Jeff Bluestone: UCSF diabetes center, T cell inhibition, regulatory T cells, and diabetes reversal
by Adam Burrack, PhD
Relevant citations:
In the first installment in this series I described an exciting new method to produce patient-specific beta cells for transplantation recently developed by the Melton laboratory at Harvard. I also briefly described the reason – T cell-mediated destruction of transplanted beta cells – that this therapy is not a cure for type 1 diabetes (T1D) on its own but will need to be paired with therapies that restrain autoreactive T cells. In the second installment in this series I described an exciting research resource, the network of pancreatic organ donors (nPOD), which provides researchers with access to the diseased pancreas from deceased individuals who suffered from T1D. Matthias von Herrath at the La Jolla Institute in San Diego led a study characterizing the degree of infiltration by CD8+ T cells in the diseased pancreas in the setting of type 1 diabetes compared to type 2 diabetes and non-diseased controls. For the next several editions of this blog I will describe in more detail the cells of the immune system responsible for destruction of insulin-producing beta cells during the run-up to diagnosis with T1D, T cells, and potential ways in which the actions of these cells could be stopped to prevent or reverse T1D.
T cells are the assassins of the immune system. They attack only what they are instructed to, and they are very thorough once specifically instructed. There are several types of T cells of the immune system. In addition to the cell surface molecule CD4 and CD8, which can be used to broadly separate T cells into ‘helper’ or ‘killer’ types, respectively, there are two types of CD4+ T cells. “Effector” CD4+ T cells promote immune responses; within lymph nodes these cells help to activate both B cells (which make antibodies, among other functions) and CD8+ ‘killer’ T cells (which are responsible for killing cells infected with viruses). The other broad type of CD4+ T cells are “regulatory” T cells. These cells are critical for down-regulating active immune responses to prevent damage to organs and for preventing autoreactive attack of organs. Studies in mice which have been made genetically deficient in regulatory T cell-specific proteins have shown that the animals will develop autoreactive responses against multiple cell and tissue types in the absence of regulatory CD4+ T cells, including beta cells of the pancreas, leading to severe disease. As one might guess from this brief description, the normal balance of effector CD4 T cells and regulatory CD4 T cells is thought to be disturbed in individuals who are genetically prone to develop T1D. However, there is evidence to support multiple interpretations: it is possible that both the balance of these cells as well as the level of efficacy of effector CD4 T cells (higher than normal) and/or regulatory CD4 T cells (lower than normal), are perturbed. As a result of this imbalance in T cell regulation, a popular experimental tactic used in attempts to prevent – or in a more realistic scenario, reverse – new-onset T1D is to re-establish balance between these two types of CD4+ T cells.
A leader in this area of T cell biology and autoimmunity has been Dr. Jeff Bluestone, PhD, at the University of San Francisco Diabetes Center. The UCSF diabetes center has been a leading institution in the research of T1D for >20 years, due in large part to the efforts of Dr Bluestone’s group. The Bluestone laboratory has focused much of its effort over the past ~10 years studying the cell biology of T cells. In a 2009 paper in the journal Diabetes (Diabetes 58:652-62, 2009), the Bluestone group conducted proof-of-principle studies isolating regulatory CD4+ T cells from the peripheral blood of T1D patients (see figure 1), determining a pattern of cell surface protein expression that would facilitate identification before expansion (see figure 2 and figure 3), expanding these cells ex vivo (outside of the patient, in tissue culture plates), and demonstrating stability of the regulatory phenotype following expansion (shown in figure 5). In short, this paper identified several proteins expressed on the cell surface of regulatory CD4+ T cells that remained stably expressed following several rounds of cell division. Critically, they also established that regulatory CD4+ T cells that had divided retain the ability to suppress the division of other T cells (see figure 6b), which is the defining characteristic of regulatory T cells.
At the other end of the spectrum, another potential clinical strategy is to inhibit T cell activation with treatment of antibodies that block the cell surface receptors that promote T cell activation. The Bluestone group has pursued this strategy as part of a multi-center collaboration. A 2013 Diabetes paper (Diabetes 62:3766-74, 2013), describes a study in which several groups treated recent-onset T1D patients with anti-CD3 antibody, which is a component of the T cell receptor. The researchers tracked insulin usage by treated subjects, C-peptide levels (C-peptide would be produced only from insulin made by the patient’s pancreas, it would not be derived from injected insulin), and HbA1c as proxies of diabetes control and survival of residual beta cells. Because this treatment was designed to block the T cell receptor in general, and not specifically block autoreactive T cells, this is a good example of a T cell-specific treatment but not an autoreactive T cell-specific treatment. Encouragingly, some patients responded to this treatment, in particular those with lower insulin requirements and lower HbA1c values at baseline (shown in figures 4 and 5). In addition, fewer activated T cells at onset of treatment correlated with enhanced efficacy of treatment. Overall, this clinical trial demonstrated that the general strategy of inhibiting autoreactive T cell destruction of insulin-producing beta cells was more effective in patients who had lower insulin requirements and fewer activated T cells at the onset of therapy, which is not the typical case with new-onset T1D. As such, this clinical trial highlights the need for more specific treatments to inhibit the actions of autoreactive T cells before a critical mass of beta cells are destroyed.
Toward this end, an active phase 1 clinical trial at UCSF through the Bluestone laboratory is attempting transfer of patient-specific regulatory CD4 T cells. Phase 1 clinical trials are designed to test safety – not efficacy – of proposed new human treatments. This clinical trial is the application of the 2009 Diabetes paper described above. In this clinical trial regulatory T cells are harvested from new-onset T1D patients, expanded in the laboratory, and transferred back into the patient. The goal with this treatment is to utilize the patient’s own regulatory T cells to specifically inhibit the actions of autoreactive T cells, thereby halting further destruction of insulin-producing beta cells, and affording beta cells the physiologic space to recover from attack and regenerate. If successful, this strategy would represent a major step forward in cell-based therapies to stop disease.