Introduction

Combined kidney/bone marrow transplantation (CKBMT) induces tolerance in both primates and humans. Since liver is thought to be more tolerogenic than kidney, we hypothesized that combined liver/bone marrow transplantation (CLBMT) should be successful. We performed this pre-clinical study in cynomolgus monkeys.

Methods

Three pairs of animals were used. All were mismatched for class I, and the first 2 pairs were mismatched for class II. Liver and ∼3 x 10^8 donor bone marrow cells/kg were transplanted on day 0. The induction regimen consisted of 1.5Gy total body irradiation on day-6, ATG (Atgam®; Pfizer) (50mg/kg) on days -2, -1, and 0, 7Gy thymic irradiation on day -1, splenectomy on day 0, rituximab (Genentech) (20mg/kg) on day -6 (2/3 animals), and 28 days of IM cyclosporine (CyA; Novartis). Anti-donor MLR was assessed by plating recipient and irradiated donor cells (1 x 10^6 each) for 5 days and pulsing with tritiated thymidine for 24 hours.

Results

The first recipient survived to day 42 with donor-specific hyporesponsiveness in MLR but died during repair of a biliary stricture with rising LFTs. He had multilineage chimerism (MC) up to 36 days, but significant plasma cell infiltrate of liver and pancreas was found on necropsy. Rituximab was added to the regimen for the second animal, which had MC up to day 40 (12 days after stopping CyA) and was sacrificed on day 69 with rising LFTs. The third lost MC between days 23-26, in association with subtherapeutic CyA blood levels, and was sacrificed on day 57 with rising LFTs. At time of necropsy, both animals had normal to increased anti-donor cellular responses but no detectable anti-donor antibody. Both had severe cellular rejection on histology with scattered plasma cells and moderate C4d deposition on portal and central veins. FACS analysis of blood, graft-infiltrating lymphocytes, and lymph nodes showed high percentages of CD8 cells with effector memory phenotype in the blood, graft, and draining node but not in mesenteric and peripheral lymph nodes.

Conclusion

Despite the success of CKBMT and presumed greater tolerogenicity of livers, we have thus far not achieved tolerance with CLBMT, despite relatively-prolonged, high levels of MC. Approaches to prevent cellular rejection with elements of humoral rejection are needed.

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