Sellas’ Cancer Vaccine Galinpepimut-S Shows Durable Effects in High-risk Myeloma Patients

Sellas Life Sciences’ cancer vaccine galinpepimut-S showed promising effects in patients with an aggressive form of multiple myeloma, researchers said in a presentation at the Annual Meeting of the Society of Hematologic Oncology (SOHO) in Houston, Texas.

The presentation was based on data from an ongoing Phase 2 study of the treatment, which showed that the majority of patients in this high-risk group were still alive after a year and a half, even though they had signs of cancer left after a stem cell transplant.

“The results of these immunodynamics assays denote a robust immunobiological foundation for the clinical effect of WT1-targeting active immunization with galinpepimut-S,” Guenther Koehne, an MD and PhD, principal investigator for the clinical trial and attending physician at the Adult Bone Marrow Transplantation Service at Memorial Sloan Kettering Cancer Center (MSKCC) in New York, said in a press release.

“The data also support our rationale for planning further studies to expand on our experience with this IO [immuno-oncology] agent,” added Koehne, who is also an associate professor of medicine at Weill Cornell Medical College.

Galinpepimut-S is a vaccine targeting a protein called WT1 (Wilms Tumor-1) — which is common in myeloma.

The study abstract, “Galinpepimut-S, a WT1-Targeting Immuno-Oncology Treatment, Induces Specific, Robust and Durable Immune Responses (IRs) in Patients (Pts) with High-Risk (HR) Multiple Myeloma (MM),” was published in the journal Clinical Lymphoma, Myeloma & Leukemia.

The open-label study, performed at MSKCC, had recruited 20 patients, and data was now available for 18 of them.

All included patients had undergone stem cell transplants and Revlimid (lenalidomide) treatment after the transplant. Fifteen had high-risk tumors.

Two weeks after the transplant they started treatment with galinpepimut-S, which was given subcutaneously with a vaccine adjuvant and the immune mediator GM-CSF. The vaccine targeted several versions of the protein.

As the vaccination schedule was completed, researchers noted that between 72 percent and 91 percent of patients had mounted an immune response to any of the protein versions. Two-thirds had immune reactions towards several versions. Results suggested that the vaccine had activated CD4 and CD8 type T-cells.

At 18 months, 88 percent of treated patients were still alive. Half of included patients had not progressed at nearly two years.

The results are impressive, given that researchers consider these patients at extremely high risk of progression and poor outcomes in the long run. This is typically also seen in patients who have stem cell transplants and maintenance treatment with immunomodulatory drugs.

Researchers said that the rates and potencies of the immune reactions correlated well with the observed clinical benefits in the form of complete or very good partial remissions.

“The correlations between IR [immune-response] and depth of clinical responses in multiple myeloma patients are both intriguing and original, and firmly establishes WT1 as a major actionable target for immunotherapy in plasma cell dyscrasias henceforth,” said Dr. Nicholas Sarlis, MD and PhD, chief medical officer at Sellas.

“This new dataset focusing on dissecting the immune mechanisms underlying the marked antimyeloma activity previously documented with galinpepimut-S underscores our steadfast commitment to advance this agent’s clinical development programs, especially in clinical settings of unmet medical need,” said Dr. Angelos Stergiou, MD, Sellas’ vice chairman and CEO.

High-risk myeloma patients who have remnants of disease after initial treatment make up a group that is underserved by standard treatments, Stergiou maintained. He also added that the data — particularly the safety of the approach — show that it might be justified to test galinpepimut-S in combination with other treatments, such as checkpoint inhibitors.