Semaphorins are a family of phylogenetically conserved soluble and transmembrane proteins. Although many soluble semaphorins deliver guidance cues to migrating axons during neuronal development, some members are involved in immune responses. For example, CD100 (also known as Sema4D), a class IV transmembrane semaphorin, signals through CD72 to effect nonredundant roles in immune responses in a ligand-receptor system that is distinct from any seen previously in the nervous system. Here we report that the class IV semaphorin Sema4A, which is expressed in dendritic cells and B cells, enhances the in vitro activation and differentiation of T cells and the in vivo generation of antigen-specific T cells. Treating mice with monoclonal antibodies against Sema4A blocks the development of an experimental autoimmune encephalomyelitis that is induced by an antigenic peptide derived from myelin oligodendrocyte glycoprotein. In addition, expression cloning shows that the Sema4A receptor is Tim-2, a member of the family of T-cell immunoglobulin domain and mucin domain (Tim) proteins that is expressed on activated T cells.

Human chromosomes or chromosome fragments derived from normal fibroblasts were introduced into mouse embryonic stem (ES) cells via microcell-mediated chromosome transfer (MMCT) and viable chimaeric mice were produced from them. Transferred chromosomes were stably retained, and human genes, including immunoglobulin (Ig) kappa, heavy, lambda genes, were expressed in proper tissue-specific manner in adult chimaeric tissues. In the case of a human chromosome (hChr.) 2-derived fragment, it was found to be transmitted to the offspring through the germline. Our study demonstrates that MMCT allows for introduction of very large amounts of foreign genetic material into mice. This novel procedure will facilitate the functional analyses of human genomes in vivo.

The class IV semaphorin Sema4A provides a costimulatory signal to T cells. To investigate the possible developmental and regulatory roles of Sema4A in vivo, we generated Sema4A-deficient mice. Although Sema4A-deficient mice develop normally, DCs and T cells from knockout mice display poor allostimulatory activities and T helper cell (Th) differentiation, respectively. Interestingly, in addition to its expression on DCs, Sema4A is upregulated on Th1-differentiating cells, and it is necessary for in vitro Th1 differentiation and T-bet expression. Consequently, in vivo antigen-specific T cell priming and antibody responses against T cell-dependent antigens are impaired in the mutant mice. Additionally, Sema4A-deficient mice exhibit defective Th1 responses. Furthermore, reconstitution studies with antigen-pulsed DCs reveal that DC-derived Sema4A is important for T cell priming, while T cell-derived Sema4A is involved in developing Th1 responses. Collectively, these results indicate a nonredundant role of Sema4A not only in T cell priming, but also in the regulation of Th1/Th2 responses.

Lymphocytes are most reliably subdivided on the basis of their receptors for antigen at the cell surface. Three subtypes of lymphocytes are well defined: B cells that bear surface immunoglobulin and make antibody, CD4+T cells with CD3 alpha beta receptors specific for antigen associated with class II major histocompatibility complex molecules, and CD8+T cells with CD3 alpha beta receptors specific for antigen associated with class I MHC molecules. These T cells are responsible for known forms of cell-mediated immunity. The discovery of a third rearranging T-cell specific gene called gamma (refs 1 and 2) has revealed the presence of a new class of T cells bearing a new receptor type, CD3 gamma delta (refs 3-7). To date, neither the function nor the specificity of cells bearing this receptor has been determined. Because gamma delta T cells are the main lymphocyte of epidermis, it was proposed that such cells could be important in surveillance of all epithelia. We have isolated intraepithelial lymphocytes from murine small intestine, and shown that they predominantly or exclusively express CD3 gamma delta receptors. Unlike the epidermal lymphocytes, these cells also express CD8, and they use a different V lambda gene to form their receptor. This strongly suggests that gamma delta T cells home in a very specific manner to epithelia, where they presumably mediate their function.

