COVID-19 can indirectly impacts cervical dysplasia due to a preoccupied and exhausted immune system.
Consequently, immune pressure on cervical tissue under SARS-CoV-2-infection is reduced because the main focus of immune defense is elsewhere. This enables rapid progression of cervical dysplasia.
The study findings were published in the peer reviewed Journal ofReproductive Immunology.
We herein presented a case of rapid progression from HPV-induced CIN 2 to microinvasive carcinoma within three months under COVID-19 in a 44-year-old woman.
Despite no signs of direct virus infection, we could show a dysregulation in immune factors and unusual courses of known markers of disease progression compared to uninfected controls hinting at signs of indirect effects of the infection on the immune system favoring disease progression.
Direct effects of COVID-19 in cervical tissue
The cervical specimen of the herein-reported case showed no evidence of direct SARS-CoV-2 infection: No conspicuous architectural disturbance of small vessels nor evidence of virus-specific RNA fragments or detectable virus protein were found. These findings are in line with previous reports of Ondič and colleagues reporting only one patient out of 23 with weak positivity in qRT-PCR (Ondič et al., 2021).
In contrast to said study that focused on asymptomatic patients, the patient in the present study showed a clinically manifest infection of SARS-CoV-2 with supposedly higher levels of virus RNA to be expected (Fajnzylber et al., 2020). Still, we did not find any signs of direct virus infection of the available cervical tissue questioning a direct infectibility of the cervix and underlining indirect effects of the viral infection on disease progression.
Another aspect speaking against the hypothesis of direct infection of cervical cells with SARS-CoV-2 is the fact that the required host-receptor angiotensin-converting enzyme 2 (ACE2) for virus entry is hardly expressed by cervical epithelial cells no protein expression detected, RNA expression 0.6 nTPM (Thul et al., 2017), Human Protein Atlas) and is thus, in contrast to the respiratory and gastrointestinal tract as well as the kidney, not considered as a high-risk tissue for SARS-CoV-2 infection(Zou et al., 2020).
Given, that infection of cervical epithelial cells with SARS-CoV-2 is unlikely, infection via endothelial cells or migrated macrophages, both populations known to be readily infected by SARS-CoV-2 (Junqueira et al., 2021, Varga et al., 2020) cannot be ruled out. Studies on a larger scale, such as the one announced by Vavoulidis et al. (Vavoulidis et al., 2020), remain to be seen.
Indirect effects of COVID-19 on cervical tissue
We found several indications that SARS-CoV-2 infection has effects on the immune system.
Apolipoprotein B mRNA editing enzyme catalytic polypeptide 3 (APOBEC3) proteins serve as antiviral defence against RNA virus infections such as HPV (Sawyer et al., 2004). Therefore, the proteins APOBEC3A and APOBEC3B are expected to be upregulated in HPV-positive patients as the disease progresses.
This is observable in our control patients with progressing CIN dysplasia without SARS-CoV-2 infection (Fig. S1 and S2) despite minor individual differences, while the index patient showed a decreasedexpression of APOBEC3A with progression of dysplasia. The absence of high expression of a virus defense mechanism despite apparent virus infection of the cervix supports our hypothesis of an altered immune response to cervical infection with HPV during clinically manifest COVID-19 disease.
Several studies have investigated the expression of PD-L1 in cervical cancer. In 34–96% of peritumoral dendritic cells of cervical cancer tissues, PD-L1 expression was detected (Enwere et al., 2017, Yang et al., 2013), while regular cervical tissue displayed a low-level expression of PD-L1 of 6,82% in dendritic cells (Chen et al., 2016). During high immune pressure, as seen in cervical neoplasms (Piersma, 2011), increasing expression of PD-L1 is expected in order to evade the immune system.
This effect is observable in the control specimens with increasing PD-L1 levels, whereas the herein-reported case showed a stable up to a slightly increased expression of PD-L1 during the course of the disease. These findings suggest lowered immune pressure as a potential sign of an exhausted immune system due to concomitant higher immune pressure in the epicentres of the SARS-CoV-2 infection.
VISTA (V-domain immunoglobulin suppressor of T cell activation) is an immune checkpoint inhibitor involved in the regulation of T cell activity and expressed on T cells and other myeloid cells (mainly monocytes, macrophages, and neutrophils (Lines et al., 2014). VISTA has been detected in both cervical squamous cell carcinoma and clear cell carcinoma of the cervix (Zong et al., 2020).
The structural similarity to PD-L1 leads to the assumption that there is likewise an increased expression in the case of a malignant event. In line with our findings on PD-L1 and our hypothesis of lower immune pressure in the cervix during COVID-19, we detected a reduced expression of VISTA in the index patient.
p53 (tumour suppressor protein 53) is a transcription factor. It is often referred to as the “guardian of the genome”. After DNA damage, it regulates the expression of genes involved in cell cycle control, induction of apoptosis, and DNA repair (Bessette et al., 1992). P53 is inhibited by the HPV oncogene E6 (Garima, 2016).
