Search

Severe Combined Immunodeficiencies (SCID) are defined by a complete absence of T lymphocytes in the blood and lymphoid organs, with variable defects in other WBC subsets depending on the gene defect. From a clinical perspective SCIDs are characterized by early development of life-threatening infections accounting for early death if untreated. The treatment of choice is allogeneic HSCT with very high success rates if a HLA identical sibling (MRD) or unrelated donor (MUD) is used. However, due to the scarcity of matched-related donors, SCID can benefit from haploidentical HSCT. In contrast to the continuous improvement of HLA compatible donor transplantations, no significant improvements have been obtained over the last twenty years for haploidentical HSCT. The profound immunodeficiency during the first months following haploidentical HSCT exposes patients to opportunistic viral, bacterial and fungal infections, which account for approximately 30-40% of the transplant related mortality (TRM). The rapid restoration of the T-cell compartment is the main aim of stem cell therapy in this setting. To this end we have recently set up a phase I/II clinical trial (ClinicalTrials.gov Identifier: NCT03879876) aiming to accelerate the immune reconstitution by injection of ex vivo generated Human T lymphoid progenitors (ProTcell TM) following haploidentical HSCT. T cell progenitors in this trial are generated in vitro within 7 days from mobilized peripheral blood (mPB) CD34 + hematopoietic stem and precursor cells (HSPCs) using our Notch ligand Delta-like 4 GMP culture platform so called SMART Immune's SMART101 product. This open-label, non-randomized study evaluates safety and efficacy of the SMART101 injection following CD34 + selected, haploidentical HSCT in SCID patients and is designed as a dose-escalation study comprising 6 doses of the SMART101 product obtained from the patient's haploidentical stem cell graft. The aim of this protocol is to define the highest efficacy dose without any toxicity. The conditioning regimen is based on Busulfan and Fludarabine according to IE-WP/EBMT guidelines with upfront administration of ATG to prevent graft rejection. Tight monitoring of ATG serum levels is applied in order to assure injection of SMART101 when ATG is below the lymphotoxicity threshold. Here we report the results of the first two SCID patients. P1 presented a homozygous Artemis deficiency. At diagnosis he had an ALC of 341/µl, with complete absence of T cells (CD3 + < 4/µl, CD4 + < 1/µl, CD8 + < 2/µl) and B cells (CD19 + 0/µl). NK cells were present in the normal range for age (CD16 +CD56 + 331/µl). In the absence of an HLA compatible donor, the patient`s father was chosen as haploidentical stem cell donor. P1 received upfront ATG (5 mg /kg total dose), Busulfan (AUC of 16058 microM.min) and Fludarabine (160 mg/m²). He received Defibrotide prophylaxis from D0 until D+21, as well as Ursodeoxycholic acid until D+80. The CD34 + immunoselected graft contained 1.04 x 10 8 nucleated cells/kg with 24.15 x10 6 CD34 + cells/kg and 4000 CD3 + cells/kg on D0. After ATG monitoring 0.12x10 6 Smart101 cells were administered at D+14 post- HSCT. In the follow-up P1 didn't develop any acute or chronic SAEs, no acute or chronic GVHD, and no infection. He was discharged at D+121 post HSCT. The day +100 post transplantation CD4 + cell count/microliter exceeded 10 times the CD4 + count of our historical cohort of RAG1/2 or Artemis deficient patients transplanted with haploidentical HSCT alone following the same conditioning regimen. At 6 months post HSCT this difference remains important (851 versus 300 CD4 + cells/µl); Ig replacement therapy could be stopped as early as 9 months post transplantation and vaccinations have been started. At last follow up; almost 14 months post HSCT P1 is alive and well. P2 had an undefined molecular SCID diagnosis. She has been treated with the same conditioning regimen and received the second dose of 0.2x10 6 CD7 + cells, but unfortunately died from severe VOD emphasizing the need to replace chemotherapy with less toxic myeloablative agents. The preliminary results obtained after injection of Human T lymphoid progenitors in P1 are encouraging. While deserving confirmation in larger numbers of patients they could represent an important step forward in improving the outcome of haploidentical HSCT for SCID. Disclosures Cavazzana: Smart Immune: Other: co-founder.

