title: Radiotherapy increases the permissiveness of established mammary tumors to rejection by immunomodulatory antibodies.
abstract: It is becoming increasingly evident that radiotherapy may benefit from coincident or subsequent immunotherapy. In this study, we examined whether the antitumor effects of radiotherapy, in established triple-negative breast tumors could be enhanced with combinations of clinically relevant monoclonal antibodies (mAb), designed to stimulate immunity [anti-(α)-CD137, α-CD40] or relieve immunosuppression [α-programmed death (PD)-1]. While the concomitant targeting of the costimulatory molecules CD137 and CD40 enhanced the antitumor effects of radiotherapy and promoted the rejection of subcutaneous BALB/c-derived 4T1.2 tumors, this novel combination was noncurative in mice bearing established C57BL/6-derived AT-3 tumors. We identified PD-1 signaling within the AT-3 tumors as a critical limiting factor to the therapeutic efficacy of α-CD137 therapy, alone and in combination with radiotherapy. Strikingly, all mice bearing established orthotopic AT-3 mammary tumors were cured when α-CD137 and α-PD-1 mAbs were combined with single- or low-dose fractionated radiotherapy. CD8+ T cells were essential for curative responses to this combinatorial regime. Interestingly, CD137 expression on tumor-associated CD8+ T cells was largely restricted to a subset that highly expressed PD-1. These CD137+PD-1High CD8+ T cells, persisted in irradiated AT-3 tumors, expressed Tim-3, granzyme B and Ki67 and produced IFN-γ ex vivo in response to phorbol 12-myristate 13-acetate (PMA) and ionomycin stimulation. Notably, radiotherapy did not deplete, but enriched tumors of functionally active, tumor-specific effector cells. Collectively, these data show that concomitant targeting of immunostimulatory and inhibitory checkpoints with immunomodulatory mAbs can enhance the curative capacity of radiotherapy in established breast malignancy.
authors.affiliation: Cancer Therapeutics Program, Sir Donald and Lady Trescowthick Laboratories, Department of Physical Sciences, Peter MacCallum Cancer Centre, East Melbourne, VIC, Australia. i.verbrugge@nki.nl
authors.forename: Inge
authors.initials: I
authors.lastname: Verbrugge
authors.forename: Jim
authors.initials: J
authors.lastname: Hagekyriakou
authors.forename: Leslie L
authors.initials: LL
authors.lastname: Sharp
authors.forename: Mara
authors.initials: M
authors.lastname: Galli
authors.forename: Alison
authors.initials: A
authors.lastname: West
authors.forename: Nicole M
authors.initials: NM
authors.lastname: McLaughlin
authors.forename: Hélène
authors.initials: H
authors.lastname: Duret
authors.forename: Hideo
authors.initials: H
authors.lastname: Yagita
authors.forename: Ricky W
authors.initials: RW
authors.lastname: Johnstone
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Smyth
authors.forename: Nicole M
authors.initials: NM
authors.lastname: Haynes
mesh_terms: D000818:Animals; D000906:Antibodies / Q000276:immunology*; D015703:Antigens, CD / Q000276:immunology; D016923:Cell Death / Q000528:radiation effects; D020287:In Situ Nick-End Labeling; D008325:Mammary Neoplasms, Experimental / Q000276:immunology / Q000473:pathology / Q000532:radiotherapy*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D011839:Radiation, Ionizing; D016176:T-Lymphocyte Subsets
chemical_list: D000906:Antibodies; D015703:Antigens, CD