The Society for Immunotherapy of Cancer (SITC) is pleased to present highlights of the latest advances in immunotherapy emerging from the 2023 AACR Annual Meeting. Below is a recap of highlighted research presented from Friday, April 14 through Wednesday, April 19, 2023.
Scientific Highlights
A PERSONALIZED MRNA CANCER VACCINE COMBINED WITH IMMUNE CHECKPOINT INHIBITORS FOR MELANOMA
CT001. A personalized cancer vaccine, mRNA-4157, combined with pembrolizumab versus pembrolizumab in patients with resected high-risk melanoma: Efficacy and safety results from the randomized, open-label Phase 2 mRNA-4157-P201/Keynote-942 trial
Jeffrey S. Weber (New York University Langone Medical Center, New York, New York) presented results from KEYNOTE-942, a phase 2 trial comparing the safety and efficacy of pembrolizumab alone versus pembrolizumab with mRNA-4157 (V940), a customizable individualized neoantigen therapy encoding up to 34 neoantigens, for patients with high risk-melanoma. Prior works indicate the potential of individual neoantigen approaches to increase endogenous neoantigen T-cell responses and induce epitope spreading. After sequencing tissue biopsies, algorithms identified patient- and tumor-specific neoantigens that could potentially bind to HLA and generate T cell responses. A single-stranded RNA encoding up to 34 neoantigen sequences was packaged with nanoparticles and administered intramuscularly. The platform used to develop mRNA-4157 was also implemented for the COVID-19 vaccine. Patients with stage IIIB, IIIC, IIID, or IV cutaneous melanoma were randomized to two arms in a 2:1 ratio. Patients in the Combination arm (n=107) received pembro (200mg IV Q3W, up to 18 cycles) and mRNA-4157 (1mg IM Q3W, up to 9 doses) after surgical resection, and patients in the Control arm (n=50) received pembro alone (200mg IV Q3W, up to 18 cycles) after surgical resection. More than 90% of patients had sufficient resected tissue quality and quantity for the manufacturing of personalized mRNA-4157 vaccine. Patient vaccines contained a median of 34 antigens, (range 9-34), and 91% of patients in the Combination arm received a vaccine including all 34 neoantigens. All patients in the trial experienced adverse events, with 25% of patients in the Combination arm and 18% of patients in the Control arm experiencing adverse events >= grade 3. 18-month recurrence-free survival (RFS) rates for the Combination arm (78.6%) were significantly higher than the Control arm (62.5%). The hazard ratio was 0.56, indicating adjuvant treatment with pembro + mRNA-4157 reduced the risk of disease recurrence by 44%. Improvement in RFS was observed in patients regardless of PD-L1 status. KEYNOTE-942 is the first positive randomized vaccine study in melanoma, and these data suggest the mRNA-4157 neoantigen vaccine is well-tolerated and produces promising clinical results. Additional analyses of trial data will be performed and presented at future conferences, and longer follow-up periods to measure RFS are needed. A phase 3 trial to confirm these results will begin in 2023.
KEYMAKER-U02: NEOADJUVANT PEMBROLIZUMAB COMBINATION THERAPY OR MONOTHERAPY FOR MELANOMA
CT002. KEYMAKER-U02 substudy 02C: Neoadjuvant pembrolizumab (pembro) + vibostolimab (vibo) or gebasaxturev (geba) or pembro alone followed by adjuvant pembro for stage IIIB-D melanoma
Reinhard Dummer (University Hospital Zurich, Zurich, Switzerland) presented results from KEYMAKER-U02, a Phase 1/2 open-label rolling arm umbrella platform trial to evaluate neoadjuvant pembrolizumab in combination or as monotherapy for stage IIIB-D melanoma. Patients were randomized to three arms in a 2:2:1 ratio. Patients in Arm 1 (n=26) received neoadjuvant pembrolizumab (pembro, 200mg IV Q3W, 2 cycles) and anti-TIGIT monoclonal antibody vibostolimab (vibo, 200mg IV Q3W, 2 cycles); patients in Arm 2 (n=25) received neoadjuvant pembro (400mg IV, 1 cycle) and oncolytic virus gebasaxturev (geba, 3x108 TCID50, 5 doses); patients in Arm 3 (n=15) received neoadjuvant pembro (400mg IV, 1 cycle) alone. Patients in all three arms received adjuvant pembro (400mg IV Q6W, up to 8 cycles) after resection. At a median follow-up of 14.1 months, most patients experienced treatment-related adverse events (trAEs; 92% Arm 1, 84% Arm 2, 80% Arm 3), and a limited number of trAEs were >= grade 3 (8% in Arm 1, 24% in Arm 2, and 7% in Arm 3). 81% of patients in Arm 1, 52% in Arm 2, and 73% in Arm 3 achieved any pathologic response. Pathological complete response (pCR) rate was 38% for Arm 1 (n=10), 28% for Arm 2 (n=7), and 40% for Arm 3 (n=6), and most patients’ diseases exhibited concordance with CT scans and pathological outcomes. 18-month relapse free survival (RFS) and event free survival (EFS) rates were 95% and 85%, respectively, for Arm 1, 87% and 70% for Arm 2, and 73% and 78% for Arm 3. Median RFS was not reached for any group. The data indicate that neoadjuvant therapies of a pembro-based combination or pembro alone followed by adjuvant pembro have manageable safety and promising clinical outcomes in patients with high-risk stage III melanoma, with pembro + vibo producing the most promising results. A Phase 3 trial (KEYVIBE-010) investigating adjuvant pembro + vibo compared with pembro alone for patients with high-risk stage II-IV melanoma is ongoing.
