Immunological insights from patients undergoing surgery on ipilimumab for metastatic melanoma.

Background: The tumor microenvironment after treatment with ipilimumab is not well described. Furthermore, the safety of surgery for patients being treated with ipilimumab for metastatic melanoma has not been well reported. This study analyzed the safety of surgery and the immune phenotype of tumors resected while on ipilimumab.

Methods: From our prospective melanoma database, we identified patients undergoing surgery for any indication within 30 days of receiving a dose of induction ipilimumab or while on maintenance ipilimumab therapy. Surgical toxicity was graded 1-5 by the Clavien classification. Tumor-infiltrating lymphocytes were classified by flow cytometry and compared with peripheral blood.

Results: 23 patients were identified who underwent 34 operations a median of 27 weeks after initiation of ipilimumab (1-123 weeks). Subcutaneous resections were the most frequent, followed by intra-abdominal and nodal procedures. Grade 1 or 2 wound complications were seen in 22% of patients. No Grade 3-5 complications were seen. Analysis of the T cell infiltrate and matched peripheral blood from ten patients showed an elevated % of CD4+FOXP3+ T-regulatory cells and a 2.8-fold lower ratio of CD8+/CD4+FOXP3+ in the tumor compared with blood (p=0.02). In addition, all CD8+ T cells had a higher expression of PD-1 in the tumor, compared with peripheral blood.

Conclusions: Surgery for patients on ipilimumab is safe. This study highlights the immunosuppressive phenotype in tumors not responding to immunotherapy. The high percentage of T-regulatory cells and low T-effector cells in progressive tumors suggests a possible mechanism of immune escape.