Introduction
The outbreak of the recent respiratory syndrome COVID-19 caused by the novel
coronavirus SARS-CoV-2 has spread from China to many countries in the world. On 11
March 2020 the World Health Organization (WHO) made the assessment that COVID-19 can
be characterized as a pandemic [1]. Although
most affected patients suffer from mild to moderate symptoms, the total number of
fatal cases exceeds that of other coronavirus infections, severe acute respiratory
syndrome (SARS) and Middle East respiratory syndrome (MERS), [2]
[3]
[4].
Regardless of the fact that currently numerous therapeutic options are under review,
so far no effective therapy could be identified [5]
[6]
[7]. Among others, interferons are considered
as possible effective antiviral drugs against coronavirus infections.
Properties of interferons and corresponding treatment strategies
Interferons are (glyco-)proteins with antiviral activity. They are members of the
cytokine family. Since they are expressed rapidly during the process of a viral
infection they form an essential part of a very early and virus-unspecific host
defense mechanism against multiple viruses [8]. Some viruses including coronaviruses are weak interferon inducers
and hence hardly activate this natural defense mechanism of the body. An
indicator of the importance of this interferon evasion strategy is the finding
that in cell culture and animal experiments interferons can strongly inhibit the
replication of coronaviruses. There are still other defense mechanisms of the
body so that most patients with a coronavirus infection recover after illness
[9]
[10]
[11]
[12]. Thus, interferon therapy in
coronavirus infections could be considered as a substitution of a compound which
is not sufficiently produced by the body during these diseases. The clinical and
pharmacological/immunological implications of the said interferon
substitution in an acute coronavirus infection will be discussed below.
Beside their antiviral properties, interferons are characterized by
antiproliferative activities relative to numerous malignant and non-malignant
cells. Furthermore, they modulate cell differentiation and a variety of humoral
and cellular immune functions. [8]
[13]
[14]
[15]
[16]. The role interferons play in
immunity and autoimmunity is rather complex, not only protective but also
pathogenic effects are described or discussed, respectively [11].
Based on their protein structures and cell-surface receptors, interferons are
divided into type I interferons (several interferon alpha subtypes, interferon
beta, interferon epsilon, interferon kappa, interferon omega), type II
interferons (interferon gamma) and type III interferons (several interferon
lambda subtypes). For more than 35 years interferons have been produced in large
quantities for clinical application via human diploid cell cultures (native
interferons) and more frequently via non-human host cells such as E. coli and
Chinese hamster ovary (CHO) cells using recombinant DNA technology (recombinant
interferons). Various interferons are available as approved drugs [15]
[16]
[17]
[18]
[19]. Because interferons are to a large
extent species-specific or have “defined host-ranges” [20], respectively, the pharmacological
effects of human interferons can expediently and reliably be investigated only
in man, in non-human primate models and in human cell cultures.
During decades of clinical experience with various interferon preparations in
numerous diseases clinicians had to learn that very different dosing regimens
and routes of administration are required in order to exploit a specific
pharmacodynamic activity of a certain interferon preparation in the treatment of
a particular disease [14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
[26]. High doses of interferons must be
applied in order to create high serum levels which are probably essential for
treatment focused on antiviral or antiproliferative interferon activities. In
contrast, immunomodulation is often achieved with low doses whereby opposing
effects (activation or inhibition) can be observed depending on a variety of
conditions [13]
[14]
[27]
[28]. Interferon beta, due to its stronger
hydrophobicity, has a much higher tissue affinity compared to interferon alpha.
Intramuscular (IM) or subcutaneous (SC) injections of interferon beta result in
only low serum levels. Whenever high serum concentration of interferon beta is
targeted, this cytokine requires the intravenous (IV) route of administration.
High serum levels are, however, not required in order to exploit the
immunomodulating potential of interferon beta since corresponding effects can be
observed with IM or SC administration of even low doses [22]
[27]
[29]
[30]
[31]
[32]
[33].
In order to prolong the elimination half-life and thus to decrease the necessary
administration frequency, some companies have developed pegylated forms of their
respective interferon preparations. Such preparations are available for human
use since the early 2000s [18]
[34]
[35].
Whenever feasible and appropriate, a local/topical application of the
interferons should be considered since a relatively high local concentration of
interferon can be achieved with a relatively low but therapeutically effective
dose, and hence systemic adverse drug reactions can be reduced or completely
avoided [14]
[18]
[36].
The therapeutic areas where interferons are used cover acute and chronic viral
infections, malignancies and immune disorders [15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
[26]. Due to the variety of indications,
it is not surprising that a regimen successfully used in one disease can be
ineffective in another. There are approved therapeutic regimens for recombinant
interferon alfa preparations concerning chronic viral hepatitis B and C and some
malignant diseases. Recombinant interferon beta preparations are only approved
for the treatment of multiple sclerosis. For the experimental treatment of other
diseases including acute viral diseases, the use of other dose regimens of
interferon beta-1a is suggested [22].
