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T memory stem cell formation: Caveat mTOR

2016; Elsevier BV; Volume: 4; Linguagem: Inglês

10.1016/j.ebiom.2016.02.019

2352-3964

Daniel H. Fowler, Luca Gattinoni,

CAR-T cell therapy research

T memory stem cells (TSCM), a rare subset of memory lymphocytes endowed with enhanced capacity of self-renewal and the potential to reconstitute the full repertoire of memory and effector cells, have recently emerged as a central player in several physiological and pathological processes. TSCM cells have been shown to mediate superior anti-tumor responses (Gattinoni et al., 2009Gattinoni L. Zhong X.S. Palmer D.C. Ji Y. Hinrichs C.S. Yu Z. Wrzesinski C. Boni A. Cassard L. Garvin L.M. Paulos C.M. Muranski P. Restifo N.P. Wnt signaling arrests effector T cell differentiation and generates CD8+ memory stem cells.Nat. Med. 2009; 15 (Epub 2009 Jun 14): 808-813https://doi.org/10.1038/nm.1982Crossref PubMed Scopus (706) Google Scholar, Gattinoni et al., 2011Gattinoni L. Lugli E. Ji Y. Pos Z. Paulos C.M. Quigley M.F. Almeida J.R. Gostick E. Yu Z. Carpenito C. Wang E. Douek D.C. Price D.A. June C.H. Marincola F.M. Roederer M. Restifo N.P. A human memory T cell subset with stem cell-like properties.Nat. Med. 2011; 17: 1290-1297https://doi.org/10.1038/nm.2446Crossref PubMed Scopus (1242) Google Scholar), harbor leukemic cancer stem cells (Nagai et al., 2015Nagai Y. Kawahara M. Hishizawa M. Shimazu Y. Sugino N. Fujii S. Kadowaki N. Takaori-Kondo A. T memory stem cells are the hierarchical apex of adult t-cell leukemia.Blood. 2015; 125 (epub 2015 apr 6): 3527-3535https://doi.org/10.1182/blood-2014-10-607465Crossref PubMed Scopus (41) Google Scholar), and serve as a reservoir for HIV infection (Buzon et al., 2014Buzon M.J. Sun H. Li C. Shaw A. Seiss K. Ouyang Z. Martin-Gayo E. Leng J. Henrich T.J. Li J.Z. Pereyra F. Zurakowski R. Walker B.D. Rosenberg E.S. Yu X.G. Lichterfeld M. HIV-1 persistence in CD4+ T cells with stem cell-like properties.Nat. Med. 2014; 20 (Epub 2014 Jan 12): 139-142https://doi.org/10.1038/nm.3445Crossref PubMed Scopus (312) Google Scholar). Because of these wide-ranging clinical implications, it is of critical importance to improve our understanding of the molecular events that induce or maintain TSCM cells. In this issue of EBiomedicine, Scholz et al. used pharmacological and genetic approaches to identify mTOR as a key signaling pathway regulating the formation of CD4+ and CD8+ TSCM cells (Scholz et al., 2016Scholz G. Jandus C. Zhang L. Grandclement C. Lopez-Mejia I.C. Soneson C. Delorenzi M. Fajas L. Held W. Dormond O. romero p. Modulation of mTOR signalling triggers the formation of stem cell-like memory T Cells.EBioMedicine. 2016; 4: 50-61Summary Full Text Full Text PDF PubMed Scopus (75) Google Scholar). It has previously been demonstrated in murine (Gattinoni et al., 2009Gattinoni L. Zhong X.S. Palmer D.C. Ji Y. Hinrichs C.S. Yu Z. Wrzesinski C. Boni A. Cassard L. Garvin L.M. Paulos C.M. Muranski P. Restifo N.P. Wnt signaling arrests effector T cell differentiation and generates CD8+ memory stem cells.Nat. Med. 2009; 15 (Epub 2009 Jun 14): 808-813https://doi.org/10.1038/nm.1982Crossref PubMed Scopus (706) Google Scholar) and human (Gattinoni et al., 2011Gattinoni L. Lugli E. Ji Y. Pos Z. Paulos C.M. Quigley M.F. Almeida J.R. Gostick E. Yu Z. Carpenito C. Wang E. Douek D.C. Price D.A. June C.H. Marincola F.M. Roederer M. Restifo N.P. A human memory T cell subset with stem cell-like properties.Nat. Med. 2011; 17: 1290-1297https://doi.org/10.1038/nm.2446Crossref PubMed Scopus (1242) Google Scholar) models that the formation of TSCM cells can be promoted by triggering WNT/β-catenin signaling. The finding that inhibition of the mTOR pathway can also favor the generation of TSCM cells has significant therapeutic implications as rapamycin and other mTOR inhibitors are FDA-approved agents that have already been used in T cell adoptive therapy clinical trials (clinicaltrials.gov.; NCT00074490, NCT01239368). As such, the contribution of Scholz et al. may accelerate the field in terms of bringing TSCM cells into the clinical