A null mutation was prepared in the mouse for CD18, the β2 subunit of leukocyte integrins. Homozygous CD18 null mice develop chronic dermatitis with extensive facial and submandibular erosions. The phenotype includes elevated neutrophil counts, increased immunoglobulin levels, lymphadenopathy, splenomegaly, and abundant plasma cells in skin, lymph nodes, gut, and kidney. Very few neutrophils were found in spontaneously occurring skin lesions or with an induced toxic dermatitis. Intravital microscopy in CD18 null mice revealed a lack of firm neutrophil attachment to venules in the cremaster muscle in response to N-formyl- methionyl-leucyl-phenylalanine. A severe defect in T cell proliferation was found in the CD18 null mice when T cell receptors were stimulated either by staphylococcal enterotoxin A or by major histocompatibility complex alloantigens demonstrating a greater role of CD11/CD18 integrins in T cell responses than previously documented. The null mice are useful for delineating the functions of CD18 in vivo.

Summary of study A multi-country randomized, placebo-controlled trial of the safety, immunogenicity and efficacy of respiratory syncytial virus (RSV) F-protein nanoparticle vaccine was undertaken in 4,636 pregnant women and their infants. RSV F-protein vaccine was safe and immunogenic in the pregnant women inducing anti-F IgG, palivizumab-competing antibodies and RSV neutralizing antibodies that were transferred to the fetus. Although the primary endpoint of prevention of RSV-specific medically-significant lower respiratory tract infection (MS-LRTI) was not met per protocol criteria for efficacy (i.e. 97.52% lower bound >30%), vaccine efficacy was 39.4% (97.52% CI: -1.0, 63.7%; p=0.0278) in infants 0-90 days age. Furthermore, there was a 58.8% (95% CI 31.9, 75.0%) lower rate of RSV LRTI with severe hypoxemia (secondary endpoint) through to 90 days of age in the expanded intent-to-treat analysis. The number of women needed to be vaccinated to prevent RSV-specific MS-LRTI or LRTI with severe hypoxemia in their infants through to 180 days of life were 88 and 82, respectively. Background RSV is the dominant cause of severe lower respiratory tract infection (LRTI) in infants, with most severe disease concentrated in younger-age infants. Methods Healthy, pregnant women between 28 and 36 weeks gestation, with expected delivery near the start of the RSV season, were randomized to a single intramuscular dose of nanoparticle RSV F-protein vaccine, or placebo in a 2:1 ratio. Their infants were followed for 180 days for medically-significant LRTI (MS-LRTI), LRTI with severe hypoxemia and/or LRTI- hospitalization. RSV detection was performed centrally by PCR. Safety evaluation continued until 364 days age. Results 4,636 women were randomized, with 4,579 live births. Over the first 90 days of life, efficacy against RSV-MS-LRTI was 39.4% (97.52%CI: -1.0, 63.7%; p=0.0278) and 41.4% (95%CI: 5.3, 61.2%) in the per protocol and expanded intent-to-treat (eITT) analyses, respectively. There was a lower rate (efficacy 58.8%; 95%CI 31.9, 75.0% in eITT analysis; not adjusted for multiplicity) of RSV-LRTI with severe hypoxemia in infants of vaccinees through 90 days age. Pneumonia reported as a serious adverse events was 49.4% less common in infants of vaccinees (2.6%) than placebo-recipients through 364 days age. Conclusions Maternal vaccination with RSV F-nanoparticle vaccine was safe and immunogenic. The prespecified primary endpoint success criterion (efficacy 97.5% lower bound ≥30%) was not achieved. However, maternal immunization was associated with reduced risk of RSV-confirmed MS-LRTI and LRTI with severe hypoxemia in early infancy. Trial Registration Number ClinicalTrials.Gov: NCT02624947. Funding statement Funded by Novavax, with supporting grant from the Bill and Melinda Gates Foundation.