Targeting cancer-associated fibroblasts in the bone marrow prevents resistance to CART-cell therapy in multiple myeloma.

Pivotal clinical trials of B-cell maturation antigen-targeted chimeric antigen receptor T (CART)-cell therapy in patients with relapsed/refractory multiple myeloma (MM) resulted in remarkable initial responses, which led to a recent US Food and Drug Administration approval. Despite the success of this therapy, durable remissions continue to be low, and the predominant mechanism of resistance is loss of CART cells and inhibition by the tumor microenvironment (TME). MM is characterized by an immunosuppressive TME with an abundance of cancer-associated fibroblasts (CAFs). Using MM models, we studied the impact of CAFs on CART-cell efficacy and developed strategies to overcome CART-cell inhibition. We showed that CAFs inhibit CART-cell antitumor activity and promote MM progression. CAFs express molecules such as fibroblast activation protein and signaling lymphocyte activation molecule family-7, which are attractive immunotherapy targets. To overcome CAF-induced CART-cell inhibition, CART cells were generated targeting both MM cells and CAFs. This dual-targeting CART-cell strategy significantly improved the effector functions of CART cells. We show for the first time that dual targeting of both malignant plasma cells and the CAFs within the TME is a novel strategy to overcome resistance to CART-cell therapy in MM.

Leukemic extracellular vesicles induce chimeric antigen receptor T cell dysfunction in chronic lymphocytic leukemia.

Chimeric antigen receptor (CAR) T cell therapy has yielded unprecedented outcomes in some patients with hematological malignancies; however, inhibition by the tumor microenvironment has prevented the broader success of CART cell therapy. We used chronic lymphocytic leukemia (CLL) as a model to investigate the interactions between the tumor microenvironment and CART cells. CLL is characterized by an immunosuppressive microenvironment, an abundance of systemic extracellular vesicles (EVs), and a relatively lower durable response rate to CART cell therapy. In this study, we characterized plasma EVs from untreated CLL patients and identified their leukemic cell origin. CLL-derived EVs were able to induce a state of CART cell dysfunction characterized by phenotypical, functional, and transcriptional changes of exhaustion. We demonstrate that, specifically, PD-L1+ CLL-derived EVs induce CART cell exhaustion. In conclusion, we identify an important mechanism of CART cell exhaustion induced by EVs from CLL patients.

GM-CSF inhibition reduces cytokine release syndrome and neuroinflammation but enhances CAR-T cell function in xenografts.

Chimeric antigen receptor T (CAR-T) cell therapy is a new pillar in cancer therapeutics; however, its application is limited by the associated toxicities. These include cytokine release syndrome (CRS) and neurotoxicity. Although the IL-6R antagonist tocilizumab is approved for treatment of CRS, there is no approved treatment of neurotoxicity associated with CD19-targeted CAR-T (CART19) cell therapy. Recent data suggest that monocytes and macrophages contribute to the development of CRS and neurotoxicity after CAR-T cell therapy. Therefore, we investigated neutralizing granulocyte-macrophage colony-stimulating factor (GM-CSF) as a potential strategy to manage CART19 cell-associated toxicities. In this study, we show that GM-CSF neutralization with lenzilumab does not inhibit CART19 cell function in vitro or in vivo. Moreover, CART19 cell proliferation was enhanced and durable control of leukemic disease was maintained better in patient-derived xenografts after GM-CSF neutralization with lenzilumab. In a patient acute lymphoblastic leukemia xenograft model of CRS and neuroinflammation (NI), GM-CSF neutralization resulted in a reduction of myeloid and T cell infiltration in the central nervous system and a significant reduction in NI and prevention of CRS. Finally, we generated GM-CSF-deficient CART19 cells through CRISPR/Cas9 disruption of GM-CSF during CAR-T cell manufacturing. These GM-CSFk/o CAR-T cells maintained normal functions and had enhanced antitumor activity in vivo, as well as improved overall survival, compared with CART19 cells. Together, these studies illuminate a novel approach to abrogate NI and CRS through GM-CSF neutralization, which may potentially enhance CAR-T cell function. Phase 2 studies with lenzilumab in combination with CART19 cell therapy are planned.