INTRATUMORAL IL-12 AND IMMUNE CHECKPOINT BLOCKADE FOR ADVANCED SOLID TUMORS
CT004. Intratumoral (IT) MEDI1191 + durvalumab (D): Update on the first-in-human study in advanced solid tumors
Eduardo Castañón (Clínica Universidad de Navarra, Pamplona, Spain) presented updated analyses from a first in-human study investigating the safety and efficacy of MEDI1191 (MEDI), an intratumoral lipid nanoparticle-formulated mRNA encoding IL-12, in combination with durvalumab (anti-PD-L1) for a variety of advanced solid tumors. 61 patients received sequential or concurrent treatment with MEDI and durvalumab. Patients in Part 1A (n=25) received injections of MEDI in subcutaneous/cutaneous lesions followed by intravenous durvalumab. Patients in Part 1B (n=27) received concurrent treatment of MEDI and durvalumab, with MEDI injected in subcutaneous/cutaneous lesions, and patients in Part 1D (n=9) received concurrent treatment of MEDI and durvalumab, with MEDI injected in deep-seated lesions. Melanoma was the most commonly represented cancer, and all patients in Part 1D had liver metastases. No dose-limiting toxicities were observed, and neither MEDI nor durvalumab were discontinued due to adverse events (AEs). Treatment-emergent AEs >= Grade 3 occurred in 41% of all patients; MEDI-related AEs >= Grade 3 occurred in 4% of patients, and durvalumab-related AEs >= Grade 3 occurred in 4% of patients. 7 patients achieved a partial response (PR), and 5 were confirmed by CT scan. Overall response rate was 8.2% (n=5), and disease control rate was 27.9% (n=17). Median duration of response (DOR) was not achieved but response durations ranted from 1.9 to 22.3 months. No patients in Part 1D achieved PR. Of the 5 patients with a confirmed PR, 3 had received prior anti-PD-(L)1 therapy, and 2 of the 3 had also received prior anti-CTLA-4 therapy. Responses were observed in a variety of tumor types, and responses were observed in injected lesions and in distant non-injectable lesions, indicating an abscopal response. IL-12 serum levels were elevated in 42/46 patients within 24 hours of MEDI injection, and increases in IFN-gamma, IFN-inducible chemokines, CD8+ T cell recruitment, and tumoral PD-L1 expression were also observed. Data indicate that intratumoral MEDI1191 with sequential or concurrent intravenous durvalumab is safe and tolerable in a variety of tumors in previously treated patients.
NIVOLUMAB-INDUCED CHANGES TO MUTATIONAL LANDSCAPES AND NEOANTIGENS IN THE TUMOR
1125. Neoantigen immunogenicity landscapes and evolution of tumor ecosystems during immunotherapy with nivolumab
Tyler Joseph Alban (Cleveland Clinic, Cleveland, Ohio) presented a prospective clinical trial of NSCLC patients treated with nivolumab (anti-PD-1) to address how tumor evolution and neoantigen immunogenicity shape treatment response. Previous studies in melanoma indicate that increased mutational expansion/tumor mutational burden over time is associated with a poor response to anti-PD-1 therapy, while more mutational contraction/reduced tumor mutational burden is associated with better outcomes, suggesting anti-PD-1 therapy induces changes in the mutational burden of tumors in responders. Pre- and on-therapy biopsies from 58 patients in trial CheckMate-153, investigating nivolumab in patients with advanced or metastatic non-small cell lung cancer (NSCLC), were analyzed by whole exome sequencing and RNA sequencing to predict neoantigens in silico. Predicted neoantigens were generated and assayed for immunogenicity. Higher tumor mutation burden during therapy was associated with a worse response to nivolumab, and an increase in total single nucleotide variants 3 weeks post-treatment was associated with decreased survival. Patients responding to therapy exhibited better immune activation and immune infiltration, measured by RNA sequencing. Comparing gene expression data from CheckMate-153 with CheckMate-083 (nivolumab for melanoma) identified sets of common genetic pathways that exhibited altered expression patterns in response to nivolumab. Of the 1453 neoantigen candidates assayed for immunogenicity, 196 were identified as being immunogenic and recognized by T cells during nivolumab treatment. T cells specific for immunogenic peptides were increased in responders compared to non-responders. In responders, the presence of T cells specific for immunogenic antigens correlated with a reduction in neoantigen colonality from pre- to on-treatment samples, suggesting tumor clones expressing immunogenic neoantigens are more likely to be reduced during therapy. Immunogenic neoantigens had unique features at position 4 that drove T cell recognition. Future directions include identifying expression profiles and VDJ sequences associated with the recognition of immunogenic neoantigens.
