The immune system is very complicated, but now, it's on a chip
Lymphoid follicles formed in a microfluidic Organ Chip replicate human
immune functions and vaccine responses in vitro

Date:
March 15, 2022
Source:
Wyss Institute for Biologically Inspired Engineering at Harvard
Summary:
Scientists have a new tool to help them tease out the immune
system's mysteries. Researchers cultured human B and T cells
inside a microfluidic Organ Chip and coaxed them to form functional
lymphoid follicles (LFs) - - structures that reside in lymph nodes
and other parts of the human body and mediate immune responses. The
LF Chip replicated human immune responses to both pathogens and
a commercial influenza vaccine in vitro, offering significant
improvement over existing preclinical models like cells in a dish
and non-human primates.



FULL STORY ==========================================================================
To quote veteran science writer Ed Yong's simple yet extremely accurate
words in The Atlantic, "The immune system is very complicated." As the
COVID-19 pandemic had made abundantly clear, science still doesn't fully understand the sophisticated defense mechanisms that protect us from
microbe invaders. Why do some people show no symptoms when infected with SARS-CoV-2 while others suffer from severe fevers and body aches? Why
do some succumb to cytokine storms of the body's own making? We still
lack exact answers to these questions.


========================================================================== Today's scientists, however, now have a new tool to help them tease
out the immune system's mysteries, thanks to a group of researchers at
the Wyss Institute for Biologically Inspired Engineering at Harvard
University. They cultured human B and T cells inside a microfluidic
Organ Chip device and coaxed them to spontaneously form functional
lymphoid follicles -- structures that reside in lymph nodes and other
parts of the human body which mediate immune responses. They consist
of different chambers that harbor "nai"ve" B cells and T cells, which
together initiate the cascade of events that leads to a full immune
response when they are exposed to a specific antigen.

In addition to allowing researchers to probe the normal function of the
immune system, these lymphoid follicle (LF) Chips can also be used to
predict immune responses to various vaccines and help select the best performers, offering significant improvement over existing preclinical
models like cells in a dish and non-human primates. The achievement is
reported today in Advanced Science.

"Animals have been the gold-standard research models for developing and
testing new vaccines, but their immune systems differ significantly from
our own and do not accurately predict how humans will respond to them. Our
LF Chip offers a way to model the complex choreography of human immune responses to infection and vaccination, and could significantly speed up
the pace and quality of vaccine creation in the future," said first author Girija Goyal, Ph.D., a Senior Staff Scientist at the Wyss Institute.

An accidental discovery Like many great scientific discoveries, the LF
Chip project is the result of serendipity in the lab. Goyal and other Wyss Institute scientists wanted to investigate how B and T cells circulating
in the blood would change their behavior once they entered a tissue,
so they obtained those cells from human blood samples and cultured
them inside a microfluidic Organ Chip device to replicate the physical conditions they would experience when they encountered an organ.



==========================================================================
When the cells were placed inside one of the two channels within the
device, nothing remarkable happened -- but when the researchers started
the flow of culture medium through the other channel to feed the cells,
they were surprised to see that the B and T cells started to spontaneously self-organize into 3D structures within the Organ Chip that appeared
similar to "germinal centers" - - structures within LFs where complex
immune reactions take place. "It was so unexpected that we completely
pivoted from the original experiment and focused on trying to figure
out what they were," said Goyal.

When the researchers started probing the mysterious structures that had
formed inside the Organ Chip under flow conditions, they found that the
cells were secreting a chemical called CXCL13. CXCL13 is a hallmark of
LF formation, both within lymph nodes and in other parts of the body
in response to chronic inflammation, such as in cancer and autoimmune conditions.

The team also found that B cells within the LFs that self-assembled
on-chip also expressed an enzyme called activation-induced cytidine
deaminase (AID), which is critical for activating B cells against specific antigens and is not present in B cells that are circulating in the blood.

Neither CXCL13 nor AID were present in cells that were cultured in a
standard 2D dish, suggesting that the scientists had indeed successfully created functional LFs from circulating blood cells.

In LFs in the human body, activated B cells mature and differentiate
into multiple types of progeny cells including plasma cells, which
secrete large amounts of antibodies against a specific pathogen. The
team detected the presence of plasma cells in the LF Chips after they
applied several stimuli used in the laboratory to activate B cells,
such as the combination of the cytokine IL-4 and an anti-CD40 antibody,
or dead bacteria. Remarkably, the plasma cells were concentrated in
clusters within the LFs, as they would be in vivo.

