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Normally, if an epithelial cell is sloughed off and
accidentally enters the bloodstream it will die.
In the last section, we covered that and that form of cell death is known anoikis.
Other methods of death include immune cell destruction because
the immune cells undergoes surveillance of the circulation at all times.
And if there are foreign cells or
foreign bodies the immune system will clear them out by phagocytosis.
Another method in which a cell that gets in the circulation can die
is by shear blood pressure which can cause extreme cell lysis.
Especially, going from the venous system into the heart and
back out of the heart, so a cell must survive that as well.
So cancer cells or CTC evade all three of these forms of cell death.
That is anoikis, immune surveillance and shear blood pressure.
And they are able to enter the circulation, and
go undetected for a period of time.
And this is a active area of research right now, so
a CTC is short for a circulating tumor cell.
And it is a cell that has entered the bloodstream and, or lymphatics, and
has the ability to survive for a period of time while in the circulation.
CTCs have been shown to exist as a single cell or,
as a hetero-cellular cluster of cells that can travel throughout the human body.
On the left, you can see a breast cancer that is localized and upon magnification,
you can see that the primary tumor typically is hetero-cellular as well.
And these cells can enter into the bloodstream directly or
through the lymphatics and then into the bloodstream.
As a single cell or a CTC cluster And then metastasis to a distant
site such as the lungs as a single cell or as a hetero-cellular cluster.
Again, a circulating tumor cell has the ability to evade anoikis
as lost metastasis suppressed genes and
fit to withstand blood pressure to get to the lungs.
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One piece of evidence that shows that have valuable CTC
are the sales that eventually form a test is this data shown here.
The more CTCs that are present in the blood of a cancer patient,
the worse that cancer patients prognosis is unfortunately.
This graph shows that when fewer than 5 CTCs were found in 7 milliliters of blood
of a breast cancer patient, those patients median survival was about 22 months.
However, when 5 or
more CTCs were found the median survival dropped to about 11 months.
In fact, the detection of CTCs is a very hot area in cancer research
because it can be used as a diagnostic and screening marker for metastatic disease.
You can imagine how difficult this is, though, in seven millilitres of blood.
There are about 50 to 60 million white blood cells on average
in the cancer cell can be hard to find in that volume.
Typically, cancer researchers only find about five CTCs in their volume.
While it is difficult in requires impressive biotechnology techniques to do
it, this is an area under investigation that we believe can help patients.
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CTCs have also been shown to associate with several other cell types.
One of these cell types are platelets.
Platelets are a nuclear cells that are involved with clotting vessel injuries.
They are found in large numbers in the blood and contribute to angiogenesis.
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Platelets also have the ability to transfer
Major Histocompatibility Complex Proteins onto CTCs, so
that the immune system does not detect them.
This allows for evasion of the immune system.
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Another cell type that has been shown experimentally to associate with CTCs
are M2 Macrophages.
M2 Macrophages are a type of white blood cell that is important for wound healing.
And these cell types have been shown experimentally to allow a cancer cell
to undergo epithelial mesenchymal transition as well as intravasate.
In experimental models in vitro,
isolated CTCs have been shown to have the proclivity to recruit cells
belonging to a myloid lineage using factors known as cytokines.
This association with myeloid cells allow CTC cells to
suppress the cell proliferation of T-cells which will target
any foreign cells by listening in the nearer response.
But this cells of regulate programmed death ligand 1 a notable checkpoint
ligand which blocks T-cell proliferation and
allows cancer cells to survive within the circulations.
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CTCs can interact with the host of others cell types while in the bloodstream
Highlighted in this illustration are platelets associated with
circulating tumor cells, monocytes associated with circulating tumor cells.
And also highlighted in this illustration is that circulating tumor cells can
have a expression of programmed death ligand 1.
Which binds to PD1 on T-cells and allows CTCs
to evade immune destruction by factor T-cells.
Let's take a closer look at the programmed death ligand 1 signaling,
shown in this illustration are two cell types.
Tumor Cells and Myeloid Cells can express programmed death ligand 1 or
programmed death ligand 2.
They bind to PD1 on T-Cells or
B-Cells and can cause B-Cells to
stop proliferating by down regulating the Psychiatric Kanis Pathway.
This is a very hot area of scientific investigation,
clinically specially with a lot of check point and
hemorrhoids in the bodies that are available to cancer patient.
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Survival during systemic circulation.
Once cells get into the blood stream they face an uphill battle.
They have to survive the circulation of the blood from the vein in which they
enter from whatever organ it may have originated from to the heart,
back out the lungs, back to the heart.
And then, throughout the arterial system where it could go anywhere and
wind up anywhere.
Sometimes, a circulating tumor cell, may just stop in the lungs and never really
into the systemic arterial system and could just develop lung metastasis.
During the transit throughout the CTCs must survive various forms of cell death,
which we've highlighted previously.
Currently, this is again a very hot area and is under investigation
to try to find CTCs from patients.
In our laboratory, we are able to detect circulating tumor cells
in blood from prostate cancer patients using prostate cancer markers.
This is what we do here at Johns Hopkins University School of Medicine.
We are able to obtained seven millilitres of blood from patients that consent and
what we do is we used markers.
They are found only on cancerous cell types from prostate cancer.
And are not on blood cell types to determine the number of
circulating tumor cells in a given sample.
Here, we use HOXB13 and
NKX3.1, both of which are expressed in prostate cancer cells.
We use DAPI, which Stains for nuclei and that's blue.
And we use a host of white blood cell marker such as CT45 to
discern a CTC from a white blood cell and shown as one CTC.
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From another cancer patient,
we obtained 7 milliliters of blood and
looked for HOXB13, NKX31.
Pan Cytokeratin positive, CD45 negative cells.
And then when we did a merge on the left side of the screen
you can see cells that are HOXB13 positive, NKX3.1.
Pan Cytokeratin positive and
white blood cell marker negative shown here and
also in the bottom we are able to brightly see a CTC, that is NKX3.1.
HOXB13, Pan Cytokeratin positive, but white blood cell marker negative.
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So recap for this section,
a CTC is a cancer cell that has the ability to survive while in circulation.
They can exist as a single cell or heterocellular clusters.
CTCs can associate with a host of different cell types,
notably immune cells while in circulation.
This association helps CTCs in various ways to evade immune destruction.
Finally, immune checkpoints expressed on T-Cells allow them to target foreign cells
In the blood.
However, CTCs and their entourage
can express programmed death-ligand 1 which allow immune circumvention.
Kenneth J. Pienta, M.D.The Donald S. Coffey Professor of Urology
Jelani ZarifProstate Cancer Researcher
Sarah AmendProstate Cancer Researcher
Haley AxelrodProstate Cancer Researcher
Kenneth ValkenburgProstate Cancer Researcher
