Dendritic cells in skin
Ralph M. Steinman, MD of the Rockefeller University (New York, NY) the discoverer of the dendritic cell and its central role in the immune system, died on September 30, 2011 at age 68 after a four-and-a-half year battle with pancreatic adenocarcinoma. On October 3, 2011, he was awarded half of the The Nobel Prize in Physiology or Medicine for 2011 “for his discovery of the dendritic cell and its role in adaptive immunity”. (The other half of the Prize was shared between Bruce A. Beutler and Jules A. Hoffmann “for their discoveries concerning the activation of innate immunity”.)
Previously, in 2007, Dr. Steinman had been awarded an Albert Lasker Basic Medical Research Award for the discovery of dendritic cells.
Dendritic cells are the principal antigen-presenting cells (APCs) in the immune system. They process antigenic material (for example, from invading bacteria and viruses, and from cancer cells), and present antigens on their surfaces to other types of immune cells, especially T cells. This results in antigen-specific activation of the T cells. Dendritic cells thus serve as the principal link between the innate and the adaptive immune system.
Nobel Prizes are not awarded posthumously, but the Nobel Committee was not aware that Dr. Steinman had died when they made the award. So the award still stands. Dr. Steinman thus has the distinction of being the only person to be awarded a Nobel Prize posthumously. The Nobel Foundation said, after reviewing the case, “The decision to award the Nobel Prize to Ralph Steinman was made in good faith, based on the assumption that the Nobel Laureate was alive.”
Nature published a “News in Focus” article on Dr. Steinman in its 13 October 2011 issue, written by Lauren Gravitz, a freelance writer and editor based in Los Angeles, California. The article details the attempt by Dr. Steinman and his colleagues to use dendritic cell-based immunotherapy to treat Dr. Steinman’s own cancer.
Ms. Gravitz met Dr. Steinman during her two-year tenure as a science writer in the Rockefeller University communications department. While she was there, Dr. Steinman educated her on the complex field of dendritic cell biology. It was also during her time at Rockefeller that Dr. Steinman was diagnosed with advanced pancreatic cancer (in March 2007). Starting at the time of his diagnosis, Dr. Steinman and his colleagues began developing and using their experiential immunotherapies against that cancer. Thus Ms. Gravitz has been following this story from the beginning, and the October 2011 Nature article is the result.
An approved and marketed dendritic cell-based immunotherapy
Only one dendritic cell-based immunotherapy, Dendreon’s Sipuleucel-T (APC8015, Provenge) for treatment of advanced prostate cancer, has been approved by the FDA. The FDA approved it on April 29, 2010, and it is considered the first approved and marketed cancer vaccine. Sipuleucel-T was the first therapeutic cellular immunotherapy for cancer to demonstrate efficacy in Phase 3 clinical trials; this led to the FDA approval. However, Sipuleucel-T only extended mean survival by four months as compared to placebo in Phase 3 clinical trials. And the treatment is expensive, costing a total of $93,000 for the full treatment of three infusions.
Since Sipuleucel-T must be prepared specifically for each patient, using the patients own dendritic cells, a discussion of this product is relevant to the case of Dr. Steinman’s experimental treatment, which also involved autologous dendritic cells.
To prepare Sipuleucel-T, a patient’s autologous dendritic cells are purified from his or her blood. The cells are then sent to a Dendreon site, where they are incubated with a fusion protein, consisting of two moieties–the antigen prostatic acid phosphatase (PAP), which is present in 95% of prostate cancer cells, and a granulocyte-macrophage colony stimulating factor (GM-CSF) moiety, which is an immune cell activator. The resulting product, APC8015 or Sipuleucel-T, is returned to the infusion center and infused into the patient. The goal is to stimulate an immune response to tumor cells carrying the PAP antigen.
Although Sipuleucel-T is the the first therapeutic cellular immunotherapy for cancer to demonstrate efficacy in Phase 3 clinical trials in terms of overall survival, neither it, nor other cancer vaccines in clinical trials, gives complete responses. In our April 27, 2011 blog post, we discussed another therapeutic cellular immunotherapy for cancer, known as adoptive immunotherapy, which does give some complete responses in metastatic melanoma. However, this therapy is experimental and difficult to standardize, and has thus attracted no commercial interest. It is not approved by the FDA, and will not be covered by third-party payers. Thus the emphasis on dendritic cell vaccines.
Using dendritic cells to stimulate immune responses to Dr. Steinman’s pancreatic cancer
There are no approved cancer vaccines for pancreatic adenocarcinoma, which has a poor prognosis (survival measured in weeks or a few months in advanced cases). The disease is generally treated with the cytotoxic drug gemcitabine (Lilly’s Gemzar). However, this treatment appears to be mainly palliative in patients with advanced pancreatic cancer, giving an improved quality of life and a 5-week improvement in median survival. Most patients soon develop resistance to treatment with this agent. Thus, when Dr. Steinman (with the help of his colleagues) attempted to treat his own pancreatic cancer, he was venturing into the unknown.
According to Ms. Gravitz’ article, Dr. Steinman had a meeting with two immunotherapy researchers who had formerly been members of his lab–Michel Nussenzweig of Rockefeller and Ira Mellman of Genentech, shortly after he had been diagnosed with pancreatic cancer. The three planned a strategy to design potential therapies for Dr. Steinman’s cancer. Dr. Nussenzweig would implant some of the tumor as xenografts in mice so that there would be enough material to work with. Dr. Mellman would start a cell line, so that drugs could be screened for activity in killing the cells. Other colleagues would look for mutations in tumor cell DNA that could be used to design drug treatments, and another would isolate surface peptides from the tumor cells so that they could be used as the basis of a vaccine. Meanwhile, Dr. Steinman would undergo conventional chemotherapy with gemcitabine in combination with whatever experimental therapies that might be deemed to have potential to treat the cancer.
