Preserving the Immunological Memory of Previous Generations

The hygiene hypothesis states that a reduction in pathogen infections over the past 60 years contributed directly to an increase in allergic and autoimmune diseases, especially in industrialized countries. Notably, the increase of specific immune-related diseases suggests that the training and establishment of the adaptive immune systems is different from previous generations and might have been affected by particular lifestyle changes such as widespread use of antibiotics and pervasive hygiene measures. Robust epidemiological data support this hypothesis, and experimental evidence from animal models showed that the occurrence of autoimmune disease can be prevented by infection with particular pathogens. Importantly, the hygiene hypothesis also implicates that future generations will not become exposed to some of the pathogens, which have shaped the immune systems of previous generations, due to their eradication in the recent decades. A hallmark of the immune system is to memorize past exposure to pathogens. Such immunological memory is mediated, in part, by long -lived memory B- and T-cells residing in primary and secondary lymphatic organs for extended periods of time. Upon re-exposure to a similar pathogenic insult, such memory cells will be re- activated allowing the organism to effectively fight the insult using prior antigenic knowledge. Can memory immune cells obtained from previous generations be used to retrospectively identify lost pathogens? Recent technological advances allow determining B- and T-cell repertoires, unique molecular signatures carried by every B- or T-cell that came in contact with a particular antigen. This has provided insights into the adaptive immune response of individuals affected by autoimmunity, allergies, infections and cancer. Intriguingly, various computational approaches are being developed which also allow deducing both antibody identity and T-cell receptor structure from DNA sequence and thereby predicting which antigen might have been targeted by these molecules. The latter is an exciting prospect since it would allow identification and potentially immunization against specific antigens that have trained the immune systems of previous generations but are rarely encountered by present a nd future generations. This proof-of-concept project aims at preserving immunological memory of previous generations. To do so, memory B-cells from the spleen and bone marrow of deceased individuals (body donors, > 70 years) will be isolated and cryo-preserved with the aim of profiling individual B-cell repertoires, deriving antibody-secreting B cells and for testing antibody diversity immediately or at some point in the future. Preserving individual immune repertoires from people who have survived until old age presents a unique but dwindling time window to harvest (soon-to-be lost) knowledge about pathogen exposure from the 1950s until now. By Biobanking such knowledge in form of viable B-cells as well as DNA sequence information, this approach might allow creating a resource for future biomedical applications including the development of vaccines against extinct pathogens that had positive immune modulatory effects on human health.

Our immune system remembers which pathogens have breached our defenses provided by the skin, airways, and intestinal tract. Such immunological memory is trained by pathogen exposure during childhood. It is mediated by special immune cells (B cells), which secrete specific proteins (antibodies) that neutralize any invading agent, even decades after our first contact with it. Notably, human exposure to most pathogens has been significantly reduced over the last century; yet an increase in allergic and autoimmune diseases has been reported in many countries during the last decades. To explain this, the 'hygiene hypothesis' states that a reduction in early childhood infections contributes directly to an increase in immune-related diseases during adulthood. If that is true, then humans who trained their immune systems a long time ago should maintain a different immunological memory than most of you who are reading this project description. In this project, we developed a proof-of-concept approach to biobank immunological memory of people who trained their immune systems before the 1950s. We accessed this memory by purifying B cells that reside in the bone marrow (BM). Importantly, BM is not only the place where all cells of our blood system originate but also a place where antibody-producing plasma B cells home in and remain for decades. The main part of the project was the development of a streamlined extraction process that allowed retrieving donor-derived B cell nuclei containing genetic information in the form of DNA or RNA, even though the genetic information was procured days after the death of the individual donor. Our unpublished data indicated that individual donors contained very low numbers of plasma B cells (<1% of all white blood cells). However, current amplification technology allows access to specific sequences, which are sufficient to inform the molecular make-up of individual antibodies produced against the pathogens each donor deemed important "to remember". Even though the official funding for the project ran its course, we are still collecting material from a representative number of donors, which will be followed by determining individual B cell receptor repertoires as a proxy for the diversity of antibody-producing cells. We envision publishing the approach and the results of the study as soon as these data are acquired. Preserving individual immune repertoires from humans who have survived until old age presents a unique but dwindling time window to harvest (soon-to-be lost) knowledge about pathogen exposure from the 1950s until now. By Biobanking such knowledge in the form of sequence information, this approach might allow creating a resource for future biomedical applications, including the development of vaccines against "extinct" pathogens that had positive immune modulatory effects on human health.