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Roche – Nature Medicine Symposium on Cancer Immunology and ImmmunotherapySeptember 11–13, 2011, Nutley, New Jersey, USA

The idea that the human immune sys-tem can fight cancer is over a century old. During that time, the idea has

fallen in and out of favor. Scientists working to develop immunotherapies have, until recently, had mixed results. Dr. Mike Burgess, head of the Oncology Discovery and Translational Area at Roche, kicked off the meeting, not-ing that the field has seen “tremendous ups and downs.” But the approval of therapies such as the antibody ipilimumab (Yervoy) and the cell-based vaccine Sipuleucel-T (Provenge) suggests that immunotherapy will play an important role in the future of cancer treatment. Researchers are now devel-oping antibodies that can help the body over-come cancer-induced immune suppression, T cells that can target and destroy tumors, and vaccines that train the immune system to recognize and kill cancer cells. Some of these therapies seem to be proving effective in clinical trials. “At last we’re beginning to see the fruits of everybody’s labor,” Burgess said.

Despite recent successes, however, major challenges remain. Even the best immuno-therapies tend to be effective in some individu-als and not in others. Scientists are working to find new ways to identify the subsets of patients who will benefit the most. They are also inves-tigating ways to combine immunotherapies with other cancer treatments, such as targeted drugs, to get even greater clinical benefits.

Role of innate immunity in cancerThe symposium kicked off with a session focused on inflammation, which plays a dual role in cancer. Chronic inflammation, such as the kind induced by hepatitis infection, can promote tumor development by hindering an anti-cancer immune response. NF-kappaB, a protein complex that controls DNA transcrip-tion and plays a central role in inflammation, regulates genes that produce anti-apoptotic molecules and can contribute to the induction

of proliferative genes. Alternatively, tumor cells can secrete cytokines that attract cells involved in inflammation, creating an inflam-matory microenvironment that favors tumor growth, drives progression of the disease, and inhibits the immune system, preventing the destruction of cancer cells. Animal and cell studies of inflammation-induced cancers suggest that the interaction between cancer cells and immune cells is a “two-way street,” explained Dr. Michael Karin, a molecular biologist at the University of California, San Diego, and the symposium’s keynote speaker. “The pre-malignant cells can produce a vari-ety of chemokines that attract immune cells into the tumor microenvironment,” he said. And immune cells produce cytokines, some of which lead to the activation of key oncogenic transcription factors.

Dr. Karin’s work shows that tumor-driven inflammation can also promote metastasis and lead to treatment failure. In 2010, he and his colleagues found that inflammation plays a key role in relapse after androgen ablation therapy, a common treatment for prostate cancer that involves blocking the production of male hormones. The therapy kills cancer cells in a mouse model of prostate cancer. But the researchers observed that the dying pros-tate cancer cells recruit B cells, which produce an inflammatory cytokine called lymphotoxin. This protein prompts any remaining prostate cancer cells to proliferate, resulting in the growth of androgen-independent tumors. Therapies aimed at curbing the inflammatory response may help ramp up the body’s natural immune response and increase the efficacy of cancer therapies.

Macrophages play a key role in initiating and maintaining inflammation. One class of macrophages, tumor-associated macrophages (TAMs), can help drive progression of cancer by promoting the formation of new blood ves-sels and suppressing adaptive immunity. High

levels of TAMs are frequently associated with adverse outcomes and may represent a thera-peutic target. Professor Alberto Mantovani, an investigator at the University of Milan in Italy, and his colleagues found that trabectedin (Yondelis), an anti-cancer compound approved in Europe in 2007 for soft-tissue sarcomas, destroys monocytes (macrophage precursors), prevents these cells form differentiating into macrophages, and reduces the production of certain pro-inflammatory cytokines like CCL2 and interleukin 6 in monocytes and macro-phages. Prof. Mantovani postulated that the efficacy of trabectedin might be due in part to the drug’s ability to destroy TAMs. In patients treated with trabectedin, the drug reduced the number of tumor-associated macrophages and decreased markers of inflammation. In mice, the compound increased the number of T-cells and decreased the number of tumor-associated macrophages. Trabectedin appears to be selec-tive, inducing apoptosis in TAMs while leav-ing lymphocytes and neutrophils untouched. “This is as close as we can get to obtaining proof of principle that targeting macrophages in humans can result in clinical benefit.” Prof. Mantovani said.

