NIH Training Grant Fellow: Jose Limon

Jose Limon

Jose's scientific interest is to explore the intricate workings of the immnune system and acquire knowledge to understand and alter processes involved in human health and disease. He joined the Furman lab in 2008 and has been a co-author on three publications with a major paper in Nature Medicine in February of 2010 where he contributed experimentally a large portion of the immunology aspect of the study.

A promising drug target frequently deregulated in many cancers is mTOR (target of rapamycin). mTOR is a serine/threonine kinase that is evolutionarily conserved from yeast to man. TOR integrates both intracellular and extracellular signals from growth factors and nutrients to promote cellular protein translation, ribosomal biogenesis, lipid synthesis and cell cycle progression.

Of the two complexes, MTORC1 is sensitive to the antibiotic rapamycin that acts as an allosteric inhibitor of the complex although it does not completely inhibit mTORC1 activity. Rapamycin and its analogs (rapalogs) are very potent at suppressing lymphocyte prolifertion and differentiation and therefore have clinical uses as immunosuppressants. However, their potent immunosuppressive capability can therefore limit their use in cancer therapy. Recently, the mTOR kinase inhibitors (mTOR-KIs) have been developed as promising cancer drugs but their effects on the immune system are largely unknown.

We have reported in Nature Medicine (PMID: 20072130) on the antileukemic efficacy of PP242, an mTOR-KI, in both transformed mouse lymphocytes, human leukemia cell lines, and primary human leukemia samples. Unexpectedly, PP242 at anti-leukemic doses had less of an effect in vitro on lymphocyte proliferation and in vivo on lymphocyte function after immunization with NP-OVA, a T cell dependent antigen. Although PP242 did not abolish lymphocyte proliferation, careful examination of the data suggested that mTOR-KIs do impact lymphocyte differentiation. Hence, mTOR-KIs might have immunomodulatory effects that may be used therapeutically to treat immune related diseases without global immunosuppression, or to augment specific immune responses.

The goal of his thesis is to define the effects of mTOR-KIs on lymphocyte differentation. Currently, work that he has completed has demonstrated that mTOR-KI treatment in vivo causes an increase in the percentage of germinal center B cells while reducing plasma IgM levels. In in vitro assays of B cell differentation, mTOR-KI treatment increased the number of IgG1 switching B cells with CD40L+IL4 stimulation and decreased the differentiation of early antibody secreting cells in LPS stimulated B cells. IgM secretion was also decreased with mTOR-KI treatment. Gene expression analysis of AID and BLIMP-1 revealed an increase in AID expression and a decrease of BLIMP-1 expression in mTOR-KI treated B cells, additionally BcI6 expression was increased with mTOR-KI treatment. Rapamycin potently inhibited B cell differentiation in all tested stimulations. Additionally, mTOR-KIs increase the production of induced regulatory T cells (iTreg) from naïve CD4 T cells.

We hypothesize that the effects on lymphocyte differentiation produced by mTOR-KI treatment are being mediated by FOXO reactivation as a consequence of decreased Akt activity. TORC2 inhibition by mTOR-KI will affect Akt phosphorylation and activity thereby increasing FOXO nuclear translocation and downstream gene expression, such as AID expression in B cells and FoxP3 epxression in T cells. He is currently taking a genetic approach by utilizing retroviruses that express different mutants of Akt or a dominant negative FOXO and testing to see if transduced cells are resistant to the differentiation effects induced by mTOR-KI treatment. He hopes that work produced from these studies will yield two separate publications on the effects mTOR-KI have on B cell and T cell differentiation and to elucidate the mechanisms of the observed effects.

Publications:

Janes MR, Vu C, Mallya S. Shieh MP, Limon JJ, Li LS, Jessen KA, Martin MB, Ren P, Lilly MB, Sender LS, Liu Y, Rommel C, Fruman DA. Efficacy of the investigational mTOR kinase inhibitor MLN0128/INK128 in models of B-cell acute lymphoblastic leukemia. Leukemia. 2012 Oct. 1. doi: 10.1038/leu.2012.276

Limon JJ and Fruman DA. Akt and mTOR in B Cell Activation and Differentitation. Front Immunol. 2012;3:228. doi: 10.3389/fimmu.2012.00228.

Limon JJ and Fruman DA. B cell receptor signaling: picky about PI3Ks. Science Signaling. 2010. 3(134):pe25.

James MR, Limon JJ, So L, Chen J, Lim RJ, Chavez MA, Vu C, Lilly MB, Mallya S, Ong ST, Konopleva M, Martin MB, Ren P, Liu Y, Rommel C, Fruman DA. Effective and selective targeting of Ph+ leukemia cells using a TORC1/2 kinase inhibitor. Nature Medicine. 2010 Feb;16(2):205-213. - Selected as F1000 Factor 6.0 "Must Read" by Faculty of 1000 Biology by Brendan Manning. Also highlighted in SciBX, Nature Reviews Cancer, Nature Reviews Drug Discovery, BioWorld Today and UCI Brief.

Chen J, Limon JJ, Blanc C, Peng SL, Fruman DA. Foxo1 regulates marginal zone B cell development. European Journal of Immunology. 2010. 40(7):1890-6.