Prevalence of Allelic Variants and Clonality of IGHV1-69 Expressing B-Cells in Patients with Different Severity of COVID 19 Disease

Introduction: Since the first months of the COVID-19 pandemic, efforts have been made to understand the importance of broadly neutralising natural antibodies in determining the response to SARS-CoV-2. Previous studies have shown that allelic variants of the IGHV1-69 gene play a dominant role in protective natural antibody responses to several other viral pathogens, including influenza virus, hepatitis C virus, human immunodeficiency virus and, most notably, the SARS-CoV-2-related viruses SARS-CoV and MERS-CoV. These allelic variants are commonly known as 51p1-related and differ from the other IGHV1-69 alleles (known as hv1263-related) in the presence of a Phe54 residue in the CDR2 region. Importantly, crystallographic studies have shown that the Phe54 residue is critical for the binding of IGHV1-69 antibodies to the SARS-CoV and MERS-CoV spike proteins. In this study, we evaluated the prevalence of 51p1 and hv1263 alleles and the clonality of 51p1- and hv1263-expressing B cells in a large cohort of healthy individuals and COVID-19 patients and correlated the findings with the severity of the disease.

Мaterials and methods: A total of 419 samples were included in the study, of which 78 asymptomatic/mildly symptomatic individuals, 200 hospitalized patients with severe disease, 94 critically ill patients and 47 healthy donors. Peripheral blood was collected 8-20 days after the onset of symptoms and total cellular RNA was extracted from whole blood using an automated procedure. Аllelle-specific Ig-gene fingerprinting of IgM heavy chain transcripts was used to simultaneously analyse the clonality of the IgM+ B-cell population and the clonality of the 51p1- and hv1263-expressing B cell populations. The significance of the differences in the prevalence of clonal B-cell populations between healthy donors and patients and between patients with different severity of the disease was calculated with the Chi-Square test.

Results: Analysis of the clonality of the IgM+ B-cell population showed a polyclonal pattern in most of the investigated healthy individuals (33/47, 70%) but in only 20% of all SARS-CoV-2 infected individuals (75/372, p<0.001). A significant difference was also observed between mildly affected and severely/critically ill patients [31/78 (39.7%) vs. 44/294 (15%), respectively) (p<0.001)], but not between severely and critically ill patients [28/200 (14,%) vs. 16/94 (17,1%), (p=n.s.)]. No 51p1 transcripts were detected in 74/372 (19.9%) of SARS-CoV-2 infected individuals and in 14/47 (29,8%) of the control group (p>0,01), while hv1263 transcripts were not detected in 155/289 (53,6%) and in 27/47 (68,6%) tasted patients and controls, respectively (p>0,05). We did not find a statistically significant difference in the prevalence of 51p1 and hv1263 alleles between patients with different disease severity. However, a significantly higher number of patients displayed clonal expansions of 51p1- or hv1263-expressing B cells (219/372(58.9%) and 118/244 (48,4%), respectively in comparison to healthy donors [5/47(10.6%) and 7/47(14.9%), respectively]. There was no statistically significant difference between mildly affected and severely/critically ill patients in the clonallity status of 51p1- 38/61 (62,3%) and 182/237 (76,7%) respectively or between hv1263- expressing B cells in the same two groups of patients [20/25 (80%) and 98/109 (89,9%), p>0.05].

Conclusions: Our results show that SARS-CoV-2 infection stimulates clonal expansions of IGHV1-69 -expressing B-cells, but this is independent of the severity of the disease. In addition, no difference in the prevalence of IGHV1-69 alleles was observed between patients at different stages of the disease, indicating that natural neutralizing antibodies encoded by this gene are not an important determinant of COVID-19 severity and progression.