Citations

Abstract Introduction: It has become increasingly apparent that chimeric antigen receptor T (CART) cell activation and differentiation level is an important determinant of CART cell fate and response to therapy. In this study, we aimed to 1) measure levels of activation-induced surface death receptors and ligands on CART cells; 2) investigate how CART cell activation could impact their fitness and clinical responses, and 3) identify cell-based targets to modulate CART cell activation, apoptosis, and cytotoxicity to improve anti-tumor activity. Methods: We performed flow cytometric studies on ex-vivo stimulated, clinically annotated CART products of patients with large B cell lymphoma from the pivotal ZUMA-1 clinical trial that led to FDA-approved Axicabtagene ciloleucel (Axi-Cel). We investigated possible correlations of a number of surface death receptors and ligands with T cell differentiation status and post-infusion CART cell expansion, utilizing samples from ZUMA-1 patients who achieved a complete response as a best outcome ('responders') vs patients who achieved stable or progressive disease('non-responders'). CART cell effector functions in vitro were measured, and CART apoptosis was assessed using Annexin V. For in vitro and in vivo functional studies, we used CART19 generated from healthy donors (HD CART19) as indicated in the specific experiment. CRISPR/Cas9 was employed during CART cell production to disrupt specific genes. A xenograft model of lymphoma was used to investigate the in vivo antitumor activity of CART19. Results: Following an ex vivo stimulation of Axi-Cel products with CD19 + target cells, we observed upregulation of death receptors and ligands in CART19 from non-responders, compared to responders. We also observed a possible association between such upregulated surface markers with CART cell differentiation as measured by CCR7 expression. In an extended in vitro co-culture assay, where HD CART19 cells were repeatedly stimulated through the CAR, we found that tumor necrosis factor α receptor 2 (TNFR2), unlike other death receptors and ligands, was persistently elevated, suggesting a possible role for TNFR2 in long-term antigen-dependent CART19 dysfunction (Figure 1A). We further found that HD CART19 upregulate TNFR2, but not TNFR1, upon CAR stimulation (Figure 1B). While non-specific TCR activation (CD3 stimulation) of HD CART19 cells protected them from activation-induced apoptosis, antigen-specific activation through the CAR resulted in significant initiation of apoptosis within 2 hours of stimulation (Figure 1C). Having identified a possible association between TNFR2 and CART19 dysfunction, we aimed to study the impact of TNFR2 knockout on HD CART19 functions. Using CRISPR/Cas9 during CART cell manufacturing, we generated TNFR2 k/o HD CART19 cells with a knockout efficiency of around 50%, where the expression levels of TNFR2 in activated CART19 cells were reduced, compared to control CART19 cells (with non-targeting gRNA CRISPR/Cas9, Figure 1D). TNFR2 k/o CART19 cells demonstrated reduced early activation surface markers compared to control CART19, as measured by CD25 and CD69 surface expression (Figure 1E), reduced apoptosis initiation as measured by the Annexin V assay (Figure 1F), and enhanced antigen-specific proliferation and cytotoxicity (Figure 1G). Finally, in an in vivo xenograft model of CD19 + lymphoma, TNFR2 k/o CART19 resulted in enhanced CART cell expansion and anti-tumor activity (Figure 1H). Conclusions: Our results indicate that TNFR2 plays a role in early activation and apoptosis initiation of CART19 following CAR stimulation with CD19 + target cells and present TNFR2 knockout as a strategy to enhance CART19 anti-tumor activity. Figure 1 Figure 1. Disclosures Cox: Humanigen: Patents & Royalties. Sakemura: Humanigen: Patents & Royalties. Ding: Merck: Membership on an entity's Board of Directors or advisory committees, Research Funding; DTRM: Research Funding; Octapharma: Membership on an entity's Board of Directors or advisory committees. Parikh: Pharmacyclics, MorphoSys, Janssen, AstraZeneca, TG Therapeutics, Bristol Myers Squibb, Merck, AbbVie, and Ascentage Pharma: Research Funding; Pharmacyclics, AstraZeneca, Genentech, Gilead, GlaxoSmithKline, Verastem Oncology, and AbbVie: Membership on an entity's Board of Directors or advisory committees. Kay: Juno