arena. TSCM cells are an ideal cell population to employ in T cell-based immunotherapies because of their enhanced capacity to engraft and ability to persist for the long-term. Using a human-into-mouse xenogeneic transplantation model, the authors found that TSCM cells manufactured in rapamycin had increased persistence relative to control naïve or central-memory T cells, recapitulating prior observations obtained using naturally occurring TSCM cell populations (Gattinoni et al., 2011Gattinoni L. Lugli E. Ji Y. Pos Z. Paulos C.M. Quigley M.F. Almeida J.R. Gostick E. Yu Z. Carpenito C. Wang E. Douek D.C. Price D.A. June C.H. Marincola F.M. Roederer M. Restifo N.P. A human memory T cell subset with stem cell-like properties.Nat. Med. 2011; 17: 1290-1297https://doi.org/10.1038/nm.2446Crossref PubMed Scopus (1242) Google Scholar). These findings are also consistent with a body of literature indicating that rapamycin-resistant human Th1/Tc1 cells have a remarkable ability to repopulate xenogeneic hosts and mediate graft-versus-host disease effects (Amarnath et al., 2010Amarnath S. Flomerfelt F.A. Costanzo C.M. Foley J.E. Mariotti J. Konecki D.M. Gangopadhyay A. Eckhaus M. Wong S. Levine B.L. June C.H. Fowler D.H. Rapamycin generates anti-apoptotic human Th1/Tc1 cells via autophagy for induction of xenogeneic GVHD.Autophagy. 2010; 6 (Epub 2010 May 16): 523-541https://doi.org/10.4161/auto.6.4.11811Crossref PubMed Scopus (33) Google Scholar). Additional in vivo functional endpoints, however, will be needed to determine the therapeutic potential of the rapamycin-generated TSCM cell populations as manufactured by Scholz et al. There is a growing interest around the possibility of targeting metabolism for immunotherapeutic interventions as it has become clear that metabolism can profoundly influence T cell functionality and fate commitment. Up to this point, the metabolic profile of TSCM cells has remained elusive. Now, Scholz et al. shed new light on the metabolic regulation of human CD4+ TSCM cells and have revealed that, similar to naïve and memory T cell populations, TSCM cells rely on fatty acid oxidation as a primary source for ATP synthesis. These findings are fundamental because they open up the possibility to promote the formation and maintenance of TSCM cells through the manipulation of fatty acid metabolism. While underlying a central role for mTOR in the generation of TSCM cells, Scholz et al. dispute a role for WNT/β-catenin signaling. The authors argue that the WNT activator, TWS119, promoted TSCM cell generation not by the conventionally recognized mechanism (GSK3β inhibition and subsequent β-catenin stabilization) but rather via an off-target effect that involved mTOR inhibition; their conclusion was based in part on their observations that neither a physiological WNT3A ligand nor alternative GSK3β inhibitors supported TSCM formation in their hands. However, the authors used WNT3A at concentrations 100-fold lower than those used in previous studies that found an active role of WNT3A in the generation of both murine and human TSCM cells (Gattinoni et al., 2009Gattinoni L. Zhong X.S. Palmer D.C. Ji Y. Hinrichs C.S. Yu Z. Wrzesinski C. Boni A. Cassard L. Garvin L.M. Paulos C.M. Muranski P. Restifo N.P. Wnt signaling arrests effector T cell differentiation and generates CD8+ memory stem cells.Nat. Med. 2009; 15 (Epub 2009 Jun 14): 808-813https://doi.org/10.1038/nm.1982Crossref PubMed Scopus (706) Google Scholar, Muralidharan et al., 2011Muralidharan S. Hanley P.J. Liu E. Chakraborty R. Bollard C. Shpall E. Rooney C. Savoldo B. Rodgers J. Dotti G. Activation of Wnt signaling arrests effector differentiation in human peripheral and cord blood-derived T lymphocytes.J. Immunol. 