Circulation August 23, 2022 Issue

This week, please join author Kory Lavine and Associate
Editor Thomas Eschenhagen as they discuss the article "Donor
Macrophages Modulate Rejection After Heart
Transplantation."


Dr. Carolyn
Lam:            


Welcome to Circulation on the Run, your weekly podcast summary
and backstage pass to the journal and its editors. We're your
co-hosts. I'm Dr Carolyn Lam, associate editor from the National
Heart Center and Duke National University of Singapore.


Dr. Greg
Hundley:          


I'm Dr. Greg Hundley, associate editor and director of the Pauley
Heart Center at VCU Health in Richmond, Virginia.


Well, Carolyn, this week's feature, we are going to the world of
preclinical science and we are going to learn about a very
important new finding pertaining to heart transplant rejection,
and macrophages may modulate this, but before we get to that
feature, how about we grab a cup of coffee and go through some of
the other articles in the issue?


Dr. Carolyn
Lam:            


I got mine. Would you like to go first, Greg?


Dr. Greg
Hundley:          


You bet, Carolyn. Well, my first study comes to us from Dr.
Michael Pencino from Duke University. Carolyn, this study was
performed to understand the predictive utility of a previously
derived polygenic risk score for long-term risk of coronary heart
disease and its additive value beyond traditional risk factors
and how that might be able to inform prevention strategies. To
accomplish this, data from adults aged 20 to 59 free of
cardiovascular health disease from the Framingham Offspring Study
and the Atherosclerosis Risk in Communities, or ARIC Study, were
analyzed. Now, since the polygenic risk score was derived from
people of predominantly European ancestry, individuals who
self-reported white race were those that were included.


Dr. Carolyn
Lam:            


Oh, interesting, so what did they find, Greg?


Dr. Greg
Hundley:          


Right, Carolyn. Somewhat surprisingly, they found that, among
9,757 participants, both the traditional risk factor score and
the polygenic risk score where significantly associated with
incident cardiovascular heart disease in young, early midlife,
and late midlife. Now, the delta C index, when the polygenic risk
score was added to the traditional risk factor, score was 0.03,
0.02, and 0.002 in the young, the early midlife, and the
late-midlife participants, respectively.


Carolyn, despite a statistically significant association between
the polygenic risk score and the 30-year risk of cardiovascular
heart disease, the C index improved only marginally with the
addition of the polygenic risk score to the traditional risk
factor model among young adults and did not improve among midlife
adults and, thus, Carolyn, the polygenic risk score, an immutable
factor, has limited clinical utility for long-term cardiovascular
heart disease prediction when added to a traditional risk factor
model.


Dr. Carolyn
Lam:            


I really like that, Greg, because I think it also tells us that
the traditional risk factors, which we can do something about,
are still very important. Isn't that great? Well, the next paper
is about POTS. Remember what that is? Should I give you a quiz?
All right. It's okay. POTS, or Postural Orthostatic Tachycardia
Syndrome, is a disorder of orthostatic intolerance that primarily
affects females of childbearing age. While the underlying
pathophysiology of POTS is not fully understood, it has been
suggested that autoimmunity may play a role. Now, the aim of this
study was to compare concentrations of autoantibodies to
cardiovascular G protein-coupled receptors between 116 POTS
patients and 81 healthy controls, and they were from Calgary,
Canada, and Malmo, Sweden.


Dr. Greg
Hundley:          


Carolyn, really interesting, so what did they find here?


Dr. Carolyn
Lam:            


The investigators, led by Dr. Raj from University of Calgary in
Canada, found that commercially available autoantibody
concentrations to G protein-coupled receptors were not increased
or altered in POTS patients relative to healthy controls as
assessed using ELISA. Now, while this study suggests that these G
protein-coupled receptor autoantibody concentrations alone cannot
explain the pathophysiology of POTS, autoantibody activity and
signals not picked up by ELISA should still be explored as these
results may provide more insights into the pathophysiology of
POTS.