LIQUID BIOPSY TO MEASURE PATIENT RESPONSE TO PERSONALIZED ANTI-CANCER VACCINES
1126. Disease monitoring with comprehensive genomics provides evidence of mechanism of action and immune evasion in patients receiving an individualized neoantigen cancer vaccine
Matthew Davis (Gritstone Bio, Inc, Emeryville, California) presented a highly sensitive circulating tumor DNA (ctDNA) monitoring assay to survey patient response and immune evasion. Patients received individualized neoantigen vaccines in the GRANITE trial, and individualized longitudinal ctDNA assays were developed. Compared with standard commercial sequencing assays, which detect around 10 to 50 sequence variants, the ctDNA monitoring assay detects around 100 variants, which represents 80% (median) of all targeted mutations. Approximately 90% of all neoantigens identified during whole exome sequencing of pre-treatment biopsy (and included in the vaccine) are captured. Molecular responses, indicated by a reduction in ctDNA, were observed in 55% of patients post-treatment for microsatellite stable colorectal cancer, and molecular response was associated with improved overall survival in these patients. Liquid biopsy allows for disease monitoring over time; molecular changes, including acquired loss of function mutations in TAP1 and HLA loss of heterozygosity, could be detected in patients post-treatment prior to the detection of new lesions. T cell and T cell receptor expansion, based on gene expression signatures in paired pre- and post-treatment tumor specimens were also identified. ctDNA monitoring assays are being used to assess clinical activity of personalized neoantigen vaccines in combination with immune checkpoint blockade for colorectal cancer in an ongoing Phase 2/3 study (NCT05141721).
CHARACTERIZING AND TARGETING TISSUE-RESIDENT MACROPHAGES IN THE TUMOR MICROENVIRONMENT
1129. Targeting tissue-resident macrophage progenitors restores anti-tumor immunity and suppresses tumor growth
Hui Chen (University of California San Diego, San Diego, California) discussed data from a preclinical study to identify and target tissue-resident macrophages. Using a genetically engineered mouse tumors, Ly6C- F4/80hi CCR2- CD206+ MerTK+ FOLR2+ macrophages were identified as tissue resident macrophages (TRMs). TRMs were found to gradually accumulate in tumors, and the accumulation pattern of TRMs was unique, compared to accumulation patterns of granulocytes and of bone marrow-derived macrophages (BMDMs). TRMs exhibited proliferative and immune suppressive gene expression signatures compared to BMDMs, and single cell RNA sequencing identified a subpopulation of highly proliferative TRMs. A novel inhibitor of CSF1R (3G8) inhibited TRM and BMDMs at the G2/M transition, which was associated with decreased tumor volume, increased T cell recruitment, and anti-tumor immunologic memory. These results indicate tissue-resident macrophage progenitor cells as key targets for developing new therapies that stimulate anti-cancer immunity.
REDIRECT: DIRECTING NK CELLS AGAINST CD30-POSITIVE PERIPHERAL T CELL LYMPHOMA
CT024. REDIRECT: A Phase 2 study of AFM13 in patients with CD30‑positive relapsed or refractory (R/R) peripheral T cell lymphoma (PTCL)
Won Seog Kim (Sungkyunkwan University School of Medicine, Seoul, Korea) reported results from a Phase 2 study of AFM13, a CD30/CD16A tetravalent bispecific Innate Cell Engager (ICE) for relapsed or refractory peripheral T cell lymphoma (R/R PTCL). Currently, no standard of care therapy is established for R/R PTCL. AFM13 associates with CD16A on natural killer (NK) cells, redirecting them and enhancing innate anti-tumor immunity against CD30+ PTCL tumor cells. Earlier studies have established that AFM13 has a manageable safety and clinical activity against CD30+ R/R cutaneous Hodgkin lymphoma (HL). The study involved 108 patients with histologically confirmed CD30+ R/R PTCL who received one or more prior lines of systemic therapy, and patients received a mean of 16 infusions (median 9). AFM13 exhibited a manageable safety profile, with 73.1% of patients exhibiting AFM13-related treatment emergent adverse events (TEAE) and 30.6% at Grade 3 or higher. Overall response rate (ORR) was 32.4% with a 10.2% complete response rate (CRR). Tumor shrinkage was observed in 82 patients. Patients with angioimmunoblastic T cell lymphoma (AITL) exhibited the highest ORR and CRR. No meaningful differences in response were observed among patient subgroups stratified by CD30 expression levels. Median duration of response was 2.3 months, and median duration of complete response was 3.6 months. Median progression free survival was 3.5 months, and median overall survival was 13.8 months. These results suggest that AFM13 may exhibit clinical efficacy in a highly treated patient population with CD30+ R/R PTCL, especially among patients with AITL. A trial of AFM13 in combination with allogenic NK cells for R/R HL is planned, and data from REDIRECT supports the development of a similar trial for AFM13 with allogenic NK cells for R/R PTCL.
