AUTHOR'SVIEW OncoImmunology1:2,205–207;March/April2012;G2012LandesBioscience New insights into the role of NK cells in cancer immunotherapy Maria Salagianni, Constantin N. Baxevanis, Michael Papamichail and Sonia A. Perez* CancerImmunologyandImmunotherapyCenter;SaintSavasCancerHospital;Athens,Greece RepetitiveinfusionsofexvivoexpandedNKcellsinducedantitumorT-cellresponsesinametastaticlungcancermouse model.ThesewerefurtherpotentiatedbyTregdepletion.ThusthecombinationofNKcell-basedimmunotherapywith other treatment modalities in the direction of adaptive response enhancement might promote long lasting antitumor immunity. NK cells are innate immune lymphocytes Given that NK cells are part of an 50% of the mice were cured; splenic T which primarily function to lyse virally integral immune network where the cells produced more IFNc and exhibited infected cells and tumor cells and to function of each component population higher cytotoxicity and proliferation © 2012 Landes Bioscience. regulate innate and adaptive immune may affect, positively or negatively, the against the CT26 cells in vitro; further- responses through the production of function of other immune cell popula- more the growth rate of distal secondary cytokines and chemokines.1,2 The role of tions, we explored the ability of NK tumors was significantly delayed, com- NK cells in tumor immunosurveillance cells to induce memory anti-tumor T cell pared with mice treated with NK cells and their potential for successful cancer immune responses in a metastatic lung alone.6 immunotherapy strategies is currently cancer mouse model. Another important parameter to be established. The effeDctivenesos of r estning, oContside rindg thatiadsoptivetly trransfierrbed cuonsiderted ewhen.applying cell-based shortly activated or ex vivo expanded NK cells would act, either indirectly, cancer immunotherapies is the ability of autologous or allogeneic NK cell-based through cross-talk with dendritic cells the adoptively transferred cells to home to immunotherapiesisexploredinpreclinical (DC)4 or directly, as antigen presenting the tumor sites. When considering solid studiesandclinicaltrials,forthetreatment cells(APC),4,5totriggerprimingoftumor- tumors, the persistence of the adoptively of hematological malignancies and solid specific T cells (Fig.1), we presumed transferred NK cells in the peripheral tumors. The main issues addressed so far that repeated administrations of ex vivo blood is not informative about their effec- in the clinical application of NK cells expanded NK cells would act as repeated tiveness to reach the tumor. This could referred to: (1) Overcoming inhibitory anti-tumor “vaccines.” Indeed, after four explain the recently published data from signals,eitherbyusingallogeneicNKcells weekly NK cell infusions we were able to a clinical trial of adoptive transfer of orbyblockinginhibitoryreceptors;(2)the detect memory systemic T cell responses autologous NK cells in patients with number of cells to be infused; and (3) the against the syngeneic CT26 tumor cells, metastatic melanoma or renal cell carci- in vivo persistence of the adoptively trans- either by in vitro testing of splenic T cell noma: although the adoptively transferred ferred NK cells in one single infusion reactivity orbyrechallengingexperimental NK cells appeared to persist in the through preconditioning lymphodepletion animalswithtumorcellsinanothersiteof peripheral circulation of patients for at regimens and IL-2 co-administration. the body.6 least one week post transfer, and in some The apparent goal ofsuchapproaches is To further optimize these anti-tumor patients for several months, no clinical toachieveaclinicalresponsebyeliminating responses, we treated tumor-bearing ani- responses were observed.7 as much as possible tumor cells by direct mals with Ontak1 (Denileukin Diftitox) Inthecaseofourlungmetastasistumor NKcell-mediatedkilling.Howevereffective to eliminate regulatory T cells (Treg), model, we found that about 60% of the immunotherapy should elicit long lasting once, two days prior to the first NK cell infused NK cells were present within the memory immune responses in order to administration. Given that activated NK lungs of the tumor-bearing animals three prevent future relapse. Although NK cells