There are no effective antiviral therapies for coronavirus disease 2019 (COVID-19) at present. Although most patients with COVID-19 have a mild or moderate course of disease, up to 5%-10% of patients may have a serious and potentially life-threatening condition, indicating an urgent need for effective therapeutic drugs. The therapeutic effect of thymosin on COVID-19 has not been previously studied. In this paper, for the first time we report a case of thymosin treatment of COVID-19.

A 51-year-old man with imported COVID-19 was admitted with definite symptoms of chest tightness, chest pain, and fatigue. The polymerase chain reaction results for severe acute respiratory syndrome coronavirus 2 were negative. The antibody test was positive, confirming the diagnosis of COVID-19. As many orally administered drugs were not well tolerated due to gastrointestinal symptoms, an emergency use of thymosin, a polypeptide consisting of 28 amino acids, was administered by injection. Finally, after the implementation of the treatment program, symptoms and lung imaging improved significantly.

In this case report, it is confirmed that thymosin may help alleviate the severity of COVID-19 symptoms.

Since the outbreak in China in December 2019, coronavirus disease 2019 (COVID-19) has spread worldwide[1]. The numbers of infections and deaths have increased significantly[2]. Although there are many reports on the treatment of COVID-19, it is clear that currently no specific drugs are available to treat COVID-19 infection[3]. Thus, new treatment strategies for COVID-19 are urgently needed to be developed. Research confirms that COVID-19 is a human-to-human transmission caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)[4]. Similar to other virally infectious diseases, the immune function plays a decisive role in the consequences of viral infection. The prognosis of the elderly and immunocompromised patients is therefore often poor[5]. Thymosin, a polypeptide consisting of 28 amino acids, can effectively regulate the body’s immunity by inducing the differentiation and maturation of T cells and enhancing the production of cytokines and B cell antibody responses, resulting in enhanced immunity in patients[6]. At the time of this writing, no thymosin-like treatment of COVID-19 has been reported. Herein, we report a clinical case of COVID-19, and introduce the effect of thymosin on the symptoms, imaging, and prognosis of a COVID-19 patient. It is hoped that this report can enrich our understanding of the current treatments for COVID-19 and explore the therapeutic potential of thymosin for patients with COVID-19.

The final diagnosis was COVID-19.

The patient was then sent to the air isolation ward for clinical observation and immediately given an oxygen therapy. The patient was also treated with arbidol and lopinavir-ritonavir, but due to obvious nausea, vomiting, and diarrhea, the drug treatments were halted. On April 28, thymosin was subcutaneously injected twice a week, at 1.6 mg per injection.

At the follow-up one month after discharge, the patient showed no discomfort, and the chest CT lesions were completely absorbed.

In this case, although the RT-PCR results were negative for SARS-CoV-2, the specific IgM and IgG antibodies for SARS-CoV-2 were all positive, indicating a clear diagnosis of COVID-19[7]. The patient was initially treated with arbidol and lopinavir-ritonavir, but because of severe nausea, vomiting, and diarrhea, the treatment was switched to thymosin injection, which was the only medicine. To date, the pathogenesis of COVID-19 is not clearly understood and there are no effective drug treatments available for the disease. Although various therapeutic drugs have been reported, their biological effects are non-specific. Thymosin, as an immune enhancer, has a therapeutic potential for the treatment of infections and immunocompromised diseases such as cancer[6,8,9]. Thymosin is a hormone with 28 amino acids naturally secreted by the thymus. It has a variety of immunomodulatory activities. It can activate Toll-like receptors in dendritic cells and other immune cells, thus enhancing the function of T-helper 1 cells, natural killer cell activity, and antibody response to T-cell-dependent antigen[10,11]. Thymosin has been used in China for the treatment of viral hepatitis for more than two decades[12]. The reason may be that thymosin can promote T lymphocyte responses and function involved in the host antiviral defenses. We report here an effective case of thymosin injection for the treatment of COVID-19 when other available antiviral drugs could not be tolerated. However, further studies are still needed to explain the exact efficacy and mechanism of thymosin on COVID-19. We summarize the patient's course of therapy schedule (Figure 2). The symptoms of chest tightness, chest pain, and fatigue gradually improved under the action of thymosin alone. Thymosin therapy may also increase the survival rate of sepsis and reduce the bacterial load in a sepsis model as reported by King and Tuthill[13]. Although there are no large-scale studies, considering the encouraging result and the proven safety for human use, we believe that thymosin may be a feasible therapeutic drug against COVID-19 and warrants further investigation. Clinical trials can verify the role of thymosin in alleviating the symptoms of COVID-19 and shortening the course of treatment in a large cohort.

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Figure 2 Symptoms and treatments of the patient outlined accordingly to days post symptom onset since April 27, 2020.

Relieving symptoms, safeness, and effectiveness make thymosin a potentially ideal choice for the treatment of COVID-19. Although we had only one case, as described here, the significant effect in alleviating symptoms of COVID-19 demonstrates the potential therapeutic effect of this naturally derived compound.