KEYNOTE-966: COMBINATION THERAPY FOR ADVANCED BILIARY TRACT CANCER
CT008. Pembrolizumab (pembro) in combination with gemcitabine and cisplatin (gem/cis) for advanced biliary tract cancer (BTC): Phase 3 KEYNOTE-966 study
R. Katie Kelley (University of California San Francisco, San Francisco, California) presented the phase 3 KEYNOTE-966 study investigating the efficacy of pembrolizumab (pembro) in combination with gemcitabine and cisplatin (gem/cis) for advanced biliary tract cancer (BTC). The TOPAZ-1 trial recently established that adding the anti-PD-L1 immune checkpoint inhibitor durvalumab to gem/cis improved OS compared to gem/cis alone for advanced BTC. Patients with locally advanced or metastatic disease with no prior systemic therapy were randomized 1:1 to receive pembro + gem/cis (n=529) or placebo + gem/cis (n=534). At a median follow-up of 25.6 months, 489 patients in the Pembro + Gem/Cis arm and 504 patients in the Placebo + Gem/Cis arm discontinued all study medication, most commonly due to progressive disease. Median overall survival for Pembro + Gem/Cis was 12.7 months, compared to 10.9 months for Placebo + Gem/Cis (HR 0.83, statistically significant). OS favored Pembro + Gem/Cis for all patient subgroups, but less benefit was observed among patients with extrahepatic or gallbladder sites of origin, compared to intrahepatic sites of origin. Median progression-free survival was 6.5 months for Pembro + Gem/Cis and 5.6 months for Placebo + Gem/Cis (HR 0.86, not statistically significant). Objective response rate was 29% for each arm, and a longer duration of response was observed in the Pembro + Gem/Cis arm (9.7 months) compared to Placebo + Gem/Cis (6.9 months). 70% and 69% of patients in the Pembro + Gem/Cis and Placebo Gem/Cis arms, respectively, experience treatment-related adverse events (TRAEs) of grades 3 –4, and TRAEs led to the death of 8 patients (2%) in the Pembro + Gem/Cis arm and 3 patients (1%) in the Placebo + Gem/Cis arm. The profiles of adverse events were similar to what has been previously reported for pembrolizumab, gemcitabine, and cisplatin. Adding pembrolizumab to gemcitabine and cisplatin produces significant improvement in overall survival and other clinically meaningful benefits, providing a new treatment option for patients with advanced BTC. Data from quality-of-life analyses and molecular profiling will be reported in the future.
CD70-DIRECTED CAR T THERAPY FOR CLEAR CELL RENAL CELL CARCINOMA
CT011. A phase 1 multicenter study (TRAVERSE) evaluating the safety and efficacy of ALLO-316 following conditioning regimen in pts with advanced or metastatic clear cell renal cell carcinoma (ccRCC)
Samer Srour (University of Texas MD Anderson Cancer Center, Houston, Texas) presented results from TRAVERSE, a phase 1 study of ALLO-316, a CD70-directed allogenic CAR T cell therapy. CD70 is expressed in 80% of cases of primary and metastatic renal cell carcinoma (RCC). ALLO-316 contains gene knockouts of the TCR alpha constant gene and of the CD52 gene to reduce risk of graft versus host disease (GVHD) and to facilitate conditioning with fludarabine, cyclophosphamide (FC) and ALLO-647. ALLO-647, an anti-CD52 monoclonal antibody, depletes host T cells without affecting allogenic CAR T cells. ALLO-316 also contains a CD20 mimotope-based intra-CAR off switch, so CAR T cells can be eliminated with rituximab. ALLO-316 was administered at four escalating dose levels and under two conditioning regimens, FC and FC with ALLO-647 (FCA). 19 patients, all with advanced or metastatic clear cell RCC, received ALLO-316 treatment. The safety profile for ALLO-316 was comparable to previous studies with autologous CAR T therapies. At a median follow-up time of 7.8 months, 11/19 patients (58%) experienced cytokine release syndrome (CRS), and one case was Grade 3. No ICANS or GVHD was observed, and the maximum tolerated dose was not reached. Overall response rate (ORR) was 17%, and disease control rate (DCR) was 89%. Of the ten patients with confirmed CD70+ tumors, ORR was 30%, DCR was 100%, and median progression-free survival was 5.0 months. CAR T expansion was observed in peripheral blood samples, and CAR T cell infiltration of tumors (measured by vector copy number) was observed in three of four available tumor aspirates. ALLO-316 exhibits a manageable safety profile and encouraging anti-tumor activity, providing a therapeutic option for a heavily pre-treated patient population. Dose escalation studies are going, and expansion cohorts are planned for the end of the year. New studies may also include other solid CD70+ tumors.
EFFICACY OF AN EGFR X LGR5 BISPECIFIC ANTIBODY FOR HEAD AND NECK SQUAMOUS CELL CANCER
CT012. Clinical activity of MCLA-158 (petosemtamab), an IgG1 bispecific antibody targeting EGFR and LGR5, in advanced head and neck squamous cell cancer (HNSCC)
Ezra E. W. Cohen (Moores Cancer Center, UC San Diego Health, San Diego, California) presented a clinical study for petosemtamab, a bispecific antibody targeting LGR5 and EGFR, for advanced head and neck squamous cell cancer (HNSCC). Petosemtamab targets cancer cells by associating with LGR5, a transmembrane receptor expressed on cancer stem cells, and blocks EGFR, a known driver of cancer growth, which is overexpressed in up to 90% of HNSCC tumors. 43 patients with recurrent or metastatic HNSCC that progressed or were intolerant to anti PD-(L)1 and platinum-based therapy received the recommend phase 2 dosing regimen of 1500 mg petosemtamab IV every other week (Q2W). Overall response rate was 37.2% (16/43), and median time to response was 1.8 months. Disease control rate was 72.1% (31/43). The median duration of response was 6.0 months, and ten of 16 responses are ongoing. Median progression free survival was 5.3 months. Responses were observed across all biomarker expression levels, including EGFR levels, and further analyses are ongoing. Regarding safety, all patients experienced an adverse event, and 53% were >= grade 3. Tumor biopsies indicated an increase in immune infiltration of the tumor in some patients with a response or stable disease. The data indicate that petosemtamab has promising clinical efficacy and a manageable safety profile in patients with pretreated HNSCC. Further clinical investigations are in development, including petosemtamab monotherapy for recurrent/resistant or metastatic disease and petosemtamab combined with pembrolizumab for initial systemic therapy of recurrent or metastatic HNSCC.
