Background: Adoptive transfer of tumor infiltrating lymphocytes (TIL) can effect long-term durable regression in patients with metastatic melanoma but has not been widely tested in common epithelial cancers. Similar to metastatic melanoma, recent studies on epithelial GI cancers report that tumor regressions can be mediated by adoptively transferred TIL recognizing non-synonymous somatic mutations. Breast cancer metastatic tumors are infiltrated by TIL and reactivity against autologous somatic mutations can be identified.

Methods: TIL were grown from a metastatic soft tissue tumor of a patient with hormone and chemotherapy-refractory ER+, HER2- breast cancer. DNA was extracted from tumor and matched normal peripheral blood samples for whole exome sequencing (WES) and RNAseq. Non-synonymous somatic mutations were identified and tested for potential recognition by autologous TIL using previously described tandem mini-gene and long peptide approaches. Recognition was assessed by IFN-γ release on ELISPOT and/or CD137 (4-1BB) upregulation with appropriate controls. Mutation reactive TIL were rapidly expanded in culture and transferred back to the patient. Adoptive cell transfer was preceded by a lymphodepleting preparative regimen and one dose of pembrolizumab. Cells were supported post-transfer with intravenous IL-2 administration, and pembrolizumab was administered for three additional doses. Deep sequencing of TCR rearrangement sequences was performed on the TIL and the pre- and post-infusion peripheral blood.

Results: The resected subcutaneous tumor no longer expressed ER and was negative for PD-L1 staining. WES/RNASeq identified 96 non-synonymous mutations for testing. Multiple CD4+ clones specifically recognizing a mutation expressed in the solute carrier SLC3A2 (p.K94T) and a single CD8+ clone recognizing a mutation in the proteasome-associated protein KIAA0368 (p.S186F) were identified with no recognition of wild-type peptides. These eight T cell clones constituted 23% of the infusion bag TIL. Nine months after transfer of 82x109 cells, the patient has an ongoing partial response, with target lesions down 96% from baseline, including multiple hepatic metastases and disabling brachial plexus adenopathy. Seven of the eight T cell clones with known reactivity persisted in the peripheral blood comprising 2.4% of all CDR3 sequences at 7 months. Only two of these TCR clones were detectable, with frequencies totaling 0.005%, in the pre-treatment circulation.

Conclusions: Tumor-infiltrating lymphocytes derived from a patient with metastatic breast cancer recognized tumor-specific non-synonymous somatic mutations, expanded in vitro and were used for adoptive cell transfer. TIL, co-administered with IL-2 and a short course of pembrolizumab, persisted in vivo and mediated regression of soft tissue, nodal and visceral metastases of breast cancer.

Citation Format: Nikolaos Zacharakis, Katarzyna Trebska-McGowan, Robert Somerville, Yong-Chen Lu, Anna Pasetto, Mary Black, Harshini Chinnasamy, Hui Xu, Jared J. Gartner, Todd D. Prickett, Paul F. Robbins, Steven A. Rosenberg, Stephanie L. Goff, Steven A. Feldman. Regression of metastatic breast cancer after adoptive cell transfer of tumor infiltrating lymphocytes and checkpoint blockade [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4982. doi:10.1158/1538-7445.AM2017-4982