Hematopoietic activity of common marmoset CD34 cells isolated by a novel monoclonal antibody MA24.

OBJECTIVE: We focused on a small New World monkey, the common marmoset (Callithrix jacchus), to establish a nonhuman primate model of the treatment of hematological disorders. In this study, we developed the first monoclonal antibodies (MAbs) against marmoset CD34 and tested the in vitro and in vivo hemopoietic activity of cell populations isolated using one of these MAbs. METHODS AND RESULTS: Marmoset cDNA encoding a human CD34 homologue was cloned from bone marrow (BM)-derived RNA using reverse transcription polymerase chain reaction and rapid amplification of cDNA ends. The amino acid sequence of the marmoset CD34 had 81% homology with the human sequence. Five mouse MAbs were raised against marmoset CD34 transfectant. One representative MAb, MA24 (IgM), reacted with approximately 0.5 to 1% of BM mononuclear cells (MNCs), where the colony-forming unit granulocyte/macrophage (CFU-GM) was enriched approximately 11- to 75-fold as compared with the whole BM MNCs. Multilineage differentiation of marmoset CD34+ cells in NOD/SCID mice was confirmed by flow cytometry 1 month after xenotransplantation. CONCLUSION: These results demonstrated that MA24 is useful for the analysis and enrichment of hematopoietic progenitor cells in the marmoset model for preclinical experiments.

Blastocyst MHC, a putative murine homologue of HLA-G, protects TAP-deficient tumor cells from natural killer cell-mediated rejection in vivo.

Blastocyst MHC is a recently identified mouse MHC class Ib gene, which is selectively expressed in blastocyst and placenta, and may be the mouse homolog of HLA-G gene the products of which have been implicated in protection of fetal trophoblasts from maternal NK cells and evasion of some tumor cells from NK cell attack. In this study, we identified two blastocyst MHC gene transcripts encoding a full-length alpha-chain (bc1) and an alternatively spliced form lacking the alpha2 domain (bc2), which may be homologous to HLA-G1 and HLA-G2, respectively. Both placenta and a teratocarcinoma cell line predominantly expressed the bc2 transcript. When these cDNAs were expressed in TAP-deficient RMA-S or TAP-sufficient RMA cells, only bc1 protein was expressed on the surface of RMA cells, but both bc1 and bc2 proteins were retained in the cytoplasm of RMA-S cells. Significantly, the RMA-S cells expressing either bc1 or bc2 were protected from lysis by NK cells in vitro. This protection was at least partly mediated by up-regulation of Qa-1(b) expression on the surface of RMA-S cells, which engaged the CD94/NKG2A inhibitory receptor on NK cells. More importantly, the bc1- or bc2-expressing RMA-S cells were significantly protected from NK cell-mediated rejection in vivo. These results suggested a role for blastocyst MHC in protecting TAP-deficient trophoblasts and tumor cells from NK cell attack in vivo.

Microanatomical localization of PD-1 in human tonsils.

PD-1 is an immunoinhibitory receptor, which belongs structurally to the CD28 family. PD-1-deficient mice show breakdown of peripheral tolerance and manifest multiple autoimmune symptoms. We previously described expression of PD-1 on activated T and B lymphocytes and myeloid cells. However, little is known about the microanatomical distribution of PD-1 in lymphoid organs. In this study, we performed immunohistochemistry using monoclonal antibodies against human PD-1. In human tonsils, PD-1 was expressed on most of T cells and a small subset of centrocytes in the light zone of germinal centers (GCs), where clonal selection of centrocytes takes place. These results suggest that PD-1 may play an important role in GC reaction.