Therapeutics: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees, Research Funding; MEI Pharma: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Dava Oncology: Membership on an entity's Board of Directors or advisory committees; Agios Pharm: Membership on an entity's Board of Directors or advisory committees; Targeted Oncology: Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; Acerta Pharma: Research Funding; Genentech: Research Funding; Behring: Membership on an entity's Board of Directors or advisory committees; CytomX Therapeutics: Membership on an entity's Board of Directors or advisory committees; Sunesis: Research Funding; TG Therapeutics: Research Funding; Tolero Pharmaceuticals: Research Funding; Abbvie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol Meyer Squib: Membership on an entity's Board of Directors or advisory committees, Research Funding; Morpho-sys: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Oncotracker: Membership on an entity's Board of Directors or advisory committees; Rigel: Membership on an entity's Board of Directors or advisory committees. Scholler: Kite: Current Employment. Bot: Kite, a Gilead Company: Current Employment; Gilead Sciences: Consultancy, Current equity holder in publicly-traded company, Other: Travel support. Mattie: Kite: Current Employment. Kim: Gilead Sciences: Current equity holder in publicly-traded company; Kite, a Gilead Company: Current Employment. Filosto: Kite, a Gilead Company: Current Employment; Tusk Therapeutics: Patents & Royalties: or other intellecular property; Gilead Sciences: Other: stock or other ownership . Kenderian: Humanigen, Inc.: Consultancy, Honoraria, Research Funding.

Abstract Anti-CD19 chimeric antigen receptor T (CART19) cell therapy has resulted in unprecedented outcomes in patients with relapsed/refractory B-cell malignancies, which led to the FDA approval for several indications. However, CART19 cell therapy is limited by the development of severe life-threatening toxicities, as well as by the limited rates of durable response. It has become apparent that myeloid cells contribute to the development of both CART cell toxicity and also to the inhibitory tumor microenvironment. We and others have identified that granulocyte-monocyte-colony-stimulating factor (GM-CSF) depletion results in decreased myeloid activation, reduced toxicities, and enhancement of CART19 cell therapy efficacy in pre-clinical models. Furthermore, we observed that GM-CSF knockout (GM-CSF k/o) in CART19 cells resulted in the improvement of their functions (in vitro and in vivo). These findings suggest that there is also a direct effect of GM-CSF on CART19 cells, which is independent of the GM-CSF impact on myeloid cell activation. To further evaluate this, we first examined GM-CSF receptor alpha (GM-CSFRα) expression by flow cytometry on resting and activated CART19 cells (using FMC63-41BBζ). When CART19 cells were stimulated with either anti-CD3/CD28 beads or lethally irradiated (120 Gy) CD19 + Nalm6 cells (B cell acute lymphoblastic leukemia cancer cell line), GM-CSFRα expression was upregulated upon both T cell receptor (TCR) (data not shown) and CAR stimulation (Figure 1A). Having demonstrated that GM-CSFRα is significantly upregulated on stimulated CART19 cells, we aimed to determine the impact of GM-CSF neutralization (clinical-grade anti-GM-CSF antibody, lenzilumab, 10 µg/mL) versus GM-CSFRα blockade (research-grade antibody, 10 µg/mL) on CART19 cell function and CART cell-monocyte interactions. An IgG isotype antibody was used as a control antibody. Neither the GM-CSF neutralizing antibody, nor GM-CSFRα blocking antibody, had any impact on CART19 cell antigen-specific killing against the CD19 + JeKo-1 cells (mantle cell lymphoma cancer cell line), in the presence or absence of CD14 + monocytes (ratio 1:1:1) isolated by magnetic beads from healthy donors (Figures 1B-C). Next, we compared the effects of GM-CSF neutralization versus GM-CSFRα blockade on CART19 cell antigen-specific proliferation. Here, CART19 cells were co-cultured with lethally irradiated CD19 + cell line JeKo-1 at 1:1 ratio in the presence of 10 µg/mL of the GM-CSF neutralizing antibody, increasing doses of the GM-CSFRα blocking antibody (10-100 µg/mL), or an IgG control. The absolute number of CART cells was measured by flow cytometry on day 5. GM-CSF neutralization did not affect CART19 cell proliferation, but GM-CSFRα