The modulation of thymosin alpha 1 in the maturation, differentiation and function of murine bone marrow-derived dendritic cells in the absence or presence of tumor necrosis factor-alpha

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.

Effect of thymosin α₁ on the phenotypic and functional maturation of dendritic cells from children with acute lymphoblastic leukemia

To determine the effect of thymosin α1 (Tα1) on the phenotypic and functional maturation of HL‑60 cells, freeze‑thaw antigen‑loaded dendritic cells (DCs) were derived from peripheral blood mononuclear cells (PBMCs) of children with acute lymphoblastic leukemia (ALL). The DCs were generated from the PBMC samples that were collected from the PB of 10 consecutive ALL children. On day 3 of culturing, the cells in the antigen + no Tα1 (AN) and antigen + Tα1 (AT) groups were incubated with 100 µl lysates obtained from freeze‑thaw cycling. After 5 days of incubation, the AT group was administered with 100 ng/ml Tα1. On day 8, the DCs were stained with fluorescein isothiocyanate‑conjugated cluster of differentiation (CD)1a, CD83 and HLA‑DR antibodies and analyzed by flow cytometry. In addition, the killing activity of cytotoxic T lymphocytes (CTLs) from the different groups on wild‑type leukemia cells was measured. The DCs in the AT group exhibited more apparent, characteristic dendritic morphologies than the control and AN group DCs. Furthermore, the lowest expression level of CD1a, and the highest expression of CD83 and HLA‑DR were observed in the AT group when compared with the AN and control groups (P<0.05). The lactate dehydrogenase release assay demonstrated that the killing rate of CTL in the AT group was significantly higher than that in the control and AN groups (P<0.01). Thus, Tα1 may markedly promote the phenotypic and functional maturation of DCs, and may serve as a suitable immunomodulator of DC‑based immunotherapy for treatment of hematological malignancies.

Dual effect of Thymosin α 1 on human monocyte-derived dendritic cell in vitro stimulated with viral and bacterial toll-like receptor agonists

OBJECTIVES

Thymosin α 1 (Tα1) recently gained interest as immune adjuvant for vaccines because of its ability to modulate the T-cell/dendritic cell (DC) axis and to improve antibody production. The objective of this study was to determine whether Tα1 would address in vitro the response of human primary monocyte-derived DC, crucial regulators of vaccine-induced immunity, upon exposure to different toll-like receptor (TLR) agonists or infection with viruses or bacteria.

METHODS

DC maturation and production of pro-inflammatory cytokines were analyzed.

RESULTS

Our data revealed a dual effect of Tα1 on DC biology upon viral or bacterial stimulation. Interestingly, Tα1 enhanced human leukocyte antigen (HLA)-I and II surface expression and secretion of IL-6, TNF-α and IL-8 when DCs were treated with viral TLR3 and TLR7/8 agonists. Similarly, in pandemic H1N1 influenza A-infected DCs, Tα1 raised the expression of maturation markers and type I and III Interferon (IFN). In contrast, following bacterial TLR2 and 4 stimulation, as well as upon Bacillus Calmette-Guerin infection, the presence of Tα1 in DC cultures drastically lowered the analyzed cellular parameters.

CONCLUSION

The knowledge that Tα1 pleiotropic effect might ameliorate anti-viral immune responses and, at the same time, dampen inflammation caused by bacterial infections could lay the groundwork for a more appropriate therapeutic application of this molecule.

Enhancement of cytotoxic T lymphocyte activity by dendritic cells loaded with Tat-protein transduction domain-fused hepatitis B virus core antigen

The protein transduction domain (PTD) of human immunodeficiency virus-1-Tat protein has a unique potency to penetrate the cellular membranes. To synthesize the sequence of Tat-PTD47-57 and hepatitis B virus core antigen (HBcAg), we spliced these sequences and linked a fusion gene into the pMAL-c2x vector. The fusion proteins were purified by affinity chromatography and pulsed with bone marrow-derived dendritic cells (DCs), and the transduction of recombinant protein was detected by immunofluorescence antibody assay. Results showed that recombinant PTD-HBcAg could penetrate into DC cytoplasm while recombinant HBcAg was detected on the surface of cells. The percentage of DC surface molecules, such as CD80, CD86 and major histocompatibility complex II, and production of cytokine (IL-12p70) induced by recombinant PTD-HBcAg were significantly higher than those induced by recombinant HBcAg or tumor necrosis factor-alpha. DCs treated with PTD-HBcAg induced T cells to differentiate into specific cytotoxic T lymphocytes (CTLs) and enhanced the CTL killing response. In conclusion, the expressed and purified PTD-HBcAg fusion protein could penetrate into cells through the plasma membrane, promote DC maturation, and enhance T cells response to generate HBcAg-specific CTLs efficiently.

