Healthcare e-Compendium
A joint initiative of DPSRU & DRSC
Healthcare e-Compendium
A joint initiative of DPSRU & DRSC
Author: Dr. Amit Srivastava
M.S., M.Ch., Sr. Cardio Thoracic Vascular Surgeon, Apex Hospital, Varanasi
download ArticleAbstract
Thymosin alpha 1 (Tα1), a 28-amino acid peptide, which enhances T-cell, dendritic cell (DC) and antibody response, modulates cytokines as well as chemokines production and blocks the steroid-induced apoptosis of thymocytes. Tα1 is also proven to decrease tumor cell growth both in vitro and in vivo and has demonstrated therapeutic usefulness in several types of cancer. Tα1 exhibits a dual mechanism of action as an immunomodulator and antiviral. Recently many clinical applications have been researched to prove the efficacy of Tα1 as either a mono or adjuvant therapy in treatment and diagnosis of diseases associated with deficiencies and/or imbalances of the immune system.
Keywords: Thymosin alpha-1, Immunomodulator
Introduction
Thymosin alpha 1 (Tα1), a 28-amino acid peptide (fig. 1), was first described and characterized from calf thymuses in 1977. This peptide enhances T-cell, dendritic cell (DC) and antibody response, modulates cytokines and chemokines production and block the steroid-induced apoptosis of thymocytes [1].
Fig 1: Thymosin alpha 1 (Tα1), a 28-amino acid peptide
Thymosin alpha-1 (thymalfasin) is produced endogenously by the thymus gland which increases T cell-mediated immune responses by several mechanisms (fig. 2), including stimulation of T cell, activation of natural killer cells and dendritic cells, and stimulation of proinflammatory cytokine release [2].
The research process of Tα1 began along with the study on the thymus, which is a vital organ for homeostatic maintenance of peripheral immune system. In 1966, Goldstein et al. first isolated and described a lymphocytopoietic factor from calf thymus, which was termed “thymosin”. The multiple action of thymosin on the immune, endocrine and central nervous systems was revised by Goldstein and Badamchian. Further purification of this factor led to the isolation of a heat-stable acetone-insoluble preparation, termed thymosin fraction 5, which could induce T cell differentiation, enhance immunological function and induce apoptosis of neuroendocrine tumor cells. The promising results seen with TF5 provided the scientific rationale to further isolate and characterize the molecules in TF5 responsible for the reconstitution of T-cell immunity. Hence, Tα1 was first purified from TF5 in 1977 and has been found to be 10–1000 times as active as TF5 evaluated in vivo and in vitro [1].
Due to its pleiotropic biological activities, Tα1 has gained interest in recent years and has been used for the treatment of various diseases in clinic. Accordingly, there is an increase in the demand for the production of this peptide. So far, Tα1 used in clinic is synthesized using solid phase peptide synthesis. Here, we summarize the genetic engineering technique to produce Tα1 using prokaryotic or eukaryotic expression systems. The effectiveness of these biological products in increasing the secretion of cytokines and in promoting lymphocyte proliferation were investigated in vitro studies. This opens the possibility for biotechnological production of Tα1 for the research and clinical applications [1].
Tα1 administration has been efficacious for SARS patients in controlling the development of the disease. Studies show that the treatment with thymosin α1 could decrease 28-day mortality in critical type COVID-19 patients, which suggest that thymosin α1 might improve host immune dysfunction and the poor prognosis of critical type patients [3]. Critical COVID-19 patients developed uncontrolled inflammatory activation, resulting in an increase in neutrophils and a decrease in the total number of lymphocytes, which are more significant in critical cases [4]. Whereas, lymphocytes play an important role in antiviral processes by balancing the fight against pathogens and decreases lymphocytes which are related to poor prognosis in many diseases [5][6]. CyTOF and microfluidic qPCR revealed that severe COVID-19 patients showed a decreased T-cell proportion, and T-cell activation as well as differentiation-related genes were downregulated [7]. Studies suggest that critical type COVID-19 patients with lower lymphocyte counts could obtain a significant benefit from thymosin α1 therapy.
Fig 2: Immune-stimulating mechanism of action of Tα1
Biological Activity
Immunoregulation
Many studies have been performed to identify the immunoregulatory activity of Tα1in vitro and in vivo (fig. 3). Evidence suggest that Tα1increased the efficiency of T cell maturation, stimulated precursor stem cell differentiation into the CD4+/CD8+ T cells and balanced CD3/CD4+/CD8+ T cells of peripheral blood mononuclear cells (PBMCs). By stimulating natural killer (NK) cells and cytotoxic lymphocytes (CD8+ T cell), Tα1could directly kill virally infected cells [8].
