In the past, I’ve sometimes been accused of being a bit of an immunotherapy bear for my dislike of cancer vaccines as a single agent therapy in advanced disease where the tumour burden is very high. That particular field has undoubtedly been a huge graveyard for many companies, much in the same way that metastatic melanoma was, until novel therapeutics and immunotherapeutics emerged to push through the envelope.
To be clear, I am though, a big fan of targeted immunotherapies such as checkpoint inhibitors and chimeric antigen receptor (CAR) T cell therapies, which have been very much to the forefront in immuno-oncology over the last two years and rightly so, with some initial trials showing some very promising results.
Both of those approaches are squarely part of the adaptive immune system and seek, in different ways, to retrain the bodies immune system to fight the tumour. More recently, the innate immune system has seen new advances as reearchers moved beyond simple vaccines to develop more thoughtful and innovative approaches that seek to outwit the very masking the cancer is trying to fool the immune system with. It’s no less exciting, just a different way of looking at the science and improving out understanding of the biology of the many diseases that cancer makes up.
In this AACR preview, I take a broad look at some innovative and novel scientific approaches, including targeting anti-CD47 and SIRPα (Stanford and Stem Cell Therapeutics), KIR and MICA (Innate Pharma) and neutrophils (Biothera).
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There are basically three different aspects relating to the immune system that the body employs to defend itself with:
- Skin – acts as a physical barrier and performs wond healing as needed
- Innate immunity – what you’re born with
- Adaptive immunity – develops over time
Today we’re going to focus on the second aspect – innate immunity – and look at how the body can be used in the fight against tumours (liquid or solid). Elements of the innate immune system include neutrophils (the largest number by far), phagocytes, natural killer (NK) cells, and macrophages, to name a few. Their job is to [eat, ingest, kill or destroy] cells tagged by the immune system for disposal. As an layman analogy, I think of them as the Pacmen army frantically hurtling around gobbling up all the spots in the arcade game.
For this preview, I researched a number of emerging areas that utilise innate aspects, including CD47, KIR and neutrophils. There are some dendritic cell and other cancer vaccines in clinical trials, but they have not been included here. My simple view is that these are unlikely to be effective enough on their own and may need to be combined with adaptive immunotherapy approaches to unleash a greater effect on the immune system. Only this morning GSK announced that their MAGE-A3 phase III trial has been stopped in NSCLC once a subset analysis suggested that a gene signature was unlikely to predict responders.
We still have a long way to go figuring out what to do with the vaccine approach and there have been many more failures than success with these. It therefore make more sense to focus and highlight the exciting new approaches that look very promising. In this preview we look at three of them:
What is CD47 and why is there so much interest in it?
CD47 is a protein that is found on the surface of many cells in the body, both normal cells and cancer cells. Because it is not specific to cancer cells, it was previously dismissed by many as a potential oncology target in humans. About a decade ago, Irving Weissman’s lab at Stanford noticed that leukemia cells (AML) produced higher levels of the protein compared to normal cells so they started to create an antibody to CD47 to test in mice. More recently, they reported those results (Willingham et a;., 2012) in mouse xenograft models and validated the concept that a) the target could be blocked and b) a clinical impact was observed.
What raised CD47 expression does is block phagocytosis i.e. the ‘don’t eat me’ signal. How does it do this? CD47 binds SIRPα on the surface of macrophages, and transmits a signal that protects cells from macrophage attack. This negative signal allows cancer stem cells to evade being destroyed, thereby ensuring their proliferation and survival. The basic idea behind Stanford’s work is that inhibiting the CD47 protein with a monoclonal antibody will lead to increased tumour cell phagocytosis and elimination.
This is all well and good, but breathless news articles such as the NY Post the same year proclaimed the PNAS data, as if it were the holy grail of cancer research with the implication that it was the answer to all cancers, as you can see from the rather lurid headlines that ensued. Many of us no doubt winced, since the last thing anyone in this field wants to see is too much hype over hope, on the basis of five mice with transplanted breast cancers being miraculously ‘cured’!
We all know that curing mice with xenografts is a lot easier than doing the same thing in patients with advanced cancer. For a start, the microenvironment in a patient’s tumour is much more complex than a transplanted one, and the tumour can also have adaptive and immunosuppressive effects.
There are quite a few unknowns here:
- How well will CD47 antibodies work in man
- How they will play out with existing therapies
- Will they will be complementary or antagonistic?A
- Can be used alone or will combinations be necessary?
