Minimal residual disease monitoring with high-throughput sequencing of T cell receptors in cutaneous T cell lymphoma

Mycosis fungoides (MF) and the leukemic presentation Sézary syndrome (SS) are clonal T cell lymphomas arising from the skin and are considered noncurable with standard therapies. To develop a specific and sensitive monitoring tool, we tested the ability of high-throughput sequencing (HTS) of T cell receptors (TCRB) to monitor minimal residual disease (MRD) after allogeneic hematopoietic cell transplantation. Genomic DNA was extracted from peripheral blood mononuclear cells (PBMCs) or skin samples. The rearranged TCRb loci were amplified using Vβ- and Jβ-specific primers, followed by HTS, to generate up to 1,000,000 reads spanning the CDR3 region of individual cells. Malignant clones were identified in diagnostic samples in all cases by a dominant CDR3 sequence. Before transplant, four patients had circulating Sézary cells by the routine flow cytometry, which was confirmed by TCRB HTS. Although the flow cytometry found no detectable Sézary cells, malignant clones were detected by TCRB HTS in all other six cases. Five patients achieved "molecular remission" in blood between +30 and +540 days after transplant. Four of these patients also achieved molecular clearance in skin after transplant. Experiments using blood samples spiked with purified Sézary cells demonstrated that TCRB HTS can detect Sézary cells at the level of 1 in 50,000 PBMCs, which is more sensitive than standard diagnostics. We have thus demonstrated the utility of TCRB HTS to assess MRD with increased sensitivity and specificity compared to other current methodologies, and to monitor response to therapy in this MF/SS patient population.