Impaired pneumococcal immunity in children after treatment for acute lymphoblastic leukaemia.

Although the substantial risk for invasive pneumococcal disease is well recognized in children after allogeneic stem cell transplantation, little is known about the specific immunity against pneumococci in children after cytotoxic therapy for acute lymphoblastic leukaemia (ALL). We therefore assessed the spontaneous reconstitution of humoral immunity against pneumococcal antigens, of total IgG and the IgG2 subclass, and of lymphocyte subsets in a total of 53 children treated for ALL. None of the patients had received pneumococcal vaccination prior to or after therapy for ALL. At 3 and 9 months after completion of chemotherapy, most patients had levels of specific antibodies to pneumococcal antigens below the presumed threshold of protection and significantly lower than those of age-matched unvaccinated healthy controls. In contrast, at 9 months after completion of therapy, only a minority of patients had immunoglobulin concentrations or lymphocyte subset counts below the age-matched reference value. Our data indicate that patients with ALL who are unvaccinated against pneumococci have a selective immunodeficiency with an impaired antibody protection against pneumococci for up to 9 months after completion of therapy. Therefore, effective prevention, including chemoprophylaxis and active immunization, has to be considered in this patient population.