Deficiency of Tfh Cells and Germinal Center in Deceased COVID-19 Patients

Summary:The COVID-19 pandemic caused by SARS-CoV2 is characterized by a remarkable variation in clinical severity ranging from a mild illness to a fatal multi-organ disease.Understanding the dysregulated human immune responses in the fatal subjects is critical for management of COVID-19 patients and the pandemic.In this study,we examined the immune cell compositions in the lung tissues and hilar lymph nodes using immunohistochemistry on 6 deceased COVID-19 patients and 4 focal organizing pneumonia(FOP)patients who underwent lung surgery and served as controls.We found a dominant presence of macrophages and a general deficiency of T cells and B cells in the lung tissues from deceased COVID-19 patients.In contrast to the FOP patients,Tfh cells and germinal center formation were largely absent in the draining hilar lymph nodes in the deceased COVID-19 patients.This was correlated with reduced IgM and IgG levels compared to convalescent COVID-19 patients.In summary,our data highlight a defect of germinal center structure in deceased COVID-19 patients leading to an impaired humoral immunity.Understanding the mechanisms of this deficiency will be one of the key points for the management of this epidemic.

Protective Efficacy of Inactivated Vaccine against SARS-CoV-2 Infection in Mice and Non-Human Primates

The ongoing coronavirus disease 2019(COVID-19)pandemic caused more than 96 million infections and over 2 million deaths worldwide so far.However,there is no approved vaccine available for severe acute respiratory syndrome coronavirus 2(SARS-CoV-2),the disease causative agent.Vaccine is the most effective approach to eradicate a pathogen.The tests of safety and efficacy in animals are pivotal for developing a vaccine and before the vaccine is applied to human populations.Here we evaluated the safety,immunogenicity,and efficacy of an inactivated vaccine based on the whole viral particles in human ACE2 transgenic mouse and in non-human primates.Our data showed that the inactivated vaccine successfully induced SARS-CoV-2-specific neutralizing antibodies in mice and non-human primates,and subsequently provided partial(in low dose)or full(in high dose)protection of challenge in the tested animals.In addition,passive serum transferred from vaccine-immunized mice could also provide full protection from SARS-CoV-2 infection in mice.These results warranted positive outcomes in future clinical trials in humans.