Patients with mutations in UNC13D gene, coding for Munc13-4 protein, suffer from type 3 Familial hemophagocytic lymphohistiocytosis (FHL3), a life-threatening disorder of the immune system which represents 25% of all FHLs. Munc13-4 controls docking of lytic granules before they fused with the plasma membrane in cytotoxic T and NK lymphocytes and it's defect results in defective cytotoxic function of these cells. Hematopoietic stem and progenitor cell (HSPC) transplantation, which is the only curative treatment for FHL3 to date, is partially successful even when a compatible donor is available because of the important inflammatory background of patients. In this context gene therapy could be a promising therapeutic option especially for those patients without any compatible donor. In this study, we took advantages from a murine model of FHL3, the Jinx mice, to investigate the feasibility of HSPC gene therapy for this pathology. Jinx mice do not spontaneously develop clinical features of hemophagocytic lymphohistiocytosis (HLH), but do so when infected with lymphocytic choriomeningitis virus (LCMV). We generated and used a self-inactivated lentiviral vector to complement HSC from Unc13d -/- (Jinx) mice and transplanted them back into the irradiated Jinx recipients. This transplantation led to the complete reconstitution of the immune system at levels comparable to that of control mice. The recipients were then challenged with LCMV. While Jinx mice reconstituted with GFP expressing HSPC developed leukopenia, anemia and body weight loss, characteristic of HLH in this murine model, gene corrected Jinx recipients developed only mild or no HLH manifestations. This reduction in HLH manifestation correlated with a significant reduction of virus titer in the liver and serum level of IFN-g and inflammatory cytokines. All these ameliorations might be explained by the restoration of cytotoxic function of CTLs as demonstrated in an in-vitro degranulation assay. Overall, this study provides data supporting the potential of HSC gene therapy in a FHL immune dysregulation such as UNC13D deficiency.

Patients with mutations in UNC13D gene, coding for Munc13-4 protein, suffer from type 3 Familial hemophagocytic lymphohistiocytosis (FHL3), a life-threatening disorder of the immune system. Munc13-4 controls docking of lytic granules before they fused with the plasma membrane in cytotoxic T and NK lymphocytes and it's defect results in defective cytotoxic function of these cells. Hematopoietic stem and progenitor cell (HSPC) transplantation, which is the only curative treatment for FHL3 to date, is partially successful even when a compatible donor is available because of the important inflammatory background of patients. In this context gene therapy could be a promising therapeutic option especially for those patients without any compatible donor. As Munc13-4's function is to allow proper cytotoxic activity in mature cytotoxic CD8+ T cells we proposed that these laters may constitute target for gene correction. We constructed a self-inactivating HIV-1 derived lentiviral vector encoding human Munc13-4 in two different pseudotypes, the high tropism VSV-G and the measles virus glycoproteins (H/F) envelope which target more efficiently lymphoid cells through the signaling lymphocyte activation molecule (SLAM) as described by Verhoeyen et al. 2011. We demonstrated that both vectors are able to stably transduce FHL3 CD8+ T cells resulting in correction of defective degranulation capacity of these cells. However comparative analysis showed that H/F pseudotyped vector was more efficient than VSV-G vector to transduce FHL3 T cells. Adoptive transfer of the gene-corrected FHL3 T cells in SCID mice bearing autologous B-LCL lymphoma led to significant tumor regression due to an efficient homing into the tumor mass and long persistence of corrected T cells in peripheral blood as compared to non-corrected T cells receiving mice. Our study shows for the first time that a lentiviral mediating gene transfer in T cells could be proposed to treat a hemophagocytic lymphohistiocytosis disorder.