Preclinical and clinical studies of interferons in coronavirus
infections
Interferons can inhibit the replication of coronaviruses in vitro and show
clinical effects in animal models [37]
[38]
[39]
[40]
[41]
[42]
[43]
[44]
[45]
[46]
[47]
[48]
[49]
[50]
[51]
[52]
[53]. In order to see if such promising
results could also be achieved in a clinical setting, clinical studies using
interferons, typically in combination with other antiviral drugs, were performed
to treat SARS and MERS [54]
[55]
[56]
[57]
[58]
[59]. In these studies, only a minor or
even no therapeutic benefit was observed, as outlined in review papers covering
not only the aforementioned clinical studies but also several case reports [5]
[60]
[61]
[62]
[63]
[64].
What could be the reason for the failure of interferons in SARS and MERS? In the
studies performed so far, dosage and administration routes were chosen as they
have been approved for interferons in the treatment of other diseases, namely
chronic viral hepatitis (recombinant interferon alfa) or multiple sclerosis
(recombinant interferon beta). Apparently, the investigators did not pay
sufficient attention to the acute character of a coronavirus induced
pneumonia demonstrating quite different pathological conditions compared to the
approved indications, and thus potentially requiring a different treatment
approach. To attain a direct antiviral effect with a systemic administration of
interferons, high daily doses leading to high serum levels maintained for
several days are required as shown, for example, in the treatment of herpes
zoster with native interferon alpha or beta [65]
[66]
[67]. With the regimens used in the above
mentioned studies as to SARS and MERS, however, only relatively low serum levels
of interferons could be achieved.
Which interferon preparation of the already approved ones should be used and how
should they be dosed and administered to achieve a therapeutic effect in acute
viral infections in general and in coronavirus caused pneumonia in particular?
In cell culture experiments, interferon beta is clearly superior to other
interferons as to inhibiting replication of coronaviruses [5]
[9]
[37]
[40]
[41]
[45]
[48]
[50]
[68]. This superiority of interferon beta
is also valid for other viruses such as herpes simplex [69]. Accordingly, interferon beta should be
the interferon of choice in the treatment of acute viral infections. Regarding
the dosage of this type of interferon in acute viral infections, data are
available for native interferon beta.
Native interferon beta in the treatment of acute viral diseases
In the early 1980s the German competent health authority approved a drug product
containing a native interferon beta produced by human fibroblasts (tradename:
Fiblaferon®) for treating acute life-threatening viral
diseases such as viral encephalitis and disseminated herpes zoster [16]
[67]. However, the documentation relative
to this product is fairly unknown to the international scientific community
because the vast majority of clinical data were published in books
and/or in German language. Since Fiblaferon® is not
marketed anymore, a recombinant interferon beta preparation would be the only
available alternative in order to assess if such preparation could also
demonstrate beneficial clinical effects in a scenario of an acute viral
infection such as coronavirus induced pneumonia. Before suggesting an
appropriate therapeutic regimen for a recombinant interferon beta, the data as
to the native interferon beta are shortly reported here. Additionally, some
unpublished data as to a recombinant CHO-derived interferon beta-1a given by the
IV route are provided.
The therapeutically effective regimen for the treatment of acute systemic viral
diseases with native interferon beta was developed by Heidemann et al. [70]
[71] in immune-compromised patients
suffering from herpes zoster. According to the “Heidemann
scheme” the native interferon beta is administered in a daily dose of
0.5 million IU per kg body weight (max. 25 million IU per day) as a continuous
24-hour IV infusion for 3–5 consecutive days. The dose for the last day
can be given in a ratio of 2:1 spread over two days. On the basis of this
treatment schedule, other acute viral diseases including virus encephalitis and
virus pneumonia were also successfully treated [16]
[67]
[72]
[73]. Due to severe side effects that were
frequently observed with this regimen, all patients had to be hospitalized under
intensive care conditions. All patients showed high fever and/or other
moderate to severe flu-like symptoms. Furthermore, rapid changes of laboratory
parameters, especially leukocytopenia, thrombocytopenia and increase of
transaminases, required daily laboratory monitoring, including determination of
the partial thromboplastin time. All side effects disappeared shortly after
termination of treatment. Careful attention had to be paid to fluid balance and
fluid substitution. For the infusion, the native interferon beta was dissolved
in a body weight dependent volume (up to 500 ml) of a physiological saline
solution plus human albumin.