- Will targeting CD47 or SIRP lead to phagocytosis of normal cells such as red blood cells, thereby leading to severe anemia?
In the last point, granted oncologists are used to dealing with myelosuppression and infections while offering growth factor support either prophylactically or reactively, but if this could be avoided then so much the better.
The good thing is that we will hopefully soon find out the answers to a few of these questions since both Stanford (anti-CD47 antibody) and Stem Cell Therapeutics (SIRPαFc antagonist) will likely be moving out of preclinical research and into the clinic over the next couple of years. The proof of the pudding will clearly be results from patients, irrespective of the tumour type.
What is KIR and why is it a promising new target?
Killer Immunoglobulin (Ig) Receptor (KIR) is a family of extracellular domains that act as inhibitory receptors. They are surface glycoproteins expressed by some natural killer (NK) cells and T cells. They recognise human MHC class I molecules, which have been shown to regulate NK cell activity. There are three groups in the KIR family:
- Type I KIR2D genes, which encode two extra-cellular domain proteins with a D1 and D2 conformation
- The structurally divergent Type II KIR2D genes which encode two extra-cellular domain proteins with a D0 and D2 conformation
- KIR3D genes encoding proteins with three extra-cellular Ig-like domains (D0, D1 and D2)
In this preview, the third type are of particular curiousity since one of the promising abstracts explores activity with an anti-KIR antibody in KIR3DL2-positive lymphomas. Interestingly, KIR3DL2 nucleotide sequences are the longest of all KIR genes.
Immune facets that have an inhibitory function make attractive targets for therapeutic intervention because they are essentially stopping something from happening, so if the ‘switch’ or ‘lock’ can be turned on again then there is potential to elicit a more effective immune response against the cancer.
Neutrophils have long been considered impotent against cancers, so what’s new?
A detailed primer on the role of neutrophils in the innate immune system and how they can be unleashed was previously posted earlier this year (see post here).
One unanswered question at that time was whether biomarkers would be found to enable researchers to
- Predict who is most likely to respond to therapy and
- Change the odds of non-responders such that they might be more likely to respond.
AACR Abstracts of Interest:
1. Targeting CD47 as a valid immunotherapeutic approach:
This year’s AACR plenary looks to be pretty exciting with leading immunotherapy experts presenting overviews on a number of different areas.
PL02–02: Weissman will be presenting the latest state of play on CD47 so this is one topic that will generate a lot of interest. A detailed update will be posted after his presentation over the weekend.
3629: Weiskopf et al., Overcoming macrophage immunosuppression in small cell lung cancer with high-affinity SIRPa variants.
This is another abstract from Weissman’s lab in at Stanford. In this work, they look at the next-generation CD47 antagonists they have developed in SCLC, a cancer with poor prognosis and where no antibodies or immunotherapies have yet been approved:
“By themselves, the high-affinity SIRPa variants are inert and therefore non-toxic in mouse and primate studies. However, when combined with tumor-specific antibodies, the high-affinity SIRPa variants act as immunotherapeutic adjuvants to antibody therapies by maximizing the ability of macrophages to destroy cancer cells.”
The human SCLC samples they tested all expressed high levels of CD47 on their surface. In addition:
“In vitro, we found that CD47-blocking therapies were able to induce macrophage phagocytosis of SCLC cell lines and primary patient samples.”
Using flow cytometry, they then screened for antibodies in order to find novel SCLC antigens that can be targeted in combination with the high-affinity SIRPa variants:
“We identified several new and established therapeutic targets on the surface of SCLC cells, including CD99, CD56, CD166, CD326, and CD164.”
No doubt future studies “will test these immunotherapeutic combinations in vivo against SCLC samples to develop novel therapeutic combinations for patients.”
5011: Uger et al., Cancer immunotherapy targeting CD47: Wild type SIRPαFc is the ideal CD47-blocking agent to minimize unwanted erythrocyte binding.
Interestingly, the concern I expressed earlier about RBCs and anemia cropped up in this abstract:
“There are several approaches available to achieve CD47 blockade, including wild type SIRPαFc fusion proteins, engineered high affinity SIRPαFcs and monoclonal antibodies. One concern with CD47-based therapies is the expression of the target on the surface of red blood cells (RBCs), which has the potential to act as a large antigen sink and cause hematological toxicity.”
It turns out that might not be too far off:
“Indeed, anemia has been reported in animals treated with high affinity SIRPαFcs variants and CD47-specific antibodies.”