Quantitative Assessment of T Cell Clonotypes in Human Acute Graft-versus-Host Disease Tissues.

Owing to the difficulty in isolating T cells from human biopsy samples, the characteristics of T cells that are infiltratinghuman acute graft-versus-host disease (GVHD) tissues remain largely uninvestigated. In the present study, TCR-ß deep sequencing of various GVHD tissue samples and concurrent peripheral blood obtained from transplant recipients was performed in combination with functional assays of tissue-infiltrating T cell clones. The T cell repertoire was more skewed in GVHD tissues than in the peripheral blood. The frequent clonotypes differed from tissue to tissue in the same patient, and the frequent clonotypes in the same tissue differed from patient to patient. Two T cell clones were successfully isolated from GVHD skin of a patient. In a cytotoxicity assay, both Tcell clones lysed patient peripheral blood mononuclear cells, but not donor-derived Epstein-Barr virus-transformed lymphoblastoid cells. Their clonotypes were identical to the most and second most frequent T cell clonotypes in the original GVHD skin and accounted for almost all of the skin-infiltrating T cells. These results suggest that human acute GVHD may result from only a few different alloreactive cytotoxic T cell clones, which differ from tissue to tissue and from patient to patient. The characterization of T cells infiltrating human GVHD tissues should be further investigated.

[Pneumocystis pneumonia prophylaxis with low-dose trimethoprim/sulfamethoxazole during rituximab-containing chemotherapy].

Although Pneumocystis pneumonia (PCP), a life-threatening infection, has been reported in patients with non-Hodgkin B-cell lymphoma (BNHL) who were treated with rituximab-containing chemotherapies (R-CTX), the PCP prophylaxis regimen awaits establishment to date. This study reports a retrospective analysis of the efficacy and safety of a low-dose trimethoprim/sulfamethoxazole (TMP/SMX) in patients with BNHL receiving R-CTX. We retrospectively analyzed 156 patients newly diagnosed with BNHL who received R-CTX at our institute from 2010 to 2015. We collected patients' clinical and laboratory data, including lymphocytes count, IgG level, PCP prophylaxis regimens, and adverse events (AEs). Patients were categorized into the following two groups based on the TMP/SMX regimen: group A (33 patients; 80 mg/400 mg×3/week) or group B (65 patients; 160 mg/800 mg×2/week). Both lymphocytes count and IgG level declined during R-CTX. No patient developed PCP. Patients in group B exhibited a significantly higher incidence of AEs (18.2% vs. 63.1%; p<0.05) and increased AST (6.1% vs. 26.6%; p<0.05), compared with those in group A. Thus, TMP/SMX (80 mg/400 mg×3/week) effectively prevents PCP and is preferable because of the lower rates of AEs.

Plasma concentrations of dasatinib have a clinical impact on the frequency of dasatinib dose reduction and interruption in chronic myeloid leukemia: an analysis of the DARIA 01 study.

BACKGROUND: Dasatinib has shown promising anti-leukemic activity against chronic myeloid leukemia (CML). However, patients receiving dasatinib frequently require dose reductions and treatment interruptions (treatment alteration). METHODS: We prospectively analyzed the frequency and significance of treatment alteration during dasatinib therapy in patients with CML. In all patients, trough plasma concentrations of dasatinib (Cmin) at steady state were assessed on day 28 of therapy. RESULTS: 28% of patients had their doses reduced at a median of 42 days, and 25% of patients had temporarily interrupted at a median of 54 days after treatment initiation. The overall dasatinib treatment alteration-free rate at 1 year was 66%. Age was significantly correlated with Cmin on day 28 (p = 0.014), and the correlation remained significant after adjusting dasatinib dose (g), body weight (kg) (Cmin/D/W) (p = 0.026). In the univariate analysis, deep molecular response, advanced PS, higher Cmin/D/W were associated with a significantly higher risk of treatment alteration (HR 4.19, 95% CI: 1.06-16.60, p = 0.041; HR 5.26, 95% CI: 1.33-20.80, p = 0.018; and HR 10.15, 95% CI: 2.55-40.48, p = 0.001, respectively). In the multivariate analysis, advanced PS and higher Cmin/D/W were correlated with the incidence of treatment alteration (HR 4.78, 95% CI: 1.01-22.70, p = 0.049; HR 6.17, 95% CI: 1.17-32.50, respectively). CONCLUSION: Current data demonstrate that patients treated with dasatinib who displayed a high Cmin/D/W value and/or advanced PS were at a high risk for altered treatment.

