Immunotherapeutic Approaches to Cancer, Part I
Training the Immune System to Better Detect and Target Tumor Cells
“Since vaccines became available for infectious diseases, we’ve had this dream of a vaccine for cancer,” notes Zihai Li, M.D., PhD, who holds the Abney Chair Remembering Sally Abney Rose in Stem Cell Biology & Therapy and serves as Chair of Microbiology & Immunology at MUSC. With recent advances in genomics and the knowledge base gained during the past twenty years about how tumors and the various components of the immune system work, Dr. Li believes that “Immunotherapy for cancer is not just a fantasy or wild dream anymore.”
Basic research findings are beginning to filter into clinical trials. David Cole, M.D., Chair of Surgery and Director of the Center for Cellular Therapy at MUSC, and the tumor immunology team at Hollings Cancer Center, including Zihai Li, M.D., PhD (program leader), Shikhar Mehrotra, PhD, Mark Rubinstein, PhD, and Chrystal Paulos, PhD, have been working to develop immunotherapeutic techniques in the laboratory that have clinical relevance, and their work is beginning to bear fruit. Dr. Cole is currently the Investigational New Drug Principal Investigator on three phase 1 clinical trials of dendritic cell vaccines open at Hollings Cancer Center, two in patients with metastatic or locally advanced pancreatic cancer (Principal Clinical Investigator: Steven H. Chin, M.D.) and one in patients with metastatic melanoma (Principal Clinical Investigator: Keisuke Shirai, M.D.).
The Basics of Tumor Immunology
The body’s immune system protects us both against invading pathogens, such as viruses, and against mutated cells within our own bodies (eg, cancer) via immune surveillance. Lymphocytes, particularly T lymphocytes or T cells, are on guard against new antigens and, upon detection, mount a defense against them. When activated, CD8+ T cells are the “killer” cells of the body, charged with purging it of any enemy invaders or internal threats.
Unlike viruses, which can easily be identified as “foreign,” cancer derives from self and so can be much harder for T lymphocytes to detect. It is adept at cloaking itself, hiding in plain sight and tricking the T cells into thinking that it does not require their attention. In other words, the tumor creates an immunosuppressed environment around it, and the T cells in that area become “tolerant” of it, unable to recognize it as an enemy and/or to mount an effective response. According to Dr. Cole, “It’s sort of a like an army of soldiers standing around. Until someone sets the alarm, they are not going to go into action to activate, divide, proliferate and attack.”
Retraining the body’s immune system to set that alarm so that T cells can mount an effective attack against tumors is one of the principal aims of immunotherapeutic approaches to cancer. Something must be done to “break the tolerance,” ie, to overcome the inability of the T cells to notice the tumor, and to enhance their ability to mount an effective defense against the cancerous cells.
Dendritic cells present antigen to T cells, thereby activating them and making them into killer cells (Figure 1). Recognition of the antigen by the T cell becomes possible when the antigen on the surface of the dendritic cell (ie, the antigen-presenting cell) binds to the appropriate receptor on the surface of the T cell. The T cell then recognizes that antigen as a threat and mounts a defense against it.
To combat the immunosuppressive environment created by the tumor, T cell–centered immunotherapeutic approaches to cancer attempt to reinvigorate the body’s immune defense by either enriching the target (the antigens presented by the dendritic cells) or by training the T cells to be more effective warriors (eg, by genetically altering the receptors on their surface so that they recognize the tumor antigen).
Both strategies require harvesting immune cells; isolating, amplifying and altering them to increase their potency; and then reinfusing them into the same host from which they were harvested. Many centers are able to undertake these studies in mice or other animal models. However, few are able to take promising basic science findings and translate them into clinical trials. MUSC is able to do so for two reasons: the close collaboration between research scientists and clinicians who serve on translational teams at Hollings Cancer Center and the availability of the Department of Surgery’s Center for Cellular Therapy (Co-Scientific Directors, Shikhar Mehrotra, PhD and Hongjun Wang, PhD; Regulatory Director, June Fried; technical support, Mingli Li, Tracy Vandenberg , and Colleen Cloud), a class six clean cell facility that provides the ultra-sterile environment needed for processing cells that are to be reinfused into patients.