The group sought to explore whether a different approach using a wild type SIRPαFc antagonist would spare the erythrocytes compared with using a CD47 monoclonal antibody. Their initial data suggests that this might be possible:
“Wild type SIRPαFc, unlike other CD47 blocking agents, exhibits very low binding to human erythrocytes. This predicts that wild type SIRPαFc will have superior pharmacokinetic properties and less toxicity in cancer patients. Furthermore, the strong binding of wild type SIRPαFc to monkey RBCs suggests that preclinical studies in non-human primates may overestimate the risk of hematological toxicity in humans.”
4082: Anderson et al., CD47 blockade to enhance adaptive anti-tumor immune responses.
This academic research looked at whether inducing tumor cell phagocytosis by CD47 blockade would enhance T-cell-mediated anti-tumor responses. The rationale behind this was that it has been reported that CD47 blockade can hinder T cell activation. They found that:
“CD47 also was expressed on CD8+ T cells and was further upregulated upon stimulation, suggesting it might play a role in immune effector function. However, in our hands CD47 blockade using antibody MIAP–301 did not inhibit activation of CD8+ T cells in vitro, and in preliminary experiments, CD47 blockade appeared to enhance activation of antigen-specific CD8+ T cells in vivo.”
2434: Soto-Pantoja et al., from the NCI/NIH have an abstract entitled: Therapeutic targeting of CD47 regulates cell bioenergetics and autophagy to reduce breast tumor growth and protect against anthracycline-mediated cardiac toxicity.
Increassed expression of CD47 has been associated with poor prognosis in several tumour types, including breast cancer and TNBC. Cardiac toxicity has often been a challenge in these regimens, however. This group had some encouraging results to report:
“We now show that CD47 blockade significantly sensitizes breast tumors to anthracycline chemotherapy while protecting cardiac tissue from the off target effects of this drug.”
“Blockade of CD47 in tumor bearing mice protected cardiac tissue indicated by reduction in fibrosis and cell death. This was associated by an increase in autophagy gene expression… blockade CD47 enhances doxorubicin reduction of breast tumor growth in a syngeneic tumor model indicating that CD47 potentiates anthracycline-mediated breast tumor therapy while protecting normal tissue from death associated with cytotoxic therapy.”
What this research suggests is that there may be an unexpected cardio-protective effect a play against some common cytotoxics known to cause problems here. They were a little vague what agents they used, other than they were CD47 antibodies, but this work is quite encouraging and I hope to learn more in San Diego.
2. Targeting KIR in lymphomas:
651: Cardine et al., Ex vivo and in vivo characterization of IPH4102, a humanized anti-KIR3DL2 antibody for the treatment of cutaneous T-cell lymphomas.
IPH2102 (lirilumab) is an anti-KIR2 antibody (KIR2DL1,2,3) being developed by Innate Pharma and BMS for the treatment of hematologic malignancies such as AML and also solid tumours in combination with either ipiliumab or nivolumab. Many of you will recall the promising leukemia data at ASH last December, for example. Since then, the phase I expansion cohort for the solid tumour studies has already been announced and phase II trials are expected to start later in 2014.
At AACR this weekend, the focus switches to T cell lymphomas, where KIR3DL2 is expressed on several subtypes of T lymphomas/leukemias, and in particular, on advanced cutaneous T cell lymphomas (CTCL). IPH4102 is a humanized IgG1 that selectively kills KIR3DL2-positive cells in vitro through antibody-dependent cell cytotoxicity (ADCC).
Little data is available yet, but the company hint at solid results with:
“IPH4102 exerts remarkable anti-tumor activity against primary KIR3DL2-positive tumor cells ex vivo: using blood taken from Sézary Syndrome patients as experimental model, we demonstrated the efficient killing of primary leukemic cells by autologous NK cells engaged by IPH4102.”
The abstract is purportedly about lymphomas, so I’m not sure why leukemias suddently pop up since Sézary Syndrome is a type of cutaneous lymphoma that was first described by Albert Sézary, it could be an unfortunate typo though!
IPH4102 is currently in preclinical development with Innate Pharma (no partner as yet) and the company have stated that an IND application should be submitted in late 2014, suggesting this agent will be entering clinical trials soon. Note that Transformed Mycosis Fungoides (TMF) and Sezary Syndrome (SS) are the most severe forms of cutaneous T-cell lymphomas with a median survival of 2 to 3 years for their advanced stages. This is likely an orphan indication where new effective therapies are still needed despite several recent FDA approvals. More analysis will follow once the data has been presented at the meeting.
