ALBERT

Description: Chimeric antigen receptor (CAR)19 T-cells exhibit powerful anti-leukemic effects in patients with B cell malignancies. However, the complexity of production of patient bespoke T cell products is a major barrier to the broader application of this approach. We are investigating a novel strategy to enable "off-the-shelf"' therapy with mismatched donor CAR19 T cells. Transcription activator-like effector nucleases (TALEN)s can be used to overcome HLA barriers by eliminating the risk of graft-versus-host disease (GvHD) through disruption of T cell receptor expression, and by simultaneously targeting CD52, cells can be rendered insensitive to the lymphodepleting agent Alemtuzumab. Administration of Alemtuzumab can then be exploited to prevent host-mediated rejection of HLA mismatched CAR19 T cells. We manufactured a bank of such cells from volunteer donor T cells under GMP conditions on behalf of Cellectis S.A for final stage validation studies using a third generation self inactivating lentiviral vector encoding a 4g7 CAR19 (CD19 scFv- 41BB- CD3ζ) linked to RQR8, an abbreviated sort/suicide gene encoding both CD34 and CD20 epitopes. Cells were then electroporated with two pairs of TALEN mRNA for multiplex targeting of both the T cell receptor alpha constant chain locus, and the CD52 gene locus. Following ex-vivo expansion, cells still expressing TCR were depleted using CliniMacs alpha/beta TCR depletion, yielding a T cell product with

Description: Background Adoptive transfer of therapeutic T cells targeting viral infection or tumour following allogeneic solid organ or hematopoietic stem cell transplantation is hindered by the requirement for immunosuppression. Recent reports have suggested the strategy of using genes encoding cyclophilin or FK506 mutants to confer resistance of T cells to calcineurin inhibitors (Brewin et al. Blood 2009;114:4792 & De Angelis et al. Blood 2009;114:4784). Mycophenolate mofetil (MMF) is another widely used immunosuppressant that acts as a non-competitive inhibitor of inosine-5’-monophosphate dehydrogenase 2 (IMPDH2), an inducible enzyme that generates guanine nucleotides for DNA and RNA synthesis in T cells. In this study, we used T cells transduced with mutated IMPDH2 that confers 〉2000-fold resistance to MMF (IMPDH2R; T333I, S351Y). Methods Genes encoding human IMPDH2R and IMPDH2CS(containing a catalytic site mutation, C331A) were cloned into SFG retroviral vectors as fusions to eGFP reporter sequences. T cells were transduced with either vector, transferred to recipient mice and evaluated in the presence or absence of MMF. Results IMPDH2R-transduced (td) murine and human T cells demonstrated a selective advantage to MMF in vitro by overcoming drug-induced G1-S phase cell cycle blockade (p=0.02, 55.0% IMPDH2R-td vs 25.6% IMPDH2CS-td cells in S phase) and preventing apoptosis (p=0.01, 22.5% vs. 39.3% Annexin V positive). Overexpression of the wild type IMPDH2 gene conferred intermediate protection against vector alone controls. To test for selection of IMPDH2R-td cells in vivo, sub-lethally irradiated (1.5-2Gy) B6.PL (Thy1.1) mice were injected with a 1:1 mix of OT-I TCR transgenic CD8 T cells transduced with IMPDH2R (CD45.1, Thy1.2) or IMPDH2CS (CD45.2, Thy1.2). Host mice received cognate peptide (SIINFEKL) in adjuvant or adjuvant alone, and no drug or MMF (200 μg/g/day) by daily ip injection. Compared to mice given adjuvant alone (spleen ratio IMPDH2R:IMPDH2CS= 1.1), selection of IMPDH2R-td T cells occurred with antigenic stimulation even in the absence of drug, indicating a moderate increase in overall proliferative/survival potential of these cells (ratio IMPDH2R:IMPDH2CS = 2.5, p=0.04). As predicted, in vivo selection of IMPDH2R-td T cells was significantly greater in the presence of MMF (ratio=7.8, drug v no drug, p=0.01). Unexpectedly, however, absolute numbers of IMPDH2R-td T cells in the spleen were actually greater in the presence of MMF rather than its absence indicating that drug resistance per se was not the sole explanation underlying the capacity of gene-modified cells to expand in vivo (27.3 x 105 MMF vs. 19.4 x 105 no MMF, p=0.01). Similarly, not only did IMPDH2R-td OT-I cells control EL4.OVA tumor in vivo better than IMPDH2CS-td OT-I cells in the presence of MMF (log rank p

