Background: Infection and disease induction of variants of HIV type 1 (HIVâ1) in vivo, especially their persistence, replication and rate of disease progression, have been found to depend on phenotypic characteristics. However, the mechanism (s) underlying these diverse phenotypic characteristics remain poorly understood. Aim: It was aimed at determining whether a SHIV that had been adapted to a monkeyâderived cell line could be used to explain the mechanism that underlies adaptive evolution of a virus to its host cell environment. Materials and Methods: Standard procedures in virology such as cell culturing, FACS analysis and ELISA were employed to measure virus replication and growth kinetics, cell viability, reverse transcriptase (RT) activity assay and CD4 cells downâregulation. Results: After about 20 passages, LT efficiently adapted to the monkeyâderived cell line and replicated much better than the parent virus. LT accumulated a number of mutations in its entire genome with a majority of them being monkey cellâspecific. Conclusion: Thus we think we have obtained a virus that may enable studies to determine which of these mutations are specifically related to in vitro viral replication and which are specifically related to cytotoxicity so as to explain the mechanism associated with viral cytotoxicity and host cell specificity.