Dr. Steinman tried eight experimental therapies, one at a time. For each of these treatment, he and his colleagues submitted a single-patient, compassionate-use protocol to the FDA, and received approval from the agency. Among these treatments were three cancer vaccines. One of them was a form of BioSante’s GVAX (now Aduro’s GVAX, as of the February 2013 acquisition) . The product GVAX Pancreas for pancreatic cancer (which is now in clinical trials) is based on human pancreatic cell lines that have been engineered to secrete GM-CSF, and have then been lethally irradiated. In the case of Dr. Steinman’s treatment, cells from his own tumor were used instead of cell lines.
The other two cancer vaccines were dendritic cell-based immunotherapies, and used dendritic cells isolated from Dr. Steinman’s own blood. The first of these immunotherapies was developed by Argos Therapeutics (Durham, NC), of which Dr. Steinman was a cofounder. It involved transfecting Dr. Steinman’s dendritic cells with RNA derived from his own tumor. The resulting dendritic cells expressed tumor antigens on their surfaces, and were injected back into Dr. Steinman’s blood to potentiate the production of tumor antigen-specific T cells. The second immunotherapy, developed by researchers at the Baylor Institute for Immunology Research (Dallas, TX) involved loading Dr. Steinman’s dendritic cells with peptide antigens from the surface of his tumor. These were also injected back into Dr. Steinman’s blood, in order to potentiate a tumor-specific immune response.
Dr. Steinman also wanted to try combination therapies with ipilimumab. Dr. Steinman tried ipilimumab as a monotherapy, but never got the permissions needed to try the combination therapy. Ipilimumab is an immunomodulator that blocks cytotoxic T-lymphocyte-associated antigen 4 (CTLA4) (a cell surface protein that transmits an inhibitory signal to T cells) to potentate an antitumor T-cell response. The FDA refused permission for the combination therapy despite his belief, and that of other leading immunologists, that the cancer vaccines were likely to work better in combination with ipilimumab. Ipilimumab (Medarex/Bristol-Myers Squibb’s Yervoy) was approved by the FDA in March 2011, and clinical trials of combination therapies of ipilimumab and dendritic-cell vaccines are in early stages.
The course of Dr. Steinman’s disease
Patients with advanced pancreatic adenocarcinoma typically have a poor prognosis. The median survival for locally advanced and for metastatic pancreatic cancer (advanced pancreatic cancer represents over 80% of individuals diagnosed with the disease) is about 10 and 6 months respectively. For all stages of pancreatic cancer combined, the 1- and 5-year relative survival rates are 25% and 6%, respectively.
However, Dr. Steinman survived for four-and-a-half years!
Did any of the treatments that Dr. Steinman received extend his life? No one can know, since with a one-patient experimental treatment there are neither controls nor statistical data as in properly controlled clinical trials.
Dr. Steinman appeared to be much more responsive to gemcitabine than is usually the case. And he had a measurable antitumor immune response, since approximately 8% of his cytotoxic T cells targeted his cancer. Was this due to his natural immunity, or due to the dendritic cell immunotherapies and/or other treatments that he received? Did Dr. Steniman’s antitumor immune response make his cancer more susceptible to gemcitabine than is usually the case? There is no way to know.
The implications of Dr. Steinman’s one-patient experimental treatment
According to Lauren Gravitz’ article, despite these unanswerable questions, Dr. Steinman’s treatment helped move the cancer vaccine field forward. For example, it showed that the leaders in the cancer vaccine field can work together as a team to design and carry out therapies. It also showed that conventional chemotherapy can be given in combination with cancer vaccines. And it also bolstered Dr. Steinman’s passionate belief that it is vitally important to move beyond in vitro studies and animal models into human studies of dendritic cell vaccines, especially given the limitations of animal models.
With respect to animal models and dendritic cell vaccines:
- Dendritic cell immunotherapies designed for use in humans cannot be directly tested in standard animal models. For example, species specificity issues made direct testing of Sipuleucel-T in rodents impossible. Therefore, in preclinical studies researchers constructed “rodent equivalents” of Sipuleucel-T. These consisted of rodent APCs loaded with fusion proteins composed of either rat PAP (rPAP) fused to rat GM-CSF (rPAP•rGM-CSF) or human PAP (hPAP) fused to murine GM-CSF (hPAP•mGM-CSF), and these surrogate versions of Sipuleucel-T were tested in rodents.
- Autologous dendritic cell immunotherapies have proven to be “remarkably safe” in human studies. Therefore, it may not be necessary to test for safety in animal models.
- Dendritic cell biology is complicated. For example, researchers are still attempting to identify human dendritic cell subsets that correspond to known mouse dendritic cell subsets, especially subsets that appear to be the most promising for vaccine design. Therefore, the results of studies carried out in mice may not be directly applicable to humans. Moreover, the use of rhesus macaques for translational studies of vaccines based on dendritic cell biology is expensive.
Should autologous dendritic cell immunotherapies/vaccines for cancer be tested directly in humans, without the use of animal models for preclinical studies? In the case of the treatment of Dr. Steinman, the FDA allowed this to happen. Authorities in the field and regulatory agencies need to continue to discuss this issue.
Meanwhile, as stated at the end of Ms. Gravitz’ article, Anna Karolina Palucka of Baylor, a researcher who had been involved in Dr. Steinman’s treatment, says that she and her colleagues at Baylor are developing an immunotherapy program against pancreatic cancer based on the data from Dr. Steinman’s one-person trial. And Baylor will honor Dr. Steinman by opening a Ralph Steinman Center for Cancer Vaccines. This will be one of many tributes to a pathbreaking physician/scientist.
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