Target antigen density governs the efficacy of anti-CD20-CD28-CD3 ζ chimeric antigen receptor-modified effector CD8+ T cells.

The effectiveness of chimeric Ag receptor (CAR)-transduced T (CAR-T) cells has been attributed to supraphysiological signaling through CARs. Second- and later-generation CARs simultaneously transmit costimulatory signals with CD3ζ signals upon ligation, but may lead to severe adverse effects owing to the recognition of minimal Ag expression outside the target tumor. Currently, the threshold target Ag density for CAR-T cell lysis and further activation, including cytokine production, has not yet been investigated in detail. Therefore, we determined the threshold target Ag density required to induce CAR-T cell responses using novel anti-CD20 CAR-T cells with a CD28 intracellular domain and a CD20-transduced CEM cell model. The newly developed CD20CAR-T cells demonstrated Ag-specific lysis and cytokine secretion, which was a reasonable level as a second-generation CAR. For lytic activity, the threshold Ag density was determined to be ∼200 molecules per target cell, whereas the Ag density required for cytokine production of CAR-T cells was ∼10-fold higher, at a few thousand per target cell. CD20CAR-T cells responded efficiently to CD20-downregulated lymphoma and leukemia targets, including rituximab- or ofatumumab-refractory primary chronic lymphocytic leukemia cells. Despite the potential influence of the structure, localization, and binding affinity of the CAR/Ag, the threshold determined may be used for target Ag selection. An Ag density below the threshold may not result in adverse effects, whereas that above the threshold may be sufficient for practical effectiveness. CD20CAR-T cells also demonstrated significant lytic activity against CD20-downregulated tumor cells and may exhibit effectiveness for CD20-positive lymphoid malignancies.

Interdigitating dendritic cell sarcoma successfully treated with ABVD therapy in which serum CEA levels correlated with disease activity.

Interdigitating dendritic cell sarcoma (IDCS) is an extremely rare neoplasm of spindle to ovoid cells with phenotypic features similar to those of interdigitating dendritic cells. No standard therapy for advanced IDCS has yet been established. According to past reports, CHOP-like regimens are often chosen as primary therapy. Herein, we report a case with advanced IDCS, for which ABVD achieved remarkable clinical improvement and serial CEA levels correlated with disease status. A 76-year-old man presented with general fatigue and pancytopenia with CEA elevation. Colonoscopy showed erosion and polyps in the colon. FDG-PET showed marked abnormal accumulation throughout the bone marrow. Pathologically, polyps of the colon and IDCS of the bone marrow were diagnosed. Although the patient received CHOP as initial therapy, clinical improvement was not significant. Subsequently, six cycles of ABVD resulted in remarkable regression of both the colonic polyps and the bone marrow infiltration. Moreover, the patient was transfusion-free after ABVD. In addition to these clinical responses, serial CEA levels normalized. Our case highlights the efficacy of ABVD for IDCS and serial CEA measurements might reflect treatment efficacy.

Chimerism status after unrelated donor bone marrow transplantation with fludarabine-melphalan conditioning is affected by the melphalan dose and is predictive of relapse.

Little is known regarding the chimerism status after reduced-intensity conditioning transplantation when bone marrow is used as a stem cell source. We prospectively analyzed lineage-specific chimerism and retrospectively evaluated clinical outcomes in 80 adult patients who underwent unrelated donor bone marrow transplantation (URBMT) with fludarabine plus melphalan (FM) as the conditioning regimen. Mixed donor chimerism (MDC) was seen in 43 and 10 % of patients at days 14 and 28, respectively. Melphalan at ≤130 mg/m(2) was associated with an increased incidence of MDC at day 28 (P = 0.03). Patients with MDC at day 14 showed a marginally increased risk of primary graft failure and a marginally decreased risk of graft-versus-host disease. In multivariate analysis, MDC at day 14 was associated with higher overall mortality (hazard ratio (HR) = 2.1; 95 % confidence interval (CI), 1.1-4.2; P = 0.04) and relapse rate (HR = 3.0; 95 % CI, 1.2-7.5; P = 0.02), but not with non-relapse mortality (HR = 1.8; 95 % CI, 0.70-4.6; P = 0.23). Thus, the FM regimen yields prompt complete donor chimerism after URBMT, but the melphalan dose significantly impacts the kinetics of chimerism. Chimerism status evaluation at day 14 may be instrumental in predicting relapse after URBMT with the FM regimen.

