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

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

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

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.

Glassman, C. R., Parrish, H. L., Deshpande, N. R., & Kuhns, M. S. (2016). The CD4 and CD3δε Cytosolic Juxtamembrane Regions Are Proximal within a Compact TCR-CD3-pMHC-CD4 Macrocomplex. Journal of immunology (Baltimore, Md. : 1950), 196(11), 4713-22.

TCRs relay information about peptides embedded within MHC molecules (pMHC) to the ITAMs of the associated CD3γε, CD3δε, and CD3ζζ signaling modules. CD4 then recruits the Src kinase p56(Lck) (Lck) to the TCR-CD3 complex to phosphorylate the ITAMs, initiate intracellular signaling, and drive CD4(+) T cell fate decisions. Whereas the six ITAMs of CD3ζζ are key determinants of T cell development, activation, and the execution of effector functions, multiple models predict that CD4 recruits Lck proximal to the four ITAMs of the CD3 heterodimers. We tested these models by placing FRET probes at the cytosolic juxtamembrane regions of CD4 and the CD3 subunits to evaluate their relationship upon pMHC engagement in mouse cell lines. The data are consistent with a compact assembly in which CD4 is proximal to CD3δε, CD3ζζ resides behind the TCR, and CD3γε is offset from CD3δε. These results advance our understanding of the architecture of the TCR-CD3-pMHC-CD4 macrocomplex and point to regions of high CD4-Lck + ITAM concentrations therein. The findings thus have implications for TCR signaling, as phosphorylation of the CD3 ITAMs by CD4-associated Lck is important for CD4(+) T cell fate decisions.