Flotetuzumab and other T-cell immunotherapies upregulate MHC class II expression on acute myeloid leukemia cells.

Acute myeloid leukemia (AML) relapse is one of the most common and significant adverse events following allogeneic hematopoietic cell transplantation (HCT). Downregulation of major histocompatibility class II (MHC-II) surface expression on AML blasts may represent a mechanism of escape from the graft-versus-malignancy effect and facilitate relapse. We hypothesized that T-cell immunotherapies targeting AML antigens would upregulate MHC-II surface expression via localized release of interferon gamma (IFN-γ), a protein known to upregulate MHC-II expression via JAK-STAT signaling. We demonstrate that flotetuzumab (FLZ), a CD123 × CD3 bispecific DART molecule, and chimeric antigen receptor expressing T cells targeting CD123, CD33, or CD371 upregulate MHC-II surface expression in vitro on a THP-1 AML cell line with intermediate MHC-II expression and 4 primary AML samples from patients relapsing after HCT with low MHC-II expression. We additionally show that FLZ upregulates MHC-II expression in a patient-derived xenograft model and in patients with relapsed or refractory AML who were treated with FLZ in a clinical trial. Finally, we report that FLZ-induced MHC-II upregulation is mediated by IFN-γ. In conclusion, we provide evidence that T-cell immunotherapies targeting relapsed AML can kill AML via both MHC-independent mechanisms and by an MHC-dependent mechanism through local release of IFN-γ and subsequent upregulation of MHC-II expression.

The tetraspanin CD53 protects stressed hematopoietic stem cells via promotion of DREAM complex-mediated quiescence.

The hematopoietic stem cell (HSC) cycle responds to inflammatory and other proliferative stressors; however, these cells must quickly return to quiescence to avoid exhaustion and maintain their functional integrity. The mechanisms that regulate this return to quiescence are not well understood. Here, we show that tetraspanin CD53 is markedly upregulated in HSCs in response to a variety of inflammatory and proliferative stimuli and that the loss of CD53 is associated with prolonged cycling and reduced HSC function in the context of inflammatory stress. Mechanistically, CD53 promotes the activity of the dimerization partner, RB-like, E2F, and multi-vulva class B (DREAM) transcriptional repressor complex, which downregulates genes associated with cycling and division. Proximity labeling and confocal fluorescence microscopy studies showed that CD53 interacts with DREAM-associated proteins, specifically promoting the interaction between Rbl2/p130 and its phosphatase protein phosphatase 2A (PP2A), effectively stabilizing p130 protein availability for DREAM binding. Together, these data identified a novel mechanism by which stressed HSCs resist cycling.

Immunosuppression and outcomes in adult patients with de novo acute myeloid leukemia with normal karyotypes.

Acute myeloid leukemia (AML) patients rarely have long first remissions (LFRs; >5 y) after standard-of-care chemotherapy, unless classified as favorable risk at presentation. Identification of the mechanisms responsible for long vs. more typical, standard remissions may help to define prognostic determinants for chemotherapy responses. Using exome sequencing, RNA-sequencing, and functional immunologic studies, we characterized 28 normal karyotype (NK)-AML patients with >5 y first remissions after chemotherapy (LFRs) and compared them to a well-matched group of 31 NK-AML patients who relapsed within 2 y (standard first remissions [SFRs]). Our combined analyses indicated that genetic-risk profiling at presentation (as defined by European LeukemiaNet [ELN] 2017 criteria) was not sufficient to explain the outcomes of many SFR cases. Single-cell RNA-sequencing studies of 15 AML samples showed that SFR AML cells differentially expressed many genes associated with immune suppression. The bone marrow of SFR cases had significantly fewer CD4+ Th1 cells; these T cells expressed an exhaustion signature and were resistant to activation by T cell receptor stimulation in the presence of autologous AML cells. T cell activation could be restored by removing the AML cells or blocking the inhibitory major histocompatibility complex class II receptor, LAG3. Most LFR cases did not display these features, suggesting that their AML cells were not as immunosuppressive. These findings were confirmed and extended in an independent set of 50 AML cases representing all ELN 2017 risk groups. AML cell-mediated suppression of CD4+ T cell activation at presentation is strongly associated with unfavorable outcomes in AML patients treated with standard chemotherapy.

Flotetuzumab as salvage immunotherapy for refractory acute myeloid leukemia.

