Based on Stabilization of Foxp3 by
Targeting JAK2 Enhances Efficacy of CD8 Induced Regulatory T Cells in the
Prevention of Graft-versus-Host Disease
Written by Supinya Iamsawat working in Dr. Xue-Zhong Yu’s
lab within the Department
of Microbiology and Immunology at the Medical University of South Carolina. Dr.
Xue-Zhong’s research profile can be found here
Transplanting
healthy donor tissue into sick patients is becoming more and more prevalent as
a treatment option. This treatment works for many different afflictions, from
organ failure, to burn victims needing skin transplants. Even leukemia can be
treated with transplantation.1
Leukemia is a name for cancer in blood cells, in which blood cells replicate
abnormally. The cancerous blood cells cannot function normally, and they hinder
the production of normal blood cells creating a multitude of symptoms. For
example, a limited ability to fight off infection since leukemia interferes
with white blood cells that are responsible for fighting off infection. More on
Leukemia and its symptoms can be found here. 2
To treat
leukemia, patients can receive a stem cell transplant from a donor meant to
help restore healthy blood cells. This means taking the donor’s healthy stem
cells and placing them inside the patient. Once the donor stem cells are inside
the patient’s body they will turn into blood cells, like red blood cells that
carry oxygen and white blood cells that fight infection. The process of
introducing donor stem cells into a patient’s body is called hematopoietic stem cell
transplantation.3 Some of the donor T cells become functional
white blood cells that fight and kill the cancerous blood cells of the patient.
This is called the graft vs leukemia effect, in which the donor stem cells are
called the “graft” and the “host” refers to the sick patient. However, the
benefits of this are limited by the side effect in which the T cells resulting
from the stem cell transplant start attacking the patient’s normal cells in a
condition called graft vs host disease.4
This disease can cause rashes and liver damage, with varying severity.
More on graft vs host disease can be found here.5
Current research is aimed at
figuring out ways to maximize the graft vs leukemia effect of the stem cell
transplantation, resulting from the new T cells killing the cancerous cells,
and minimize the graft vs host disease where the new T cells harm the patient.
In
this paper Iamsawat and colleagues show that treatment with an alteration of an
induced regulatory T cell can relieve graft vs host disease, while maintaining
the graft vs leukemia effect in mice. Regulatory T cells6 have been used to alleviate graft vs host side
effects in mice previously.7 The
function of regulatory T cells is to prevent healthy cells from being harmed
during the process of fighting against the foreign material, through controlling
and limiting the immune response. Induced regulatory T cells are cells that
first exist as regular, infection fighting T cells, before they become
regulatory. Iamsawat and colleagues used the induced regulatory T cell that
comes from a CD8 T cell,8
hence the name, CD8 induced regulatory T cell (CD8 iTreg). These has been shown
to have significant graft vs leukemia effects in mice, however, CD8 iTregs
struggle to treat the graph vs host side effects because they often lose their
expression of Foxp3 during immune responses. Foxp3 is a gene, responsible for a
large part of the induced regulatory T cells’ suppressive function. CD8 iTregs are
prone to losing the expression of Foxp3 in the presence of inflammation signals
which are chemicals secreted by immune cells, used to recruit more cells to
assist in fighting infection.8
This creates a problem because when the CD8 iTregs arrive at the immune
response, instead of suppressing it as intended, they lose their expression of
Foxp3 and in doing so, they can turn into T cells that contribute to the
excessive immune response. Iamsawat and colleagues have engineered CD8 iTregs
that lack a gene called JAK2 which is involved in the pathway of losing Foxp3
expression and turning into an effector cell.9 They hypothesized their JAK2-/- CD8 iTregs will
alleviate graft vs host side effects, while maintaining the beneficial graft vs
leukemia effects because these engineered T cells will not lose expression of
Foxp3, and thus will maintain their suppressive function throughout the immune
response preventing the harm of healthy cells.
The
researchers first examined whether their engineered JAK2-/- CD8 iTregs
expressed more Foxp3 than normal CD8 iTregs using flow cytometry. Flow cytometry
is a method of detecting proteins that are expressed on the surface of the cell.
An in depth explanation of flow cytometry can be found here.10
They found that their JAK2-/- CD8 iTregs expressed significantly
more Foxp3 than the normal CD8 induced regulatory T cells. Next, they tested
the ability of the CD8 to alleviate graft vs host disease in mice. Mice were
radiated to decrease their amount of healthy blood cells, mimicking the
condition that humans are in when they receive donor stem cells. They then were
injected with healthy mice T cells to induce graft vs host disease. The mice
that were treated with the researcher’s JAK2-/- CD8 iTregs survived
at a much higher rate (about 70% of the mice survived beyond 80 days), than
mice that were treated with normal CD8 iTregs, in which all of the mice died
within 60 days. Further, their data suggests that the JAK2-/- CD8
iTregs are successful in treating graft vs host disease because JAK2-/-
CD8 iTregs influence the transferred T cells to start expressing Foxp3
themselves and become regulatory T cells, contributing to the prevention of
immune responses directed at the host’s healthy cells.
