T cell immunity to measles viral proteins in infants and adults after measles immunization.

Vaccination of infants against measles remains of global importance, and proposed new vaccine strategies include the use of measles proteins or synthetic peptides as immunogens. We studied cell-mediated immunity to whole measles antigen and measles proteins in immune adults and infants after measles vaccine. Further, we measured CD8+ T cell responses to peptide pools corresponding to the nucelocapsid (N) measles protein in adults given measles vaccine. Cell-mediated immune responses to three of four measles proteins were equivalent to those against whole measles antigen in immune adults. Responses to the fusion (F) protein were lower in infants compared to whole measles antigen (p < or = 0.03). Infant responses to both whole measles antigen and the F protein were lower compared with these responses in adults (p < or = 0.001). CD8+ T cell responses to N peptide pools varied, and differed between immune HLA-A2-positive individuals compared with naive and HLA-A2-negative subjects after measles vaccination. The measles-specific T cell adaptive response of infants is limited compared to adults, including responses to the F protein.

Humoral and cell-mediated immune responses to an early 2-dose measles vaccination regimen in the United States.

BACKGROUND: Shifts in peak measles incidence to children <12 months old and the associated high mortality support the study of an early 2-dose measles vaccine regimen. METHODS: Fifty-five infants were vaccinated with measles vaccine at age 6 (n=32) or 9 (n=23) months, followed by measles-mumps-rubella (MMR)-II vaccine at age 12 months. A control group received MMR-II only at age 12 months. Measles-specific humoral and cell-mediated immunity were evaluated before, 12 weeks after measles immunization, and 24 weeks after MMR-II. RESULTS: Measles-specific T cell proliferation after both doses of vaccine was equivalent, regardless of age or the presence of passive antibodies. Seroconversion rates, geometric mean titers, and the percentage of infants with antibody titers >120 mIU after the first measles vaccine were lower in infants vaccinated at age 6 months, regardless of the presence of passive antibodies, but measles humoral responses increased after the administration of MMR-II vaccine in children initially vaccinated at age 6 or 9 months. CONCLUSION: Measles vaccination elicits T cell responses in infants as young as 6 months old, which may prime the humoral response to the second dose. Initiating measles vaccination as an early 2-dose regimen results in an immunologic response that is likely to have clinical benefits in developed and developing countries.