CAR T cell therapy and the tumor microenvironment: Current challenges and opportunities.

Chimeric antigen receptor (CAR) T cell therapy has demonstrated remarkable outcomes in individuals with hematological malignancies, but its success has been hindered by barriers intrinsic to the tumor microenvironment (TME), particularly for solid tumors, where it has yet to make its mark. In this article, we provide an updated review and future perspectives on features of the TME that represent barriers to CART cell therapy efficacy, including competition for metabolic fuels, physical barriers to infiltration, and immunosuppressive factors. We then discuss novel and promising strategies to overcome these obstacles that are in preclinical development or under clinical investigation.

Challenges of chimeric antigen receptor T-cell therapy in chronic lymphocytic leukemia: lessons learned.

Development of chimeric antigen receptor T cell (CART) therapy has led to an unprecedented success against B-cell leukemia and lymphoma and resulted in U.S. Food and Drug Administration-approved treatment protocols. Despite the initial clinical response in B cell-related malignancies, high relapse rates suggest that much work is needed to uncover mechanisms of resistance. In chronic lymphocytic leukemia (CLL), the durable activity of CAR T-cells is limited, and CAR T-cell therapy success is lower than in other malignancies. T cells from these patients are vulnerable to a state of dysfunction because of stresses including chronic infection, rapid cell cycle on antigen recognition, immunosuppressive tumor microenvironment, and cancer-related treatments. T cells are also introduced to additional stresses when cultured ex vivo during the CAR T-cell manufacturing process. All these factors contribute to the limited regenerative capacity of T cells, which can lead to CAR T-cell treatment failure. In this article, we review the challenges of CAR T-cell therapy in patients with CLL and discuss potential strategies to overcome these challenges.

Dynamic Imaging of Chimeric Antigen Receptor T Cells with [18F]Tetrafluoroborate Positron Emission Tomography/Computed Tomography.

T cells genetically engineered to express chimeric antigen receptors (CAR) have shown unprecedented results in pivotal clinical trials for patients with B cell malignancies or multiple myeloma (MM). However, numerous obstacles limit the efficacy and prohibit the widespread use of CAR T cell therapies due to poor trafficking and infiltration into tumor sites as well as lack of persistence in vivo. Moreover, life-threatening toxicities, such as cytokine release syndrome or neurotoxicity, are major concerns. Efficient and sensitive imaging and tracking of CAR T cells enables the evaluation of T cell trafficking, expansion, and in vivo characterization and allows the development of strategies to overcome the current limitations of CAR T cell therapy. This paper describes the methodology for incorporating the sodium iodide symporter (NIS) in CAR T cells and for CAR T cell imaging using [18F]tetrafluoroborate-positron emission tomography ([18F]TFB-PET) in preclinical models. The methods described in this protocol can be applied to other CAR constructs and target genes in addition to the ones used for this study.

Host-Viral Interactions at the Maternal-Fetal Interface. What We Know and What We Need to Know.

