Competitive Repopulation and Allo-Immunologic Pressure Determine Chimerism Kinetics after T Cell-Depleted Allogeneic Stem Cell Transplantation and Donor Lymphocyte Infusion.

After allogeneic stem cell transplantation (alloSCT), patient-derived stem cells that survived the pretransplantation conditioning compete with engrafting donor stem cells for bone marrow (BM) repopulation. In addition, donor-derived alloreactive T cells present in the stem cell product may favor establishment of complete donor-derived hematopoiesis by eliminating patient-derived lymphohematopoietic cells. T cell-depleted alloSCT with sequential transfer of potentially alloreactive T cells by donor lymphocyte infusion (DLI) provides a unique opportunity to selectively study how competitive repopulation and allo-immunologic pressure influence lymphohematopoietic recovery. This study aimed to determine the relative contribution of competitive repopulation and donor-derived anti-recipient alloimmunologic pressure on the establishment of lymphohematopoietic chimerism after alloSCT. In this retrospective cohort study of 281 acute leukemia patients treated according to a protocol combining alemtuzumab-based T cell-depleted alloSCT with prophylactic DLI, we investigated engraftment and quantitative donor chimerism in the BM and immune cell subsets. DLI-induced increase of chimerism and development of graft-versus-host disease (GVHD) were analyzed as complementary indicators for donor-derived anti-recipient alloimmunologic pressure. Profound suppression of patient immune cells by conditioning sufficed for sustained engraftment without necessity for myeloablative conditioning or development of clinically significant GVHD. Although 61% of the patients without any DLI or GVHD showed full donor chimerism (FDC) in the BM at 6 months after alloSCT, only 24% showed FDC in the CD4+ T cell compartment. In contrast, 75% of the patients who had received DLI and 83% of the patients with clinically significant GVHD had FDC in this compartment. In addition, 72% of the patients with mixed hematopoiesis receiving DLI converted to complete donor-derived hematopoiesis, of whom only 34% developed clinically significant GVHD. Our data show that competitive repopulation can be sufficient to reach complete donor-derived hematopoiesis, but that some alloimmunologic pressure is needed for the establishment of a completely donor-derived T cell compartment, either by the development of GVHD or by administration of DLI. We illustrate that it is possible to separate the graft-versus-leukemia effect from GVHD, as conversion to durable complete donor-derived hematopoiesis following DLI did not require induction of clinically significant GVHD.

Effect of alemtuzumab-based T-cell depletion on graft compositional change in vitro and immune reconstitution early after allogeneic stem cell transplantation.

BACKGROUND AIMS: To reduce the risk of graft-versus-host disease (GVHD) after allogeneic stem cell transplantation (alloSCT), T-cell depletion (TCD) of grafts can be performed by the addition of alemtuzumab (ALT) "to the bag" (in vitro) before transplantation. In this prospective study, the authors analyzed the effect of in vitro incubation with 20 mg ALT on the composition of grafts prior to graft infusion. Furthermore, the authors assessed whether graft composition at the moment of infusion was predictive for T-cell reconstitution and development of GVHD early after TCD alloSCT. METHODS: Sixty granulocyte colony-stimulating factor-mobilized stem cell grafts were obtained from ≥9/10 HLA-matched related and unrelated donors. The composition of the grafts was analyzed by flow cytometry before and after in vitro incubation with ALT. T-cell reconstitution and incidence of severe GVHD were monitored until 12 weeks after transplantation. RESULTS: In vitro incubation of grafts with 20 mg ALT resulted in an initial median depletion efficiency of T-cell receptor (TCR) α/ß T cells of 96.7% (range, 63.5-99.8%), followed by subsequent depletion in vivo. Graft volumes and absolute leukocyte counts of grafts before the addition of ALT were not predictive for the efficiency of TCR α/ß T-cell depletion. CD4pos T cells were depleted more efficiently than CD8pos T cells, and naive and regulatory T cells were depleted more efficiently than memory and effector T cells. This differential depletion of T-cell subsets was in line with their reported differential CD52 expression. In vitro depletion efficiencies and absolute numbers of (naive) TCR α/ß T cells in the grafts after ALT incubation were not predictive for T-cell reconstitution or development of GVHD post- alloSCT. CONCLUSIONS: The addition of ALT to the bag is an easy, fast and generally applicable strategy to prevent GVHD in patients receiving alloSCT after myeloablative or non-myeloablative conditioning because of the efficient differential depletion of donor-derived lymphocytes and T cells.

