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Treatment outcome of relapsed or refractory AML patients remains dismal and new treatment options are needed. Adoptive cell therapy using CAR-T cells is a potentially interesting approach in this.Several potentially interesting AML targets are being investigated with CAR-T therapy with over 60 clinical trials listed on clinicaltrials.gov. The first clinical data are only just emerging with mixed results, once more proving that further research is needed.Adoptive cell therapy using chimeric antigen receptor T cells is being investigated in AML through many clinical trials. So far, no AML-specific antigen has been identified, requiring additional strategies to mitigate on-target off-tumor toxicity and to increase efficacy. Focus point is to acquire control over the CAR T cells once administered. Strategies to do so include biodegradable CARs, inducible CARs, suicide-switch containing CARs and two-component modular CARs. Limited and mixed results are available, confirming the risk of lasting toxicity for nonswitchable CARs. Initial results of modular CARs suggest toxicity can be mitigated whilst maintaining CAR activity by the use of modular CAR concepts that allows for 'ON' and 'OFF' switching.

Background: Conventional CAR-T cells targeting CD123 in rrAML have achieved objective responses, but led to long-lasting myelosuppression due to expression of CD123 on progenitor cells. UniCAR-T-CD123 is a rapidly switchable two-component CAR-T therapy. An inert universal CAR-T cell (UniCAR-T) is combined with a CD123-specific soluble targeting module with a short half-life (TM123). By administering or withholding the continuous infusion of TM123, the UniCAR-T-cell can be rapidly switched on and off. Within the ongoing Phase IA study in rrAML, we investigated the expansion kinetics of UniCAR-T cells during TM123 administration in peripheral blood and bone marrow as well as cytokine profiles of treated patients. Methods: Prior to administration of autologous UniCAR-T cells, patients received a standard Flu/Cy lymphodepletion regimen at day -5 to -3. TM123 was administered as continuous infusion over 24 days starting at day 0. At day 1 a single dose of UniCAR-T cells was given. Dosing started with 1 x 108 UniCAR-T cells and 0.5 mg TM123 per day in patient 1. Patient 2 received the same TM123 dose and a UniCAR-T dose of 2.5 x 108 cells. Patient 3 received the same cell dose as patient 2 but a higher TM123 dose (1 mg/day). Pharmacokinetic of UniCAR-T and TM123 was determined from peripheral blood and bone marrow by droplet digital PCR and TM123-specific ELISA, respectively. Cytokine levels were measured by microfluidic immunoassay. Results: All 3 patients treated so far achieved an objective response, with one showing a PR and two a CRi. Treatment proved to be tolerable, no DLTs were observed to date and adverse events were mild. Grade 1 CRS (fever) was observed in 2 patients but subsided within 48 h after use of antipyretics. Myelosuppression was observed starting after lymphodepletion, which immediately recovered after TM123 withdrawal on day 24 in all patients, providing evidence for the rapid off-switch of UniCAR-T cells post TM123 administration. UniCAR-T cells expanded in all patients in peripheral blood and bone marrow comparable to data reported for conventional CD123 CAR-T products, and were so far detectable for up to 6 months after administration. Expansion kinetics were TM123-dependent. Patients showed periods of transient increase of IL-6, IFN-γ and TNF-α levels preceding peak expansion and decreasing after termination of TM123 administration. One patient showed additional coinciding momentary elevation of GM-CSF and IL-2. Conclusions: The initial clinical and translational results of UniCAR-T-CD123 represent, to our understanding, a first time evidence for a well-tolerated and effective rapidly switchable CAR-T product. Even though the number of patients treated so far is limited, the data obtained provide clinical proof-of-concept for the opportunity to abrogate side effects by withdrawal of TM123. Enrollment into the Phase IA study is ongoing. Citation Format: Armin Ehninger, Julia Riewaldt, Cordula Gründer, Kristin Franke, Maria Schreiber, Martin Wermke, Sabrina Kraus, Carla Kreissig, Jan Koedam, Michael Pehl, Gerhard Ehninger, Marc Cartellieri. Expansion kinetics and cytokine profiles of UniCAR-T-CD123, a rapidly switchable two-component CAR-T therapy, in patients with relapsed/refractory AML [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1506.

The efficacy of azacitidine has been demonstrated in acute myeloid leukemia (AML) patients with 20-30% bone marrow (BM) blasts, but limited data is available on patients with >= 30% blasts. We analyzed 55 newly diagnosed AML patients, treated with azacitidine. The overall response rate was 42%. Median overall survival (OS) was 12.3 months. We confirmed poor-risk cytogenetics, therapy-related AML, performance score >= 2, and white blood cell count >= 15x10(9)/L as independent adverse predictors for OS. The BM blast percentage, however, had no impact on OS (P=0.55).In conclusion, administration of azacitidine is effective in AML patients with 20-30% and >30% BM blasts. (C) 2013 Elsevier Ltd. All rights reserved.

