A phase 2 study of an off-the-shelf, multi-neoantigen vector (ADXS-503) in patients with metastatic non–small cell lung cancer either progressing on prior pembrolizumab or in the first-line setting

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Background: ADXS-503 (A503) is an off-the-shelf, attenuated Listeria monocytogenes (Lm)-based immunotherapy bioengineered to elicit potent T-cell responses against 22 tumor antigens commonly found in non-small-cell lung cancer (NSCLC, i.e. 11 hotspot mutations and 11 tumor-associated antigens, TAAs). Pembrolizumab (pembro) is a programmed death receptor-1 (PD-1)-blocking antibody approved for the treatment of advanced lung cancer. A503 and pembro have complementary mechanisms of immune activation and reversal of immune tolerance. Methods: A phase 2 study of A503 ± pembro is being conducted in patients with metastatic squamous or non-squamous NSCLC. In Part B of the study, A503 was added-on to pembro within 12 weeks of the first scan showing disease progression following pembro (per RECIST criteria v1.1). In Part C of the study, A503 and pembro were administered to previously untreated patients. Both A503 (1x108 CFU) and pembro (200 mg) were infused by IV every 3 weeks until disease progression or limiting toxicity. Results: A total of 17 patients have been treated/evaluated from Part B (n = 14/13) and Part C (n = 3/3). Pembro + A503 was well tolerated in both parts of the study, with mostly grade 1–2, transient and reversible treatment-related adverse events, the most common being fever (47%), chills (35%), fatigue (29%) and nausea (21%). There have been no added immune-related toxicities associated with the combination. Of the 13 evaluable patients in Part B, 2 achieved partial response (PR) and 4 achieved stable disease (SD), yielding an objective response rate (ORR) of 15.4% and a disease control rate (DCR) of 46.2%. Two patients from Part C also achieved SD (DCR 67%). The 2 PRs in Part B have been durable (i.e. 710 and 189 days) as were 5 of the SDs: 3 in Part B (i.e. 448, 175, 117 days) and 2 in Part C (i.e. 322 and 175 days). Both patients with PR in Part B are still undergoing therapy in addition to the other patients who achieved SD. Patients who seem to achieve clinical benefit in both parts of the study include those with PD-L1 expression ≥ 50% and those who show proliferation and/or activation of NK and CD8+ T cells within the first weeks of therapy. In addition, patients with prior pembro exposure ≥ 6 months and DCR > 6 months seem to have clinical benefit when A503 is added to pembro (Part B). Conclusions: The addition of A503 to pembro after disease progression on pembro appears to be well tolerated and induced antigen-specific T-cell responses and durable disease control in 46% of patients in Part B and 67% of patients in Part C. Additional patients are currently being enrolled into both parts of the study to further explore the potential of A503 to restore or enhance sensitivity to checkpoint inhibitors. Clinical trial information: NCT03847519.

Abstract 1671: Evaluation of total PD-1 expression using multi-color flow cytometry in metastatic non-small Cell lung cancer patients treated with multi-neoantigen vector (ADXS-503) alone and in combination of pembrolizumab to assess T-cell & T-cell memory subsets

