Correction of hemophilia as a proof of concept for treatment of monogenic diseases by fetal spleen transplantation

Abstract

Previous clinical attempts to correct genetic deficiencies such as hemophilia or Gaucher disease by transplantation of allogeneic spleen were associated with aggressive graft versus host disease, mediated by mature T cells derived from the donor spleen. We show that a fetal pig spleen harvested at the embryonic day 42 stage, before the appearance of T cells, exhibited optimal growth potential upon transplantation into SCID mice, and the growing tissue expressed factor VIII. Transplantation of embryonic day 42 spleen tissue into hemophilic SCID mice led to complete alleviation of hemophilia within 2–3 months after transplant, as demonstrated by tail bleeding and by assays for factor VIII blood levels. These results provide a proof of principle to the concept that transplantation of a fetal spleen, obtained from a developmental stage before the appearance of T cells, could provide a novel treatment modality for genetic deficiencies of an enzyme or a factor that can be replaced by the growing spleen tissue.

Extrahepatic sources of factor VIII potentially contribute to the coagulation cascade correcting the bleeding phenotype of mice with hemophilia A

“…Recent studies using a cell therapy approach 8,9 or cell typespecific knockout experiments indicated that FVIII is produced largely in liver sinusoidal endothelial cells (LSEC); 10,11 although FVIII mRNA was present in endothelial cells of kidneys, spleen and lungs, it was absent in endothelial cells of the brain and heart. 10,[12][13][14][15] These findings were in agreement with studies showing that hemophilic patients benefited from transplantation of the spleen in the long-term. 16,17 On the other hand, early studies in hemophilic dogs did not show longterm correction and other reports described the spleen as only a store for FVIII-expressing cells.…”

Role of bone marrow transplantation for correcting hemophilia A in mice

“…5,6 Nonetheless, extrahepatic organs probably contributed in FVIII production, as indicated by FVIII synthesis in spleen, lungs, or pancreatic islets. [6][7][8] This was in agreement with lack of plasma FVIII deficiency after OLT with donor liver from dogs or people with hemophilia A because such donor liver cells would not have synthesized or secreted FVIII. 9,10 Therefore, whether nonendothelial cells, and cells in extrahepatic organs, could also produce FVIII was not excluded.…”

“…The ability of endothelial cells in liver and other organs, as well as of nonhepatic cell types, to produce FVIII offer frameworks for understanding alterations in FVIII levels during diseases. 47 Similarly, transplantation studies showing efficacy of dissociated spleen cells or splenic tissue in people with hemophilia should be accounted for by FVIII production in monocytes, besides endothelial cells, 7,48,49 because the spleen is a major reservoir of MNCs and macrophages. 50 After splenic cell transplants, plasma FVIII activity levels peaked in 4 to 7 days, 48 which was in agreement with our studies of KCs and MSCs transplants, which showed control of bleeding after 3 days.…”

“…Although FVIII was cloned from T cells, 12 and transplantation of lymphatic tissue was thought to correct hemophilia in dogs, 13 whether lymphocytes did express FVIII was uncertain, because correction of hemophilia by transplanted organs (eg, spleen) included other cell types. 7,14,15 Because BM cells may generate multiple lineages, the potential of BM-derived cells in FVIII production seemed relevant to us. Previously, BM transplantation studies in hemophilia A, 40 years ago, were limited to just 3 dogs and 2 persons.…”

Embryonic pig pancreatic tissue for the treatment of diabetes in a nonhuman primate model

“…This strategy is based on the growing evidence, over the past 5 decades, demonstrating maternal immune tolerance to the fetus (2,3), and on recent observations that embryonic tissues exhibit reduced immunogenicity in various transplantation settings (4)(5)(6)(7). Considering that very early embryonic tissues are associated with a substantial risk of teratoma formation, we have attempted, during the past several years, to define the earliest gestational time point that does not pose a teratoma risk for transplantation of different embryonic pig tissues, including kidney (6), heart (unpublished), spleen (8), pancreas, liver, and lung (7) into SCID mice. Once this threshold was established, we were able to further characterize an optimal gestational window for transplantation based on growth potential and immunogenicity.…”