Dr. Greg
Hundley:          


Very nice, Carolyn. Well, my next study comes to us from the
world of pulmonary arterial hypertension. Carolyn, clinical
worsening is commonly used as an endpoint in pulmonary arterial
hypertension trials. These authors, led by Dr. Steeve Provencher
from the Institut Universitaire de Cardiologie Pneumologie de
Quebec, aimed to assess the trial-level surrogacy of clinical
worsening for mortality in pulmonary artery hypertension trials
and whether the various clinical worsening components were
similar in terms of frequency of occurrence, treatment-related
relative risk reduction and importance to patients.


Dr. Carolyn
Lam:            


Okay, so what did they find?


Dr. Greg
Hundley:          


Right, Carolyn, so they searched MEDLINE, Embase and the Cochrane
Library for trials evaluating the effects of pulmonary arterial
hypertension on clinical worsening and, among 35 independent
cohorts, so 9,450 patients, the effects of pulmonary arterial
hypertension-specific therapies on clinical worsening modestly
correlated with mortality. Additionally, study-level clinical
worsening was not found to be a surrogate for mortality in
pulmonary arterial-hypertension trials. Moreover, components of
clinical worsening largely vary in frequency, response to therapy
and importance to patients and, thus, are not necessarily
interchangeable.


Dr. Carolyn
Lam:            


Thank you, Greg. Can I tell you about some other papers in
today's issue? There's a Research Letter from Dr. Cosentino on
cardiorenal outcomes with ertugliflozin by baseline metformin
use, and this is a post hoc analysis of the VERTIS CV trial.


Dr. Greg
Hundley:          


Oh, very good, Carolyn. Well, I've got an exchange of letters
from Professors Boriani and Steinberg regarding the article
“Driving Restrictions and Early Arrhythmias in Patients Receiving
a Secondary Prevention Implantable Cardioverter-Defibrillator,
the DREAM-ICD-II Study.” There's also an ECG Challenge from
Professor Gao entitled “Syncope in a 3-Year-Old Child During the
Perioperative Period. What is the diagnosis? What Signs Point
Toward Impending Life-threatening Event?”


Then, finally, there's a nice, On My Mind piece from Professor
Greenland entitled “Insurance Payers Should Cover Selective
Coronary Artery Calcium Testing in Intermediate Risk Primary
Prevention Patients.” Well, Carolyn, how about we get on to that
feature discussion and dive into the world of rejection after
heart transplantation?


Dr. Carolyn
Lam:            


Yay. Here we go.


Dr. Greg
Hundley:          


Welcome, listeners, to this feature discussion on August 23rd. We
have a very interesting article today to discuss with our author
and associate editor pertaining to preclinical science and
cardiac transplant rejection. Our author today is Dr. Kory Lavine
from Washington University in St. Louis and our associate editor
today is Dr. Thomas Eschenhagen from Hamburg, Germany. Welcome
gentlemen.


Kory, we'll start with you. Can you describe for us some of the
background information pertaining to the construct of your study
and what was the hypothesis that you wanted to address?


Dr. Kory
Lavine:              


Well, thank you for having me. Our study focused on heart
transplant rejection, which remains a major clinical challenge
that limits both the survival of heart transplant recipients as
well as availability of donor hearts. Current clinical practice
really focuses on suppressing the immune system in a global way,
and that is somewhat effective, but carries important risks that
include infection and life-threatening malignancies.


Many studies have appropriately focused on immune cells that
infiltrate the transplanted heart that come from the recipient to
search for new ways to suppress the immune system safely. What
we've understood and learned over the past several years is that
the donor heart has its own immune system and its own immune
cells, and the majority of those immune cells that come with the
donor heart are macrophages that can be broadly divided into two
distinct lineages with different functions, tissue-resident
macrophages, which lack the cell surface receptors CCR2, and
monocyte-derived macrophages with expressed cell surface
receptors CCR2. We tested the hypothesis in this study that these
macrophages that come with the donor heart remain active for a
period of time after transplantation and play important roles in
either suppressing or accelerating heart transplant rejection.