Description: We identified all patients who developed blast crisis before the advent of imatinib therapy and in whom stored marrow samples were available from a database of CML patients in a major teaching hospital. mRNA was extracted and cDNA synthesized successfully in 20 of 22 cases. The cDNA was subjected to real time PCR for quantification of BCR-ABL transcripts. The ABL allele not involved in the t(9;22) translocation was excluded from mutational analysis by subjecting the cDNA to nested PCR. This was achieved by amplifying from exons 13 and 10 of the BCR and ABL moieties of the BCR-ABL fusion gene using primers B2A and JAMR, respectively. The resulting amplicon was then subjected to nested PCR using primers, NTPB+ and NTPE-, sited within exons 4 and 10 of the ABL gene. The nested PCR yielded an 863 bp fragment in length containing the entire BCR-ABL kinase domain. To test for successful amplification an aliquot of the PCR products were electrophoresed through 2.0% agarose gel. In all cases, a single amplicon was observed and the PCR reaction subjected to magnetic purification. The purified amplicon were then sequenced by Sanger’s dideoxy chain termination reaction using Big-Dye ABI 310 sequencer (Applied Biosystems, Foster City, USA). In each case, the sequence obtained was compared with the published ABL type 1a sequence, Genbank M14752, using Blast 2 software. No mutations were found in any patient. This suggests the absence of a mutated kinase in a proportion of greater than approximately 30% of the total BCR-ABL kinase, due to the limit of detection of the technique. Our results suggest that the predominant form of BCR-ABL in the setting of blast crisis (in the absence of imatinib) is wild type. This goes against theories that kinase mutations confer an intrinsic ‘gain of function’ or a proliferative advantage to a CML clone. Instead, it is likely that mutant forms of BCR-ABL which are relatively resistant to imatinib binding gain prominence through positive selection with the presence of imatinib within the cell milieu.

Description: We sought kinase domain (KD) mutations at the start of treatment with dasatinib in 46 chronic myeloid leukemia (CML) patients resistant to or intolerant of imatinib. We identified BCR-ABL mutant subclones in 12 (26%) cases and used pyrosequencing to estimate subsequent changes in their relative size after starting dasatinib. Four patients lost their mutations, which remained undetectable, 3 patients retained the original mutation or lost it only transiently, 3 lost their original mutations but acquired a new mutation (F317L), and 2 developed another mutation (T315I) in addition to the original mutation within the same subclone. This study shows that expansion of a mutant Ph-positive clone that responds initially to a second generation tyrosine kinase inhibitor may be due either to late acquisition of a second mutation in the originally mutated clone, such as the T315I, or to acquisition of a completely new mutant clone, such as F317L.

Description: Relapsed and refractory B-lineage acute lymphoblastic leukemia remain the leading cause of cancer related death in children and young adults. Clinical studies of adoptive cell immunotherapy, re-directing T cells against CD19 by endowing them with a chimeric antigen receptor (CAR), have shown considerable clinical responses. To date, 3 different binding domains (scFv) targeting CD19 have been used in CARs taken forward in clinical trials and we have constructed a new CD19-CAR, derived from a different anti-human CD19 antibody, clone CAT. Whether different binding affinities of the CD19 targeting domain, when significantly different, could affect CAR-mediated T cell functionality has not been evaluated in depth. We therefore investigated the impact of scFv affinity on CAR-mediated T cell function in vitro, as well as on anti-tumour efficacy in vivo. We have generated 3 CD19-CARs only differing in their scFv, which were derived from 3 anti-human CD19 antibodies (Clones FMC63, 4G7 & CAT) respectively. All other structural variables of the CAR and the use of the 4-1BB endodomain were identical. The Kd values obtained by Biacore Surface Plasmon resonance (SPR) analysis ranged from 8.8 x 10-10 to 1.1 x 10-7. Differences in affinity were predominantly determined by the off-rates, leading to significantly quicker dissociation from its target in CAT scFv compared to FMC63 and 4G7. CAT-CAR transduced T-cells showed enhanced cytotoxic responses to the CD19+ cell line SUPT1-CD19 in 51Cr release assays (p

