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Hello, I'm Don Ganem, I'm a professor of microbiology and infectious disease at the University of California in San Francisco
and investigator of the Howard Hughes Medical Institute.
I'd like to tell you today about one of the great detective stories
of contemporary biomedical research.
It's a story about a tumor called Kaposi's sarcoma. It was discovered over 130 years ago
and it was once thought to be very rare, but in the late twentieth century, with the supervention of the AIDS epidemic,
this tumor became one of the important public health problems in America and Western Europe
and it continues to be a public health problem in Africa and the Mediterranean basin.
It's a story that involves many different lines of work, clinical medicine, epidemiology, virology, molecular genetics, cell biology.
And for that reason, it's a fun story to talk about in a venue like this.
One of the most interesting things about KS is that it reveals how much physicians and scientists can learn from one another
if they would only learn how to listen to one another.
So, I'm going to tell you this story in a historical way, and we're going to begin at the beginning.
So, let's start with considering a little bit about KS as a disease.
So, our story begins back in 1872 with this man, Moritz Kaposi.
Kaposi was a dermatologist in Hungary and he described initially 5 patients with what he called "multiple idiopathic,"
idiopathic means we don't know what causes it,
"pigmented nodules of the skin."
Now, we recognize that this tumor, which predominantly involves the skin,
comes in several different forms. So, the classical form, this is the form that is generally attributed to Kaposi,
is an indolent tumor. This is a tumor that patients can live with for many years.
It's often said in medicine that KS is a tumor that patients die with, but not of.
It's an indolent tumor principally involving the skin. Kaposi described it in elderly men of Mediterranean extraction,
but now we know that other groups can be affected as well.
The tumor is typically localized to the lower extremities, and very rarely disseminates,
fewer than 10 percent of cases have dissemination outside the skin.
Many years after Kaposi died, it was recognized that KS also occurs in Africa
and is in fact more frequent in Africa than it is in the Mediterranean basin.
In fact, before the AIDS epidemic occurred in Africa, in a cancer hospital in Kampala, Uganda,
10 percent of all the surgery that was done for cancer was done for Kaposi's sarcoma.
So, this is an extraordinarily common tumor in Africa.
Clinically the endemic form resembles the classical form,
except that the disease a) occurs in younger people and b) can be locally invasive, invading underlying bone and other structures.
It is also common for the disease to involve lymph nodes in young children.
Now, in the mid-20th century with the advent of organ transplantation,
another form of KS was soon discovered.
And this is a form that is histologically very similar to the traditional form, but is much more aggressive in the clinic.
There's widespread dissemination to many sites in the skin and dissemination to organs
and this is attributed to the immunosuppressed nature of a transplant recipient.
And finally, as I think everyone knows, with the advent of the AIDS epidemic,
the most aggressive form of KS was described, KS became an extraordinarily common tumor in patients with AIDS
and in AIDS, as in the transplant recipient, it is a very aggressive disease.
The disease can be widespread, involving large regions of the skin, as I'll show you.
And can even involve major viscera, like the lungs.
At this level of the discussion, it's very important to emphasize that all these forms of KS have a common histology.
Under the microscope, they are virtually indistinguishable.
These differences have to do with their distribution, their tropisms for different organs,
in the whole organism, but under the microscope, it appears to be one process.
Now, let's talk a little bit about classical KS because this form of the disease undergoes a very slow evolution in the patient over time.
It begins, as you can see at the top of the slide,
with what's called a patch lesion. This is the earliest lesion that a dermatologist can recognize as being KS.
And as you can see, this lesion on the arch of the foot, is not even a mass, it's not even a nodule,
it's a flat region that's red and if you were to biopsy this lesion,
you'd see that in addition to the tumor cells of KS, there are many inflammatory cells,
T-cells, B-cells, monocytes and macrophages.
They're almost more prominent at this stage than the actual tumor itself,
so you can see, there isn't even a mass here yet.
With the passage of time, there is evolution to this so-called plaque-like form.
The lesion gets slightly elevated, becomes harder, indurated, and it's a little bit swollen, or edematous.
And with time, and this usually takes years, those plaque-like forms evolve into the nodular form,
shown below. This is an actual mass, it's in this case a dome shaped mass,
and as you can see, all of these lesions are discolored and they're discolored a reddish purple.
And the reason for that is that all of these lesions are displaying a tremendous number of new blood vessels.
I think you can see in the patch lesion at the top that the lesion is red.
