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Case Reports
. 2015 Jun 26:8:78.
doi: 10.1186/s13045-015-0173-x.

Conditioning with rabbit versus horse ATG dramatically alters clinical outcomes in identical twins with severe aplastic anemia transplanted with the same allogeneic donor

P T Vo  1 , J Pantin  2 , C Ramos  3 , L Cook  3 , E Cho  3 , R Kurlander  4 , H Khuu  5 , J Barrett  6 , S Leitman  7 , R W Childs  8
Affiliations
Case Reports

Conditioning with rabbit versus horse ATG dramatically alters clinical outcomes in identical twins with severe aplastic anemia transplanted with the same allogeneic donor

P T Vo et al. J Hematol Oncol. .

Abstract

Severe aplastic anemia (SAA) is a rare disorder leading to bone marrow failure, which if left untreated, is invariably fatal. Conventional therapies with immunosuppressive therapy or allogeneic hematopoietic stem cell transplantation (HSCT) are highly effective. HSCT can offer a greater outcome in younger patients who have an available HLA match-related donor. Recent studies showing the addition of antithymocyte globulin (ATG) to the conditioning regimen improves engraftment and reduces the risk of graft-versus-host disease (GVHD).There are currently two ATG preparations in the USA, equine (or horse) and rabbit ATG. These agents are pharmacologically distinct, having significant differences in their pharmacokinetics and in vivo immunosuppressive effects [N Engl J Med 365(5):430-438, 2011]. Here, we report a case of two monozygotic twins with constitutional SAA that evolved to myelodysplastic syndrome (MDS) who both underwent allogeneic peripheral blood stem cell transplantation (PBSC) from the same single HLA antigen mismatched sibling donor with the only difference in the transplant regimen being the type of ATG used in the preparative regimen; one twin received horse ATG and the other received rabbit ATG during conditioning. This report emphasizes that dramatic differences in donor T cell chimerism and clinical outcomes including GVHD can occur as a consequence of the type of ATG that is utilized in the transplant conditioning regimen. These differences highlight that these agents should not be considered interchangeable drugs when used in this setting.

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Figures

Fig. 1
Fig. 1
a Twin #1 chimerism timeline. b Twin #2 chimerism timeline
Fig. 2
Fig. 2
Comparison of T cell chimerism between twins
Fig. 3
Fig. 3
a, b Twin #2 (left) 5 years and 3 months post-transplant and twin #1 (right) 6 years and 8 months post-transplant. c, d Twin #2 (left) 10 years and 6 months post-transplant and twin #1 (right) 11 years and 11 months post-transplant
See this image and copyright information in PMC

References

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    1. Scheinberg P, Young NS, et al. Horse versus rabbit antithymocyte globulin in acquired aplastic anemia. N Engl J Med. 2011;365(5):430–8. doi: 10.1056/NEJMoa1103975. - DOI - PMC - PubMed
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    1. Champlin RE, Horowitz MM, van Bekkum DW, et al. Graft failure following bone marrow transplantation for severe aplastic anemia: risk factors and treatment results. Blood. 1989;73:606–13. - PubMed
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