Prion diseases are caused by propagation of misfolded forms of the normal cellular prion protein PrP C , such as PrP BSE in bovine spongiform encephalopathy (BSE) in cattle and PrP CJD in Creutzfeldt-Jakob disease (CJD) in humans 1 . Disruption of PrP C expression in mice, a species that does not naturally contract prion diseases, results in no apparent developmental abnormalities [2][3][4][5] . However, the impact of ablating PrP C function in natural host species of prion diseases is unknown. Here we report the generation and characterization of PrP C -deficient cattle produced by a sequential gene-targeting system 6 . At over 20 months of age, the cattle are clinically, physiologically, histopathologically, immunologically and reproductively normal. Brain tissue homogenates are resistant to prion propagation in vitro as assessed by protein misfolding cyclic amplification 7 . PrP C -deficient cattle may be a useful model for prion research and could provide industrial bovine products free of prion proteins.To generate PrP C -deficient (PRNP −/− ) cattle, we transfected a male Holstein primary fetal fibroblast line 6594 with first and second knockout (KO) vectors (pBPrP(H)KOneo and pBPrP (H)KOpuro vectors) 6 to sequentially disrupt the two alleles of PRNP. PRNP −/− fetal cell lines were established at 40-60 d of gestation and three of the PRNP −/− fetal cell lines (5211, 5232 and 4296) were recloned to produce calves (Table 1 and Fig. 1a). To verify that the calves possess the PRNP −/− genotype, we collected ear biopsies and established fibroblast cell lines for genotyping. Genotyping was done by genomic PCR specific to each gene targeting event 6 (primer pairs: neoF7 × neoR7 and puroF14 × puroR14, Fig. 1b COMPETING INTERESTS STATEMENTThe authors declare competing financial interests (see the Nature Biotechnology website for details).Reprints and permissions information is available online at http://npg.nature.com/reprintsandpermissions/ NIH Public Access Fig. 1c) and confirmed the disruption of PRNP-specific mRNA expression in PRNP −/− calves. For protein expression analysis, we performed PrP-specific western blot analyses on fibroblasts (Fig. 1d), peripheral blood lymphocytes (Fig. 1e) and brain stem (Fig. 1f) from wild-type and PRNP −/− calves using the mouse anti-bovine PrP monoclonal antibody F89. We detected PrP-specific bands in the wild-type calves, whereas no reaction was observed in PRNP −/− calves and negative control mouse fibroblasts. These data clearly demonstrate that the PRNP gene is functionally inactivated in the PRNP −/− calves.PRNP −/− cattle were monitored for growth and general health status from birth to 20 months of age. Mean birth weight was 46 kg and average daily gain was 0.91 kg/d to 10 months. Both values were in the normal range for Holstein bulls. Serum chemistry was evaluated at 6 months of age and compared with published reference ranges. All the values for PRNP −/− calves (n = 12) were well within the reference range (Supplementary Table 1) and obvious abnormalities w...

CD100 belongs to the semaphorin family, several members of which are known to act as repulsive axonal guidance factors during neuronal development. We have previously demonstrated that CD100 plays a crucial role in humoral immunity. In this study, we show that CD100 is also important for cellular immunity through the maturation of dendritic cells (DCs). CD100−/− mice fail to develop experimental autoimmune encephalomyelitis induced by myelin oligodendrocyte glycoprotein peptide, because myelin oligodendrocyte glycoprotein-specific T cells are not generated in the absence of CD100. In vitro studies with T cells from OVA-specific TCR-transgenic mice demonstrate that Ag-specific T cells lacking CD100 fail to differentiate into cells producing either IL-4 or IFN-γ in the presence of APCs and OVA peptide. In addition, DCs from CD100−/− mice display poor allostimulatory capabilities and defects in costimulatory molecule expression and IL-12 production. The addition of exogenous soluble rCD100 restores normal functions in CD100−/− DCs and further enhances functions of normal DCs. Furthermore, treatment of Ag-pulsed DCs with both soluble CD100 and anti-CD40 before immunization significantly enhances their immunogenicity. This treatment elicits improved T cell priming in vivo, enhancing both primary and memory T cell responses. Collectively, these results demonstrate that CD100, which enhances the maturation of DCs, is essential in the activation and differentiation of Ag-specific T cells.

Antigen-specific human polyclonal antibodies (hpAbs), produced by hyperimmunization, could be useful for treating many human diseases. However, yields from available transgenic mice and transchromosomic (Tc) cattle carrying human immunoglobulin loci are too low for therapeutic applications. We report a Tc bovine system that produces large yields of hpAbs. Tc cattle were generated by transferring a human artificial chromosome vector carrying the entire unrearranged, human immunoglobulin heavy (hIGH) and kappa-light (hIGK) chain loci to bovine fibroblasts in which two endogenous bovine IgH chain loci were inactivated. Plasma from the oldest animal contained >2 g/l of hIgG, paired with either human kappa-light chain (up to approximately 650 microg/ml, fully human) or with bovine kappa- or lambda-light chain (chimeric), with a normal hIgG subclass distribution. Hyperimmunization with anthrax protective antigen triggered a hIgG-mediated humoral immune response comprising a high proportion of antigen-specific hIgG. Purified, fully human and chimeric hIgGs were highly active in an in vitro toxin neutralization assay and protective in an in vivo mouse challenge assay.

The use of a human chromosome or its fragment as a vector for animal transgenesis may facilitate functional studies of large human genomic regions. We describe here the generation and analysis of double trans-chromosomic (Tc) mice harboring two individual human chromosome fragments (hCFs). Two transmittable hCFs, one containing the Ig heavy chain locus (IgH, Ϸ1.5 Mb) and the other the light chain locus (Ig, Ϸ2 Mb), were introduced into a mouse strain whose endogenous IgH and Ig loci were inactivated. In the resultant double-Tc͞double-knockout mice, substantial proportion of the somatic cells retained both hCFs, and the rescue in the defect of Ig production was shown by high level expression of human Ig heavy and chains in the absence of mouse heavy and chains. In addition, serum expression profiles of four human Ig ␥ subclasses resembled those seen in humans. They mounted an antigen-specific human antibody response upon immunization with human serum albumin, and human serum albumin-specific human monoclonal antibodies with various isotypes were obtained from them. These results represent a generation of mice with ''humanized'' loci by using the transmittable hCFs, which suggest that the Tc technology may allow for the humanization of over megabase-sized, complex loci in mice or other animals. Such animals may be useful not only for studying in vivo functions of the human genome but also for obtaining various therapeutic products.