SIB #454- SARS CoV2 induces long lasting immunity

 The Study: SARS-CoV-2 infection induces long-lived bone marrow plasma cells in humans

 Overview: This study sought to determine whether long lived bone marrow plasma cells (BMPCs), a long lasting source of protective antibodies, remain in the system following Covid infection.

 Key Points: 

·         It is known that SAS-Cov2 patients have a significantly reduced likelihood of reinfection. 

·         This fact stands in contrast with early reports documenting rapidly declining antibody levels in SARS-CoV-2 patients within a few months of infection.  

·         The authors sought to better determine whether or not protective immunity against SARS-CoV-2 was likely to be temporary as well.   

·         More recent reports are indicating that antibody levels actually decline more slowly than originally thought.  

·         It is known that “durable serum antibody titers are maintained by long-lived plasma cells” in the bone marrow. These BMPCs are a type of non-replicating, antigen-specific plasma cells that remain in the bone marrow long after the virus has been eliminated.  

·         This study examined 77 individuals with a history of “mild” SARS-CoV2 infections approximately seven months after infection to determine if BMPCs were detectable. 

·         Blood samples were collected approximately 1 month after infection. 

·         Follow up blood draws were done three times at approximately 3 month intervals. 

·         Twelve of the participants received vaccination during the follow up period and blood samples obtained after vaccination were excluded from the analysis.  

·         “Additionally, bone marrow aspirates were collected from eighteen of the participants 7 to 8 months after infection and from eleven healthy volunteers with no history of SARS-CoV-2 infection or vaccination.” These eleven healthy subjects served as a control group. 

·         While SARS-CoV-2 antibodies were undetectable in the eleven control subjects, 74 of 77 convalescent participants had detectable antibody titers approximately 1 month after onset of symptoms. 

·         For the first four months after infection, antibody levels “decreased from a mean of 6.3 to 5.7 however in the next seven months the decay rate slowed and levels were still at 5.3 at the end of the study.  

·         The authors state this “relatively rapid early decline” in antibodies followed by a slower decay “is consistent with a transition of serum antibodies from being secreted by short-lived plasmablasts to a smaller but more persistent population of long-lived plasma cells (BMPCs) generated later in the immune response.”*    

·         To investigate whether or not these patients were actually developing a “virus specific long-lived BMPC compartment”, the authors examined the bone marrow aspirates which had been obtained on the smaller subset of 18 post covid subjects and compared them to those of the 11 healthy volunteers with no history of infection.   

·        SARS CoV2 antibody secreting BMPCs  (for both IgG and IgA antibodies) were detected in 15 and 9 of the 18 convalescent participants, respectively, but were not found in any of the 11 control participants.*

  ·         Author’s Conclusions: The data provides “strong evidence” that SARS CoV2 infection induces the production of anti spike IgG antibodies for at least seven months  and long lived immune response via BMPCs appears to “provide the host with a persistent source of preformed protective antibodies”. *

Reviewer's Comments: For the better part of the pandemic, the popular press has promoted the terrifying notion that antibodies to the virus were short lived and consequently we would all be subject to repeated infections in a never ending pandemic. Scary stuff indeed.  Thankfully, thanks to a growing list of studies, the future doesn’t appear nearly so bleak. Unlike the seasonal variants of coronaviruses which contribute to the common colds we all experience from time to time, SARS CoV2 appears to produce robust, long lasting immune responses and the likelihood of reinfection appears quite low.

*All Emphasis and Parenthesis shown above are ours and were not included in the original article.

Reviewer:  Mark R. Payne DC 

Reference:  Jackson S. Turner , Wooseob Kim , Elizaveta Kalaidina , Charles W. Goss , Adriana M. Rauseo , Aaron J. Schmitz , Lena Hansen, Alem Haile , Michael K. Klebert , Iskra Pusic , Jane A. O’Halloran , Rachel M. Presti & Ali H. Ellebedy. J. Nature Published online 24 May 2021.

Link to Full Text: https://www.nature.com/articles/s41586-021-03647-4_reference.pdf