Expression and hydroxylamine cleavage of thymosin alpha 1 concatemer

Human thymosin alpha 1 (Tα1) is an important peptide in the development and senescence of immunological competence in human, and many studies have reported the expression of this peptide. In this study, we designed and synthesized the Tα1 gene according to the E. coli codon usage preference and constructed a 6×Tα1 concatemer. The latter was inserted into an E. coli expression vector pET-22b (+), and transformed into E. coli BL21 (DE3). After induction with IPTG, the concatemer protein was successfully expressed in E. coli then cleaved by hydroxylamine to release the Tα1 monomer. Gly-SDS-PAGE and mass spectrometry confirmed that the recombinant protein was cleaved as intended. The bioactivity of the Tα1 monomer was analyzed by lymphocyte proliferation and by mitochondrial activity in two different tumor cell lines. This study provides a description of the preparation of a bioactive Tα1, which may prove useful in future biomedical research.

Liposomal plasmid DNA encoding human thymosin alpha and interferon omega potently inhibits liver tumor growth in ICR mice

AIM

To evaluate the potential therapeutic effect of liposomal gene delivery, genes encoding for human thymosin alpha1 (Talpha1) and interferon omega1 were injected via the tail vein into mice bearing a Hep-A-22 liver tumor.

METHODS

The cDNA of human Talpha1 and interferon omega1 were obtained by synthesis or reverse transcription-polymerase chain reaction (RT-PCR), respectively. Eukaryotic expressing vectors pIRES2, encoding Talpha1 and/or interferon omega1, were constructed and injected with liposome via the tail vein into ICR mice bearing a Hep-A-22 tumor. The potency of tumor inhibition was evaluated when three treated groups were compared with the group receiving the empty vector. Apoptosis of tumor cells was investigated by analyzing DNA fragmentation.

RESULTS

Only the group treated with dual-gene plasmid reached an eligible level of tumor inhibition (43%). The difference in tumor weight was statistically significant between the Talpha1 gene or the interferon omega1 gene treated groups and the control (P<0.05), and highly significant between the dual-gene treated group and the control (P<0.01). DNA ladder was observed in the tumor cells from the purpose gene treated groups but not from the control.

CONCLUSION

The dual-gene plasmid-liposome complex showed more potent inhibition than the single gene constructs on the growth of Hep-A-22 tumor cells in mice, which may be attributed to indirect and additive induction of apoptosis in tumor cells by increased expression of Talpha1 and interferon omega1.

Induction of Tc1 response and enhanced cytotoxic T lymphocyte activity in mice by dendritic cells transduced with adenovirus expressing HBsAg

We evaluated the potential of dendritic cells (DCs) engineered to express antigen of hepatitis B virus (HBV) in priming Th/Tc and HBV-specific CTL responses in mice. Recombinant adenovirus expressing hepatitis B surface antigen (HBsAg) (Ad-S) was constructed, and bone marrow-derived DCs were transduced with Ad-S or pulsed with HBsAg protein. Mice were injected with either Ad-S-transduced DCs or HBsAg-pulsed DCs or plasmid DNA encoding HBsAg twice at 3-week intervals. We showed that adenovirus infection had no further effect on the phenotype, the ability to induce IFN-gamma-producing Th1/Tc1 response or the T cell stimulatory capacity of already mature DCs in vitro. We also showed that immunization with Ad-S-transduced DCs effectively induced Tc1 cells and HBsAg-specific CTLs in vivo and down-regulated the circulating HBsAg and HBV DNA in HBV transgenic mice. Furthermore, these efficacies were stronger than that of HBsAg-pulsed DCs and plasmid DNA. Thus, DCs transduced with recombinant adenovirus may be a promising candidate for an effective CTL-based therapeutic vaccine against HBV.