In humans, the hemochorial placenta is a unique temporary organ that forms during pregnancy to support fetal development, gaseous exchange, delivery of nutrition, removal of waste products, and provides immune protection, while maintaining tolerance to the HLA-haploidentical fetus. In this review, we characterize decidual and placental immunity during maternal viral (co)-infection with HIV-1, human cytomegalovirus (HCMV), and Zika virus. We discuss placental immunology, clinical presentation, and epidemiology, before characterizing host susceptibility and cellular tropism, and how the three viruses gain access into specific placental target cells. We describe current knowledge on host-viral interactions with decidual and stromal human placental macrophages or Hofbauer cells, trophoblasts including extra villous trophoblasts, T cells, and decidual natural killer (dNK) cells. These clinically significant viral infections elicit both innate and adaptive immune responses to control replication. However, the three viruses either during mono- or co-infection (HIV-1 and HCMV) escape detection to initiate placental inflammation associated with viral transmission to the developing fetus. Aside from congenital or perinatal infection, other adverse pregnancy outcomes include preterm labor and spontaneous abortion. In addition, maternal HIV-1 and HCMV co-infection are associated with impaired fetal and infant immunity in postnatal life and poor clinical outcomes during childhood in exposed infants, even in the absence of vertical transmission of HIV-1. Given the rapidly expanding numbers of HIV-1-exposed uninfected infants and children globally, further research is urgently needed on neonatal immune programming during maternal mono-and co-infection. This review therefore includes sections on current knowledge gaps that may prompt future research directions. These gaps reflect an emerging but poorly characterized field. Their significance and potential investigation is underscored by the fact that although viral infections result in adverse consequences in both mother and developing fetus/newborn, antiviral and immunomodulatory therapies can improve clinical outcomes in the dyad.

GM-CSF disruption in CART cells modulates T cell activation and enhances CART cell anti-tumor activity.

Inhibitory myeloid cells and their cytokines play critical roles in limiting chimeric antigen receptor T (CART) cell therapy by contributing to the development of toxicities and resistance following infusion. We have previously shown that neutralization of granulocyte-macrophage colony-stimulating factor (GM-CSF) prevents these toxicities and enhances CART cell functions by inhibiting myeloid cell activation. In this report, we study the direct impact of GM-CSF disruption during the production of CD19-directed CART cells on their effector functions, independent of GM-CSF modulation of myeloid cells. In this study, we show that antigen-specific activation of GM-CSFKO CART19 cells consistently displayed reduced early activation, enhanced proliferation, and improved anti-tumor activity in a xenograft model for relapsed B cell malignancies. Activated CART19 cells significantly upregulate GM-CSF receptors. However, the interaction between GM-CSF and its upregulated receptors on CART cells was not the predominant mechanism of this activation phenotype. GM-CSFKO CART19 cell had reduced BH3 interacting-domain death agonist (Bid), suggesting an interaction between GM-CSF and intrinsic apoptosis pathways. In conclusion, our study demonstrates that CRISPR/Cas9-mediated GM-CSF knockout in CART cells directly ameliorates CART cell early activation and enhances anti-tumor activity in preclinical models.

In vivo CART cell imaging: Paving the way for success in CART cell therapy.

Chimeric antigen receptor T (CART) cells are a promising immunotherapy that has induced dramatic anti-tumor responses in certain B cell malignancies. However, CART cell expansion and trafficking are often insufficient to yield long-term remissions, and serious toxicities can arise after CART cell administration. Visualizing CART cell expansion and trafficking in patients can detect an inadequate CART cell response or serve as an early warning for toxicity development, allowing CART cell treatment to be tailored accordingly to maximize therapeutic benefits. To this end, various imaging platforms are being developed to track CART cells in vivo, including nonspecific strategies to image activated T cells and reporter systems to specifically detect engineered T cells. Many of these platforms are clinically applicable and hold promise to provide valuable information and guide improved CART cell treatment.

Resistance to CART cell therapy: lessons learned from the treatment of hematological malignancies.

Chimeric antigen receptor T (CART) cell immunotherapy has yielded significant clinical success in treating certain hematological malignancies. However, despite high initial response rates, most patients eventually relapse. Resistance to CART cell therapy can stem from tumor cell mutations, T cell defects, and tumor microenvironment (TME) immunosuppression. Tumor cells can downregulate target antigen expression to evade CART cell detection or mutate death receptor pathways to resist CART cell cytotoxicity. Patient T cells can be intrinsically defective, and CART cells often undergo exhaustion. The TME is abundant with immunosuppressive cells and factors which contribute to suboptimal CART cell activity. Collectively, issues originating in tumor cells, T cells, and the TME present significant hurdles to long-term remission after CART cell therapy. Various strategies to combat CART cell resistance have shown promise in preclinical studies and early clinical trials and are crucial to achieving durable responses.

