Download Advances in Immunotherapy: Abhijit Guha Award Presentation

GENERAL SCIENTIFIC SESSION 4
GENERAL SCIENTIFIC SESSION 4
Advances in Immunotherapy: Abhijit Guha Award
Presentation
John H. Sampson, MD, PhD,
MBA
Department of Neurosurgery, Duke University Medical Center, Durham, North Carolina
Correspondence:
John H. Sampson, MD, PhD, MBA,
Department of Neurosurgery,
Duke University Medical Center,
DUMC 3050,
Durham, NC 27710.
E-mail: [email protected]
Copyright © 2016 by the
Congress of Neurological Surgeons.
CLINICAL NEUROSURGERY
A
lthough my area of expertise, the area that
I have studied most, is immunotherapy, I
wanted to start by taking a step back and
looking a little bit at cancer in general. Despite
what we know about cancer, until quite recently
perhaps, we have had a very difficult time treating
this disease, and it still claims the highest number
of lives in the United States. When it comes right
down to it, cancer is actually a very simple process.
It really just involves a mutation of a gene, a very
small change in something that is actually quite
simple. Yet, we still have such a difficult time
trying to understand how to treat this disease.
When I started in the field of neuro-oncology,
most people were working on chemotherapy and
small-molecule inhibitors. The thought at the
time was fairly simple: There was a particular
pathway that would be activated by a mutation,
and the activation of this pathway could be
stopped by a small-molecule inhibitor or by
inhibiting the particular genes and proteins
downstream that this mutation was causing to
be overactive or underactive, leading to autonomous cell growth. What we certainly learned very
quickly is that tumors are not quite that simple
and that tumors activate and inactivate genes and
dysregulate cell growth in many ways. As we
stopped one pathway, another would pop up, and
then another and another. We really cannot stop
cancer this way except in rare circumstances.
Cancer is very darwinian; it does not have a plan
going forward. It simply randomly mutates, and
when it finds something that is advantageous,
something that thwarts our best efforts at therapy,
it simply uses that pathway. This unpredictability,
of course, makes it very, very difficult for us to have
any sort of organized approach to cancer therapy.
In thinking about this, I decided to take
a different approach, and 20 years ago, I went
into the field of immunotherapy. I was told that it
was a career-ending decision, which I did not take
lightly. Yet, looking back now, I must say that I
could not have timed this change better because
the field of immunotherapy has become the most
important area in cancer therapy. Today, and for
the past couple of years now in fact, more than
half of the drugs for cancer approved by the Food
and Drug Administration have been immunotherapies. So, my timing was perfect, but it was
not always clear which road I should travel.
Many people for many years rejected the idea of
immunotherapy, even though it was not a new idea.
We did not understand much about the immune
system, and we would typically be shunned at many
scientific meetings because immunotherapy was
thought to be hocus pocus or pseudoscience. Since
that time, and over the past couple of decades, we
have learned a tremendous amount about the
immune system. We have learned that tumors
actually can produce antigens that will be delivered
to dendritic cells (DCs) and that we can use these
antigens (proteins that are shed by tumors) to
immunize patients. When we immunize patients,
we can have these cells transmit the information to
the lymph node, where they interact with T cells.
We also learned that the tumor has innumerable
ways of thwarting that response and reducing our
ability to produce an effective immune response
against the tumor. More recently, we have understood that this interaction between DCs, which
coordinate the immune responses in our body, and
T cells, which are the executors of that response, is
very complex. Understanding this biology has now
led to a number of therapies that I think will show
a great deal of promise in our field and have already
shown a great deal of promise in other cancers.
I was very fortunate early in my career to have
mentorship by people such as Darell Bigner and
Bert Vogelstein, who, along with Albert Wong,
discovered the type III epidermal growth factor
receptor mutation (EGFRvIII) 2 decades ago.
When I started in the field of immunotherapy,
many of the proteins that were being targeted
were overexpressed normal proteins, that is,
proteins that were stimulating cell growth and
were overexpressed by the tumor cell, causing
their continued growth. These are proteins that
are normal, and our immune systems have
exquisite systems with multiple levels of backup
to make sure we do not respond to normal
proteins in our body, which protects us from
autoimmunity. I also realized that if we were
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SAMPSON
effective at targeting these normal proteins, we might expect that
we would have a tremendous amount of toxicity, because targeting
those proteins would lead to autoimmunity. As we have progressed
in the field of immunotherapy, every time we have tried to target
normal proteins, and we have done that successfully, it has led to
autoimmunity, sometimes life-threatening autoimmunity. So,
starting to focus my interest then on tumor-specific mutations
seemed like a logical approach, but what was a disappointing
surprise as we started to learn more about the genetics of these
tumors was that most of the mutations in tumors are simply
random, very incidental to the oncogenic process, and, perhaps
most important, patient specific.
Tumorigenesis appears to be a very darwinian approach, and
every patient is different, so it became very difficult to understand
how we might develop drugs that would target patients in a broad
way. The EGFRvIII served as a very good example because it was
fairly frequent in tumors such as glioblastoma, where it occurs in
about a third of patients. It was also consistent from patient to
patient, and it really was important to the oncogenic process.
