Celldex Therapeutics, Inc. announced positive results from a Phase 1 multi-dose study of CDX-301 (FMS-like tyrosine kinase-3 ligand) demonstrating that CDX-301 was well-tolerated and can safely and effectively mobilize hematopoietic cell populations in healthy volunteers. The data support future development of CDX-301 in a number of indications, including hematopoietic stem cell transplant and cancer immunotherapy. Results were presented in a poster entitled ‘A Phase 1 Trial of the Hematopoietic Growth Factor CDX-301 (rhuFlt3L) in Healthy Volunteers' on December 10, 2012 at 6:00 pm ET at the American Society of Hematology 54th Annual Meeting and Exposition.

Study Results: 30 healthy volunteers were enrolled across seven cohorts. The first five cohorts assessed escalating doses of CDX-301 (from 1 ug/kg to 75 ug/kg) as a five-day regimen, while the final two cohorts assessed CDX-301 (at 25 ug/kg) as seven- and 10-day regimens. All volunteers completed dosing and safety follow-up.

Short-term dosing of five days resulted in significant mobilization of dendritic and stem cells, with the more mobilization achieved at the maximum dose. Ten-day dosing significantly enhanced the circulation of white blood cells and monocytes compared to the five-day regimen. Analysis on the expansion of stem cells, dendritic cells and other cell populations are still being conducted and will be presented at a future medical meeting.

CDX-301 was generally well-tolerated. Transient Grade 1 lymphadenopathy was observed in five volunteers and Grade 1 diarrhea was observed in two volunteers. One possible dose-limiting toxicity (DLT) was observed in a volunteer with a remote history of community acquired pneumonia (CAP) who developed CAP on study day 12.

The volunteer responded rapidly to antibiotics and fully recovered. No additional infections or DLTs were observed in the study. No anti-CDX-301 antibodies were detected in any volunteers through the end of study follow-up.