cellsareresistanttoTreg-inducedsuppres- days after their i.v. infusion and rapidly havebeendemonstratedtopossessmemory sion, we hypothesized that elimination of declined to 25% after one week. Given against viruses,3 there is no evidence yet Tregs prior to T cell priming would lead that activated NK cells are known to thatthiscouldalsoapplytothediversityof to more robust, long lasting immune infiltratethelungtissuewithinminutesof tumorassociatedantigens(TAA). responses. Indeed, under these conditions i.v. injection and can be retained by the *Correspondenceto:SoniaA.Perez;Email:[email protected] Submitted:09/14/11;Revised:10/11/11;Accepted:10/13/11 http://dx.doi.org/10.4161/onci.1.2.18398 www.landesbioscience.com OncoImmunology 205 © 2012 Landes Bioscience. Do not distribute. Figure1.AdoptivetransferofexvivoactivatedandexpandedNKcellscanactastumor-specificactiveimmunotherapy,inducinglonglastinganti-tumor Tcellresponses.NKcellscanbeeffectivelyactivatedandexpandedinvitrobycytokinesincombinationwithGCsand/orother“stress”signals(a).Adoptively transferredactivatedNKcellscanlysetumorcellsthusleadingtotherelease/productionofapoptoticbodies/TAAs(b).Suchtumor-derivedmaterialwillbe processedandpresentedtoCD4andCD8Tcells(i)directly,bytheactivatedNKcellswhichexpressMHCclassIandclassIImolecules(c)or(ii)indirectly, throughNKcell-mediatedactivationandpolarizationofDCs.ThiscanbeachievedbyactivatedNKcell-producedcytokines(IFNc,TNFa,GM-CSF)(d)orby directcell-to-cellcontact(i.e.,NKp30-NKp30L)(e).Furthermore,activatedNKcellsexpressingcostimulatorymolecules(e.g.,CD86,OX40L,etc)canprovide efficientcostimulationtoTcells(throughCD28,OX40,etc)(f).TheconcertedactionofcytokinesproducedbytheactivatedNKsandDCs(IFNc,IL-12)(g)will supportTh1responses.TheeffectiveprimingandrestimulationofTcellsbyNKcellsand/orDCswillinducetheproliferationanddifferentiationofCD4+and CD8+intoeffector/memoryandcentralmemorycellsthatcanconferlonglastingantitumorimmunity(h).Improvementoftheseresponsescanbeachieved throughinhibitionofimmunomodulatorymechanisms(e.g.,TregcellandMDSCelimination/inhibition,anti-CTLA4oranti-PD1targetingetc)asappliedin othervaccinationstrategies(e.g.,peptidevaccines,wholecellvaccines,DC-basedvaccinesetc.). tumor,8 we can assume that only few NK Furthermore, NK cells expanded in the active and passive immunotherapiesaswell cells remained in the circulation. presence of glucocorticoids (GC) express aswithotherpotentialmodalitiesofcancer The NK cells used in our preclinical high levels of CXCR3 and CXCR4,6,10 therapy including chemotherapy, radio- model were ex vivo expanded with IL-15 indicating their increased potential to therapyandbiologicaltherapies.Thisnovel in the presence of hydrocortisone, a com- home to the tumor sites. biological role ascribes NK cells a central bination that as we have previously Ourdataputforwardanadditional,sofar position in the field of active cancer demonstrated, both in human and mice, unappreciated role for NK cells acting as immunotherapies in the context of perso- significantly accelerates NK cell prolifera- potent “cellular vaccines” inducing and/or nalized medicine. The exploitation of the tion,renderingthesecellsmoreresistantto boosting endogenous adaptive antitumor multi-talented NK cells against cancer is cytokine-induced cell death without com- responses. In this context, NK cell-based still in its infancy and needs to be quickly promising their functional potential.6,9,10 cellular therapy could be combined with exploredunderanewperspective. 206 OncoImmunology Volume1Issue2 References 6. Salagianni M,Lekka E,MoustakiA,IliopoulouEG, 9. PerezSA,MahairaLG,DemirtzoglouFJ,Sotiropoulou BaxevanisCN,PapamichailM,etal.NKcelladoptive PA,IoannidisP,IliopoulouEG,etal.Apotentialrole 1. SutluT,AliciE.Naturalkillercell-basedimmunother- transfer combined with Ontak-mediated regulatory forhydrocortisoneinthepositiveregulationofIL-15- apy in cancer: current insights and future prospects. Tcelleliminationinduceseffectiveadaptiveantitumor activated NK-cell proliferation and survival. Blood J Intern Med 2009; 266:154-81; PMID:19614820; immune responses. 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J ClinInvest2004;114:1612-23;PMID:15578093 © 2012 Landes Bioscience. Do not distribute. www.landesbioscience.com OncoImmunology 207