Therefore, with increasing HPV oncogene E6, p53 expression is usually more and more inhibited, leading to progressing dysplasia. As expected, p53 was decreased in the presented case suggesting that the general carcinogenesis pathway of HPV-associated cervix carcinoma proceeds in the same way as in comparative studies without concomitant symptomatic COVID-19.
Another aspect of COVID-19 effects discussed is the change in DNA methylation. Several studies showed that COVID-19 can lead to hyper- but especially hypomethylation of promotors of several genes (Muhmammad, 2021; Konigsberg, 2021; Balnis et al., 2021) by DNA-methyltransferases (DNMTs).
Muhammad and colleagues could show that DNMT1, 3a, and 3b are significantly decreased in SARS-CoV-2 transfected cells. Interestingly, HPV also changes DNA methylation substantially leading to methylation of tumor suppressor genes during the development of dysplasia (Zhang, 2011; Au Yeung et al., 2010; Hu, 2019).
Therefore, we wanted to test if COVID-19 with expected contrary methylation effects compared to HPV can change the expression of DNMT1 and 3a in the cervix tissue. In cervix carcinoma, DNMT1 and 3a are slightly but not significantly decreased. Nevertheless, the expected increase of DNMT3a expression, which is observable in both control patients, cannot be seen in the index patient, giving rise to the hypothesis that SARS-CoV-2 infection has a global impact on DNA methylation and might reduce DNMT expression in the cervix.
However, our samples were taken three months after SARS-CoV-2 infection and showed no signs of direct virus infection, limiting the data interpretation. Further investigations in larger cohorts during and shortly after COVID-19 are needed to evaluate this aspect.
Blood tests three months after COVID-19 showed a substantial reduction of lymphocytes (14%, abs. 0.79×109/L; norm:22–49%, 1.05–2.87×109/L), eosinophils (0%, norm: 1–5%), T-cells (596/μl, norm: 700–2100/μl), NK-cells (57μl, norm: 90–600μl), and thrombocytes (137×109/L; norm: 171–388×109/L); a frequently described residual after COVID-19 (Bermejo-Martin et al., 2020, Diao et al., 2020, Ruan et al., 2020; Zong et al., 2021) and a sign of a high turnover of immune cells. A low number of remaining immune cells can fuel the progression of malignant events (Castelino et al., 1997), especially in immune-sensitive tumors, supporting our thesis of an exhausted immune system due to COVID-19 leading to disease progression.
On a further note, Demirbaş and colleagues report a case of HPV-induced mucocutaneous verrucae vulgares, which regressed spontaneously within one month after symptomatic SARS-CoV-2 infection suggesting a COVID-19 induced excessive inflammatory response to the herpes virus infection with a consecutive paradoxical immune response (Demirbaş et al., 2021). On the contrary, in the case presented, symptomatic COVID-19 lead to a disease progression (in the malignant counterpart) of HPV-induced tumors. We therefore, consider a paradoxical immune reaction due to COVID-19, but this reaction seems not be consistent or specific to COVID-19.
Nevertheless, we do not assume a general positive effect of COVID-19 on HPV-infected tissue. Contrarily, an immune activation could have been induced by a wide variety of triggers. An immune activation due to infection certainly depends on the severity of COVID-19 and the immune system’s capacities.
A rather mild infection could activate the immune system but does not demand it in excess, thus avoiding exhaustion of the immune system potentially resulting in a favorable role of COVID-19 on HPV-induced tumors.
On the other hand, a more severe cause of disease might have an adverse effect on (herpes-)virus- or immunological-induced dysplasia because the immune system is quickly utilized and exhausted.
Despite the detailed analyses performed, our hypothesis cannot be proven based on data from one index patient. Rather, this study is intended to be a stimulus for scientific discourse on the potential impact of COVID-19 on cervical dysplasia and to raise awareness among the scientific community to identify similar courses of disease and recruit them into larger studies.
Further, as at the time of infection in 2020 no SARS-CoV-2 vaccine had been developed, no conclusions can be drawn about the potential impact of SARS-CoV-2 vaccination on immunologic aspects of cervical dysplasia.
In summary, our findings endorse the hypothesis that COVID-19 negatively impacts cervical dysplasia due to lower immune pressure on cervical dysplasia by means of an altered gene expression pattern and an exhausted and depleted immune system without direct SARS-CoV-2 infection of the cervix.
These findings are interesting in clinical practice as (I) patients with early cervical dysplasia should be assessed not only for known diseases or treatments leading to immunosuppression (e.g., COVID or immunosuppressive therapy for CED) but also for immunological diseases such as COVID-19 and (II) if present shorter control intervals should be considered.
Even though the patient showed a moderate symptomatic infection, there was no evidence of direct infection of cervical cells by SARS-CoV-2. Instead, the results suggest that COVID-19 indirectly impacts cervical dysplasia due to a preoccupied and exhausted immune system favouring disease progression.
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