SAFETY AND EFFICACY OF A BCMAXCD3 BISPECIFIC ANTIBODY WITH LOW CD3 AFFINITY FOR MULTIPLE MYELOMA
CT013. Safety and efficacy from the phase 1/2 first-in-human study of REGN5459, a BCMA×CD3 bispecific antibody with low CD3 affinity, in patients with relapsed/refractory multiple myeloma
Attaya Suvannasankha (Indiana University Simon Cancer Center and Roudebush VAMC, Indianapolis, Indiana) presented safety and efficacy data from an ongoing first-in-human phase 1/2 trial of REGN5459, a BCMAxCD3 bispecific antibody for relapsed/refractory multiple myeloma (R/R MM). REGN5459 binds to BCMA on MM cells, and the low affinity to CD3 on T cells has shown to trigger T cell activation and plasma cell depletion with low cytokine release in preclinical models. The Phase 1 dose escalation study explored doses ranging from 3 mg to 900 mg weekly (IV, QW for 16 weeks, then reduced to Q2W). Step-up dosing schema were used to mitigate cytokine release syndrome (CRS). In the Phase 2 dose expansion study, step-up-dosing increased over three weeks, and full weekly dosing with 480 mg began on week 4. 43 patients participated in the study, and almost all patients were heavily pre-treated, with 95.3% of patients previously receiving at least 3 prior treatments. One dose limiting toxicity at the 900 mg dose level occurred. Treatment-emergent adverse events (TEAEs) occurred in 100% of patients, and 74.4% were Grade 3 or 4. CRS occurred in 23 (53.5%) patients, and 2 cases of Grade 3 CRS were reported. Patient responses increased with escalating doses. At a median duration of 9 months, overall response rate (ORR) was 65.1% across all dose levels. 58.1% of patients exhibited a very good partial remission (VGPR) or better, and 51.2% exhibited a complete remission (CR) or better. At the higher dose range (480-900 mg; n=21), ORR was 90.5%, 76.2% was VGPR or better, and 61.9% was CR or better. Among the 19 patients with available minimum residual disease (MRD) data, 79% (15) were MRD negative at the 10-5 threshold. Median time to response was 0.8 months, and median duration of response (DOR) was not reached at the 9-month follow-up. The expected probability for maintaining response at 12 months is 78.1%. REGN5459 showed early, deep, and durable responses and a manageable safety profile among heavily treated patients with R/R MM. Further investigation of REGN5459 is under consideration.
LONGITUDINAL STUDY OF THE GUT MICROBIOME PRE- AND POST-NEOADJUVANT IMMUNE CHECKPOINT BLOCKADE FOR MELANOMA
3463. Longitudinal microbiome-immune dynamics in melanoma patients treated with immune checkpoint inhibitor immunotherapy
Rebecca C. Simpson (Melanoma Institute Australia, The University of Sydney, Sydney, Australia) reported a study investigating the relationship of gut microbiome and immunotherapy outcomes for treatment of melanoma. Previous studies indicate that response rates to immunotherapy for melanoma are higher among patients with Ruminococcaceae-dominated gut microbiomes than among patients with Bacteroidaceae-dominated microbiomes. In this study, longitudinal profiling of gut microbiome and circulating immune cell subsets for patients with stage III melanoma treated with combination anti-PD-1/anti-CTLA-4 therapy in the neoadjuvant setting, six weeks prior to surgery. Pre- and post-treatment stool samples and peripheral blood samples from 126 patients from Australia and the Netherlands were analyzed and profiled. Most analyses presented from the Australian cohort. Combination anti-PD-1/anti-CTLA-4 therapy was associated with increased frequency of CD8+ effector memory T cells and reduced frequency of regulatory T cells (Treg). Treg reduction was dominant among patients who responded to combination therapy (responders), compared to patients who did not respond to therapy (non-responders). Reduction of Treg also correlated with a higher baseline abundance of Bacteriodaceae. More severe immune-related adverse events (irAEs) were also associated with a reduction in Treg and Bacteriodaceae-dominated microbiota. This analysis suggests the gut microbiome plays a role in balancing response to immunotherapy and the risk of irAEs by setting the stage of the immune response before and during immunotherapy. Further analysis of this cohort and cohorts from other geographic regions may inform the development of future therapeutic strategies to increase clinical efficacy, decrease irAEs, and allow more for more targeted treatment of irAEs.
