HTLV stands for human T cell leukemia virus. HTLV-1 is a virus that attacks specific kinds of white blood cells called T cells. T cells are part of the natural defense system of the body. HTLV-1 has been associated with leukemia and lymphoma. In addition, approximately 1% of all patients infected with HTLV-1 develops a condition known as HTLV-1 associated myelopathy (HAM) / tropical spastic paraparesis (TSP).