Addition of Astatine-211-Labeled Anti-CD45 Antibody to TBI as Conditioning for DLA-Identical Marrow Transplantation: A Novel Strategy to Overcome Graft Rejection in a Canine Presensitization Model: "Radioimmunotherapy to Overcome Transfusion-Induced Sensitization"

Abstract

In a canine model of presensitization using donor blood transfusions, 100% of historical control dogs receiving 9.2 Gy total body irradiation (TBI) conditioning before dog leukocyte antigen (DLA)-identical marrow grafts had graft rejection. In this presensitization model, we investigated whether the addition of monoclonal antibody (mAb)-based targeted radioimmunotherapy (RIT) with astatine-211 (²¹¹At) to TBI could overcome graft rejection. ²¹¹At is an alpha-particle-emitting isotope that has a short path length, very high energy, and a short t½ of 7.2 hours, which allowed targeting radiation to the T cells responsible for graft rejection. Normal canine recipients were given three preceding transfusions of unirradiated whole blood on days -24, -17, and -10 before transplant from their DLA-identical marrow donors. ²¹¹At-anti-CD45 mAb was administered on day -3, and TBI followed by marrow grafts on day 0. Six of the 7 dogs (86%) achieved sustained engraftment as assessed by 100% donor chimerism in mononuclear cells, granulocytes, and CD3⁺ T cells. One dog receiving the lowest CD34⁺ cell content (0.35 × 10⁶ cells/kg) rejected the graft. There were no late rejections in dogs followed up to 1 year. Graft-versus-host disease was seen in one dog. ²¹¹At-anti-CD45 mAb in combination with TBI as conditioning was successful in abrogating graft rejection in 86% of dogs in this presensitization model. ²¹¹At-anti-CD45 mAb conditioning with TBI may serve as a novel promising strategy to overcome graft rejection in heavily transfused patients with red cell disorders.

Keywords: Astatine-211; DLA-identical marrow transplantation; Graft rejection; Transfusion sensitized.

Figure 1.. Hematology following ²¹¹At-anti-CD45 mAb conditioning with 9.2Gy TBI.

All dogs experienced neutropenia, lymphocytopenia, and thrombocytopenia with a median neutrophil nadir of 20 cells/μ L, median lymphocyte nadir of 18 cells/μ L and median platelet nadir of 4.5 × 10³/μ L.

Figure 2.. Percentage of donor chimerism in granulocytes, mononuclear cells, and CD3⁺ cells in dogs treated with ²¹¹At-anti-CD45 mAb conditioning with 9.2Gy TBI DLA-identical HCT.

Six of seven dogs achieved 100% donor chimerism. H734 rejected the graft on day 14 after transplantation.

Figure 3.. Mixed leukocyte cultures.

Results from mixed leukocyte cultures performed on PBMC collected from a representative dog (H824) treated with 0.188 mCi/kg ²¹¹At-labled anti-CD45 mAb is shown here. Testing was performed on PBMC collected prior to sensitization (day -24) and one week after the last sensitization prior to infusion of the ²¹¹At-labled anti-CD45 mAb (day-3 before transplantation.) Data are expressed as mean counts per minute from triplicate wells of recipient response to donor cells, cells from an unrelated dog, and to concanavalin A as internal assay control.

Figure 4.. Diagram of treatment plan

Canine recipients were given three preceding transfusions of irradiated whole blood from DLA-identical marrow donors on days -24, -17, and -10. 211-At-labeled anti-CD45 mAb was given on day -3. TBI (9.2Gy) and bone marrow were given on day 0. Blood counts and chemistry were analyzed on days -7, -3, 0. They were evaluated daily until full hematopoietic recovery, then, once a week until the end of study.