NEOADJUVANT IMMUNE CHECKPOINT BLOCKADE INITIATES A CD8 T CELL ANTI-TUMOR MEMORY RESPONSE IN MOUSE MODELS OF LUNG CANCER
3472. A tumor draining lymph node CD8 T cell memory response is pivotal for a decrease in metastatic recurrence after neoadjuvant anti PD-1 therapy for NSCLC
Tatiana Delgado Cruz (Weill Cornell Medicine, New York, New York) reported a preclinical study to identify predictors of response to neoadjuvant immune checkpoint blockade (ICB) for non-small cell lung cancer (NSCLC) and to identify mechanisms underlying long-term disease-free response to neoadjuvant ICB. To study cancer recurrence, cancer survival, and systemic metastatic disease, a mouse model of resectable lung cancer was constructed using the highly metastatic lung adenocarcinoma cell line 344sq. Tumor draining lymph nodes (tdLNs) in this mouse model contained high levels of PD-1+ CD8 memory T cells compared with tumor and non-draining LNs. Mice treated with anti-PD-1 prior to surgery exhibited increased levels of central memory CD8 T cells in tdLNs after treatment, and systemic cancer recurrence was delayed in mice treated with ICB compared to controls. Median survival was also increased for mice that received ICB. Mice responding to ICB exhibited higher levels of stem cell-like memory CD8 T cell subsets (PD-1+ CXCR5+) in tdLNs compared to non-responders. Inhibiting trafficking of CD8 T cells from the lymph nodes abrogated the anti-cancer immune response in the tumor. An IL-15 agonist used in combination with PD-1 blockade reduced tumor burden for all mice, increased CXCR5+ memory subpopulations in tdLNs, decreased metastatic recurrences, and increased survival. T cell receptor (TCR) and single cell RNA sequencing detected matching T cell clones present in both tdLNs and tumors. Tumor-matching clones were identified more than 100 days after tumor resection, suggesting these cells can persist. Stem cell-like memory T cells were also identified in tdLNs of patients receiving neoadjuvant ICB for early-stage NSCLC. TCR and RNA sequencing of cells from tdLNs and tumors from these patients are in development. The preclinical data provide strong evidence that therapeutic strategies promoting a T cell memory response within tdLN may drive protection against recurrence.
THE ROLE OF HDAC8 IN IMMUNE ESCAPE IN MELANOMA
3465. HDAC8 regulates immune escape in melanoma through increased transcription of inhibitory cytokines that increase accumulation of myeloid-derived suppressor cells (MDSCs)
Chao Zhang (Moffitt Cancer Center, Tampa, Florida) presented results from a preclinical study investigating the role of HDAC8, a class I histone deacetylase, in immune escape in melanoma. Previous works have shown HDAC8 is upregulated in some cancers, and it can interact with chromatin and non-histone proteins to promote cancer proliferation and immune evasion, but its exact role in melanoma is unclear. A genetically engineered inducible mouse model of melanoma was used to explore the effects of HDAC8 overexpression on the tumor microenvironment (TME). HDAC8 overexpression correlated with poor survival in the mouse model, and gene expression profiles indicated HDAC8 overexpression was associated with suppression of the immune response. Single cell RNA sequencing and immunohistochemistry indicated HDAC8 overexpression was associated with increased levels of myeloid-derived suppressor cells (MDSCs) and decreased levels of lymphocytes in tumors. Mouse melanoma cell lines overexpressing HDAC8 exhibited increased levels of IL-11 production. Chromatin surrounding the c-Jun and IL-11 loci were more accessible in HDAC8-overexperssing cell lines, suggesting the IL-11 gene is highly transcriptionally active when HDAC8 is over expressed. Adding IL-11 to mouse cell cultures increased MDSC expansion and polarization, and T cell proliferation was blocked when co-cultured with MDSCs cultured in the presence of IL-11. The data led to development of a model in which HDAC8 promotes immune escape through expression of the transcription factor c-Jun, increasing IL-11 expression, which promotes MDSC expansion and accumulation in the TME, blocking T cell proliferation. This model suggests HDAC8 inhibition is a potential novel therapeutic strategy to reduce immune suppression and improve patient response to immunotherapy.
IDENTIFYING PROGNOSTIC FACTORS FOR BLADDER CANCER
3436. Reduced p63 expression is linked to a low density of regulatory T-cells and unfavorable prognosis in muscle-invasive urothelial carcinoma of the bladder
Elena Bady (University Medical Center Hamburg-Eppendorf, Hamburg, Germany) discussed a study investigating the relationship between the p63 transcription factor and anti-tumor immunity in muscle-invasive bladder cancer (MIBC). Tissue microarrays of 2710 urothelial bladder carcinomas were stained with 22 antibodies, including p63. p63 was expressed in normal urothelial cells and 72% of tumors at high levels. Loss of p63 staining was associated with higher tumor grade and invasiveness and poorer overall survival. Multiplex fluorescent immunohistochemistry staining of tumor samples using a bleach and stain approach was performed to identify cell subpopulations, immune cell functional state, and spatial parameters of the tumor microenvironment. Results were associated with patient outcomes, and 16 parameters were identified as independent prognostic features; the strongest predictor of survival was the direct contact of CD8+ T cells with tumor cells. Low p63 expression was only linked to a low density of T helper cells and regulatory T cells, suggesting p63 likely does not directly regulate the anti-tumor immune response. These data show that p63 is downregulated in a fraction of invasive, advanced urothelial cancers and associated with poor prognosis. The presence of intraepithelial CD8+ cytotoxic T cells is also a strong prognostic marker. Used together, loss of p63 expression and intratumoral CD8 T cell density may offer insights for stratifying patients for treatment, underscoring the prognostic role of the TME in MIBC.
