We generated a novel CD19CAR (CAT) with a lower affinity than FMC63, the binder utilised in many clinical studies. CAT CAR T cells showed increased proliferation/cytotoxicity in vitro and enhanced proliferative capacity and anti-tumor activity than FMC63 CAR T cells in a xenograft model. In a clinical study (CARPALL, NCT02443831), 12/14 patients with relapsed/refractory pediatric BALL obtained molecular remission after CAT CAR T cell therapy. CAR T cell expansion compared favourably with published data on other CD19CARs and persistence was demonstrated in 11 of 14 patients at last follow-up. Toxicity was low with no severe cytokine release syndrome. At a median follow up of 14 months, 5/14 patients (37%) remain in molecular CR with circulating CAR T cells.

Genome editing of allogeneic T cells can provide “off-the-shelf” alternatives to autologous chimeric antigen receptor (CAR) T cell therapies. Disruption of T cell receptor α chain (TRAC) to prevent graft-versus-host disease (GVHD) and removal of CD52 (cluster of differentiation 52) for a survival advantage in the presence of alemtuzumab have previously been investigated using transcription activator–like effector nuclease (TALEN)-mediated knockout. Here, we deployed next-generation CRISPR-Cas9 editing and linked CAR expression to multiplexed DNA editing of TRAC and CD52 through incorporation of self-duplicating CRISPR guide RNA expression cassettes within the 3’ long terminal repeat of a CAR19 lentiviral vector. Three cell banks of TT52CAR19 T cells were generated and cryopreserved. A phase 1, open-label, non-randomized clinical trial was conducted and treated six children with relapsed/refractory CD19-positive B cell acute lymphoblastic leukemia (B-ALL) (NCT04557436). Lymphodepletion included fludarabine, cyclophosphamide, and alemtuzumab and was followed by a single infusion of 0.8 × 10 6 to 2.0 × 10 6 CAR19 T cells per kilogram with no immediate toxicities. Four of six patients infused with TT52CAR19 T cells exhibited cell expansion, achieved flow cytometric remission, and then proceeded to receive allogeneic stem cell transplantation. Two patients required biological intervention for grade II cytokine release syndrome, one patient developed transient grade IV neurotoxicity, and one patient developed skin GVHD, which resolved after transplant conditioning. Other complications were within expectations, and primary safety objectives were met. This study provides a demonstration of the feasibility, safety, and therapeutic potential of CRISPR-engineered immunotherapy.

Treosulfan is given off‐label in pediatric allogeneic hematopoietic stem cell transplant. This study investigated treosulfan's pharmacokinetics (PKs), efficacy, and safety in a prospective trial. Pediatric patients ( n = 87) receiving treosulfan‐fludarabine conditioning were followed for at least 1 year posttransplant. PKs were described with a two‐compartment model. During follow‐up, 11 of 87 patients died and 12 of 87 patients had low engraftment (≤ 20% myeloid chimerism). For each increase in treosulfan area under the curve from zero to infinity (AUC (0‐∞) ) of 1,000 mg hour/L the hazard ratio (95% confidence interval) for mortality increase was 1.46 (1.23–1.74), and the hazard ratio for low engraftment was 0.61 (0.36–1.04). A cumulative AUC (0‐∞) of 4,800 mg hour/L maximized the probability of success (> 20% engraftment and no mortality) at 82%. Probability of success with AUC (0‐∞) between 80% and 125% of this target were 78% and 79%. Measuring PK at the first dose and individualizing the third dose may be required in nonmalignant disease.

