Intensive treatment for childhood acute lymphoblastic leukemia reduces immune responses to diphtheria, tetanus, and Haemophilus influenzae type b.

OBJECTIVES: Immunity to diphtheria toxoid (D), tetanus toxoid (T), and Haemophilus influenzae type b (Hib) is affected in children with acute lymphoblastic leukemia (ALL). The aims were to examine immunity and to compare the response to immunization at 1 or 6 months after treatment.

METHODS: Thirty-one patients were immunized with DT and conjugated Hib vaccine (ActHib) at 1 month or 6 months after treatment of ALL with the NOPHO 92 protocol. Antibody levels were determined before and 3 weeks after vaccination. Specific T and Hib antibody-secreting cells of IgG/IgA/IgM isotypes were analyzed in peripheral blood using an ELISPOT technique.

RESULTS: All specific antibody levels decreased during ALL treatment, and protective levels after treatment were noted for 17% against D, 33% against T, and 100% against Hib. No high-risk patient had full D or T protection after treatment. After vaccination all the standard- and intermediate-risk patients achieved full protection against D, T, and Hib. The high-risk group showed insufficient immune response (full protection after vaccination: D 56%, T 22%, Hib 78%). No difference was found between vaccination at 1 month or 6 months after treatment. The poor antibody production in the high-risk group correlated to low numbers of antibody-secreting cells.

CONCLUSIONS: Nonprotective antibody levels against D, T, and Hib after childhood ALL are more common than previously thought. Insufficient immune response was restricted to the high-risk group and was related to a low number of memory B cells in this study. Immunizations should be included in follow-up after childhood ALL, and the policy should be adapted to treatment intensity.