Abstract CT180: Safety and efficacy of vibostolimab (vibo) plus pembrolizumab (pembro) and coformulation of vibo/pembro in ovarian cancer naive to PD-1/PD-L1 inhibitors

Background: The anti-TIGIT antibody vibo in combination with pembro has shown promising antitumor activity in anti-PD-1/PD-L1-naive NSCLC. In the ongoing phase 1 trial (NCT02964013), we evaluated the safety and efficacy of these drugs given in combination (vibo + pembro) or as a coformulation (vibo/pembro) for the treatment of ovarian cancer naive to PD-1/PD-L1 inhibitors.

Methods: Patients had locally advanced unresectable or metastatic ovarian cancer naive to PD-1/PD-L1 inhibitors that progressed after ≥1 line of therapy, including platinum therapy. Patients were nonrandomly assigned to receive vibo (200 mg IV Q3W) + pembro (200 mg IV Q3W) or as the coformulation (vibo/pembro) at the same dose for ≤35 cycles (~2 years) or until disease progression (PD), toxicity, or patient withdrawal. Primary end points were safety and tolerability. Secondary and exploratory end points included PK, objective response rate (ORR), duration of response (DOR), and progression-free survival (PFS) by investigator review per RECIST v1.1. PD-L1 positivity was defined as a combined positive score (CPS) of ≥1 or when CPS was missing, as a tumor proportion score of ≥1% or as a mononuclear immune cell density score of ≥2.

Results: Of 61 patients enrolled, 21 received vibo + pembro, and 40 received vibo/pembro. Median age was 58 years; 48% of patients had ECOG performance status 1, 15% had BRCA1 and/or BRCA2 mutations, 87% received ≥2 lines of prior therapy (66%, bevacizumab; 41%, PARP inhibitor), and 74% had platinum-resistant disease (PD <6 months after platinum). PD-L1 status was positive in 21 patients, negative in 31 patients, and unknown in 9 patients. Median follow-up was 13 months (range, 9-15). Treatment-related adverse events (TRAEs) occurred in 79% of all patients; 13% were grade 3 or 4. No deaths due to TRAEs were reported. The most common TRAEs (≥20%) were fatigue (23%), pruritus (23%), and rash (20%). PK exposure was similar between treatment groups. ORR was 8% (95% CI, 3-18) in all patients and 24% (95% CI, 8-47) in patients with PD-L1-positive tumors. Median DOR was 19 months (range, 4-19). The disease control rate at 6 months was 11% (95% CI, 5-22) in all patients and 24% (95% CI, 8-47) in patients with PD-L1-positive tumors. Median PFS was 2 months (95% CI, 2-2) in all patients and 2 months (95% CI, 2-8) in patients with PD-L1-positive tumors.

Conclusions: Safety and PK were comparable with vibo + pembro combination and the vibo/pembro coformulation in patients with platinum-resistant locally advanced unresectable or metastatic ovarian cancer naive to PD-1/PD-L1 inhibitors. Antitumor activity was equivalent between the combination and coformulation, with responses limited to PD-L1-positive tumors. Vibo/pembro coformulation may offer a safe and convenient treatment option in these patients; further investigations of antitumor activity by PD-L1 status are needed.

Citation Format: Ruth Perets, Martin Gutierrez, Sun Young Rha, Sarah Taylor, Brian Stein, Antonio Jimeno, Ira Winer, Diana Chen, Tanya Keenan, Mohini Rajasagi, Mallika Lala, Jane Healy, Ronnie Shapira-Frommer. Safety and efficacy of vibostolimab (vibo) plus pembrolizumab (pembro) and coformulation of vibo/pembro in ovarian cancer naive to PD-1/PD-L1 inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT180.

Abstract CT508: Safety and efficacy of vibostolimab (vibo) plus pembrolizumab (pembro) in patients (pts) with cervical cancer naive to PD-1/PD-L1 inhibitors

Background: The anti-TIGIT antibody vibo in combination with pembro was well tolerated across all doses in the dose-escalation phase of the ongoing phase 1 study in pts with advanced solid tumors (NCT02964013); promising antitumor activity of vibo + pembro was observed in anti-PD-1/PD-L1-naive NSCLC. We present initial results of the dose-expansion phase in pts with advanced cervical cancer naive to PD-1/PD-L1 inhibitors.

