Jiashun Li

Rejection responses to allogeneic hepatocytes by reconstituted SCID mice, CD4, KO, and CD8 KO mice.

Introduction. The purpose of the current study was to investigate the capacity of CD4+, CD8+, or non-T cells to independently initiate acute rejection of allogeneic hepatocytes using reconstituted SCID, CD4 or CD8 knockout (KO) recipient mice. Methods. Allogeneic hepatocytes (FVB/N, H-2q) were transplanted into C57BL/6.SCID (H-2b), CD4 KO (H-2b), CD8 KO (H-2b), or beige/beige (H-2b) mice. SCID mice with functioning hepatocellular allografts subsequently received purified non-T cells (NTC), CD4+, or CD8+ splenocytes. Some mice were treated with anti-CD4, anti-CD8, and/or anti-nk1.1 mAb. Recipient mice were also assessed for donor-reactive delayed-type hypersensitivity (DTH) responses and donor-reactive alloantibody production. Results. Median hepatocellular allograft survival time (MST) was 28 days in CD4+ reconstituted SCID mice and 14 days in CD8+ reconstituted SCID mice. SCID hosts reconstituted with NTC demonstrated indefinite hepatocellular allograft survival (>120 days). MST was 10 days in untreated beige/beige (NK cell deficient) mice. MST was 14 days in untreated, 35 days in anti-CD4 mAb treated, and 10 days in anti-nk1.1 mAb treated CD8 KO mice. MST was 10 days in untreated, 35 days in anti-CD8 mAb treated, and 7 days in anti-nk1.1 mAb treated CD4 KO mice. Donor-reactive DTH responses were not detected in reconstituted SCID mice, were minimal in CD4 KO mice, and were prominent in CD8 KO mice after rejection of allogeneic hepatocytes. Similarly, donor-reactive alloantibody, was not detected in CD4 KO hosts, but was readily detected in CD8 KO hosts. Conclusions. These studies show that both CD4+ and CD8+ T cells (but not host NTC) can independently initiate the rejection of allogeneic hepatocytes. While hepatocyte rejection by isolated CD4+ T cells is not surprising, rejection by CD8+ T cells (in the absence of CD4+ T cells) was unusual, and may explain the failure of “standard” immunosuppressive regimens to suppress acute rejection of allogeneic hepatocytes, as noted in prior studies. Furthermore, NK cells do not appear to be required for either CD4+ T cell or CD8+ T cell initiated hepatocyte rejection.

Costimulation pathways in host immune responses to allogeneic hepatocytes.

BACKGROUND This study investigated the role of the CD28/B7 (blocked by CTLA4Ig) and CD40/CD40L (blocked by MR1) costimulation pathways on in vivo host T-cell- mediated immune responses to allogeneic hepatocytes. METHODS Survival of allogeneic hepatocytes (H-2q) in C57BL/6 (H-2b) mice untreated or treated with MR1, CTLA4Ig, L6 (control fusion protein), or a combination of MR1 and CTLA4Ig fusion protein was determined. RESULTS Median survival time for hepatocellular allografts was 10, 84, 10, 10, and 84 days in untreated (n= 10), MR1-treated (n=7) (P<.0001), CTLA4Ig-treated (n=7) (P=0.02), L6-treated (n=3) (P, not significant), and the combination of MR1- and CTLA4Ig-treated (n=6) (P=0.0003) groups, respectively. CONCLUSIONS Host treatment with MR1, but not CTLA4Ig, prolonged hepatocellular allograft survival. These data suggest that CD28/B7 interactions appear relatively unimportant, whereas CD40/CD40L interactions provide critical costimulator signals for T-cell-dependent immune responses to allogeneic hepatocytes.

In vivo immune response to allogeneic hepatocytes

T HE PURPOSE of the following study was to determine the in vivo fate of allogeneic hepatocytes (Hc) in a functional model of hepatocyte transplantation (Hc TX) in mice. The Hc TX model used in this study involved the creation of mice which expressed the transgene human alpha-1-antitrypsin (hAlAT) (under control of the hAlAT promoter) in the liver. Hc isolated from the transgenic donors produce and secrete hAlAT such that detection of the genetic “marker” protein (hAlAT) in recipient serum after Hc TX reflects the survival and intact metabolic function of the transplanted Hc. The advantages of this model include (1) the use of a direct method for monitoring graft function and survival (secretion of hAlAT), (2) histologic confirmation of hepatocellular graft survival can be determined easily by immunohistochemical analysis for Hc bearing the transgene hAlAT, (3) transgenic donor Hc may be transplanted into a variety of murine hosts which allows us to assess the influence of particular immunodeficient states as well as differences in host/donor MHC disparities on hepatocellular graft survival, and (4) permits the distinction between immunologic and nonimmunologic factors (including primary nonfunction, poor engraftment, and senescence of transplanted Hc) which may affect graft function and survival after Hc TX. One potential disadvantage of the model is that the genetic marker protein (hAlAT) may elicit an immune response which adversely affects graft survival. In the current study, this functional model of Hc TX was used to determine the fate of the transplanted Hc in syngeneic, allogeneic, and immunoincompetent hosts.