Evaluation of Humoral Immunity Following COVID-19 in Pregnancy

Background

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), commonly known as Coronavirus Disease-19 (COVID-19), is a global pandemic with 7,410,000 confirmed cases and 418,000 deaths as of 13th June 2020. It is believed that SARS-CoV-2 shares 79.6% of its sequence identity with SARS-CoV and resembles some clinical outcomes like viral pneumonia. However, it causes milder symptoms in majority of people infected, and can be an asymptomatic infection in some individuals. Just in the 21st century, we have seen three major coronavirus (CoV) outbreaks: SARS-CoV, Middle East respiratory syndrome (MERS)-CoV, and the novel SARS-CoV-2, which have resulted in many deaths and have posed a real threat to public health. In fact, during SARS more pregnant women required intensive care and ventilation, and the number of deaths was higher when compared to non-pregnant adults. This is partly because in pregnancy, the risk of viral pneumonia is greater compared to the general population.

Understanding T and B cell mediated immunity in COVID-19 participants may hold the key to developing better vaccines and efficient treatment plans. To date there is only one study that has investigated circulatory T follicular helper cells (cTFH), which like there germinal centre counterparts are a specialised effector cluster of differentiation 4 (CD4) T cell that induces B cell activation, and differentiation into class-switched and antibody secreting long-lasting plasmablasts. This study observed an increase in cTFH during pregnancy. However, studies in older patients, which comprise another high risk group, have shown mixed results with cTFH showing lower levels of activation. This will impact on long term antibody production following infection or vaccination. We propose that circulatory cTFH, and B cells may not be as activated in both pregnant women and patients with severe to critical patients when compared with mild to moderate patients resulting in less or poorly functioning anti-SARS-CoV-2 antibodies. Therefore, we expect in infected pregnant individuals the development of long-term immunity may be worse when compared to non-pregnant people with similar disease severity, making them more susceptible to re-infection. Compared to influenza, which is another respiratory illness with significant morbidity in pregnancy and has a current vaccination program, we expect that the same measures of immunity will be less pronounced post COVID-19 infection. Furthermore, the development of long-term immunity will be less effective in patients with severe illness, who for the most part, comprise a particularly high-risk group including the elderly and patients with multiple comorbidities. It is vital that we expand our knowledge of long-lasting immunity in individuals who have recovered from COVID-19 to see how long these individuals are protected against re-infection and whether they develop long lasting immunity. Moreover, there is no current research establishing the parameters of seroprotective immunity. Previous research has suggested that SARS-CoV specific Immunoglobin G (IgG) declines significantly within 2 years with some reports showing a complete loss within 6 years in most SARS-CoV recovered patients. This may equate to a loss of long-term protection. The investigators of this study propose measuring SARS-CoV-2 specific IgG levels by doing memory B cell (Enzyme-Linked ImmunoSpot) ELISpots and comparing the data with cTFH and B cell flow cytometry panels. The research team will be able to profile the generation and persistence of protective antibodies produced by infected individuals who go on to recover. The findings from this study will generate hypotheses to be tested in larger studies of COVID-19 recovered pregnant patients, and also assist researchers working trying to understand the effectiveness of the vaccines in pregnancy once these become commercially available.

Research Question

In pregnant individuals who have recovered from COVID-19:

1. How long will their SARS-CoV-2 specific Immunoglobulin G (IgG) levels remain in peripheral blood, what is the rate of decline and how does this compare to non-pregnant individuals?
2. How did their T cell mediated immune function differ from non-pregnant patients during the infection?
3. How do their SARS-CoV-2 specific memory T cell differ when compared to severe to non-pregnant patients' post-recovery?
4. How does antibody production, and B and T cell function post COVID-19 infection in pregnancy compare with influenza infection and vaccination?

Hypothesis

The investigators hypothesise that pregnant patients with COVID-19 will develop a less robust and measurable B-cell response when compared to influenza infected/vaccinated women and non-pregnant individuals, and that their seroprotective antibody responses will decline by 12 months post infection.

Study Aims

1. Establish robust assays to measure SARS-CoV-2-specific IgG from individuals who have recovered from COVID-19 infection and track these levels over a 12-month period to measure any decline. In pregnancy, compare this to influenza antibodies produced after infection and vaccination.
2. Measure frequency of activated cTFH, and antigen-secreting cells (ASCs) at days 7-14 of symptom onset in pregnant patients with COVID-19 and compare with non-pregnant groups, and pregnant influenza infected and influenza vaccinated. In addition, compare between non-pregnant groups with mild to moderate symptoms when compared to severe to critical patients.
3. Measure frequency of activated memory B cells at day 28 in pregnant patients with COVID-19 and compare with non-pregnant groups, and pregnant influenza infected and influenza vaccinated. In addition, compare between non-pregnant groups with mild to moderate symptoms when compared to severe to critical patients.
4. Measure frequency of CD4 and cluster of differentiation 8 (CD8) T cells in pregnant patients with COVID-19 and compare with non-pregnant groups, and pregnant influenza infected and influenza vaccinated. In addition, compare between non-pregnant groups with mild to moderate symptoms when compared to severe to critical patients.
5. Quantify antigen-specific memory T cells and measure frequency of activated T cells in all patient groups.
6. Quantification of SARS-CoV-2 viral load from infected participants.

Study Design

This study will be a prospective observational project to investigate the potential decline of protective immunity in pregnancy after participants have recovered from SARS-CoV-2. The research team will compare these findings with non-pregnant patients who have had COVID-19 and developed mild to moderate symptoms or severe to critical participants. Patients who go on to join a SARS-CoV-2 vaccine trial will not be excluded but the vaccination date will be recorded, and their results interpreted accordingly. In order to compare COVID-19 infection with another respiratory infection and assess long term protective immunity with an intervention already in place in this patient group designed to provide seroprotective antibodies, the investigators will investigate influenza and influenza vaccine. Therefore, data from pregnant patients will also be compared with influenza infected pregnant women and those who have received the influenza vaccination.