Prevention and control of human immunodeficiency virus (HIV) infections require a vaccine providing long-lasting protection. The most promising vaccine up to date consists of a regimen of immunization with genetically engineered HIV proteins, including the surface glycoprotein gp120, with a resulting efficacy of ~30%. Recent evidence indicates antibodies produced against variable envelope region 2 (V2) of gp120 in primates are associated with higher levels of protection, while antibodies produced against variable envelope region 1 (V1) have an opposite and interfering effect. Researchers at the National Cancer Institute (NCI) and New York University (NYU) have developed V1-deleted gp120 immunogens using Simian immunodeficiency virus (SIV), and observed an increase in antibodies against V2 in macaques upon immunization. NCI is seeking parties interested in co-developing and/or licensing V1-deleted gp120 immunogens for their use in an improved HIV vaccine.