Original Articles: Translational ResearchEnrichment of melanoma-associated T cells in 6-thioguanine-resistant T cells from metastatic melanoma patientsZuleger, Cindy L.a; Newton, Michael A.a,,b; Ma, Xiuyub; Ong, Irene M.a,,b,,c; Pei, Qinglinf; Albertini, Mark R.a,,d,,eAuthor Information aUniversity of Wisconsin Carbone Cancer Center, University of Wisconsin School of Medicine and Public Health Departments of bBiostatistics and Medical Informatics cObstetrics and Gynecology dMedicine, University of Wisconsin School of Medicine and Public Health eMedical Service, William S. Middleton Memorial Veterans Hospital, Madison, Wisconsin fDepartment of Biostatistics, University of Florida, Gainesville, Florida, USA Received 26 September 2018 Accepted 7 May 2019 Supplemental Digital Content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's website, www.melanomaresearch.com. Correspondence to Mark R. Albertini, MD, University of Wisconsin Clinical Sciences Center, Room K6/530, 600 Highland Avenue, Madison, WI 53792, USA, Tel: +1 608 263 0117; fax: +1 608 265 8133; e-mail: firstname.lastname@example.org Melanoma Research: February 2020 - Volume 30 - Issue 1 - p 52-61 doi: 10.1097/CMR.0000000000000625 Buy SDC Metrics Abstract This study examines whether 6-thioguanine resistant T cells (mutant) from metastatic melanoma patients are enriched for melanoma-associated T cells compared to T cells obtained analogously without thioguanine selection (wild-type). Melanoma-associated antigen pentamer staining was performed on 5 tumour and 9 peripheral blood samples from metastatic melanoma patients. T cell receptor beta chain repertoire was examined via Sanger sequencing of mutant and wild-type in blood and tumour from metastatic melanoma patients at times of tumour progression (n = 8) and via Illumina sequencing in tumour derived T cells and in uncultured T cells (uncultured), wild-type and mutant from blood before and after immune checkpoint blockade (n = 1). Mutant from tumour (3 of 5; P < 0.001), but not blood (0 of 9), were enriched compared to wild-type for binding melanoma-associated antigen pentamers. T cell receptor beta analysis in patients with tumour progression (n = 8) detected increased melanoma associated T cells in mutant compared to wild-type from blood (Monte Carlo P = 10−7). Comparison of blood samples before and after immune checkpoint blockade with prior tumor from one metastatic melanoma patient detected increased T cell receptor beta sharing between tumour and mutant compared to tumour and wild-type or tumour and uncultured: 11.0% (72/656), 1.5% (206/13 639) and 1.3% (381/29 807), respectively (Monte Carlo P = 10−7 for mutant versus wild-type and mutant versus uncultured). These data demonstrate that mutant in metastatic melanoma patients are enriched for melanoma-associated T cells and are candidate probes to study in vivo melanoma-reactive T cells. Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.