title: Anti-PD-1 synergizes with cyclophosphamide to induce potent anti-tumor vaccine effects through novel mechanisms.
abstract: Programmed death-1 receptor (PD-1) is expressed on T cells following TCR activation. Binding of this receptor to its cognate ligands, programmed death ligand (PDL)-1 and PDL-2, down-regulates signals by the TCR, promoting T-cell anergy and apoptosis, thus leading to immune suppression. Here, we find that using an anti-PD-1 antibody (CT-011) with Treg-cell depletion by low-dose cyclophosphamide (CPM), combined with a tumor vaccine, induces synergistic antigen-specific immune responses and reveals novel activities of each agent in this combination. This strategy led to complete regression of established tumors in a significant percentage of treated animals, with survival prolongation. We show for the first time that combining CT-011 and CPM significantly increases the number of vaccine-induced tumor-infiltrating CD8(+)  T cells, with simultaneous decrease in infiltrating Treg cells. Interestingly, we find that CT-011 prolongs Treg-cell inhibition induced by CPM, leading to a sustainable significant synergistic decrease of splenic and tumor-infiltrated Treg cells. Surprisingly, we find that the anti-tumor effect elicited by the combination of CT-011 and CPM is dependent on both CD8(+)  and CD4(+)  T-cell responses, although the antigen we used is a class I MHC-restricted peptide. Thus, we describe a novel and effective therapeutic approach by combining multiple strategies to target several tumor-mediated immune inhibitory mechanisms.
authors.affiliation: Cancer Vaccine Section, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Mikayel
authors.initials: M
authors.lastname: Mkrtichyan
authors.forename: Yana G
authors.initials: YG
authors.lastname: Najjar
authors.forename: Estella C
authors.initials: EC
authors.lastname: Raulfs
authors.forename: Maher Y
authors.initials: MY
authors.lastname: Abdalla
authors.forename: Raed
authors.initials: R
authors.lastname: Samara
authors.forename: Rinat
authors.initials: R
authors.lastname: Rotem-Yehudar
authors.forename: Larry
authors.initials: L
authors.lastname: Cook
authors.forename: Samir N
authors.initials: SN
authors.lastname: Khleif
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000008:administration & dosage / Q000276:immunology; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism*; D060890:B7-H1 Antigen / Q000276:immunology* / Q000378:metabolism; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D018414:CD8-Positive T-Lymphocytes / Q000187:drug effects / Q000276:immunology; D019496:Cancer Vaccines / Q000276:immunology; D003520:Cyclophosphamide / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D008213:Lymphocyte Activation; D051379:Mice; D008810:Mice, Inbred C57BL; D009374:Neoplasms, Experimental / Q000276:immunology / Q000628:therapy*; D050725:Papillomavirus E7 Proteins / Q000008:administration & dosage / Q000276:immunology; D061027:Programmed Cell Death 1 Ligand 2 Protein / Q000276:immunology* / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell; D050378:T-Lymphocytes, Regulatory / Q000187:drug effects / Q000276:immunology / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D051017:Apoptosis Regulatory Proteins; D060890:B7-H1 Antigen; D019496:Cancer Vaccines; C498919:Cd274 protein, mouse; D050725:Papillomavirus E7 Proteins; C556978:Pdcd1lg2 protein, mouse; D061027:Programmed Cell Death 1 Ligand 2 Protein; D011948:Receptors, Antigen, T-Cell; C059731:oncogene protein E7, Human papillomavirus type 16; D003520:Cyclophosphamide