Thymosin alpha1: a historical overview

Phenotypic drug discovery: a case for thymosin alpha-1

Phenotypic drug discovery (PDD) involves screening compounds for their effects on cells, tissues, or whole organisms without necessarily understanding the underlying molecular targets. PDD differs from target-based strategies as it does not require knowledge of a specific drug target or its role in the disease. This approach can lead to the discovery of drugs with unexpected therapeutic effects or applications and allows for the identification of drugs based on their functional effects, rather than through a predefined target-based approach. Ultimately, disease definitions are mostly symptom-based rather than mechanism-based, and the therapeutics should be likewise. In recent years, there has been a renewed interest in PDD due to its potential to address the complexity of human diseases, including the holistic picture of multiple metabolites engaging with multiple targets constituting the central hub of the metabolic host-microbe interactions. Although PDD presents challenges such as hit validation and target deconvolution, significant achievements have been reached in the era of big data. This article explores the experiences of researchers testing the effect of a thymic peptide hormone, thymosin alpha-1, in preclinical and clinical settings and discuss how its therapeutic utility in the precision medicine era can be accommodated within the PDD framework.

Robust Chemical Synthesis of "Difficult Peptides" via 2-Hydroxyphenol-pseudoproline (ψ2-hydroxyphenolpro) Modifications

The challenging preparation of "difficult peptides" has always hindered the development of peptide-active pharmaceutical ingredients. Pseudoproline (ψpro) building blocks have been proven effective and powerful tools for the synthesis of "difficult peptides". In this paper, we efficiently prepared a set of novel 2-(oxazolidin-2-yl)phenol compounds as proline surrogates (2-hydroxyphenol-pseudoprolines, ψ2-hydroxyphenolpro) and applied it in the synthesis of many well-known "difficult peptides", including human thymosin α1, amylin, and β-amyloid (1-42) (Aβ42).

Advancement from Small Peptide Pharmaceuticals to Orally Active Piperazine-2,5-dion-Based Cyclopeptides

The oral delivery of peptide pharmaceuticals has long been a fundamental challenge in drug development. A new chemical platform was designed based on branched piperazine-2,5-diones for creating orally available biologically active peptidomimetics. The platform includes a bio-carrier with "built-in" functionally active peptide fragments or bioactive molecules that are covalently attached via linkers. The developed platform allows for a small peptide to be taken with a particular biological activity and to be transformed into an orally stable compound displaying the same activity. Based on this approach, various peptidomimetics exhibiting hemostimulating, hemosuppressing, and adjuvant activity were prepared. In addition, new examples of a rare phenomenon when enantiomeric molecules demonstrate reciprocal biological activity are presented. Finally, the review summarizes the evolutionary approach of the short peptide pharmaceutical development from the immunocompetent organ separation to orally active cyclopeptides and peptidomimetics.

Thymosin α1 and Its Role in Viral Infectious Diseases: The Mechanism and Clinical Application

Thymosin α1 (Tα1) is an immunostimulatory peptide that is commonly used as an immune enhancer in viral infectious diseases such as hepatitis B, hepatitis C, and acquired immune deficiency syndrome (AIDS). Tα1 can influence the functions of immune cells, such as T cells, B cells, macrophages, and natural killer cells, by interacting with various Toll-like receptors (TLRs). Generally, Tα1 can bind to TLR3/4/9 and activate downstream IRF3 and NF-κB signal pathways, thus promoting the proliferation and activation of target immune cells. Moreover, TLR2 and TLR7 are also associated with Tα1. TLR2/NF-κB, TLR2/p38MAPK, or TLR7/MyD88 signaling pathways are activated by Tα1 to promote the production of various cytokines, thereby enhancing the innate and adaptive immune responses. At present, there are many reports on the clinical application and pharmacological research of Tα1, but there is no systematic review to analyze its exact clinical efficacy in these viral infectious diseases via its modulation of immune function. This review offers an overview and discussion of the characteristics of Tα1, its immunomodulatory properties, the molecular mechanisms underlying its therapeutic effects, and its clinical applications in antiviral therapy.

