Kevin G. Haworth

Multilineage polyclonal engraftment of Cal-1 gene-modified cells and in vivo selection after SHIV infection in a nonhuman primate model of AIDS

We have focused on gene therapy approaches to induce functional cure/remission of HIV-1 infection. Here, we evaluated the safety and efficacy of the clinical grade anti-HIV lentiviral vector, Cal-1, in pigtailed macaques (Macaca nemestrina). Cal-1 animals exhibit robust levels of gene marking in myeloid and lymphoid lineages without measurable adverse events, suggesting that Cal-1 transduction and autologous transplantation of hematopoietic stem cells are safe, and lead to long-term, multilineage engraftment following myeloablative conditioning. Ex vivo, CD4+ cells from transplanted animals undergo positive selection in the presence of simian/human immunodeficiency virus (SHIV). In vivo, Cal-1 gene-marked cells are evident in the peripheral blood and in HIV-relevant tissue sites such as the gastrointestinal tract. Positive selection for gene-marked cells is observed in blood and tissues following SHIV challenge, leading to maintenance of peripheral blood CD4+ T-cell counts in a normal range. Analysis of Cal-1 lentivirus integration sites confirms polyclonal engraftment of gene-marked cells. Following infection, a polyclonal, SHIV-resistant clonal repertoire is established. These findings offer strong preclinical evidence for safety and efficacy of Cal-1, present a new method for tracking protected cells over the course of virus-mediated selective pressure in vivo, and reveal previously unobserved dynamics of virus-dependent T-cell selection.

Semi-automated closed system manufacturing of lentivirus gene-modified haematopoietic stem cells for gene therapy

Haematopoietic stem cell (HSC) gene therapy has demonstrated potential to treat many diseases. However, current state of the art requires sophisticated ex vivo gene transfer in a dedicated Good Manufacturing Practices facility, limiting availability. An automated process would improve the availability and standardized manufacture of HSC gene therapy. Here, we develop a novel program for semi-automated cell isolation and culture equipment to permit complete benchtop generation of gene-modified CD34+ blood cell products for transplantation. These cell products meet current manufacturing quality standards for both mobilized leukapheresis and bone marrow, and reconstitute human haematopoiesis in immunocompromised mice. Importantly, nonhuman primate autologous gene-modified CD34+ cell products are capable of stable, polyclonal multilineage reconstitution with follow-up of more than 1 year. These data demonstrate proof of concept for point-of-care delivery of HSC gene therapy. Given the many target diseases for gene therapy, there is enormous potential for this approach to treat patients on a global scale.

Lack of viral control and development of combination antiretroviral therapy escape mutations in macaques after bone marrow transplantation.

Objective:We have previously demonstrated robust control of simian/human immunodeficiency virus (SHIV1157-ipd3N4) viremia following administration of combination antiretroviral therapy (cART) in pigtailed macaques. Here, we sought to determine the safety of hematopoietic stem cell transplantation (HSCT) in cART-suppressed and unsuppressed animals. Design:We compared disease progression in animals challenged with SHIV 100 days post-transplant, to controls that underwent transplant following SHIV challenge and stable cART-dependent viral suppression. Methods:SHIV viral load, cART levels, and anti-SHIV antibodies were measured longitudinally from plasma/serum from each animal. Flow cytometry was used to assess T-cell subset frequencies in peripheral blood and the gastrointestinal tract. Deep sequencing was used to identify cART resistance mutations. Results:In control animals, virus challenge induced transient peak viremia, viral set point, and durable suppression by cART. Subsequent HSCT was not associated with adverse events in these animals. Post-transplant animals were challenged during acute recovery following HSCT, and displayed sustained peak viremia and cART resistance. Although post-transplant animals had comparable plasma levels of antiretroviral drugs and showed no evidence of enhanced infection of myeloid subsets in the periphery, they exhibited a drastic reduction in virus-specific antibody production and decreased T-cell counts. Conclusions:These results suggest that virus challenge prior to complete transplant recovery impairs viral control and may promote drug resistance. These findings may also have implications for scheduled treatment interruption studies in patients on cART during post-HSCT recovery: premature scheduled treatment interruption could similarly result in lack of viral control and cART resistance.