Dr. Greg
Hundley:          


What was the hypothesis that you wanted to address with your
study?


Dr. Kory
Lavine:              


Yeah, so our prior work and others' work within this field had
suggested that tissue-resident macrophages, CCR2-negative
macrophages, are inflammatory, and CCR2-positive macrophages have
the opposite functions being inflammatory and play roles in
potentiating and initiating inflammation in the heart. In this
study, we hypothesized that CCR2-negative macrophages would
protect from rejection, while CCR2-positive macrophages may
promote heart transplant rejection and could serve as a new
therapeutic target to prevent rejection in transplant recipients.


Dr. Greg
Hundley:          


Excellent. Kory, can you describe for us the study design that
you used to test your hypothesis?


Dr. Kory
Lavine:              


Yeah. The study design and approach we used involved a mouse
model of heart transplantation where we transplant a donor heart
into a recipient mouse that's fully mismatched at all the MHC
loci, and this serves as a nice model for both cellular and
antibody-mediated rejection. To facilitate tracking these donor
macrophages, we used various genetic lineage tracing systems and,
to study their phenotypes, we used single-cell RNA sequencing
and, to understand their function, we used mouse models that
allow us to specifically deplete each of the donor macrophage
populations as well as genetic models to manipulate their
activation and signaling.


Dr. Greg
Hundley:          


The outcome measures were going to be what?


Dr. Kory
Lavine:              


Yeah. The outcome measures for transplant rejection in this mouse
model are allograph survival, so the survival of the transplanted
heart. We're able to directly look at how much rejection is
present by histopathology, and then we're able to observe various
mechanistic features using detailed phenotyping such as
single-cell RNA sequencing and T-cell activation assays.


Dr. Greg
Hundley:          


Very nice, Kory. Well, all, our listeners, we're very excited to
hear what were your study results?


Dr. Kory
Lavine:              


We learned that donor macrophages are dynamic and they survive
for a period of time after transplantation or eventually lost due
to transplant rejection. When we phenotyped the macrophages that
came from the donor heart, we learned that they remained
transcriptionally distinct from immune cells that enter the heart
that were derived from the recipients, and they had important and
distinct functions. If we depleted the tissue-resident
macrophages that were CCR2-negative, we observed reduced
allograph survival and increased rejection. If we depleted
CCR2-positive macrophages that came from the donor heart, we
observed improved allograph survival and reduced rejection.


Mechanistically, we learned that CCR2-positive macrophages are
activated through a MyD88-dependent pathway and, if we inhibited
MyD88 cytokines which controls the expression of pro-inflammatory
cytokines and chemokines, we could prolong the survival of the
donor heart for a very significant period of time, reduce
rejection and prevent the development of T-cells that would
attack the donor heart. From a mechanistic aspect, what we
uncovered is that this signaling pathway in CCR2-positive
macrophages regulated the recruitment of an activation of
antigen-presenting cells which played important roles in
generating T-cells that would target the transplanted heart.


Dr. Greg
Hundley:          


It sounds like a really informative and leap forward in the whole
sphere of transplant rejection. Well, listeners, now we're going
to turn to our associate editor, Dr. Thomas Eschenhagen.


Thomas, you have many papers come across your desk. What
attracted you to this particular paper and then, secondly, how do
you put the results of this study really in the context of other
research examining heart transplant rejection?


Dr. Thomas
Eschenhagen:          


Yeah, thanks for having me. I mean, first, we got attracted by
this paper because it's somewhat an out-of-the-box approach. It's
not the standard approach to improve the systemic
immunosuppression as many studies did and with actually a lot of
success over the last 30 years, survivor got much better. There
had been a lot of progress in the field of transplantation
medicine as we all know, but as Kory said already, we still have
30% rejection, and these immunosuppressions come at a price.
Having this study which turns around somehow the argumentation
and looks at the donor organ was something which really attracted
us. It uses advanced methods and it applies somewhat in a
practical way a concept which emerged over the last, I don't
know, maybe decade this concept that macrophages are really very
different kind of cells. They're all called macrophages, but
they're quite different and even maybe in certain respects having
opposing effect.


