Haemophilus influenzae type b polyribosylribitol phosphate polysaccharide–protein conjugate (Hib PRP-protein conjugate)

Haemophilus influenzae type b polyribosylribitol phosphate polysaccharide conjugated to a carrier protein is the active antigenic component in Hib conjugate vaccines. The core antigen, polyribosylribitol phosphate (PRP), is a linear, repeating polysaccharide forming the capsule of Haemophilus influenzae type b. The unconjugated polysaccharide is poorly immunogenic in infants because it elicits a T cell–independent response, leading to weak and short-lived antibody production. To enhance immunogenicity, PRP is covalently linked to a carrier protein (commonly tetanus toxoid, diphtheria toxoid, CRM197, or Neisseria meningitidis outer membrane protein), creating a conjugate that elicits a robust T cell–dependent immune response and immunologic memory. This approach has transformed Hib vaccine efficacy, virtually eliminating invasive Hib disease where widely used. The molecule is not a therapeutic target such as a receptor, enzyme, or transporter, but rather a synthetic antigen used for vaccination, meaning it should not be classified as a “drug target” in the conventional sense[1][2][4][6].

Other names

Hib conjugate vaccineHaemophilus influenzae type b polysaccharide conjugateHib PRP conjugatePRP-TT (when tetanus toxoid is used as carrier)PRP-OMP (when outer membrane protein is carrier)PRP-D (when diphtheria toxoid is carrier)PRP-CRM197 (when CRM197 is carrier)

Conjugated PRP elicits T-cell–dependent production of anti-PRP antibodies, resulting in immune protection against Hib infection[2][4][6]