Vacc-4x is being developed by Bionor Immuno AS as a therapeutic vaccine to be used in conjunction with antiretroviral therapies by individuals infected with HIV. The vaccine is comprised of four synthetic peptides describing sequences from within the highly conserved HIV core protein p24, which are thought to induce T-cell-mediated responses. Vacc-4x was assessed in 51 patients infected with HIV in one phase I and one phase II clinical trial and was demonstrated to be safe and generally well tolerated with no significant adverse events. Promisingly, the vaccine was reported to induce cell-mediated immunity, with a third of vaccinees eligible for follow-up remaining off antiretroviral therapy and being essentially symptom-free 4 years after treatment. Nonetheless, without the inclusion of a placebo group, the data will be looked upon with a degree of skepticism in the scientific community. A phase IIb, placebo-controlled clinical trial to address this issue is currently ongoing, with data expected to become available by the end of 2010. If Vacc-4x vaccinees demonstrate significantly better responses than the placebo group in this trial, the prospects for Vacc-4x could be highly promising.