Immunological risks of adult T-cell leukemia at primary HTLV-I infection

A small percentage of human T-cell leukemia virus type-I (HTLV-I)-infected individuals develop adult T-cell leukemia (ATL). In animal experiments, inoculation of HTLV-1 via the oral route, which is the main route of mother-to-child viral transmission in humans as a result of breastfeeding, induced host HTLV-1-specific T-cell unresponsiveness and resulted in increased viral load. This strongly suggested that the known epidemiological risk factors for ATL (i.e. vertical HTLV-1 infection and elevated viral load) are linked by an insufficient HTLV-1-specific T-cell response. Recent findings on the antitumor effects of Tax-targeted vaccination in rats and the reactivation of Tax-specific T cells in ATL patients as a result of hematopoietic stem cell transplantation imply promising immunological approaches for the prophylaxis and therapy of ATL.