Proposed dosage of recombinant interferon beta in acute viral
infections
In the late 1980s clinical pilot studies with a recombinant CHO derived
interferon beta-1a were performed in 15 adult male and female patients suffering
from viral hepatitis, viral encephalitis or herpes zoster (data not published).
The Heidemann scheme was applied and final daily doses of 50 to 150 µg
(declared as 10–30 million IU) - corresponding to 0.6–2.7
µg per kg individual body weight - were administered. Daily doses of
more than 1.3 µg interferon beta-1a per kg body weight could hardly be
given for 5 consecutive days due to high fever, leukopenia and/or
increase of transaminases. Therapy had to be discontinued prematurely in 2 out
of 4 patients who were treated with doses between 1.3 and 1.7 µg per kg
body weight, and in additional 2 out of 2 patients treated with higher dosage.
However, in all 9 patients treated with <1.3 µg per kg body
weight therapy could be performed as scheduled. Side effects were very similar
to those observed under high dose native interferon beta and also disappeared
shortly after termination of treatment.
According to these data, a daily dose of 1.2 µg per kg body weight (max.
90 µg per day) seems to be the maximum tolerated dose (MTD) of
interferon beta-1a given as a 24-hour continuous IV infusion for 3–5
consecutive days. Thus, relative to the IU the MTD for the recombinant
interferon beta-1a is apparently lower than the MTD for the native interferon
beta. In juvenile herpes simplex virus encephalitis, a dose of 1.0 µg
(declared as 0.2 million IU) interferon beta-1a per kg body weight (max. 60
µg per day) was used as a 24-hour continuous IV infusion and well
tolerated but showed no additional therapeutic effect to aciclovir which was
given as the basic antiviral treatment [74]. In viral encephalitis, higher dosage of interferon beta-1a than
in other acute viral diseases might be required due to the repairing activities
of interferon beta on the blood-brain barrier which is disturbed in viral
encephalitis [75]
[76]. Nevertheless, the aforementioned MTD
should be widely exploited not only in viral encephalitis but also in other
severe acute viral diseases in order to achieve a potential therapeutic
effect.
The data about interferon beta composed and analysed here are intended to
encourage clinicians to perform clinical studies using recombinant interferon
beta-1a in severe viral infections with another but probably more appropriate
regimen (≤ 90 µg daily given as a 24-hour continuous IV
administration for 3–5 consecutive days) than the approved ones in
multiple sclerosis (30 µg IM once weekly for Avonex®
or 44 µg SC three times a week for Rebif®,
respectively). With the suggested regimen, however, more severe and still other
adverse drug reactions can occur because of the high daily dose and the IV route
of administration.
It has to be emphasized that the proposed dose and regimen is only appropriate
for treating acute viral infections and only valid for the non-pegylated
recombinant interferon beta-1a but not for other approved recombinant interferon
beta preparations, i.e. pegylated interferon beta-1a or E. coli derived
interferon beta-1b preparations, where the highest tolerated daily dose - if
given as continuous 24-hour IV infusion for 3–5 days - has not yet been
determined. A detailed discussion of the comparability of the different
interferon beta preparations as well as of the determination of their biological
and specific activities is given elsewhere [22]
[77]
[78].
Feasibility of the proposed interferon beta-1a dosage in coronavirus
infections
Is the regimen proposed for interferon beta-1a in acute viral infections also
applicable for treating severe coronavirus infections?
Due to the expected side effects of the proposed regimen for interferon beta-1a
in coronavirus infections, only patients with a life-threatening course of their
disease will be suitable candidates for this kind of treatment. During severe
coronavirus infections, fever, lymphocytopenia and increase of transaminases are
often observed [2]
[3]
[9]
[79]. These symptoms may prevent high dose
IV administration of interferon beta-1a since they are also common side effects
of the proposed therapeutic regimen. Therefore, suitable patients have to be
determined at an early stage of their disease, and treatment has to be started
when the patients are still in a condition and willing to tolerate the side
effects mentioned above. It has still to be decided if the MuLBSTA score [80] or another score predicting the risk of
mortality in viral pneumonia may be useful to identify such patients.
