A challenge that science communicators frequently face when discussing the process whereby a scientific discovery eventually leads to a medical breakthrough is the time that this often takes, indeed by the time that the reports of exciting clinical trial outcomes start to appear in the press the role of the scientists who made the initial discoveries is often relegated to a passing comment…if it is mentioned at all. An example of this comes from the Weizmann Wave blog, produced by the Weizmann Institute of Science.
You may remember reports last month on the very promising results of a small clinical trial where a new immunotherapy technique was used to eradicate cancer cells in patients with Chronic Lymphocytic Leukemia (CLL), a blood cancer for which currently available treatments are often inadequate. That trial, conducted by scientists at the University of Pennsylvania led by Professor Carl June, involved removing T-cells from the patient, treating the cells with a lentiviral vector that encodes for a Chimeric Antigen Receptor which recognises a protein named CD19 that is found on B-cells, including the cancer cells responsible for CLL, and then infusing the transformed T-cells back into the patients. As the reported in the Los Angeles Times the results were dramatic, within a few weeks of the infusion the modified T-cells expanded rapidly and targeted the cancer cells in all three paients, so that a year later two of the three patients were still in complete remission.
It’s exciting stuff but as the Weizmann Wave reports the Press Release issued by Penn Medicine noted that this was a “cancer treatment breakthrough 20 years in the making” but “didn’t, however, explain those “20 years in the making.””. The Weizmann Wave goes on to discuss the pioneering basic scientific research undertaken by Professor Zelig Eshhar at theWeizman Institute of Science in the late 1980’s, which you can read about here.
Of course between the basic research undertaken by Prof. Eshhar and his colleagues in the 1980’s and the clinical trial whose outcome was announced last month there was a lot of work to be done. It would be impractical to describe all the different discoveries that made this immunotherapy possible, but one discovery in particular highlights the importance of animal research to this breakthrough.
There have been previous attempts to use Chimeric Antigen Receptors to target T-cells to attack cancer, but these had disappointing results in clinical trials. A major improvement made by the University of Pennsylvania team was to include an additional motif – named the CD137 co-stimulatory molecule- which greatly enhances the cancer killing ability of the infused T-cells. In a recent paper published in the Journal of Cancer the University of Pennsylvania team point out that the decision to include CD137 (called 4-1BB in mice) in their Chimeric Antigen Receptor construct was based on promising results in studies undertaken in mice:
Our group has tested a CAR directed against CD19 linked to the CD137 (4-1BB) co-stimulatory molecule signaling domain to enhance activation and signaling after recognition of CD19. By inclusion of the 4-1BB signaling domain, in vitro tumor cell killing, and in-vivo anti-tumor activity and persistence of CART-19 cells in a murine xenograft model of human ALL (acute lymphoblastic leukemia) is greatly enhanced”
Indeed, in a paper published by Professor June and colleagues in the journal Molecular Therapy in 2009 they describe this work in much more detail, highlighting just how groundbreaking the results were:
Previous in vitro studies have characterized the incorporation of CD137 domains into CARs.10,11,29 Our results represent the first in vivo characterization of these CARs and uncover several important advantages of CARs that express CD137 that were not revealed by the previous in vitro studies. We demonstrated that CARs expressing the CD137 signaling domain could survive for at least 6 months in mice bearing tumor xenografts. This may have significant implications for immunosurveillance, as well as for tumor eradication. For example, in a mouse prostate cancer xenograft model, survival of CAR+ T cells for at least a week was required for tumor eradication.30
Long-term survival of the CARs did not require administration of exogenous cytokines, and these results significantly extend the duration of survival of human T cells expressing CARs shown in previous studies.17,31 To our knowledge, this is the first report demonstrating elimination of primary leukemia xenografts in a preclinical model using CAR+ T cells. Furthermore, complete eradication was achieved in some animals in the absence of further in vivo therapy, including prior chemotherapy or subsequent cytokine support.
The long-term control of well-established tumors by immunotherapy has rarely been reported. Most preclinical models in a therapeutic setting have tested tumors that have been implanted for a week or less before initiation of therapy.32 After establishing leukemia 2–3 weeks before T cell transfer, we found that many animals had long-term control of leukemia for at least 6 months. The efficacy of targeted, adoptive immunotherapy in this xenograft model of primary human ALL compares favorably to our prior experience testing the antileukemic efficacy of single cytotoxic (ref. 27 and data not shown) or targeted agents,26 where we have observed extension of survival but not cure of disease. Additionally, we have not previously observed the ability to control xenografted ALL for a period of as long as 6 months.”
These results led directly to the clinical trial reported last month.
So there you have it, behind the headlines are years of graft by hard-working and innovative scientists, who utilised a wide range of experimental approaches – among which animal studies figure prominently – to develop a novel therapy for CLL. As Professor Bruce Levine points out in the video above, the key to success is often keeping one hand in the basic research lab and the other in the clinic.