Michael S Kuhns

Michael S Kuhns

Associate Professor, Immunobiology
Associate Professor, Genetics - GIDP
Associate Professor, BIO5 Institute
Primary Department
Department Affiliations
Contact
(520) 626-6461

Work Summary

Work Summary

Michael Kuhns' research program is focused on (i) increasing our basic understanding of how T cell fate decisions are made (e.g. development, activation, differentiation, effector functions), and (ii) increasing their working knowledge of how to manipulate these decisions to direct T cells towards a desired outcome, such as increasing responses to vaccines or tumors, preventing transplant rejection, or attenuating autoimmunity.

Research Interest

Research Interest

What we’re interested in: For all vertebrates, from mice to humans, vaccine-induced and naturally primed immunity to pathogens require that coordinated, multi-cellular responses emerge from a myriad of ‘conversations’ that take place between cells of the immune system. These conversations occur via cytokines and chemokines that are secreted by one cell and detected via receptors on other cells. They also occur via direct contacts between membrane-bound molecules at the interface between two cells. Ultimately, these conversations are responsible for insuring that an appropriate immune response occurs in the appropriate place, and at the appropriate time, to fight an infection without inducing an inappropriate response to commensal organisms or self-antigens. The molecules on T cells that are involved in these conversations include but are not limited to: the T cell receptor (TCR), which provides clonotypic antigen specificity to T cells; the CD3δε, γε, and ζζ signaling dimers that connect the TCR to the intracellular signaling machinery; the CD8 and CD4 coreceptors that provide major histocompatibility molecule (MHC)-restriction for T cells that recognize antigenic peptides bound to class I or II MHC, respectively; and costimulatory molecules, such as CD28, that provide information about the activation state of an antigen presenting cell (APC) and thus the context in which an antigen occurs. We are interested in understanding how the individual contributions from this chorus of molecules are integrated to achieve the critical balance between tolerance of self-antigens and protective immunity against pathogenic infection. Specifically, we are working to understand how the information that is critical for T cells to decide if and how they should respond to antigen is conveyed from an antigen presenting cell (APC) to a T cell. We are using a variety of classic molecular, cellular, and biochemical techniques, as well as more modern live cell imaging approaches, to probe the molecular mechanisms involved in these processes. We are also developing mouse model systems to determine how individual mechanisms contribute to T cell responses in vivo during pathogenic infection or autoimmunity. Altogether, our work is aimed at increasing our basic and practical appreciation of T cell responses and regulation.

Publications

Parrish, H. L., Glassman, C. R., Keenen, M. M., Deshpande, N. R., Bronnimann, M. P., & Kuhns, M. S. (2015). A Transmembrane Domain GGxxG Motif in CD4 Contributes to Its Lck-Independent Function but Does Not Mediate CD4 Dimerization. PloS one, 10(7), e0132333.

CD4 interactions with class II major histocompatibility complex (MHC) molecules are essential for CD4+ T cell development, activation, and effector functions. While its association with p56lck (Lck), a Src kinase, is important for these functions CD4 also has an Lck-independent role in TCR signaling that is incompletely understood. Here, we identify a conserved GGxxG motif in the CD4 transmembrane domain that is related to the previously described GxxxG motifs of other proteins and predicted to form a flat glycine patch in a transmembrane helix. In other proteins, these patches have been reported to mediate dimerization of transmembrane domains. Here we show that introducing bulky side-chains into this patch (GGxxG to GVxxL) impairs the Lck-independent role of CD4 in T cell activation upon TCR engagement of agonist and weak agonist stimulation. However, using Forster's Resonance Energy Transfer (FRET), we saw no evidence that these mutations decreased CD4 dimerization either in the unliganded state or upon engagement of pMHC concomitantly with the TCR. This suggests that the CD4 transmembrane domain is either mediating interactions with an unidentified partner, or mediating some other function such as membrane domain localization that is important for its role in T cell activation.

Chambers, C. A., Kuhns, M. S., & Allison, J. P. (1999). Cytotoxic T lymphocyte antigen-4 (CTLA-4) regulates primary and secondary peptide-specific CD4(+) T cell responses. Proceedings of the National Academy of Sciences of the United States of America, 96(15), 8603-8.