HA-1H T-Cell Receptor Gene Transfer to Redirect Virus-Specific T Cells for Treatment of Hematological Malignancies After Allogeneic Stem Cell Transplantation: A Phase 1 Clinical Study.

Graft-vs.-leukemia (GVL) reactivity after HLA-matched allogeneic stem cell transplantation (alloSCT) is mainly mediated by donor T cells recognizing minor histocompatibility antigens (MiHA). If MiHA are targeted that are exclusively expressed on hematopoietic cells of recipient origin, selective GVL reactivity without severe graft-vs.-host-disease (GVHD) may occur. In this phase I study we explored HA-1H TCR gene transfer into T cells harvested from the HA-1H negative stem-cell donor to treat HA-1H positive HLA-A*02:01 positive patients with high-risk leukemia after alloSCT. HA-1H is a hematopoiesis-restricted MiHA presented in HLA-A*02:01. Since we previously demonstrated that donor-derived virus-specific T-cell infusions did not result in GVHD, we used donor-derived EBV and/or CMV-specific T-cells to be redirected by HA-1H TCR. EBV and/or CMV-specific T-cells were purified, retrovirally transduced with HA-1H TCR, and expanded. Validation experiments illustrated dual recognition of viral antigens and HA-1H by HA-1H TCR-engineered virus-specific T-cells. Release criteria included products containing more than 60% antigen-specific T-cells. Patients with high risk leukemia following T-cell depleted alloSCT in complete or partial remission were eligible. HA-1H TCR T-cells were infused 8 and 14 weeks after alloSCT without additional pre-conditioning chemotherapy. For 4/9 included patients no appropriate products could be made. Their donors were all CMV-negative, thereby restricting the production process to EBV-specific T-cells. For 5 patients a total of 10 products could be made meeting the release criteria containing 3-280 × 106 virus and/or HA-1H TCR T-cells. No infusion-related toxicity, delayed toxicity or GVHD occurred. One patient with relapsed AML at time of infusions died due to rapidly progressing disease. Four patients were in remission at time of infusion. Two patients died of infections during follow-up, not likely related to the infusion. Two patients are alive and well without GVHD. In 2 patients persistence of HA-1H TCR T-cells could be illustrated correlating with viral reactivation, but no overt in-vivo expansion of infused T-cells was observed. In conclusion, HA-1H TCR-redirected virus-specific T-cells could be made and safely infused in 5 patients with high-risk AML, but overall feasibility and efficacy was too low to warrant further clinical development using this strategy. New strategies will be explored using patient-derived donor T-cells isolated after transplantation transduced with HA-1H-specific TCR to be infused following immune conditioning.

A minority of T cells recognizing tumor-associated antigens presented in self-HLA can provoke antitumor reactivity.

