Coinfection of Macaques with Simian Immunodeficiency Virus and Simian T Cell Leukemia Virus Type I: Effects on Virus Burdens and Disease Progression

To test the hypothesis that coinfection with human immunodeficiency virus (HIV) and human T cell leukemia/lymphoma virus types I or II (HTLV-I or -II) accelerates progression to AIDS, pig-tailed macaques were inoculated with the simian counterparts, SIV and STLV-I. During 2 years of follow-up of singly and dually infected macaques, no differences in SIV burdens, onset of disease, or survival were detected. However, in the first coinfected macaque that died of AIDS (1 year after infection), >50% of CD4+ and CD8+ lymphocytes expressed CD25. On the basis of the low incidence of HTLV-I- and STLV-I-associated disease during natural infections, this early evidence of neoplastic disease was unexpected. While these results demonstrate that coinfection with SIV and STLV-I has no influence on the development of immunodeficiency disease, they do establish a reliable macaque model of persistent STLV-I infection.