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Summary Viral respiratory infections (VRIs) contribute to the morbidity and transplant‐related mortality (TRM) after allogeneic haematopoietic stem cell transplantation (HSCT) and strategies to prevent and treat VRIs are warranted. We monitored VRIs before and after transplant in children undergoing allogeneic HSCT with nasopharyngeal aspirates (NPA) and assessed the impact on clinical outcome. Between 2007 and 2017, 585 children underwent 620 allogeneic HSCT procedures. Out of 75 patients with a positive NPA screen (12%), transplant was delayed in 25 cases (33%), while 53 children started conditioning with a VRI. Patients undergoing HSCT with a positive NPA screen had a significantly lower overall survival (54% vs. 79%) and increased TRM (26% vs. 7%) compared to patients with a negative NPA. Patients with a positive NPA who delayed transplant and cleared the virus before conditioning had improved overall survival (90%) and lower TRM (5%). Pre‐HSCT positive NPA was the only significant risk factor for progression to a lower respiratory tract infection and was a major risk factor for TRM. Transplant delay, whenever feasible, in case of a positive NPA screen for VRIs can positively impact on survival of children undergoing HSCT.

Juvenile idiopathic arthritis (JIA) is a heterogeneous condition and therapeutic strategies vary in different JIA types. The routinely accepted practice to start with Sulphasalazine (SS) as the first line treatment in patients with HLA B27 positive JIA proves to be ineffective in a large proportion of children.Objectiveto investigate HLA B27 positive JIA patients clinical characteristics, determined HLA B27 allele types and their connection with antirheumatic treatment in homogenous patient groups.Materials and methods56 patients diagnosed with JIA and observed over the period 2006 to 2009 included in the study. HLAB27 allele types were determined using PCR method.ResultsIn HLA B27 positive JIA patients mean disease onset was 12.34 ± 3.3 years. Most common (44%) JIA type was enthesitis related arthritis. Positive response to the treatment with SS was found in 32% of patients, Methotrexate (MTX) - in 43%, combined treatment - SS with MTX was effective in 12.5%. 12.5% of patients required combination MTX with Enbrel.Eight HLA B27 allele types were found in JIA patients in Latvia: *2702, *2703, *2704, *2705, *2710, *2715, *2717, *2728. The most common was *2705 - in 55% of cases. Among all the patients enthesitis related arthritis most commonly occurred in patients with HLAB*2705 allele (OR = 2.01, p < 0.02), oligoarthritis in patients with *2710 allele (OR = 3.0, p < 0.04) and polyarthritis with *2717 allele (OR = 3.0, p < 0.05). In patients with *2705 allele effective treatment was MTX (OR = 1.13, p < 0.03) and MTX with SS (OR = 2.02, p < 0.05), but in patients having *2703 allele - MTX with Enbrel (OR = 2.94, p < 0.02).ConclusionsThere are 8 different HLA B27 alleles in JIA patients in Latvia and the most common is *2705, but in order to assert them to be disease associated alleles, more extensive studies are needed, including control group of HLA B27 positive healthy individuals. Standard treatment approach with SS proves to be unsatisfactory in the majority of JIA patients. To improve children's quality of life achieving rapid disease control, the first line treatment in HLA B27 positive patients should be MTX. In order to start with the most appropriate drug it is necessary to determine HLAB 27 type at the onset of disease.

