Reduced Overall T-Cell Receptor Diversity As an Indicator of Aggressive Cutaneous T-Cell Lymphoma

Introduction: Mycosis fungoides (MF) is a T-cell lymphoma that originates in the skin and can progress in late stages to involve blood, lymph nodes, or viscera. Large cell transformed mycosis fungoides (LCT-MF) is an aggressive subtype of MF associated with a higher likelihood of malignancy progression and mortality. Given that T-cell receptor (TCR) diversity is an indicator of cancer prognosis and outcome in several malignancies, we sought to investigate changes in T-cell repertoire diversity in LCT-MF. We interrogated the repertoire in non-leukemic MF, including both early-stage (patch and plaque, IA-IIA) and skin limited late-stage MF (tumor and erythroderma, IIB-IIIA).

Methods: After approval by Thomas Jefferson University Institutional Review Board Committee, a review of clinical data was performed on patients with MF at the Jefferson Cutaneous Lymphoma Clinic. Patients included in the study had a confirmed diagnosis of MF based on clinical, histological, and molecular data as well as adequate specimens for analysis. We evaluated staging and disease progression by 2022 NCCN guidelines. We included 61 lesional skin samples and 43 serum samples from 32 MF patients and 23 aged-matched healthy subjects. We used high-throughput sequencing (HTS) assays to interrogate the TCRb complementarity determining region 3 (CDR3) sequences in blood and skin of enrolled patients as well as blood of healthy subjects 13 (Adaptive Biotechnologies). ImmunoSEQ Analyzer provided T-cell diversity metrics, Simpson's clonality score and maximum frequency, as well as Vb usage.

Results: We first compared blood T-cell repertoire diversity among age-matched healthy subjects and MF patients without blood involvement. The diversities of the T-cell repertoire in blood of both non-leukemic MF and non-leukemic LCT-MF patients were significantly lower, compared to their age-matched healthy subjects. However, the diversity scores did not differ between the MF and LCT-MF cohorts in blood (Figure 1). In contrast, LCT-MF skin specimens possessed significantly lower T-cell clonal diversity (Figure 2) and distinct Vb usage in comparison to MF. There was no difference in T-cell diversity between early-stage and late-stage MF cohorts.

Conclusion: Overall, our data demonstrate that LCT-MF T-cells in the skin, not blood, exhibit a less diverse clonal repertoire when compared to MF. We find that the transformation of malignant cells in the skin does not accompany changes in blood repertoire. Instead, the transformation events in the skin mirror a reduction of overall T-cell diversity in the skin of patients with LCT-MF, compared to their non-transformed counterparts. While skin T-cell repertoire diversity distinguishes transformed and non-transformed MF, the skin diversity metrics do not differ between early- and late-stage disease. This finding implies that the shift in skin T-cell diversity seen in LCT-MF is not related to stage. Rather, we posit that shifts in T-cell diversity may be influenced by the early transformation event itself.

Figure 1: Simpson's clonality scores of blood T-cell repertoire in healthy subjects, MF, and LCT-MF. Statistically significant differences between cohort groups are marked by asterisks (** = p<0.001, *** = p <0.0001).

Figure 2: Simpson's clonality scores of skin T-cell repertoire in MF and LCT-MF. Statistically significant differences between cohort groups are marked by asterisks (*** = p <0.0001).

Porcu:Daiichi, Kyowa: Honoraria, Membership on an entity's Board of Directors or advisory committees; Innate Pharma: Honoraria, Membership on an entity's Board of Directors or advisory committees; BeiGene: Membership on an entity's Board of Directors or advisory committees; Morphosys: Membership on an entity's Board of Directors or advisory committees; DrenBio: Consultancy; Teva: Honoraria, Research Funding; Ono: Membership on an entity's Board of Directors or advisory committees; ADCT: Membership on an entity's Board of Directors or advisory committees; Loxo: Membership on an entity's Board of Directors or advisory committees; Viracta: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Nikbakht:Helsinn: Membership on an entity's Board of Directors or advisory committees, Research Funding; Kyowa Kirin: Membership on an entity's Board of Directors or advisory committees.