Combination of DPX-Survivac, Low Dose Cyclophosphamide, and Pembrolizumab in Recurrent/Refractory DLBCL: The Spirel Study

Introduction: Recurrent/refractory diffuse large B cell lymphoma (DLBCL) remains an area of unmet clinical need. Although autologous stem cell transplant (ASCT), and more recently chimeric antigen receptor (CAR) T cell therapy, have made a significant impact, many patients are ineligible for these treatments due to advanced age, comorbidities, or financial or geographical limitations, or they have relapsed following these treatments.

Survivin, a novel target in DLBCL, is overexpressed in approximately 60% of untreated DLBCL with higher rates in relapsed disease. DPX-Survivac, a T cell activating therapy, elicits a strong and prolonged immune response against tumors expressing survivin. DPX-Survivac is combined with pembrolizumab, an anti-PD-1 checkpoint inhibitor, and intermittent low dose cyclophosphamide (CPA), used for an immunomodulatory effect. Pre-clinical studies have demonstrated increased efficacy of this DPX-based drug combination in controlling of tumor growth in murine tumor models, resulting in improved survival (Weir et al. J Immunother Cancer 2016).

Methods: "SPiReL" is a Phase 2 non-randomized, open label, efficacy and safety study. Subjects with recurrent/refractory DLBCL with confirmed survivin expression are eligible for participation. Participants must also be ineligible for curative therapy. Study treatment includes administering two doses of 0.5 mL of DPX-Survivac 3 weeks apart followed by up to six 0.1 mL doses every 8 weeks. Intermittent low dose cyclophosphamide is administered orally at 50 mg twice daily for 7 days followed by 7 days off. Pembrolizumab 200 mg is administered every 3 weeks. Study participants continue active therapy for up to one year or until disease progression, whichever occurs first.

The primary objective is to document the response rate to this treatment combination using modified Cheson criteria. Secondary objectives include duration of response and safety. Exploratory endpoints include T cell response, tumor immune cell infiltration, and gene expression analysis.

Enrollment is ongoing with a goal of up to 25 subjects in this national, multi-center study. Trial design is shown below the text.

Results: At the time of data cut-off, 23 subjects have been screened and 12 have been enrolled. The demographics of enrolled subjects include: median age is 75.5 years (50-82), with 3 male subjects participating. The median number of prior therapies is 2.5 (1-6), with 4 subjects having previously undergone ASCT. The median time from diagnosis to screening is 31 months (8-151). Of the 12 enrolled subjects, 3 were not evaluable for clinical efficacy due to early disease progression. One subject has not yet reached the first time point for assessment.

In the Per Protocol analysis of 8 evaluable subjects ("PP", N = 8); as compared to a Full Analysis Set ("FAS", N = 11); 7 of 8 subjects (PP = 87.5%) demonstrated clinical benefit, including 6 with tumor regressions (FAS = 63.6%); 2 subjects (PP = 25%) achieved a complete response, 1 of whom has completed the 1 year study period (FAS = 18.2%); 3 subjects (PP = 37.5%) had a partial response (FAS = 27.3%); and 3 (PP = 37.5%) had stable disease remaining on study for 4, 6 and 8 months (FAS = 27.3%).

This treatment combination is well-tolerated with mostly grade 1 and 2 adverse events reported; a single grade 3 maculopapular rash and 1 case of grade 4 cytopenia has been observed.

Of the 23 screened subjects, survivin expression analysis was performed on 18 subjects. All of the 18 samples analyzed were survivin positive, with a range of 60%-100% of lymphoma cells expressing survivin.

Preliminary analysis of peripheral blood T cell responses to survivin by ELISPOT assay shows 2 of 4 subjects had strong survivin-specific T cell responses. Both of these subjects had clinical responses.

Summary: DPX-Survivac, in combination with pembrolizumab and low dose cyclophosphamide, demonstrates clinical activity and a favorable safety profile in recurrent/refractory DLBCL with 87.5% of evaluable subjects deriving clinical benefit, including 2 complete responses (25%) and 3 partial responses (37.5%) to date. Enrollment is continuing to further explore the synergistic effect of this combination in this population.

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