Oncolytics Virus Replication Using Pelareorep (Reolysin) and Carfilzomib in Relapsed Myeloma Patients Increases PD-L1 Expression with Clinical Responses

Rationale: Immune checkpoint inhibitors, including those targeting programmed cell death protein 1 (PD-1), are tempting in immunosuppressive cancers such as multiple myeloma (MM). PD-1 inhibition alone has not been effective (Lesokhin, JCO, 2016). Evidence suggests that tumor response is determined by tumor PD-L1 expression and presence of infiltrating cytotoxic T-cell lymphocytes (CTLs). Intravenous Pelareorep (Reolysin), the infusible form of reovirus (RV), has been shown to upregulate IFN-regulated gene expression, CTL infiltration, and the PD1/PD-L1 axis in myeloma cell lines (Kelly KR et al, Leukemia, 2018) and in patients with brain tumors (Samson A et al, Sci Trans Med, 2018).

Introduction:Viral oncolytic therapy with Pelareorep is supported by preclinical data indicating that its antitumor activity results from direct cytolysis and immune responses against infected MM cells. Our phase 1 single agent Reolysin trial in patients with relapsed MM confirmed the tolerability of Pelareorep and demonstrated preferential infection into myeloma cells but not microenvironmental cells in the marrow by intracellular staining for RV genome. In PART ONE of our follow-up trial, Carfilzomib (Kyprolis)-sensitive patients were accrued. Correlative studies included bone marrow aspirate pretreatment on cycle 1 day 1 and day 9 to assess RV infection of myeloma cells, replication within myeloma cells, and PD-L1 expression on myeloma cell surface. Pelareorep, Carfilzomib, and 20 mg IV Dexamethasone were all infused per the standard Carfilzomib schedule on days 1, 2, 8, 9, 15 and 16 of a 28-day cycle.

Part ONE: Carfilzomib-sensitive patients were infused at dose level one with Pelareorep 3 x 10¹⁰TCID₅₀/day and Carfilzomib 20 mg/m² on days 1 and 2 of cycle 1 and 27 mg/m² thereafter, on days 1, 2, 8, 9, 15 and 16 of a 28-day cycle. The MTD will be determined as the highest dose combination with fewer than 33% DLTs observed in cycle 1. There were 2 VGPRs, 2 PRs, 1 MR, and one patient with stable disease after cycle 1. All evaluable patients showed RV infection and replication in the post-treatment BM aspirates. In the 4 bortezomib-refractory patients in the first cohort, all have shown viral replication, and this correlated directly with activated caspase-3 in the MM cells and clinical response.

Part TWO: Carfilzomib-refractory patients were treated with Carfilzomib 20 mg/m² on days 1 and 2 of cycle 1, and 56 mg/m² thereafter. Seven patients have been enrolled to date. In 3 patients processed to date with both pre- and post-treatment biopsies available, RV infection was detected in myeloma cells (2 patients) and endothelial cells (one patient). Replication was not seen. In these patients there was no strong evidence of increased activated caspase-3 expression in myeloma cells, nor was there a statistically significant increased CD8 cell infiltration or checkpoint protein expression after treatment.

Conclusion: An increase in viral infection, viral replication, and PD-L1 expression on the surface of myeloma cells has been demonstrated in patients that had a clinical response to protocol therapy. A future study to assess the safety and tolerability of PD-1 inhibition in relapsed myeloma patients is now open to accrual (NCT03605719). Dose escalation is ongoing and the effects of the addition of Reolysin to Carfilzomib/Dexamethasone will be determined in this trial.