Human immunodeficiency virus type 1 (HIV-1) hardly replicates in Old World monkeys. Recently, a mutant HIV-1 clone, NL-DT5R, in which a small part of gag and the entire vif gene are replaced with SIVmac239-derived ones, was shown to be able to replicate in pigtail monkeys but not in rhesus monkeys (RM). In the present study, we found that a modified monkey-tropic HIV-1 (HIV-1mt), MN4-5S, acquired the ability to replicate efficiently in cynomolgus monkeys as compared with the NL-DT5R, while neither NL-DT5R nor MN4-5S replicated in RM cells. These results suggest that multiple determinants may be involved in the restriction of HIV-1 replication in macaques, depending on the species of macaques. The new HIV-1mt clone will be useful for studying molecular mechanisms by which anti-viral host factors regulate HIV-1 replication in macaques. (C) 2010 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.