Methods: Pts with histologically confirmed, locally advanced, or metastatic cervical cancer who failed prior standard-of-care chemotherapy or who experienced early progression on definitive chemoradiation and were naive to PD-1/PD-L1 inhibitors were randomly assigned 1:1 to receive 1 of 2 doses of vibo (200 or 700 mg) + pembro (200 mg) Q3W for ≤35 cycles (~2 y) or until PD, toxicity, or pt withdrawal. Primary end points were safety and tolerability. Secondary and exploratory end points included ORR, DOR, and PFS by investigator review per RECIST v1.1.

Results: Median age of the 80 pts with cervical cancer was 49 y; 58% had an ECOG PS of 1; 53% received ≥2 prior lines of therapy; and 61% had PD-L1-positive tumors. 41 pts received vibo 200 mg, and 39 received vibo 700 mg. Median follow-up was 12 mo (range, 5-26). Treatment-related AEs (TRAEs) occurred in 27 pts in each treatment group (66%, vibo 200 mg; 69%, vibo 700 mg). The most frequent TRAEs (≥15%) were rash (22%), increased lipase (17%), and pruritus (17%) with vibo 200 mg + pembro and pruritus (28%), pyrexia (21%), rash (15%), and fatigue (15%) with vibo 700 mg + pembro. Grade 3 or 4 TRAEs occurred in 29% (vibo 200 mg + pembro) and 18% (vibo 700 mg + pembro). No deaths due to TRAEs were reported. Efficacy is reported in the Table.

Conclusions: Vibo + pembro was safe in pts with advanced cervical cancer. Antitumor activity was comparable between the 2 doses of vibo studied and responses were observed irrespective of PD-L1 status. Based on these data, the RP2D for vibo remains 200 mg Q3W.

Efficacy By Treatment Group By PD-L1 Statusa Vibo 200 mg + Pembro n = 41 Vibo 700 mg + Pembro n = 39 PD-L1-positive n = 49 PD-L1-negative n = 21 Confirmed ORR, % (95% CI) 15 (6-29) 23 (11-39) 20 (10-34) 14 (3-36) CR, n (%) 2 (5) 5 (13) 6 (12) 1 (5) PR, n (%) 4 (10) 4 (10) 4 (8) 2 (10) SD, n (%) 12 (29) 7 (18) 14 (29) 3 (14) PD, n (%) 18 (44) 19 (49) 20 (41) 12 (57) Median DOR, months (range)b Not reached (10 to 31+) Not reached (4+ to 35+) Not reached (4+ to 35+) Not reached (21 to 27+) Median PFS, months (95% CI) 2 (2-4) 2 (2-4) 4 (2-4) 2 (1-4) CR, complete response; DOR, duration of response; PD, progressive disease; ORR, objective response rate; PFS, progression-free survival; PR, partial response; SD, stable disease. aPD-L1 status was unknown in 10 patients; data were pooled across treatment groups. PD-L1 positivity was defined as combined positive score (CPS) ≥1 or when CPS was missing, as tumor proportion score ≥1% or mononuclear immune cell density score ≥2. b“+” indicates no PD present at the time of the last disease assessment.

Citation Format: Ronnie Shapira-Frommer, Ruth Perets, Mark Voskoboynik, Kathryn Mileham, Adnan Nagrial, Brian Stein, Vincent Chung, Martin Gutierrez, Diana Chen, Tanya Keenan, Mohini Rajasagi, Jane Healy, Sun Young Rha. Safety and efficacy of vibostolimab (vibo) plus pembrolizumab (pembro) in patients (pts) with cervical cancer naive to PD-1/PD-L1 inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT508.

Putative Biomarkers of Clinical Benefit With Pembrolizumab in Advanced Urothelial Cancer: Results from the KEYNOTE-045 and KEYNOTE-052 Landmark Trials

PURPOSE

In an exploratory analysis, we investigated the association between programmed death ligand 1 (PD-L1), tumor mutational burden (TMB), T-cell-inflamed gene expression profile (TcellinfGEP), and stromal signature with outcomes of pembrolizumab in urothelial carcinoma (UC).

