A 60-year old female, black race, with a familiar history of diabetes and a silent personal medical history, presented to the center of Hematology in Cuneo with diffuse itching and cutaneous erythroderma on August 2020. At clinical examination, she had no fever, no night sweats, moderate weight loss, bilateral axillary and inguinal lymphadenopathy (about 2 centimeters), no hepato- or splenomegaly. The initial laboratory tests showed remarkable leukocytosis with absolute lymphocytosis (white cells blood count (WBC) 10,300/mm3, neutrophils 21%, lymphocytes 71%), normal hemoglobin and platelets levels and elevated serum lactate dehydrogenase (LDH) level. Abdominal ultrasound (US) scan showed some enlarged liver hilum and mesenteric lymph nodes. The CT scan and a positron emission tomography (PET) scan confirmed the enlarged activated lymph nodes in multiple sites above and below the diaphragm (bilateral cervical, axillary, iliac, inguinal, mesenteric and liver hilum). Flow cytometry on peripheral blood lymphocytes showed an invasion by a CD3+, CD4+, CD7+ T lymphocytes (87% of total lymphocyte count, 6344 cells/microL), with a monotypic expression of variable region Vbeta 12 of T-cell receptor. Multiple site biopsies (cutaneous, right axillary lymph node and bone marrow biopsy biopsy) showed an invasion by CD2+, CD3+, CD5+, CD7+ and CD4+ T lymphocytes. A diagnosis of SS was made and the patient started systemic treatment with steroids. After an initial clinical benefit on itching and cutaneous erythroderma, in December 2020 the patient showed a new worsening of both symptoms, with increasing lymphocytosis and growing adenopathies. On December 23rd 2020, a second line treatment with mogamulizumab at the standard dose of 1 mg/kg on day 1, 8, 15, 22 of cycle 1 and on day 1, 15 for the subsequent courses, was started. At the screening analyses, the patient was found to be anti-HBc Ab positive, with normal transaminase levels, HBsAg and HBV DNA negative. A standard HBV reactivation prophylaxis was started before starting mogamulizumab therapy. Since the second administration of mogamulizumab, a clear clinical benefit on itching and erythroderma was observed, as well as a progressive reduction of peripheral leukocytosis and lymphocytosis (Figure 1). Six cycles of mogamulizumab were performed and well tolerated, without any complication. At the same time, a bone marrow donor was searched: the patient had no siblings, matched unrelated donor (MUD) research was negative, but the patient had an available haploidentical son. The treatment with mogamulizumab was stopped in June 2021, after reaching an almost complete disease remission, and the patient underwent haploidentical allotransplant. In order to reduce the risk of acute Graft Versus Host Disease (aGVHD), a wash out period of 2 months from mogamulizumab infusion and allotransplant was performed. The restaging of disease showed a complete cutaneous response, a complete regression of peripheral blood lymphocytosis with negative peripheral blood flow cytometry and negative bone marrow cytometry and biopsy and a good partial response on lymphadenopathy. The patient underwent allotransplant in a good global partial response, with a Sorror score 1 (for HBV prophylaxis). The transplant was planned on August 2021, but then delayed until September 2021, because of donor positivity for malaria PCR. After antimalarial treatment and the negativization of plasmodium PCR on two consecutive analyses, the peripheral blood stem cells (PBSC) collection was performed. A cytomegalovirus (CMV) reactivation prophylaxis with letermovir from the day of transplant (the patient was CMV positive) and an antifungal prophylaxis with micafungin were administered. A transplant conditioning regimen with thiotepa-cyclophosphamide-fludarabine, followed by total-body irradiation (TBI) 200 rads, was used. On day 0, she received fresh PBSC by haploidentical son donor, containing a total of 9.56 x 106 CD34+ cells/kg. She started GVHD prophylaxis with immunosuppressive therapy with cyclophosphamide (day +3 and +4 from transplant), mycophenolate from day +4 to day +35 and cyclosporine from day +4. The clinical post-transplant course was good, with neutrophil recovery observed on day +15 and platelets recovery on day +21. A standard anti-infective prophylaxis for CMV, HBV, antifungal, antiviral was performed, as well as a weekly monitoring of CMV, EBV, Aspergillosis and malaria plasmodium. The admission period was complicated only by a grade 1 mucositis, without the need of a parenteral feeding support, and by a methicillin-sensitive Staphylococcus aureus bacteremia with fever lasting one day with prompt response to antibiotic treatment. The patient was discharged on day +28. The post-transplant clinical course was uneventful, without any clinical concerns and no GVHD onset. Now she is on day +150 post-transplant, in good health, with a complete disease remission (PFS not reached) and no GVHD signs.