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Personalized cancer vaccine may enhance checkpoint inhibitor activity



Combining a personalized cancer vaccine with an immune checkpoint inhibitor induced neoantigen-specific immune responses in most patients with advanced solid tumors in a phase 1b study.

Only two clinical responses were seen in this early investigation of the vaccine, RO7198457, combined with the PD-L1 inhibitor atezolizumab. However, T-cell responses were observed in about three-quarters of the patients evaluated, according to study investigator Juanita Lopez, MB BChir, PhD.

Those immune responses, coupled with preliminary evidence of infiltration of RO7198457-stimulated T cells into tumors, suggest the viability of this individualized anticancer strategy, according to Dr. Lopez, a consultant medical oncologist at The Royal Marsden NHS Foundation Trust and The Institute of Cancer Research, London.

“Failure of T-cell priming is a major cause of lack of response to immune checkpoint inhibitors,” Dr. Lopez said in an interview. “We hoped that, by eliciting a tumor-specific T-cell response, we would be able to overcome this.”

Preclinical data suggested the combination of vaccine and immune checkpoint inhibitors improved outcomes, which prompted the current study, added Dr. Lopez, who presented results from this study at the American Association for Cancer Research virtual meeting II.

Dr. Lopez noted that mutated neoantigens are recognized as foreign and have been shown to induce stronger T-cell responses, compared with shared antigens, likely because of a lack of central tolerance.

“Most of these mutated neoantigens are not shared between the patients, and therefore, targeted neoantigen-specific therapy requires an individualized approach,” she explained.

RO7198457 is manufactured on a per-patient basis and includes as many as 20 tumor-specific neoepitopes.

Study details

Dr. Lopez presented results from dose-escalation and expansion cohorts of the study, which included 142 patients with advanced solid tumors. The patients had colorectal, skin, kidney, lung, urothelial, breast, gynecologic, and head and neck cancers.

Most patients had low or no PD-L1 expression, and nearly 40% had received prior treatment with a checkpoint inhibitor.

Patients received nine doses of RO7198457 at 25-50 mcg during the 12-week induction stage. They then received RO7198457 every eight cycles until disease progression. Patients received atezolizumab at 1,200 mg on day 1 of each 21-day cycle.

Induction of proinflammatory cytokines was observed at each dose tested, and ex vivo T-cell responses were noted in 46 of 63 patients evaluated, or 73%.

T-cell receptors specific to RO7198457 were present posttreatment in a patient with rectal cancer, providing some preliminary evidence suggesting infiltration of RO7198457-stimulated T cells in the tumor, Dr. Lopez said.

There were two clinical responses. A patient with rectal cancer had a complete response, and a patient with triple-negative breast cancer had a partial response.

The combination of RO7198457 with atezolizumab was generally well tolerated, and the maximum tolerated dose was not reached, Dr. Lopez said. Most adverse events were grade 1/2, and immune-mediated adverse events were rare.

Implications and next steps

This study furthers earlier observations from neoantigen vaccine studies by linking dosing of the vaccine to dosing with immune checkpoint inhibitor, rather than giving the vaccine in the period leading up to immune checkpoint inhibitor administration, according to former AACR President Elaine R. Mardis, PhD, of Nationwide Children’s Hospital and The Ohio State University College of Medicine, both in Columbus.

That said, the implications for clinical practice remain unclear, according to Dr. Mardis.

“This combination did elicit an immune response that was highly specific for the neoantigen vaccine, but most patients did not receive a clinical benefit of disease response,” Dr. Mardis said in an interview. “This tells us the combination approach used was, overall, not quite right, and we need to continue to innovate in this area.”

The low clinical response rate in the study was likely caused in part by the fact that patients had very advanced disease and were heavily pretreated, according to Dr. Lopez

Randomized phase 2 studies of RO7198457 are now underway, Dr. Lopez said. One is a study of RO7198457 plus atezolizumab as adjuvant treatment for non–small cell lung cancer (NCT04267237). Another is testing RO7198457 in combination with pembrolizumab as first-line treatment for melanoma (NCT03815058).

The current study was funded by Genentech and BioNTech. Dr. Lopez reported disclosures related to Roche/Genentech, Basilea Pharmaceutica, and Genmab. Dr. Mardis reported disclosures related to Quiagen NV, PACT Pharma, Kiadis Pharma NV, and Interpreta.

SOURCE: Lopez J et al. AACR 2020, Abstract CT301.

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