PATIENTS AND METHODS

Patients with advanced UC received first-line pembrolizumab 200 mg every 3 weeks in the single-arm phase II KEYNOTE-052 trial (NCT02335424) and salvage pembrolizumab 200 mg every 3 weeks or chemotherapy (paclitaxel/docetaxel/vinflunine) in the randomized phase III KEYNOTE-045 trial (NCT02256436). The association of each biomarker (continuous variable) with objective response rate (ORR), progression-free survival (PFS), and overall survival (OS) was evaluated using logistic regression (ORR) and Cox PH (PFS, OS), adjusted for ECOG PS; nominal P values were calculated without multiplicity adjustment (one-sided, pembrolizumab; two-sided, chemotherapy). Significance was prespecified at α = 0.05.

RESULTS

In KEYNOTE-052, PD-L1, TMB, and TcellinfGEP were significantly associated with improved outcomes; stromal signature was significantly associated with worse outcomes. In KEYNOTE-045, although findings for TMB and TcellinfGEP with pembrolizumab were consistent with those of KEYNOTE-052, PD-L1 was not significantly associated with improved outcomes, nor was stromal signature associated with worse outcomes with pembrolizumab; chemotherapy was not associated with outcomes in a consistent manner for any of the biomarkers. Hazard ratio (HR) estimates at prespecified cutoffs showed an advantage for pembrolizumab versus chemotherapy regardless of PD-L1 or TMB, with a trend toward lower HRs in the combined positive score ≥10 and the TMB ≥175 mutation/exome subgroup. For TcellinfGEP, PFS and OS HRs were lower in the TcellinfGEP-nonlow subgroup regardless of treatment.

CONCLUSIONS

Multiple biomarkers characterizing the tumor microenvironment may help predict response to pembrolizumab monotherapy in UC, and potential clinical utility of these biomarkers may be context-dependent.

Association of TMB and PD-L1 with efficacy of first-line pembrolizumab (pembro) or pembro + chemotherapy (chemo) versus chemo in patients (pts) with advanced urothelial carcinoma (UC) from KEYNOTE-361

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Background: The 3-arm, open-label, phase 3 KEYNOTE-361 study (NCT02853305) evaluated first-line pembro ± chemo vs chemo in advanced UC regardless of PD-L1 status. The trial did not meet its primary end points of superior PFS and OS with pembro + chemo vs chemo and thus analysis of pembro monotherapy (mono) vs chemo was exploratory. We explored the association of TMB status and PD-L1 combined positive score (CPS) with clinical outcomes in KEYNOTE-361. Methods: In pts with TMB and/or PD-L1 data, the association between TMB (via whole exome sequencing) and PD-L1 (via PD-L1 IHC 22C3 pharmDx) and clinical outcomes (ORR, PFS, and OS) was evaluated. In each treatment arm, the hypotheses regarding the associations were evaluated using logistic regression (ORR) and Cox proportional hazards regression (PFS; OS), and 1-sided (pembro; pembro + chemo) and 2-sided (chemo) P values were calculated; significance was prespecified at α = 0.05 without multiplicity adjustment. Clinical utility was assessed using prespecified cutoffs of 175 mut/exome (TMB) and CPS 10 (PD-L1). Clinical data cutoff was April 29, 2020. Results: 820/993 pts (82.6%) had evaluable TMB data (pembro, 252; pembro + chemo, 282; chemo, 286). TMB (log10) was significantly positively associated with ORR, PFS, and OS for pembro ( P < 0.001, < 0.001, and 0.007, respectively) and PFS and OS for pembro + chemo ( P= 0.007 and 0.010, respectively). The area under the receiver operating characteristics (AUROC) curve (95% CI) for discriminating response was 0.64 (0.56-0.71) for pembro, 0.53 (0.46-0.60) for pembro + chemo, and 0.52 (0.45-0.59) for chemo. Efficacy by TMB cutoff is reported in the Table. All 993 pts had PD-L1 data (pembro, 302; pembro + chemo, 349; chemo, 342). PD-L1 was significantly positively associated with PFS for pembro ( P= 0.006) and ORR for pembro + chemo ( P= 0.042) but not chemo. Efficacy by PD-L1 CPS is reported in the Table. Conclusions: Strong associations were observed between TMB and all 3 clinical outcomes (ORR, PFS, and OS) with pembro mono in the first-line setting and a reduced association was observed between TMB and clinical outcomes with pembro + chemo. No consistent associations were observed between PD-L1 and clinical outcomes with pembro mono or pembro + chemo. Clinical trial information: NCT02853305. [Table: see text]