Approximately 50% of acute myeloid leukemia (AML) patients do not respond to induction therapy (primary induction failure [PIF]) or relapse after <6 months (early relapse [ER]). We have recently shown an association between an immune-infiltrated tumor microenvironment (TME) and resistance to cytarabine-based chemotherapy but responsiveness to flotetuzumab, a bispecific DART antibody-based molecule to CD3ε and CD123. This paper reports the results of a multicenter, open-label, phase 1/2 study of flotetuzumab in 88 adults with relapsed/refractory AML: 42 in a dose-finding segment and 46 at the recommended phase 2 dose (RP2D) of 500 ng/kg per day. The most frequent adverse events were infusion-related reactions (IRRs)/cytokine release syndrome (CRS), largely grade 1-2. Stepwise dosing during week 1, pretreatment dexamethasone, prompt use of tocilizumab, and temporary dose reductions/interruptions successfully prevented severe IRR/CRS. Clinical benefit accrued to PIF/ER patients showing an immune-infiltrated TME. Among 30 PIF/ER patients treated at the RP2D, the complete remission (CR)/CR with partial hematological recovery (CRh) rate was 26.7%, with an overall response rate (CR/CRh/CR with incomplete hematological recovery) of 30.0%. In PIF/ER patients who achieved CR/CRh, median overall survival was 10.2 months (range, 1.87-27.27), with 6- and 12-month survival rates of 75% (95% confidence interval [CI], 0.450-1.05) and 50% (95% CI, 0.154-0.846). Bone marrow transcriptomic analysis showed that a parsimonious 10-gene signature predicted CRs to flotetuzumab (area under the receiver operating characteristic curve = 0.904 vs 0.672 for the European LeukemiaNet classifier). Flotetuzumab represents an innovative experimental approach associated with acceptable safety and encouraging evidence of activity in PIF/ER patients. This trial was registered at www.clinicaltrials.gov as #NCT02152956.

A History of Anatomical Eponyms of the Ulnar Nerve.

The ulnar nerve has a long and often misunderstood history with eponym usage. We describe the history of eponym usage in the anatomy of the ulnar nerve-who, when, what, where, and how. The relevant anatomy is investigated from proximal to distal, from the Arcade of Struthers to Osborne's band, to forearm ulnar nerve to median nerve connections, to Guyon's canal. We hope to provide a historical perspective of interest, resolve any controversies in semantic definitions, and create a comprehensive library of eponymous terms related to ulnar nerve anatomy.

Immune Escape of Relapsed AML Cells after Allogeneic Transplantation.

BACKGROUND: As consolidation therapy for acute myeloid leukemia (AML), allogeneic hematopoietic stem-cell transplantation provides a benefit in part by means of an immune-mediated graft-versus-leukemia effect. We hypothesized that the immune-mediated selective pressure imposed by allogeneic transplantation may cause distinct patterns of tumor evolution in relapsed disease. METHODS: We performed enhanced exome sequencing on paired samples obtained at initial presentation with AML and at relapse from 15 patients who had a relapse after hematopoietic stem-cell transplantation (with transplants from an HLA-matched sibling, HLA-matched unrelated donor, or HLA-mismatched unrelated donor) and from 20 patients who had a relapse after chemotherapy. We performed RNA sequencing and flow cytometry on a subgroup of these samples and on additional samples for validation. RESULTS: On exome sequencing, the spectrum of gained and lost mutations observed with relapse after transplantation was similar to the spectrum observed with relapse after chemotherapy. Specifically, relapse after transplantation was not associated with the acquisition of previously unknown AML-specific mutations or structural variations in immune-related genes. In contrast, RNA sequencing of samples obtained at relapse after transplantation revealed dysregulation of pathways involved in adaptive and innate immunity, including down-regulation of major histocompatibility complex (MHC) class II genes ( HLA-DPA1, HLA-DPB1, HLA-DQB1, and HLA-DRB1) to levels that were 3 to 12 times lower than the levels seen in paired samples obtained at presentation. Flow cytometry and immunohistochemical analysis confirmed decreased expression of MHC class II at relapse in 17 of 34 patients who had a relapse after transplantation. Evidence suggested that interferon-γ treatment could rapidly reverse this phenotype in AML blasts in vitro. CONCLUSIONS: AML relapse after transplantation was not associated with the acquisition of relapse-specific mutations in immune-related genes. However, it was associated with dysregulation of pathways that may influence immune function, including down-regulation of MHC class II genes, which are involved in antigen presentation. These epigenetic changes may be reversible with appropriate therapy. (Funded by the National Cancer Institute and others.).