Association between pretreatment lymphocyte count and efficacy of immune-enhancing therapy in acute necrotising pancreatitis: a post-hoc analysis of the multicentre, randomised, placebo-controlled TRACE trial

Background

Immune-enhancing thymosin alpha 1 (Tα1) therapy may reduce infected pancreatic necrosis (IPN) in acute necrotising pancreatitis (ANP). However, the efficacy might be impacted by lymphocyte count due to the pharmacological action of Tα1. In this post-hoc analysis, we tested the hypothesis that pre-treatment absolute lymphocyte count (ALC) determines whether patients with ANP benefit from Tα1 therapy.

Methods

A post-hoc analysis of data from a multicentre, double-blind, randomised, placebo-controlled trial testing the efficacy of Tα1 therapy in patients with predicted severe ANP was performed. Patients from 16 hospitals of China were randomised to receive a subcutaneous injection of Tα1 1.6 mg every 12 h for the frst 7 days and 1.6 mg once a day for the following 7 days or a matching placebo during the same period. Patients who discontinued the Tα1 regimen prematurely were excluded. Three subgroup analyses were conducted using the baseline ALC (at randomisation), and the group allocation was maintained as intention-to-treat. The primary outcome was the incidence of IPN 90 days after randomisation. The fitted logistic regression model was applied to identify the range of baseline ALC where Tα1 therapy could exert a maximum effect. The original trial is registered with ClinicalTrials.gov, NCT02473406.

Findings

Between March 18, 2017, and December 10, 2020, a total of 508 patients were randomised in the original trial, and 502 were involved in this analysis, with 248 in the Tα1 group and 254 in the placebo group. Across the three subgroups, there was a uniform trend toward more significant treatment effects in patients with higher baseline ALC. Within the subgroup of patients with baseline ALC≥0.8 × 10ˆ9/L (n = 290), the Tα1 therapy significantly reduced the risk of IPN (covariate adjusted risk difference, -0.12; 95% CI, -0.21,-0.02; p = 0.015). Patients with baseline ALC between 0.79 and 2.00 × 10ˆ9/L benefited most from the Tα1 therapy in reducing IPN (n = 263).

Interpretation

This post-hoc analysis found that the efficacy of immune-enhancing Tα1 therapy on the incidence of IPN may be associated with pretreatment lymphocyte count in patients with acute necrotising pancreatitis.

Funding

National Natural Science Foundation of China.

Novel evidence of Thymosin α1 immunomodulatory properties in SARS-CoV-2 infection: Effect on innate inflammatory response in a peripheral blood mononuclear cell-based in vitro model

The peculiar property of Thymosin alpha 1 (Tα1) to act as master regulator of immune homeostasis has been successfully defined in different physiological and pathological contexts ranging from cancer to infection. Interestingly, recent papers also demonstrated its mitigating effect on the "cytokine storm" as well as on the T-cell exhaustion/activation in SARS-CoV-2 infected individuals. Nevertheless, in spite of the increasing knowledge on Tα1-induced effects on T cell response confirming the distinctive features of this multifaceted peptide, little is known on its effects on innate immunity during SARS-CoV-2 infection. Here, we interrogated peripheral blood mononuclear cell (PBMC) cultures stimulated with SARS-CoV-2 to disclose Tα1 properties on the main cell players of early response to infection, namely monocytes and myeloid dendritic cells (mDC). Moving from ex vivo data showing an enhancement in the frequency of inflammatory monocytes and activated mDC in COVID-19 patients, a PBMC-based experimental setting reproduced in vitro a similar profile with an increased percentage of CD16⁺ inflammatory monocytes and mDC expressing CD86 and HLA-DR activation markers in response to SARS-CoV-2 stimulation. Interestingly, the treatment of SARS-CoV-2-stimulated PBMC with Tα1 dampened the inflammatory/activation status of both monocytes and mDC by reducing the release of pro-inflammatory mediators, including TNF-α, IL-6 and IL-8, while promoting the production of the anti-inflammatory cytokine IL-10. This study further clarifies the working hypothesis on Tα1 mitigating action on COVID-19 inflammatory condition. Moreover, these evidence shed light on inflammatory pathways and cell types involved in acute SARS-CoV-2 infection and likely targetable by newly immune-regulating therapeutic approaches.