Comprehensive analysis of cancer-associated somatic mutations in class I HLA genes

Detection of somatic mutations in HLA genes using whole-exome sequencing (WES) is hampered by the high polymorphism of the HLA loci, which prevents alignment of sequencing reads to the human reference genome. We describe a computational pipeline that enables accurate inference of germline alleles of class I HLA-A, -B and -C genes and subsequent detection of mutations in these genes using the inferred alleles as a reference. Analysis of WES data from 7,930 pairs of tumor and healthy tissue from the same patient revealed 298 non-silent HLA mutations in tumors from 266 patients. These 298 mutations are enriched for likely functional mutations, including putative loss-of-function events. Recurrence of mutations suggested that these ‘hotspot’ sites were positively selected. Cancers with recurrent somatic HLA mutations were associated with upregulation of signatures of cytolytic activity characteristic of tumor infiltration by effector lymphocytes, supporting immune evasion by altered HLA function as a contributory mechanism in cancer.

Abstract 1093: Sensitive detection of somatic mutations in class I HLA genes reveals enrichment for functional events in cancer

Recent studies have revealed enhanced somatic mutation rate in HLA genes in several tumor types and has strongly implicated HLA dysfunction as a possible mediator of immune evasion. Mutation detection in this highly polymorphic and GC-rich locus, however, is complicated by suboptimal alignment to the canonical reference genome and lowered capture efficiency. To address this challenge, we developed the POLYSOLVER (POLYmorphic loci reSOLVER) algorithm for accurate inference of class I HLA-A, -B and -C alleles from whole exome sequencing (WES) data, which can then be used for more sensitive and specific mutation detection. POLYSOLVER comprises two broad steps: alignment optimization and subsequent inference of the alleles using a Bayesian classifier. When applied to 133 HapMap samples of known HLA type, POLYSOLVER outperformed other publicly available tools with an overall protein-level accuracy of 97% and was particularly more powerful at low sequencing depths with an overall accuracy of 96%.

To accurately detect HLA mutations in tumor samples, we performed HLA typing by applying POLYSOLVER to the paired germline sample, re-aligned the HLA reads from both tumor and normal to the inferred HLA alleles while filtering out likely erroneous alignments, and then applied standard tools (MuTect and Strelka) to detect somatic mutations by comparing the re-aligned tumor and normal HLA reads. Based on orthogonal RNA-Seq validation, we estimate an improvement in sensitivity from 57.1% to 94.3% and specificity from 43.8% to 81.3% over standard methods.

Pan-cancer analysis of TCGA data from 3,608 tumor/normal pairs by POLYSOLVER across 12 tumor types revealed 147 non-silent HLA mutations in 121 patients. We identified colon adenocarcinoma to be significantly affected by somatic mutation in class I HLA genes, further supporting HLA mutation as a common oncogenic mechanism. By contrast, HLA mutations were not detected in chronic lymphocytic leukemia (n = 129). Alterations likely to have a functional effect, including loss-of-function, were significantly enriched in HLA mutations compared to non-HLA mutations (P &lt; 2.2×10-16). We also observed that 70 of the 147 total HLA mutations (47.6%) fell in 23 recurrent sites suggesting positive selection at these positions. Finally, we determined that the majority of the detected mutations mapped to regions critical for antigen presentation.

In addition to enabling better detection of HLA mutations, accurate HLA typing by POLYSOLVER can also be used to study germline associations of HLA alleles in diseases, and in donor screening for organ transplantation. It may be extended to extracting typing and mutation information from whole genome or RNA sequencing data and from other polymorphic regions in the genome such as MHC class II, TAP1 and TAP2 genes, and MIC-A and MIC-B ligands. POLYSOLVER hence is a generally applicable analysis framework to address these otherwise challenging loci.