blocking antibody significantly inhibited CART19 cell proliferation in a dose-dependent manner. Then, we assessed the effects of GM-CSF neutralizing antibody (20 µg/mL) versus GM-CSFRα blocking antibody (20 µg/mL) on CART19 cell antigen-specific proliferation in the presence of healthy donor monocytes (ratio 1:1:0.5) on day 3. Flow cytometric analysis revealed that GM-CSF neutralization, but not GM-CSFRα blockade, mitigated monocyte-suppression of CART19 antigen-specific proliferation (Figure 1E). In summary, our findings indicate significant differences on CART cell functions and CART cell-monocyte interactions when a specific cytokine, GM-CSF, is neutralized compared to blocking its receptor. Further mechanistic studies are ongoing to assess the functions of GM-CSFRα k/o and GM-CSF k/o CART cells. Figure 1 Figure 1. Disclosures Sakemura: Humanigen: Patents & Royalties. Parikh: Pharmacyclics, MorphoSys, Janssen, AstraZeneca, TG Therapeutics, Bristol Myers Squibb, Merck, AbbVie, and Ascentage Pharma: Research Funding; Pharmacyclics, AstraZeneca, Genentech, Gilead, GlaxoSmithKline, Verastem Oncology, and AbbVie: Membership on an entity's Board of Directors or advisory committees. Kay: Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; Tolero Pharmaceuticals: Research Funding; CytomX Therapeutics: Membership on an entity's Board of Directors or advisory committees; MEI Pharma: Research Funding; Dava Oncology: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Morpho-sys: Membership on an entity's Board of Directors or advisory committees; TG Therapeutics: Research Funding; Acerta Pharma: Research Funding; Genentech: Research Funding; Rigel: Membership on an entity's Board of Directors or advisory committees; Behring: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Sunesis: Research Funding; Targeted Oncology: Membership on an entity's Board of Directors or advisory committees; Juno Therapeutics: Membership on an entity's Board of Directors or advisory committees; Bristol Meyer Squib: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees; Oncotracker: Membership on an entity's Board of Directors or advisory committees; Agios Pharm: Membership on an entity's Board of Directors or advisory committees. Durrant: Humanigen Inc.: Current Employment. Ahmed: Humanigen Inc.: Current Employment, Current equity holder in publicly-traded company. Chappell: Humanigen Inc.: Current Employment, Current equity holder in publicly-traded company, Divested equity in a private or publicly-traded company in the past 24 months. Cox: Humanigen: Patents & Royalties. Kenderian: Humanigen, Inc.: Consultancy, Honoraria, Research Funding.

Abstract Although chimeric antigen receptor T (CART)–cell therapy has been successful in treating certain hematologic malignancies, wider adoption of CART-cell therapy is limited because of minimal activity in solid tumors and development of life-threatening toxicities, including cytokine release syndrome (CRS). There is a lack of a robust, clinically relevant imaging platform to monitor in vivo expansion and trafficking to tumor sites. To address this, we utilized the sodium iodide symporter (NIS) as a platform to image and track CART cells. We engineered CD19-directed and B-cell maturation antigen (BCMA)–directed CART cells to express NIS (NIS+CART19 and NIS+BCMA-CART, respectively) and tested the sensitivity of 18F-TFB-PET to detect trafficking and expansion in systemic and localized tumor models and in a CART-cell toxicity model. NIS+CART19 and NIS+BCMA-CART cells were generated through dual transduction with two vectors and demonstrated exclusive 125I uptake in vitro. 18F-TFB-PET detected NIS+CART cells in vivo to a sensitivity level of 40,000 cells. 18F-TFB-PET confirmed NIS+BCMA-CART-cell trafficking to the tumor sites in localized and systemic tumor models. In a xenograft model for CART-cell toxicity, 18F-TFB-PET revealed significant systemic uptake, correlating with CART-cell in vivo expansion, cytokine production, and development of CRS-associated clinical symptoms. NIS provides a sensitive, clinically applicable platform for CART-cell imaging with PET scan. 18F-TFB-PET detected CART-cell trafficking to tumor sites and in vivo expansion, correlating with the development of clinical and laboratory markers of CRS. These studies demonstrate a noninvasive, clinically relevant method to assess CART-cell functions in vivo.