Antitumor
Tα1 has been shown to decrease tumor cell growth both in vitro and in vivo and has demonstrated therapeutic usefulness in several types of cancers. Tα1 was observed to exhibit anti-proliferative effects on HepG2 human hepatoma cells and SPCA-1 lung adenocarcinoma cells. Moody et al. investigated the effects of Tα1 on mammary carcinogenesis in fisher rats and found that Tα1 could reduce mammary carcinoma incidence and prolong survival time [9].
Protection against oxidative damage
Tα1 had protective effects against oxidative damage. Tα1 had a positive influence on liver superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activity and thereby limited free radical damages to hepatic tissue. Similarly, it was reported that Tα1 could improve streptozotocin-induced pancreatic lesions and diabetes by reducing malondialdehyde (MDA), increasing GSH level and enhancing the activities of both SOD and catalase (CAT), suggesting that Tα1 treatment could greatly enhance the overall antioxidative capability of pancreatic tissues [10].
Other functions
Tα1 possesses the ability of influencing the central nervous system [11]. Its modulatory effect on the excitatory synaptic transmission in cultured hippocampal neurons was found [12]. Similarly, when it was combined with chemotherapeutics in treating cancers, Tα1 could prevent patients from chemotherapy-induced neurotoxicities [13]. Moreover, Tα1 has potent effects in promoting endothelial cell migration, angiogenesis as well as wound healing [14].
How Does Thymosin Alpha 1 Work?
Although the mechanism of action of thymosin has not been totally defined, but it primarily exhibits dual mechanism of action as immunomdulator and antiviral. Tα1 as immunomodulator increases the efficiency of T-cell maturation and to increase the ability of T-cells to produce lymphokines such as IFN, IL-2 and IL-3 following antigen and/or mitogen activation and to upregulate and express high affinity lymphokine receptors [15]. Thymosin is classified as a biological response modifier on the basis of these effects on lymphocyte markers and lymphocyte functional activity both in vivo and in vitro. Initial studies demonstrated that thymosin at induced markers of mature T-cell differentiation on lymphocytes from the bone marrow of adult thymectomized mice [16]. Subsequent studies defined thymosin to act as antiviral as it inhibits viral replication and also increases MHC class1 expression. This dual activity is perhaps the reason why Tα1 exhibits such a wide range of bioactivities.
Figure 3: Immunoregulation and antiviral action of Tα1
Latest Studies on Use of Thymosin Alpha 1 in Treating Covid-19 Patients in Elderly Renal Dialysis Patient
Patients with end-stage renal disease (ESRD) on hemodialysis, in addition to their intrinsic kidney disease and frequent burden of comorbidities, also have increased risk of exposure to communicable diseases as they are treated several times each week at hemodialysis centers with several other patients and clinic staff in attendance. The majority of patients are over 60 years of age and many are receiving immunosuppressive medications. Accordingly, ESRD patients are particularly susceptible to COVID-19 infection.
Thymosin alpha 1, Tα1 is a naturally occurring peptide that has been evaluated for its immunomodulatory activities and related therapeutic potential in several conditions and diseases, including infectious disease and cancer. Tα1 has been used clinically in pilot studies for treatment of severe acute respiratory syndrome (SARS) and other lung infections including acute respiratory distress syndrome (ARDS) and chronic obstructive pulmonary disorder (COPD), as well as infections after bone marrow transplant. Larger clinical trials have shown significant efficacy for treatment of severe sepsis and hepatitis B, along with certain cancers such as melanoma, hepatocellular, and lung cancer. Tα1 has also demonstrated improvement in response to vaccines in the elderly and in patients immunocompromised by renal disease. The beneficial clinical effects of Tα1 result from activation of toll-like receptor (TLR) 9 in dendritic and other immune system cells, resulting in augmentation of T helper (Th1) function, natural killer (NK) cell activity, and increased antibody responses to T-cell dependent antigens. Importantly, Tα1 also leads to an increase in IL-10 producing regulatory T cells, which create feedback inhibition of cytokine production, hence dampening immune response and preventing a pro-inflammatory cytokine storm.
It is our hypothesis that a course of Tα1 administered to individuals at high risk for COVID-19 infection (hemodialysis patients 60 years and older) will reduce the rate of COVID-19 infection and severity of infection with COVID-19, compared to untreated individuals in the same hemodialysis units with comparable risk. The study will also evaluate the need for hospitalization in those patients who do not become infected with COVID-19 [17].