Tumor-associated antigens (TAAs) are monomorphic self-antigens that are proposed as targets for immunotherapeutic approaches to treat malignancies. We investigated whether T cells with sufficient avidity to recognize naturally overexpressed self-antigens in the context of self-HLA can be found in the T-cell repertoire of healthy donors. Minor histocompatibility antigen (MiHA)-specific T cells were used as a model, as the influence of thymic selection on the T-cell repertoire directed against MiHA can be studied in both self (MiHApos donors) and non-self (MiHAneg donors) backgrounds. T-cell clones directed against the HLA*02:01-restricted MiHA HA-1H were isolated from HA-1Hneg/HLA-A*02:01pos and HA-1Hpos/HLA-A*02:01pos donors. Of the 16 unique HA-1H-specific T-cell clones, five T-cell clones derived from HA-1Hneg/HLA-A*02:01pos donors and one T-cell clone derived from an HA-1Hpos/HLA-A*02:01pos donor showed reactivity against HA-1Hpos target cells. In addition, in total, 663 T-cell clones (containing at least 91 unique clones expressing different T-cell receptors) directed against HLA*02:01-restricted peptides of TAA WT1-RMF, RHAMM-ILS, proteinase-3-VLQ, PRAME-VLD, and NY-eso-1-SLL were isolated from HLA-A*02:01pos donors. Only 3 PRAME-VLD-specific and one NY-eso-1-SLL-specific T-cell clone provoked interferon-γ production and/or cytolysis upon stimulation with HLA-A*02:01pos malignant cell lines (but not primary malignant samples) naturally overexpressing the TAA. These results show that self-HLA-restricted T cells specific for self-antigens such as MiHA in MiHApos donors and TAAs are present in peripheral blood of healthy individuals. However, clinical efficacy would require highly effective in vivo priming by peptide vaccination in the presence of proper adjuvants or in vitro expansion of the low numbers of self-antigen-specific T cells of sufficient avidity to recognize endogenously processed antigen.

What does cell therapy manufacturing cost? A framework and methodology to facilitate academic and other small-scale cell therapy manufacturing costings.

BACKGROUND AIMS: Recent technical and clinical advances with cell-based therapies (CBTs) hold great promise in the treatment of patients with rare diseases and those with high unmet medical need. Currently the majority of CBTs are developed and manufactured in specialized academic facilities. Due to small scale, unique characteristics and specific supply chain, CBT manufacturing is considered costly compared to more conventional medicinal products. As a result, biomedical researchers and clinicians are increasingly faced with cost considerations in CBT development. The objective of this research was to develop a costing framework and methodology for academic and other small-scale facilities that manufacture cell-based therapies. METHODS: We conducted an international multi-center costing study in four facilities in Europe using eight CBTs as case studies. This study includes costs from cell or tissue procurement to release of final product for clinical use. First, via interviews with research scientists, clinicians, biomedical scientists, pharmacists and technicians, we designed a high-level costing framework. Next, we developed a more detailed uniform methodology to allocate cost items. Costs were divided into steps (tissue procurement, manufacturing and fill-finish). The steps were each subdivided into cost categories (materials, equipment, personnel and facility), and each category was broken down into facility running (fixed) costs and operational (variable) costs. The methodology was tested via the case studies and validated in developer interviews. Costs are expressed in 2018 euros (€). RESULTS: The framework and methodology were applicable across facilities and proved sensitive to differences in product and facility characteristics. Case study cost estimates ranged between €23 033 and €190 799 Euros per batch, with batch yield varying between 1 and 88 doses. The cost estimations revealed hidden costs to developers and provided insights into cost drivers to help design manufacturing best practices. CONCLUSIONS: This framework and methodology provide step-by-step guidance to estimate manufacturing costs specifically for cell-based therapies manufactured in academic and other small-scale enterprises. The framework and methodology can be used to inform and plan cost-conscious strategies for CBTs.

Generation and infusion of multi-antigen-specific T cells to prevent complications early after T-cell depleted allogeneic stem cell transplantation-a phase I/II study.

Prophylactic infusion of selected donor T cells can be an effective method to restore specific immunity after T-cell-depleted allogeneic stem cell transplantation (TCD-alloSCT). In this phase I/II study, we aimed to reduce the risk of viral complications and disease relapses by administrating donor-derived CD8pos T cells directed against cytomegalovirus (CMV), Epstein-Barr virus (EBV) and adenovirus antigens, tumor-associated antigens (TAA) and minor histocompatibility antigens (MiHA). Twenty-seven of thirty-six screened HLA-A*02:01pos patients and their CMVpos and/or EBVpos donors were included. Using MHC-I-Streptamers, 27 T-cell products were generated containing a median of 5.2 × 106 cells. Twenty-four products were administered without infusion-related complications at a median of 58 days post alloSCT. No patients developed graft-versus-host disease during follow-up. Five patients showed disease progression without coinciding expansion of TAA/MiHA-specific T cells. Eight patients experienced CMV- and/or EBV-reactivations. Four of these reactivations were clinically relevant requiring antiviral treatment, of which two progressed to viral disease. All resolved ultimately. In 2/4 patients with EBV-reactivations and 6/8 patients with CMV-reactivations, viral loads were followed by the expansion of donor-derived virus target-antigen-specific T cells. In conclusion, generation of multi-antigen-specific T-cell products was feasible, infusions were well tolerated and expansion of target-antigen-specific T cells coinciding viral reactivations was illustrated in the majority of patients.