Description: Abstract 3009 Background: Interactions between tumour cells and host cells within the microenvironment are important in promoting the development of cancer. Tumor niches provide crucial anti-apoptotic and anti-proliferative signals that drive tumor chemoresistance. The CXCR4-CXCL12 chemokine axis forms a critical component of this niche. CXCL12 produced by stromal cells has direct pro-survival effects upon tumor cells, promotes metastasis and recruits CXCR4-expressing regulatory T cell populations that block anti-tumour immunity. In this study, we have tested the hypothesis that targeting therapeutic T cells to CXCR4-dependent niches will improve eradication of tumours in mice. Methods: The murine CXCR4 gene was inserted into retroviral vector, pMP71. Murine T cells were transduced with CXCR4 or control vector and tested for homing in vitro to CXCL12 through chemotaxis assays. In vivo imaging of the putative endosteal bone marrow (BM) niche was performed by multiphoton imaging through cranial frontal bones in osteoblast (collagen 1-α-GFP) reporter mice. In vivo trafficking, competitive transfer and memory recall experiments were performed following transfer of transduced T cells to syngeneic, sub-lethally irradiated mice. Anti-tumour reactivity of CXCR4-transduced T cells was tested in models of allogeneic BM transplantation (BMT). Results: CXCR4-transduced T cells demonstrated enhanced migration towards CXCL12 in vitro. No differences in viability, phenotype or function were observed in CXCR4-transduced versus control T cells in the presence or absence of CXCL12. In competitive assays, CXCR4-transduced CD8 T cells demonstrated a 2-fold greater capacity than controls to home to the BM by 24h after transfer to sub-lethally-irradiated recipients. Multiphoton imaging through cranial frontal bones indicated that fluorescently labelled CXCR4-transduced T cells were closer than control cells to the endosteum (13 μm versus 17 μm, p

Description: Introduction: A recent phase I/II study of blinatumomab in children with relapsed/refractory B cell acute lymphoblastic leukaemia (B-ALL), found 39-51% achieved complete, often MRD negative, remission after two cycles of therapy. Higher responses were observed in patients with less than 50% bone marrow blasts, compared to greater than 50% (55.6% vs 32.7% (95% CI 30.8-78.5 and 20.3-47.1 respectively)1. Furthermore, an adult study showed complete minimal residual disease (MRD) response rates of 78% when blinatumomab was used to treat MRD-positive ALL in haematological remission 2. Hence response rates (and toxicity) to blinatumomab are highly correlated with pre-treatment disease burden. We present preliminary data showing an excellent response to blinatumomab in children and young adults with resistant B-ALL who had persistent MRD, or after debulking chemotherapy to achieve a partial remission. Methods: Eleven patients were identified through a national survey. The mean age of patients was 10 years (range 0.7-22 years, 3 infants and 1 Down syndrome ALL). All patients had B-lineage ALL which was CD19 positive. None had active CNS disease at the point of receiving blinatumomab. Prior to administration of blinatumomab, all patients either had persistent MRD following several courses of intensive chemotherapy or received debulking chemotherapy for heavier marrow infiltrates. Pre-blinatumomab chemotherapy to which the patients had failed to obtain an adequate MRD response included UKALL 2011 Regimens A or C, UKALL R3, Interfant 06 or NOPHO high risk blocks. Patients received 5-15 µg/m2 of blinatumomab for 1-2 cycles prior to definitive therapy. Results: Pre-blinatumomab, all patients except one were in morphological remission with MRD measurable by PCR (0.003-1%), the remaining patient had 9% marrow disease by morphology. After 1-2 cycles of blinatumomab all patients had negative MRD when measured by flow cytometry and/or by PCR, giving a 100% response rate. This was followed by Haemopoietic stem cell transplant (HSCT) in nine patients and the remaining two are awaiting transplant. Further data on patient characteristics, CNS status, relapse and survival outcome are being collected and will be presented at the meeting. Minimal toxicity was observed; of the seven patients in whom toxicity data were available, three had grade 1 CRS, which resolved spontaneously without interruption of therapy or treatment with corticosteroids or Tocilizumab. One patient reported grade 1 neurotoxicity. This preliminary UK experience demonstrates that excellent MRD response is observed with minimal toxicity in children and young adults who receive blinatumomab for persistent MRD or after debulking chemotherapy. This provided a bridge to transplant in patients who would otherwise not have benefited from the procedure because of persistent MRD. We are planning to extend these observations by undertaking a study of this strategy in first high-risk B-ALL relapse. Stackelberg Av, Locatelli F, Zugmaier G, et al. Phase I/Phase II Study of Blinatumomab in Pediatric Patients With Relapsed/Refractory Acute Lymphoblastic Leukemia. Journal of Clinical Oncology. 2016;34(36):4381-4389. Gokbuget N, Dombret H, Bonifacio M, et al. Blinatumomab for minimal residual disease in adults with B-cell precursor acute lymphoblastic leukemia. Blood. 2018;131(14):1522-1531. Disclosures Ghorashian: Celgene: Other: travel support; Novartis: Honoraria. Marks:Novartis: Consultancy; Pfizer: Consultancy; Amgen: Consultancy. Vora:Amgen: Other: Advisory board; Novartis: Other: Advisory board; Jazz: Other: Advisory board; Medac: Other: Advisory board; Pfizer: Other: Advisory board.