In addition to driving progression of pri-mary tumors, macrophages can also facilitate metastasis. Tumors manipulate their microen-vironment to enhance their ability to grow and evade the immune system. Dr. Jeffrey Pollard, a molecular biologist at Albert Einstein College of Medicine, and his colleagues recently iden-tified a new class of metastasis-associated macrophages, or “MAMs.” These cells express a receptor called CCR2, which binds to the chemokine CCL2. Blocking CCL2-CCR2 sig-naling with a neutralizing antibody inhibited the recruitment of inflammatory monocytes, reduced metastasis and prolonged the survival of mice with cancer. Pollard and his colleagues found that MAMs facilitate the movement of circulating tumor cells from the primary tumor

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Another cancer immunotherapy still in the pipeline aims to limit immune suppres-sion by blocking a different receptor found on the surface of T-cells — programmed death-1 (PD-1). The main ligand for PD-1 is an immu-noglobulin-like molecule called B7-HI (PD-L1), which is found on many human cancers. Blocking PD-1 may enable a more efficient immune response in the face of cancer. In the first human trial, 39 patients with a variety of cancers were treated with intermittent doses of anti-PD-1. Two of the participants experi-enced partial responses and one experienced a complete response. Dr. Suzanne Topalian, an immunotherapist at Johns Hopkins University, and her colleagues are now working on a phase 1/2 multicenter trial of the therapy. This group is also investigating whether an antibody that blocks B7-H1 would have a similar effect in cancer patients.

Antibody-based treatments such as ipilim-umab and anti-PD1 aren’t without side effects. Drs. Allison and Topalian noted that ipilim-umab and the PD-1 antibody had the poten-tial to induce inflammation in normal tissues, causing toxicity in some patients.

Increasing the binding affinity of antibod-ies to existing cancer targets may also improve efficacy and lead to better clinical outcomes. Dr. Pablo Umaña, an investigator with Roche Glycart AG, and other researchers at Roche are working to engineer antibodies that bind more tightly by changing the sugar molecule. The team has developed two “glycoengineered”

They can make cancer cells more visible to the immune system, block the growth fac-tors cancer cells need to proliferate, and stop the formation of new blood vessels. They can also inhibit tumors from suppressing the local immune environment by blocking receptors on the surface of immune cells that normally pre-vent cell activation and proliferation. The idea of stopping the negative molecular feedback received a boost in March 2011 when the FDA approved ipilimumab, a new therapy for late-stage melanoma. A monoclonal antibody, the drug works by binding to CTLA-4, a receptor on cytotoxic T lymphocytes that would other-wise keep T cells from proliferating efficiently. “Since you’re treating the immune system and not the tumor this is potentially useful for any kind of cancer,” said Dr. James Allison, an immunologist at the Memorial Sloan-Kettering Cancer Center in New York.

Since the first trial in 2006, 6,500 patients have been treated with ipilimumab. Not every-one has responded to the therapy, but those that did “appear to be cured” Dr. Allison said. At the symposium, Allison reviewed the pre-clinical and clinical studies leading to ipilim-umab’s approval. Researchers are still trying to better understand ipilimumab’s mechanism of action as well as to identify those most likely to respond to the therapy. Combining anti-bodies like ipilimumab with cancer vaccines, targeted therapies or other antibodies that block immune suppression may enhance the antibody’s efficacy.

out of the blood vessels and into surrounding tissue. CCR2 represents a new target for breast cancer.

The innate immune system also includes natural killer cells, which can recognize tumor cells via a receptor on their surface called natu-ral killer cell p-30 related protein or NKp30. In patients with gastrointestinal sarcoma (GIST), NKp30 is downregulated, suggesting a dimin-ished ability of natural killer cells to find and destroy tumor cells or that NKp30 has already engaged with ligands. Notably, this receptor has three isoforms. Dr. Laurence Zitvogel, an oncologist at the Institut Gustave Roussy, and her colleagues found that expression of one iso-form (NKp30c) over the other two (NKp30a and NKp30b) correlated with reduced overall survival in 80 GIST patients. In the four years after these patients were taking imatinib, indi-viduals with the “c” isoform experienced 21 relapses and 15 deaths. Patients with isoforms “a” or “b” experienced 20 relapses but only 5 deaths. The “c” isoform sends an immunosup-pressive signal to dendritic cells promoting IL-10 secretion, which likely accounts for its association with poor outcomes. The NKp30 isoforms can be used not only as a biomarker to predict clinical outcomes, they can also help researchers select clinical trial participants.

