Adult T-cell Leukemia/Lymphoma

HTLV-1–driven CD4+ T-cell malignancy — four clinical subtypes, aggressive course in acute and lymphomatous disease, and mogamulizumab-based therapy

Key Points

• Adult T-cell leukemia/lymphoma (ATLL) is caused by human T-lymphotropic virus type 1 (HTLV-1), endemic in southwestern Japan, the Caribbean, sub-Saharan Africa, and parts of South America; only ~2–5% of HTLV-1–infected individuals develop ATLL over a 40–60 year latency period.
• ATLL is divided into four clinical subtypes — acute, lymphomatous, chronic, and smoldering — with the aggressive subtypes (acute and lymphomatous) accounting for ~70% of cases and carrying a median OS of less than 1 year with conventional chemotherapy.
• Neoplastic cells are CD4+, CD25+, CCR4+, FoxP3+ regulatory T cells with a "flower cell" morphology (multilobulated nuclei) in peripheral blood and characteristic hypercalcemia driven by PTHrP secretion and osteoclast activation.
• Mogamulizumab (anti-CCR4 monoclonal antibody) is approved in Japan for ATLL and has demonstrated improved OS vs. CHOP; it is increasingly used in Western centers and is particularly active in the leukemic component of disease.
• Antiviral therapy combining zidovudine (AZT) and interferon-alpha (IFN-α) has activity particularly in the chronic/smoldering and leukemic subtypes; the combination with mogamulizumab is under investigation.
• Allogeneic stem cell transplantation is the only potentially curative treatment for aggressive ATLL, with long-term OS of 30–50% in patients achieving remission prior to transplant; the graft-versus-ATLL effect is critical.

Etiology, Epidemiology, and Pathogenesis

ATLL is caused by HTLV-1, a delta-retrovirus that infects CD4+ T cells via cell-to-cell transmission (blood transfusion, breast-feeding, sexual contact). Global HTLV-1 prevalence is estimated at 5–10 million infected individuals. Endemic regions include southwestern Japan (Kyushu, Okinawa, Nagasaki), the Caribbean basin, equatorial Africa, the Middle East, and parts of South America and Melanesia. In the United States, HTLV-1 is found predominantly in immigrants from endemic regions and in IV drug users. Only 2–5% of HTLV-1 carriers develop ATLL after a latency of 40–60 years. The virus…

Clinical Subtypes and Presentation

The Shimoyama classification (1991, updated by Katsuya 2015) defines four ATLL subtypes based on blood involvement, lymphadenopathy, organ involvement, calcium, and LDH: **Acute ATLL (~55% of cases):** The most aggressive subtype. Presents with leukocytosis with circulating flower cells, lymphadenopathy, hepatosplenomegaly, hypercalcemia (PTHrP-mediated), and skin lesions. Opportunistic infections (P. jirovecii, CMV, Strongyloides, fungi) are common due to profound immunosuppression. LDH is markedly elevated. Median OS with conventional CHOP: 6–13 months. **Lymphomatous ATLL (~20% of…

Diagnosis and Staging

Diagnosis of ATLL requires: 1. Demonstration of HTLV-1 antibody seropositivity (ELISA confirmed by Western blot or PCR) 2. Histopathology showing T-cell lymphoma/leukemia 3. CD4+, CD25+, CCR4+ immunophenotype; CD7 loss is characteristic; FoxP3 is expressed in most cases 4. "Flower cells" or polylobulated nuclei in peripheral blood (pathognomonic but not invariable) 5. Clonal T-cell receptor gene rearrangement with clonal HTLV-1 proviral integration Diagnostic workup includes complete blood count with differential, comprehensive metabolic panel (calcium, LDH, albumin), peripheral blood flow…

Treatment

**Smoldering and Chronic ATLL:** Watchful waiting is appropriate for truly asymptomatic smoldering ATLL with stable disease. For patients requiring treatment, antiviral therapy with zidovudine (AZT) + interferon-alpha (IFN-α) is preferred — a strategy supported by retrospective studies and meta-analyses showing superior outcomes versus chemotherapy in indolent subtypes. Mogamulizumab monotherapy is an active option. Intensive chemotherapy should be avoided unless transformation occurs. **Acute and Lymphomatous ATLL:** Conventional CHOP and CHOP-like regimens produce CR rates of only 15–30%…

Prognosis, Infection Prophylaxis, and Supportive Care

Prognosis for aggressive ATLL subtypes remains poor despite modern therapy. Median OS for acute ATLL is 6–13 months and for lymphomatous ATLL is 10–16 months with available systemic therapy. Indolent subtypes (chronic, smoldering) have significantly better survival but are not curable without allogeneic SCT. HTLV-1–driven immunosuppression predisposes patients to severe opportunistic infections: - **Strongyloides stercoralis hyperinfection:** HTLV-1 specifically impairs anti-Strongyloides immunity; all ATLL patients from endemic regions should be screened with serology and treated with…