Description: Abstract 3152 Alloreactive immune responses directed against malignant cells in recipients of allogeneic hematopoietic stem cell transplants are able to cure patients with hematological cancers. However, such immune responses may cause severe morbidity when directed against healthy recipient tissue, resulting in graft-versus-host disease (GvHD). Naturally occurring regulatory T cells (Tregs) are CD4+ T cells characterized by their expression of the transcription factor Foxp3. Whilst adoptively transferred polyclonal Tregs suppress GvHD in several murine models, their lack of specificity may compromise beneficial immunity against malignancy or infection. The generation of MHC class I-restricted, alloantigen-specific Tregs would allow them to recognize antigen presented directly on GvHD target tissues, concentrating their sites of activation at these tissues and possibly reducing the potential for non-specific immune suppression. We have generated ‘converted’ Tregs through retroviral transfer of genes encoding Foxp3 and specific MHC class I-restricted T cell receptors (TCRs) into polyclonal conventional CD4+ T cells. We used the 2C-TCR, which recognizes the MHC class I molecule H-2Ld, expressed in Balb/c and other H-2d mice, in complex with the ubiquitously expressed peptide p2Ca; and the MH-TCR, which recognizes the MHC class I molecule H-2Db, expressed in B6 and other H-2b mice, in complex with the male peptide WMHHNMDLI. In vitro, Foxp3 2C-TCR-transduced B6 polyclonal CD4+ T cells were hyporesponsive to stimulation and suppressed the alloreactive proliferative response of B6 CD4+ and CD8+ T cells to Balb/c splenocytes, consistent with the acquisition of regulatory function. When adoptively transferred to lethally irradiated Balb/c recipients of MHC-mismatched B6 bone marrow and conventional T cells, Foxp3 2C-TCR-transduced B6 polyclonal CD4+ T cells significantly reduced early proliferation of donor T cells, weight loss and GvHD score in the recipients. Similarly, polyclonal CD4+ T cells transduced with Foxp3 and the MH-TCR caused marked suppression of allogeneic responses both in vitro and in vivo. However, while both the 2C-TCR and the MH-TCR conferred specificity to their cognate antigens in vitro, the potent suppression in these in vivo models was independent of the cognate antigen for the transduced TCRs. This non-specific suppression was markedly reduced when class I-restricted TCRs were transduced into OT-II Rag1-/- CD4+ T cells that are transgenic for a single endogenous TCR. These findings demonstrate an important role for the endogenous TCRs in driving non-specific suppression by polyclonal CD4+ T cells transduced with Foxp3 and class I-restricted TCRs, and suggest that strategies to downregulate endogenous TCRs will be required to achieve antigen-specific suppression in TCR gene-modified regulatory T cells. Disclosures: No relevant conflicts of interest to declare.

