CDX-301 is soluble, recombinant human FMS-like tyrosine kinase-3 ligand (Flt3L) that acts by uniquely binding FMS-like tyrosine kinase-3 (Flt3, CD135), which is expressed on hematopoietic stem cells (HSC), early progenitor cells, immature thymocytes, and steady state dendritic cells, resulting in the proliferation, differentiation, development and mobilization of these cells in the bone marrow, peripheral blood and lymphoid organs. CDX-301 is in clinical development for multiple cancers. Celldex believes CDX-301 may hold significant opportunity for synergistic development in combination with other proprietary molecules in the Company's portfolio. To this end, CDX-301 is being studied in combination with CDX-1140 in the ongoing Phase 1 study of CDX-1140.  In this study, CDX-301 is being used as a priming agent to potentially increase the number of dendritic cells available to respond to CDX-1140.

A Phase 1 study of CDX-301 evaluated seven different dosing regimens of CDX-301 to determine the appropriate dose for further development based on safety, tolerability and biological activity. The data from the study were consistent with previous clinical experience and demonstrated that CDX-301 has an acceptable safety profile to date and can mobilize dendritic cell and hematopoietic stem cell populations in healthy volunteers. The study was published in the journal Bone Marrow Transplantation in 2015.

Early promising data from an investigator-initiated pilot study of CDX-301 were presented in a plenary session at the American Association for Cancer Research Annual Meeting in April 2018. This ongoing, Phase 2 study is evaluating the combination of CDX-301 and stereotactic body radiotherapy (SBRT) in up to 29 patients with advanced non-small cell lung cancer (NSCLC). The presentation included data from nine patients, seven of whom were previously treated with anti-PD(L)1 checkpoint inhibitors. The one-week course of treatment included subcutaneous injections of CDX-301 and SBRT directed to a single lung tumor lesion. Enrollment is ongoing. Progression-free survival at four weeks (PFS4) was achieved in 56% (5/9) of patients overall and in 100% (5/5) of patients who experienced partial responses (PRs) by PERCIST. Notably, PRs were observed in non-irradiated tumors in 56% (5/9) of patients at two months; 3 PRs (3/9) were confirmed by immune-related response criteria (irRC). In the patients previously treated with immune checkpoint inhibitors, 71% (5/7) experienced PRs and PFS4 versus 0% (0/2) in patients not treated with an anti-PD(L)1 therapy. SBRT in combination with CDX-301 induced and reactivated anti-tumor immune responses in patients who had progressive disease on checkpoint inhibitors. No dose-limiting toxicities were observed, and enrollment is ongoing.

For more information on the CDX-301 program, view recent scientific presentations and publications.