ANTIBODY-RESPONSE TO PNEUMOCOCCAL VACCINE IN CHILDREN RECEIVING BONE-MARROW TRANSPLANTATION

Fifty-three pediatric patients given an allogeneic or an autologous bo ne marrow transplantation (BMT) were immunized with a polyvalent pneum ococcal capsular polysaccharide vaccine (Pneumovax II). Vaccine was ad ministered six months or more after BMT and the pneumococcal IgM, tota l IgG, and IgG subclasses levels were evaluated before and three weeks after immunization. Immunization promoted a significant rise in antib ody serum levels (P < 0.000001), and all children vaccinated more than two years after transplantation responded to pneumococcal polysacchar ides, whereas only 20-30% and 50% of patients given BMT between six mo nths and one year and one and two years, respectively, mounted an effe ctive antibody production (P < 0.0001). In univariate analysis, lapse of time from BMT to vaccination, chronic graft-versus-host disease occ urrence, and female sex influenced the response rate. However, in mult ivariate analysis, only time between marrow transplant and immunizatio n was a powerful predictor of response, Interestingly, four of 11 pati ents with IgG2 deficiency before immunization normalized serum levels of this IgG subclass after the pneumococcal antigenic challenge. Our s tudy suggests that time after transplant is the major factor influenci ng the recovery of immune reactivity to polysaccharide antigens. This seems to confirm the hypothesis that ontogeny of the B-cell repertoire follows a predetermined sequential program in which polysaccharide an tigens are some of the last to evoke an antibody response.