PURPOSE: The benefit of routine pre-emptive screening for severe acute respiratory syndrome coronavirus 2 infections in patients with cancer before cancer-directed therapies is unclear. Herein, we characterize the outcomes of a cohort of patients with cancer who were diagnosed with COVID-19 by routine screening (RS) in comparison with those diagnosed on the basis of clinical suspicion or exposure history (nonroutine screening [NRS]). METHODS: A multisite prospective observational study was conducted at three major and five satellite campuses of the Mayo Clinic Cancer Center between March 18 and July 31, 2020. The primary outcome was COVID-19–related hospital admission. Secondary outcomes included intensive care unit admissions and all-cause mortality. RESULTS: Five thousand four hundred fifty-two patients underwent RS in the outpatient setting only, and 44 (0.81%) were diagnosed with COVID-19. RS detected 19 additional patients from the scheduled inpatient admissions for surgical or interventional procedures or inpatient chemotherapy. One hundred sixty-one patients were diagnosed with COVID-19 on the basis of NRS. COVID-19–related hospitalization rate (17.5% v 26.7%; P = .14), intensive care unit admission (1.6% v 5.6%; P = .19), and mortality (4.8% v 3.7%; P = .72) were not significantly different between the RS and NRS groups. In the multivariable analysis, age ≥ 60 years (odds ratio, 4.4; P = .023) and an absolute lymphocyte count ≤ 1.4 × 109/L (odds ratio, 9.2; P = .002) were independent predictors of COVID-19–related hospital admission. CONCLUSION: The COVID-19 positivity rate was low on the basis of RS. Comparing the hospital admission and mortality outcomes with the NRS cohort, there were no significant differences. The value of routine pre-emptive screening of asymptomatic patients with cancer for COVID-19 remains low.

6539 Background: The impact of insurance status on survival in diffuse large B‐cell lymphoma (DLBCL), the most common aggressive lymphoma, has not been evaluated after the implementation of the Affordable Care Act (ACA). The aim of this study is to compare overall survival (OS) in patients across insurance status groups and in the periods before and after the ACA. Methods: Adult patients with newly diagnosed DLBCL were identified from the National Cancer Database. The analysis was restricted to patients 64 years of age or younger as most patients 65 years or older are eligible for Medicare under the ACA. The 2004-2017 period was chosen to represent the immunochemotherapy era preceding and following the ACA. Logistic regression was used to explore associations between abstracted variables and insurance status groups. The Kaplan-Meier method and Cox proportional hazards model were used for survival analysis. Results: 93,692 adults (age < 64 years) with newly diagnosed DLBCL and known insurance status were identified (41.3% female, median age 54 years [range: 18 – 64], 81.8% White and 12.1% Black). 7,211 (7.7%) patients were uninsured, 64,744 (69.1%) had private insurance, 11,936 (12.7%) had Medicaid, and 9,801 (10.5%) had Medicare. When compared to insured patients (private insurance, Medicaid or Medicare), uninsured patients were more likely to have a median household outcome of < $38,000 [OR 1.93 (95% CI 1.79-2.07)], less likely to receive chemotherapy [OR 0.69 (0.64-0.77)], more likely to be male [OR 1.14 (1.07-1.21)], more likely to be non-White [OR 1.30 (1.20-1.40], and more likely to present with stage III or IV disease [OR 1.24 (1.16-1.32)]. Uninsured patients had an inferior OS [HR 1.21 (95% CI 1.15-1.27)] when compared to insured patients after adjustment for baseline comorbidity (Charlson-Deyo score ≥2), advanced stage, treatment with chemotherapy, and sociodemographic factors including sex, age, race, household income, facility type (academic/community), and location (urban/rural). With a median follow-up time of 14.8 years (95% CI 14.6-not reached), median OS was lower in uninsured patients [13.4 years (12.3-not reached) vs 14.8 years (14.7-not reached); p < 0.0001]. Despite the lack of major changes in DLBCL therapies, a diagnosis after the implementation of the ACA (in 2010 or later) was associated with a superior OS when compared with the outcomes of patients diagnosed in 2010 or earlier [HR 0.93 (95% CI 0.90-0.95)]. Similarly, five-year OS was superior in the insured group [HR 0.93 (95% CI 0.89-0.96)]. Conclusions: Uninsured patients with DLBCL and < 64 years old had inferior OS when compared with insured patients, and uninsured status emerged as an independent risk factor for inferior OS. Our data highlight the independent effect of insurance disparities - a potential indicator of variations in access to health care - on survival in DLBCL.