Precision for Medicine (Precision) developed and qualified two 17 color flow immunophenotyping assays to be used as pharmacodynamic biomarkers for Advaxis clinical studies in patients with Metastatic Non-Small Cell Lung Cancer treated with ADXS-503 alone and in combination with Pembrolizumab (Pembro). ADXS-503 (A503) is an off-the-shelf, attenuated Listeria monocytogenes (Lm)-based immunotherapy bioengineered to elicit potent T-cell responses against 22 tumor antigens commonly found in NSCLC. Pembrolizumab (Pembro) is a programmed death receptor-1 (PD-1)-blocking antibody approved for the treatment of advanced lung cancer. A503 and Pembro have complementary mechanisms of immune activation and reversal of immune tolerance. Here, we qualified two multi-color flow cytometry assays to quantify total PD-1 expression in cryopreserved peripheral blood mononuclear cells (PBMCs) from individuals that were treated either with A503 only or with A503 in combination with Pembro. The detection of free PD-1 and Pembro-bound PD-1 was achieved by co-staining a partially competing αPD-1 antibody (clone PD1.3.1.3) with a biotinylated αHu-IgG4 antibody. The robustness of the assay was demonstrated using a nine-point half-log serial dilution of Pembro, where the highest concentration was 10µg/mL and the lowest concentration was 0.001µg/mL, including a no drug control. The assay conditions were optimized for sensitivity, optimal signal:noise ratio, detection of free and drug bound receptor by titrating and testing various commercial αPD-1 antibody clones and tertiary reagents to detect biotinylated αHu-IgG4. The Pembro bound receptor was detected using a biotinylated αHu-IgG4 antibody, while the free receptors were quantified using a commercial αPD-1 antibody. The assay was able to quantify free and drug bound PD-1 in the intended immune cell types without compromising the staining of other cell surface and intra-nuclear markers. Majority of the evaluable patients, 6 out of 8, had increased counts of NK, CD4+ and CD8+ T-cells, including TCM, TEM and memory stem cells after the administration of ADXS-503 ± Pembro. PD1 expression on circulating CD4+, CD8+ and NK T-cells was also increased while PD-L1 expression was elevated in on-therapy tumor biopsies in some of these patients. Measuring total PD-1 in T-cells can be more challenging in patients on Pembrolizumab therapy as no known commercial non-competing αPD-1 antibody clones are available. This novel assay will facilitate the evaluation of total PD-1 expression as a pharmacodynamic biomarker in T-cells when PD-1 blockade is being used. These results also support that combination of ADXS-503 with PD-1 blockade could lead to enhancement of efficacy of anti-tumor immunotherapy.

Citation Format: Venkat Mohanram, Natalya Belkina, Angelina R. Bisconte, Jonathan W. Goldman, Gregory J. Gerstner, Missak Haigentz, Thomas Stinchcombe, Balazs Halmos, Surya Vangala, Victor Kabala, Dinesh Simkhada, Cristiane Metran, Darren Davis, Megan Parsi, Andres A. Gutierrez, Deborah Phippard, Suresh S. Ramalingam. Evaluation of total PD-1 expression using multi-color flow cytometry in metastatic non-small Cell lung cancer patients treated with multi-neoantigen vector (ADXS-503) alone and in combination of pembrolizumab to assess T-cell & T-cell memory subsets [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1671.

A phase 1 study of an off-the shelf, multi-neoantigen vector (ADXS-503) in subjects with metastatic non-small cell lung cancer (NSCLC) progressing on pembrolizumab as last therapy

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Background: ADXS-503 (A503) is an off-the-shelf, attenuated Listeria monocytogenes (Lm)-based immunotherapy bioengineered to elicit potent T cell responses against 22 tumor antigens commonly found in NSCLC (i.e., 11 hotspot mutations and 11 tumor-associated antigens, TAAs). Pembrolizumab (Pembro) is a programmed death receptor-1 (PD-1)- blocking antibody approved for the treatment of advanced lung cancer. A503 and Pembro have complementary mechanisms of immune activation and reversal of immune tolerance. Methods: A phase 1 study of A503 ± Pembro has been conducted in patients (pts) with metastatic squamous or non-squamous NSCLC. In dose-escalation part B, A503 was added-on to Pembro within 12 weeks of the first scan showing disease progression per RECIST criteria v1.1. Both, A503 (1 x108 CFU) and Pembro (200 mg) were infused by IV every 3 weeks until disease progression or limiting toxicity. The dose-escalation cohort has established safety, tolerability and immunogenicity of the combination therapy and it has been further expanded to evaluate efficacy (Goldman JW et.al., SITC 2020). Results: Nine pts have been treated and evaluated in Part B. Pembro + A503 combo has been well tolerated and without immune related AEs. Of the nine evaluable pts, one has achieved partial response (PR) and 3 stable disease (SD), yielding an overall response rate (ORR) of 11% and disease control rate (DCR) of 44%. Two patients have had clinical benefit for over 12 months (i.e., one PR and one SD) and both of them had been on Pembro therapy for 2 years before enrollment. The two other pts with SD have sustained it for almost 6 months thus far. Seven pts have been evaluated for immunogenicity. In all pts there was a transient release of pro-inflammatory cytokines and proliferation of cytotoxic- and memory-CD8+ T cells. Seven evaluable pts had antigen-specific T cells within 1-2 weeks after starting therapy and 4/7 showed antigen spreading. Conclusions: ADXS-503 as an add-on therapy to Pembro at disease progression has been well tolerated and it has induced antigen specific-T cell responses and durable disease control in 44% of pts. Part B cohort is currently enrolling additional pts to further explore the potential reversal of Pembro resistance with ADXS-503. Clinical trial information: NCT03847519.