Specific antibody synthesis in vitro. II. Age-associated thymosin enhancement of antitetanus antibody synthesis

Historical review of thymosin α 1 in infectious diseases

INTRODUCTION

Thymosin α 1 (Tα1) is a peptidic biological response modifier, which plays a significant role in activating and regulating various cells of the immune system. For the above-mentioned activities it is expected to exert a clinical benefit in the treatment of diseases where the immune system is altered.

AREAS COVERED

Several clinical trials have been carried out with Tα1 for treatment or prevention of many different infectious diseases such as hepatitis B and C, sepsis and Aspergillosis in bone marrow-transplanted patients. Data available on the use of Tα1 in infectious disease as well as a vaccine enhancer will be reviewed to possibly generate new working hypothesis.

EXPERT OPINION

Tα1 has been widely used in thousands of patients. Nevertheless, there are some issues that have not yet been properly addressed (i.e., dose, schedule, combination treatments, end-points to be evaluated in clinical trials). In the most recent clinical trials Tα1 has been used at higher doses than those commonly used in the past showing a direct proportionality between the dose and the effect. The safety profile of Tα1 is excellent and it is virtually devoid of toxicity.

Thymosin α1 continues to show promise as an enhancer for vaccine response

Thymosin α1 (Tα1) is an immune-modulating peptide that can be expected to improve response to vaccinations, as stimulated dendritic cells and T cells can act in concert to increase antibody production along with an improved cytotoxic response from the T cells themselves. Tα1 demonstrated efficacy in preclinical studies; subsequently, it was shown to enhance response to vaccinations in difficult-to-treat populations, including individuals immune suppressed due to age or hemodialysis, and leading to a decrease in later infections. During the 2009 pandemic outbreak of H1N1 influenza, mouse and ferret studies confirmed that the use of higher doses of Tα1 allowed for fewer injections than those used in the previous clinical studies. In addition, a clinical study with Focetria™ MF59-adjuvanted monovalent H1N1 vaccine showed that treatment with Tα1 twice provided an earlier and greater response to the vaccine (P < 0.01).

Thymosin Alpha 1 as an Adjunct to Influenza Vaccination in the Elderly: Rationale and Trial Summaries

From a clinical perspective, the immune deficiency of aging (immune senescence) is not profound. In fact, it may be of little clinical consequence. However, older people are prone to chronic and debilitating disorders which alone, or in concert with the medications used in their treatment, may add to the age effect and create a more clinically relevant immune deficiency. As a result, many older people are susceptible to infection. Furthermore, it is now well recognized that older people respond less well to immunization protocols. Protection against influenza by vaccination with hemagluttinin is the prototype example. Despite programs that have raised vaccination rates dramatically over the past three decades, influenza remains a major cause of morbidity and mortality in the elderly. This, in part, is due to the fact that vaccine responses are reduced in older recipients. Strategies are under development to enhance vaccine efficacy in this population and one such strategy is the adjuvant use of thymosin alpha 1 (Talpha1). In both animal experiments and human trials, there has been demonstrated enhancement of vaccine responses. The findings to date warrant additional efforts to further examine the role of Talpha1 in augmenting specific vaccine responses both in the elderly or in younger subjects in situations in which there are suboptimal quantities of immunizing antigen available.

Effect of rIL-2 treatment on anti-tetanus toxoid response in the elderly

To explore the effects of interleukin-2 (IL-2) treatment in a vaccination protocol in the elderly, we administered low-dose rIL-2 to a group of aged subjects before primary tetanus toxoid immunization. A specific antibody response was detectable in the serum of 6/8 treated individuals after primary immunization, but in only 2/6 untreated controls; following antigenic boosting, specific antibody levels remained relatively unchanged in all the seroconverters. The data were confirmed by studying the ability to produce tetanus-specific antibodies in vitro, and by isoelectrofocusing analysis of serum anti-tetanus antibodies; this latter study showed a more restricted clonal response to the immunogen in untreated individuals. On the other hand, the study of the in vitro proliferative response to tetanus toxoid did not evidence clear differences between the two groups. On the whole, these data seem to indicate that a short-term rIL-2 treatment is able to potentiate the antibody response to tetanus toxoid, and may be a useful tool to improve humoral responses to vaccines in aged subjects.

