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

Background: Recurrent/refractory (r/r) DLBCL presents a major treatment challenge, especially in the setting of patients who are ineligible for, or relapsing after, potentially curative treatments such as autologous stem cell transplant (ASCT) and chimeric antigen receptor T cell (CAR-T) therapy. Efficacious treatment options that are well-tolerated and easily accessible in this population represent a critical unmet medical need.

DPX-Survivac is a targeted T cell activation therapy against cancers expressing survivin. Survivin plays an essential role in cancer biology and represents a target of choice to disrupt tumour progression. DPX-Survivac's mechanism of action relies on its ability to generate robust and durable survivin-specific T cells that migrate to, infiltrate and kill tumour cells. DPX-Survivac is administered with intermittent, low dose cyclophosphamide (CPA) used as an immunomodulator. In nonclinical studies, treatment with DPX-Survivac increases PD-L1 and PD-1 expression providing the rationale for combination with pembrolizumab.

Methods: "SPiReL" is a Phase 2 non-randomized, open label, efficacy and safety study. Subjects with r/r DLBCL with confirmed survivin expression are eligible for participation. Subjects must also be ineligible for potentially curative therapy. The treatment and testing regimen is shown in the figre below.

The primary objective of SPiReL is to document a minimum Objective Response Rate (ORR) of 24% (in 6/25 subjects) using the modified Cheson criteria (2007). Secondary objectives include safety, duration of response and time to next treatment. Exploratory endpoints include T cell response, tumour immune cell infiltration, and biomarker analysis.

Results: At data cut-off, 22 subjects have been enrolled in the study. The median age is 75.5 years (50-82). Thirteen of 22 subjects (59.1%) are GCB sub-type, 8 subjects (36.4%) are non-GCB and 1 subject (4.5%) has primary cutaneous DLBCL, leg type. The median number of prior therapies is 2 (1-7), with 4 subjects having previously undergone ASCT and 5 subjects with transformed disease. Of the 22 enrolled subjects, 8 are not evaluable per protocol for clinical efficacy due to early disease progression. Four subjects are active on treatment, 3 of which have not yet reached the first time point for assessment.

Clinical outcome was analyzed for the Full Analysis Set (FAS) (n=19) and in the Per Protocol (PP) analysis (n=11). Of 11 subjects in the PP, 7 subjects (63.6%) have achieved an objective response, meeting the study's primary endpoint; 3 subjects (27.3%) with a CR and 4 subjects (36.4%) with a PR. Three subjects (27.3%) achieved SD and thus clinical benefit was demonstrated in 10/11 (90.9%) of evaluable subjects. Two subjects (18.2%) have completed the 1 year treatment period, 8 subjects (72.7%) discontinued treatment due to disease progression, and 1 subject (9.2%) discontinued treatment due to an unrelated Adverse Event (AE). Including the entire FAS, the objective response rate was 7/19 (36.8%).

This treatment combination is well-tolerated, only 11% of Treatment Related AEs (TRAEs) were assessed as Grade 3 or higher. The majority of the Grade 1 and 2 TRAEs were Injection Site Reactions (ISRs) related to DPX-Survivac. Ten serious AEs were reported, of which 3 were considered related to study treatment. No subjects have discontinued study treatment due to a TRAE.

Analyses of peripheral blood T cell responses to survivin by ELISpot assay shows that 7/7 subjects who achieved an objective response have survivin-specific T cell response. One subject with PD also showed a survivin-specific T cell response, supporting the mechanism of action and the role of DPX-Survivac in anti-tumor activity.

Summary: DPX-Survivac and low dose CPA in combination with pembrolizumab, demonstrates promising clinical activity in recurrent/refractory DLBCL with 10/11 (90.9%) of evaluable subjects deriving clinical benefit with minimal toxicity. The primary endpoint of this study has been reached with 7/11 (63.6%) of evaluable subjects achieving an objective response warranting further exploration of DPX-Survivac in this population. Enrollment is continuing to further define the patient population most likely to benefit from this well-tolerated therapy.

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