Blockade of CD40-CD154 interferes with human T cell engraftment in scid mice.

Antibodies to the ligand for CD40 (CD154) have been shown to exert profound effects on the development of cell-mediated immune responses in mice. The present study shows that an antibody to human CD154 (hCD40L) inhibits in vivo Tetanus toxoid (TT) specific secondary antibody responses in hu-PBL-scid mice, as well as the expansion of xenoreactive human T cells in the scid mice. A possible cause for the reduced expansion of xenoreactive, human T cells, was the decreased expression of murine B7.1 and B7.2 caused by the administration of anti-hCD40L. Therefore, it may be that defective maturation of murine antigen-presenting cells impeded the priming and expansion of human xenoreactive T cells.

Regulation of human cell engraftment and development of EBV-related lymphoproliferative disorders in Hu-PBL-scid mice.

Human PBMC engraft in mice homozygous for the severe combined immunodeficiency (Prkdcscid) mutation (Hu-PBL-scid mice). Hu-PBL-NOD-scid mice generate 5- to 10-fold higher levels of human cells than do Hu-PBL-C.B-17-scid mice, and Hu-PBL-NOD-scid beta2-microglobulin-null (NOD-scid-B2mnull) mice support even higher levels of engraftment, particularly CD4+ T cells. The basis for increased engraftment of human PBMC and the functional capabilities of these cells in NOD-scid and NOD-scid-B2mnull mice are unknown. We now report that human cell proliferation in NOD-scid mice increased after in vivo depletion of NK cells. Human cell engraftment depended on CD4+ cells and required CD40-CD154 interaction, but engrafted CD4+ cells rapidly became nonresponsive to anti-CD3 Ab stimulation. Depletion of human CD8+ cells led to increased human CD4+ and CD20+ cell engraftment and increased levels of human Ig. We further document that Hu-PBL-NOD-scid mice are resistant to development of human EBV-related lymphoproliferative disorders. These disorders, however, develop rapidly following depletion of human CD8+ cells and are prevented by re-engraftment of CD8+ T cells. These data demonstrate that 1) murine NK cells regulate human cell engraftment in scid recipients; 2) human CD4+ cells are required for human CD8+ cell engraftment; and 3) once engrafted, human CD8+ cells regulate human CD4+ and CD20+ cell expansion, Ig levels, and outgrowth of EBV-related lymphoproliferative disorders. We propose that the Hu-PBL-NOD-scid model is suitable for the in vivo analysis of immunoregulatory interactions between human CD4+ and CD8+ cells.

Enhanced human CD4+ T cell engraftment in beta2-microglobulin-deficient NOD-scid mice.

Genetic crosses produced NOD/LtSz mice doubly homozygous for the severe combined immunodeficiency (scid) mutation and the beta2m (B2m) null allele. Both NOD/LtSz-scid/scid and NOD/LtSz-scid/scid B2m(null) mice lacked mature lymphocytes and serum Ig. However, homozygosity for the B2m(null) allele also resulted in the absence of MHC class I expression, loss of NK cell activity, accumulation of iron in the liver, and rapid clearance of human IgG1. NOD/LtSz-scid/scid B2m(null) mice supported markedly elevated levels of human T cell engraftment, compared with NOD/LtSz-scid/scid control animals, following injection with human PBMC. The increased engraftment was associated with a major increase in the number of human CD4+ T cells. Following injection with 20 million human PBMC, levels of human CD4+ T cells in the peripheral blood and spleen of NOD/ LtSz-scid/scid B2m(null) mice were 6- to 7-fold higher than those in NOD/LtSz-scid/scid mice and >50-fold higher than those in C.B-17-scid/scid mice. The resulting normalization of CD4+/CD8+ ratios in NOD/LtSz-scid/scid B2m(null) mice is in sharp contrast to that observed in NOD/LtSz-scid/scid mice or in C.B-17-scid/scid mice. Circulating human IgG was cleared 6-fold more rapidly in NOD/LtSz-scid/scid B2m(null) mice than in NOD/LtSz-scid/scid mice. This rapid IgG clearance suggested a failure of the engrafted human lymphoid cells to maintain high circulating levels of human IgG. The higher levels of human CD4+ T cells and the normalization of the CD4:CD8 ratio that are observed in human PBMC-engrafted NOD/LtSz-scid/scid B2m(null) mice suggest that this system may be an excellent model for studies of HIV pathogenesis.

NOD/LtSz-Rag1null mice: an immunodeficient and radioresistant model for engraftment of human hematolymphoid cells, HIV infection, and adoptive transfer of NOD mouse diabetogenic T cells.

Development of a small animal model for the in vivo study of human immunity and infectious disease remains an important goal, particularly for investigations of HIV vaccine development. NOD/Lt mice homozygous for the severe combined immunodeficiency (Prkdcscid) mutation readily support engraftment with high levels of human hematolymphoid cells. However, NOD/LtSz-scid mice are highly radiosensitive, have short life spans, and a small number develop functional lymphocytes with age. To overcome these limitations, we have backcrossed the null allele of the recombination-activating gene (Rag1) for 10 generations onto the NOD/LtSz strain background. Mice deficient in RAG1 activity are unable to initiate V(D)J recombination in Ig and TCR genes and lack functional T and B lymphocytes. NOD/LtSz-Rag1null mice have an increased mean life span compared with NOD/LtSz-scid mice due to a later onset of lymphoma development, are radioresistant, and lack serum Ig throughout life. NOD/LtSz-Rag1null mice were devoid of mature T or B cells. Cytotoxic assays demonstrated low NK cell activity. NOD/LtSz-Rag1null mice supported high levels of engraftment with human lymphoid cells and human hemopoietic stem cells. The engrafted human T cells were readily infected with HIV. Finally, NOD/LtSz-Rag1null recipients of adoptively transferred spleen cells from diabetic NOD/Lt+/+ mice rapidly developed diabetes. These data demonstrate the advantages of NOD/LtSz-Rag1null mice as a radiation and lymphoma-resistant model for long-term analyses of engrafted human hematolymphoid cells or diabetogenic NOD lymphoid cells.