Whole body clonality analysis in an aggressive STLV-1 associated leukemia (ATLL) reveals an unexpected clonal complexity

HTLV-1 causes Adult T cell Leukemia/Lymphoma (ATLL) in humans. We describe an ATL-like disease in a 9 year-old female baboon naturally infected with STLV-1 (the simian counterpart of HTLV-1), with a lymphocyte count over 1010/L, lymphocytes with abnormal nuclear morphology, and pulmonary and skin lesions. The animal was treated with a combination of AZT and alpha interferon. Proviral load (PVL) was measured every week. Because the disease continued to progress, the animal was euthanized. Abnormal infiltrates of CD3+CD25+ lymphocytes and Tax-positive cells were found by histological analyses in both lymphoid and non-lymphoid organs. PVL was measured and clonal diversity was assessed by LM-PCR (Ligation-Mediated Polymerase Chain Reaction) and high throughput sequencing, in blood during treatment and in 14 different organs. The highest PVL was found in lymph nodes, spleen and lungs. One major clone and a number of intermediate abundance clones were present in blood throughout the course of treatment, and in organs. These results represent the first multi-organ clonality study in ATLL. We demonstrate a previously undescribed clonal complexity in ATLL. Our data reinforce the usefulness of natural STLV-1 infection as a model of ATLL