CTLA-4-deficient mice develop a fatal lymphoproliferative disorder, characterized by polyclonal expansion of peripheral lymphocytes. To examine the effect of restricting the CD4(+) TCR repertoire on the phenotype of CTLA-4-deficient mice and to assess the influence of CTLA-4 on peptide-specific CD4(+) T cell responses in vitro, an MHC class II-restricted T cell receptor (AND TCR) transgene was introduced into the CTLA-4(-/-) animals. The expression of the AND TCR transgene by CD4(+) T cells delays but does not prevent the lymphoproliferation in the CTLA-4(-/-) mice. The CD4(+) T cells become preferentially activated and expand. Interestingly, young AND TCR(+) CTLA-4(-/-) mice carrying a null mutation in the rag-1 gene remain healthy and the T cells maintain a naive phenotype until later in life. We demonstrate that CTLA-4 regulates the peptide-specific proliferative response generated by naive and previously activated AND TCR(+) RAG(-/-) T cells in vitro. The absence of CTLA-4 also augments the responder frequency of cytokine-secreting AND TCR(+) RAG(-/-) T cells. These results demonstrate that CTLA-4 is a key regulator of peptide-specific CD4(+) T cell responses and support the model that CTLA-4 plays a differential role in maintaining T cell homeostasis of CD4(+) vs. CD8(+) T cells.

Kuhns, M. S., Epshteyn, V., Sobel, R. A., & Allison, J. P. (2000). Cytotoxic T lymphocyte antigen-4 (CTLA-4) regulates the size, reactivity, and function of a primed pool of CD4+ T cells. Proceedings of the National Academy of Sciences of the United States of America, 97(23), 12711-6.

We examined how cytotoxic T lymphocyte antigen-4 (CTLA-4) regulates heterogeneous CD4(+) T cell responses by using experimental autoimmune encephalomyelitis (EAE), a CD4(+) T cell-mediated disease that is subject to regulation by CTLA-4. Disease incidence and severity were used as measures of in vivo CD4(+) T cell responses. The frequency, cytokine production, and reactivity of primed T cells were determined from animals immunized with proteolipid protein (PLP)-139-151 (disease agonist), PLP-Q (disease antagonist), or both peptides, and treated with control or anti-CTLA-4 antibody to analyze the responding population. CTLA-4 blockade exacerbated disease in PLP-139-151-primed animals and overcame disease antagonism in coimmunized animals, but did not permit disease induction in PLP-Q-primed animals. Experimental autoimmune encephalomyelitis enhancement was associated with increased frequencies of cytokine-producing cells and increased ratios of IFN-gamma to IL-4 secretors responsive to PLP-139-151. Priming with PLP-Q elicited IL-4 and IL-2, but not IFN-gamma secretors cross-reactive with PLP-139-151. Strikingly, CTLA-4 blockade was found to decrease rather than increase the frequencies of cross-reactive IL-4 and IL-2 secretors. Thus, CTLA-4 engagement limits the size, but increases the breadth, of reactivity of a primed pool of CD4(+) T cells, consequently regulating its function.

Newell, E. W., Ely, L. K., Kruse, A. C., Reay, P. A., Rodriguez, S. N., Lin, A. E., Kuhns, M. S., Garcia, K. C., & Davis, M. M. (2011). Structural basis of specificity and cross-reactivity in T cell receptors specific for cytochrome c-I-E(k). Journal of immunology (Baltimore, Md. : 1950), 186(10), 5823-32.

T cells specific for the cytochrome c Ag are widely used to investigate many aspects of TCR specificity and interactions with peptide-MHC, but structural information has long been elusive. In this study, we present structures for the well-studied 2B4 TCR, as well as a naturally occurring variant of the 5c.c7 TCR, 226, which is cross-reactive with more than half of possible substitutions at all three TCR-sensitive residues on the peptide Ag. These structures alone and in complex with peptide-MHC ligands allow us to reassess many prior mutagenesis results. In addition, the structure of 226 bound to one peptide variant, p5E, shows major changes in the CDR3 contacts compared with wild-type, yet the TCR V-region contacts with MHC are conserved. These and other data illustrate the ability of TCRs to accommodate large variations in CDR3 structure and peptide contacts within the constraints of highly conserved TCR-MHC interactions.

Kuhns, M. S., & Davis, M. M. (2012). TCR Signaling Emerges from the Sum of Many Parts. Frontiers in immunology, 3, 159.

"How does T cell receptor signaling begin?" Answering this question requires an understanding of how the parts of the molecular machinery that mediates this process fit and work together. Ultimately this molecular architecture must (i) trigger the relay of information from the TCR-pMHC interface to the signaling substrates of the CD3 molecules and (ii) bring the kinases that modify these substrates in close proximity to interact, initiate, and sustain signaling. In this contribution we will discuss advances of the last decade that have increased our understanding of the complex machinery and interactions that underlie this type of signaling.