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 month s after revaccination in 60 previously vaccinated subjects (9.4 +/- 3. 4 years of age) who had either undetectable or low plaque reduction ne utralization (PRN) titers (<200). PRN titers were increased in all sub jects at 1 month (590 +/- 61; range, 129-2513) but fell again in 66% o f subjects by 6 months (214 +/- 29; range, 30-794). At 6 months, 23 (3 8%) had subprotective (<120) or borderline (<200) PRN titers. Lymphopr oliferative responses to measles virus antigens were low overall befor e 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, 1.4-8 0) 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 t iters had SIs greater than or equal to 3. At 6 months after revaccinat ion, 18 subjects (78%) with PRN titers less than or equal to 200 had S Is greater than or equal to 3. These data suggest that cellular respon ses to measles virus may be better sustained than antibody titers afte r vaccination and revaccination in some subjects.