Development of [89Zr]DFO-elotuzumab for immunoPET imaging of CS1 in multiple myeloma.

PURPOSE: Multiple myeloma (MM) is a bone marrow malignancy that remains mostly incurable. Elotuzumab is an FDA-approved therapeutic monoclonal antibody targeted to the cell surface glycoprotein CS1, which is overexpressed in MM cells. Identifying patients who will respond to CS1-targeted treatments such as elotuzumab requires the development of a companion diagnostic to assess the presence of CS1. Here, we evaluated [89Zr]DFO-elotuzumab as a novel PET tracer for imaging CS1 expression in preclinical MM models. METHODS: Conjugation of desferrioxamine-p-benzyl-isothiocyanate (DFO-Bz-NCS) to elotuzumab enabled zirconium-89 radiolabeling. MM.1S-CG cells were intravenously injected in NOD SCID gamma (NSG) mice. Small animal PET imaging with [89Zr]DFO-elotuzumab (1.11 MBq/mouse, 7 days post-injection), [89Zr]DFO-IgG (1.11 MBq/mouse, 7 days post-injection), and [18F]FDG (7-8 MBq, 1 h post-injection) was performed. Additionally, biodistribution of [89Zr]DFO-elotuzumab post-imaging at 7 days was also done. In vivo specificity of [89Zr]DFO-elotuzumab was further evaluated with a blocking study and ex vivo autoradiography. RESULTS: [89Zr]DFO-elotuzumab was produced with high specific activity (56 ± 0.75 MBq/nmol), radiochemical purity (99% ± 0.5), and yield (93.3% ± 1.5). Dissociation constant of 40.4 nM and receptor density of 126 fmol/mg was determined in MM.1S-CG cells. Compared to [89Zr]DFO-IgG, [89Zr]DFO-elotuzumab localized with a significantly higher standard uptake value in tumor-bearing bone tissue (8.59 versus 4.77). Blocking with unlabeled elotuzumab significantly reduced (P < 0.05) uptake of [89Zr]DFO-elotuzumab in the bones. Importantly, while [18F]FDG demonstrated similar uptake in the bone and muscle, [89Zr]DFO-elotuzumab showed > 3-fold enhanced uptake in bones. CONCLUSION: These data demonstrate the feasibility of [89Zr]DFO-elotuzumab as a companion diagnostic for CS1-targeted therapies.

Extensive Tumoral Calcinosis of the Hand.

Tumoral calcinosis is a rare and benign subtype of calcinosis cutis, a group of disorders involving soft tissue calcium deposition. Only 250 cases have been described since 1898; hand involvement is exceedingly rare. We report a case of extensive calcinosis within the flexor sheath of the little finger. Presentation included a painful mass over the volar aspect of the little finger, restricted digit motion, and skin compromise at the site of the mass. Surgical debulking was performed resulting in restoration of finger function.

Tourniquet Use for Short Hand Surgery Procedures Done Under Local Anesthesia Without Epinephrine.

PURPOSE: Wide-awake local anesthesia no tourniquet (WALANT) is an increasingly popular surgical technique. However, owing to surgeon preference, patient factors, or hospital guidelines, it may not be feasible to inject patients with solutions containing epinephrine the recommended 25 minutes prior to incision. The purpose of this study was to assess pain and patient experience after short hand surgeries done under local anesthesia using a tourniquet rather than epinephrine for hemostasis. METHODS: Ninety-six consecutive patients undergoing short hand procedures using only local anesthesia and a tourniquet (LA-T) were assessed before and after surgery. A high arm pneumatic tourniquet was used in 73 patients and a forearm pneumatic tourniquet was used in 23. All patients received a local, unbuffered plain lidocaine injection. No patients received sedation. Pain related to local anesthesia, pneumatic tourniquet, and the procedure was assessed using a visual analog scale (VAS). Patient experience was assessed using a study-specific questionnaire based on previous WALANT studies. Tourniquet times were recorded. RESULTS: Mean pain related to anesthetic injection was rated 3.9 out of 10. Mean tourniquet related pain was 2.9 out of 10 for high arm pneumatic tourniquets and 2.3 out of 10 for forearm pneumatic tourniquets. Patients rated their experience with LA-T favorably and 95 of 96 patients (99%) reported that they would choose LA-T again for an equivalent procedure. Mean tourniquet time was 9.6 minutes and only 1 patient had a tourniquet inflated for more than 20 minutes. Tourniquet times less than 10 minutes were associated with less pain than tourniquet times greater than 10 minutes (P < .05); however, both groups reported the tourniquet to be on average less painful than the local anesthetic injection. CONCLUSION: Short wide-awake procedures using a tourniquet are feasible and well accepted. Local anesthetic injection was reported to be more painful than pneumatic tourniquet use. Tourniquets for short wide-awake procedures can be used in settings in which preprocedure epinephrine injections are logistically difficult or based on surgeon preference. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic IV.

