Busulfan, fludarabine, and melphalan are effective conditioning for pediatric and young adult patients with myeloid malignancies underdoing matched sibling or alternative donor transplantation.

BACKGROUND: Allogeneic hematopoietic cell transplantation (allo-HCT) remains a curative option for patients with high-risk myeloid malignancies. PROCEDURE: We present our 10-year experience (October 2012 to October 2021) of consecutive allo-HCT in patients with myeloid malignancies treated on the pediatric HCT service and conditioned with myeloablative targeted dose-busulfan (BU), fludarabine (FLU), and melphalan (MEL). Twenty-three children, adolescents, and young adult patients (CAYA) (median age 15.4 years) with acute myeloid leukemia (AML, n = 17), myelodysplastic syndrome (MDS, n = 4), or chronic myeloid leukemia (CML, n = 2) underwent allo-HCT post-BU-FLU-MEL. Four patients had treatment-related AML/MDS. Donor/stem cell source was matched sibling donor (MSD) PBSC (n = 7), matched unrelated donor (MUD) PBSC (n = 2), umbilical cord blood (UCB) (n = 3), or haploidentical-BMT (n = 11). Risk stratification was low (n = 2), intermediate (n = 15), high (n = 3), and very high risk (n = 1). The two patients with CML had failed tyrosine kinase inhibitor therapies. RESULTS: With a median follow-up of 41.6 months, the relapse rate is only 4.5% with an overall survival (OS) 100%, progression-free survival (PFS) 95.5%, and graft-versus-host-free-relapse-free survival (GRFS) 67.8%. The donor source and the acute graft-versus-host disease (GvHD) prophylaxis regimen significantly impacted grade II-IV aGvHD 66.7% versus 19.2% (p = .039) and chronic graft-versus-host-disease (cGvHD) 66.7% versus 0% (p = .002) in the patients receiving MSD or MUD PBSC compared to haplo-BMT, respectively, resulting in improved GRFS in haplo-BMT, 83.3% compared to 40% matched donor peripheral blood stem cell transplant (PBSCT) (p = .025). CONCLUSIONS: Our results demonstrate that BU-FLU-MEL is efficacious conditioning for disease control in young patients with myeloid malignancies undergoing MSD or alternative donor allo-HCT, but in the setting of PBSC grafts with cyclosporine A-methotrexate (CSA-MTX) GvHD prophylaxis, it results in an unacceptably high incidence of GvHD.

Feasibility and Efficacy of Partially Replacing Post-Transplantation Cyclophosphamide with Bendamustine in Pediatric and Young Adult Patients Undergoing Haploidentical Bone Marrow Transplantation.

Post-transplantation cyclophosphamide (PT-CY) is the most widely applied graft-versus-host disease (GVHD) prophylaxis regimen in T-cell replete haploidentical bone marrow transplantation (haplo-BMT). Although PT-CY has met with great success in the haplo-BMT arena by suppressing GVHD, patients without acute GVHD have high relapse rates. One strategy to reduce relapse rates being explored by others is a dosage reduction of PT-CY. We have taken a different approach in evaluating whether partially replacing PT-CY with post-transplantation bendamustine (PT-BEN) would be advantageous, an idea based on our preclinical research identifying several beneficial immunomodulatory properties of BEN. We therefore initiated and completed a Phase Ia trial to evaluate the progressive substitution of PT-CY with PT-BEN (ClinicalTrials.gov identifier NCT02996773). We compared outcomes between 13 patients with high-risk hematologic malignancies who received PT-CY/BEN and 31 contemporaneous haplo-BMT recipients treated with the same myeloablative conditioning regimens but receiving only PT-CY. We found that partial replacement of PT-CY with PT-BEN (PT-CY/BEN) on day +4 was well tolerated and associated with significantly earlier trilineage engraftment. We also report favorable trends toward significant improvements on univariate and multivariate analyses with PT-CY/BEN compared with PT-CY with respect to rates of chronic GVHD (hazard ratio [HR], .08; 95% confidence interval [CI], .005 to 1.11; P = .06), and GVHD-free relapse-free survival (GRFS) (HR, .22; 95% CI, .05 to .86; P = .039). Our human trial has now transitioned to Phase Ib, which will further evaluate the safety and potential benefits of PT-CY/BEN. Herein we also expand our pediatric, adolescent, and young adult experience to 31 patients, demonstrating overall survival, progression-free survival, and GRFS at 3 years of 85.6%, 76.1%, and 58.2%, respectively, in a largely racial/ethnic minority cohort. PT-CY/BEN appears to be a promising treatment option that requires further evaluation.

