight the need for further clinical evaluation of the consequences of repeated immunotherapeutic treatments, IL-6 inhibition in this population, and consideration for a wash-out period from further immunotherapy to allow for immune system recovery post anti-CTLA-4 treatment. Clinical trial information: NCT04123470 .