If you were to press on that lesion, it would blanche, all the red cells, all that red is coming from red blood cells
inside of new blood vessels in the tumor. So, this is a highly angiogenic tumor.
As the lesion progresses, you can see it becomes darker and darker, more purple,
patients often think they have a bruise that isn't healing,
and the reason for that is that these new blood vessels that are formed in this tumor
are not normal and they're fragile and they rupture and red cells leak out into the tissue and undergo degradation
and as they do, their heme pigments get discolored and oxidized and that's what's responsible for the purplish hue of the lesion.
But you can tell from the fact that the lesions are red or purple to the naked eye
that these are loaded with new blood vessels, highly abnormal new blood vessels.
So, now we're going to move from classical KS to the form of KS that's much more familiar to Westerners
and that is KS in the context of *** infection.
And shown here is an example of an AIDS patient with dermal KS, KS of the skin.
And you can see, unlike those classical lesions where there might be one or two or three spots on the lower extremity,
here, we see dozens of spots all over the torso. But again, if you were to biopsy each one of these spots,
it would look, under the microscope, just like the lesions in the classical case.
There are just more of them and they are widely spread over the entire body.
These lesions can be very disfiguring when they occur on the face,
first of all, they cannot be hidden and they become obvious stigmata of the underlying immunodeficiency.
They're very socially stigmatizing.
You can see in this patient, virtually the entire bulb of the nose has been replaced,
the ears extensively replaced, and that is actually a feature of KS lesions,
that they tend to occur at the tips of extremities, at places where the temperature is slightly lower than the core body temperature,
for reasons that are still unexplained, the nose, the ears, the tip of the ***, the toes,
these are all places where KS lesions tend to get very bad.
The other feature of KS in patients with AIDS is that large, confluent areas can be seen,
as in this patient, and interestingly, these confluent areas are often symmetric.
You can see in this case, both thighs are very extensively involved with nearly confluent regions of KS
in addition to the patches of KS over the torso.
So, again very potentially disfiguring.
But even though all of those skin lesions are stigmatizing and disfiguring,
the skin disease, as bad as it can be, and it often requires X-ray therapy for palliation,
the skin disease, no matter how bad it is, is not life threatening.
So, what kills patients with AIDS related KS?
What kills them is involvement of vital organs
and the most commonly involved vital organ in AIDS related KS is the lung.
So, shown at the top here is a chest X-ray of an AIDS patient with pulmonary KS
and you can see that both lungs are heavily infiltrated with abnormal tissue.
And this tissue, if you biopsied it, would prove to be KS.
At the bottom, there's an example of an autopsy specimen of the stomach of a patient who had developed KS in the stomach.
KS frequently involves the gastrointestinal tract,
less commonly in the stomach than it does in the colon.
But as you can see again, the mucosal surface of the stomach is studded with red spots that, on biopsy, proved to be KS.
Patients die of these complications, especially pulmonary KS leads to respiratory failure.
Intestinal, or a GI KS, can lead to abdominal pain and occasionally bleeding.
But the most common cause of death from KS is pulmonary KS and lung failure.
Ok, now, I've been using the word sarcoma to describe KS and that would imply that KS is a traditional form of cancer.
So, a sarcoma, for those of you who don't know, is a cancer of the connective tissue,
of the mesenchymal tissues, muscle, fibrocytes, et cetera.
KS is named a sarcoma but in fact, it is a very atypical lesion and differs from classical cancer in many ways.
And the first and most important way is at the level of the light microscope.
So, if you look under the microscope of most tumors, they are monotonous,
they are the product of the clonal outgrowth of a single cell and a slice through that nodule
would show that, you know, a fairly monotonous collection of tumor cells, which are all derived from the same cell
and are therefore all of the same cell type.
When you biopsy KS, it's quite a different story.
There are many different cell types in the lesion, as I'll show you in a second.
When the lesion becomes nodular, the main cell in the mass is something called a spindle cell.
And it's called a spindle cell because it is shaped in an elongated, it is an elongated shape, structured like a spindle.
For many years, pathologists discussed what cells gave rise to spindle cells,
now we know that they derive from endothelial cells.
Endothelial cells are the cells that line blood vessels and lymphatics.
But in addition to those spindle cells, the tumor cells, there are many inflammatory cells, as I've mentioned.
T-cells and B-cells, monocytes and macrophages, and then there are these abundant abnormal new blood vessels, or neovascular spaces,
oftentimes with extravasated red cells, red cells that have leaked out of them into the tissue.
And then had their globin pigments degraded to something called hemosiderin.