SAFETY AND EFFICACY OF SALMONELLA-IL2 WITH STANDARD OF CARE CHEMOTHERAPY FOR PANCREATIC CANCER
CT035. Addition of Salmonella-IL2 to FOLFIRINOX for metastatic stage 4 pancreatic cancer nearly doubles median survival
Daniel A. Saltzman (Salspera, Oakdale, Minnesota) presented results from a Phase 1 study of Salmonella-IL2, an attenuated strain of Salmonella that carries human gene for IL-2. Salmonella-IL2, a novel intratumoral drug platform, is administered orally and colonizes tumor cells and interstitial tumor space. Preclinical studies have shown that Salmonella-IL2 carries out anti-tumor activity by inducing tumor susceptibility to chemotherapy, producing IL-2 (which promotes proliferation and cytotoxicity of NK cells), competing with tumor cells for nutrients and other molecules necessary for tumor growth, and inducing an adjuvant immune response. Samonella-IL2 has shown efficacy and safety in a canine phase 1 clinical trial. In this human Phase 2 study, Salmonella-IL2 was added to standard of care chemotherapy for stage 4 metastatic pancreatic adenocarcinoma. Patients in Arm 1 were treated with Salmonella-IL2 + FOLFIRINOX (n=20, Q2W), and patients in Arm 2 were treated with Salmonella-IL2 + Gemcitabine/Abraxane (n=8, Q2W or Q3W). Results from Arm 1 were reported. Median survival in Arm 1 was 24 months, compared to 11.1 months for historic controls, and the partial response rate with 73%. For both trial arms, 37 adverse events occurred in 20 patients, and none were attributed to the study drug. These data indicate that adding Salmonella-IL2 to standard of care FOLFIRNOX is safe and doubles patient survival, compared to historic controls, supporting the development of larger phase 3 trials of Salmonella-IL2 for pancreatic cancer and other solid tumors.
SAFETY AND EFFICACY OF AN OFF-THE-SHELF KRAS-TARGETING VACCINE COMBINED WITH IMMUNE CHECKPOINT BLOCKADE FOR RESECTED PANCREATIC CANCER
CT036. Safety and immunogenicity of a first-in-human mutant KRAS long peptide vaccine combined with ipilimumab/nivolumab in resected pancreatic cancer: Preliminary analysis from a phase I study
Saurav D. Haldar (Johns Hopkins University, Baltimore, Maryland) presented results from a single-arm, first-in-human, phase 1 study of a mutant KRAS (mKRAS)-specific pooled synthetic long peptide (SLP) vaccine combined with ipilimumab and nivolumab (ipi/nivo) after curative-intent surgery for pancreatic ductal adenocarcinoma (PDAC). The off-the-shelf vaccine targeted 6 mKRAS subtypes (G12D, G12R, G12V, G12A, G12C, G13D), and vaccine and ipi/nivo were administered after surgery and perioperative chemotherapy. 11 patients participated in the study. At a median follow-up of 10.7 months, 8 patients achieved mKRAS-specific T cell response, defined as a >5-fold increase in IFN-gamma-producing mKRAS specific T cells 17 weeks after vaccination. Median disease-free survival (DFS) was 6.4 months, and median overall survival was not reached. Patients with an mKRAS-specific T cell response demonstrated significant improvement in median DFS, compared to patients without a T cell response (Not Reached vs 2.8 months). The mKRAS G12D subtype produced the lowest T cells responses, and G12R and G12V were most immunogenic. 6 of the 11 patients experienced disease recurrence: recurrence occurred in all three patients with the G12D subtype, 2/6 patients had the G12V subtype, and 1/2 patient had the G12R subtype. Most adverse events were grade 1 (88.3%) or grade 2 (12.8%). 4 patients experienced grade 3 immune related adverse events, and 2 patients discontinued ipi/nivo. The results indicate that the SLP mKRAS vaccine combined with ipi/nivo is tolerated and immunogenic, and induction of an mKRAS-specific T cell response was associated with improved DFS. Analyses of biospecimens collected before, during, and after the trial are currently underway to identify biomarkers of immune response and resistance.
MECHANISM OF ACTION OF ANTI-TIGIT ANTIBODY TIRAGOLUMAB TO IMPROVE IMMUNE CHECKPOINT BLOCKADE
5712. Anti-TIGIT antibody tiragolumab leverages myeloid cells and regulatory T cells to improve PD-L1 checkpoint blockade
Namrata S. Patil (Genentech Inc, South San Francisco, California) presented post-study analyses of biospecimens from the CITYSCAPE study to characterize the mechanism of action behind the clinical efficacy of tiragolumab + atezolizumab (atezo; anti-PD-L1) over atezo alone for non-small cell lung cancer (NSCLC). Tiragolumab is an anti-TIGIT-antibody with active IgG1/kappa Fc, and it blocks binding of the inhibitory receptor TIGIT to its ligand. CITYSCAPE, was a phase 2 trial where chemotherapy-naïve patients with locally advanced/metastatic NSCLC received placebo + atezo or tiragolumab + atezo. Patients receiving tiragolumab + atezo showed significant improvement in overall survival and response rate, specifically among patients expressing high PD-L1 (Tumor Positivity Score >=50%). Analyses of pre-treatment tumor samples and pre- and on-treatment serum samples indicated that high levels of myeloid cells and regulatory T cells (Treg) were associated with treatment benefit in the tiragolumab + atezo arm, compared with the atezo monotherapy arm, suggesting that interactions of macrophage/myeloid cells with T cells are important for the clinical benefits associated with tiragolumab. Using a mouse tumor model, combination treatment with tiragolumab + atezo leads to effective tumor control, which is dependent on the active Fc domain of tiragolumab. In the mouse model, addition of tiragolumab to atezo reprograms cells in the tumor at the gene expression level by upregulating myeloid cell antigen presentation, downregulating Treg-mediated immunosuppression, and reducing exhaustion and increasing memory gene signatures in CD8+ T cells. These changes are dependent on tiragolumab Fc activity. This exploratory biomarker analysis suggests that the clinical benefit of tiragolumab + atezo is associated with myeloid and Treg cells, and preclinical models suggest that clinical benefits associated with anti-TIGIT antibody occurs through non-canonical interactions of the antibody Fc region with myeloid cells and Treg cells.