Mobilization of allogeneic peripheral blood stem cell donors with intravenous plerixafor mobilizes a unique graft.

A single subcutaneous (SC) injection of plerixafor results in rapid mobilization of hematopoietic progenitors, but fails to mobilize 33% of normal allogeneic sibling donors in 1 apheresis. We hypothesized that changing the route of administration of plerixafor from SC to IV may overcome the low stem cell yields and allow collection in 1 day. A phase 1 trial followed by a phase 2 efficacy trial was conducted in allogeneic sibling donors. The optimal dose of IV plerixafor was determined to be 0.32 mg/kg. The primary outcome of reducing the failure to collect ≥2 × 106 CD34+/kg recipient weight in 1 apheresis collection to ≤10% was not reached. The failure rate was 34%. Studies evaluating the stem cell phenotype and gene expression revealed a novel plasmacytoid dendritic cell precursor preferentially mobilized by plerixafor with high interferon-α producing ability. The observed cytomegalovirus (CMV) viremia rate for patients at risk was low (15%), as were the rates of acute grade 2-4 graft-versus-host disease (GVHD) (21%). Day 100 treatment related mortality was low (3%). In conclusion, plerixafor results in rapid stem cell mobilization regardless of route of administration and resulted in novel cellular composition of the graft and favorable recipient outcomes. These trials were registered at clinicaltrials.gov as #NCT00241358 and #NCT00914849.

Continuous blockade of CXCR4 results in dramatic mobilization and expansion of hematopoietic stem and progenitor cells.

Interaction between the chemokine receptor CXCR4 and its chief ligand CXCL12 plays a critical role in the retention and migration of hematopoietic stem and progenitor cells (HSPCs) in the bone marrow (BM) microenvironment. In this study, qualitative and quantitative effects of long-term pharmacologic inhibition of the CXCR4/CXCL12 axis on the HSPC compartment were investigated by using 3 structurally unrelated small molecule CXCR4 antagonists. A >10-fold increase in mobilization efficiency was achieved by administering the antagonists as a subcutaneous continuous infusion for 2 weeks compared to a single bolus injection. A concurrent increase in self-renewing proliferation leading to a twofold to fourfold expansion of the HSPC pool in the BM was observed. The expanded BM showed a distinct repopulating advantage when tested in serial competitive transplantation experiments. Furthermore, major changes within the HSPC niche associated with previously described HSPC expansion strategies were not detected in bones treated with a CXCR4 antagonist infusion. Our data suggest that prolonged but reversible pharmacologic blockade of the CXCR4/CXCL12 axis represents an approach that releases HSPC with efficiency superior to any other known mobilization strategy and may also serve as an effective method to expand the BM HSPC pool.

Enhanced in utero allogeneic engraftment in mice after mobilizing fetal HSCs by α4ß1/7 inhibition.

In utero hematopoietic cell transplantation (IUHCT) is a novel nonmyeloablative approach that results in donor-specific tolerance and mixed allogeneic chimerism. Clinical application is limited by low levels of donor cell engraftment. Competition from endogenous hematopoietic stem cells (HSCs) for limited "space" in fetal hematopoietic organs remains a significant barrier to successful IUHCT. AMD3100, a CXCR4 inhibitor, and firategrast, an α4ß1 and α4ß7 integrin inhibitor (α4ß1/7), have been shown to disrupt HSC retention in the postnatal hematopoietic niche. We hypothesized that maternal administration of AMD3100 and/or firategrast prior to IUHCT would mobilize endogenous HSCs from the fetal liver (FL) and result in preferential FL homing of donor HSCs and enhanced long-term engraftment following IUHCT in an allogeneic mouse model. We demonstrate that (1) both agents cross the placenta with rapidly detectable fetal serum concentrations following maternal administration; (2) firategrast treatment alone or with AMD3100 mobilizes endogenous HSCs from the FL and results in increased FL homing of donor HSCs following IUHCT; and (3) enhanced donor HSC homing following firategrast treatment translates into increased long-term multilineage donor cell engraftment. This approach highlights the potential of mobilization strategies to overcome barriers to successful engraftment and increase the clinical promise of IUHCT.

