Tucaresol, a substituted benzaldehyde, was being developed by Glaxo Wellcome for the prevention of sickle cell disease. Tucaresol was designed to interact with haemoglobin to increase oxygen affinity and has been shown to inhibit sickling in vitro. Tucaresol is also a low-molecular-weight compound that enhances co-stimulatory signaling to CD4 cells. Immune induction is dependent on transient covalent bonding (Schiff base formation) between carbonyls and amines expressed on antigen presenting cell (APC) and T-cell surfaces. Tucaresol substitutes for the natural donor of carbonyl groups to mimic the transient bonding that is essential for T-cell activation. In preliminary studies, tucaresol has been shown to stimulate HIV-specific cytotoxic T lymphocyte responses and generation of naive T cells via thymopoiesis in patients receiving ART who have suppressed viremia. Tucaresol appears to specifically increase type 1 cytokine production. Tucaresol has been used in trials studying the treatment of HIV infections. However, the development of tucaresol for HIV, Hepatitis B and sickle cell diseas treatment has been discontinued.