Vaccines for Moraxella catarrhalis

Vaccine development for Moraxella catarrhalis is in the antigen identificat ion stage. M. catarrhalis does not appear to synthesize secreted antigens s uch as exotoxins, nor does it appear to possess a carbohydrate capsule. Mod ified forms of these antigens are usually good vaccine components. There is some interest in whole bacterial cells and membrane fractions, but the sea rch has largely focused on purified outer surface antigens. All of the pres ent antigens have been selected based on the response seen in animals, alth ough the antibody response seen in people exposed to the bacterium provides some guidance. The antibody response provides information related to the c ross-strain preservation of epitopes and whether they are surface exposed. Antigens that elicit antibodies that have complement dependent bactericidal capacity, opsonophagocytic activity or interfere with one of the antigen's known functions such as adhesion or nutrient acquisition are particularly valued. In addition to examining the antibody response, some antigens have been evaluated in a murine pulmonary clearance model. Using these assays an d model, several vaccine candidates have been identified. The antigens may be roughly classified by the function they serve the bacterium. One set app ears to promote adhesion to host tissues and includes the hemagglutinins, u biquitous surface protein AI (UspA1), and possibly the CD protein. A second set is involved in nutrient acquisition. This set includes the lactoferrin binding protein A (LbpA) and lactoferrin binding protein B (LbpB), the tra nsferrin binding protein A (TbpA) and transferrin binding protein B (TbpB), the CD and E porins, and the Catarrhalis outer membrane protein B (CopB). A third set is comprised of antigens involved in virulence and it includes lipooligosaccharide (LOS) and the ubiquitous surface protein A2 (UspA2). An tigens of unknown function, such as the 200K protein, may also be vaccine c andidates. The antigens that are most suitable will be determined in clinic al studies that are only beginning now. (C) 2000 Elsevier Science Ltd. All rights reserved.