Cellular immunosenescence: an overview

Recent studies on space flights suggest that certain T cell immunologic activities are vulnerable to microgravitation. It would be desirable to know the extent to which these changes can be prevented or reversed. Since the changes observed are analogous to the effects of aging on immunity, a brief overview is presented of our current knowledge of age-related changes in immune cells and of the various interventional methods which have been used successfully in preventing the decline with age and in elevating the levels of immune functions of old individuals.

Augmentation of influenza antibody response in elderly men by thymosin alpha one. A double-blind placebo-controlled clinical study

Influenza remains a major cause of illness and death in elderly people despite current vaccination programs. One factor is an immunization failure rate in the elderly that may be as high as 50%. To test whether administration of thymosin alpha 1 would result in greater antibody production, we administered it (900 micrograms/m2 subcutaneously twice weekly for eight doses) in conjunction with the 1986 trivalent influenza vaccine. Ninety men (65-99 years old, mean age 77.3 years) were randomized double-blind to receive thymosin alpha 1 or placebo by the same schedule; the sera from 85 of these men were acceptable for analysis. The two groups were similar with respect to underlying disease, medications, and age. No toxicity was observed in either group. Antibody response rate was defined as a four-fold rise in antibody titer over 3-6 weeks following vaccination and was measured by an enzyme-linked immunosorbent assay (ELISA). Analysis was performed on treatment groups and subgroups divided by the mean age: the older group consisted of subjects aged 77 years and older, and the younger group those aged from 65-76 years. Baseline and change in absolute antibody levels were compared by t test and using age as a continuous variable by multiple regression analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

A pituitary-thymus connection during aging

Thymic involution is a normal consequence of aging. It has often been speculated that if this age-associated atrophy of the thymus gland could be prevented, the natural decline that occurs in a number of T-cell-mediated immune responses could be reversed. It has recently become clear that thymic involution can indeed be reversed by altering the hormonal environment of aged animals. These data support the concept of an active and functional pituitary-thymus axis. Since thymic reconstitution can result in restoration of some T-cell responses, it would appear that intrinsic defects which exist in T cells of aged animals can be at least partially reversed. This suggests that the aged environment plays a greater role in the decline of T-cell functions than has been previously recognized. Furthermore, phorbol esters and calcium ionophores can restore suppressed proliferative responses of T cells from aged rodents, so we speculate that intrinsic defects in T cells of aged subjects lie between the recognition system for antigen/lectin and intracellular transmission of this signal.

Thymosins and anti-thymosins: properties and clinical applications

For years, scientists have searched for ways to trigger the body's own defenses against cancer and other diseases associated with abnormal immunity. This search has led to the discovery of a number of important new biological and chemical substances that augment, direct or restore many of the normal defenses of the body. These substances are in essence the natural drugs of the body that endow us with immunity and resistance to disease. Now called biological response modifiers (BRMs), most of these 'new medicines', such as thymosins, lymphokines, and interferons, occur naturally in the body, while others, synthetic immunomodulators and thymomimetic agents (drugs that mimic thymic function) have been created in the laboratory. Previously, therapeutic drug development in this area relied upon chemical synthesis or introduction of bacterial adjuvants, or modified viral compounds and substances, which were foreign to the body. Therefore, they did not and do not rely upon or use the body's natural immune and biological response systems for protection against disease, function and response to the environment. Although scientists have known about BRMs for years, isolating and purifying them so that they could be used to treat diseases has been extremely difficult. Many of these substances, such as the lymphokines, occur in the body in minute amounts and normally do not circulate in the blood. The development of new technologies for isolation and large scale synthesis, e.g. solid phase peptide synthesis, high-pressure liquid chromatography microsequencing and genetic engineering, has now permitted scientists to isolate, purify, and synthesize BRMs in sufficiently large quantities to allow human clinical trials. In this paper we will focus on the potential clinical applications of the thymosins and anti-thymosins.

