Abstract
Background aims. Previously, cytotoxic T lymphocyte antigen 4 (CTLA4) immunoglobulin (Ig) has been shown to allow sustained engraftment in dog leukocyte antigen (DLA)-identical hematopoietic cell transplant (HCT) after non-myeloablative conditioning with 100 cGy total body irradiation (TBI). In the current study, we investigated the efficacy of pre-transplant CTLA4-Ig in promoting engraftment across a DLA-mismatched barrier after non-myeloablative conditioning. Methods. Eight dogs were treated with CTLA4-Ig and donor peripheral blood mononuclear cells (PBMC) prior to receiving 200 cGy TBI followed by transplantation of granulocyte–colony-stimulating factor (G-CSF) mobilized peripheral blood stem cells from DLA haplo-identical littermates with post-grafting immunosuppression. A control group of six dogs was conditioned with 200 cGy only and transplanted with grafts from DLA haplo-identical littermates followed by post-grafting immunosuppression. Results. In vitro and in vivo donor-specific hyporesponsiveness was demonstrated on day 0 before TBI in eight dogs that received CTLA4-Ig combined with donor PBMC infusions. Four of five dogs treated with increased doses of CTLA4-Ig achieved initial engraftment but eventually rejected, with a duration of mixed chimerism ranging from 12 to 22 weeks. CTLA4-Ig did not show any effect on host natural killer (NK) cell function in vitro or in vivo. No graft-versus-host disease (GvHD) was observed in dogs receiving CTLA4-Ig treatment. Conclusions. Non-myeloablative conditioning with 200 cGy TBI and CTLA4-Ig combined with donor PBMC infusion was able to overcome the T-cell barrier to achieve initial engraftment without GvHD in dogs receiving DLA haplo-identical grafts. However, rejection eventually occurred; we hypothesize because of the inability of CTLA4-Ig to abate natural killer cell function.
Acknowledgments
The authors are indebted to Drs Howard Shulman and George Sale for pathology studies, to Michele Spector, DVM, the investigators who participated in the weekend treatments, and the technicians in the canine facilities. We also would like to thank Stacy Zellmer for DLA typing. The authors are indebted to Richard Boismenu, PhD, Repligen Corporation (Needham, MA), who kindly provided RG2077 (recombinant human CTLA4 linked to human IgG1 heavy chain) and generously helped in CTLA4-Ig level measurement. We also appreciate Amgen for the gift of canine G-CSF. We are grateful for the assistance of Helen Crawford, Bonnie Larson and Sue Carbonneau for manuscript preparation.
Research funding was provided by the National Institutes of Health (Bethesda, MD) grants P01HL036444, P01CA078902 and P30CA015704. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health nor its subsidiary institutes and centers. YC was supported by a grant from China Scholarship Council and Shandong University. TF was supported by a fellowship from the Kirin Brewery Company Ltd. BK, was supported by a fellowship from the Danish Cancer Society.
Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.