CCR5-edited gene therapies for HIV cure: Closing the door to viral entry

Human immunodeficiency virus (HIV) was first reported and characterized more than three decades ago. Once thought of as a death sentence, HIV infection has become a chronically manageable disease. However, it is estimated that a staggering 0.8% of the worlds population is infected with HIV, with more than 1 million deaths reported in 2015 alone. Despite the development of effective anti-retroviral drugs, a permanent cure has only been documented in one patient to date. In 2007, an HIV-positive patient received a bone marrow transplant to treat his leukemia from an individual who was homozygous for a mutation in the CCR5 gene. This mutation, known as CCR5Δ32, prevents HIV replication by inhibiting the early stage of viral entry into cells, resulting in resistance to infection from the majority of HIV isolates. More than 10 years after his last dose of anti-retroviral therapy, the transplant recipient remains free of replication-competent virus. Multiple groups are now attempting to replicate this success through the use of other CCR5-negative donor cell sources. Additionally, developments in the use of lentiviral vectors and targeted nucleases have opened the doors of precision medicine and enabled new treatment methodologies to combat HIV infection through targeted ablation or down-regulation of CCR5 expression. Here, we review historical cases of CCR5-edited cell-based therapies, current clinical trials and future benefits and challenges associated with this technology.

A Combined In Vivo HSC Transduction/Selection Approach Results in Efficient and Stable Gene Expression in Peripheral Blood Cells in Mice

We recently reported on an in vivo hematopoietic stem cell (HSC) gene therapy approach. It involves the subcutaneous injections of G-CSF/AMD3100 to mobilize HSCs from the bone marrow into the peripheral blood stream and the intravenous injection of an integrating helper-dependent adenovirus vector system. HSCs transduced in the periphery homed back to the bone marrow, where they persisted long-term. However, high transgene marking rates found in primitive bone marrow HSCs were not reflected in peripheral blood cells. Here, we tested small-molecule drugs to achieve selective mobilization and transduction of HSCs. We found more efficient GFP marking in bone marrow HSCs but no increased marking in the peripheral blood cells. We then used an in vivo HSC chemo-selection based on a mutant of the O6-methylguanine-DNA methyltransferase (mgmtP140K) gene that confers resistance to O6-BG/BCNU and should give stably transduced HSCs a proliferation stimulus and allow for the selective survival and expansion of progeny cells. Short-term exposure of G-CSF/AMD3100-mobilized, in vivo-transduced mice to relatively low selection drug doses resulted in stable GFP expression in up to 80% of peripheral blood cells. Overall, the further improvement of our in vivo HSC transduction approach creates the basis for a simpler HSC gene therapy.

A distinct hematopoietic stem cell population for rapid multilineage engraftment in nonhuman primates

A population of hematopoietic stem cells with superior engraftment and repopulating abilities has been identified in nonhuman primates. Refining the gold standard CD34-positive hematopoietic cells are the gold standard for stem cell therapy and transplantation of stem cell–enriched grafts. However, most of the cells within this population will not contribute to engraftment. Using a robust nonhuman primate transplantation model, Radtke et al. identified a stem cell–enriched subpopulation of CD34-positive cells that was exclusively responsible for multilineage engraftment. The cell dose of this subpopulation correlated with neutrophil and platelet recovery and reliably predicted overall transplant success. The authors observed phenotypic and transcriptomic similarities between these cells and human hematopoietic cells with high engraftment and repopulating potential. These data suggest a refined subpopulation of CD34-positive cells for use in transplantation and gene therapy/editing approaches. Hematopoietic reconstitution after bone marrow transplantation is thought to be driven by committed multipotent progenitor cells followed by long-term engrafting hematopoietic stem cells (HSCs). We observed a population of early-engrafting cells displaying HSC-like behavior, which persisted long-term in vivo in an autologous myeloablative transplant model in nonhuman primates. To identify this population, we characterized the phenotype and function of defined nonhuman primate hematopoietic stem and progenitor cell (HSPC) subsets and compared these to human HSPCs. We demonstrated that the CD34+CD45RA−CD90+ cell phenotype is highly enriched for HSCs. This population fully supported rapid short-term recovery and robust multilineage hematopoiesis in the nonhuman primate transplant model and quantitatively predicted transplant success and time to neutrophil and platelet recovery. Application of this cell population has potential in the setting of HSC transplantation and gene therapy/editing approaches.