In the EGFRvIII, there is a deleted segment, a part that is
removed from the extracellular domain. It splits the gene in a way
that maintains the read frame but inserts a novel glycine and brings
2 distant parts of the protein together. This protein sequence then
becomes something that is not present anywhere else in the body
but is present only in the tumor. That is exactly what we would
hope the immune system would be able to respond to, so we simply
took that protein sequence and attached it to a nonspecific
adjuvant called KLH. This drug now is known as Rindopepimut
because it has been licensed to Celldex Therapeutics.
The first thing that we noticed, in fact it was Amy Heimberger
who noticed it, was that patients who received this vaccine, even
though some of them would experience recurrence, no longer
expressed EGFRvIII mutation in their tumors. Wild-type expression was maintained, however. This suggested to us that maybe we
were doing something. As many of you know, single-arm phase II
trials can often provide misleading results. However, if we can build
evidence that we are doing something biologically, we can have
more confidence that we are actually having a significant effect.
The other thing we started to notice was that patients with bulky
tumor masses started to have radiographic responses, which
certainly was unexpected. We almost naively expected responses
to occur very quickly. With immunotherapy, as has been borne out
now over the long term, the responses are often quite delayed,
sometimes taking 3, 6, or even 9 months, and sometimes, patients
with these types of responses actually have an increase in the
enhancement of their mass before it starts to shrink. This
information and findings from a number of phase II trials at both
Duke and MD Anderson and then across the United States
showed that we were perhaps extending survival in these patients,
and that led to what we call the ACT IV Trial, a large, blinded,
randomized trial conducted at . 240 sites in 26 countries
worldwide that recently completed accrual.
In the meantime, because we had started to see some responses
in patients with bulky disease, we asked whether patients with
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recurrent tumors and bulky disease might also respond to
immunotherapy. This went against the conventional wisdom that
tumors were so immunosuppressive that we really could not treat
bulky tumors. The ReACT Trial was developed to study this
theory and was led by Dave Reardon and me. This study took
patients who had not received bevacizumab and randomized them
in 1-to-1 in a blinded fashion to receive bevacizumab and a control
vaccine, which consisted of everything but EGFRvIII peptide, vs
the study vaccine, which included the EGFRvIII peptide. We
showed in those patients that we were able to see responses much
more frequently, almost twice as often, in patients who received
the control vaccine and that those responses were much more
durable. In addition, we were able to show that patients not only
could come off steroids more frequently but also could stay off
steroids for a longer period of time with these vaccines. Finally, in
both the intent-to-treat population (ie, any patient who was
considered for vaccine) and per-protocol patient population (ie,
those who received the appropriate protocol-based vaccine), we
saw a statistically significant improvement in survival. This is very
rarely, if ever, seen in patients with recurrent glioblastoma.
One of the difficulties with the EGFRvIII vaccine, however, is that
it attacks glioblastoma in only a third of patients and a particular
genetic subset. More than a decade ago, Charles Cobbs identified
antigens or proteins from Cytomegalovirus that appear to be present in
glioblastoma tumors. To date, this remains a controversial finding,
although multiple laboratories across the country have now
confirmed the finding. In fact, if you ask Cytomegalovirus biologists
what cells they use to grow their viruses in vitro, it turns out they use
glioblastoma cells. So, there appears to be a specific tropism for this
particular virus in these tumors. The IE 1 and pp65 proteins of the
Cytomegalovirus are present fairly homogeneously in these tumors,
but they are not present in the normal brain. This allowed us to
subvert Cytomegalovirus proteins for a tumor-specific vaccination.
Moreover, we knew very well how to produce immune responses
against viral antigens. We did an initial study targeting this virus, and
I must say that the results were not spectacular. As we would have
expected, patients died at about 18 months, and they progressed
usually within 6 to 12 months.
This failure caused us to think about what we were not doing right.
We looked at the literature and got the suggestion that if we did
something at the vaccine site to precondition it, then we might be able
to generate better immune responses. Taking a clue from some
preclinical data from other laboratories, we decided to do something
similar in our patients and randomize them to a skin preparation
before vaccination with unpulsed DCs or a shot of tetanus. These
were patients who were previously immune to tetanus. Our
hypothesis was that this would create sort of an immunologically
stimulated milieu in which our vaccine would be well received. We
randomized these patients to each arm, and then we gave them
Cytomegalovirus pp65 RNA–loaded DCs. Patients then underwent
standard-of-care treatment. On their fourth vaccine, we radiolabeled
the DCs that we gave at the vaccine site and looked at whether they
migrated to the lymphoid effectively. Each patient received either the
unpulsed DCs or the tetanus unilaterally and then received
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ADVANCES IN IMMUNOTHERAPY: ABHIJIT GUHA AWARD PRESENTATION
immunizations on both sides of the groin with Cytomegalovirus
pp65-pulsed DCs, but they had preconditioning on only the 1 side.