Have CD19-directed immunotherapy and haploidentical hematopoietic cell transplantation transformed pediatric B-cell acute lymphoblastic leukemia into a chronic disease?

The treatment of pediatric B-cell acute lymphoblastic leukemia (B-ALL) has undergone several recent advancements, leading to an increased amount of treatment options for relapsed patients. The development of immunotherapies such as anti-CD19 chimeric antigen receptor(CAR) T cells and bispecific T-cell engagers has given clinicians therapeutic options with less expected toxicity when compared to standard re-induction chemotherapy. This is especially beneficial in patients with toxicities from their prior treatment. Along with this, the emergence of haploidentical hematopoietic cell transplantation (HCT) has increased opportunity for patients to receive HCT who may not have had an available matched donor. We present four patients who have received all of these therapies in different combinations to treat multiple relapses. Because of the success of achieving remission as well as decreasing toxicity, the patients are alive and well up to 15 y after the original B-ALL diagnosis, rendering this as a chronic disease for them.

Is polycystic kidney disease associated with malignancy in children?

BACKGROUND: Polycystic kidney disease (PKD) is an inherited condition characterized by progressive development of end-stage renal disease, hypertension, hepatic fibrosis, and cysts in the kidney, liver, pancreas, spleen, thyroid, and epididymis. While malignancies have been reported in association with PKD in adults, the incidence of malignancies in children with PKD is not currently known. METHODS: We report on five patients with a known history of PKD who developed a malignancy as children at the University of California, Los Angeles and the University of Colorado Anschutz Medical Campus. Patients were included from 2012 to 2017. RESULTS: We present five patients with a history of PKD diagnosed with a malignancy during childhood without any additional known mutations to suggest a genetic predisposition to develop cancer. This includes the first reported case of hepatocellular carcinoma in a patient with autosomal recessive polycystic kidney disease. CONCLUSION: Our report illustrates the potential that PKD may be associated with an increased risk for developing cancer, even in children. Further research is necessary to better understand this relationship.

A Cetuximab-Mediated Suicide System in Chimeric Antigen Receptor-Modified Hematopoietic Stem Cells for Cancer Therapy.

Using gene modification of hematopoietic stem cells (HSC) to create persistent generation of multilineage immune effectors to target cancer cells directly is proposed. Gene-modified human HSC have been used to introduce genes to correct, prevent, or treat diseases. Concerns regarding malignant transformation, abnormal hematopoiesis, and autoimmunity exist, making the co-delivery of a suicide gene a necessary safety measure. Truncated epidermal growth factor receptor (EGFRt) was tested as a suicide gene system co-delivered with anti-CD19 chimeric antigen receptor (CAR) to human HSC. Third-generation self-inactivating lentiviral vectors were used to co-deliver an anti-CD19 CAR and EGFRt. In vitro, gene-modified HSC were differentiated into myeloid cells to allow transgene expression. An antibody-dependent cell-mediated cytotoxicity (ADCC) assay was used, incubating target cells with leukocytes and monoclonal antibody cetuximab to determine the percentage of surviving cells. In vivo, gene-modified HSC were engrafted into NSG mice with subsequent treatment with intraperitoneal cetuximab. Persistence of gene-modified cells was assessed by flow cytometry, droplet digital polymerase chain reaction (ddPCR), and positron emission tomography (PET) imaging using 89Zr-Cetuximab. Cytotoxicity was significantly increased (p = 0.01) in target cells expressing EGFRt after incubation with leukocytes and cetuximab 1 µg/mL compared to EGFRt+ cells without cetuximab and non-transduced cells with or without cetuximab, at all effector:target ratios. Mice humanized with gene-modified HSC presented significant ablation of gene-modified cells after treatment (p = 0.002). Remaining gene-modified cells were close to background on flow cytometry and within two logs of decrease of vector copy numbers by ddPCR in mouse tissues. PET imaging confirmed ablation with a decrease of an average of 82.5% after cetuximab treatment. These results give proof of principle for CAR-modified HSC regulated by a suicide gene. Further studies are needed to enable clinical translation. Cetuximab ADCC of EGFRt-modified cells caused effective killing. Different ablation approaches, such as inducible caspase 9 or co-delivery of other inert cell markers, should also be evaluated.

