Table Of ContentAUTHOR'SVIEW
OncoImmunology1:2,247–248;March/April2012;G2012LandesBioscience
Host CD73 impairs anti-tumor immunity
Marko Salmi1,2,3,* and Sirpa Jalkanen1,3
1MediCityResearchLaboratory;UniversityofTurku;Turku,Finland;2DepartmentofMedicalBiochemistryandGenetics;UniversityofTurku;Turku,Finland;
3NationalInstituteofHealthandWelfare;Tykistökatu;Turku,Finland
Keywords: tumor-infiltrating leukocytes, enzymes, adenosine, leukocyte traffic
The enzymatic activity of CD73 produces immune-suppressing adenosine. In CD73 deficient hosts, tumor growth and
tumorinfiltrationbyTregsandtype2immunosuppressivemacrophagesisreduced.PharmacologicalinhibitionofCD73
in wild-type mice has similar tumor-suppressing effects. Host CD73 on leukocytes and endothelial cells is thus
detrimental forthe anti-tumor immunity.
CD73/ecto-5'-nucleotidase is a cell-surface of host CD73 to the tumor progression wild-type mice. Nevertheless, binding of
proteinexpressedonasubsetofleukocytes, and anti-tumor immunity.7 isolatedwild-typetumor-infiltratingleuko-
©includ ing2CD4+0CD25+1FoxP32+ Tregs , vLas- aAltnhoughdthemaejorityosfboth CBD4+anid ocytesstoCDc73-dieficeient tnumorvcasculeature .
cular and lymphatic endothelial cells and CD8+T-cellsinthelymphnodesnormally was impaired by ~50% when compared
certain epithelial cells.1 It is an ecto- express CD73, the absence of CD73 did with the binding to the wild-type CD73
enzyme, which dephosphorylates extra- not alter their numbers.7 Nevertheless, expressing tumor vasculature in in vitro
cellular AMP into adenosine (Fig.1).2-4 the extracellular adenosinergic signaling adhesion assays. Thus, CD73 appears not
This reaction is an integral part of the cascade of T-lymphocytes was abnormal tobenecessaryfortheformationoftumor
adenosinergic signaling pathway that in CD73-deficient mice. CD73-negative neovessels, but is expressed on those, and
Do not distribute.
encompasses the following sequential T-cells showed much higher ATPase and may contribute to the leukocyte immigra-
hydrolyzing reactions: ATP → ADP → ADPase activities, and practically no ecto- tionintothetumors(Fig.1).
AMP → adenosine → inosine. ATP and 5'-nucleotidase activity when compared The lack of CD73 might also alter
ADP generally give rise to pro-inflamma- with the wild-type controls. Thus, since immune-suppressing functions of tumor
tory signals via purinergic P2X and P2Y the ATP and ADP hydrolyzing activities infiltrating leukocytes. To study this alter-
receptors. Adenosine, in contrast, binds are increased, and the dephosphorylation native, we enumerated different leukocyte
to adenosine receptors and evokes anti- of AMP into adenosine is reduced in subtypes from the tumors. We did not
inflammatory responses. The enzymatic the CD73-deficient mice, the net effect observeanygenotype-specificdifferencesin
activity of CD73 is involved in the appearstobetheaccumulationofAMP. the overall numbers of intratumoral CD4+
regulation of leukocyte extravasation, vas- The growth of primary subcutaneous T-helper cells, CD8+ T-cytotoxic cells
cular barrier function, and immunosup- tumors from CD73-negative melanoma or F4/80+ macrophages.7 However, the
pressive functions of Tregs, which are all cells, and their metastases to the draining tumors grown in CD73-deficient hosts
relevant to tumor immunity. lymph nodes were attenuated in CD73- hadsignificantlyfewerFoxP3+lymphocytes
CD73 can also be expressed on certain deficient hosts.7 Since CD73 is normally and macrophagemannosereceptor-positive
cancer cell types.5,6 These include leuke- expressedbothontheendotheliumandon (type2)macrophagesinthetumors.More-
mia, glioblastoma, melanoma, ovarian, leukocytes,wenextstudiedwhichofthese over, in microarray analyses the tumor
gastric, colon and breast cancer. In these celltypeswouldberelevantforthealtered infiltrating leukocytes in the CD73-
cells CD73 activity confers increased anti-tumor responses. deficient mice had more IFNc and NOS2
migratory and invasive capacity and aug- Since adenosine is proangiogenic, the mRNA (both markers of type 1 polarized
ments neovascularization of the tumors. CD73 deficiency might result in an ineffi- macrophages) than the wild-type controls.