Thymosin α-1 in cancer therapy: Immunoregulation and potential applications

Thymosin α-1 (Tα-1) is an immunomodulating polypeptide of 28 amino acids, which was the first peptide isolated from thymic tissue and has been widely used for the treatment of viral infections, immunodeficiencies, and especially malignancies. Tα-1 stimulates both innate and adaptive immune responses, and its regulation of innate immune cells and adaptive immune cells varies under different disease conditions. Pleiotropic regulation of immune cells by Tα-1 depends on activation of Toll-like receptors and its downstream signaling pathways in various immune microenvironments. For treatment of malignancies, the combination of Tα-1 and chemotherapy has a strong synergistic effect by enhancing the anti-tumor immune response. On the basis of the pleiotropic effect of Tα-1 on immune cells and the promising results of preclinical studies, Tα-1 may be a favorable immunomodulator to enhance the curative effect and decrease immune-related adverse events of immune checkpoint inhibitors to develop novel cancer therapies.

Thymosin alpha1 use in adult COVID-19 patients: A systematic review and meta-analysis on clinical outcomes

OBJECTIVE

Thymosin alpha1 (Ta1) is widely used to treat patients with coronavirus disease 2019 (COVID-19), however, its effect remains unclear. This systematic review and meta-analysis aimed to evaluate the effect of Ta1 as a COVID-19 therapy.

METHODS

PubMed, EMBASE, the Cochrane library, Web of Science, and the reference lists of relevant articles were searched to identify eligible studies. Assessment of heterogeneity was done using the I-squared (I²) test and random/fixed effect analysis was done to determine the risk ratio (RR). We polled the data related to mortality mainly by using Review Manager 5.4. Predefined subgroup analyses and sensitivity analyses were also performed.

RESULTS

A total of 9 studies were included, on a total of 5352 (Ta1 = 1152, control = 4200) patient outcomes. Meta-analysis results indicated that Ta1 therapy had no statistically significant effect on mortality [RR 1.03 (0.60, 1.75), p = 0.92, I² = 90 %]. Subgroup analyses demonstrated that the beneficial effect in mortality was associated with mean age＞60 years in the Tα1 group [RR 0.68 (0.58, 0.78), p < 0.0000.1, I² = 0 %], the proportion of female ≤ 40 % in the Tα1 group [RR 0.67 (0.58, 0.77), p < 0.0000.1, I² = 0 %], and severe/critical COVID-19 patients [RR 0.66 (0.57, 0.76), p < 0.0000.1, I² = 0 %]. Sensitivity analysis further demonstrated the results to be robust.

CONCLUSIONS

The results of this meta-analysis do not support the use of Ta1 in hospitalized adult COVID-19 patients.

Peptide ILE-GLU-TRP (Stemokin) Potential Adjuvant Stimulating a Balanced Immune Response

Vaccines are widely used worldwide to prevent and protect from various infections. A variety of modern approaches to developing prophylactic and therapeutic vaccines is growing. In almost all cases, adjuvants are necessary to obtain an effective immune response.This work investigated the possibility of using the pharmaceutical peptide drug Stemokin as an adjuvant stimulating a balanced Th1/Th2 response.A study was conducted to compare the activity of Stemokin versus the approved adjuvant Alhydrogel in a murine vaccination model with the approved VAXIGRIP® vaccine.The first proof-of-concept experimental study shows that the peptide Ile-Glu-Trp has the adjuvant vaccine properties and anti-HA IgG2a enhancing response, revealing a Th1- favoring balanced Th1/Th2 immunomodulation.