Targeting CD123 in acute myeloid leukemia using a T-cell-directed dual-affinity retargeting platform.

T-cell-directed killing of tumor cells using bispecific antibodies is a promising approach for the treatment of hematologic malignancies. Here we describe our preclinical work with a dual-affinity retargeting (DART) molecule generated from antibodies to CD3 and CD123, designed to redirect T cells against acute myeloid leukemia blasts. The CD3×CD123 DART (also referred to as MGD006/S80880) consists of 2 independent polypeptides, each composed of the VH of 1 antibody in tandem with the VL of the other antibody. The target antigen CD123 (interleukin 3RA) is highly and differentially expressed in acute myeloid leukemia (AML) blasts compared with normal hematopoietic stem and progenitor cells. In this study we demonstrate that the CD3×CD123 DART binds to both human CD3 and CD123 to mediate target-effector cell association, T-cell activation, proliferation, and receptor diversification. The CD3×CD123 DART also induces a dose-dependent killing of AML cell lines and primary AML blasts in vitro and in vivo. These results provide the basis for testing the CD3×CD123 DART in the treatment of patients with CD123(+) AML.

Management of Pisotriquetral Instability.

Pisotriquetral instability is an often-overlooked condition that can lead to ulnar-sided wrist pain and dysfunction. Various case series and biomechanical studies have been published regarding the diagnosis and treatment of this condition. We review current methods for examining, diagnosing, and treating pisotriquetral instability.

Performance Outcomes After Hook of Hamate Fractures in Major League Baseball Players.

CONTEXT: Major League Baseball (MLB) players are at risk of hook of hamate fractures. There is a paucity of data assessing the effect of a hook of hamate fracture on MLB players' future athletic performance. OBJECTIVE: To determine if MLB players who sustain hook of hamate fractures demonstrate decreased performance upon return to competition when compared with their performance before injury and that of their control-matched peers. DESIGN: Retrospective case-control design. SETTING: Retrospective database study. PARTICIPANTS: 18 MLB players who sustained hook of hamate fractures. METHODS: Data for 18 MLB players with hook of hamate fractures incurred over 26 seasons (1989-2014) were obtained from injury reports, press releases, and player profiles ( www.mlb.com and www.baseballreference.com ). Player age, position, number of years in the league, mechanism of injury, and treatment were recorded. Individual season statistics for the 2 seasons immediately prior to injury and the 2 seasons after injury for the main performance variable-Wins Above Replacement-were obtained. Eighteen controls matched by player position, age, and performance statistics were identified. A performance comparison of the cohorts was performed. MAIN OUTCOME MEASURES: Postinjury performance compared with preinjury performance and matched-controls. RESULTS: Mean age at the time of injury was 25.1 years with a mean of 4.4 seasons of MLB experience prior to injury. All injuries were sustained to their nondominant batting hand. All players underwent operative intervention. There was no significant change in Wins Above Replacement or isolated power when preinjury and postinjury performance were compared. When compared with matched-controls, no significant decline in performance in Wins Above Replacement the first season and second season after injury was found. CONCLUSION: MLB players sustaining hook of hamate fractures can reasonably expect to return to their preinjury performance levels following operative treatment.

Phase I/II Study of Intravenous Plerixafor Added to a Mobilization Regimen of Granulocyte Colony-Stimulating Factor in Lymphoma Patients Undergoing Autologous Stem Cell Collection.