In Vivo Murine-Matured Human CD3+ Cells as a Preclinical Model for T Cell-Based Immunotherapies

Adoptive cellular immunotherapy is a promising and powerful method for the treatment of a broad range of malignant and infectious diseases. Although the concept of cellular immunotherapy was originally proposed in the 1990s, it has not seen successful clinical application until recent years. Despite significant progress in creating engineered receptors against both malignant and viral epitopes, no efficient preclinical animal models exist for rapidly testing and directly comparing these engineered receptors. The use of matured human T cells in mice usually leads to graft-versus-host disease (GvHD), which severely limits the effectiveness of such studies. Alternatively, adult apheresis CD34+ cells engraft in neonatal non-obese diabetic (NOD)-severe combined immunodeficiency (SCID)-common γ chain–/– (NSG) mice and lead to the development of CD3+ T cells in peripheral circulation. We demonstrate that these in vivo murine-matured autologous CD3+ T cells from humans (MATCH) can be collected from the mice, engineered with lentiviral vectors, reinfused into the mice, and detected in multiple lymphoid compartments at stable levels over 50 days after injection. Unlike autologous CD3+ cells collected from human donors, these MATCH mice did not exhibit GvHD after T cell administration. This novel mouse model offers the opportunity to screen different immunotherapy-based treatments in a preclinical setting.

HIV infection results in clonal expansions containing integrations within pathogenesis-related biological pathways

The genomic integration of HIV into cells results in long-term persistence of virally infected cell populations. This integration event acts as a heritable mark that can be tracked to monitor infected cells that persist over time. Previous reports have documented clonal expansion in people and have linked them to proto-oncogenes; however, their significance or contribution to the latent reservoir has remained unclear. Here, we demonstrate that a directed pattern of clonal expansion occurs in vivo, specifically in gene pathways important for viral replication and persistence. These biological processes include cellular division, transcriptional regulation, RNA processing, and posttranslational modification pathways. This indicates preferential expansion when integration events occur within genes or biological pathways beneficial for HIV replication and persistence. Additionally, these expansions occur quickly during unsuppressed viral replication in vivo, reinforcing the importance of early intervention for individuals to limit reservoir seeding of clonally expanded HIV-infected cells.

Novel lineage depletion preserves autologous blood stem cells for gene therapy of Fanconi anemia complementation group A

A hallmark of Fanconi anemia is accelerated decline in hematopoietic stem and progenitor cells (CD34 +) leading to bone marrow failure. Long-term treatment requires hematopoietic cell transplantation from an unaffected donor but is associated with potentially severe side-effects. Gene therapy to correct the genetic defect in the patient’s own CD34+ cells has been limited by low CD34+ cell numbers and viability. Here we demonstrate an altered ratio of CD34Hi to CD34Lo cells in Fanconi patients relative to healthy donors, with exclusive in vitro repopulating ability in only CD34Hi cells, underscoring a need for novel strategies to preserve limited CD34+ cells. To address this need, we developed a clinical protocol to deplete lineage+(CD3+, CD14+, CD16+ and CD19+) cells from blood and marrow products. This process depletes >90% of lineage+cells while retaining ≥60% of the initial CD34+cell fraction, reduces total nucleated cells by 1–2 logs, and maintains transduction efficiency and cell viability following gene transfer. Importantly, transduced lineage− cell products engrafted equivalently to that of purified CD34+ cells from the same donor when xenotransplanted at matched CD34+ cell doses. This novel selection strategy has been approved by the regulatory agencies in a gene therapy study for Fanconi anemia patients (NCI Clinical Trial Reporting Program Registry ID NCI-2011-00202; clinicaltrials.gov identifier: 01331018).