Molecular advances in immunotherapyOne overwhelming message from the meeting was that antibody immunotherapies hold tre-mendous promise in the fight against cancer.

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Faculty of the Roche–Nature Medicine Symposium on Cancer Immunology and Immunotherapy. From left to right: Glenn Dranoff, Dmitry Gabrilovich, Alison Farrell, Robert Vonderheide, Pablo Umana, Hy Levitsky, Jim Allison, Mike Burgess, Laurence Zitvogel, Jacques Banchereau, Karolina Palucka, Juan Carlos López, Carl June, Jeffrey Pollard, Alberto Mantovani, Robert Schreiber, Michael Karin. Not pictured: Suzanne Topalian, Nick Restifo, Michael Caligiuri.

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in a single individual’s tumor. “Let’s make a vac-cine for that cancer patient and that tumor,” he said. But targeted therapies have their own drawbacks, pointed out Dr. Hyam Levitsky, head of Cancer Immunology and Experimental Medicine at Roche and Adjunct Professor of Oncology at Johns Hopkins. “If there’s a lesson in here for all of those who aspire to develop targeted therapies, it’s that there are multiple targets,” he said. “Just because [a drug is] doing what you want it to do to your target doesn’t mean you know everything that it’s doing.” Imatinib, for example, in addition to inhibiting the abelson kinase in Ph chromosome+ leu-kemia, also appears to enhance some parts of the immune system while having a deleterious effect on other parts.

Dr. Levitsky reviewed the results of a pilot study of 19 patients with chronic phase chronic myeloid leukemia (CML) involving a cancer vaccine consisting of irradiated CML cells engineered to express granulocyte macro-phage colony stimulating factor, a cytokine that helps white blood cells grow. In this pilot trial, the response rate was 58%; 11 patients saw a greater than 10-fold decrease in disease burden. Seven of the responders had complete molecular responses (five durable), meaning the abnormal BCR-ABL transcripts normally found in the blood of individuals with CML were undetectable.

In an attempt to decipher why some patients responded and others didn’t, the researchers screened the blood of five of the participants for CML antibodies. Screening of a cDNA expression library made from CML

and destroy burgeoning tumors. The elimina-tion phase has not been directly observed in humans or animals, but studies comparing tumorigenesis in immunocompromised mice and mice with intact immune systems suggest that the immune system has the power to iden-tify and kill cancer cells.

Some rare cancer cell variants may survive elimination. The second phase, called ‘equi-librium’, describes when cancer cells are able to avoid destruction, but the immune system keeps their growth in check. The tumor cells are essentially dormant. Evidence for the equi-librium phase comes from studies of mice that, when treated with low doses of a carcinogen, harbor cancer cells over long periods of time without developing tumors. When research-ers depleted these animals’ T cells, however, tumors appeared.

In the third phase, ‘escape’, the cancer cells acquire the ability to circumvent the immune system. The cells proliferate and, ultimately, visible tumors emerge. Dr. Schreiber explained that escape is possible because pressure from the immune system has given rise to cancer cell variants that are less immunogenic or immu-nosuppressive. Dr. Schreiber and his colleagues are now working to uncover antigens that are specific to edited tumors in the hope of devel-oping an individualized cancer vaccine.

Personalized medicine formed a major theme of the symposium. In the past, drug developers have focused on antigens that are expressed in a particular tumor type across many different cancer patients. A better strategy, Dr. Schreiber offered, might be to focus on antigens that exist

antibodies—GA101 and GA201. Researchers are now testing GA101, a treatment for B-cell malignancies, in a phase 3 trial. Like the anti-bodies rituximab and ofatumumab, GA101 binds to CD20, a protein expressed on the surface of B cells. Dr. Umaña pointed out that GA101 appears to be more potent and effica-cious than either of these approved drugs.

GA201, an antibody designed to block the epidermal growth factor receptor, has shown promise in treating colorectal cancer. The therapy is now being tested in a phase 1 trial.

Pro- versus antitumorigenic actions of the immune systemProfessor Robert Schreiber, an immunologist at the Washington University School of Medicine, began the third session by outlining his cancer immunoediting hypothesis, “the only thing I talk about nowadays,” he joked. Schreiber and his colleagues coined the term ‘immunoediting’ a decade ago to “try and describe some of the complex interactions that go on between the immune system and the developing tumor,” he said. The immune system protects against cancer by destroying tumor cells, but it also can also facilitate tumor growth either by changing the immunogencity of the tumor or attenuating the anti-tumor immune response. “This is the basis of cancer immunotherapy,” Schreiber said.