Dendritic Cell Vaccines
Dendritic cell vaccines are intended to add more relevant targets to the surface of the dendritic cell to increase the chance that a receptor on the T cell surface will recognize one or more of those target antigens and be alerted of a threat and the need to mount an attack. Dendritic cells are isolated from white cells harvested from the patient in a process known as leukapheresis. They are then pulsed with recognized tumor-associated antigens so that they will present an enriched target for the T cell. In the phase 1 trials under way at MUSC, isolated dendritic cells are pulsed with four such tumor-associated antigens. According to Dr. Cole, “It’s like pinning four different red bull’s-eyes on the bull.” The modified and amplified dendritic cells are then reinfused into the patient in hopes that they will stimulate an enhanced T cell response.
Many institutions are running clinical trials with dendritic cell vaccines; however, the trials at MUSC are novel in that they are testing whether the toll-like receptor 3 agonist poly(I:C) could be an effective adjuvant, ie, whether it could stimulate the immune system and enhance the potency of a dendritic cell vaccine.
FIGURE 1. T cell receptor gene transfer. After isolation from a cancer patient, T cells are genetically modified to express a novel tumor-specific T cell receptor.
In 2008, Drs. Cole and Salem reported their laboratory’s findings that poly(I:C) augmented antigen-specific responses when tumor-specific T cells were adoptively transferred into recipient mice conditioned with cyclophosphamide (for lymphodepletion) prior to adoptive transfer.¹ This basic science research provided the underpinnings for the three phase 1 clinical trials with poly(I:C) currently under way at Hollings Cancer Center.
In all three phase 1 clinical trials involving poly(I:C), the dendritic cells will be cultured with the adjuvant ex vivo and then the patient will be conditioned by an administration of poly(I:C) at the time of dendritic vaccine administration.
Transduced T Cell Receptor Adoptive T Cell Transfer
Dendritic cell vaccines that stimulate an enhanced T cell response inside the patient by enriching the target antigens available on dendritic cells represent only one of many immunotherapeutic approaches. Another strategy is to amplify the number and enhance the specificity of the lymphocytes themselves ex vivo and then reinfuse them into the patient (Figures 1 and 2). This technique, dubbed adoptive cell transfer, was pioneered by Steven A. Rosenberg, M.D., PhD, at the National Institutes of Health (NIH) for treatment of patients with metastatic melanoma.²
Rosenberg harvested tumor-infiltrating cells (TILs; ie, lymphocytes that had left the bloodstream to infiltrate into the tumor), cultured and amplified them in the presence of the cytokine interleukin (IL)-2, which induces rapid proliferation, and then rein- fused them into patients with metastatic melanoma. An objective, measurable response in tumor size was seen in roughly one third of patients. Recent data suggest that percentage can increase to over 50% when patients are preconditioned with chemotherapy and total body irradiation before reinfusion of the TIL. Such depletion of lymphocytes enhances the objective response because it creates a cytogenic environment and opens up a space niche for the infused, enhanced TILs.
Recognizing that the lymphocytes taken from a cancer patient, especially those in the region of the tumor, have an exhausted phenotype, other researchers evolved this technique by integrating the transduction (genetic alteration) of T cell receptors (TCRs) of T cells derived from the peripheral blood. In transduced TCR adoptive T cell transfer, T cells derived from the patient are reinvigorated by enriching them with T cell receptors that are specific to the patient’s type of cancer. The number of potential T cell receptors is astronomically high, and T cells bearing few (or none) of the receptors relevant to a given cancer are likely not to engender a robust response, especially in the tolerizing environment induced by cancer cells. By studding the T cell with the receptors known to be most relevant to the cancer in question, the T cell becomes much more likely to detect or notice the cancer that is trying to remain clandestine and to mount a response against it. These enhanced T cells are then greatly expanded in number and, once the patient has been lymphodepleted, are reinfused. Again, this differs from vaccination, which attempts to stimulate the body’s own immune system to increase its production of T cells in response to an enriched antigen target. Adoptive cell therapy is more direct and does not depend on the middleman of the dendritic cell. This technique involves greatly amplifying and otherwise enhancing the T cells ex vivo and then reinfusing them into the lymphodepleted host to attack the tumor.