After
showing that their JAK2-/- CD8 iTreg cells do indeed treat graft vs
host disease, they needed to show that the cells maintained their effectiveness
at killing cancerous cells. The researchers injected the mice with leukemic (cancerous
blood) cells on the same day that they injected the various types of T cells. The
specific type of leukemic cell that they used expresses a protein allowing the
researchers to use flow cytometry to monitor the growth of these cancerous
cells over time. The group of mice that were not given any T cells at all,
showed tumor growth at 30 days after they were given the cancerous cells,
ensuring that the leukemia cells create tumors in mice if not treated with
regulatory T cells. The group that was given normal CD8 iTregs did not show
signs of tumor growth, however these mice suffered from graft vs host disease
that eventually killed all of the mice around the 40th day after
receiving the cancer cells. The group of mice given JAK2-/- CD8
iTreg cells maintained the graft vs leukemia effect of regular CD8 iTregs, as
there were no signs of tumor relapse, but also significantly alleviated some of
the graft vs host disease because about 30% of the mice survived past the 80th
day after receiving cancer. With this experiment, the researchers show that removing
the gene JAK2 from the CD8 iTreg cell helps to alleviate graft vs host disease,
while maintaining the ability of normal CD8 iTregs to fight off cancerous
cells.
The
researchers did one last experiment mirroring the last one, but this time used
a drug called pacritinib that is an inhibitor of JAK2. Inhibiting JAK2 in this
way, showed similar results as treatment with JAK2-/- CD8 iTreg
cells. Mice treated with CD8 iTregs and pacritinib together showed decreased
graft vs host disease and maintained the graft vs leukemia effects. This paper
suggests that inhibiting JAK2 is a plausible method for treating graft vs host
disease in humans, however more research must be done aimed at revealing, with
greater certainty, the effectiveness that this would have in human patients. In
their mice model of the graft vs leukemia effect of JAK2-/- CD8
iTregs, about 30% of the mice survived being given cancerous cells with no
signs of tumor growth. Though this is significantly higher the 0% survival rate
for the other groups, it is not a high percentage in itself. Furthermore, there
are four main types of leukemia and various subtypes, so more research must be
done to see if the effects of JAK2 inhibition are present throughout all types.
Iamsawat’s
work provides a step forward towards the goal of separating the damaging graft
vs host disease from the beneficial graft vs leukemia effect. The effect of
inhibiting JAK2 can be kept in researcher’s minds as further research goes into
enhancing the ability of transplanted donor stem cells to combat cancer, while
avoiding healthy tissue. The more efficient transplanting stem cells becomes,
the more it can be utilized to assist in donor tissue transplantation, and to
keep cancers in remission. Remember, you can check out this paper and other
research by Dr. Xue-Zhong’s lab yourself using the links at the top!
References
1. Dickinson, A. M., Norden,
J., Li, S., Hromadnikova, I., Schmid, C., Schmetzer, H., &
Jochem- Kolb, H. 2017. Graft-versus-Leukemia Effect Following
Hematopoietic Stem Cell Transplantation
for Leukemia. Frontiers in immunology 8: 496.
Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5461268/
2.
“Leukemia.”
2018. Retrieved from:
3.
Franks, I., Biggers,
A. 2017 June 26. “What is hematopoietic stem cell transplantation?”
4.
Kolb, H.
J. 2008. Graft-versus-leukemia effects of transplantation and
donor
lymphocytes. Blood, 112: 4371-4383
5.
“About graft versus
host disease (GvHD)” 2017. Retrieved from:
6. Corthay,
A. 2009. How do regulatory T cells work? Scandinavian journal of
immunology, 70(4): 326-36. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2784904/
7. Zhang,
N., & Bevan, M. J. (2011). CD8(+) T cells: foot soldiers of the immune
system. Immunity, 35(2):
161-8. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3303224/
8.
Beres, A., R. Komorowski, M. Mihara,
W. R. Drobysk. 2011. Instability of Foxp3
expression limits the ability of induced regulatory T cells to
mitigate graft versus host disease. Clin. Cancer Res. 17: 3969–3983
9.
Betts, B.C., D. Bastian, et al. 2018. Targeting
JAK2 reduces GVHD and xenograft
rejection
through regulation of T cell differentiation. Proc. Natl. Acad. Sci.
USA 115: 1582–1587.
10.
Jahan-Tigh, R.R., C. Ryan, et al. 2012.
Research Techniques Made Simple: Flow
Cytometry.
Journal of Investigative Dermatology. 132(10):
1-6. Retrieved from: https://www.sciencedirect.com/science/article/pii/S0022202X1535487
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