I think many people know about this M1/M2 concept. It's CCR2
receptor positive and negative. It's criticized by some people,
but here we see that it really seems to be really important and,
of course, then the third argument why we really like the story
is that it has a specific, clear translation impact. I mean,
looking at the heart, the donor heart, and potentially even
treating the donor heart before transplanting it is something
which comes immediately out of the story, and that's something
which we found super attractive.


Dr. Greg
Hundley:          


Really interesting, so really understanding the mechanism and
focusing on donor hearts. Well, listeners, let's circle back with
Kory.


Kory, given that, what do you think is the next study that really
needs to be performed in this sphere of research?


Dr. Kory
Lavine:              


I think Thomas said it exactly as we're thinking about it, so the
next area that we're really excited to attack and we're hopeful
that the field will focus on is ways to build methods and
technologies to treat the donor heart between the time of
procurement and the time of transplant, when it's being
transported and potentially even being perfused for a period of
time. We're really interested in finding approaches to identify
small molecules and other potential biologic therapies that could
be used to prevent the activation of donor CCR2-positive
macrophages.


It's a really attractive approach because treating the donor
heart ex vivo decreases the risk of adversely affecting other
organs that may be transplanted if you're treating the donor, for
instance, and it may decrease the risk of immunosuppression and
infection by not having to treat the recipient and we're catching
the heart in this window where the risks are much lower.


The other area that we're really excited to focus on is trying to
identify the exact mediators that are generated from donor
CCR2-positive macrophages that mediate the recruitment and
activation of antigen-presenting cells because that would
represent another potential therapeutic target.


Dr. Greg
Hundley:          


Very nice. Thomas, what are your thoughts about what might be the
next study to be performed really in this sphere of research?


Dr. Thomas Eschenhagen:


It's obviously something rather a question to Kory than to me,
but I agree to what he said. I think it is pretty obvious what
are the next steps mechanistically on the one hand, but
practically on the other hand. I mean, at this point, we are at
the mouse level, so the question is to which extent can this
concept be translated into larger animals and then finally in
humans? I was wondering, given these newer methods to keep donor
hearts alive for long, extended periods, I was wondering which
extent you are already collaborating with the respective groups
who develop this approach because that obviously would increase
the window of opportunity here for drugs. I think it's really an
exciting and pretty visible next steps which we see here, and I
can just hope that you're going this path and that it will be
successful.


Dr. Greg
Hundley:          


Kory, any thoughts on those collaborations that Thomas just spoke
of?


Dr. Kory
Lavine:              


We're definitely establishing collaborations to focus on ex vivo
profusion of donor hearts because that's, as Thomas mentioned, is
a perfect window to manipulate the immune populations that are
within the donor heart. Those studies have to be team science,
they have to be collaborative and they have to have a focus on
large animals and then moving into clinic. We're definitely
forming those collaborations and excited to work as a group.


Dr. Greg
Hundley:          


Very nice. Well, listeners, what an exciting paper to discuss
here as part of this feature discussion from the world of
preclinical science. We want to thank Dr. Kory Lavine from
Washington University in St. Louis, Missouri, and also our own
associate editor, Dr. Thomas Eschenhagen from Hamburg Germany,
for really bringing us this research study highlighting that
distinct populations of donor and recipient macrophages coexist
within the transplanted heart, and donor CCR2-positive
macrophages are key mediators of allograph rejection and deletion
of MyD88 signaling in donor macrophages is sufficient to suppress
rejection and extend allograph survival.


Well, on behalf of Carolyn and myself, we want to wish you a
great week, and we will catch you next week on the run.


Dr. Greg
Hundley:          


This program is copyright of the American Heart association,
2022. The opinions expressed by the speakers in this podcast are
their own and not necessarily those of the editors or of the
American Heart Association. For more, please visit
ahajournals.org.