Infants with SCD respond to 7VPnC vaccine with antibody concentrations that are at least as high as infants without SCD. Infants immunized with 7VPnC vaccine at 2, 4, and 6 months of age developed antibody concentrations in the same range as those achieved among infants without SCD enrolled in a large trial that demonstrated vaccine efficacy against invasive disease. Significant rises were seen in antibody concentrations to all 7VPnC serotypes after the PS-23 booster in children receiving schedule A or B.

BACKGROUND AND OBJECTIVE: Susceptibility to encapsulated bacteria is well known in sickle cell disease (SCD). Hydroxyurea use is common in adults and children with SCD, but little is known about hydroxyurea’s effects on immune function in SCD. Because hydroxyurea inhibits ribonucleotide reductase, causing cell cycle arrest at the G1–S interface, we postulated that hydroxyurea might delay transition from naive to memory T cells, with inhibition of immunologic maturation and vaccine responses. METHODS: T-cell subsets, naive and memory T cells, and antibody responses to pneumococcal and measles, mumps, and rubella vaccines were measured among participants in a multicenter, randomized, double-blind, placebo-controlled trial of hydroxyurea in infants and young children with SCD (BABY HUG). RESULTS: Compared with placebo, hydroxyurea treatment resulted in significantly lower total lymphocyte, CD4, and memory T-cell counts; however, these numbers were still within the range of historical healthy controls. Antibody responses to pneumococcal vaccination were not affected, but a delay in achieving protective measles antibody levels occurred in the hydroxyurea group. Antibody levels to measles, mumps, and rubella showed no differences between groups at exit, indicating that effective immunization can be achieved despite hydroxyurea use. CONCLUSIONS: Hydroxyurea does not appear to have significant deleterious effects on the immune function of infants and children with SCD. Additional assessments of lymphocyte parameters of hydroxyurea-treated children may be warranted. No changes in current immunization schedules are recommended; however, for endemic disease or epidemics, adherence to accelerated immunization schedules for the measles, mumps, and rubella vaccine should be reinforced.

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Cell wall teichoic acids of some gram-positive bacteria are potent activators of the alternative pathway of complement. It is unclear, however, whether the other form of teichoic acid, cell membrane lipoteichoic acid (LTA), can also activate the alternative pathway. In the present study, radiolabelled pneumococcal LTA was found to bind spontaneously to sheep erythrocytes in a temperature-and time-dependent fashion. In addition, the presence of pneumococcal LTA on the erythrocyte surface was verified by the fact that they could be agglutinated by a myeloma protein (TEPC-15) specific for choline, a constituent of pneumococcal LTA. Pneumococcal LTA when fixed to the surface of erythrocytes was able to activate the alternative pathway of complement in both guinea pig serum deficient in the fourth component of complement and human serum deficient in the second component of complement, resulting in lysis of the sensitized erythrocytes. The sensitizing principle of the LTA preparation was removed before erythrocyte sensitization by immunoabsorption, using the choline-specific TEPC-15 myeloma protein. These data demonstrate that purified pneumococcal LTA will bind to sheep erythrocytes and endow them with the ability to activate the alternative pathway.

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