Engraftment of Human Peripheral Blood Lymphocytes in Normal Strains of Mice

Abstract

AbstractTransplantation of bone marrow from SCID mice into le-thally irradiated normal mice can potentially endow the normal recipients with characteristics typical of the immune-deficient SCID mouse. In the present study, we investigated whether intraperitoneal grafting of human peripheral blood lymphocytes (PBLs), which has been documented in the SCID mouse, can also be achieved in irradiated BALB/c mice radioprotected with SCID bone marrow. Evaluation of different radiation protocols suggested that, considering the quality of engraftment and rate of survival, optimal results were obtained with split dose total body irradiation (TBI; 4 Gy followed 3 days later by 10 Gy). Monitoring of mouse T cells in peripheral blood indicated an inverse correlation between the presence of such cells and the engraftment of human CD45+ cells in the peritoneum. Also, engraftment of human PBLs in nude BALB/c mice, conditioned with the same radiation protocol, was significantly higher than that achieved in their normal counterparts. Further improvement of human PBL engraftment was found when the mice were thymectomized 2 weeks before conditioning with split TBI. After transplantation of 80 × 106 human PBLs in such recipients, a marked engraftment of human T cells and B cells in the peritoneum cavity could be detected for at least 2 months, whereas significant amounts of human Ig could be detected for more than 3 months. Migration of human PBLs into internal organs such as spleen, liver, kidney, and lungs (and into thymus in nonthymectomized mice) was found within a few days of grafting and also persisted for 2 to 3 months. The majority of the engrafted lymphocytes were single-positive CD4+ and CD8+ T lymphocytes, about 50% of which were activated, as judged by their expression of HLA-DR. Staining with anti-CD25 antibody was lower compared with that found with anti-HLA-DR. CD20+ B cells were detected in all of the above-mentioned internal organs, but were mainly concentrated in the spleen. CD14+ monocytes could be detected only during the first week posttransplant of PBLs. Total human Ig in peripheral blood reached an average of 2.8 mg/mL 14 days posttransplant, and continued to be significant for several months. In vitro transformation by Epstein-Barr virus of human B cells from different tissues could be established 30 days after transplantation and led to outgrowth of two lgG+ cell lines, two IgM+ cell lines, and one IgA+ cell line, producing 0.6 to 4.2 µg/mL human Ig in the supernatant. Sporadic manifestations of graft-versus-host disease were observed, but the survival of human → mice chimera, during a follow-up period of 100 days, was about 50% to 60%, similar to that found in a control group transplanted with SCID bone marrow but without human PBLs. Epstein-Barr virus lymphoma, usually found in a large proportion of SCID mice transplanted with human PBLs from sero-positive donors, was not observed throughout the study. Transplantation of human PBLs in other recipients, such as C3H/HeJ, CBA/J, or transgenic C57BL/6-HLA class I (B7) mice, which are H-2 incompatible with the SCID mouse, was also achieved by using SCID bone marrow for radioprotection. Also, the engraftment of human PBLs in the outbred immune-deficient BNX mouse, which was found to be inadequate after sublethal TBI (4 Gy), was markedly improved by using lethal TBI (12 Gy) followed by radioprotection with SCID bone marrow. The use of lethal TBI followed by radio-protection with SCID bone marrow provides a general approach to achieve engraftment of human PBLs in several normal strains of mice.