Loss of the GPI-anchor in B-lymphoblastic leukemia by epigenetic downregulation of PIGH expression.

Adult B-lymphoblastic leukemia (B-ALL) is a hematological malignancy characterized by genetic heterogeneity. Despite successful remission induction with classical chemotherapeutics and novel targeted agents, enduring remission is often hampered by disease relapse due to outgrowth of a pre-existing subclone resistant against the treatment. In this study, we show that small glycophosphatidylinositol (GPI)-anchor deficient CD52-negative B-cell populations are frequently present already at diagnosis in B-ALL patients, but not in patients suffering from other B-cell malignancies. We demonstrate that the GPI-anchor negative phenotype results from loss of mRNA expression of the PIGH gene, which is involved in the first step of GPI-anchor synthesis. Loss of PIGH mRNA expression within these B-ALL cells follows epigenetic silencing rather than gene mutation or deletion. The coinciding loss of CD52 membrane expression may contribute to the development of resistance to alemtuzumab (ALM) treatment in B-ALL patients resulting in the outgrowth of CD52-negative escape variants. Additional treatment with 5-aza-2'-deoxycytidine may restore expression of CD52 and revert ALM resistance.

High Mutation Frequency of the PIGA Gene in T Cells Results in Reconstitution of GPI Anchor-/CD52- T Cells That Can Give Early Immune Protection after Alemtuzumab-Based T Cell-Depleted Allogeneic Stem Cell Transplantation.

Alemtuzumab (ALM) is used for T cell depletion in the context of allogeneic hematopoietic stem cell transplantation (alloSCT) to prevent acute graft-versus-host disease and graft rejection. Following ALM-based T cell-depleted alloSCT, relatively rapid recovery of circulating T cells has been described, including T cells that lack membrane expression of the GPI-anchored ALM target Ag CD52. We show, in a cohort of 89 human recipients of an ALM-based T cell-depleted alloSCT graft, that early lymphocyte reconstitution always coincided with the presence of large populations of T cells lacking CD52 membrane expression. In contrast, loss of CD52 expression was not overt within B cells or NK cells. We show that loss of CD52 expression from the T cell membrane resulted from loss of GPI anchor expression caused by a highly polyclonal mutational landscape in the PIGA gene. This polyclonal mutational landscape in the PIGA gene was also found in CD52- T cells present at a low frequency in peripheral blood of healthy donors. Finally, we demonstrate that the GPI-/CD52- T cell populations that arise after ALM-based T cell-depleted alloSCT contain functional T cells directed against multiple viral targets that can play an important role in immune protection early after ALM-based T cell-depleted transplantation.

The simultaneous isolation of multiple high and low frequent T-cell populations from donor peripheral blood mononuclear cells using the major histocompatibility complex I-Streptamer isolation technology.

