Co-Administration of Mgta-145 and Plerixafor Rapidly Mobilizes High Numbers of Hematopoietic Stem Cells and Graft-Versus-Host Disease Inhibiting Monocytic Cells in Non-Human Primates (2019)

The majority of bone marrow transplants (BMTs) utilize granulocyte-colony stimulating factor (G-CSF) mobilized peripheral blood (mPB) as the source of hematopoietic stem cells (HSCs). Mobilization with G-CSF requires a multi-day dosing regimen and fails to mobilize a large proportion of CD34+CD90+CD45RA- HSCs, the cell type responsible for hematopoietic engraftment. Moreover, up to 80% of allogenic recipients will experience significant side effects such as acute graft-versus-host disease (GvHD), even though G-CSF mPB contains a small and variable number of immunosuppressive monocytes (Vendramin et al., BBMT 2014). Identification of a mobilizing regimen that consistently and rapidly produces high numbers of HSCs and immunosuppressive monocytes without the need for G-CSF would be ideal. We previously reported that MGTA-145, a CXCR2 agonist, rapidly mobilizes HSCs when combined with the CXCR4 inhibitor, plerixafor (Blood 2017 130:1920). In the present study, detailed profiling was performed at 0 through 24 hours after mobilization of non-human primates (NHPs) with a single dose of MGTA-145, plerixafor, or MGTA-145 plus plerixafor versus a multi-dose, five-day regimen of G-CSF.MGTA-145 plus plerixafor led to a 19-fold increase in number of CD34+CD90+CD45RA- HSCs within four hours of dosing (p<0.001, n=13, Figure 1A), corresponding to 4-fold higher numbers than obtained by G-CSF alone, and resulting in rapid engraftment in an autologous NHP transplant. Immune profiling of graft subsets revealed a 19-fold increase over baseline in the number of CD34dim monocytes within four hours of dosing (p<0.001, n=13, Figure 1A) that suppressed T cell proliferation in vitro (p<0.05). Frequency and number of CD34dim monocytes was 2-3 fold higher with MGTA-145 plus plerixafor versus G-CSF or plerixafor alone (p<0.01, n=3-5) and correlated with HSC mobilization (p<0.001). To test immunosuppressive capabilities in vivo, we transplanted 6 × 106 peripheral blood mononuclear cells (PBMCs) isolated from naïve unmobilized NHPs or NHPs mobilized with G-CSF or MGTA-145 plus plerixafor. NSG mice transplanted with unmobilized PBMCs had significantly higher number of T cells and increased T cell activation in vivo. Notably, all (13/13) mice transplanted with unmobilized PBMCs died of acute GvHD compared to 2/6 mice transplanted with G-CSF PBMCs and 1/8 mice transplanted with MGTA-145 plus plerixafor PBMCs (Figure 1B, p<0.001). PBMCs depleted of CD34dim monocytes were transplanted into NSG mice to assess whether this immunosuppressive effect is due to CD34dim monocytes.As the risk of GvHD remains a significant clinical problem in the allogenic setting, MGTA-145 plus plerixafor may rapidly mobilize an advantageous graft relative to the standard of care, G-CSF, since MGTA-145 plus plerixafor results in significantly higher numbers of both engraftable HSCs and highly immunosuppressive monocytes. The majority of bone marrow transplants (BMTs) utilize granulocyte-colony stimulating factor (G-CSF) mobilized peripheral blood (mPB) as the source of hematopoietic stem cells (HSCs). Mobilization with G-CSF requires a multi-day dosing regimen and fails to mobilize a large proportion of CD34+CD90+CD45RA- HSCs, the cell type responsible for hematopoietic engraftment. Moreover, up to 80% of allogenic recipients will experience significant side effects such as acute graft-versus-host disease (GvHD), even though G-CSF mPB contains a small and variable number of immunosuppressive monocytes (Vendramin et al., BBMT 2014). Identification of a mobilizing regimen that consistently and rapidly produces high numbers of HSCs and immunosuppressive monocytes without the need for G-CSF would be ideal. We previously reported that MGTA-145, a CXCR2 agonist, rapidly mobilizes HSCs when combined with the CXCR4 inhibitor, plerixafor (Blood 2017 130:1920). In the present study, detailed profiling was performed at 0 through 24 hours after mobilization of non-human primates (NHPs) with a single dose of MGTA-145, plerixafor, or MGTA-145 plus plerixafor versus a multi-dose, five-day regimen of G-CSF. MGTA-145 plus plerixafor led to a 19-fold increase in number of CD34+CD90+CD45RA- HSCs within four hours of dosing (p<0.001, n=13, Figure 1A), corresponding to 4-fold higher numbers than obtained by G-CSF alone, and resulting in rapid engraftment in an autologous NHP transplant. Immune profiling of graft subsets revealed a 19-fold increase over baseline in the number of CD34dim monocytes within four hours of dosing (p<0.001, n=13, Figure 1A) that suppressed T cell proliferation in vitro (p<0.05). Frequency and number of CD34dim monocytes was 2-3 fold higher with MGTA-145 plus plerixafor versus G-CSF or plerixafor alone (p<0.01, n=3-5) and correlated with HSC mobilization (p<0.001). To test immunosuppressive capabilities in vivo, we transplanted 6 × 106 peripheral blood mononuclear cells (PBMCs) isolated from naïve unmobilized NHPs or NHPs mobilized with G-CSF or MGTA-145 plus plerixafor. NSG mice transplanted with unmobilized PBMCs had significantly higher number of T cells and increased T cell activation in vivo. Notably, all (13/13) mice transplanted with unmobilized PBMCs died of acute GvHD compared to 2/6 mice transplanted with G-CSF PBMCs and 1/8 mice transplanted with MGTA-145 plus plerixafor PBMCs (Figure 1B, p<0.001). PBMCs depleted of CD34dim monocytes were transplanted into NSG mice to assess whether this immunosuppressive effect is due to CD34dim monocytes. As the risk of GvHD remains a significant clinical problem in the allogenic setting, MGTA-145 plus plerixafor may rapidly mobilize an advantageous graft relative to the standard of care, G-CSF, since MGTA-145 plus plerixafor results in significantly higher numbers of both engraftable HSCs and highly immunosuppressive monocytes. Figure 1.