Immune enhancement in patients with predicted severe acute necrotising pancreatitis: a multicentre double-blind randomised controlled trial

PURPOSE

Infected pancreatic necrosis (IPN) is a highly morbid complication of acute necrotising pancreatitis (ANP). Since there is evidence of early-onset immunosuppression in acute pancreatitis, immune enhancement may be a therapeutic option. This trial aimed to evaluate whether early immune-enhancing Thymosin alpha 1 (Tα1) treatment reduces the incidence of IPN in patients with predicted severe ANP.

METHODS

We conducted a multicentre, double-blind, randomised, placebo-controlled trial involving ANP patients with an Acute Physiology and Chronic Health Evaluation II (APACHE II) score ≥ 8 and a computed tomography (CT) severity score ≥ 5 admitted within 7 days of the advent of symptoms. Enrolled patients were assigned to receive a subcutaneous injection of Tα1 1.6 mg every 12 h for the first 7 days and 1.6 mg once a day for the subsequent 7 days or matching placebos (normal saline). The primary outcome was the development of IPN during the index admission.

RESULTS

A total of 508 patients were randomised, of whom 254 were assigned to receive Tα1 and 254 placebo. The vast majority of the participants required admission to the intensive care unit (ICU) (479/508, 94.3%). During the index admission, 40/254(15.7%) patients in the Tα1 group developed IPN compared with 46/254 patients (18.1%) in the placebo group (difference -2.4% [95% CI - 7.4 to 5.1%]; p = 0.48). The results were similar across four predefined subgroups. There was no difference in other major complications, including new-onset organ failure (10.6% vs. 15%), bleeding (6.3% vs. 3.5%), and gastrointestinal fistula (2% vs. 2.4%).

CONCLUSION

The immune-enhancing Tα1 treatment of patients with predicted severe ANP did not reduce the incidence of IPN during the index admission.

Thymodepressin-Unforeseen Immunosuppressor

The paper summarizes the available information concerning the biological properties and biomedical applications of Thymodepressin. This synthetic peptide drug displays pronounced immunoinhibitory activity across a wide range of conditions in vitro and in vivo. The history of its unforeseen discovery is briefly reviewed, and the current as well as potential expansion areas of medicinal practice are outlined. Additional experimental evidence is obtained, demonstrating several potential advantages of Thymodepressin over another actively used immunosuppressor drug, cyclosporin A.

The Efficacy and Safety of Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitor Combined With Thymosin in Advanced Non-Small Cell Lung Cancer Patients Harboring Active Epidermal Growth Factor Receptor Mutations

Objective

To explore the efficacy and safety of EGFR-TKI combined with thymosin therapy in advanced non-small cell lung cancer (NSCLC) patients harboring active EGFR mutations.

Methods

Patients confirmed as advanced NSCLC with active EGFR mutations were recruited from August 2008 to July 2018 retrospectively. Patients treated with EGFR-TKI were classified as the EGFR-TKI group. And those received EGFR-TKI and thymosin therapy were designated as the EGFR-TKI plus thymosin group. The primary endpoint was progression-free survival (PFS). The secondary endpoints included overall survival (OS), tumor response and adverse effects.

Results

The median PFS was significantly longer in EGFR-TKI plus thymosin group than that in EGFR-TKI group (14.4 months vs. 9.2 months; HR=0.433, 95% CI 0.322 - 0.582, P<0.0001). The median OS was also prolonged in EGFR-TKI plus thymosin group than that in EGFR-TKI group (29.5 months vs. 19.8 months; HR=0.430, 95% CI 0.319 - 0.580, P<0.0001). The objective response rate in EGFR-TKI plus thymosin group and EGFR-TKI group were 60.0% versus 60.8% (P=0.918). The disease control rate was 96.9% in EGFR-TKI plus thymosin group and 97.7% in EGFR-TKI group (P=1.000). There were no significant differences in adverse effects between the two groups. The number of CD3⁺T cells in peripheral blood decreased significantly after treatment including both CD3⁺CD4⁺T and CD3⁺CD8⁺T subsets in EGFR-TKI group, but not in EGFR-TKI plus thymosin group.