InhibitionofcancercellCD73activitycan cient angiogenic switch in tumors. We Together these data suggest that the
impair tumor progression. found that CD73 is indeed induced in intratumoral accumulation of immune
The potential role of host CD73 in a subpopulation of neoangiogenic vessels suppressive cell types, Tregs and type 2
tumor growth has not been addressed. within the melanomas.7 However, there macrophages, is compromised in the
In our study, we used CD73-negative wasnodifference inthenumbers ofblood absenceofhostCD73(Fig.1).
tumor cells (B16 melanomas) and CD73- or lymphatic neovessels within the tumors Adenosinergic signaling can be mani-
deficient mice to dissect the contribution when comparing CD73-deficient and pulatedpharmacologicallyinvivo.Apyrase
*Correspondenceto:MarkoSalmi;Email:[email protected]
Submitted:09/30/11;Accepted:10/04/11
http://dx.doi.org/10.4161/onci.1.2.18310
www.landesbioscience.com OncoImmunology 247
©Figur e1.2TheCD073onhe1matopo2eticand noLn-hemaatopotinccellsodfthehoestregulsatesan ti-tBumorimimunoity.ThesenzymcaticacitiviteyCD73nisdepicctedatethe .
top.TheinvolvementofendothelialandleukocyteCD73inleukocyteextravasationandimmunesuppressioninwild-typeandCD73-deficientmiceare
illustrated.CD73regulatesrecruitmentofbothCD73-positiveand-negativeleukocytesbymodulatingtheendothelialadhesionmoleculesandpermeability,
andCD73mayalsohavedirectadhesivefunctions.Immunesuppressionismainlymediatedthroughtheproductionofadenosine.Inaddition,certaincancer
typesexpressCD73,anditaugmentsthemigrationofthesemalignantcellsandfurtherrendersthetumormicroenvironmentmoreimmune-suppressing.
hydrolyzes ATP and ADP into AMP, They show that ablation of host CD73 involved in tumor progression (Fig.1).
Do not distribute.
and AMPCP, a non-hydrolyzable nucleo- suppresses the growth of several tumor Tumorcell CD73enhancesthe migratory
tide analog, inhibits CD73 activity. We cells types in vivo. At least in OVA- properties of malignant cells and con-
observed that peritumoral injections of expressing model tumors, lack of host tributes to the immuno-evasion. On the
either apyrase or AMPCP significantly CD73 results in increased accumulation host leukocytes, CD73 activity also
retarded melanoma progression and of antigen-specific, IFNc producing contributes to the immunosuppression.
inhibited accumulation of immune- CD8+ T cells in the tumors. In Tregs On normal and neoangiogenic vessels,
suppressing cell types in wild-type mice.7 CD73 was shown to be functionally CD73 regulates the influx of leukocytes.
The same drugs had no effect on tumor important for their mune-suppressing Inhibition of CD73, which is induced
growth in CD73-deficient hosts. Thus, functions in tumors. Moreover, the under hypoxic conditions in tumors, by
pharmacological lowering of peritumoral endothelial CD73 was involved in the enzyme inhibitors, siRNA or function
ATP levels or adenosine production phe- recruitment of both anti-tumor leukocytes blocking monoclonal antibodies results
notypically reproduced the effects seen in andblood-bornemetastaticmelanomacells in attenuated tumor progression. There-
gene deletion experiments. alsoinvivo. fore, ectoenzymatic modulation of cancer
Recently, these findings have been Thus, the emerging concept is that may offer attractive therapeutic options in
recapitulatedbytwoindependentgroups.8,9 CD73 on bothhostand tumor cell side is future.
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