Pre-clinical development of gene modification of haematopoietic stem cells with chimeric antigen receptors for cancer immunotherapy.

Patients with refractory or recurrent B-lineage hematologic malignancies have less than 50% of chance of cure despite intensive therapy and innovative approaches are needed. We hypothesize that gene modification of haematopoietic stem cells (HSC) with an anti-CD19 chimeric antigen receptor (CAR) will produce a multi-lineage, persistent immunotherapy against B-lineage malignancies that can be controlled by the HSVsr39TK suicide gene. High-titer third-generation self-inactivating lentiviral constructs were developed to deliver a second-generation CD19-specific CAR and the herpes simplex virus thymidine kinase HSVsr39TK to provide a suicide gene to allow ablation of gene-modified cells if necessary. Human HSC were transduced with such lentiviral vectors and evaluated for function of both CAR and HSVsr39TK. Satisfactory transduction efficiency was achieved; the addition of the suicide gene did not impair CAR expression or antigen-specific cytotoxicity, and determined marked cytotoxicity to ganciclovir. NSG mice transplanted with gene-modified human HSC showed CAR expression not significantly different between transduced cells with or without HSVsr39TK, and expression of anti-CD19 CAR conferred anti-tumor survival advantage. Treatment with ganciclovir led to significant ablation of gene-modified cells in mouse tissues. Haematopoietic stem cell transplantation is frequently part of the standard of care for patients with relapsed and refractory B cell malignancies; following HSC collection, a portion of the cells could be modified to express the CD19-specific CAR and give rise to a persistent, multi-cell lineage, HLA-independent immunotherapy, enhancing the graft-versus-malignancy activity.

Novel association of familial testicular germ cell tumor and autosomal dominant polycystic kidney disease with PKD1 mutation.

Adolescent brothers were diagnosed with testicular germ cell tumors within the same month. Both were found to have multiple renal cysts on pretreatment imaging done for staging. The proband, his brother, and their mother, were all found to have a novel splice variant in intron 8 of the PKD1 gene by clinical exome sequencing. This is the second family reported with both familial testicular germ cell tumor (FTGCT) and autosomal dominant polycystic kidney disease (ADPKD), and the first described association of FTGCT with a splice variant in PKD1. We suggest that this novel variant in PKD1 may convey increased risk for FTGCT in addition to causing ADPKD.

In Vitro Generation of Human NK Cells Expressing Chimeric Antigen Receptor Through Differentiation of Gene-Modified Hematopoietic Stem Cells.

NK cells represent a very promising source for adoptive cellular approaches for cancer immunotherapy, and extensive research has been conducted, including clinical trials. Gene modification of NK cells can direct their specificity and enhance their function, but the efficiency of gene transfer techniques is very limited. Here we describe two protocols designed to generate mature human NK cells from gene-modified hematopoietic stem cells. These protocols use chimeric antigen receptor as the transgene, but could potentially be modified for the expression any particular transgene in human NK cells.