Clinical Effect of Thymosin Alpha-1 on Various Diseases
Recently many clinical applications have been researched to prove the efficacy of Tα1 as either a mono or adjuvant therapy in treating and diagnosis of diseases associated with deficiencies and/or imbalances of the immune system. The many fields of applications are shown in the figure 4 [18].
Figure 4: Emerging clinical applications of Thymosin α1 [1]
Infectious Diseases
Tα1 has been effective in improving immune responses and in arresting the progression of many viral, bacterial, and fungal infections in mice [19]. Moreover, many studies have been reported that indicate that Tα1 alone and/or in combination with other biological response modifiers (BRMs) is clinically effective in treating different infectious diseases [20].
Severe sepsis
Using Tα1 as a single agent, Chen et al, have reported that Tα1 upregulated immune function in patients with severe sepsis. Researchers observed that that using Tα1 in combination with standard antimicrobial therapy had significantly higher cumulative survival rate and it also shortened time of mechanical ventilation, use of antibiotics, and stay in the intensive care unit (ICU) [21]. Zhao et al, have reported similar results, with addition there were significant improvements in the number of lymphocytes and CD14+ monocytes and HLA-DR [22].
Acute Respiratory Distress Syndrome (ARDS)
ARDS has extremely high mortality rate and with patients on ventilation support. Study on ARDS patient who had recent renal transplant suffering from severe pneumonia found that after receiving Tα1 showed an improved outcome [23]. In a follow up trial, Ji et al, observed the death rate was significantly reduced; and also found that Tα1 significantly increased the number of CD4+ and CD8+ lymphocytes, suggesting that repairing cellular immunity reinforces resistance to CMV [24].
Severe Acute Respiratory Syndrome (SARS)
SARS is caused by novel coronaviruses, and the cure is still under development. Gao et al, in a study reported out that timely administration of a cocktail of antivirals, steroids and immuno-enhancers, including IFNα-2b and Tα1, to SARS patients was efficacious in helping to control the development of the disease and in improving patients' prognosis and controlling the spread of SARS [25].
Acquired Immune Deficiency Syndrome (AIDS)
Various studies suggest that thymosin may be useful in treating AIDS in combination with antivirals. A pilot study showed that Tα1 was effective in significantly increasing functioning immune responses [26]. In multicenter studies, a combination of Tα1 and zidovudine with IFN-α was found to improve and maintain CD4 counts and to reduce HIV virus titers [27].
Pseudomonas aeruginosa Pneumonia
Pseudomonas infections are major clinical problems of immunocompromised and aging populations. Clinical report of Tα1 on critically ill hospitalized patients was carried out by Huang et al. They found a significant decrease of infection rate, white blood cell (WBC) count, C-reactive protein, TNFα, and IL-6 in their study [28].
In a follow up study patients were treated with Sulperazone and Tα1; Li et al, reported that immunological function improved and reduced inflammation, and had a synergistic effect on drug-resistant P. aeruginosa pneumonia [29].
Hepatitis B and C, Severe Chronic Hepatitis, and Spontaneous Peritonitis
Thymosin has been clinically indicated for treating the infections by hepatitis viruses. In the first reported pilot study, Tα1 was found to significantly improve the remission rate in advanced chronic hepatitis B [30]. Tα1 in combination with IFN-α and/or antivirals have also shown promise [31]. Study on patients with HCV, the remission rates in patients treated with Tα1 in combination with interferon were greater than those obtained with interferon alone [32]. In addition, other biochemical responses at the end was seen to be improved.
An interesting pilot trial in patients with severe chronic hepatitis (SCH) has been reported by Gao et al. They observed patients receiving Tα1 in addition to conventional therapy had improved survival [33].
Cancer
Many cancers are associated with significant deficiencies in cellular immunity [34]. In addition, standard treatments for cancer (i.e., surgery, radiotherapy and chemotherapy) usually depress cellular immunity.
Lung Cancer
The first randomized double-blind Phase II trial by Schulof et al, found Tα1 as an adjuvant to conventional radiation therapy significantly prolonged survival and increase the disease-free interval particularly in patients with nonbulky tumors, and with NSCLC [35]. Similar beneficial effects of Tα1 as an adjuvant to chemotherapy and IFN-α have been reported, along with an added ability to reduce the toxicity of conventional chemotherapy, in patients with NSCLC [36-37].
