Posts Tagged ‘cellular immunity’

Antibody-dependent enhancement in coronaviruses

11 April, 2020

This is a condensation / concatenation of a series of 13 tweets put up recently by someone who tweets as “The Immunologist” with the handle @eclecticbiotech. I was impressed enough by it that I thought it deserved to be all in one piece – and he agreed. He also declined any more accreditation, saying only “No credit necessary. This thread is entirely due to the important work carried out by fellow scientists”.


A thread on antibody-dependent enhancement (ADE) in coronaviruses from The Immunologist.

While developing vaccines, treating patients with convalescent plasma, and considering immunity passports, we must first understand the complex role of antibodies in SARS, MERS and COVID19.

Rabbits infected with MERS develop antibody responses but are not protected upon rechallenge and worsened pulmonary pathology observed. Passive transfer of infected rabbit serum to naïve rabbits not protective and enhances lung inflammation.

Analysis of 9 healthcare workers infected with MERS found most severe cases had highest anti-spike antibody titres. Three asymptomatic patients and one patient with mild disease had no detectable antibody response on the basis of ELISA and IFA.

Macaques vaccinated with MVA encoding full-length SARS-COV spike protein have worsened lung pathology upon rechallenge. Transferring purified anti-spike IgG into naïve macaques results in all recipients developing acute diffuse alveolar damage.

SARS-COV ADE is strongly mediated by anti-spike antibodies rather than anti-nucleocapsid antibodies. Diluted sera containing anti-spike IgG can increase in vitro infectivity.

Serum containing anti-spike antibodies enables spike-pseudotyped lentiviral particles to infect human macrophages (which do not express ACE2). Could this similarly allow SARSCoV2 to enter cell types outside the natural tropism?

Antibodies targeting the receptor-binding domain (RBD) of the spike protein can cross-neutralize both human and palm civet SARS coronaviruses. Could cross-neutralizing antibodies from previous common cold coronaviruses provide ADE to SARSCoV2?

Clinical data from SARS shows early seroconversion associated with more severe disease and higher mortality (also correlated with advanced age). 32/347 patients (9.2%) had no detectable antibodies.

A very thorough paper demonstrating immunization with various SARS coronavirus vaccine constructs results in pulmonary immunopathology after challenge with SARS-COV virus. Consistent findings in multiple animal models

In COVID19, anti-spike antibodies higher in elderly/middle-aged patients than young patients. 10/175 (5.7%) of patients have no detectable anti-spike antibodies. Anti-spike antibody titres positively correlate with CRP, an inflammatory biomarker.

Similarly, anti-spike IgG positively correlated with age in COVID19. Interesting how the relationship between age and antibody titres is more linear in females. Additionally, anti-spike IgG positively correlated with inflammatory marker LDH

Questions to consider:

Why do some COVID19 patients not make detectable antibody responses? Do these patients have a more potent CD8+ T-cell (CTL) response? Does cross-reactivity of anti-spike antibodies from previous coronavirus exposure increase risk of severe disease?

Are antibodies produced by SARSCOV2 infection protective from reinfection? If so, how durable is this protection and how long will it last? Do anti-spike antibodies provide ADE and worsen pulmonary immunopathology in COVID19 comparable to SARS and MERS in vivo models?


Sage questions indeed – and ones that anyone developing vaccines to SARS2 should take seriously.

Answers to questions can be directed to TI on Twitter, or put up here for relaying. Enjoy!

Gag-Specific Cellular Immunity Determines In Vitro Viral Inhibition and In Vivo Virologic Control following Simian Immunodeficiency Virus Challenges of Vaccinated Rhesus Monkeys

24 August, 2012

See on Scoop.itVirology News

“We observed that CD8+ lymphocytes from 23 vaccinated rhesus monkeys inhibited replication of SIV in vitro. Moreover, the magnitude of inhibition prior to challenge was inversely correlated with set point SIV plasma viral loads after challenge. In addition, CD8 cell-mediated viral inhibition in vaccinated rhesus monkeys correlated significantly with Gag-specific, but not Pol- or Env-specific, CD4+ and CD8+ T lymphocyte responses. These findings demonstrate that in vitro viral inhibition following vaccination largely reflects Gag-specific cellular immune responses and correlates with in vivo virologic control following infection. These data suggest the importance of including Gag in an HIV-1 vaccine in which virologic control is desired.”

 

In other words: having Gag or a gag gene included in a vaccine against SIV given to monkeys was more important than having Pol or Env when it came to control of virus replication – although, as has been shown elsewhere, Env responses are important for protecting against acquisition.  This has important implications for human vaccines – although “monkeys aren’t men, and mice lie” – and in particular for the South African SAAVI vaccines, which elicit quite good Gag-specific cellular responses.

 

We wait in hope.  Graphic showing immune cells associated with HIV control courtesy of Russell Kightley Media.

See on jvi.asm.org