Peptide T is a synthetically produced protein derived from gp120 - the protein on the surface of HIV particles which binds to the CD4 molecule on the surface of some human cells. Peptide T was discovered in 1986 when scientists were screening for gp120 derived peptides which might block HIV infection.  Test-tube studies showed that peptide T interferes with the way HIV binds onto immune cells. Specifically, it disrupts gp120 binding and HIV's use of the CCR5 co-receptor.

It was later discovered that peptide T has the same basic chemical structure as certain proteins in the brain (neuropeptides) such as VIP. A natural protein found in the brain and the gut, VIP is involved in transmitting messages (a neurotransmitter).