VERTICAL TRANSMISSION OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 - INSIGHTS FROM STUDIES OF MULTIPLE PREGNANCIES

Because twins share an in utero environment and genetic relationships, similarities and differences between them can provide insight into th e epidemiology and natural history of infectious agents, especially hu man immunodeficiency virus type 1 (HIV-1). Three projects were summari zed: HIV-1 transmission and AIDS-free survival in The International Re gistry of HIV-Exposed Twins; cloning and sequencing of HIV-1 proviral sequences in two sets of identical twins; and transmission and natural history of ovine lentivirus (OvLV) in twin lambs. Both HIV-1 and OvLV transmission were increased for first-born twins. With HIV-1, progres sion to AIDS appeared independent of zygosity. Development of pneumoni tis with experimental OvLV infection was highly concordant in monozygo tic lambs. Finally, the identical infected twins in one set had interm ingling of each infant's HIV-1 quasispecies, whereas in the second set each twin had its own distinct cluster of quasispecies around a mater nal sequence. The studies indicate that most transmission occurs durin g labor or delivery, and they suggest that immunogenetics may not affe ct susceptibility to different HIV-1 quasispecies but may affect the m anifestations of specific opportunistic diseases.