MYCOSIS FUNGOIDES: NOVEL THERAPEUTIC APPROACHES TARGETING THE CUTANEOUS LYMPHOCYTE ANTIGEN (CLA)

Background Mycosis fungoides (MF) is the most common form of cutaneous T cell lymphoma. There are currently few effective therapies for the treatment of MF. Treatments for the early stages generally consist of a skin-directed therapy, and treatments for the late stages are generally systemic, and often combined. Although the initial stages of mycosis fungoides have a moderate clinical course, 30% of patients relapse or prove to be refractory to currently used treatments and are destined to progress to advanced stages of the disease for which, in fact, there is not a curative treatment. Therefore, the development of new therapeutic strategies is fundamental. While the Cutaneous Lymphocyte Antigen (CLA) is strongly expressed by MF tumor cells, it could be a specific molecular target for the treatment of MF. The aim of the whole PhD project was to investigate novel therapeutic approaches targeting CLA for the treatment of MF. The first specific aim was to investigate the antitumor effect of a CLA-targeted Near‐infrared photoimmunotherapy (NIR-PIT) on MF cells and the second specific aim was to investigate the antitumor effect of an antibody-drug conjugate (ADC) consisting of an anti-CLA monoclonal antibody and monomethyl auristatin E (MMAE). Methods In vitro validation of anti-CLA monoclonal antibody-based approaches were performed using a MF cell line called Myla CD4+ cell line. In vivo studies are ongoing on zebrafish embryo model of MF created by the injection of Myla CD4+ cells into the yolk sac at 2 days post fertilization. Results Treatment with anti-CLA monoclonal antibody alone or near infrared light irradiation alone exhibited very modest pro-death effects, while the combination of the two induced a substantial increase in death in the MF cell line showing that CLA-targeted NIR PIT has a marked anti-tumor effect in vitro. Conversely, the anti-CLA-MMAE antibody drug conjugate exhibited in vitro lower cytotoxic activity compared to anti-CLA monoclonal antibody or MMAE alone. In vivo validation phases studies are ongoing to investigate the efficacy of these anti-CLA monoclonal antibody-based approaches. Preliminary data are encouraging but are still under evaluation. Discussion An anti-CLA monoclonal antibody-based approach may represent a novel and highly selective treatment for this disease. While CLA-targeted NIR-PIT shows a marked anti-tumor effect on MF cells in vitro, it is an attractive candidate for in vivo studies and ultimately for clinical trials. The anti-CLA-MMAE ADC shows low cytotoxicity activity in vitro which could be explained by the lack of internalization of the ADC into the cells. However, it has recently been demonstrated that in vivo non-internalizing antibodies may have potent anti-cancer activity thanks to proteolytic release of MMAE in the subendothelial extracellular matrix. Thus, anti-CLA-MMAE ADC may be effective in vivo. The xenotransplantation experiments performed to evaluate the proliferation of MF cells in zebrafish embryos have given very positive and extremely encouraging results, confirming the possible use of this animal species as a model for the study of this pathology.