Katz Lab

MS is engendered by encephalitogenic T cells with specificity for self-antigens of myelinated nerves of the central nervous system (CNS). These disease-causing T cells are a rather scarce population and have thus far eluded specific therapeutic interventions. Modest progress has been made with a number of immunosuppressive or immunomodulatory therapies (IMT), but here the underlying plan of attack remains suppression of T cells in their entirety in order to inhibit the detrimental few. These IMT are the equivalent of declaring martial law on the immune system; curtailing the well-behaved and beneficial T cell to stop the rare and rogue bad actor. In fact, the current strategies have four major drawbacks:

1. They lack specificity

2. They increase risks of opportunistic infections and cancers

3. They produce substantial off-target, agent-specific organ toxicities

4. Perhaps most critically they often do not eliminate the encephalitogenic T cells themselves.

Thus, it is clear that there is an urgent need to find novel and non-toxic means of controlling infrequent, yet injurious T cells, while maintaining beneficial memory and naïve T cells to combat pathogens.

We believe we have just such an approach. By definition encephalitogenic T cells are activated during these overt symptomatic periods, and herein lies their Achilles heel; activated T cells are prime targets for therapeutic intervention. As T cells toggle between precise states – naïve, activated effector, quiescent and activated memory – they exhibit unique ineluctable properties that when engaged can specifically target their demise; this is particularly true of activated effector T cells, such as encephalitogenic T cells during symptomatic periods. Activated T cells unlike their naïve, regulatory (Treg) and quiescent memory counterparts exhibit a strong DNA damage response (DDR) in vivo, and display striking up-regulation of p53-driven processes. As such activated effector T cells are ripe for off-label application of existing chemotherapeutic agents in wide clinical use or under current clinical testing that target the DDR, and/or amplify p53-driven apoptosis. This is done by combating distinct proteins in the p53-activation pathway; namely the p53 regulator, MDM2, and the critical cell cycle control proteins Chk1 and Chk2. Because quiescent naïve, Treg and memory T cells are not undergoing an active DDR, they are strikingly resistant to this p53-driven death. We have found that non-genotoxic combination therapies focus therapeutic specificity on activated T cells, while sparing naïve, Treg and memory T cells. Thus, rather than using broad and blunt suppression, unwanted activated encephalitogenic T cells can be selectively purged by exploiting the p53 pathway.

Collaborators: Michael B Jordan, MD

Funding: Pending

The detrimental immune response of auto-reactive and allo-reactive T cells to host antigens is the fundamental and therapeutic problem in autoimmunity and transplantation, respectively. For example, to impart an effective cure for type 1 diabetes (T1D), we would need to:

1. Prevent or halt the T cell-mediated destruction of insulin-producing, pancreatic beta cells.

2. Preserve the host islet cell mass or its surgically-supplied replacement islets from destruction by antigen-specific T cells.

To date, these goals remain unfulfilled.

While progress has been made with new non-steroidal T cell immunosuppressive drugs, we must still resort to global suppression of T cell-mediated immunity to inhibit the few deleterious effector T cells responsible for syngeneic or allogeneic islet cell destruction.

Recently, we found that as T cells transition between their three major states – naïve, activated and memory – they express distinct patterns of pro- and anti-apoptotic Bcl-2 family members. This dynamic modulation between pro-apoptotic (Bim, Bax, and Bak) and anti-apoptotic (Bcl-2 Bcl-xL, and Mcl-1) molecules has profound biologic significance and forms a regulatory circuit that controls the survival of individual populations of T cells. Owing to these unique expression patterns, naïve, activated, and memory T cells also exhibit differential sensitivity to apoptosis, with activated T cells being most sensitive.

We have used small-molecule antagonists of Bcl-2 family members to target T cells for destruction based on activation state. One of these compound preferentially targets activated T cells and does not require Bim for cell death induction. Our preliminary data demonstrate that in vivo treatment with this small molecule antagonist completely protects mice from diabetes following adoptive transfer of diabetogenic T cells. Based on these data, we hypothesize that this protective effect stems from its preferential inhibition of Mcl-1 molecules in activated T cells. Importantly, the selectivity sensitivity of activate T cells to BH3 antagonism suggests an innovative means of attacking the current problems inherent to broad-based immunosuppression. Rather than using broad immunosuppression, unwanted auto- and allo-reactive T cells should be acutely activated, in vivo, and then differentially targeted for apoptosis using specific BH3-domain antagonists. This would spare beneficial adaptive immunity, while purging undesirable rogue T cells.

Collaborators: David A Hildeman, PhD

Funding: NIH R01 DK081175

T1D is the most common childhood autoimmune disease, and is caused by the T lymphocyte-mediated destruction of insulin-producing pancreatic beta cells. The activation, functional maturation and regulation of these diabetogenic, or disease-causing, T cells are greatly influenced by the inherited constellation of diabetes susceptibility alleles thereby constituting the genetic predisposition that promotes autoimmunity. However the cell biological and molecular mechanisms by which these disease-inducing alleles impact the behavior of diabetogenic T cells T remains obscure. It has become increasingly clear that a new path forward is needed.

Comparative studies at molecular and cellular levels have identified numerous biological alterations in immune regulation in T1D, particularly between T effector (Teff) and T regulatory (Treg) cells, that suggest two competing hypotheses with respect to T cell activation and regulation in T1D: one favors improper/reduced Treg cell function, and the other an over-exuberant response by Teff cells to self-antigen. Unfortunately, current molecular and cellular approaches has not been able to provide conclusive evidence to differentiate between these to competing explanations, nor provide a framework that can reliably predict how T cells will respond when molecular components of their transduction machinery are altered in concentration or function, such as in the case of genetic polymorphism.

We believe a new synthesis of genetics, cellular and molecular immunology, in silico modeling and single-cell measurements in vitro is required if we are to determine the underlying framework for how small genetic variance spawn significant disease prevalence. The idd3/Il2 genetic variants provide the ideal test. Experimentally, the Idd3 encoded variance in IL-2 is small, at best twofold, and close to the technical resolution of expression assays, yet it reduces the T1D by over fourfold. Cellular and molecular assays suggest that both Teff and Treg cells are faced with the challenge of integrating numerous and varied signals, such as ligand recognition, spatial-temporal dynamics, and all-or-nothing signals, when deciding to respond antigen; and both rely on and compete for IL-2 to facilitate and tune their decision making. Recently, in context with model antigen systems, Dr. Grégoire Altan-Bonnet developed a multiplex mathematical model to explain how IL-2 signaling dynamics and intercellular variability in IL-2 and IL-2 receptor (IL-2R) expression at a single cell level can account for dramatically different responses between Teff and Treg cells to defined antigens. We believe that extending this application framework to “the idd3 controversy” can provide a clear and definitive resolution of the two competing hypotheses to explain the effect of Il2 polymorphism in T1D.

Collaborators: Grégoire Altan-Bonnet (Center for Cancer Research, NCI)

Funding: Pending