Treatment of relapsed/refractory severe aplastic anemia in children: Evidence-based recommendations.

Severe aplastic anemia (SAA) is a rare potentially fatal hematologic disorder. Although overall outcomes with treatment are excellent, there are variations in management approach, including differences in treatment between adult and pediatric patients. Certain aspects of treatment are under active investigation in clinical trials. Because of the rarity of the disease, some pediatric hematologists may have relatively limited experience with the complex management of SAA. The following recommendations reflect an up-to-date evidence-based approach to the treatment of children with relapsed or refractory SAA.

Treatment of newly diagnosed severe aplastic anemia in children: Evidence-based recommendations.

Severe aplastic anemia (SAA) is a rare potentially fatal hematologic disorder. Although overall outcomes with treatment are excellent, there are variations in management approach, including differences in treatment between adult and pediatric patients. Certain aspects of treatment are under active investigation in clinical trials. Because of the rarity of the disease, some pediatric hematologists may have relatively limited experience with the complex management of SAA. The following recommendations reflect an up-to-date evidence-based approach to the treatment of children with newly diagnosed SAA.

A familial SAMD9 variant present in pediatric myelodysplastic syndrome.

Myelodysplastic syndrome (MDS) is a rare pediatric diagnosis characterized by ineffective hematopoiesis with potential to evolve into acute myelogenous leukemia (AML). In this report, we describe a unique case of a 17-yr-old female with an aggressive course of MDS with excess blasts who was found to have monosomy 7 and a SAMD9 germline variant, which has not previously been associated with a MDS phenotype. This case of MDS was extremely rapidly progressing, showing resistance to chemotherapy and stem cell transplant, unfortunately resulting in patient death. It is imperative to further investigate this rare variant to aid in the future care of patients with this variant.

An evaluation of the disparities affecting the underdiagnosis of pediatric cancer in Western Kenya.

INTRODUCTION: Western Kenya is home to approximately 24 million people, with 10 million children under the age of 15 years.1 Based on estimates of cancer incidence in similar populations from around the world, approximately 1500 patients should be diagnosed with pediatric cancer each year. This article describes the international collaboration that investigates potential barriers preventing the effective diagnosis of pediatric patients with cancer. METHODS: Here, we describe a multidisciplinary and sequential approach to better evaluate the complex factors affecting the lack of appropriate diagnosis of pediatric cancer in Western Kenya. RESULTS: Internal review at a large tertiary hospital noted 200-250 patients were diagnosed annually, suggesting the remaining 75%-80% of patients go undiagnosed and do not receive treatment. Following our screening process at a local referring hospital, 41 malaria slides demonstrated both morphologic and genetic evidence of leukemia. Knowledge assessments of local providers at referring institutions suggested a lack of education and training as the factors that contribute to lower rates of diagnosis. DISCUSSION: Through a multi-step approach, our teams were better able to isolate potential issues impeding the appropriate and timely diagnosis of pediatric cancer in Kenya.

Diagnostic work-up for severe aplastic anemia in children: Consensus of the North American Pediatric Aplastic Anemia Consortium.

The North American Pediatric Aplastic Anemia Consortium (NAPAAC) is a group of pediatric hematologist-oncologists, hematopathologists, and bone marrow transplant physicians from 46 institutions in North America with interest and expertise in aplastic anemia, inherited bone marrow failure syndromes, and myelodysplastic syndromes. The NAPAAC Bone Marrow Failure Diagnosis and Care Guidelines Working Group was established with the charge of harmonizing the approach to the diagnostic workup of aplastic anemia in an effort to standardize best practices in the field. This document outlines the rationale for initial evaluations in pediatric patients presenting with signs and symptoms concerning for severe aplastic anemia.

Splenic macrophage phagocytosis of intravenously infused mesenchymal stromal cells attenuates tumor localization.