Citation Format: Sachet A. Shukla, Mohini Rajasagi, Philip Dixon, Grace Tiao, Michael S. Lawrence, Carrie Sougnez, Vladimir Brusic, Kristian Cibulskis, Adam Kiezun, Catherine J. Wu, Gad Getz. Sensitive detection of somatic mutations in class I HLA genes reveals enrichment for functional events in cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1093. doi:10.1158/1538-7445.AM2015-1093

Haematological malignancies: at the forefront of immunotherapeutic innovation

The recent successes of cancer immunotherapies have stimulated interest in the potential widespread application of these approaches; haematological malignancies have provided both initial proofs of concept and an informative testing ground for various immune-based therapeutics. The immune-cell origin of many of the blood malignancies provides a unique opportunity both to understand the mechanisms of cancer immune responsiveness and immune evasion, and to exploit these mechanisms for therapeutic purposes.

HLA-binding properties of tumor neoepitopes in humans

Cancer genome sequencing has enabled the rapid identification of the complete repertoire of coding sequence mutations within a patient's tumor and facilitated their use as personalized immunogens. Although a variety of techniques are available to assist in the selection of mutation-defined epitopes to be included within the tumor vaccine, the ability of the peptide to bind to patient MHC is a key gateway to peptide presentation. With advances in the accuracy of predictive algorithms for MHC class I binding, choosing epitopes on the basis of predicted affinity provides a rapid and unbiased approach to epitope prioritization. We show herein the retrospective application of a prediction algorithm to a large set of bona fide T cell-defined mutated human tumor antigens that induced immune responses, most of which were associated with tumor regression or long-term disease stability. The results support the application of this approach for epitope selection and reveal informative features of these naturally occurring epitopes to aid in epitope prioritization for use in tumor vaccines.

CD40L-Tri, a novel formulation of recombinant human CD40L that effectively activates B cells

CD40L has a well-established role in enhancing the immunostimulatory capacity of normal and malignant B cells, but a formulation suitable for clinical use has not been widely available. Like other TNF family members, in vivo and in vitro activity of CD40L requires a homotrimeric configuration, and growing evidence suggests that bioactivity depends on higher-order clustering of CD40. We generated a novel formulation of human recombinant CD40L (CD40L-Tri) in which the CD40L extracellular domain and a trimerization motif are connected by a long flexible peptide linker. We demonstrate that CD40L-Tri significantly expands normal CD19+ B cells by over 20- to 30-fold over 14 days and induces B cells to become highly immunostimulatory antigen-presenting cells (APCs). Consistent with these results, CD40L-Tri-activated B cells could effectively stimulate antigen-specific T responses (against the influenza M1 peptide) from normal volunteers. In addition, CD40L-Tri could induce malignant B cells to become effective APCs, such that tumor-directed immune responses could be probed. Together, our studies demonstrate the potent immune-stimulatory effects of CD40L-Tri on B cells that enable their expansion of antigen-specific human T cells. The potent bioactivity of CD40L-Tri is related to its ability to self-multimerize, which may be facilitated by its long peptide linker.

Thymocyte expansion and maturation: crosstalk of CD44v6 on thymocytes and panCD44 on stroma cells

Re-acquisition of immunocompetence after allogeneic bone marrow cell (BMC) transplantation depends on intrathymic maturation of the allogeneic T progenitor cells. We recently reported that CD44 promotes progenitor homing into the thymus and T-cell maturation and now elucidate the molecular mechanisms of CD44-supported thymocyte maturation. Lethally irradiated, tumor-bearing mice, allogeneically reconstituted with T-cell-depleted BMC and a small number of common lymphoid progenitor 2 cells (CLP2) from transgenic (TG) mice, that express ratCD44v4-v7 under the Thy1 promoter, showed accelerated immunocompetent T-cell recovery compared with mice reconstituted with non-transgenic (NTG) CLP2. In addition, graft-versus-host disease was strongly reduced after tumor vaccination. TG, but not NTG double-negative (DN) thymocytes showed high proliferative potential, accompanied by constitutive association of lck with CD44. Importantly, when thymocyte adhesion was strengthened by anti-CD44, co-cultures of DN thymocytes with thymic stroma supported DN thymocyte maturation. The close contact between DN thymocytes and thymic stroma promoted persisting activation of lck and ERK1/2, particularly in CD44v6(+) DN thymocytes. Thus, intrathymic T-cell maturation in allogeneically reconstituted, leukemia-bearing hosts can be considerably accelerated by high CD44v6 expression in early thymocytes, in which proliferation-supporting signals are initiated by a crosstalk between CD44v6 on thymocytes and panCD44 on the thymic stroma.