FIGURE 2. Adoptive transfer of T cells that have been genetically modified with a tumor-specific T cell receptor
One advantage of transduced TCR adoptive T cell transfer over adoptive transfer using TILs is that the T cells for the former can be obtained from a simple blood draw while the TILs for the latter must be isolated from a tumor, a time-consuming and complicated process in a patient who is quickly running out of time.
Although MUSC is one of many institutions working toward clinical trials of transduced TCR adoptive T cell transfer, it is the only one testing the efficacy of IL-12 as an adjuvant in this setting. Unlike IL-2, the cytokine used by Rosenberg, which has been associated with producing cells that are already fairly near apoptosis (programmed cell death), meaning that their viability after adoptive cell transfer is not likely to be good, IL-12 tends to produce T cells that are further removed from apoptosis (ie, they are central memory rather than effector memory cells) and thus more likely to survive longer once transferred.³ IL-12 also enhances the cytolytic capacity of the T cells in a number of other ways, including an increase in the levels of granzyme B.
In August 2011, a two-institution (Loyola University in Chicago, IL, and MUSC) Program Project grant was awarded (Principal Investigator [PI], Dr. Nishimura; MUSC site co-PI, Dr. Cole) by the NIH to allow the collaborative immunotherapy research group to further study and realize the potential of transduced TCR adoptive T cell transfer. Program project grants (P01s) are awarded to three to five researchers who are acknowledged experts in a field to encourage them to work synergistically to advance a key scientific concept with clinical promise. Dr. Nishimura already has a clinical trial under way at Loyola using adoptive cell transfer of peripheral blood–derived transduced T cells with low-dose IL-2, and Dr. Cole and his team are working with their collaborators at Loyola towards opening a phase 1 trial at MUSC within the next year that will focus on adoptive cell transfer of peripheral blood–derived, IL-12–cultured transduced T cells.
A Pipeline for Translating Novel Therapies into Patients
MUSC’s Hollings Cancer Center has all the necessary tools— translational teams of basic scientists and clinicians and a top- flight clean cell facility—to begin to bring immunotherapeutic discoveries made in its own laboratories (eg, the potency of poly(I:C) and IL-12 as adjuvants) into clinical trial. According to Dr. Cole, “We are trying to get a pipeline of novel therapies going into patients.” Three phase 1 trials of dendritic cell vaccines with poly(I:C) as adjuvant are currently under way. A phase 1 clinical trial of transduced TCR adoptive T cell transfer using IL-12 as an adjuvant is in the works and expected within the year. Simultaneously, discoveries continue to be made at the basic science level. For example, Dr. Paulos’ group has shown increased antitumor efficacy with adoptive cell transfer in mouse models when blood is enriched with Th₁₇ cells (a subset of CD4 T cells) and ICOS is used as an adjuvant. Dr. Mehrotra has found that IL-15 is another potent adjuvant for use with transduced TCR adoptive T cell transfer. These basic science findings will point the way toward more novel therapies for patients with cancer and serve as the basis of future phase 1 clinical trials.
Part II in this series will examine other immunotherapeutic strategies to cancer, including stem cell transplant, antibody-mediated immunity (including the identification of a human-derived superantigen for cancer) and cytokine therapy.
To learn more about immunotherapy-based clinical trials, call MEDULINE at 843-792-2200 and ask for Alan Brisendine.
¹ Salem ML, Diaz-Montero CM, El-Naggar SA, et al. The TLR3 agonist poly(I:C) targets CD8+ T cells and augments their antigen-specific responses upon their adoptive transfer into naïve recipient mice. Vaccine. 2009; 27(4):549-557. doi:10.1016/j.vaccine.2008.11.013
² Rosenberg A, Yannelli JR, Yang JC, et al. Melanoma with autologous tumor-infiltrating lymphocytes and interleukin 2. J Natl Cancer Inst. 1994; 86(15):1159-1166. doi: 10.1093/jnci/86.15.1159
³ Rubinstein MP, Cloud CA, Garrett TC, et al. Ex vivo interleukin-12- priming during CD8+ T cell activation dramatically improves adoptive T cell transfer antitumor efficacy in a lymphodepleted host. J. Am Coll Surg. 2012; 214(4):700–707.
This article originally appeared in the January/February 2013 issue of Progressnotes.