Dr Haldar on Outcomes for NeoAg-VAX With or Without Pembrolizumab in MSS mCRC

“We found that most patients did mount an effective T-cell response to this vaccine platform.”

S. Daniel Haldar, MD, an assistant professor in the Department of Gastrointestinal Medical Oncology of the Division of Cancer Medicine at The University of Texas MD Anderson Cancer Center, and an adjunct assistant professor in the Department of Oncology at Johns Hopkins University School of Medicine, discussed outcomes for the personalized neoantigen vaccine NeoAg-VAX with or without pembrolizumab (Keytruda) in patients with microsatellite stable metastatic colorectal cancer.

An investigator-initiated, single-center, open-label, nonrandomized pilot study (NCT02600949) evaluated the safety and feasibility of administering NeoAg-VAX alone (cohort A, n = 13) or in combination with PD-1 inhibition (cohort B, n = 15; 8 patients from cohort A were retreated) in patients with MSS mCRC. Patients underwent tissue collection, followed by at least 1 line of standard-of-care chemotherapy during vaccine generation. Following vaccine administration, patients in cohort B received intravenous pembrolizumab (Keytruda) at 200 mg every 3 weeks.

Overall, NeoAg-VAX was associated with a favorable safety profile, Haldar said. The most common adverse effects were mild injection site reactions, including injection site burning (36%) and injection site pain (21%).

Additionally, the vaccine was feasible to generate for most patients (85.7%). However, the investigators encountered some barriers to generating this customized product, he explained. A total of 8 patients were not able to proceed with vaccination because of symptomatic disease progression or declining performance status (n = 5), the absence of measurable disease after bridging therapies (n = 2), and travel constraints (n = 1).

Furthermore, using the interferon-gamma ELISPOT to evaluate the strength of T-cell responses to the vaccine, the investigators found that most patients achieved an effective T-cell response with NeoAg-VAX treatment, he noted. However, rates of tumor shrinkage in response to the vaccine were minimal, demonstrating a limitation of this treatment, according to Haldar.

Disclosures: Dr Haldar reported performing a consultant role with Sift Biosciences; receiving grant/research support from Shionogi, Summit Therapeutics, and Bristol Myers Squibb; and receiving honoraria/travel support from DAVA Oncology.