Conclusions

Combination of EGFR-TKI and thymosin can significantly prolong the PFS and OS compared with EGFR-TKI monotherapy without more adverse events, which offers a new strategy in clinic.

Thymic Aging May Be Associated with COVID-19 Pathophysiology in the Elderly

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused the global pandemic of coronavirus disease 2019 (COVID-19) and particularly exhibits severe symptoms and mortality in elderly individuals. Mounting evidence shows that the characteristics of the age-related clinical severity of COVID-19 are attributed to insufficient antiviral immune function and excessive self-damaging immune reaction, involving T cell immunity and associated with pre-existing basal inflammation in the elderly. Age-related changes to T cell immunosenescence is characterized by not only restricted T cell receptor (TCR) repertoire diversity, accumulation of exhausted and/or senescent memory T cells, but also by increased self-reactive T cell- and innate immune cell-induced chronic inflammation, and accumulated and functionally enhanced polyclonal regulatory T (Treg) cells. Many of these changes can be traced back to age-related thymic involution/degeneration. How these changes contribute to differences in COVID-19 disease severity between young and aged patients is an urgent area of investigation. Therefore, we attempt to connect various clues in this field by reviewing and discussing recent research on the role of the thymus and T cells in COVID-19 immunity during aging (a synergistic effect of diminished responses to pathogens and enhanced responses to self) impacting age-related clinical severity of COVID-19. We also address potential combinational strategies to rejuvenate multiple aging-impacted immune system checkpoints by revival of aged thymic function, boosting peripheral T cell responses, and alleviating chronic, basal inflammation to improve the efficiency of anti-SARS-CoV-2 immunity and vaccination in the elderly.

Thymosin Alpha 1 Reduces the Mortality of Severe Coronavirus Disease 2019 by Restoration of Lymphocytopenia and Reversion of Exhausted T Cells

BACKGROUND

Thymosin alpha 1 (Tα1) had been used in the treatment of viral infections as an immune response modifier for many years. However, clinical benefits and the mechanism of Tα1 treatment for COVID-19 patients are still unclear.

METHODS

We retrospectively reviewed the clinical outcomes of 76 severe COVID-19 cases admitted to 2 hospitals in Wuhan, China, from December 2019 to March 2020. The thymus output in peripheral blood mononuclear cells from COVID-19 patients was measured by T-cell receptor excision circles (TRECs). The levels of T-cell exhaustion markers programmed death-1 (PD-1) and T-cell immunoglobulin and mucin domain protein 3 (Tim-3) on CD8+ T cells were detected by flow cytometry.

RESULTS

Compared with the untreated group, Tα1 treatment significantly reduced the mortality of severe COVID-19 patients (11.11% vs 30.00%, P = .044). Tα1 enhanced blood T-cell numbers in COVID-19 patients with severe lymphocytopenia. Under such conditions, Tα1 also successfully restored CD8+ and CD4+ T-cell numbers in elderly patients. Meanwhile, Tα1 reduced PD-1 and Tim-3 expression on CD8+ T cells from severe COVID-19 patients compared with untreated cases. It is of note that restoration of lymphocytopenia and acute exhaustion of T cells were roughly parallel to the rise of TRECs.

CONCLUSIONS

Tα1 treatment significantly reduced mortality of severe COVID-19 patients. COVID-19 patients with counts of CD8+ T cells or CD4+ T cells in circulation less than 400/μL or 650/μL, respectively, gained more benefits from Tα1. Tα1 reversed T-cell exhaustion and recovered immune reconstitution through promoting thymus output during severe acute respiratory syndrome-coronavirus 2 infection.

