This research study is being conducted to assess the safety and efficacy of IPH4102, an investigative medication (medication not approved by the Food and Drug Administration (FDA) for subjects diagnosed with Sézary Syndrome (SS) or Mycosis Fungoides (MF) over the age of 18. Participants will be asked to complete the following research procedures: Vital signs, Physical Exam, Medical History, Blood and Urine tests, Ct scans (Computed tomography, an X-Ray image) or PET/CT scans (a positron emission tomography scan), Skin biopsies and subject questionnaires. The duration of study participation will be variable. Participants will receive IPH4102 until disease progresses or participants develop an unacceptable toxicity secondary to IPH4102. Participation could last up to 2 years.

You may be eligible for this study if you meet the following criteria:

• Conditions: T-cell lymphoma, Chemotherapy, Sézary Syndrome, SS, Mycosis Fungoides, MF
• Age: 18 years - 99 years
• Gender: All