Conditional Deletion of Pdcd1 Identifies the Cell-Intrinsic Action of PD-1 on Functional CD8 T Cell Subsets for Antitumor Efficacy

Programmed cell death-1 (PD-1) blockade has a profound effect on the ability of the immune system to eliminate tumors, but many questions remain about the cell types involved and the underlying mechanisms of immune activation. To shed some light on this, the cellular and molecular events following inhibition of PD-1 signaling was investigated in the MC-38 colon carcinoma model using constitutive (PD-1 KO) and conditional (PD1cKO) mice and in wild-type mice treated with PD-1 antibody. The impact on both tumor growth and the development of tumor immunity was assessed. In the PD-1cKO mice, a complete deletion of Pdcd1 in tumor-infiltrating T cells (TILs) after tamoxifen treatment led to the inhibition of tumor growth of both small and large tumors. Extensive immune phenotypic analysis of the TILs by flow and mass cytometry identified 20-different T cell subsets of which specifically 5-CD8 positive ones expanded in all three models after PD-1 blockade. All five subsets expressed granzyme B and interferon gamma (IFNγ). Gene expression analysis of the tumor further supported the phenotypic analysis in both PD-1cKO- and PD-1 Ab-treated mice and showed an upregulation of pathways related to CD4 and CD8 T-cell activation, enhanced signaling through costimulatory molecules and IFNγ, and non-T-cell processes. Altogether, using PD-1cKO mice, we define the intrinsic nature of PD-1 suppression of CD8 T-cell responses in tumor immunity.

Functional defect of peripheral neutrophils in mice with induced deletion of CXCR2

Type 2 CXC chemokine receptor CXCR2 plays roles in development, tumorigenesis, and inflammation. CXCR2 also promotes demyelination and decreases remyelination by actions toward hematopoietic cells and nonhematopoietic cells. Germline CXCR2 deficient (Cxcr2(-/-) ) mice reported in 1994 revealed the complexity of CXCR2 function and its differential expression in varied cell-types. Here, we describe Cxcr2(fl/fl) mice for which the targeting construct was generated by recombineering based on homologous recombination in E. coli. Without recombination Cxcr2(fl/fl) mice have CXCR2 expression on neutrophils in peripheral blood, bone marrow and spleen. Cxcr2(fl/fl) mice were crossed to Mx-Cre mice in which Cre recombinase is induced by Type I interferons, elicited by injection with polyinosinic-polycytidylic acid (poly(I:C)). CXCR2-deficient neutrophils were observed in poly(I:C) treated Cxcr2(fl/fl) ::Mx-Cre(+) (Cxcr2-CKO) mice, but not in poly(I:C) treated Cxcr2(f//+) ::Mx-Cre(+) mice. CXCR2 deletion was mainly observed peripherally but not in the CNS. Cxcr2-CKO mice showed impaired neutrophil migration in sterile peritonitis. Cxcr2-CKO mice reported here will provide a genetic reagent to dissect roles of CXCR2 in the neutrophil granulocyte lineage. Furthermore Cxcr2(fl/fl) mice will provide useful genetic models to evaluate CXCR2 function in varied cell populations.

Design and Generation of Gene-Targeting Vectors

This unit provides an overview of the major types of mutant alleles that can be generated by gene targeting in ES cells. It presents the growing public resources of premade gene targeting vectors, modified ES cells, and mutant mice. General guidelines for the design of targeting vectors are followed by protocols for the construction of vectors to generate knockout (KO), conditional KO, and subtle mutant alleles. Curr. Protoc. Mouse Biol. 1:199-211. © 2011 by John Wiley & Sons, Inc.