The age-related decline in antibody response is transferred by old to young bone marrow transplantation

The immune response declines with age. This decline correlates with thymic involution and involves primarily a loss in T-cell function, whereas humoral immunity is more variably affected. In the current experiments we have measured immunoglobulin synthesis in vitro after mitogen stimulation, and specific antibody response after vaccination. We found that the response to pokeweed mitogen by non-specific immunoglobulin production, and the response to vaccine was shown to be transferred to lethally irradiated young mice by old to young bone marrow transplantation. Both pokeweed mitogen and tetanus toxoid require T-cell help for optimal response, and, therefore, our observations are in accordance with the age-associated decline in T-cell immunity. The finding that young hosts transplanted with old bone marrow produce less antibody than young hosts transplanted with young bone marrow highlights the importance of the decline in cellular function with age.

Interleukin-2 and aging: decreased interleukin-2 production in healthy older people does not correlate with reduced helper cell numbers or antibody response to influenza vaccine and is not corrected in vitro by thymosin alpha 1

The capacity of lymphocytes obtained from healthy young or old volunteers to produce interleukin-2 was measured and the results were compared with other measures of immune function. The in vitro effect of thymosin alpha 1 on interleukin-2 production was also measured. Interleukin-2 was lower in lymphocytes from the elderly, and individuals with low production also had lower proliferative responses in vitro to phytohemagglutinin. These individuals did not have a reduced helper T-cell number, abnormal ratio of helper to suppressor T-cells or reduced antibody production in response to vaccine. Thymosin alpha 1 did not have a consistent effect on interleukin-2 production.

Effect of thymosin alpha one on specific antibody response and susceptibility to infection in young and aged mice

The antibody response to a variety of antigens has been shown to diminish with age. We investigated the capacity for Thymosin Alpha One (T alpha 1) treatment to augment antibody production in tetanus toxoid (TT) and pneumococcal capsular polysaccharide (PN) inoculated young and old mice. We also measured survival of these immunized mice after aerosol exposure to Streptococcus pneumoniae. As predicted antibody response to TT, but not PN, was significantly reduced in the old animals and T alpha 1 augmented antitetanus antibody in both young and old mice. T alpha 1 did not have an effect on anti pneumococcal antibody production. All mice that had received PN did have an antibody response, yet survival after exposure to the organism was strikingly less in the old animals. Our data support the contention that antibody response to T-dependent antigens (such as tetanus toxoid) falls with aging but can be reconstituted somewhat by thymic factors. Furthermore, for T-independent antigen (such as pneumococcal capsular antigens) the age-related changes are less evident. In the latter situation, the presence of a brisk antibody response after vaccination was not sufficient to prevent pneumonia and death in old animals.

Influenza and aging: age-related changes and the effects of thymosin on the antibody response to influenza vaccine

Despite massive immunization programs, influenza remains a major cause of morbidity and mortality for elderly people. This may occur because immune senescent recipients may respond to vaccination with inadequate antibody production. We measured antibody response to the trivalent 1983-1984 influenza vaccine in young and elderly volunteers and found a significantly reduced response in the latter. The age-associated decreased antibody production was also observed in lymphocyte cultures in which specific antiinfluenza antibody synthesis was measured. In these cultures, however, the addition of a thymic hormone preparation (either thymosin fraction 5 or thymosin alpha 1) was shown to enhance specific antibody synthesis to a greater extent in the cultures established from the elderly volunteers. If this in vitro observation of thymosin induced increased antibody production reflects what might occur in a clinical trial in which elderly subjects receive thymosin coincident with vaccine, greater protection against influenza infection may result.