Immunogenicity Study of an Anti-pneumococcal Vaccination Strategy in Patients With Sickle Cells Disease

Streptococcus pneumoniae is the major cause of bacterial infection in patients with sickle cells disease. The 23-valent pneumococcal polysaccharide vaccine (PSV) is supposed to be poorly immunogenic in these patients. We want to evaluate whether a prime with a 13-valent pneumococcal conjugate vaccine (PCV), able to induce immunologic memory, would improve the immune response against SP polysaccharides (SPP). Primary objective: To evaluate and compare the specific antibody response to a prime-boost vaccine strategy combining PCV prime at W0 followed by the administration of PSV boost at W4, to the administration of PSV alone at W4 in patients with sickle cells disease. Secondary objectives: Evaluation and comparison of the specific antibody response to the thirteen pneumococcal serotypes shared by the PCV and PSV vaccines, 4 weeks after the single PSV vaccination for patients from Group 1 or 4 weeks after the boost PSV vaccination for patients from group 2. Evaluation of the duration of the specific antibody response at W24 and 96. Evaluation of the T CD4 lymphocyte response to the CRM 197 protein. Safety of the vaccines. Study Design: Randomised, monocentric, controlled phase II study of the immunological efficacy of a prime boost strategy combining the sequential administration of the PCV and PSV, compared to the administration of the PSV alone. 180 adults patients with sickle cells disease will be included. The primary endpoint : proportion of responders at W8 to at least 10 of thirteen serotypes. Secondary endpoints : Proportion of responders at W8 according to 4 categories of responders: 5-7; 3-4; 2-1 and 0. Evaluation of the pneumococcal opsonophagocytic activity (OPA) at baseline and W8 for each serotype, defined as the proportion of patients with OPA \> 1:8 geometric mean of the specific antibody titers proportion of patients who experienced an increase of specific antibody levels 1 g/ml. Evaluation of the priming effect of the PCV vaccine in the group 1. Duration of the specific antibody responses at week 24 and W96. CD4 T lymphocyte responses to the CRM 197 protein (proliferative and cytokine production) at weeks 0, 8 and 12. Safety of the vaccines frequency of Streptococcus pneumoniae infections. Statistical Considerations: With a sample size of 180 patients, and a randomization ration of 1:1, the study will have a power of at least 90% to show a difference of 25% category between the group receiving PCV and PSV vs the group receiving PSV alone (two-sided type I error = 5%). The primary comparison between both groups will be performed using a Chi2 test for independent groups or a Fisher exact test where appropriate.