The study shows that older people make fewer antibodies after a tetanus booster, but when a thymus‑derived peptide (Thymosin Fraction 5, which includes thymosin‑α1) is added to their immune cells in the lab, it boosts antibody production, especially in the elderly. This hints that thymosin could help improve vaccine responses in older adults, though real‑world trials are still needed.

A decline in T cell function accounts for many of the observed age-related deficient immune responses. Specific antibody response to many antigens requires T cell cooperation, and deficient antibody response to such antigens has been demonstrated with aging. In an effort to assess the potential reconstitutive capacity of Thymosin Fraction 5, in vitro antitetanus antibody production was measured in tetanus toxoid booster-immunized young and old volunteers. 22 young and 12 old volunteers were immunized with tetanus toxoid and plasma antitetanus antibody and in vitro lymphocyte production of antitetanus antibody was measured. Plasma antitetanus antibody response was significantly greater in the young. In vitro antitetanus antibody synthesis was negligible prior to immunization and peaked in cultures established 1 week after immunization from both young and old. When Thymosin Fraction 5 was added to the cultures, however, there was a dose-related enhancement of antibody synthesis in 7 of 10 from the group of elderly volunteers, but only 3 of 12 from the younger group. Our data indicate that specific antibody response is deficient in the elderly, but can be enhanced in vitro by thymosin. A future clinical trial of thymosin as an adjuvant to active immunization for the elderly is warranted.