The cancer immunoediting hypothesis arose out of the observation that that cancer cells from tumors grown in immune deficient mice will invariably grow when transplanted into other immune deficient mice, but in wild-type mice with intact immune systems, half of these tumors are rejected. Tumors grown in wild-type mice, on the other hand, grow equally well in immune deficient mice and wild type mice, suggesting that the immune system has ‘edited’ them to be less immunogenic.

This process has three phases. In the first phase, called ‘elimination’ or ‘immunosur-veillance’, the innate and adaptive arms of the immune system work together to identify

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Panoramic view of the lecture hall at the beginning of the symposium.

Michael Karin, Keynote speaker of the symposium, delivering his lecture.

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Dr. Palucka has led a number of clini-cal trials involving dendritic cell vaccines, most focused on stage IV melanoma. Taken together, these studies show that dendritic cell vaccines are safe and effective. In some cases, the researchers have observed tumor regres-sion for up to a decade. At least one dendritic cell vaccine, Sipuleucel-T (Provenge), has already made it to market. That’s the good news, Dr. Palucka said. The bad news is that the vaccines only work in a fraction of can-cer patients. “So we are working hard to learn what’s the difference between the patients that benefit and don’t, and then how to improve these strategies,” she said.

Meanwhile, because dendritic cell vaccines work by activating T cells, other groups are investigating the feasibility of directly admin-istering activated T cells, a strategy called ‘adoptive T cell transfer’. Dr. Carl June, an oncologist at the University of Pennsylvania, and his colleagues have engineered T cells to work against chronic lymphocytic leuke-mia (CLL), a cancer of B-cells. In this strat-egy the researchers extract T cells from the patients’ blood and engineer them to express an antibody-based chimeric antigen recep-tor (CAR). Previous efforts using CARs have faced poor yields when culturing T- cells and difficulties related to gene transfer, and sub-sequent clinical trials have failed due to poor T cell engraftment. Dr. June’s group hopes to overcome these challenges by using an antigen binding domain that targets CD19, a protein uniquely expressed by B-cells and

they saw some efficacy. Of the 21 patients who received this treatment, four showed a partial response. But when they examined biopsies from the responders’ tumors, they saw no sign of T cells. So the researchers went back to mice to gain a better understanding. Using a differ-ent mouse model, they found that the therapy activates macrophages, which begin killing cancer cells. The next clinical trial will look at the same therapy in patients who will receive chemotherapy and the CD40 antibody before they undergo surgery for removal of their tumors. Examining tumor samples from these patients may shed more light on the potential immune mechanisms of action behind the approach.

Cellular advances in immunotherapyThe final session of the conference focused on cell-based therapies. Dr. Karolina Palucka, an immunologist at the Baylor Institute for Immunology Research, discussed treatments involving dendritic cells, which facilitate com-munication between the innate and adaptive arms of the immune system. Because den-dritic cells have the power to activate T cells, researchers have made them a main target of cancer vaccines. These particular vaccines work in two ways: One strategy involves har-vesting dendritic precursor cells from patients, culturing the cells with antigen outside the body in a lab dish, and then re-injecting the modified cells back into the patient. The second strategy involves delivering antigens directly to dendritic cells still inside the body.

cells identified a total of 28 candidate anti-gens, most of which had not been previously recognized as being leukemia-associated antigens. They then searched the patients’ serum for antibodies to these antigens. Whereas antibodies specific for 12 of these were present both before and after vaccina-tion (but absent from the majority of healthy volunteers), antibodies to sixteen antigens were detectable only after vaccination. The antigens identified have been implicated in diverse pathways, including cell cycle regula-tion, programmed cell death, and regulation of transcription and translation. Whereas no single antigen was recognized in all patients who had a clinical response, clinical respond-ers generated a far more diverse pattern of antigen recognition than those whose disease failed to respond.

The harmful role of inflammation in curbing an anti-cancer immune response is especially evident in pancreatic ductal adeno-carcinoma (PDA), an almost universally lethal disease. In this disease, leukocytes infiltrate the tumor tissue and orchestrate an immunosup-pressive inflammatory reaction. By the time the disease becomes invasive, half of all cells in the tumor are leukocytes. Work by Dr. Robert Vonderheide, a researcher at the University of Pennsylvania, in mice suggests that the bulk of these are immune suppressive cells including regulatory T cells and macrophages. He and his colleagues found no evidence of an anti-tumor response by either cytotoxic T cells or T helper cells. The cells did not appear to be activated.

