Clinic to Bench and Bench to Clinic: Developing Safer Biologics
On the 13thof March 2006 six men entered Northwick Park to participate in a first-in-man study. At 8:00 they began receiving an infusion of TGN1412 a humanised monoclonal antibody targeting the CD28 receptor. The antibody therapy was intended to be a therapy for B cell chronic lymphocytic leukemia (B-CLL). Within minutes, the patients began reporting headaches, fever and pain. Soon, this has worsened to severe pain and swelling resulting in the men being moved to intensive care. Many of them stayed for weeks and one patient did not leave hospital for months. Some reports have suggested that they will suffer problems with their immune systems for the rest of their lives.
So how do we prevent another Northwick Park incident? It isn’t the case that they simply went into these trials without preparation, there were all the usual in vivo and in vitro experiments performed. In experiments with monkeys, there were no “clinically visible side effects”. When we spoke with Harald Kropshofer, Senior Personalised Healthcare Leader, Pharmaceutical Development at Hoffmann-La Roche he put it succinctly; “[i]t turned out that the humans are different”.
Humans are different and this means that in some cases, the whole battery of usual preliminary tests will not reveal a risk that could be present if the drug were to react with the human immune system in vivo. With the bench to clinic pathway is not being predictive enough, Dr Kropshofer suggests that it may be time to incorporate better clinic to bench information. Describing his work on whole blood toxicity assays, Dr Kropshofer said
The concept is that you just use fresh human whole blood, add the drug of question, add a concentration, which reflects the peak exposure in man and we do this before we go into Phase 1 clinical trials and we just see whether there is, out of 40/50 different samples, any individual who is reacting in terms of release of typical proinflammatory cytokines, which is IL-6, TNFα, IL-8 or IL-10. So we have a whole battery of end points included in this type of assay and as long as we see no cytokine release, we are happy and this is a go signal, this is green light for moving to the next step. As soon as we would see a cytokine release, meaning an elevation of the typical proinflammatory cytokines, we would have to go back and see what quality of the drug or the drug formulation gives rise to such a response and we are quite happy, so far, that we did that because, by using this test, we had the good news that not a single monoclonal antibody or biotherapeutic drug we brought into Phase 1 so far gave rise to any of those acute cytokine release related adverse events.
These tests perhaps can help to overcome the problem of not being human enough. Whole blood assays also have the advantage of being relatively technically straightforward and can be run during later phase clinical trials to potentially predict whether a person will exhibit cytokine release.
T Cell Assays
Measuring T cell response is also an important step towards understanding whether a patient is likely to produce anti-drug antibodies. It is important to create a model which is as close to in vivo as possible, so Dr Kropshofer’s team mimics dendritic cells presenting protein HLA complexes to T lymphocytes.
We mimic exactly this by isolating those dendritic cells from individual to individual and try to bring them together in a test tube with autologous T lymphocytes, so peripheral T lymphocytes from the blood of the same donor where we get the dendritic cells from. And we do this from healthy volunteer to healthy volunteer or from patient to patient and can see whether there is peptide being really presented by the dendritic cells and whether those peptide HLA complexes give rise to activation of T lymphocytes. So, what we measure at the end is, in absence or presence of a drug, whether T lymphocytes proliferate and/or secrete T lymphocyte-specific cytokines and this can be done in conventional assays, which just count the number of T lymphocytes before and after exposure to the drug.
These assays along with whole blood assays test both the innate and adaptive response and could potentially give a better indication of whether or not a patient is likely to undergo a hypersensitivity reaction.
Assays such as these will not replace other in vivo or in vitro tests, but they can act as an additional safety measure. When I asked Dr Kropshofer where he thought the field was headed, he closed with these thoughts.
So, I believe we will not expand into more sophisticated preclinical animal studies. I do see a way forward if we are successful in making mice more human, but it can only be an additional help; it will not be the only help. The real steps bringing us forward is the patient, is the healthy volunteer showing the adverse event at the level of the human immune system and the reason for this is the human immune system is too different from any other species and so, on top of that, we, as humans, are among us, too different, so we have our different genomic equipment and our receptors are different. We learn about SNPs and we learn about individual difference at that molecular level and we need to do that in the future so that maybe in a decade, we are in better shape in the diagnosis and prognosis of immunotoxicological side effects of drugs and I’m sure we will make it, but it’s still quite a challenge.