Inhibition of c-Kit is not required for reversal of hyperglycemia by imatinib in NOD mice.

AIM/HYPOTHESIS: Recent studies indicate that tyrosine kinase inhibitors, including imatinib, can reverse hyperglycemia in non-obese diabetic (NOD) mice, a model of type 1 diabetes (T1D). Imatinib inhibits c-Abl, c-Kit, and PDGFRs. Next-generation tyrosine kinase inhibitors for T1D treatment should maintain activities required for efficacy while sparing inhibition of targets that might otherwise lead to adverse events. In this study, we investigated the contribution of c-Kit inhibition by imatinib in reversal of hyperglycemia in NOD mice. METHODS: The T670I mutation in c-Kit, which confers imatinib resistance, was engineered into the mouse genome and bred onto the NOD background. Hematopoietic stem cells (HSCs) from NOD.c-Kit(T670I) mice and NOD.c-Kit(wt) littermates were expanded in the presence or absence of imatinib to verify imatinib resistance of the c-Kit(T670I) allele. Diabetic mice were treated with imatinib at the onset of hyperglycemia for three weeks, and blood glucose was monitored. RESULTS: In vitro expansion of HSCs from NOD.c-Kit(wt) mice was sensitive to imatinib, while expansion of HSCs from NOD.c-Kit(T670I) mice was insensitive to imatinib. However, in vivo treatment with imatinib lowered blood glucose levels in both strains of mice. CONCLUSIONS/INTERPRETATION: The HSC experiment confirmed that, in NOD.c-Kit(T670I) mice, c-Kit is resistant to imatinib. As both NOD.c-Kit(T670I) and NOD.c-Kit(wt) mice responded comparably to imatinib, c-Kit inhibition does not substantially contribute to the efficacy of imatinib in T1D. Thus, we conclude that inhibition of c-Kit is not required in next-generation tyrosine kinase inhibitors for T1D treatment, and may be selected against to improve the safety profile.

Interleukin-15 rescues tolerant CD8+ T cells for use in adoptive immunotherapy of established tumors.

CD8+ T cells can mediate eradication of established tumors, and strategies to amplify tumor-reactive T-cell numbers by immunization or ex vivo expansion followed by adoptive transfer are currently being explored in individuals with cancer. Generating effective CD8+ T cell-mediated responses to tumors is often impeded by T-cell tolerance to relevant tumor antigens, as most of these antigens are also expressed in normal tissues. We examined whether such tolerant T cells could be rescued and functionally restored for use in therapy of established tumors. We used a transgenic T-cell receptor (TCR) mouse model in which peripheral CD8+ T cells specific for a candidate tumor antigen also expressed in liver are tolerant, failing to proliferate or secrete interleukin (IL)-2 in response to antigen. Molecular and cellular analysis showed that these tolerant T cells expressed the IL-15 receptor alpha chain, and could be induced to proliferate in vitro in response to exogenous IL-15. Such proliferation abrogated tolerance and the rescued cells became effective in treating leukemia. Therefore, high-affinity CD8+ T cells are not necessarily deleted by encounter with self-antigen in the periphery, and can potentially be rescued and expanded for use in tumor immunotherapy.

c-Myb and p300 regulate hematopoietic stem cell proliferation and differentiation.

Precise control of hematopoietic stem cell (HSC) proliferation and differentiation is needed to maintain a lifetime supply of blood cells. Using genome-wide ENU mutagenesis and phenotypic screening, we have identified a mouse line that harbors a point mutation in the transactivation (TA) domain of the transcription factor c-Myb (M303V), which reduces c-Myb-dependent TA by disrupting its interaction with the transcriptional coactivator p300. The biological consequences of the c-Myb(M303V/M303V) mutation include thrombocytosis, megakaryocytosis, anemia, lymphopenia, and the absence of eosinophils. Detailed analysis of hematopoiesis in c-Myb(M303V/M303V) mice reveals distinct blocks in T cell, B cell, and red blood cell development, as well as a remarkable 10-fold increase in the number of HSCs. Cell cycle analyses show that twice as many HSCs from c-Myb(M303V/M303V) animals are actively cycling. Thus c-Myb, through interaction with p300, controls the proliferation and differentiation of hematopoietic stem and progenitor cells.