"These findings were especially exciting because they confirmed that
we had a functional model that could be used to unravel some of the complexities of the human immune system, including its responses to
multiple types of pathogens," said Pranav Prabhala, a Technician at the
Wyss Institute and second author of the paper.



========================================================================== Predicting vaccine efficacy on-a-chip Now that the scientists had a
functional LF model that could initiate an immune response, they explored whether their LF Chip could be used to replicate and study the human
immune system's response to vaccines.

In the human body, vaccination induces special cells called dendritic
cells to take up the injected pathogen and migrate to lymph nodes,
where they present fragments of them on their surface. There, these antigen-presenting cells activate the B cells with the assistance of local
T cells in the LF, causing the B cells to differentiate into plasma cells
that produce antibodies against the pathogen. To replicate this process,
the researchers added dendritic cells to LF Chips along with B and T
cells from four separate human donors. They then inoculated the chips
with a vaccine against the H5N1 strain of influenza along with an adjuvant called SWE that is known to boost immune responses to the vaccine.

LF Chips that received the vaccine and the adjuvant produced significantly
more plasma cells and anti-influenza antibodies than B and T cells grown
in 2D cultures or LF Chips that received the vaccine but not the adjuvant.

The team then repeated the experiment with cells from eight different
donors, this time using the commercially available Fluzone?influenza
vaccine, which protects against three different strains of the virus
in humans. Once again, plasma cells and anti-influenza antibodies were
present in significant numbers in the treated LF Chips. They also measured
the levels of four cytokines in the vaccinated LF Chips that are known
to be secreted by activated immune cells, and found that the levels of
three of them (IFN-?, IL-10, and IL-2) were similar to those found in
the serum of humans who had been vaccinated with Fluzone?.

The Wyss researchers are now using their LF Chips to test various
vaccines and adjuvants in collaboration with pharmaceutical companies
and the Gates Foundation.

"The flurry of vaccine development efforts sparked by the COVID-19
pandemic were impressive for their speed, but the increased demand
suddenly made traditional animal models scarce resources. The LF Chip
offers a cheaper, faster, and more predictive model for studying human
immune responses to both infections and vaccines, and we hope it will streamline and improve vaccine development against many diseases in
the future," said corresponding author Donald Ingber, M.D., Ph.D.,
who is the Founding Director of the Wyss Institute as well as the Judah
Folkman Professor of Vascular Biology at Harvard Medical School (HMS)
and Boston Children's Hospital, and Professor of Bioengineering at the
Harvard John A. Paulson School of Engineering and Applied Sciences.

Additional authors of the paper include Yunhao Zhai, Min Sun Kim, Aditya
Patil, Danielle Curran, Jaclyn Long, Abidemi Junaid, and Tom Ferrante from
the Wyss Institute; Bruce Bausk, Tal Gilboa, Limor Cohen, and David Walt
from the Wyss Institute, Brigham and Women's Hospital, and HMS; and former
Wyss Institute members Gautam Mahajan, Liangxia Xie, Roey Lazarovits,
Adam Mansour, Sanjay Sharma, Oren Levy, and Rachelle Prantil-Baun.

This research was supported by DARPA under Cooperative Agreement
Number W911NF- 12-2-0036, the National Institutes of Health under
grant UG3HL141797, the Bill and Melinda Gates Foundation, BARDA under
contract 75A50121C00075, and the Wyss Institute for Biologically Inspired Engineering.


========================================================================== Story Source: Materials provided
by Wyss_Institute_for_Biologically_Inspired_Engineering_at
Harvard. Original written by Lindsay Brownell. Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. Girija Goyal, Pranav Prabhala, Gautam Mahajan, Bruce Bausk,
Tal Gilboa,
Liangxia Xie, Yunhao Zhai, Roey Lazarovits, Adam Mansour,
Min Sun Kim, Aditya Patil, Danielle Curran, Jaclyn M. Long,
Sanjay Sharma, Abidemi Junaid, Limor Cohen, Thomas C. Ferrante,
Oren Levy, Rachelle Prantil‐Baun, David R. Walt, Donald
E. Ingber. Ectopic Lymphoid Follicle Formation and Human
Seasonal Influenza Vaccination Responses Recapitulated in an
Organ‐on‐a‐Chip. Advanced Science, 2022; 2103241
DOI: 10.1002/advs.202103241 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220315150120.htm

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