Epithelioid hemangioendothelioma (EHE) is a rare vascular neoplasm which typically originates from liver, lung, or bone. Due to the low incidence of disease, the most effective treatment is not easily studied and much of the information known about EHE has been learned through case reports and case series. In this case, we will present an uncommon form of primary soft tissue EHE with local recurrence, bone metastasis, and lymphangitic spread to the lungs leading to respiratory failure. Imaging of the chest was atypical for EHE with intraseptal thickening and hilar lymphadenopathy. Respiratory failure was progressive despite aggressive multimodal treatment. This case highlights an unusually aggressive recurrence and metastasis of primary soft tissue EHE with atypical pulmonary imaging findings.

Abstract Abstract Importance: The benefit of routine screening for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections in patients with cancer before cancer-directed therapies is unclear. Herein, we characterize the outcomes of a cohort of cancer patients diagnosed with Coronavirus Disease 2019 (COVID-19) by routine screening in comparison with those diagnosed based on clinical suspicion or exposure history (non-routine screening). Objective: To describe and compare the outcomes of cancer patients diagnosed with COVID-19 on routine screening vs. non-routine screening at a multi-site tertiary cancer center. To identify risk factors for COVID-19-related hospital admission. Design: A multi-site prospective observational study was conducted between March 18 and July 31, 2020. Setting: Three major and 5 satellite campuses of the Mayo Clinic Cancer Center. Participants: Adult patients diagnosed with active cancer within the past five years and confirmed SARS-CoV-2 infection were included. Primary Outcomes and Measures: Clinical and laboratory data were assessed as independent variables. The primary outcome was COVID-19-related hospital admission. Secondary outcomes included intensive care unit (ICU) admissions and all-cause mortality. Results: Between March 18 and July 31, 2020, 5452 patients underwent routine screening in the outpatient setting, 44 (0.81%) were diagnosed with COVID-19. Routine screening detected additional 19 patients from inpatient and pre-procedural settings; 161 patients were diagnosed with COVID-19 based on non-routine screening. The median age of the entire cohort at diagnosis was 54 years, and 95 patients (42.2%) were female. COVID-19 related-hospitalization rate (17.5% vs. 26.7%, p=0.14), ICU admission (1.6% vs. 5.6%, p=0.19), and mortality (4.8% vs. 3.7%, p=0.72) were not significantly different between routine screening and non-routine screening groups. In the multivariable analysis, age ≥ 60 years (odds ratio: 4.4, p=0.023) and an absolute lymphocyte count ≤1.4 × 109/L (odds ratio: 9.2, p=0.002) were independent predictors of COVID-19-related hospital admission. Conclusions and Relevance: The COVID-19 positivity rate was low based on routine screening. Comparing the outcome with the non-routine screening cohort, there was no significant difference. These results led to an important practice change at our cancer center. We currently follow a testing strategy based on symptoms, exposure, risk factors, and clinical judgment. Citation Format: Zhuoer Xie, Antoine N. Saliba, Jithma Abeykoon, Umair Majeed, Daniel Almquist, Julia Wiedmeier-Nutor, Evandro Bezerra, Xavier Andrade-Gonzalez, Ashley Hickman, Karl Sorenson, Sagar Rakshit, Christopher Wee, Sri Tella, Anuhya Kommalapati, Nadine Abdallah, Joshua Pritchett, Mariza De Andrade, Dipesh Uprety, Andrew Badley, Joleen Hubbard, Naseema Gangat, Carrie A. Thompson, Thomas Witzig, Robert R. McWilliams, Konstantinos Leventakos, Thorvardur R. Halfdanarson. Outcomes of COVID-19 in patients with cancer: Results of a prospective observational comparison of routine screening strategy versus testing based on clinical suspicion [abstract]. In: Proceedings of the AACR Virtual Meeting: COVID-19 and Cancer; 2021 Feb 3-5. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(6_Suppl):Abstract nr S06-03.

