Systemic administration of CTLA4-Ig or anti-CD40 ligand antibody inhibits second-set rejection of mouse liver allografts

Lentiviral expression of CTLA4Ig inhibits primed xenogeneic lymphocyte proliferation and cytokine responses

BACKGROUND

Co-stimulatory blockade is known to inhibit lymphocyte responses and to prolong allograft and xenograft survival. The present study examines the effect of transgenic expression of cytotoxic T lymphocyte-associated molecule-4 immunoglobulin (CTLA4Ig) by a porcine endothelial cell line (PIEC) transduced by a lentiviral vector, on primed xenogeneic T-cell proliferative and cytokine responses.

METHODS

Splenocytes from mice primed with PIEC were used as responder cells in a secondary proliferative assay. CTLA4Ig transduced and wild-type PIEC were used as stimulator cells. Responder cells were assayed for proliferation and cytokine production.

RESULTS

Proliferation was profoundly inhibited by CTLA4Ig transduced cells compared with control cells. Cytokine analysis by enzyme linked immunospot demonstrated that production of interferon-gamma, IL4 (interleukin 4) and IL10 was inhibited by CTLA4Ig transduced cells compared with control cells.

CONCLUSION

CTLA4Ig inhibited primed indirect xenogeneic T-cell proliferative and cytokine responses in vitro. Expression of immunomodulatory molecules by xenogeneic tissues has potential therapeutic applications for future xenotransplantation.

Induction of long-term graft acceptance by a combination treatment of donor splenocytes and CTLA4Ig in a high responder rat liver transplantation model

The CTLA4Ig has led to an improved survival rate in various allograft transplantation models. We investigated in a high responder rat model (Dark Agouti to Lewis) of orthotopic liver transplantation (ORLT), whether an additional adoptive cell transfer can enhance the effect of CTLA4Ig. After transplantation, recipients (n = 13/group) were treated with donor or third-party splenocytes alone or in combination with CTLA4Ig. Administration of splenocytes alone had no significant effect on survival (median 13 days, range 9-14) compared with untreated controls (median 10 days, range 8-12). CTLA4Ig monotherapy prolonged survival to a median of 30 days (range 11-150) but resulted in long-term graft rejection. The additional administration of third-party splenocytes showed no significant improvement over CTLA4Ig monotherapy. Only the combination of donor splenocytes with CTLA4Ig led to long-term graft acceptance (>150 days) without clinical and/or histological signs of rejection. A higher rate of apoptosis could be detected in livers at early time-points in long-term survivors receiving CTLA4Ig and donor splenocytes. Analysis of cytokine mRNA expression revealed a decrease of interleukin-2 at early time-points in all groups receiving CTLA4Ig; whereas, interferon-gamma was increased in long-term survivors receiving CTLA4Ig and donor cells or donor cells alone. The combination of CTLA4Ig and donor derived splenocytes is potent to induce long-term survival and graft acceptance. The mechanisms appear to involve the induction of an early inflammatory impulse and apoptosis.

The effect of CD28/B7 blockade on alloreactive T and B cells after liver cell transplantation

BACKGROUND

Hepatocyte cell lines are beginning to be developed as universal donors for isolated liver cell transplantation, which is a less invasive method than orthotopic liver transplantation for treatment of metabolic liver disease. The immune response to isolated liver cell transplantation and its modification by costimulatory blockade are as yet not well delineated.

METHODS

Adenovirus expressing CTLA4Ig was used to study blockade of the costimulatory CD28/B7 pathway in murine models of hepatocyte transplantation, and the effects on alloreactive T and B cells were studied.

RESULTS

CTLA4Ig delayed rejection of subcutaneously administered C57L-derived murine hepatoma cells in CBA/J recipients for >50 days. Activation and cytokine secretion by allospecific CD4+ and CD8+ T cells were initially blocked by CTLA4Ig; delayed rejection was associated with tumor infiltration by CD8+ T cells that did not secrete interferon-gamma. CTLA4Ig failed to block transplant rejection in primed mice, indicating that memory effector T cells were resistant to its action. In contrast, CTLA4Ig suppressed both naive and memory alloreactive B cells. High levels of CTLA4Ig mediated acceptance of hepatoma cells delivered directly into the spleen. However, isolated primary C57BL/6 mouse hepatocytes delivered into the spleen were rejected with only moderately delayed kinetics.

CONCLUSIONS

Transplant antigenicity, transplant site, and CTLA4Ig dose all affected the survival of transplanted liver cells. CD8+ T cells are significant mediators of hepatocyte transplant rejection and are relatively resistant to costimulatory blockade with CTLA4Ig. Strategies to specifically antagonize CD8+ T cells or to modulate MHC class I expression in association with costimulatory blockade by CTLA4Ig may enhance the clinical feasibility of transplanting allogeneic hepatocytes.