Retrovirus Epidemiology Donor Study I (REDS I)

BACKGROUND:

HIV is known to be transmissible by blood, blood components, or plasma derivatives. The risk of contracting HIV infection from blood transfusion has been greatly reduced in the United States by implementing stringent criteria for donor acceptance, HIV antibody screening, and new methods of virus inactivation in coagulation factor concentrates. There are additional human retroviruses, however, that may pose a threat to the safety of the nation's blood supply.

The human T-cell lymphotropic retroviruses share many properties, including a preferred tropism for certain lymphocytes and similar modes of transmission. They also differ significantly from each other and on this basis are divided into two distinct groups: the human T-cell lymphocytropic viruses (HTLVs) and the human immunodeficiency viruses (HIVs). HTLV-I, a transforming virus, is the prototype of the first group (HTLVs). It is associated with adult T-cell leukemia (ATL) and is thought to be involved in a central nervous system disorder referred to as tropical spastic paraparesis. This group also includes HTLV-II, which is associated with a T-cell malignancy different from ATL. A newly isolated human retrovirus, termed HTLV-V, may be the etiologic agent of cutaneous T-cell lymphoma/leukemia, and may also be added to this group. HIV, previously known as HTLV-III or lymphadenopathy virus (LAV), a nontransforming virus, causes acquired immunodeficiency syndrome (AIDS) and is the prototype of the second group (HIVs). New members of this group of nontransforming human retroviruses were isolated from individuals in different countries of Africa. LAV-2, also referred to as HIV-2, was isolated from two AIDS patients in Africa, and the first case of AIDS in the United States caused by HIV-2 was reported in January, 1988. A third member of this group, HIV-3, was detected in Africa.

Although the HTLV family of retroviruses is distinct from the HIV family, both groups of viruses infect human T4 (CD4) lymphocytes preferentially and alter the host's T-cell functions. Whereas HTLV-I or HTLV-II primarily induce transformation and proliferation of T Lymphocytes and cause T-cell lymphoma/leukemia in humans, HIV and HIV-2 induce T-cell cytopathology that leads to depletion of CD4 cells.

The spread of HIV by blood transfusion represents a highly efficient mode of transmission. Blood components from donors with antibody to HIV have been shown to transmit the virus with frequencies of greater than 90 percent. Packed red blood cells, platelets, or fresh frozen plasma are all equally effective in transmitting the virus to recipients. It is highly likely, therefore, that recipients who receive blood from donors with antibody to HIV will themselves become infected with the virus. Fortunately, the likelihood of such an occurrence in the United States is now rare due to the implementation of screening procedures and other safeguards. When the study was initiated in 1989, there was a growing concern, however, that human retroviruses other than HIV might threaten the safety of the United States blood supply.