Introduction Immune-mediated hematologic disorders are relatively rare but potentially life-threatening immune-related adverse events (irAE) with immune checkpoint inhibitor (ICI) therapy (Shiuan, Beckermann et al 2017). The management strategy often relies on systemic corticosteroids and other immunosuppressant agents in steroid-refractory cases (Brahmer, Lacchetti et al 2018). We hereby describe our institution's experience in diagnosing and managing immune-related hematologic adverse events (ir-h-AE). Methods We retrospectively searched the electronic health record for all ir-h-AE diagnosed by treating providers and confirmed by study authors between 2015 and 2020. The search included patients on ICI and the following conditions: immune-related neutropenia (IRN), autoimmune hemolytic anemia (AIHA), cold agglutinin disease (CAD), immune thrombocytopenia (ITP), immune-related pancytopenia, aplastic anemia (AA), and pure red cell aplasia (PRCA). For AIHA, PRCA, and CAD, partial response (PR) was defined as hemoglobin greater than 10 g/dL but &lt; 12 g/dL and 2 g/dL above the nadir without blood product transfusion. Complete response (CR) was defined as hemoglobin of ≥ 12 g/dL and 2 g/dL above the nadir without blood product transfusion (Peñalver, Alvarez-Larrán et al. 2010). For ITP, CR was defined as platelet count ≥ 100 × 109/L and absence of bleeding. PR was defined as platelet count ≥ 30 × 109/L and ≥ two-fold increase from the baseline count and absence of bleeding (Gómez-Almaguer, Tarín-Arzaga et al. 2013). For IRN, CR was defined as absolute neutrophil count (ANC) ≥ 1500/ mm3 on 2 consecutive measurements separated by 7 days; PR was defined as ANC ≥ 500/ mm3 sustained over 7 days. JMP® 14.1 was used for data analysis. Results Seventeen patients were identified, 9 (52.9%) of whom were female (table 1). Median age was 68 years (range 26-78). The most common pre-existing malignancies were melanoma (6 patients, 35.3%), non-small cell lung cancer (4 patients, 23.5%), and gastrointestinal cancer (3 patients, 17.6%). The ir-h-AE included 7 patients (41.2%) with warm AIHA, 4 (23.5%) with ITP (1 had immune-related pancytopenia that resolved with ITP persisting), 3 (17.6%) with IRN, 1 with AA, 1 with CAD, and 1 with PRCA and mild ITP. All patients had received an ICI dose within 60 days of diagnosis (range 3-52 days, median 18 days). Only 1 patient had a concomitant chronic autoimmune disorder (antinuclear antibody-positive arthritis). Four patients (23.5%) were receiving chemotherapy. Sixteen patients (94.1%) required treatment and received corticosteroids. Eight out of 15 evaluable patients (53.3%) responded to corticosteroids only. Another 4 responders (26.7%) required additional therapies including intravenous immunoglobulins (IVIG) (4, 23.5%) and/or rituximab (4, 23.5%). Overall response rate was 71.4% for AIHA and 100% for IRN. ITP was likely underrepresented in our cohort, and the response rate of 66.7% is likely lower than the response rate in clinical practice. This could be related to the fact that many mild thrombocytopenia cases are not further evaluated in clinical practice. None of our patients died from the sequelae of an ir-h-AE. Two patients (11.8%) died within 30 days of ir-h-AE diagnosis (disseminated intravascular coagulation likely due to the underlying malignancy and sepsis from bacterial pneumonia). At the time of ir-h-AE diagnosis, the malignancy was showing evidence of response in 9 patients (52.9%), progression in 6 patients (35.3%), and stability in 2 patients (11.8%). ICI therapy was permanently discontinued in 9 patients (52.9%) and temporarily held