Melanoma
Late-stage metastatic melanoma is resistant to most forms of therapy. In the first trial of Tα1 by Rasi et al, they studied Tα1 in combination with DTIC and natural IFN-α. Patients showed an improved overall response rate with a shortened mean duration of response [38]. In the second trial by Lopez et al, done using Tα1 in combination with DTIC and IL-2; patients showed better response rate and lesser median time to progression [39].
In Phase II multi-center, randomized open-label study of patients with stage IV melanoma, trial was designed to evaluate different dose levels of Tα1 in combination with DTIC chemotherapy, with/without low-dose IFN-α. It was observed Tα1 at all dose levels was well-tolerated in all treated patients, with no serious adverse events attributed to the drug. Results reported as tripled overall response rate and extended overall survival time [40].
Hepatocellular Carcinoma (HCC)
There is a strong connection between HCC and chronic hepatitis B and C [41]. The first Phase II trial of Tα1 in patients with HCC was reported in Italy by Stefanini et al. They observed the addition of Tα1 following chemotherapy with doxorubicin significantly increased the survival obtained by transcatheter arterial chemoembolization (TACE) [42]. Many other subsequent clinical studies observed similar results.
Chemoprotection during Lung and Breast Cancers Treatment
The addition of Tα1 therapy appears to offer protection from some of the toxicities of chemotherapy. In a study by An et al, on patients with advanced lung or advanced breast cancer treated with chemotherapy found that Tα1 given before and after chemotherapy reduced neurotoxicities in patients [43].
In another study focusing on quality of life (QoL) issues in patients receiving chemotherapy by Chen, obtained results of significant increase in QoL scores in terms of appetite, sleep, fatigue, daily activity and overall feeling of well-being, and reduced depression [44].
Immune Deficiencies
Thymosin’s modulate immune activity and may be used to restore depressed immune systems. Most of the congenital immune deficiencies are T-cell-dependent; that is, the defective immune activity is due to a partial or complete absence of mature T-cells, resulting from a deficiency of thymus hormone production [45-46]. Tα1 has been used to stimulate the formation and development of an effective T-cell immunity.
Autoimmune Diseases
Autoimmune diseases are distinguished by an abnormally sensitive and over-responsive immune system. In preclinical studies, Tα1 restored immune balance and increased the level of suppressor T-cells. Tα1 has been found to be safe and without either significant side effects or a narrow therapeutic index. In pilot clinical studies, Tα1, has relieved symptoms in rheumatoid arthritis, systemic lupus erythematosus and Sjögren's syndrome [47].
Aging and Immune Senescence
Immunity basically declines with age with contributing factors including a decline in thymus-related cellular function, an accumulation of memory cells, and dysregulated inflammatory mediators. Of these, T-cells, are most affected by age. This may be linked to the universally occurring age-associated thymus gland involution and resultant shrinkage of the naïve T-cell compartment [48-49].
A decline in T-cell immunity and possibly serum levels of Tα1 appears to correspond with an increase in immune senescence associated with aging, and studies suggest that Tα1 may be possible to improve immunologic responses in the elderly by manipulating the blood levels of thymus hormones [49].
Boosting Vaccine Efficacy
An early example of the use of Tα1 as an adjuvant to boost the efficacy of a vaccine in an immunodeficient patient population with renal disease on hemodialysis was carried out by Shen et al. They observed the patients receiving Tα1 responded positively with protective antibody levels to the hepatitis vaccine [50]. Ershler et al found that they could significantly enhance antibody responses and immunity to influenza with Tα1 [51]. Many other trials had similar results of the greater antibody levels with no toxicity observed.
Conclusion
Role of Tα1 in improving the immune response is long known since the discovery of the molecule over the last century. The advances in our knowledge of potential clinical application has improved since. Tα1 alone or in combination with other drugs or standard therapies offer many opportunities to boost and regulate the immune responses improving the outcomes. Recently many clinical studies support the use of Tα1 which in synergy with other treatment options; and are providing broad and novel insights into understanding the underlying mechanisms as well. Utilizing this knowledge we will be able to grow the ability to intervene in a number of serious life-threatening and/or chronic diseases with the ways in which the immune system affects disease processes. This translate into the successful treatment of many diseases that have a high morbidity and mortality, while improving patients’ quality of life.
Reference
Juan Li, Chun Hui Liu, Feng Shan Wang Juan Li, Chun Hui Liu, Feng Shan Wang