2011; 187 (Epub 2011 Oct 19): 5221-5232https://doi.org/10.4049/jimmunol.1101585Crossref PubMed Scopus (50) Google Scholar). In their experiments, the lack of activity of the GSK3β antagonist indirubin-3-monoxime was potentially attributable to its weak selectivity and inability to trigger downstream WNT signals (Meijer et al., 2003Meijer L. Skaltsounis A.L. Magiatis P. Polychronopoulos P. Knockaert M. Leost M. Ryan X.P. Vonica C.A. Brivanlou A. Dajani R. Crovace C. Tarricone C. Musacchio A. Roe S.M. Pearl L. Greengard P. GSK-3-selective inhibitors derived from Tyrian purple indirubins.Chem. Biol. 2003; 10: 1255-1266Summary Full Text Full Text PDF PubMed Scopus (691) Google Scholar). In sharp contrast, the highly selective, 6-bromoinduribin derivatives, which are capable of stabilizing β-catenin (Meijer et al., 2003Meijer L. Skaltsounis A.L. Magiatis P. Polychronopoulos P. Knockaert M. Leost M. Ryan X.P. Vonica C.A. Brivanlou A. Dajani R. Crovace C. Tarricone C. Musacchio A. Roe S.M. Pearl L. Greengard P. GSK-3-selective inhibitors derived from Tyrian purple indirubins.Chem. Biol. 2003; 10: 1255-1266Summary Full Text Full Text PDF PubMed Scopus (691) Google Scholar), have successfully been employed to generate TSCM cells (Gattinoni et al., 2009Gattinoni L. Zhong X.S. Palmer D.C. Ji Y. Hinrichs C.S. Yu Z. Wrzesinski C. Boni A. Cassard L. Garvin L.M. Paulos C.M. Muranski P. Restifo N.P. Wnt signaling arrests effector T cell differentiation and generates CD8+ memory stem cells.Nat. Med. 2009; 15 (Epub 2009 Jun 14): 808-813https://doi.org/10.1038/nm.1982Crossref PubMed Scopus (706) Google Scholar). It is also important to underscore that the authors did not provide evidence of the ability of these 'ineffective' agents to activate WNT/β-catenin signaling. Indeed, Scholz et al. employed as a WNT operational readout the phosphorylation of GSK3β serine 9, a post-translational modification mediated by AKT and not involved in WNT signaling (Mcmanus et al., 2005Mcmanus E.J. Sakamoto K. Armit L.J. Ronaldson L. Shpiro N. Marquez R. Alessi D.R. Role that phosphorylation of GSK3 plays in insulin and Wnt signalling defined by knockin analysis.EMBO J. 2005; 24 (Epub 2005 Mar 24): 1571-1583Crossref PubMed Scopus (501) Google Scholar) (gold standard assays would consist of measurement of unphosphorylated β-catenin and WNT-reporter activity). In a final attempt to support their conclusion of TWS119 action outside of the GSK3β/WNT pathway realm, the authors used an elegant model involving β- and γ-catenin deficient T cells. However, conclusions based on these experiments carry the major caveat that WNT signal transmission is substantially maintained in double-deficient T cells (Jeannet et al., 2008Jeannet G. Scheller M. Scarpellino L. Duboux S. Gardiol N. Back J. Kuttler F. Malanchi I. Birchmeier W. Leutz A. Huelsken J. Held W. Long-term, multilineage hematopoiesis occurs in the combined absence of beta-catenin and gamma-catenin.Blood. 2008; 111 (Epub 2007 Sep 28): 142-149Crossref PubMed Scopus (190) Google Scholar). Further research will therefore be required to more definitively test the extent to which GSK3β inhibitors such as TWS119 might mediate their effect on TSCM cells independent of the WNT pathway. In summary, Scholz et al. have tackled a critical issue in biomedicine relating to human CD4+ and CD8+ T memory stem cell generation and function. Although the molecular mechanism(s) of TSCM cell generation remain nebulous vis-à-vis the relative role of WNT/β-catenin or mTOR modulation, the current report certainly provides a nidus of information that will guide subsequent investigations. Hopefully, with the attainment of a refined molecular understanding and the development of alternative pharmacologic inhibitors, an ability to effectively modulate TSCM cells for therapeutic purposes will be realized. Modulation of mTOR Signalling Triggers the Formation of Stem Cell-like Memory T CellsRobust, long-lasting immune responses are elicited by memory T cells that possess properties of stem cells, enabling them to persist long-term and to permanently replenish the effector pools. Thus, stem cell-like memory T (TSCM) cells are of key therapeutic value and efforts are underway to characterize TSCM cells and to identify means for their targeted induction. Here, we show that inhibition of mechanistic/mammalian Target of Rapamycin (mTOR) complex 1 (mTORC1) by rapamycin or the Wnt-β-catenin signalling activator TWS119 in activated human naive T cells leads to the induction of TSCM cells. Full-Text PDF Open Access