Combinatorial approaches to the prevention and treatment of HIV-1 infection

The discovery of the human immunodeficiency virus type 1 (HIV-1) in 1982 soon led to the identification and development of antiviral compounds to be used in treatment strategies for infected patients. Early in the epidemic, drug monotherapies frequently led to treatment failures because the virus quickly developed resistance to the single drug. Following the advent of highly active antiretroviral therapy (HAART) in 1995, dramatic improvements in HIV-1-infected patient health and survival were realized as more refined combination therapies resulted in reductions in viral loads and increases in CD4+ T-cell counts. In the absence of an effective vaccine, prevention of HIV-1 infection has also gained traction as an approach to curbing the pandemic. The development of compounds as safe and effective microbicides has intensified and has focused on blocking the transmission of HIV-1 during all forms of sexual intercourse. Initial preclinical investigations and clinical trials of microbicides focused on single compounds effective against HIV-1. However, the remarkable successes achieved using combination therapy to treat systemic HIV-1 infection have subsequently stimulated the study and development of combination microbicides that will simultaneously inhibit multiple aspects of the HIV-1 transmission process by targeting incoming viral particles, virus-infected cells, and cells susceptible to HIV-1 infection. This review focuses on existing and developing combination therapies, covering preclinical development, in vitro and in vivo efficacy studies, and subsequent clinical trials. The shift in focus within the microbicide development field from single compounds to combination approaches is also explored.