BACKGROUND: Adoptive transfer of donor-derived T cells can be applied to improve immune reconstitution in immune-compromised patients after allogeneic stem cell transplantation. The separation of beneficial T cells from potentially harmful T cells can be achieved by using the major histocompatibility complex (MHC) I-Streptamer isolation technology, which has proven its feasibility for the fast and pure isolation of T-cell populations with a single specificity. We have analyzed the feasibility of the simultaneous isolation of multiple antigen-specific T-cell populations in one procedure by combining different MHC I-Streptamers. METHODS: First, the effect of combining different amounts of MHC I-Streptamers used in the isolation procedure on the isolation efficacy of target antigen-specific T cells and on the number of off-target co-isolated contaminating cells was assessed. The feasibility of this approach was demonstrated in large-scale validation procedures targeting both high and low frequent T-cell populations using the Good Manufacturing Practice (GMP)-compliant CliniMACS Plus device. RESULTS: T-cell products targeting up to 24 different T-cell populations could be isolated in one, simultaneous MHC I-Streptamer procedure, by adjusting the amount of MHC I- Streptamers per target antigen-specific T-cell population. Concurrently, the co-isolation of potentially harmful contaminating T cells remained below our safety limit. This technology allows the reproducible isolation of high and low frequent T-cell populations. However, the expected therapeutic relevance of direct clinical application without in vitro expansion of these low frequent T-cell populations is questionable. DISCUSSION: This study provides a feasible, fast and safe method for the generation of highly personalized MHC I-Streptamer isolated T-cell products for adoptive immunotherapy.

CD4 Donor Lymphocyte Infusion Can Cause Conversion of Chimerism Without GVHD by Inducing Immune Responses Targeting Minor Histocompatibility Antigens in HLA Class II.

Under non-inflammatory conditions HLA class II is predominantly expressed on hematopoietic cells. Therefore, donor CD4 T-cells after allogeneic stem cell transplantation (alloSCT) may mediate graft-vs.-leukemia reactivity without graft-vs.-host disease (GVHD). We analyzed immune responses in four patients converting from mixed to full donor chimerism without developing GVHD upon purified CD4 donor lymphocyte infusion (DLI) from their HLA-identical sibling donor after T-cell depleted alloSCT. In vivo activated T-cells were clonally isolated after CD4 DLI. Of the alloreactive T-cell clones, 96% were CD4 positive, illustrating the dominant role of CD4 T-cells in the immune responses. We identified 9 minor histocompatibility antigens (MiHA) as targets for alloreactivity, of which 8 were novel HLA class II restricted MiHA. In all patients, MiHA specific CD4 T-cells were found that were capable to lyse hematopoietic cells and to recognize normal and malignant cells. No GVHD was induced in these patients. Skin fibroblasts forced to express HLA class II, were recognized by only two MiHA specific CD4 T-cell clones. Of the 7 clones that failed to recognize fibroblasts, two targeted MiHA were encoded by genes not expressed in fibroblasts, presentation of one MiHA was dependent on HLA-DO, which is absent in fibroblasts, and T-cells recognizing the remaining 4 MiHA had an avidity that was apparently too low to recognize fibroblasts, despite clear recognition of hematopoietic cells. In conclusion, purified CD4 DLI from HLA-identical sibling donors can induce conversion from mixed to full donor chimerism with graft-vs.-malignancy reactivity, but without GVHD, by targeting HLA class II restricted MiHA.

Rapid Generation of Marker-Free P. falciparum Fluorescent Reporter Lines Using Modified CRISPR/Cas9 Constructs and Selection Protocol.

The CRISPR/Cas9 system is a powerful genome editing technique employed in a wide variety of organisms including recently the human malaria parasite, P. falciparum. Here we report on further improvements to the CRISPR/Cas9 transfection constructs and selection protocol to more rapidly modify the P. falciparum genome and to introduce transgenes into the parasite genome without the inclusion of drug-selectable marker genes. This method was used to stably integrate the gene encoding GFP into the P. falciparum genome under the control of promoters of three different Plasmodium genes (calmodulin, gapdh and hsp70). These genes were selected as they are highly transcribed in blood stages. We show that the three reporter parasite lines generated in this study (GFP@cam, GFP@gapdh and GFP@hsp70) have in vitro blood stage growth kinetics and drug-sensitivity profiles comparable to the parental P. falciparum (NF54) wild-type line. Both asexual and sexual blood stages of the three reporter lines expressed GFP-fluorescence with GFP@hsp70 having the highest fluorescent intensity in schizont stages as shown by flow cytometry analysis of GFP-fluorescence intensity. The improved CRISPR/Cas9 constructs/protocol will aid in the rapid generation of transgenic and modified P. falciparum parasites, including those expressing different reporters proteins under different (stage specific) promoters.