Efficacy and safety of CDX-301, recombinant human Flt3L, at expanding dendritic cells and hematopoietic stem cells in healthy human volunteers

Bone Marrow Transplant. 2015 Jul;50(7):924-30. doi: 10.1038/bmt.2015.74. Epub 2015 Apr 27.


Fms-like tyrosine kinase-3 ligand (Flt3L) uniquely binds the Flt3 (CD135) receptor expressed on hematopoietic stem cells (HSCs), early progenitor cells, immature thymocytes and steady-state dendritic cells (DCs) and induces their proliferation, differentiation, development and mobilization in the bone marrow, peripheral blood and lymphoid organs. CDX-301 has an identical amino-acid sequence and comparable biological activity to the previously tested rhuFlt3L, which ceased clinical development over a decade ago. This Phase 1 trial assessed the safety, pharmacokinetic, pharmacodynamic and immunologic profile of CDX-301, explored alternate dosing regimens and examined the impact of rhuFlt3L on key immune cell subsets. Thirty healthy volunteers received CDX-301 (1-75 μg/kg/day) over 5-10 days. One event of Grade 3 community-acquired pneumonia occurred. There were no other infections, dose-limiting toxicities or serious adverse events. CDX-301 resulted in effective peripheral expansion of monocytes, hematopoietic stem and progenitor cells and key subsets of myeloid DCs and plasmacytoid DCs, with no clear effect on regulatory T cells. These data from healthy volunteers support the potential for CDX-301, as monotherapy or in combination with other agents, in various indications including allogeneic HSC transplantation and immunotherapy, but the effects of CDX-301 will need to be investigated in each of these patient populations.

Publication types

  • Clinical Trial, Phase I
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Dendritic Cells / immunology*
  • Female
  • Healthy Volunteers
  • Hematopoietic Stem Cell Transplantation / methods*
  • Humans
  • Male
  • Middle Aged
  • Transplantation Conditioning / methods*
  • Young Adult
  • fms-Like Tyrosine Kinase 3 / genetics*
  • fms-Like Tyrosine Kinase 3 / metabolism*


  • FLT3 protein, human
  • fms-Like Tyrosine Kinase 3