CELLULAR-IMMUNITY IN MEASLES-VACCINE FAILURE - DEMONSTRATION OF MEASLES ANTIGEN-SPECIFIC LYMPHOPROLIFERATIVE RESPONSES DESPITE LIMITED SERUM ANTIBODY-PRODUCTION AFTER REVACCINATION

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 greater than or equal to 3. At 6 months after revaccination, 18 subjects (78%) with PRN titers less than or equal to 200 had SIs greater than or equal to 3. These data suggest that cellular responses to measles virus may be better sustained than antibody titers after vaccination and revaccination in some subjects.