We saw the hot spots where we injected the vaccine and then saw
where the vaccine migrated to the lymph nodes. In the patients who
received preconditioning with unpulsed DCs, we saw a slight
increase in the migration of the vaccinating DCs to the lymph node
over what was present in the literature, but not much. However, in
the patients preconditioned with tetanus, we saw a considerably
improved migration of the DCs to the lymphoid, and of course, if
the DCs do not make it to the lymph node, then they are not going
to produce an effective immune response.
We also started to notice that tumors in these patients, the ones
in whom we saw better DC migration, were actually not
progressing. It turned out that there was a very strong correlation
between progression-free survival and overall survival and DC
migration. This study was randomized. It was prospective. It was
blinded. We were able to show that the progression-free survival in
the patients who received tetanus was . 36.6 months and the
overall survival was . 50 months. In fact, as these data have
matured, half of our patients who received this vaccine have lived
. 5 years with newly diagnosed, histologically confirmed
glioblastoma. Unfortunately, the control patients in this study
who received unpulsed DCs progressed and died, as you might
expect given the typical clinical course of glioblastoma.
We went to the laboratory to try to understand why this was
working, because I actually thought this was a fluke. I challenged
one of our graduate students, Kristen Batich, to try to understand
this. The first thing we noticed quite by accident, because we did
not expect this, was that when we put the DCs in both sides, even
though only 1 side got the tetanus, we got an increase in the
migration on both sides. This was one of those serendipitous
findings that someone brought to one of our laboratory meetings,
saying “Hey, I think there is a problem with the data here because
we really should not be seeing migration on the contralateral
side.” What we learned from that, or what we hypothesized from
that, was that this must be a systemic effect. Something must be
happening throughout the patient to help this migration occur
and maybe help stimulate the immune responses.
I think that most of the people in funding organizations would
this call this a fishing expedition, but because we had serum saved
from patients, we literally looked at every chemokine and cytokine
known to see if there was anything that would predict the
responses here. We did the same experiments in mice. Quite
fortuitously, we found that the chemokine CCL3, also known as
macrophage inflammatory protein-1a, was elevated not only in
all the mice but also in all the humans, and nothing else was
significantly elevated.
We then looked at CCL3 knockout mice to see if we could
reverse this effect if we knocked out this gene. We could. If CCL3
is knocked out, the enhanced DC migration completely goes
away. Perhaps most important, we were later able to show that if
we give CCL3 simply as a drug intravenously, we can produce the
same effects that tetanus does given intradermally. Therefore, we
now believe that we can use this chemokine as a drug to
CLINICAL NEUROSURGERY
profoundly affect immune responses throughout the host. On
the basis of these data in both our patients and mouse models,
along with the mechanisms studies, we were able to publish this
finding in Nature recently.
So, what are the current problems? Where will we fail to cure
patients with this devastating disease? As I mentioned before,
cancer is darwinian, and despite our attempts to vaccinate against
a particular antigen, the cancer may simply discard this antigen to
“adapt” to the immune response. So, unless we kill all the cells in
the patient, cells will remain that have a different genetic
complement, and those cells may again produce a tumor that
we have to reanalyze and reapproach through immunotherapy or
in combination with other therapies.
One of the main problems with immunotherapy is that there
can be what we call antigen escape variants, which make it difficult
for us to treat patients with just vaccines alone. Recently, however,
there has been an explosion in the field of a less specific
immunotherapy approach: checkpoint inhibition. These are
drugs, usually antibodies, that can either stimulate T cells or block
interactions that typically turn T cells off. A plethora of these drugs
are now coming on the market. In fact, these drugs have been
approved for several cancers, even stage 4 melanoma, for which
there has never been a drug that had significant efficacy.
Fortunately, we have been lucky enough to study this in
glioblastoma with Bristol Myers Squibb in a large, international,
randomized phase 3 trial looking at the PD-1–specific antibody
Nivolumab. Accrual to this trial has finished, and we should hear
results soon. However, there is some concern that patients with
glioblastoma may not have enough mutations for these drugs to
work effectively. It is starting to be shown that the number of
mutations in these cancers predisposes patients to respond to
these drugs. But what about patients with medulloblastoma who
have very, very few mutations? I do not think we are quite over
the wall yet with all of these cancers.
Finally, despite my initial comments that cancer was based on
a particular mutation that we can target, the reality is that as we learn
more about our genome, we find that there are a number of
alterations in tumor cells that are not specific mutations in the
genome. These are things like methylation or posttranslational
modifications of proteins that could have very profound effects and
may not be detected by the immune system. We still have a number
of challenges ahead, and I look forward to every milestone in the
journey as we continue the fight against glioblastoma.
Disclosure
John H. Sampson has held a consultant or advisory role for Celldex Therapeutics
and BrainLab; reports stock ownership of Istari, honoraria from Bristol-Myers
Squibb, and research funding from Celldex Therapeutics. He holds no employment
or leadership positions nor has he given expert testimony that conflicts with this
work. He receives funding under the Duke University Faculty Plan from license fees
paid to Duke University by Celldex Therapeutics. Duke University also has the
potential to receive patent-related royalties. John H. Sampson has an equity interest
in Annias Therapeutics, which has optioned intellectual property from Duke
related to the use of the pepCMV Vaccine in the treatment of glioblastoma
multiforme.
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