A breakthrough against Chronic Lymphocytic Leukemia…thank the mice!

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.

Paul Browne

3 thoughts on “A breakthrough against Chronic Lymphocytic Leukemia…thank the mice!

  1. Thank you so much. I’ve followed this treatment with interest and sense there is something more about patient UPN 02 than just a different reaction or a decreased response due to steroids. Why did UPN 02 seemingly get sicker that 01 and 03 to begin with. It’s interesting that the Cytokine response was altered but wonder if because this was a Leukemia and not a solid tumor malignancy, the patients may simply have been less prone to develop a cachexia syndrome.

    I remain a bit concerned that CART19 and the additional vectors they have developed are being defined by terms like treatment for “b-cell malignancies” or “mesothelioma, pancreatic or ovarian cancers.” These are treatments that may prove excellent in annihilating proteins (benign and malignant cells) but not all patients with these diseases will express these proteins and not all the cancers will express these proteins in totality for all cells. The solid tumor malignancies particularly within the peritoneal cavity which is coated with benign Mesothelin, may be more problematic for the cytokine reaction. Perhaps successful treatment will come from trials that obtain pre-treatment confirmation of protein expression, rather than a summary of a type of cancer.

    I look forward to following this site.

  2. Dear Mr/Dr. Browne,

    Do you know if the CART19 patients experienced any type of Cachexia Syndrome as a result of the Cytokine Storm? If so, was there any distinguishing presentations of such amongst the three patients in the trial?

    Thank you

    1. Hi Salian, that’s an interesting question. Since this post went up the group have published a more detailed report on this study in Science Translational Medicine (http://www.ncbi.nlm.nih.gov/pubmed/21832238 and http://stm.sciencemag.org/content/3/95/95ra73.full), and the answer is that so far as I can see from what they report in the paper there was no cachexia syndrome.

      In their results section they report that :

      “The peak time of cytokine elevation in (patients) UPN 01 and 03 correlated temporally with both the previously described clinical symptoms and the peak levels of CART19 cells detected in the blood for each patient. Notably, cytokine modulations were transient, and levels reverted to baseline relatively rapidly despite continued functional persistence of CART19 cells. Only modest changes in cytokine levels were noted in UPN 02, possibly as a result of corticosteroid treatment. ”

      It’s worth noting that patients UPN 01 and UPN03 were the patients in which complete remission was seen, and in their discussion the authors note that:

      “Although our second-generation CAR T cells led to considerable clinical effects, the lysis of at least a kilogram of tumor burden in all three patients was accompanied with the delayed release of potentially dangerously high levels of cytokines in two of the patients (9). We did not observe classical cytokine storm effects; however, our trial was designed to mitigate this possibility by deliberate infusion of CART19 cells over a period of 3 days and by using signaling domains that did not promote secretion of IL-2 and TNF-α. ”

      So while the cytokine elevation is something that needs to be monitored it is not necessarily a road block to further development of this therapy, and may indeed be an unavoidable consequence of therapies such as this which result in the rapid destruction of a large number of tumor cells by the immune system.

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