Primary T cells from cutaneous T-cell lymphoma skin explants display an exhausted immune checkpoint profile

Cutaneous T-cell lymphoma (CTCL) develops from clonally expanded CD4+ T cells in a background of chronic inflammation. Dendritic cells (DCs) are potent T-cell stimulators; yet despite DCs' extensive presence in skin, cutaneous T cells in CTCL do not respond with effective anti-tumor immunity. We evaluated primary T-cell and DC émigrés from epidermal and dermal explant cultures of skin biopsies from CTCL patients (n = 37) and healthy donors (n = 5). Compared with healthy skin, CD4+ CTCL populations contained more T cells expressing PD-1, CTLA-4, and LAG-3; and CD8+ CTCL populations comprised more T cells expressing CTLA-4 and LAG-3. CTCL populations also contained more T cells expressing the inducible T-cell costimulator (ICOS), a marker of T-cell activation. DC émigrés from healthy or CTCL skin biopsies expressed PD-L1, indicating that maturation during migration resulted in PD-L1 expression irrespective of disease. Most T cells did not express PD-L1. Using skin samples from 49 additional CTCL patients for an unsupervised analysis of genome-wide mRNA expression profiles corroborated that advanced T3/T4 stage samples expressed higher levels of checkpoint inhibition genes compared with T1/T2 stage patients or healthy controls. Exhaustion of activated T cells is therefore a hallmark of both CD4+ and CD8+ T cells directly isolated from the lesional skin of patients with CTCL, with a continuum of increasing expression in more advanced stages of disease. These results justify identification of antigens driving T-cell exhaustion and the evaluation of immune checkpoint inhibition to reverse T-cell exhaustion earlier in the treatment of CTCL. Overall design: RNA-seq correlated with tumor stages

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Querfeld C, Leung S, Myskowski PL, Curran SA, Goldman DA, Heller G, Wu X, Kil SH, Sharma S, Finn KJ, Horwitz S, Moskowitz A, Mehrara B, Rosen ST, Halpern AC, Young JW