So, here's a light microscopic section through a skin lesion of KS
and you can see at the top, the epithelial cells of the skin, they're normal, and they're not involved,
the process of KS involves the deeper regions of the soft, of connective tissue underneath the skin.
This is the so-called dermis, so, the epidermis, the epithelial cells are normal,
the process involves the dermis and right off, you can see even without being a pathologist,
that there's a lot of red stuff in this section.
All that red stuff are red blood cells within new, abnormal vascular spaces.
So, you can see right away the tremendous angiogenic component here.
It's harder to see at this magnification, but there are scattered throughout the dermis, a lot of inflammatory cells,
B-cells, T-cells, et cetera, monocytes.
And, in addition, weaving in and out of the plane of the section are the spindle cells.
You don't see them very well in this image because they are weaving in and out of the plane of the section,
when the microtome goes through the section, you can't see them well.
But every once in a while, just by chance, the microtome will cleave them along the correct sectional plane
and you can see them. So, here's a nice example from a case of KS in the GI tract,
and here, you can see the spindle cells lined up as they've been cut along their long axis.
And you can see now why they're called spindle cells, because they are very elongated.
Now, I like to think of KS, so, KS is clearly an extremely complicated process under the light microscope.
I like to think of KS as being derived from three components that are not independent of one another,
but that can be thought of slightly separately.
Of course, like any cancer, there's a proliferative component.
And in the case of KS, the cells doing the proliferation are these spindle cells.
They're the cells that are going to give rise to the mass, or the nodule at the end of the day.
In addition, there's a process of inflammation and on top of that, is a process of angiogenesis.
These things are related to one another, but we're going to think and talk about each of them separately
because the viral infection that causes KS makes separate and different contributions to each one of these things.
Ok, so what is the origin of the spindle cell? I've mentioned to you already that everyone's confident that they are derived from endothelial cells,
the cells that line blood vessels and lymphatics,
and that is derived from the fact that they stain for a variety of endothelial markers,
CD34, CD31, are present in most spindle cells, but spindle cells are themselves a heterogeneous collection.
Most of them don't stain for classical endothelial markers, like Factor VIII or Von Willebrand's factor,
but a few percent of them do.
So, that's another feature of spindle cells, they're not monotonous, they're heterogeneous.
They're not uniform. A big question has been whether they're derived from vascular endothelium,
the cells that line blood vessels, or lymphatic endothelium, the cells that line lymphatic tubes,
structures that drain fluid from tissues.
And for many years, there was a conviction that KS derives from lymphatic endothelium,
and that may be so, what drove that conviction was the fact that markers like podoplanin, VEGF receptor-3 and LYVE-1,
which are classical markers of lymphatic endothelium, regularly stain a KS lesion.
But all of this conventional wisdom was overturned in 2004 when it was described by several groups,
Chris Boshoff, Mike Lagunoff, Michael Detmar, that when KSHV infects vascular endothelial cells in culture,
it causes them to express many lymphatic markers.
Conversely, if you infect lymphatic endothelium in culture with the KS virus, they often express many vascular endothelial markers.
And this reprogramming of endothelium may explain why KS cells display markers of both lineages.
So, I think we're probably never going to know for sure whether KS derives from a lymphatic or a vascular endothelium,
because the viral infection that's linked to this tumor changes the expression program.
So, at the moment, we have simply to say that they're of endothelial origin and leave it at that.
Now, I want to emphasize a bunch of other extremely unusual features of KS.
Things that strongly differentiate KS from ordinary, garden variety cancer.
First of all, the lesions are multi-centric, I think you're already seen that, that these lesions occur all over the body
and interestingly, they don't occur in a pattern of a primary tumor followed by a bunch of metastasis.
Most patients will come to medical attention, yeah, they have three or four spots that appeared more or less simultaneously,
and they're partner noticed three or four additional spots on the back.
Not a story of one mass followed by, later in time, a lot of other distant metastases.
And in fact, if you biopsy these different lesions, you can often show that they are not related to one another.
KS lesions are frequently oligoclonal or polyclonal.
Now, there are examples in the literature of clonal KS.
And I think this is consistent with the idea, that like any polyclonal process in evolution,
over time, some clones will do better than others and there will be cases where all the lesions are related to one another.
But biopsies and clonality studies tend to show that many of these lesions are not related to one another
and represent independent occurrences. One's always taught in classical cancer biology that tumors are genetically unstable,
this is what drives aneuploidy and chromosomal rearrangements in tumors.
