On March 19, 2018 SELLAS Life Sciences Group, Inc. (NASDAQ:SLS) ("SELLAS" or "the Company") reported the presentation of open label Phase 2 clinical and immunological data for its lead cancer immunotherapeutic candidate, galinpepimut-S (GPS), in the treatment of high-risk multiple myeloma at the 44th Annual European Society for Blood and Marrow Transplantation (EBMT) Meeting (Press release, Sellas Life Sciences, MAR 19, 2018, View Source [SID1234525471]). Safety results from the study were also presented. The EBMT presentation is being delivered by Guenther Koehne, M.D., Ph.D., Chief of Bone Marrow Transplantation and Hematologic Oncology at Miami Cancer Institute, Baptist Health South Florida.

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Median progression-free survival (PFS) of 23.6 months was reported in the high-risk disease setting, compared to historically inferior outcomes while on an immunomodulatory drug (IMID) or proteasome inhibitor post-ASCT maintenance. Median overall survival has not been reached to date. The open-label Phase 2 study consisted of 19 patients with multiple myeloma who had high-risk cytogenetics at diagnosis and remained at least minimal residual disease (MRD)-positive after a successful autologous stem cell transplant ("ASCT").

"These results are encouraging particularly given the patients’ poor prognosis due to their high-risk cytogenetic profile at disease presentation and their still harboring minimal residual disease prior to GPS treatment", said Angelos M. Stergiou, M.D., Sc.D. h.c., President and CEO of Sellas. "The improved PFS at 23.6 months in this setting instills further confidence in our advancing GPS development as an important immuno-therapeutic treatment option for aggressive multiple myeloma."

GPS was administered to patients in the study who achieved a stable disease or better status following ASCT, but still exhibited at least measurable minimal residual disease. GPS, a novel WT1-targeting direct immunizer, was evaluated as consolidation therapy to potentially stimulate a highly-specific immune response against WT1 to prevent or delay myeloma progression.

In the study, key data findings were:

Clinical activity was linked to antigen-specific immune responses.

GPS stimulated time-dependent and robust CD4+ T cell or CD8+ T cell immune responses (IRs) specific for all four WT1 peptides within GPS, two of which are heteroclitic (mutated, by design). In addition, GPS stimulated similar IRs against the two counterpart native peptides. The IRs were confirmed in up to 91% of patients across HLA allele types, with multivalent IRs emerging in up to 64% of patients.

Multifunctional cross-epitope T cell reactivity was observed in 75% of patients to antigenic epitopes against which hosts were not specifically immunized, in a pattern akin to epitope spreading.

The GPS data suggest a distinctive link between clinical and immune responses, which has not been previously described for a peptide vaccine in multiple myeloma. The results offer mechanistic underpinnings for immune activation against WT1 in patients with aggressive multiple myeloma and are supportive of further testing of the putative anti-myeloma activity of GPS in more extensive clinical studies.
Dr. Koehne’s complete EBMT presentation covering the GPS results can be accessed at: www.sellaslifesciences.com/publications/galinpepimut-s-gps/default.aspx.

"High-risk multiple myeloma is a disease subset with high potential of short-term disease progression following autologous stem cell transplants, providing opportunities to improve on this limited clinical outcome. We are seeing an encouraging signal from GPS in our Phase 2 study with progression-free survival (PFS) exceeding historical outcomes with standard therapies," stated Guenther Koehne, M.D., Ph.D. Dr. Koehne added that "Currently, post-transplant maintenance therapies for these difficult-to-treat patients are seemingly limited, with PFS rarely exceeding 12-14 months". Dr. Koehne was the Principal Investigator for this study while at MSKCC.

About galinpepimut-S (GPS):
GPS is a heteroclitic multivalent, multi-peptide cancer immunotherapeutic agent composed of four peptides, addressing over 20 epitopes, and derived from the WT1 protein, which has been ranked by the National Cancer Institute as a top priority among cancer antigens for immunotherapy. Importantly, because the WT1 antigen is overexpressed in many malignancies, and is not found in most normal tissues, GPS has the potential to be a broad immunotherapy, effective across a multitude of diverse cancer types and patient populations.