3. Targeting MICA and NK cells
The second abstract from Innate Pharma that piqued my curiousity explores MICA targeting. MICA (as well as MICB and ULPBs) is a ligand for the activating receptor NKG2D, which is expressed on NK cells and some T cells in man. MICA and MICB are expressed during cellular stress and during viral infections. In addition, they are up-regulated in tumor cells; the receptor-ligand combination may therefore play a critical role in the immune response of some cancers.
You can see how it all fits together in the schematic below:
The immune system relies on many signaling molecules to detect danger, and NKG2D appears to be an important contributor to this recognition. NKG2D also appears to function, at least in some cells, as a co-stimulatory molecule. T cell co-stimulation refers to activation of signaling pathways that are complementary to those activated through the antigen-specific T cell receptor.
5037: Blery et al, Targeting MICA with therapeutic antibodies for the treatment of cancer.
At present, Innate are in the late Discovery phase with this approach, having generated numerous compounds and will need further work to refine and select a final candidate for more extensive preclinical testing:
“Altogether, we have generated a panel of anti-MICA mAbs with diverse functional properties. Ongoing work aims to choose the best candidate for humanization and further clinical development.”
Conceptually, this is a unique and compelling idea. Much work will be needed to figure out which particular tumour types will offer the best shots on goal and which compound will provide the optimal pharmacocologic and clinical benefit.
For those interested in the company, Innate have a third abstract at AACR focused on BTG-ADC comparing their compound to Seattle Genetics brentuximab vedotin (Adcetris), although this is not the focus of this review.
4. Unleashing an army of neutrophils on solid tumours
Neutrophils are phagocytic and usually one of the ‘first-responders’ of inflammatory cells to migrate towards the site of inflammation. With cancer, though, because it arises from ‘self’ cells they may not respond to an ‘attack’ in the same way that they do with a wound or cut on the skin. They need to be mobilised to recognise the cancer as an enemy. What Biothera have been doing is precisely that – finding a novel way to to mobilise the army of neutrophils.
2834: Gorden Identification of a critical level of anti-beta glucan IgG antibody necessary for response to soluble beta-glucan therapy and its application as a biomarker for analysis in clinical trials.
At the recent IASLC meeting in January, Biothera presented some encouraging clinical data with their compound called Imprime PGG (see here). The agent is a “yeast derived soluble beta-glucan” immunotherapeutic. One obvious question that needed to addressed was could we learn something from the responders and find a useful biomarker that could predict a response?
In this follow-up research, it looks as though the answer may well be yes. Previously, the company have shown that:
“in vitro binding and functional response to Imprime-PGG in whole blood correlates with the level of anti-beta-glucan antibodies (ABA) as determined by ELISA.”
In the current work, Gorden stated that:
“In donors with high ABA levels, stimulation with Imprime-PGG corresponds with higher levels of complement cascade activation, neutrophil binding, modulation of surface markers and IL–8 production. Additionally we have shown that when intravenous immunoglobulin preparations (IVIG) containing high levels of ABA is added to a whole blood sample, it increases the binding and functional response to Imprime-PGG in vitro.”
They therefore hypothethised that:
“The level of ABA in patient serum could serve as a potential biomarker predictive of positive clinical outcome.”
What did the results actually show?
“The level of ABA is critical to Imprime-PGG response and provides evidence for an IgG ABA range where response to stimulation occurs that can be used a clinical biomarker.”
In other words, patients with high ABA levels are more likely to respond to the Imprime infusions and for those patients with low ABA levels, adding exogenous ABA may provide some clinical benefit by enabling a better response than they might otherwise experience.
More on this later after the data has been presented and I’ve had a chance to speak with the scientists, but it looks potentially quite promising thus far. I f the biomarker can be validated in clinical trials, then potentially the impact of this would be higher response rates in patients.
What does all this mean?
Immunotherapy, in multiple different forms, is very much coming of age with fresh ideas and new approaches driving some exciting technological happenings in oncology, both for liquid and solid tumours. While we have heard much about adaptive immunotherapy with CAR T cells and anti-PD–1 and PD-L1 antibodies over the last 2 years, we shouldn’t forget or ignore what is happening in the innate immunotherapy space. The potential for combining innate methods with existing therapies such as monoclonal antibodies or chemotherapies to reduce the tumour burden and then unleash the immune system is something to think about too. Granted, we are still in the early stages right now, and the there’s more that we don’t know than we do know, yet it’s a very exciting time for cancer research as immunotherapy begins to come of age.
Disclosure: I own stock in Innate Pharma and Stem Cell Therapeutics