in 6 patients (35.3%). Three of the 5 patients (60%), who were rechallenged with ICI therapy, had recurrence of the same ir-h-AE (AIHA) with adequate response to therapy. Non-hematologic irAE (7 patients, 41.2%) included 3 patients with hepatitis, 2 with thyroiditis, 2 with pneumonitis, 1 with colitis, and 1 with dermatitis. Conclusion Our clinical experience with ir-h-AE highlights the importance of exercising vigilance in assessing the hematologic parameters of patients receiving ICI therapy. While relatively rare, ir-h-AE may impact the clinical course of patients with cancer and their eligibility for therapies that have the potential of offering durable control of the underlying malignancy. ir-h-AE respond to classical therapies including corticosteroids, IVIG, and rituximab. Disclosures Block: Merck: Research Funding; Bristol-Myers Squibb: Research Funding; Genentech: Research Funding; Pharmacyclics: Research Funding; Marker Therapeutics: Research Funding; Transgene: Research Funding; Immune Design: Research Funding. Kottschade:Bristol-Myers Squibb: Consultancy, Research Funding.

Although CD19-directed chimeric antigen receptor T cell (CART19) therapy is highly effective and was FDA approved for certain B-cell malignancies, most patients relapse after CART infusion within the first 1-2 years due to inadequate CART expansion in vivo. Vesicular stomatitis virus (VSV) has the ability to infect and lyse cancer cells. Clinical trials of VSV oncolytic therapy indicate that VSV efficiently infects cancer cells as well as innate immune cells. Therefore, we hypothesized that in patients who achieve suboptimal response to CART19, VSV engineered to express CD19 will augment anti-tumor activity through 1) direct lysis of cancer cells and 2) infecting cancer cells and innate immune cells with CD19 to further stimulate CART19. To test our hypothesis, human CD19 or GFP (control) was engineered between the glycoprotein and large-protein (Fig.1A) in a modified VSV backbone. A matrix inactivating mutation (M51R) rendered it incapable of suppressing anti-viral reactions of infected targets, potentially promoting its immunogenicity. First, we tested the anti-tumor activity of VSV-CD19 and VSV-GFP against the luciferase (luc)+CD19+ acute lymphoblastic leukemia cell line NALM6 and the luc+CD19- acute myeloid leukemia cell line MOLM13. VSV-CD19 and VSV-GFP successfully lysed NALM6 (Fig.1B) or MOLM13, both in vitro and in vivo (data not shown). Next, we investigated the efficiency of VSV-CD19 in infecting tumor and immune cells. 24 hours after exposure to VSV-CD19 or VSV-GFP, we analyzed the surface expression of CD19 on MOLM13 and revealed efficient CD19 delivery (Fig.1C). Next, we assessed VSV infection of peripheral blood mononuclear cells (PBMCs) from healthy donors (HDs). Freshly isolated HD PBMCs were infected with VSV-CD19 for 6 hours and subsequently assessed for CD19 expression. Consistent with findings from clinical trials, VSV-CD19 selectively infected and induced CD19 expression on monocytes while other cells were not affected (Fig.1D). To exclude potential toxicities against CART19, we co-cultured CART19 with VSV-CD19 or VSV-GFP using second-generation 4-1BB costimulated CART19. Both VSV-CD19 and VSV-GFP did not infect CART19 as evident by preservation of CART19 viability and lack of CD19 or GFP expression (Fig.1E). Having demonstrated that VSV-CD19 specifically delivered CD19 to monocytes, we next tested whether the infected monocytes stimulated CART19. VSV-CD19 infected monocytes induced potent antigen-specific proliferation of CART19 (Fig.1F) and resulted in enhanced anti-tumor