Thymosin Stimulation of Vaccine Responses
Immune senescence, a normal aging process, has been related to a gradual decline in thymus function and thymic peptide production.
The lack of thymic factors may contribute to the decline in immune function, particularly the T-cell component. In the elderly,
quantitative and qualitative analysis of a specific antibody response after vaccination has been shown to be compromised when
compared with the response in young subjects.20,41 Impairment of cell-mediated immunity also has been demonstrated in hemodialysis patients.42–44
In two preclinical studies, administration of thymosin alpha 1 to mice was shown to increase antibody response to tetanus
toxoid (TT) and influenza vaccination.19,21 In the first study, thymosin alpha 1 was administered at 0.5 ug/kg to old (23 months) and young (2–3 months) mice on the
day of vaccination and for each of four additional days after vaccination. Old mice that were not treated with thymosin alpha
1 had a significantly lower antibody response than young mice. Thymosin alpha 1 treatment resulted in significantly greater
(p < 0.05) anti-TT antibody in both young and old mice, and appeared to restore the antibody response in the old mice close
to levels seen in the young animals. In the second study, mice were pretreated with thymosin alpha 1 (10 ug/day for five days),
and virus-specific CTL response was determined after vaccination with the influenza vaccine (Figure 1). Thymosin treatment
increased the vaccine response of old (24–26 months) mice to that seen in young (2–6 months) mice.
Figure 1. Thymosin alpha 1 treatment increases specific CTL response after influenza vaccination21
In vitro antibody synthesis by human peripheral blood lymphocytes (PBL) also has been shown to be augmented by treatment with thymosin
alpha 1. In this study, Ershler and colleagues examined age-related changes in antibody response to influenza vaccine in humans,
and tested the capacity of TF-5 or thymosin alpha 1 to enhance specific antibody synthesis in vitro.20 They found that the antibody response following influenza vaccination was lower in elderly subjects (>65 years) compared
to young subjects (<30 years). PBLs were then isolated from immunized young and old subjects and were incubated in vitro with either TF-5 at doses of 50, 100, 200 ug/mL or thymosin alpha 1 at doses of 0.01, 0.1, or 1.0 ng/mL. In vitro augmentation of the antibody response by either TF-5 or thymosin alpha 1 was detected in PBLs from 16 of the 28 elderly volunteers,
compared to seven of the 30 young volunteers. In addition, there were twice as many responders (six versus three) in the 1
ng/mL thymosin alpha 1 group compared to the 0.01 ng/mL group, indicating a possible dose response that correlates with the
endogenous level of circulating thymosin alpha 1 in healthy individuals (about 1 ng/mL).
Because thymosin alpha 1 can enhance T-cell–dependent specific antibody production, the addition of thymosin alpha 1 to vaccination
programs for immunocompromised individuals should be effective. Five clinical studies have been undertaken and have demonstrated
effectiveness of thymosin alpha 1 in increasing vaccine response, both in elderly subjects or patients undergoing hemodialysis,
and after either influenza or hepatitis vaccination, as shown in Tables 1 and 2, respectively.
Table 1. Response to influenza vaccine
In a pilot trial, the effect of thymosin alpha 1 on influenza vaccination was evaluated by Gravenstein, et al., at the University
of Wisconsin and Cornell Medical Center.45 Nine elderly subjects (age range 65 to 99 years) who had been nonresponsive to influenza vaccination in the previous year
were given biweekly thymosin alpha 1 injections for five weeks following a single injection of seasonal influenza vaccine.
A total of 67% (6/9) responded with high levels of anti-influenza antibodies, compared to a historical rate of 10% after revaccination
in elderly subjects.
Table 2. Response to hepatitis B vaccine
This pilot trial was followed by a double-blind, randomized, placebo-controlled study conducted by the same researchers, at
the Wisconsin Veterans' Administration Medical Center, Madison.46 Ninety male veterans over 64 years of age (range 65 to 99 years) were randomized to receive either thymosin alpha 1 or placebo
biweekly for four weeks following injection with the trivalent vaccine. Effective immunization was defined as a four-fold
or greater rise in antibody titer over a period of three to six weeks as measured by ELISA. About 69% (31/45) of thymosin-treated
subjects were effectively immunized, compared to 52% (21/40) with placebo (p = 0.023). The differences seen were greater in
subjects older than 77 years; the relationship between antibody levels and age also was significant (p < 0.039). As seen in
the mouse studies, the antibody levels seen after treatment with thymosin alpha 1 were comparable to those seen in younger
In a study conducted at George Washington University, 330 elderly subjects were vaccinated with the trivalent seasonal influenza
vaccine (B/Ann Arbor, A/H3N2 Leningrad, A/H1N1 Taiwan).47 Biweekly doses of thymosin alpha 1 were given for either two weeks (120 subjects) or four weeks (100 subjects) after vaccination;
placebo was given for two weeks (110 subjects). In the subjects treated with thymosin for four weeks, greater antibody levels
were seen compared to placebo or two weeks of thymosin (p = 0.015). In addition to the improved antibody response, the subjects
treated with thymosin alpha 1 for four weeks also had a significantly decreased incidence of influenza, from 19% in patients
receiving influenza vaccine with placebo to 5.5% in patients receiving the vaccine in combination with thymosin alpha 1 (p
= 0.002) (Figure 2).
Figure 2. Thymosin alpha 1 treatment decreases influenza incidence47
In a study with 97 patients immunocompromised by chronic renal failure and undergoing hemodialysis, vaccination with monovalent
A/Taiwan/1/86 (H1N1) vaccine followed by biweekly injections of thymosin for four weeks also led to improved response.48 Four weeks after vaccination, 71% (34/48) of subjects treated with thymosin alpha 1 had a four-fold or higher titer of specific
antibody, compared to 43% (21/49) for those treated with placebo after vaccination (p < 0.002). This effect was long-lasting:
eight weeks after vaccination the thymosin-treated subjects still had a rate of 65% response, compared to only 24% in the
placebo-treated patients (p < 0.001).
Finally, the effect of thymosin on increasing response to vaccination was also seen with hepatitis B vaccine. In a study with
23 hemodialysis patients, nonresponders to a previous course of Heptavax vaccination were retreated with three vaccine injections
one-month apart, with five biweekly injections of thymosin given after each vaccination. When response was measured three
months later, 64% (7/11) of thymosin-treated patients had clinically significant anti-HBsAg titers, compared to 17% (2/12)
of placebo-treated patients. The effect of thymosin was also long-lasting: measured after 12 months, 45% of the thymosin-treated
patients still had clinically significant titers, whereas none of the placebo-treated patients retained theirs (p < 0.002).