A proof of concept study: Human C48-placenta immunoregulatory factor is an effective, single therapeutic agent enabling allogeneic, nonmanipulated murine bone marrow transplantation

Objective: Cloned placenta immunoregulatory ferritin (PLIF) contains a novel, nonferritin bioactive domain (C-48) with immunodulatory activity. We documented that treatment of whole human bone marrow cells with PLIF and its subcloned C48 proteins resulted in myeloid progenitor cell growth and differentiation and T-cell suppression via an effect on the cytokine network. We tested whether this differential effect supports allogeneic bone marrow transplantation with long-lasting tolerance without any further treatments. Materials and Methods: Splenocyte-enriched C3H (H2^k) whole bone marrow was transplanted into C57Bl (H2^b) recipients after total body irradiation. Recipients were injected with recombinant C48 (3mg/kg, intraperitoneal) for 21 days or with glutathione S-transferase. Animals were monitored for survival, chimerism, and clinical signs of graft-vs-host disease (GVHD). Next, chimera whole bone marrow was transplanted to secondary myeloablated C57Bl (H2^b) hosts without treatment. Results: Mice that received C48 treatment following allogeneic splenocyte-enriched bone marrow transplantation demonstrated full-donor chimerism without GVHD mortality, and normal blood cell counts in 75% of recipients. Secondary transplants from the full chimera to myeloblated C57Bl hosts showed 100% engraftment, no GVHD mortality, and no impairment in the long-term hematopoietic reconstitution potential. Allogeneic response of spleen cells from secondary chimeras against donor C3H (H2^k) and recipient C57Bl (H2^b) were similar to syngeneic response, whereas reactivity to third party (DBA H2^d) was significantly enhanced. Conclusions: Findings of this study provide the proof of concept that C48-a novel, single, bifunctional therapeutic modality enabled successful allogeneic, unmanipulated bone marrow transplantation without GVHD, and with lasting specific tolerance.