activity against luc+NALM6 in vitro (Fig.1G). Next, we aimed to confirm these findings in vivo. We generated luc+CART19 to track CART19 expansion in vivo. Freshly isolated HD monocytes were infected with VSV-CD19 ex vivo. After 4 hours, VSV-CD19 was washed away and immunocompromised NSG mice were intravenously injected with VSV-CD19 infectedmonocytes. After 24 hours, 3.5x106 of luc+untransduced T cells (UTD) or luc+CART19 were injected intravenously. The T cell expansion was assessed by bioluminescence imaging (BLI). VSV-CD19 infected monocytes specifically stimulated and expanded CART19 (Fig.1H). Finally, we tested whether VSV-CD19 can stimulate and rescue suboptimal anti-tumor effects of CART19 in vivo using a NALM6 relapsed model. Here, 1x106 luc+NALM6 were injected intravenously into NSG mice on day -6. At day -1, mice were imaged and randomized according to tumor burden to receive 1x106 UTD or CART19 on day 0. Subsequently, at day 4, mice were re-imaged and randomized. At day 5, HD monocytes were injected intravenously. Three hours after administering monocytes, mice received 1x107 VSV-CD19 or VSV-GFP (Fig.1I). BLI revealed that CART19 plusVSV-CD19 showed better tumor control than CART19 monotherapy or CART19 plus VSV-GFP (Fig.1J-K). Furthermore, CART19 plus VSV-CD19 exhibited long-term survival (Fig.1L). In summary, VSV-CD19 not only demonstrated direct anti-tumor effects but also specifically delivered CD19 to monocytes and tumor cells, thereby re-stimulating and enhancing the anti-tumor activity of CART19. This work provides a rationale to study VSV-CD19 in patients who demonstrate only suboptimal response to CART19. This approach could also be applied to augment CART therapy in other tumors. Figure 1 Disclosures Sakemura: Humanigen: Patents & Royalties. Eckert:Genentech: Current Employment. Cox:Humanigen: Patents & Royalties. Parikh:Ascentage Pharma: Research Funding; GlaxoSmithKline: Honoraria; Verastem Oncology: Honoraria; MorphoSys: Research Funding; Genentech: Honoraria; Pharmacyclics: Honoraria, Research Funding; AbbVie: Honoraria, Research Funding; Merck: Research Funding; Janssen: Honoraria, Research Funding; TG Therapeutics: Research Funding; AstraZeneca: Honoraria, Research Funding. Kay:Dava Oncology: Membership on an entity's Board of Directors or advisory committees; Oncotracker: Membership on an entity's Board of Directors or advisory committees; Bristol Meyer Squib: Membership on an entity's Board of Directors or advisory committees, Research Funding; Agios Pharma: Membership on an entity's Board of Directors or advisory committees; Cytomx: Membership on an entity's Board of Directors or advisory committees; MEI Pharma: Research Funding; Rigel: Membership on an entity's Board of Directors or advisory committees; Tolero Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Acerta Pharma: Research Funding; Astra Zeneca: Membership on an entity's Board of Directors or advisory committees; Morpho-sys: Membership on an entity's Board of Directors or advisory committees; Abbvie: Research Funding; Juno Theraputics: Membership on an entity's Board of Directors or advisory committees; Sunesis: Research Funding. Peng:Imanis: Other: Equity Ownership. Russell:Imanis: Other: Equity Ownership. Kenderian:Mettaforge: Patents & Royalties; Humanigen: Consultancy, Patents & Royalties, Research Funding; Lentigen: Research Funding; Torque: Consultancy; Novartis: Patents & Royalties, Research Funding; Kite: Research Funding; Gilead: Research Funding; Juno: Research Funding; BMS: Research Funding; Tolero: Research Funding; Sunesis: Research Funding; MorphoSys: Research Funding.