We cloned TIM 3 as a molecule differentially expressed on IFN-g producing T cells and has emerged as a major
inhibitory molecule necessary for the termination of effector T cell responses. Tim 3 expression is increased on
effector T cells in human chronic viral infections and cancers, rendering them dysfunctional. In contrast, in human
autoimmune diseases, there is loss of Tim 3 expression on effector T cells, rendering them highly pro-
inflammatory and pathogenic. Because of its role in T cell exhaustion, Tim 3 is being targeted in multiple clinical
trials for cancer. Tim 3 is also expressed constitutively on dendritic cells (DCs), however, the role and function
of Tim 3 on DCs is not well understood and this is especially important to understand, in the view of clinical trials
that are underway with anti-Tim 3 antibodies.
As in T cells, Tim 3 is co-expressed in DCs with its adapter protein Bat-3, where Bat-3 acts as a molecular “gate-
keeper”, that restricts Tim 3 signaling and function. To understand the function of Tim 3 in DCs, we have
generated conditional “knock-out” mice of both Tim 3 and Bat-3 in DCs. Initial studies indicate that unrestricted
signaling of Tim 3 in the absence of Bat-3, makes Bat-3-deficient DCs tolerogenic such that they do not effectively
induce inflammatory T cell responses and the mice are resistant to development of autoimmunity. Based on our
preliminary data, we hypothesize that unabated Tim 3 signaling in DCs promotes generation of tolerogenic DCs.
To address this hypothesis, we propose two specific aims:
1. Determine how the Tim 3/Bat-3 interaction regulates development of tolerogenic DCs. We have observed
that unopposed signaling of Tim 3, by deleting Bat-3, specifically in DCs inhibits development of multiple
autoimmune diseases including Experimental Autoimmune Encephalomyelitis (EAE) which is the focus
of this proposal. Using conditional “knock-out” mice for both Tim 3 and Bat-3 in DCs, we propose to
determine whether resistance to autoimmunity in Bat-3 cKO mice is partly or completely restored by
deletion of Tim 3 from the same set of DCs. Furthermore, this will also allow us to determine how loss of
Bat-3 regulates DC phenotype and function.
2. Determine the molecular mechanism by which interaction of Tim 3 and the Smad/TGF-b pathway
promotes the generation of tolerogenic DCs. Using an unbiased proteomic screen to identify molecules
that bind to the Tim 3 tail in the absence of Bat-3, we identified Smad-2, a transducer of TGF-b pathway,
as a Tim 3 interacting protein. This novel observation allows us to study the mechanism by which Tim 3
mediates its inhibitory function, specifically we will be able to determine the molecular basis by which Tim
3/Smad/TGF-b pathway promotes the development of tolerogenic DCs. Using high density temporal
transcriptional analysis of the Tim 3 and Bat-3 deficient DCs, we propose to develop transcriptional
networks by which the Tim 3:Bat-3 pathway mediates its inhibitory function in DCs.
The proposed studies will identify how the Tim 3:Bat-3 pathway makes DCs tolerogenic, providing critical
information that could be exploited to benefit multiple human diseases. While repressing Tim 3 function could
augment immune responses in chronic viral infections and cancer, boosting Tim 3 signals could dampen
autoimmune diseases and promote antigen specific tolerance.