Plerixafor, given subcutaneously with granulocyte colony-stimulating factor (G-CSF), improves autologous stem cell collection in patients with lymphoma and multiple myeloma. Intravenous (i.v.) administration of plerixafor allows administration of plerixafor on the same day as pheresis and it may improve stem cell collection. The primary objectives of this phase I/II study were to determine the maximum tolerated dose of i.v. plerixafor and the efficacy of i.v. plerixafor + G-CSF to mobilize ≥ 2 × 106 CD34+ cells/kg from patients with lymphoma. In phase I, 25 patients were treated with G-CSF + i.v. plerixafor at escalating doses; in phase II, 36 patients were treated with G-CSF + plerixafor .40 mg/kg. The treatment was well tolerated. Fifty-nine of 61 patients (98%) met the collection goal and 47 of 61 patients (77%) collected ≥ 5.0 × 106 CD34+ cells/kg in a median of 2 pheresis days. Analysis of CD34+ hematopoietic stem and progenitor cells (HSPCs) revealed that G-CSF-mobilized grafts were enriched with CD34+CD45RA-CD123+/- primitive HSPCs whereas plerixafor preferentially mobilized CD34+CD45RA+CD123++ plasmacytoid dendritic cell precursors. In conclusion, i.v. plerixafor is well tolerated and effective when added to G-CSF for the mobilization of stem cells from patients with lymphoma, with mobilization kinetics and stem cell collections that compare favorably with subcutaneous dosing.

Severe Cytokine-Release Syndrome after T Cell-Replete Peripheral Blood Haploidentical Donor Transplantation Is Associated with Poor Survival and Anti-IL-6 Therapy Is Safe and Well Tolerated.

Use of high-dose post-transplantation cyclophosphamide for graft-versus-host disease prophylaxis has expanded the use of unmanipulated haploidentical hematopoietic cell transplantation. The immediate post-transplantation course in T cell-replete peripheral blood haploidentical hematopoietic cell transplantation (haplo-HCT) is often complicated by symptoms resembling cytokine-release syndrome (CRS), previously described in recipients of targeted cellular therapeutics. However, we know little about the incidence and impact of CRS on outcomes in these patients. To understand this syndrome in haplo-HCT patients, we reviewed data from 75 consecutive patients who received granulocyte colony-stimulating factor-mobilized T cell-replete peripheral blood haplo-HCT at a single center. Using CRS criteria described in recipients of chimeric antigen receptor T cell therapies, we found 65 of 75 (87%) met criteria for CRS, although most cases were only mild (grades 1 or 2). However, 9 patients (12%) experienced severe (grades 3 or 4) CRS. Median survival was 2.6 months (95% confidence interval [CI], .43 to 5.8) in patients with severe CRS, compared with 13.1 months (95% CI, 8.1 to not reached) in patients with mild CRS. Transplantation-related mortality was worse in the severe CRS cohort with a hazard ratio of 4.59 (95% CI, 1.43 to 14.67) compared with that in the mild CRS cohort. Severe CRS patients had a significant delay in median time for neutrophil engraftment. Serum IL-6 levels were measured in 10 haplo-HCT patients and were elevated in the early post-transplantation setting. Seven patients with CRS were treated with tocilizumab, resulting in a complete resolution of their CRS symptoms. Severe CRS represents a potential complication of peripheral blood haplo-HCT and is associated with worse outcomes. Anti-IL-6 receptor therapy is associated with rapid resolution of the CRS symptoms.

[(18)F]FHBG PET/CT Imaging of CD34-TK75 Transduced Donor T Cells in Relapsed Allogeneic Stem Cell Transplant Patients: Safety and Feasibility.

Described herein is a first-in-man attempt to both genetically modify T cells with an imagable suicide gene and track these transduced donor T cells in allogeneic stem cell transplantation recipients using noninvasive positron emission tomography/computerized tomography (PET/CT) imaging. A suicide gene encoding a human CD34-Herpes Simplex Virus-1-thymidine kinase (CD34-TK75) fusion enabled enrichment of retrovirally transduced T cells (TdT), control of graft-versus-host disease and imaging of TdT migration and expansion in vivo in mice and man. Analysis confirmed that CD34-TK75-enriched TdT contained no replication competent γ-retrovirus, were sensitive to ganciclovir, and displayed characteristic retroviral insertion sites (by targeted sequencing). Affinity-purified CD34-TK75(+)-selected donor T cells (1.0-13 × 10(5))/kg were infused into eight patients who relapsed after allogeneic stem cell transplantation. Six patients also were administered 9-[4-((18)F)fluoro-3-hydroxymethyl-butyl]guanine ([(18)F]FHBG) to specifically track the genetically modified donor T cells by PET/CT at several time points after infusion. All patients were assessed for graft-versus-host disease, response to ganciclovir, circulating TdT cells (using both quantitative polymerase chain reaction and [(18)F]FHBG PET/CT imaging), TdT cell clonal expansion, and immune response to the TdT. This phase 1 trial demonstrated that genetically modified T cells and [(18)F]FHBG can be safely infused in patients with relapsed hematologic malignancies after allogeneic stem cell transplantation.