A NOVEL TRANSGENE VECTOR PLATFORM TO ENHANCE CAR-T CELL ACTIVITY IN SOLID TUMORS
5746. Flexible tumor-specific cytokine and antigen delivery through the T-SIGn vector platform enables effective CAR-T cell therapy against solid tumors
Maria Stella Sasso (Akamis Bio, Abingdon, United Kingdom) described the novel Tumor Specific ImmunoGene (T-SIGn) platform which generates tumor-targeting adenoviral vectors that can deliver combinations of transgenes to the tumor. Transgenes can encode immune modulators such as cytokines, antibodies, or ligands, and transgenes are expressed specifically within the tumor microenvironment to activate antitumor activity. Two T-SIGn programs to enhance CAR T therapy were discussed. One program combines IL-12/IL-15 and chemokine encoding vectors NG-796A (CCL21) and NG-794A (CXCL9) with anti-HER2 CAR T cell therapy. In mouse xenograft models of HER2+ lung cancer, either NG-796A or NG-794A, when combined with anti-HER2 CART cells, resulted in complete tumor clearance. Serum IFN-gamma concentration was also elevated in mice treated with NG-796A or NG-794A, compared to an empty vector control. In another proof-of-concept study, a T-SIGn vector (NG-1124) encoding a bispecific adaptor protein, anti-HER2 scFV-CD19, delivered a CAR T target antigen (CD19) to a tumor endogenously expressing HER2. A HER2+ CD19- cancer cell line transformed with vector NG-1124 was killed by anti-CD19 CAR T cells in vitro, while cancer cells transformed with empty vector were unaffected. Similar results were obtained in vivo studies using mouse xenograft models of HER2+ CD19- lung cancer: mice treated with NG-1124 showed increased CAR T activity in tumors. Of note, approximately 40% of vector-negative tumor cells expressed CD19, suggesting secreted anti-Her2-CD19 can spread from vector-positive tumor cells to nearby vector-negative tumor cells. These preclinical studies indicate that T-SIGn vectors encoding immune modulators like IL-12 and IL-15 have potential to increase cell therapy efficacy by boosting CAR T cell recruitment and activity. T-SIGn vectors can also be used to express CAR target antigens within the tumor, increasing CAR T cell activity and reducing on-target, off-tumor toxicity. Multiple T-SIGn programs are at different stages of clinical development, and two are in phase 1 clinical trials.
USING CELL-FREE DNA FOR GENOTYPING AND TRACKING PATIENT RESPONSE TO CAR T CELL THERAPY FOR MULTIPLE MYELOMA
5707. Tumor and immune determinants of response to anti-BCMA CAR T-cell therapy in multiple myeloma using cell-free DNA
Mia Carleton (Stanford University School of Medicine, Stanford, California) discussed Cancer Personalized Profiling by Deep Sequencing (CAPP-Seq), a non-invasive approach using cell free DNA (cfDNA) to identify tumor genotype, track tumor mutations and molecular response to therapy, detect minimal residual disease, and identify mechanisms of resistance to therapy for multiple myeloma (MM). A total of 231 samples from 24 patients receiving anti-BCMA CAR T therapy for multiple myeloma were obtained before, during, and after therapy. Within this cohort, 71% of patients had achieved a very good partial response or better by day 28 after CAR T cell infusion. A median of 101 single nucleotide variants (SNVs) were detected per patient (range 13-253), and 8% of SNVs detected were coding mutations. Among the 34 plasma samples that could be validated with paired bone marrow samples, 72% of SNVs identified in bone marrow were also detected in plasma samples. CAR-specific cfDNA correlated with CAR T cell count by flow cytometry, especially withing the first few weeks following infusion. cfDNA was also an accurate marker later in treatment, after CAR T cells left peripheral circulation and remained in specific tissues. Levels of circulating tumor DNA (ctDNA) were predictive of patient response to CAR T therapy, with higher ctDNA levels associated with an increased risk of disease progression. CAR cfDNA was also predictive of therapeutic response, with persistence of CAR cfDNA at day 28 being associated with decreased risk of disease progression. MM CAPP-Seq also detected copy number loss of BCMA and/or chromosome 16 in patients leading up to relapse. Loss of chromosome 16/BCMA was detected in 3 of 11 patients at relapse, suggesting deletion of BCMA may be a more common mechanism of resistance than previously thought. 3 of the 23 patients were found to have BCMA loss prior to CAR T treatment, and this loss correlated with poor outcomes. These results suggest that using CAPP-Seq to track ctDNA and CAR-cfDNA tracking has potential to genotype tumors, monitor disease progression, and identify mechanisms of resistance, and ctDNA and CAR-cfDNA can serve as prognostic biomarkers at specific timepoints of CAR T cell therapy for MM. Future studies include validating MM-CAPP-Seq data with bone marrow for tracking minimal residual disease and investigating immune microenvironment factors that affect response to therapy.