Whilecheckpointblockadehasprovidedunprecedentedclinicalbenefit,therearestillmanycancerpatientswho remain unresponsive to therapy. Given that the presence of tumor-infiltrating CD8+ T cells predicts clinical responses, there has been increased focus on what spontaneously generates this ?inflamed? tumor microenvironment.Inansweringthisquestion,currentapproacheshaveidentifiedphagocytosedtumorDNAas the ligand that activates cGAS-STING pathway in BATF3-dependent DCs to elicit type I IFN signaling that ultimatelymaturesDCsandeffectivelyprimesTcells.Theseapproaches,however,dependprimarilyontumor models that highly express infectious endogenous retroviruses (ERVs), which is absent in human cancers. Becausethere is the possibility that type I IFN and innate sensorsarebeing erroneously induced,wepropose touseERV-freeimmunogenicYUMMERmelanomalinesdevelopedbyMarcusBosenbergtostudytheinnate sensors involved in activating DCs. Based on preliminary data demonstrating that tumor rejection is STING- dependentbutcGAS-independentandrecentstudiesshowingthatchromosomalinstability(CIN)incancercan autonomouslyactivatecGAS-STING-NFkBpathway,wehypothesizethatCINisactivatingtumorproductionof cGAMPwhichthentransactivatesSTINGinnearbyBATF3-dependentDCs,leadingtoNFkBsignalingandDC maturation.Todirectlytestthis,Iwillpursuethefollowingaims.
Formy firstaim, Iwilldeterminethehostcell type in which STING expression is required for cancer immunosurveillance. To accomplish this, I will subcutaneouslyimplantYUMMERcellsinmicelackingvariousDClineagesandscreenforanydeficienciesin tumorrejection,trackingtumorvolumeandmeasuringDCactivationandTcellinfiltrationbyflowcytometry.For mysecondaim,Iwillidentifythetumor-derivedligandthatisresponsibleforactivatinghostSTING.To do this, I will induce CIN in YUMM cells (the non-immunogenic parental cell line of YUMMER lines) by overexpressingthedominantnegativealleleofmicrotubuledepolymerizingkinesin(MCAK)totestwhetherCIN issufficienttoinduceahostSTING-dependentrejection.WewillalsostablyknockoutcGASinYUMMERcells toassesswhetherspontaneousrejectioncanbeabrogatedintheabsenceoftumorcGAMPproduction.
Formy third aim, I will elucidate the downstream signaling pathway elicited by host STING. By conditionally knockingoutNFkBpathwaycomponentsintheidentifiedDClineage,wewillverifywhetherNFkBisrequiredfor cancer immunosurveillance. Next, we will utilize RNA-Seq of sorted DCs to identify potential cytokines driving tumorrejectionandverifythattheseidentifiedcytokinesarerequiredforimmunosurveillancebyadministration of depleting cytokines. If our hypothesis proves true, we will have identified how the innate immune system broadly recognizes cancer as a pathogen to initiate a specific adaptive response. We expect that our findings willuncovernewstrategiestoconvert?cold?tumorsinto?hot?onesthatcanbetargetedwithcheckpointinhibition.
Despite the recent advancements in immunotherapy, there are still many cancer patients who remain unresponsive to treatment. While it is widely thought that infiltrationof tumor by tumor-specific CD8+ T cells predicts clinical responses, it is still unknown which characteristics of cancer aredetected by the host immune systemto prime T cells andgenerate an inflamed tumor microenvironment.By elucidating the innate immune mechanisms that underlie cancer immunosurveillance leading to spontaneous tumor rejection, this project will help uncover novel therapeutic strategies to convert ?cold? tumors into ?hot? ones that can subsequently be targetedbycheckpointinhibition.
