Cong Yu

USE OF (CA)N POLYMORPHISMS TO DETERMINE THE ORIGIN OF BLOOD CELLS AFTER ALLOGENEIC CANINE MARROW GRAFTING

We have used a polymerase chain reaction-based assay measuring polymorphic (CA)n repeats, a class of simple sequence repeats, to assess the success of allogeneic canine marrow transplants. Results were compared with those obtained with karyotype analysis of dividing cells in recipients that were sex mismatched with their marrow donors. Twenty recipients were conditioned for transplantation of genotypically DLA-identical littermate marrow by 450 cGy of total-body irradiation. In 2 recipients, results could not be compared, since either only cytogenetic or dinucleotide (CA)n marker data existed. Both dogs had autologous marrow recovery. In 15 of the remaining 18 recipients, complete agreement was found between the results obtained with dinucleotide (CA)n markers, cytogenetic studies, and granulocyte changes after transplantation. Seven of the 15 showed eventual autologous recovery, 6 displayed mixtures of host and donor cells, and 2 showed donor-type hematopoiesis. Two of the 18 dogs showed mixed chimerism with (CA)n markers and autologous recovery by cytogenetics, findings that may be related to differences in cells analyzed by the two techniques–i.e., all nucleated cells by (CA)n markers versus dividing cells by cytogenetics. In one additional recipient, results of marrow cytogenetics, granulocyte changes, and (CA)n markers were consistent with a successful allograft, while peripheral blood cytogenetics suggested autologous recovery, possibly the result of erroneous blood sampling. Polymerase chain reaction-based testing for dinucleotide repeat (CA)n polymorphisms, originally developed for genetic mapping in the dog, is useful and reliable when compared with cytogenetic studies, in assessing the success of allogeneic marrow transplants in dogs.

Current and future preparative regimens for bone marrow transplantation in thalassemia.

Abstract: Preparative regimens for marrow allografts in thalassemia have two objectives. One is eradication of diseased marrow and the other suppression of host‐versus‐graft (HVG) reactions so that the allograft survives. A common regimen to accomplish these goals has combined high‐dose busulfan with cyclophosphamide. Postgrafting immunosuppression with cyclosporine/methotrexate has been used for GVHD prevention. Some patients may die from regimen‐related toxicity. Overall event‐free survival is 75%. Occasional patients have become mixed donor/host hematopoietic chimeras and, yet, disease symptoms have abated. This has raised the possibility of developing safer and less toxic transplant programs that result in stable mixed hematopoietic chimerism. We have devised such a program in dogs consisting of a nonlethal dose of total body irradiation (200 cGy) before and a novel combination of mycophenolate mofetil and cyclosporine after transplant. Mixed donor/host chimerism (≥ 50% donor cells in all lineages) has persisted for > 80 weeks, even though immunosuppression was discontinued after five weeks.

What role for fty720, a novel immunosuppressive agent, in canine nonmyeloablative hematopoietic stem cell transplantation?

BACKGROUNDnStable mixed donor/host hematopoietic chimerism was almost uniformly achieved in dogs given 200 cGy total body irradiation (TBI) before, and a short course of immunosuppression after, transplantation of marrow from dog leukocyte antigen-identical littermates, but was transient when the TBI dose was decreased to 100 cGy. Here, we examined whether stable engraftment could be achieved in five dogs given FTY720 (days -5 and -4), followed by 100 cGy TBI, dog leukocyte antigen-identical marrow grafts, and mycophenolate mofetil/cyclosporine.nnnRESULTS AND CONCLUSIONSnAlthough all five dogs showed initial engraftment, four dogs rejected their grafts within 11 weeks, whereas one dog was euthanized on day 17 due to enteritis. This was not different from the control dogs not given FTY720 (P=0.32). Thus, FTY720 failed to enhance allogeneic engraftment in this model, perhaps due to in vivo T-cell depletion of the graft resulting from sequestration of donor lymphocytes in host central lymphoid tissues.

Facilitation of DLA-incompatible marrow grafts by donor-specific serum transferrin?

Studies in mice have shown that donor-specific plasma transferrin (TF) given to the recipient in the peritransplant period facilitates engraftment of marrow from histoincompatible donors. Dogs given 920 cGy of total body irradiation (TBI) and infused with marrow from an unrelated major histocompatibility complex (DLA) different donor generally fail to engraft; only approximately 20% of dogs achieve sustained engraftment. We have now investigated in this model whether the infusion of donor-specific plasma TF would facilitate engraftment. Ten dogs were given TBI, followed at 23 h by an intravenous dose of TF, at 24 h by marrow from the same donor, and another dose of TF at 48 h; six dogs also received postgrafting methotrexate (MTX). Seven dogs (three of four without MTX, four of six with MTX) had sustained engraftment, and three dogs failed to engraft. A single dog given third-party TF failed to engraft. Among five dogs not given TF two achieved sustained engraftment. This pilot study suggests that donor-specific TF facilitates engraftment of DLA-incompatible marrow. Further studies are warranted.

New Strategies for Hematopoietic Stem Cell Transplantation

Transplantation of allogeneic hematopoietic stem cells (HSC) is widely used in the treatment of a variety of malignant and nonmalignant hematological diseases. The treatment as it is currently defined includes three major components: n n1. n nconditioning regimens to both eradicate the underlying disease and suppress the host’s immune system in preparation for the graft; n n n n n2. n ninfusion of the HSC graft to both rescue the recipient from otherwise lethal marrow toxicity of the conditioning regimen and eliminate host resistance and residual leukemia via graft-versus-host (GVH) reactions; and n n n n n3. n npostgrafting immunosuppression to control graft-versus-host disease (GVHD) and establish long-term graft-host tolerance.