Potential Anti-SARS-CoV-2 Therapeutics That Target the Post-Entry Stages of the Viral Life Cycle: A Comprehensive Review

The coronavirus disease-2019 (COVID-19) pandemic continues to challenge health care systems around the world. Scientists and pharmaceutical companies have promptly responded by advancing potential therapeutics into clinical trials at an exponential rate. Initial encouraging results have been realized using remdesivir and dexamethasone. Yet, the research continues so as to identify better clinically relevant therapeutics that act either as prophylactics to prevent the infection or as treatments to limit the severity of COVID-19 and substantially decrease the mortality rate. Previously, we reviewed the potential therapeutics in clinical trials that block the early stage of the viral life cycle. In this review, we summarize potential anti-COVID-19 therapeutics that block/inhibit the post-entry stages of the viral life cycle. The review presents not only the chemical structures and mechanisms of the potential therapeutics under clinical investigation, i.e., listed in clinicaltrials.gov, but it also describes the relevant results of clinical trials. Their anti-inflammatory/immune-modulatory effects are also described. The reviewed therapeutics include small molecules, polypeptides, and monoclonal antibodies. At the molecular level, the therapeutics target viral proteins or processes that facilitate the post-entry stages of the viral infection. Frequent targets are the viral RNA-dependent RNA polymerase (RdRp) and the viral proteases such as papain-like protease (PLpro) and main protease (Mpro). Overall, we aim at presenting up-to-date details of anti-COVID-19 therapeutics so as to catalyze their potential effective use in fighting the pandemic.

Thymosin α1: burying secrets in the thymus

Thymosin α1 (Tα1), an epithelial cell (EC)-derived cytokine, has the strong ability to modulate signals delivered through innate immune receptors on dendritic cells (DCs), thus instructing the initiation of appropriate immune responses to T cells. In its ability to activate indoleamine 2,3-dioxygenase 1-dependent tolerogenic programs in DCs, Tα1 pivotally contributes to the maintenance of self-tolerance by regulating the function of regulatory T (Treg) cells. How Tα1 may contribute to the Treg cell ontogeny is not known. The transcriptional regulator autoimmune regulator (AIRE) is known to control central and peripheral tolerance. AIRE is highly expressed in thymic medullary ECs where it controls the ectopic expression of tissue restricted antigens for negative selection. The absence of AIRE-induced tissue-specific antigens in the thymus can lead to autoimmunity in the antigen-expressing target organ. Recently, AIRE protein has been detected in peripheral lymphoid organs, suggesting that peripheral AIRE may play a complementary role. We have addressed the possible relationship between AIRE and Tα1 and discovered an intricate crosstalk, whereby AIRE may promote prothymosin cleavage to Tα1, and Tα1 in turn transcriptionally regulates AIRE expression. Thus, similar to other members of thymic stromal poietins, Tα1 expressed within the thymus and peripheral tissues regulates the EC/DC crosstalk required for salutary immune homeostasis.

Current adjuvants and new perspectives in vaccine formulation

Given the important role of adjuvants in prophylactic vaccines, identification and development of new adjuvants with enhanced efficacy and safety is necessary. The use of adjuvants with immunopotentiating properties that can direct the immune responses to humoral or cell-mediated immunity and can induce T-cell responses has made it possible to design more protective vaccines. Although current regulations focus on traditional adjuvants, notably aluminum and calcium salts, advances have been made in regulatory considerations. The regulatory agencies for the evaluation of medicinal products are actively drafting guidance on requirements for the evaluation of new adjuvants. This article briefly summarizes the most widely studied adjuvants in vaccination, including those licensed for human vaccines and the regulatory aspects relevant to adjuvant quality at development stages.