Development of a Clinically Relevant Reporter for Chimeric Antigen Receptor T-cell Expansion, Trafficking, and Toxicity.

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.

GM-CSF Neutralization With Lenzilumab in Severe COVID-19 Pneumonia: A Case-Cohort Study.

OBJECTIVE: To assess the efficacy and safety of lenzilumab in patients with severe coronavirus disease 2019 (COVID-19) pneumonia. METHODS: Hospitalized patients with COVID-19 pneumonia and risk factors for poor outcomes were treated with lenzilumab 600 mg intravenously for three doses through an emergency single-use investigational new drug application. Patient characteristics, clinical and laboratory outcomes, and adverse events were recorded. We also identified a cohort of patients matched to the lenzilumab patients for age, sex, and disease severity. Study dates were March 13, 2020, to June 18, 2020. All patients were followed through hospital discharge or death. RESULTS: Twelve patients were treated with lenzilumab; 27 patients comprised the matched control cohort (untreated). Clinical improvement, defined as improvement of at least 2 points on the 8-point ordinal clinical endpoints scale, was observed in 11 of 12 (91.7%) patients treated with lenzilumab and 22 of 27 (81.5%) untreated patients. The time to clinical improvement was significantly shorter for the lenzilumab-treated group compared with the untreated cohort with a median of 5 days versus 11 days (P=.006). Similarly, the proportion of patients with acute respiratory distress syndrome (oxygen saturation/fraction of inspired oxygen<315 mm Hg) was significantly reduced over time when treated with lenzilumab compared with untreated (P<.001). Significant improvement in inflammatory markers (C-reactive protein and interleukin 6) and markers of disease severity (absolute lymphocyte count) were observed in patients who received lenzilumab, but not in untreated patients. Cytokine analysis showed a reduction in inflammatory myeloid cells 2 days after lenzilumab treatment. There were no treatment-emergent adverse events attributable to lenzilumab. CONCLUSION: In high-risk COVID-19 patients with severe pneumonia, granulocyte-macrophage colony-stimulating factor neutralization with lenzilumab was safe and associated with faster improvement in clinical outcomes, including oxygenation, and greater reductions in inflammatory markers compared with a matched control cohort of patients hospitalized with severe COVID-19 pneumonia. A randomized, placebo-controlled clinical trial to validate these findings is ongoing (NCT04351152).

First Clinical Use of Lenzilumab to Neutralize GM-CSF in Patients with Severe COVID-19 Pneumonia.

BACKGROUND: In COVID-19, high levels of granulocyte macrophage-colony stimulating factor (GM-CSF) and inflammatory myeloid cells correlate with disease severity, cytokine storm, and respiratory failure. With this rationale, we used lenzilumab, an anti-human GM-CSF monoclonal antibody, to treat patients with severe COVID-19 pneumonia. METHODS: Hospitalized patients with COVID-19 pneumonia and risk factors for poor outcomes were treated with lenzilumab 600 mg intravenously for three doses through an emergency single-use IND application. Patient characteristics, clinical and laboratory outcomes, and adverse events were recorded. All patients receiving lenzilumab through May 1, 2020 were included in this report. RESULTS: Twelve patients were treated with lenzilumab. Clinical improvement was observed in 11 out of 12 (92%), with a median time to discharge of 5 days. There was a significant improvement in oxygenation: The proportion of patients with SpO2/FiO2 < 315 at the end of observation was 8% vs. compared to 67% at baseline (p=0.00015). A significant improvement in mean CRP and IL-6 values on day 3 following lenzilumab administration was also observed (137.3 mg/L vs 51.2 mg/L, p = 0.040; 26.8 pg/mL vs 16.1 pg/mL, p = 0.035; respectively). Cytokine analysis showed a reduction in inflammatory myeloid cells two days after lenzilumab treatment. There were no treatment-emergent adverse events attributable to lenzilumab, and no mortality in this cohort of patients with severe COVID-19 pneumonia. CONCLUSIONS: In high-risk COVID-19 patients with severe pneumonia, GM-CSF neutralization with lenzilumab was safe and associated with improved clinical outcomes, oxygen requirement, and cytokine storm.