Engineering resistance to CD33-targeted immunotherapy in normal hematopoiesis by CRISPR/Cas9-deletion of CD33 exon 2

CD33 has long been pursued as immunotherapeutic target in acute myeloid leukemia (AML) [1, 2]. Improved survival with gemtuzumab ozogamicin (GO) validates this approach [3]. Partly stimulated by GO’s success, several investigational CD33-directed therapeutics are currently in clinical testing [4]. However, CD33 expression on normal hematopoietic cells leads to “on-target, off-leukemia” toxicity with significant morbidity/mortality from profound cytopenias, limiting the use of CD33-directed immunotherapies [4]. This toxicity should be minimal if normal blood cells did not express the epitope targeted by these antibodies. Supporting the feasibility of CD33-engineering the hematopoietic system are the findings that CD33-deficient mice have a very mild phenotype and show no difference in cellular response to pro-inflammatory stimuli compared to wild-type animals, indicating functional degeneracy between CD33 and other proteins [5]. Moreover, recent studies have shown that CRISPR/Cas9-mediated disruption of the CD33 coding region in CD34+ hematopoietic stem and progenitor cells (HSPCs) may not affect engraftment [6], suggesting that the generation of CD33-manipulated hematopoiesis is a clinically viable strategy to protect from “off-leukemia” cell toxicity of CD33-directed immunotherapy. Here we have investigated an alternative, precise CD33 genome-editing approach that would only eliminate exon 2 and therefore the V-set immunoglobulin-like domain, which is the target of all current clinical CD33directed approaches. Our editing strategy is expected to result in expression of a naturally occurring shorter isoform of CD33 (CD33) but not full-length CD33 (CD33), which may minimize potential adverse effects associated with disruption of the entire CD33 locus. We used CRISPR/ Cas9 [7–10] to accomplish this goal and functionally assessed genome-edited human hematopoietic cells in vitro and in immunodeficient mice. Human myeloid ML-1 cells and human fetal liver CD34 + HSPCs were used for our studies. ML-1 cells were maintained as described [11]. Human fetal liver CD34+ cells were enriched by immunomagnetic separation from tissue obtained from Advance Bioscience Resources Inc. (ABR, Alameda, CA). Cells were cultured in StemSpan SFEMII media (StemCell Technologies, Cambridge, WA) supplemented with penicillin/streptomycin (Life Technologies, Carlsbad, CA), Stem cell factor , Thrombopoietin (both PeproTech, Rocky Hill, NJ), and FLT3-L (Miltenyi Biotec, Auburn, CA). CRISPR/Cas9-editing was carried out by electroporation of purified Cas9 protein (TrueCut Cas9 V2; ThermoFisher Scientific, Waltham, MA) complexed with synthetic guide RNAs (sgRNAs; Supplementary Table 1), which were modified at the 5′ and 3′ ends with 2′O-methyl-3′-phosphorothiate (Synthego, Redwood City, CA) using the ECM 380 Square Wave Electroporation system (Harvard Apparatus, Cambridge, MA) [12]. For evaluation of colony-forming units (CFUs), 1500 CD34+ cells were seeded in 3.5 mL ColonyGEL 1402 (ReachBio, Seattle, WA) and scored after 12–14 days. CFU DNA was extracted in QuickExtract (Epicentre, Madison, WI). We quantified drug-induced cytotoxicity as described previously [11, 13]. Briefly, parental and CRISPRengineered ML-1 cells were incubated in 96-well round These authors contributed equally: Olivier Humbert, George S. Laszlo and Hans-Peter Kiem, Roland B. Walter