Furthermore, severe cases of coronavirus infections are characterized by a
hyper-inflammatory lung pathology induced by an excessive accumulation of
inflammatory cells and high serum levels of pro-inflammatory cytokines
(“cytokine storm”) [9]
[12]
[79]
[81]
[82]
[83]
[84]. In a mouse model as to MERS mouse
interferon beta administered via the intranasal route showed opposing effects on
this inflammatory response depending on the time of administration. Early
treatment with interferon beta on 6 and 24 hours post infection (p.i.), i.e.
before peak virus replication occurred, protected mice from fatal outcome, while
late treatment on day 2 and 4 p.i., i.e. after peak virus replication, resulted
in fatal pneumonia through increased inflammatory cell infiltration in the lungs
and enhanced pro-inflammatory cytokine expression [52]. In another mouse model as to MERS, the
effects of early and late administered mouse interferon beta given by the SC
route were not equally distinct or not found at all [53]. Regarding SARS, experiments were
performed with cynomolgus macaques treated with pegylated human interferon
alfa-2b administered by the IM route in two different settings: In the
prophylactic group the animals received the drug on days −3, −1,
1, and 3, in the post exposure group on days 1 and 3 p.i. [39]. Interferon treatment reduced viral
replication and pulmonary damage in both groups, even though these effects were
more distinct in the prophylactic than in the post exposure group. Protective
effects, i.e. prevention of severe inflammation and reduction of mortality, were
also observed in other non-human primate models relative to MERS. In these
experiments the monkeys (rhesus macaques or common marmosets, respectively)
received human interferon alfa-2b or beta-1b, respectively, by the SC route. The
initial dose was administered 8 hours p.i. followed by further one to three
doses until 56 hours p.i., i.e. in these models all doses were given prior to
the peak of clinical signs and viral loads [47]
[49]. Taken together, the results obtained
in animal models also indicate that interferon treatment of coronavirus infected
patients should be started at an early stage of their disease in order to
achieve a potential protective effect because a (too) late initiation of
interferon treatment is possibly not only therapeutically ineffective but can
even lead to an exacerbation of the disease.
As to humans, there are no data available how high doses of interferon beta-1a
given by the IV route act on an exaggerated inflammation. In the treatment of
multiple sclerosis with interferon beta, it is assumed that an anti-inflammatory
effect of this cytokine is obtained by the approved IM or SC administration of
medium doses [85]. In contrast, during
local, i.e. intralesional, treatment of basal cell carcinoma with low doses of
interferon beta-1a, often an inflammation of the lesion is induced before
subsequent healing [86]. Similar
observations were made after intralesional treatment of melanoma metastases with
low doses of interferon beta-1a [32].
Accordingly, interferon beta can have anti-inflammatory and pro-inflammatory
effects depending on the disease (stage), dosage and administration route. A
dual mode of action in inflammation is also known for interferon gamma [13]
[14]
[28].
Relative to the infections with the novel coronavirus SARS-CoV-2, it will be
interesting to learn the results of interferon studies planned or just started
in China (ClinicalTrials.gov, search terms: “coronavirus” and
“interferon”). In some of these studies, the patients receive a
recombinant interferon alfa or beta preparation via oral spray or inhalation,
respectively, possibly leading to a much higher drug concentration in the
affected organ than with the “standard” SC or IM administration
of different interferons previously used in SARS and MERS (see above). In a
patient with COVID-19, however, the inhalation of interferon alfa-2b given
together with lopinavir and ritonavir tablets did not prevent his lethal outcome
[84].
Concluding remarks
The therapeutic role that interferons can play in the treatment of coronavirus
infections has still to be determined. Interferons are potent inhibitors of
virus replication as shown in several cell culture and animal experiments (see
above). Thus, interferons have been used and should also further be considered
in the treatment of coronavirus infections. However, due to their pleiotropic
effects and possible different actions depending to a large extent on the immune
status, the outcome of any clinical application of interferons is often hard to
predict [18]
[21].
The relevance of results elaborated in cell culture or animal models needs to be
scrutinized relative to various factors with impact on the specific clinical
scenario. For example, the window for a supposed successful therapeutic
administration of interferon after onset of symptoms but prior to the peak of
virus replication is very different in humans and experimentally infected mice
or monkeys. Furthermore, the peak for virus replication is generally unknown in
patients. Also the comparison of the results obtained in one animal model with
those found in another one is difficult due to differences in animal species,
delivery route, dose, start, frequency and duration of administration,
interferon subtype and/or active viral antagonism of innate immunity
[52]
[53]. In addition, there are still further
aspects to be considered if findings in the different animal models studying
antivirals for coronavirus infections are assessed [87].
A therapeutic regimen successfully used with an interferon in one human disease
might not be effective or tolerated in another one or another stage of the
disease. That could be the reason for the reported failure of interferon
treatment in SARS and MERS where low-dose and medium-dose regimens were applied
as approved for virus hepatitis and multiple sclerosis. In the past, high-dosed
native interferon beta given by the IV route was successfully used for the
treatment of various acute viral diseases. As to recombinant interferon beta-1a
the MTD for a high dose IV administration has already been determined. It
remains an open question if this dosage is therapeutically effective in severe
coronavirus infections and if it can safely be applied in patients with a poor
survival prognosis at an early stage of their disease.
