Rapid and Progressive CD4⁺ Decline in a Monkey Infected with an SIV/HIV-1 Chimeric Virus

We previously constructed a simian immunodeficiency virus/human immunodeficiency virus type 1 (HIV-1) chtmeric virus, NM-3rN to generate a pathogenic HIV-1 in macaque monkeys. During the in vivo passage of this virus in several monkeys, a viral strain, R43-56 was obtained which acquired a better replication ability in vivo. MM121, one of the three monkeys inoculated with the R43-56, showed weight loss, diarrhea and a rapid and continuous decrease in CD4⁺ lymphocytes at the moribund stage. An autopsy revealed generalized lymphadenopathy, dehydration, and ileocecal intussusception. In situ hybridization showed that the virus infection was in systemic lymphoid organs. We are presently monitoring the survivors to obtain candidates for a more virulent virus. R43-56 may be a better challenge virus and useful tool for human acquired immunodeficiency syndrome research.