Abstract 3841 The efficacy of azacitidine in the treatment of high risk myelodysplastic syndromes (MDS), chronic myelomonocytic leukaemia (CMML) and acute myeloid leukaemia (AML) (20–30% blasts) has been demonstrated. To investigate the efficacy of azacitidine in daily clinical practice and to identify predictors for response, we analyzed a cohort of 90 MDS, CMML and AML patients who have been treated in a Dutch compassionate patient named program. Patients received azacitidine for a median of 5 cycles (range 1–19). The overall response rate (CR/PR/HI) was 57% in low risk MDS, 53% in high risk MDS, 50% in CMML, and 39% in AML patients. Median overall survival (OS) was 13.0 (9.8–16.2) months. In multivariate analysis we confirmed that circulating blasts (HR 0.48, 95% CI 0.24–0.99; p=.05) and poor risk cytogenetics (HR 0.45, 95% CI 0.22–0.91; p=.03) are independent predictors for OS. Interestingly, in this analysis we also identified platelet doubling after the first cycle of azacitidine as a simple and independent positive predictor for OS (HR 5.4, 95% CI 0.73–39.9; p=.10). Of the 90 treated patients, 14 (16%) had an at least two-fold increase in platelet count after the first cycle of azacitidine, which was associated with significant better OS (p=.01, according to logrank test) (figure). Of these 14 patients 13 could be classified according the azacitidine prognostic scoring system for OS as recently proposed by Itzykson et al. (Blood:2011;117:403); 6 patients belonged to the low risk and 7 to the intermediate risk group. Median baseline platelet count of these patients was 35 x109/L (range 2–290 x109/L). Characteristics of this subgroup of patients were not significantly different from the patients without platelet doubling. Interestingly, platelet doubling was observed in all cytogenetic risk groups, in patients with and without circulating blasts, and in patients who are transfusion dependent and independent. In conclusion, routine administration of azacitidine to patients with variable risk groups of MDS, CMML and AML is feasible and subgroups with distinct efficacy of azacitidine treatment can be identified. Disclosures: Wijermans: Centocor Ortho Biotech Research & Development: Research Funding.

Abstract 5032 Myelodysplastic syndromes (MDS) are a heterogeneous group of hematopoietic stem cell disorders characterized by dysplasia and cytopenia in one or more cell lineages. The WHO2001 classification recognizes MDS associated with del (5q) as a distinct entity. Previous data have shown that Lenalidomide can reduce transfusion requirements and reverse cytological and cytogenetic abnormalities in patients with MDS and del (5q). In this study we aimed to evaluate the efficacy of Lenalidomide in MDS patients with a del (5q) cytogenetic abnormality. Patients were eligible for inclusion if they had a chromosome 5q deletion with or without additional cytogenetic abnormalities. Between 2007 and 2009, 19 patients after signing informed consent were eligible for response in this patient named program. According to the WHO2001 classification the diagnoses were RCMD (n = 6), RAEB-1 (n = 3), RAEB-II (n = 2) and 5q-syndrome (n = 8). The median age was 68 [range 53 – 85]. At baseline 13 patients had an isolated del (5q), 3 patients had 1 additional cytogenetic abnormality and 3 patients had more than 1 additional cytogenetic abnormality. Patients received Lenalidomide at a daily dose of 10 mg for 21 days of a 28 days cycle. The dose and schedule were adjusted based on drug toxicity and blood count. Response was evaluated using the IWG2006 response criteria (Cheson et al, Blood 2006). Two patients stopped Lenalidomide treatment due to drug toxicity before completion of the first cycle. According to the IWG2006 criteria, 7 patients showed a complete remission (CR), 7 stable disease (SD) and 3 patients showed disease progression (PD) under treatment. Patients with a CR showed a significantly better overall survival (OS) (median 37.9 weeks, range 17.7 – 40.3 weeks ) compared to patients with SD (median 17.6 weeks, range 7.7 – 33.9 weeks) and PD (median 8.8 weeks, range 8.8 – 13.7) groups (p = 0.007). From the patients with CR and cytogenetic evaluation during follow up, five had a complete cytogenetic response. Median pre-treatment Hb was 5.3 mmol/L [range 4.3 – 6.9], absolute neutrophil count (ANC) 1.45×10̂9/L [range 0.40 – 11.36] and thrombocytes 218.5×10̂9/L [range 38 – 902]. Erythroid response (HI-E) was achieved in 11 patients after a median of 2.5 cycles [range 2 – 4] and sustained for 8 cycles [range 3 – 16]. Patients that achieved HI-E showed a significant increase in Hb (median 7.0 mmol/L, p < 0.001), the non-responders a stable Hb (median 5.1 mmol/L, p = 0.3661). Achievement of HI-E was significantly associated with improved OS (p = 0.02). Neutrophil response could be evaluated in 2 patients because the pre-treatment ANC was normal (ANC ≥ 1×10̂9/L) for the majority of the patients. One patient with pre-treatment ANC of 0.4×10̂9/L responded after 1 cycle (ANC 1.2×10̂9/L) and response was sustained for 11 cycles. Platelet response could be evaluated in 5 patients with pre-treatment platelets of Disclosures: No relevant conflicts of interest to declare.

Keratinocytes have been isolated from rabbit cornea, esophagus, and skin by trypsinization. The freshly isolated cells differed in their morphology, growth characteristics in culture, transglutaminase activity (a marker for differentiation), and the composition of glycoprotein-derived fucopeptides. A clear relationship has been shown between the proportion of low-molecular-weight fucopeptides and the pattern of keratinization, being minimal in cornea and maximal in skin. Comparison with earlier literature suggests that this relationship may be a general feature of epithelial tissue. After several passages in culture, all differences between the three cell types disappeared. The unusual elution pattern of the fucopeptides on gel filtration suggests the possibility of a block at an early stage of glycoprotein synthesis under culture conditions.