Cellular Immunity in Measles Vaccine Failure: Demonstration of Measles Antigen-Specific Lymphoproliferative Responses despite Limited Serum Antibody Production after Revaccination

Abstract

Measles antigen-specific immune responses were evaluated 1 and 6 months after revaccination in 60 previously vaccinated subjects (9.4 ± 3.4 years of age) who had either undetectable or low plaque reduction neutralization (PRN) titers <200). PRN titers were increased in all subjects at 1 month (590 ± 61; range, 129–2513) but fell again in 66% of subjects by 6 months (214 ± 29; range, 30–794). At 6 months, 23 (38%) had subprotective <120) or borderline <200) PRN titers. Lymphoproliferative responses to measles virus antigens were low overall before revaccination (mean stimulation index [SI], 2.6 ± 0.4; range, 0.5–13.5) but were readily detectable at 1 (SI, 14.8 ± 2.6; range, 1.4–80) and 6 months after revaccination (SI, 9.4 ± 1.8; range, 1.1–87). Before revaccination, 10 of the subjects (50%) with low positive PRN titers had SIs ⩾3. At 6 months after revaccination, 18 subjects (78%) with PRN titers ⩽200 had SIs ⩾3. These data suggest that cellular responses to measles virus may be better sustained than antibody titers after vaccination and revaccination in some subjects.