Introduction: The CARPALL study (NCT02443831) employed a novel CD19CAR (CAT-41BBz CAR) with a faster off rate than the Kymriah FMC63-41BBz CAR (CAT 3.1x10-3s-1, FMC 6.8 x 10-5s-1), with equivalent on-rate (CAT 2.2 x 105, FMC 2.1 x 105). We herein report updated outcomes and CAR T cell persistence with an additional 6 months follow up from a submitted manuscript (Ghorashian et al., Nat Med, submitted) Methods: Patients aged &lt;25 years with high risk, relapsed CD19+ B-ALL were eligible on this multi-centre, open label, non-randomised phase I study of autologous CAT-41BBz CAR T cells. Patients were followed to a data cut-off of 07/18/2019. CAT-41BBz CAR T cells were generated by magnetic bead activation of leucapheresed PBMCs, lentiviral transduction, followed by bioreactor expansion and magnetic bead removal prior to cryopreservation. All patients received lymphodepletion (fludarabine + cyclophosphamide) followed by 1x106/kg CAR T cells. Presence of CAR T cells in the blood and bone marrow (BM) was assessed (flow cytometry and qPCR) monthly for 6 months, then 6 weekly to 1 year and then 3 monthly. BM MRD was assessed (IgH qPCR, flow cytometry) at the same time-points up to 2 years to establish durability of responses as a stand-alone therapy. Primary end-points were incidence of grade 3-5 toxicity and the proportion of patients achieving molecular remission. Results: Of 17 patients recruited, 14 were treated due to manufacturing failure in 3 patients.The median age was 9 years (range 1-19 years). All patients had advanced ALL with a median of 4 prior therapy lines. 10 of 14 patients (71%) had relapsed post allogeneic SCT. Prior to lymphodepletion, 4 patients had &gt;5% BM disease, 6 had disease between 5x10-2and 1x10-5, 4 were BM MRD negative having had recurrent isolated CNS disease. Median transduction efficiency was 31% (range 16.5 to 96.4%). 12/14 treated patients received the anticipated dose of 1x106CAR T cells/kg (2 received 0.9x106/kg). Considering all evaluable patients, (n=14 for CAR T cell persistence by qPCR, n=13 by flow) the geometric mean of Cmax was 128 912/µg DNA and of the area under the curve between D0 and D28 was 1,721,355 copies/ µg DNA (Table 1). At the point of maximal expansion, a median of 35% of circulating T cells were CAR+. Median half-life was 34 days (range 3-102). CAR T cells continued to be detectable by qPCR in 11 of 14 (79%) patients at last assessment and by flow cytometry up to 30 months post infusion in 8 of 13(61%). Median duration of CAR T persistence by flow was 261 days (range 7-917). 3 patients failed to have persistence of CAR T cells beyond 1 month. T cell mediated anti-CAR specific cytotoxic activity was detected in 2/2 evaluable patients. Updated persistence data will be presented at the meeting Cytokine release syndrome (CRS) occurred in 13 (93%, grade 1 n=9, grade 2 n=4). None developed ≥grade 3 CRS, had CRS-related ICU admission, or received Tocilizumab. CRS was associated with modest elevations of IL-6, IFN-γand IL-10. Grade 2 neurotoxicity was observed in 3 patients and resolved spontaneously. One patient had grade 4 leucoencephalopathy presumed due to chemotherapy as well as grade 5 sepsis. Ten patients (71%) had grade 3-4 cytopenia persisting beyond day 28 or recurring afterthis. 12/14 (86%) patients achieved molecular complete or continuing complete remission at a median of 30 days post infusion (range 30-90 days, Table 2). At a median follow-up of 20.3 months, 4/14 (29%) evaluable patients remain MRD negative. 5 relapsed with CD19-disease, 1 with CD19+ disease. The median duration of EFS (based on death or morphological relapse) has not been reached, 12 month EFS = 52%, OS = 70% (Figures 1, 2 and Table 3). Conclusion: We noted excellent CAR T cell expansion and persistence in a ALL cohort treated with the fast off-rate CAT-41BBz CAR despite their lower BM disease at treatment compared to other studies. The kinetics documented for all evaluable patients showed a 5-fold greater CAR T cell expansion and 2-fold longer half-life than responders in published series utilising tisagenlecleucel in a similar ALL cohort (Mueller et al., Blood 2017). Patients had a favourable toxicity profile with no severe (grade 3-4) CRS and equivalent disease outcomes to the ELIANA study despite having similarly advanced disease (Maude et al., NEJM 2018292). These data suggest long lived CAR T cell persistence supports stand-alone therapy for ALL with durable responses. Disclosures Ghorashian: Celgene: Honoraria; novartis: Honoraria; UCLB: Patents & Royalties: UCLB. Kramer:UCLB: Patents & Royalties. Ciocarlie:Servier: Other: Financial Support. Farzaneh:Autolus Ltd: Equity Ownership, Research Funding. Pule:Autolus: Employment, Equity Ownership, Patents & Royalties. Amrolia:UCLB: Patents & Royalties.