That kind of genetic instability is not a feature of KS.
KS spindle cells, if micro dissected out and examined, don't have any chromosomal rearrangements.
Typically, they're diploid. Now, there are rare exceptions to that,
but by and large these tumors are not nearly as genetically unstable as classical cancer.
And another feature that's quite striking, is that, and this was well described in the classical era,
even before the AIDS epidemic, that rare cases of spontaneous remission of KS are known.
It's not especially common, but it does happen, and it happens much more frequently in immunodeficient patients
if immune function is partially restored.
So, transplant patients who have their dose of cyclosporine lowered will often have a remission,
without any chemotherapy and this is also frequent in AIDS patients whose underlying *** disease
is arrested with antiretroviral therapy. So, that does not happen in patients with lymphoma or lung cancer,
who have these similar ministrations. So, again, we're talking about a disease that's really on the cusp between the benign and the malignant.
One particularly interesting feature of KS that I want to spend quite a bit of time on in this lecture
is the fact that there seems to be a relationship with other inflammatory states.
Back in the 80's and early 90's, before the advent of good therapies for ***,
doctors who saw patients with KS often remarked on the following sort of occurrence.
Patients with stable dermal KS, who had a few lesions of KS but were otherwise not seriously afflicted,
if they came into the hospital with an AIDS related infection, pneumocystis pneumonia,
cryptococcal meningitis, something like that, a severe inflammatory state, and if they survived that infection,
in the weeks that followed, sometimes their KS would rage out of control and have widespread dissemination of dermal KS
or develop visceral KS. Again, this wasn't a uniform occurrence,
but it was frequent enough to be noticed by many practicing AIDS clinicians.
Another example of that is shown here.
Patients with KS at a distant site, if they undergo surgery, may develop a local lesion of KS right at the site of the incision.
So, this is a slide illustrating a patient who had gum surgery
and six days after the surgery on the gums,
developed a florid lesion of KS right at the site of the incision
and this tumor was so bad that it ultimately had to be treated with X-ray therapy in order to be resolved.
And this is an image from a paper by Jennifer Webster-Cyriaque, a very talented AIDS clinician in North Carolina.
So, this is a well-known phenomenon in clinical medicine.
So, there appears to be some very strong relationship between local inflammation
and the development of KS.
Now, KS was a difficult process to study in the laboratory for many years
because it was very, very difficult, it turned out, to grow KS cells from a clinical lesion.
This problem was solved by Bob Gallo at the NIH in the late 80's and early 90's.
He developed methods for growing KS cells reproducibly in culture
and the trick was something that was very counterintuitive for a cancer biologist.
In cancer biology, we always tell students that cancer cells lose their dependence on exogenous growth factors.
This is why, for example, many cancer cells will grow in low serum.
That's considered a classical sign of transformation.
With KS cells, it's just the opposite. These cells have an exaggerated dependence on extracellular growth factors.
Gallo showed that the only method he could develop that would reproducibly allow spindle cells to grow from a KS biopsy
was to grow them in the conditioned medium of activated T-cells.
A cytokine and growth factor rich environment.
Even when cultivated like that, and they could be maintained indefinitely in such a medium,
but they didn't display the properties of morphologic transformation.
They didn't undergo, they wouldn't grow in soft agar, they wouldn't form tumors in nude mice.
In fact, Gallo showed, with Barbara Ensoli that if these cells were implanted into a nude mouse,
they would survive for ten days, maybe two weeks, and then involute.
During the time that they survived in the mouse,
they provoked a transient angiogenic response in the surrounding murine tissue.
And then when the human implant disappeared, or apoptosed, that angiogenic process involuted.
So, these experiments, and the clinical behaviour of KS and the histology of KS,
gave rise to a general understanding that what KS is really about is that it's a disorder of paracrine signaling.
It's spindle cells produce pro-inflammatory and pro-angiogenic factors
that recruit these inflammatory T- and B-cells and monocytes into the lesion.
Those inflammatory cells in turn recruit more inflammatory cells through the production of cytokines and chemokines,
but also, cross-feed the spindle cell component, supplying it with survival factors
that are necessary for the prevention of apoptosis and possibly growth factors that stimulate their proliferation.
So, all of KS could be understood now as a complicated paracrine minuet
where these different cell populations that are visible in the biopsy
are talking to one another, communicating with one another in a complicated way.
And that leaves us now with the question, how does this all begin?
What is the factor that initiates that process?
And this is where we'll pick up in part 2.