Description: Karl S Peggs and Sarah J Albon contributed equally to the work and are joint first author Introduction Alemtuzumab reduces the incidence of GVHD after unrelated donor stem cell transplant (MUD SCT) but delays immune reconstitution resulting in high morbidity/mortality from viral infections. Previous studies have suggested that adoptive transfer of allodepleted donor T cells (ADTs) improves immunity after SCT but this has never been tested in a randomised study. We developed a methodology for selective immunomagnetic depletion of alloreactive T-cells upregulating CD25 and CD71 after activation with host dendritic cells (DC) and showed that ADTs retain anti-viral responses with minimal host alloreactivity (Samarasinghe et al Blood 2010). We have now tested whether ADTs can safely be used to improve immune reconstitution after MUD SCT for haematological malignancies in a randomised Phase II multi-centre clinical study; ICAT (NCT01827579). Methods Patients undergoing Alemtuzumab-based peripheral blood SCT from a 9/10 or 10/10 MUD for haematological malignancy were randomised 2:1 to receive either the ATIMP (ADTs) or standard of care. Two weeks prior to SCT, patients randomised to ATIMP underwent a leucapheresis from which DCs were generated. Irradiated patient-derived DCs were then co-cultured with peripheral blood mononuclear cells (PBMC) from an unstimulated leucapheresis/500ml blood draw from the donor to activate alloreactive T cells. Four days later, the co-culture was depleted of CD25+ and CD71+ fractions by immunomagnetic depletion on the CliniMACs, sampled for residual alloreactivity and sterility, and cryopreserved. Patients randomised to the ATIMP were scheduled to receive 3 escalating doses of ADTs (0.1x106/Kg at day 30, 0.3x106/Kg at day 60 and 1x106/Kg at day 90 post-SCT) until either there was 〉grade 1 aGVHD or they had normal circulating T cells (〉700/µL). The primary end-point of the study was circulating CD3+ T cell count at 4 months post-SCT with one-sided 15% significance level. Acute/chronic GVHD were graded using the Seattle/NIH criteria respectively. Results Twenty one patients were treated, 13 on the ATIMP arm and 8 on the control arm. The median age was 53 years and 67% (14) were male. 12 were AML/Myelodysplasia, 5 NHL, 3 CLL/CML and 1 HL. The median follow-up time is 14 months. Five of 13 ATIMP patients received 1 dose of ADTs, 4/13 2 doses and 4/13 all 3 doses. The incidence of acute and chronic GVHD was comparable between the arms. Overall, 7/13 ATIMP patients developed significant (〉Grade 2) acute GVHD compared to 4/8 of the control arm (p〉0.99). 3/13 patients in the ATIMP arm and 2/8 patients in the control arm developed severe aGVHD (all Grade 3). Three of 13 ATIMP cohort patients developed chronic GVHD (1 mild, 1 moderate, 1 severe), compared to 3/8 (all mild) in the control cohort. At 4 months, the circulating CD3+ T cell count mean was 730/µL (range 10-4080) in the ATIMP group and 212.5/µL (range 10-500) in the control group (1-sided p=0.11). However, the data was not normally distributed (Wilcoxon 1-sided p=0.18). Three ATIMP patients had high CD3+ T cell count at 4 months (〉1000/µL). At 6 months, the mean circulating CD3+ T cell count was 833.6/µL (range 20-2690) and 327.5/µL (range 10-860). At month 4, the mean PHA stimulation index in the ATIMP arm was 16.8 (range 0.67- 73.1) vs 3.8 (range 1.1-8.2) in the control group. At 4 and 6 months post-SCT, spectratyping analysis showed no evidence of a difference in Vβ diversity between the 2 arms in both CD4+ and CD8+ cells. The 1-year survival rate in the ATIMP cohort is 92% vs 88% in the control, and 1-year disease free survival rate 67% in the ATIMP cohort vs 70% in the control. Conclusions These data suggest that adoptive transfer of ADTs improves T cell reconstitution in some patients after MUD SCT and that the GVHD rates were similar between ATIMP and control groups. Figure 1: Kinetics of T cell recovery after transplant in ATIMP (blue) and Control (red) patients. Mean +/- SEM shown. Figure 1 Disclosures Peggs: Gilead: Consultancy, Speakers Bureau; Autolus: Membership on an entity's Board of Directors or advisory committees. Ghorashian:UCLB: Patents & Royalties: UCLB; Celgene: Honoraria; novartis: Honoraria. Amrolia:UCLB: Patents & Royalties.