Anti-CD44 induces apoptosis in T lymphoma via mitochondrial depolarization

A blockade of CD44 can interfere with haematopoietic and leukemic stem cell homing, the latter being considered as a therapeutic option in haematological malignancies. We here aimed to explore the molecular mechanism underlying the therapeutic efficacy of anti-CD44. We noted that in irradiated mice reconstituted with a bone marrow cell transplant, anti-CD44 exerts a stronger effect on haematopoietic reconstitution than on T lymphoma (EL4) growth. Nonetheless, in the non-reconstituted mouse anti-CD44 suffices for a prolonged survival of EL4-bearing mice, where anti-CD44-prohibited homing actively drives EL4 cells into apoptosis. In vitro, a CD44 occupancy results in a 2–4-fold increase in apoptotic EL4 cells. Death receptor expression (CD95, TRAIL, TNFRI) remains unaltered and CD95 cross-linking-mediated apoptosis is not affected. Instead, CD44 ligation promotes mitochondrial depolarization that is accompanied by caspase-9 cleavage and is inhibited in the presence of a caspase-9 inhibitor. Apoptosis becomes initiated by activation of CD44-associated phosphatase 2A (PP2A) and proceeds via ERK1/2 dephosphorylation without ERK1/2 degradation. Accordingly, CD44-induced apoptosis could be mimicked by ERK1/2 inhibition, that also promotes EL4 cell apoptosis through the mitochondrial pathway. Thus, during haematopoietic stem cell reconstitution care should be taken not to interfere by a blockade of CD44 with haematopoiesis, which could be circumvented by selectively targeting leukemic CD44 isoforms. Beyond homing/settlement in the bone marrow niche, anti-CD44 drives leukemic T cells into apoptosis via the mitochondrial death pathway by CD44 associating with PP2A. Uncovering this new pathway of CD44-induced leukemic cell death provides new options of therapeutic interference.

Thymus repopulation after allogeneic reconstitution in hematological malignancies

OBJECTIVE

Active vaccination in the allogeneically reconstituted tumor-bearing host essentially requires donor T-cell tolerance. To create a basis for vaccination in the allogeneically reconstituted, lymphoma-bearing host, we elaborate a reconstitution protocol that supports thymus repopulation and tolerance induction.

METHODS

Myeloreductively conditioned, lymphoma-bearing mice were vaccinated after reconstitution with hematopoietic progenitor cells. Readout systems included recovery of donor-derived T cells, graft vs host disease (GVHD), anti-host and anti-lymphoma cytotoxicity, as well as tumor growth rate and tumor rejection.

RESULTS

In tumor-free mice, myeloreductive conditioning, together with natural killer cell depletion of the host and transfer of T cell-depleted bone marrow cells, allows reconstitution without severe GVHD. However, in hematological malignancies, donor-derived T-progenitor cells hardly immigrated into the thymus. As a consequence, the frequency of severe GVHD was significantly increased, which prohibited active vaccination. Thymus repopulation became improved by strengthening myeloreductive conditioning; by supporting thymocyte expansion via interleukin-7; and, most strongly, by a small dose of donor-derived CD4(+)CD8(+) thymocytes, which preferentially homed into the thymus. Active vaccination, in combination with this reconstitution protocol, did not strengthen GVHD, but significantly improved survival time and survival rate of lymphoma-bearing mice.

CONCLUSION

The negative impact of hematological malignancies on thymus repopulation and central tolerance induction can, at least in part, be corrected by application of a small number of donor-derived T-progenitor cells.