Production of Nα-acetylated thymosin α1 in Escherichia coli

BACKGROUND

Thymosin α1 (Tα1), a 28-amino acid Nα-acetylated peptide, has a powerful general immunostimulating activity. Although biosynthesis is an attractive means of large-scale manufacture, to date, Tα1 can only be chemosynthesized because of two obstacles to its biosynthesis: the difficulties in expressing small peptides and obtaining Nα-acetylation. In this study, we describe a novel production process for Nα-acetylated Tα1 in Escherichia coli.

RESULTS

To obtain recombinant Nα-acetylated Tα1 efficiently, a fusion protein, Tα1-Intein, was constructed, in which Tα1 was fused to the N-terminus of the smallest mini-intein, Spl DnaX (136 amino acids long, from Spirulina platensis), and a His tag was added at the C-terminus. Because Tα1 was placed at the N-terminus of the Tα1-Intein fusion protein, Tα1 could be fully acetylated when the Tα1-Intein fusion protein was co-expressed with RimJ (a known prokaryotic Nα-acetyltransferase) in Escherichia coli. After purification by Ni-Sepharose affinity chromatography, the Tα1-Intein fusion protein was induced by the thiols β-mercaptoethanol or d,l-dithiothreitol, or by increasing the temperature, to release Tα1 through intein-mediated N-terminal cleavage. Under the optimal conditions, more than 90% of the Tα1-Intein fusion protein was thiolyzed, and 24.5 mg Tα1 was obtained from 1 L of culture media. The purity was 98% after a series of chromatographic purification steps. The molecular weight of recombinant Tα1 was determined to be 3107.44 Da by mass spectrometry, which was nearly identical to that of the synthetic version (3107.42 Da). The whole sequence of recombinant Tα1 was identified by tandem mass spectrometry and its N-terminal serine residue was shown to be acetylated.

CONCLUSIONS

The present data demonstrate that Nα-acetylated Tα1 can be efficiently produced in recombinant E. coli. This bioprocess could be used as an alternative to chemosynthesis for the production of Tα1. The described methodologies may also be helpful for the biosynthesis of similar peptides.

Thymosin alpha 1: biological activities, applications and genetic engineering production

Thymosin alpha 1 (Tα1), a 28-amino acid peptide, was first described and characterized from calf thymuses in 1977. This peptide can enhance T-cell, dendritic cell (DC) and antibody responses, modulate cytokines and chemokines production and block steroid-induced apoptosis of thymocytes. Due to its pleiotropic biological activities, Tα1 has gained increasing interest in recent years and has been used for the treatment of various diseases in clinic. Accordingly, there is an increasing need 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 methods 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.

RimJ is responsible for N(alpha)-acetylation of thymosin alpha1 in Escherichia coli

N(alpha)-Acetylation is one of the most common protein modifications in eukaryotes but a rare event in prokaryotes. Some endogenously N(alpha)-acetylated proteins in eukaryotes are frequently reported not to be acetylated or only very partially when expressed in recombinant Escherichia coli. Thymosin alpha1 (Talpha1), an N(alpha)-acetylated peptide of 28 amino acids, displays a powerful general immunostimulating activity. Here, we revealed that a fusion protein of thymosin alpha1 and L12 is partly N(alpha)-acetylated in E. coli. Through deletion of some N(alpha)-acetyltransferases by Red recombination, we found that, when rimJ is disrupted, the fusion protein is completely unacetylated. The relationship of rimJ and N(alpha)-acetylation of Talpha1 was further investigated by gene rescue and in vitro modification. Our results demonstrate that N(alpha)-acetylation of recombinant Talpha1-fused protein in E. coli is catalyzed by RimJ and that fully acetylated Talpha1 can be obtained by co-expressing with RimJ. This is the first description that an ectopic protein acetylation in bacterial expression systems is catalyzed by RimJ, a known prokaryotic N(alpha)-acetyltransferase.