SCID mouse as a model for transplantation studies.

Mice expressing the severe combined immunodeficiency trait (SCID) lack functional T and B lymphocytes and have been widely used for the study of B- cell development and for cancer and HIV research. The purpose of this study was to evaluate the SCID mouse as a potential model for T-cell maturation and transplantation studies. C3H/HEN SCID mice screened by fluorescence-activated cell sorting (FACS) and radial immunodiffusion assay (RID) were verified homozygous recessive if CD3-, CD22-, and serum (IgG) <5 mg/liter. C3H/HEN SCID mice pretreated with 250 R total-body gamma irradiation were reconstituted with 2.5 to 4 x 10(7) donor bone marrow cells derived from [syngeneic (syn): male wild-type C3H/HEN, allogeneic (allo): male BALB/c or C57BL/6) mice by intravenous injection. Four weeks post-transplant, engraftment was determined by FACS; repopulation of blood, thymus, and spleen; RID; and histologic evaluation. Immune function against donor, recipient, and third-party antigen was assayed in vitro by mixed lymphocyte response (MLR) and in vivo by full-thickness skin grafting. Greater than 90% of both syngeneic and allogeneic reconstitutions expressed CD3+, CD4+, CD8+, and CD22+ cells of donor origin in peripheral blood and spleen. FACS analyses of lymphocyte subpopulations in blood and spleen were not significantly different between reconstituted SCID mice and wild-type C3H/HEN or BALB/c controls, with engraftment stable for >4 months. No evidence of graft-versus-host disease was observed in stable, long-term (>4 months postreconstitution) chimeras. White blood cell, total thymocyte, and total splenocyte counts were significantly elevated (P < 0.05: ANOVA, Student's t) following reconstitution of homozygous SCID mice to levels found in wild-type controls. Serum (IgG) for reconstituted allo- and syn-SCID mice was consistently > 150 mg/liter (n = 22), with histologic lymphocyte engraftment of spleen, duodenum, and thymus. Histologic examination of lymphocyte engraftment in spleen, duodenum, and thymus was indistinguishable from normal controls in SCID mice after reconstitution. Prior to reconstitution, scant lymphoid cells were observed at these sites. Allo-SCID splenocyte response against third-party antigen was significantly elevated (P < 0.01: ANOVA, Student's t) when compared with donor and recipient antigen response with a proliferation index (PI) comparable to wild-type controls. Unreconstituted SCID mice were unresponsive. In vivo, allo-SCID mice demonstrated rejection of only third-party skin grafts between postoperative days 9 and 14 (controls: postoperative days 7 and 11). The SCID mouse model demonstrates in vitro and in vivo B- and T-cell immune function comparable to that of wild-type mice and provides a useful model for T-cell maturation and transplantation studies.