title: Definitive activation of endogenous antitumor immunity by repetitive cycles of cyclophosphamide with interspersed Toll-like receptor agonists.
abstract: Many cancers both evoke and subvert endogenous anti-tumor immunity. However, immunosuppression can be therapeutically reversed in subsets of cancer patients by treatments such as checkpoint inhibitors or Toll-like receptor agonists (TLRa). Moreover, chemotherapy can leukodeplete immunosuppressive host elements, including myeloid-derived suppressor cells (MDSCs) and regulatory T-cells (Tregs). We hypothesized that chemotherapy-induced leukodepletion could be immunopotentiated by co-administering TLRa to emulate a life-threatening infection. Combining CpG (ODN 1826) or CpG+poly(I:C) with cyclophosphamide (CY) resulted in uniquely well-tolerated therapeutic synergy, permanently eradicating advanced mouse tumors including 4T1 (breast), Panc02 (pancreas) and CT26 (colorectal). Definitive treatment required endogenous CD8+ and CD4+ IFNγ-producing T-cells. Tumor-specific IFNγ-producing T-cells persisted during CY-induced leukopenia, whereas Tregs were progressively eliminated, especially intratumorally. Spleen-associated MDSCs were cyclically depleted by CY+TLRa treatment, with residual monocytic MDSCs requiring only continued exposure to CpG or CpG+IFNγ to effectively attack malignant cells while sparing non-transformed cells. Such tumor destruction occurred despite upregulated tumor expression of Programmed Death Ligand-1, but could be blocked by clodronate-loaded liposomes to deplete phagocytic cells or by nitric oxide synthase inhibitors. CY+TLRa also induced tumoricidal myeloid cells in naive mice, indicating that CY+TLRa's immunomodulatory impacts occurred in the complete absence of tumor-bearing, and that tumor-induced MDSCs were not an essential source of tumoricidal myeloid precursors. Repetitive CY+TLRa can therefore modulate endogenous immunity to eradicate advanced tumors without vaccinations or adoptive T-cell therapy. Human blood monocytes could be rendered similarly tumoricidal during in vitro activation with TLRa+IFNγ, underscoring the potential therapeutic relevance of these mouse tumor studies to cancer patients.
authors.affiliation: Department of Immunology, Mayo Clinic in Arizona, Scottsdale, AZ, USA.
authors.forename: Soraya Zorro
authors.initials: SZ
authors.lastname: Manrique
authors.affiliation: Department of Immunology, Mayo Clinic in Arizona, Scottsdale, AZ, USA.
authors.forename: Ana L
authors.initials: AL
authors.lastname: Dominguez
authors.affiliation: Department of Immunology, Mayo Clinic in Arizona, Scottsdale, AZ, USA.
authors.forename: Noweeda
authors.initials: N
authors.lastname: Mirza
authors.affiliation: Department of Immunology, Mayo Clinic in Arizona, Scottsdale, AZ, USA.
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Spencer
authors.affiliation: Department of Immunology, Mayo Clinic in Arizona, Scottsdale, AZ, USA.
authors.forename: Judy M
authors.initials: JM
authors.lastname: Bradley
authors.affiliation: Department of Immunology, Lerner Research Institute, Cleveland, OH, USA.
authors.forename: James H
authors.initials: JH
authors.lastname: Finke
authors.affiliation: Department of Biochemistry and Molecular Biology, Mayo Clinic in Arizona, Scottsdale, AZ, USA.|Division of Pulmonary Medicine, Mayo Clinic in Arizona, Scottsdale, AZ, USA.
authors.forename: James J
authors.initials: JJ
authors.lastname: Lee
authors.affiliation: Department of Immunology, Mayo Clinic in Arizona, Scottsdale, AZ, USA.
authors.forename: Larry R
authors.initials: LR
authors.lastname: Pease
authors.affiliation: Department of Immunology, Mayo Clinic in Arizona, Scottsdale, AZ, USA.|Department of Biochemistry and Molecular Biology, Mayo Clinic in Arizona, Scottsdale, AZ, USA.|Division of Hematology/Oncology, Mayo Clinic in Arizona, Scottsdale, AZ, USA.
authors.forename: Sandra J
authors.initials: SJ
authors.lastname: Gendler
authors.affiliation: Department of Immunology, Mayo Clinic in Arizona, Scottsdale, AZ, USA.|Division of Hematology/Oncology, Mayo Clinic in Arizona, Scottsdale, AZ, USA.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Cohen
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D003520:Cyclophosphamide / Q000494:pharmacology*; D005260:Female; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology; D007369:Interferon Inducers / Q000494:pharmacology; D007371:Interferon-gamma / Q000276:immunology / Q000378:metabolism; D008325:Mammary Neoplasms, Experimental / Q000188:drug therapy* / Q000276:immunology / Q000378:metabolism; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008819:Mice, Nude; D022423:Myeloid Cells / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D009838:Oligodeoxyribonucleotides / Q000494:pharmacology*; D011070:Poly I-C / Q000494:pharmacology*; D013601:T-Lymphocytes / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism; D050378:T-Lymphocytes, Regulatory / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D051193:Toll-Like Receptors / Q000819:agonists* / Q000378:metabolism
chemical_list: C423449:CpG ODN 1826; D007166:Immunosuppressive Agents; D007369:Interferon Inducers; D009838:Oligodeoxyribonucleotides; D051193:Toll-Like Receptors; D007371:Interferon-gamma; D003520:Cyclophosphamide; D011070:Poly I-C
keywords: Immunology and Microbiology Section, Immune response, Immunity; cancer immunotherapy, chemotherapy, TLR agonists, MDSCs, Tregs