Porter Anderson

DO PILI PLAY A ROLE IN PATHOGENICITY OF HAEMOPHILUS INFLUENZAE TYPE B

Surface components of Haemophilus influenzae type b (Hib) responsible for mucosal adherence were identified through assay of in-vitro attachment to human buccal epithelial cells (EC). Among many Hib strains from cerebrospinal fluid, blood, or the nasopharynx (NP), two isolates from NP were found to be exceptionally adherent. Adherence correlated with agglutination of human red blood cells (RBC). The adherent strains displayed pili, not previously described for Hib or other encapsulated H. influenzae. Moreover, highly adherent, piliated subpopulations of bacteria could be selected from any strain, but were lost upon subculture. Thus, the potential to express pili may be general for Hib and may aid the NP colonisation which precedes systemic invasion by this organism. Piliation was correlated with the amount of an outer membrane protein with a molecular weight of about 20,000 daltons, which had proved to be immunogenic in an 8-month-old child.

Prospects for overcoming maturational and genetic barriers to the human antibody response to the capsular polysaccharide of Haemophilus influenzae type b

The isolated capsular polysaccharide induces antibody protective against invasive infections by H. influenzae b. Maturation of responsiveness is slow such that infants are not protected. Several protein-coupled versions of the antigen are being tested for immunogenicity in early infancy. The relation of structure to immunogenicity is not completely defined, but all induce a booster-type antibody response with protective potential. Primary vaccination in infancy appears to mimic natural priming, activating clones of B lymphocytes that can later be restimulated by uncoupled polysaccharide. Prospects appear good for immunizing normal infants and also children with immunoregulatory defects predisposing to infection.

Serum antibody responses of weanling mice and two-year-old children to pneumococcal-type 6A–protein conjugate vaccines of differing saccharide chain lengths

Type 6A pneumococcal polysaccharide (PS) fractions having mean lengths 2, 7, or 14 repeat units were coupled to tetanus toxoid, giving conjugates T-6A-2, T-6A-7 or T-6A-14. In weanling outbred mice, type-6A serum antibody responses were minimal to T-6A-7 but significantly higher to T-6A-2 and T-6A-14. In contrast, two-year-old humans responded increasingly to T-6A-2, T-6A-7, and T-6A-14; type 6B antibody rose, but variably. Upon challenge with 6B PS at age 3 yr, conjugate-primed children made anamnestic responses. T-6A-14, containing the longest saccharide chains (and highest saccharide:protein mass ratio) excelled in priming as well as antibody induction.

Non-interference between two protein carriers when used with the same polysaccharide for pneumococcal conjugate vaccines in 2-year-old children.

The carriers tetanus toxoid (T) and diphtheria CRM-197 (C) were compared in conjugate vaccines using identical coupling chemistry and polysaccharide (PS) loading, for safety and immunogenicity in 2-year-old children. Also tested were a mixture of halved doses of both carriers bearing the same PS serotypes. For this study, PS types 6A, 14, 19F, and 23F (separately) were coupled to T or C by reductive amination at PS/protein ratios of 0.50+/-0.18. With each carrier the four PS types were combined, giving the tetravalent vaccines T-6, -14, -19, -23 or C-6, -14, -19, -23 containing 50 microg of the carrier and roughly 20 microg total PS per ml of saline (no adjuvant). The children received primary (1) injections of 50 microg (protein) of either vaccine or a mixture of 25 microg of both; identical secondary (2) injections were given 2 months afterwards. Sera were taken before the 1 and 2 and 1 month post-2, and serum IgG responses to the four PS were determined by ELISA. For geometric mean (GM) post-1 antibody, C-6, -14, -19, -23 exceeded T-6, -14, -19, -23 for type 19F; for 2 antibody, T-6, -14, -19, -23 exceeded C-6, -14, -19, -23 for type 14, but C-6, -14, -19, -23 and the T/C mixture exceeded T-6, -14, -19, -23 for the type 23F response. No other differences were significant. Analyzed by individual fold-rises, C-6, -14, -19, -23 and the T/C mixture exceeded T-6, -14, -19, -23 for types 19F and 23F. Thus, there was no consistent difference between the T and C carriers; rather, the results differed by serotype. When a mixture of halved doses of T-6, -14, -19, -23 and C-6, -14, -19, -23 was injected, neither negative nor positive interference with the PS antibody responses was found. Anticipating multivalent PS conjugate vaccines of the future to be used in infancy, this strategy would have two hypothetical advantages worth further investigation-avoiding carrier epitopic overload by reducing each carrier dosage and recruiting T-helper activity by both carriers for each PS.

Haemophilus b Oligosaccharide-CRM197 and Other Haemophilus b Conjugate Vaccines: A Status Report

Haemophilus influenzae type b (Haemophilus b) is a major cause of life-threatening and debilitating diseases in infants and young children. In the United States, it is the most common cause of bacterial meningitis, and also causes other invasive diseases, such as epiglottitis, septic arthritis, cellulitis, pneumonia and bacteremia. In 1985, United States Public Health officials estimated that, despite the availability of potentially effective antibiotics and medical care, up to 1 in every 200 children in the USA develops an invasive Haemophilus b disease before the age of five years (Cochi et al., 1985). The 1985 report by the U.S. National Academy of Science on establishing vaccine priorities in the United States (NRC, 1985) estimated the annual vaccine preventable costs of Haemophilus b disease to be approximately 425 million dollars, and ranked Haemophilus b vaccine among the highest priorities for needed new vaccines.