Effect of expression of ICOS in cutaneous T-cell lymphoma and its targeting on killing of malignant cells.

Abstract

e20040 Background: Advanced stage cutaneous T-cell lymphomas (CTCLs) remain an unmet medical need. Immunomodulatory agents such as mogamulizumab, anti-KIR3DL2 and brentuximab vedotin (BV), an anti-CD30 antibody–drug conjugate (ADC) coupled to monomethyl-auristatin-E (MMAE), provided encouraging results but new targeted therapies are needed. Inducible Co-Stimulator (ICOS), a T-cell costimulatory receptor involved in the development of CTCLs, arouses interest. Methods: We used immunohistochemistry to study ICOS expression in skin biopsies of 23 patients with early-stage mycosis fungoides (MF), 12 with transformed MF (TMF) and 17 with Sézary Syndrome (SS), at diagnosis or in relapse. ICOS expression by circulating Sézary cells and regulatory T cells (Tregs) in patients with SS was evaluated using flow cytometry, and compared to healthy donors (HD) lymphocytes. In 5 patients with SS, we also analyzed concomitant biopsies from involved nodes. Then, we investigated the efficacy of anti-ICOS ADCs generated by coupling murine anti-ICOS monoclonal antibodies with MMAE, in comparison to BV. We used ICOS+ CTCL cell lines (MyLa and MJ), murine xenograft models with MyLa and ICOS+ Patient Derived Xenografts (PDXs) from patients with SS and angioimmunoblastic T-cell lymphoma (AITL). Results: ICOS was highly expressed by the cutaneous atypical lymphocytic infiltrates in respectively 61%, 75% and 88% of patients with early-stage MF, TMF and SS, such as in the 5 patients with node involvement. ICOS expression by circulating Sézary cells was strong: 69±7.3% versus 38.8±7.1% of non-tumoral CD4+ cells ( p< 0.009; CI95%: 8.7-51.6); and 31±3.2% of CD4+ cells in HD ( p< 0.0001; CI95%:20.3-46.3). Percentages of ICOS+ Tregs were significantly higher in patients with SS than in HD. In CTCL cell lines, we observed a significant dose-dependent decrease in cell viability in the presence of anti-ICOS ADCs. In a mouse xenograft model (MyLa), anti-ICOS ADCs provided a longer overall survival (OS) than BV (HR = 15.2;CI95%:3.2-71.1; p< 0.0006). Finally, in ICOS+ PDXs anti-ICOS ADCs significantly improved OS, and reduced the number of tumor cells in the blood, bone marrow and spleen. No evidence of ADC toxicity was observed in treated mice. Conclusions: All together our results show that ICOS is a therapeutic target of interest in CTCLs and provide the preliminary basis for a therapeutic trial