To invoke a cytotoxic T cell response in PDA patients, Vonderheide’s group adminis-tered a monoclonal antibody designed to bind to CD40, a protein necessary for activation of antigen-presenting cells, which can then acti-vate T cells. In mice, chemotherapy followed by administration of anti-CD40 led to rejec-tion of tumors due to a T-cell response. And, when they assessed this therapy combination in patients with late-stage pancreatic cancer,

The Roche Award for Cancer Immunology and Immunotherapy.

Mike Burgess (left) and Jacques Banchereau (right) present Jim Allison (center) the Roche Award for Cancer Immunology and Immunotherapy.

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derived suppressor cells), which produce large amounts of a reactive oxygen species called peroxynitrite (PNT). PNT appears to interfere with the formation of class II major histocom-patibility complex, the protein that presents antigen on the cell’s surface. As a result, tumor cells don’t express the peptides that the adop-tive T cells were designed to recognize, allow-ing the tumor cells to escape. Drugs that inhibit the formation of reactive oxygen or nitrogen species might be able to block production of PNT and enhance the efficacy of T-cell thera-pies. Because tumor-associated inflammation is not universal and can vary widely, some indi-viduals may respond to T-cell transfer while others don’t.

Another way to make adoptive T-cell therapies more effective might be to admin-ister younger, more naive T-cells. Work by Dr. Nicholas Restifo, a senior investigator at the National Cancer Institute’s Center for Cancer Research, suggests that naive T-cells have more anti-tumor activity than fully differentiated effector T cells.

While some researchers focus on T-cell transfer, others are working to generate T cell responses though the use of cytokines. One such cytokine, granulocyte macrophage-stim-ulating colony factor (GM-CSF), has proven effective in at least six clinical trials in both solid tumors and hematological malignancies. GM-CSF is also a component of the recently approved Provenge vaccine. But, in some studies, the therapy has failed to improve outcomes. Dr. Glenn Dranoff, an oncologist at the Dana-Farber Cancer Institute, and his colleagues have been trying to gain a better understanding of how it works. GM-CSF has long been recognized an immune activator, but Dr. Dranoff found that the cytokine can also promote immune tolerance by increas-ing levels of regulatory T cells. “Animals that lack this cytokine, as they age, develop chronic inflammatory and autoimmune disease,” he said. “Knowing these two completely oppo-site functions of the cytokine helps provide a framework for understanding why different trials get different results.”

lysis syndrome, with high fevers ten to 25 days after receiving the initial infusion.

On the upside, Dr. June noted that the proce-dure costs just $15,000, far less than many anti-body therapies. “One common misconception is that cell therapies like this are expensive,” Dr. June said. And, for those who respond, the effects appear to be lasting. June speculates that this therapy could be used for other types of cancers, but moving such therapies past the boutique phase will likely prove challenging. He pointed out that no successful business models exist for cell-based cancer therapies like CARs, however Dendreon is attempting to launch a similar therapy with customized dendritic cells.

The riddle of why adoptive T-cell therapies only have efficacy in 20-40 percent of patients was addressed by Dr. Dmitry Gabrilovich, an immunologist at H. Lee Moffitt Cancer Center. Dr. Gabrilovich’s studies show that inflamma-tion causes an influx of myeloid cells (activated macrophages, granulocytes, and myeloid-

plasma cells. This domain is attached to other domains that stimulate the T-cell and produce T cell-specific signaling. These cells are cul-tured outside the body and administered to the patients.

To date, Dr. June and his colleagues have tested this therapy in three patients with CLL. Two of the three patients who have received the treatment are in complete remission more than one year after treatment. The third had only a partial response that has been sustained for a year. Tests revealed that the T cells persisted in the blood and even migrated to the bone marrow in all three patients. Dr. June added that, according to his team’s analysis, each CAR cell killed 1,000 or more tumor cells. The major drawback of the therapy, however, is that it targets healthy B-cells as well as cancerous ones, as does the antibody therapy rituximab (Rituxan). As a result, patients who receive the treatment will be immunosuppressed for life. And, as a separate concern, the two patients who responded showed delayed signs of tumor

Panoramic view of the poster hall during a lunch break.