Mesenchymal stromal cells (MSCs) possess remarkable tumor tropism, making them ideal vehicles to deliver tumor-targeted therapeutic agents; however, their value in clinical medicine has yet to be realized. A barrier to clinical utilization is that only a small fraction of infused MSCs ultimately localize to the tumor. In an effort to overcome this obstacle, we sought to enhance MSC trafficking by focusing on the factors that govern MSC arrival within the tumor microenvironment. Our findings show that MSC chemoattraction is only present in select tumors, including osteosarcoma, and that the chemotactic potency among similar tumors varies substantially. Using an osteosarcoma xenograft model, we show that human MSCs traffic to the tumor within several hours of infusion. After arrival, MSCs are observed to localize in clusters near blood vessels and MSC-associated bioluminescence signal intensity is increased, suggesting that the seeded cells expand after engraftment. However, our studies reveal that a significant portion of MSCs are eliminated en route by splenic macrophage phagocytosis, effectively limiting the number of cells available for tumor engraftment. To increase MSC survival, we transiently depleted macrophages with liposomal clodronate, which resulted in increased tumor localization without substantial reduction in tumor-associated macrophages. Our data suggest that transient macrophage depletion will significantly increase the number of MSCs in the spleen and thus improve MSC localization within a tumor, theoretically increasing the effective dose of an anti-cancer agent. This strategy may subsequently improve the clinical efficacy of MSCs as vehicles for the tumor-directed delivery of therapeutic agents.

Identification of a murine CD45-F4/80lo HSC-derived marrow endosteal cell associated with donor stem cell engraftment.

Hematopoietic stem cells (HSCs) reside in specialized microenvironments within the marrow designated as stem cell niches, which function to support HSCs at homeostasis and promote HSC engraftment after radioablation. We previously identified marrow space remodeling after hematopoietic ablation, including osteoblast thickening, osteoblast proliferation, and megakaryocyte migration to the endosteum, which is critical for effective engraftment of donor HSCs. To further evaluate the impact of hematopoietic cells on marrow remodeling, we used a transgenic mouse model (CD45Cre/iDTR) to selectively deplete hematopoietic cells in situ. Depletion of hematopoietic cells immediately before radioablation and hematopoietic stem cell transplantation abrogated donor HSC engraftment and was associated with strikingly flattened endosteal osteoblasts with preserved osteoblast proliferation and megakaryocyte migration. Depletion of monocytes, macrophages, or megakaryocytes (the predominant hematopoietic cell populations that survive short-term after irradiation) did not lead to an alteration of osteoblast morphology, suggesting that a hematopoietic-derived cell outside these lineages regulates osteoblast morphologic adaptation after irradiation. Using 2 lineage-tracing strategies, we identified a novel CD45-F4/80lo HSC-derived cell that resides among osteoblasts along the endosteal marrow surface and, at least transiently, survives radioablation. This newly identified marrow cell may be an important regulator of HSC engraftment, possibly by influencing the shape and function of endosteal osteoblasts.

Hematopoietic cell transplantation for a child with OSTM1 osteopetrosis.

HCT prior to onset of neurologic symptoms in children with OSTM1 osteopetrosis does not halt neurologic progression.

Hematopoietic derived cells do not contribute to osteogenesis as osteoblasts.

Despite years of extensive investigation, the cellular origin of heterotopic ossification (HO) has not been fully elucidated. We have previously shown that circulating bone marrow-derived osteoblast progenitor cells, characterized by the immunophenotype CD45-/CD44+/CXCR4+, contributed to the formation of heterotopic bone induced by bone morphogenetic protein (BMP)-2. In contrast, other reports have demonstrated the contribution of CD45+ hematopoietic derived cells to HO. Therefore, in this study, we developed a novel triple transgenic mouse strain that allows us to visualize CD45+ cells with red fluorescence and mature osteoblasts with green fluorescence. These mice were generated by crossing CD45-Cre mice with Z/RED mice that express DsRed, a variant of red fluorescent protein, after Cre-mediated recombination, and then crossing with Col2.3GFP mice that express green fluorescent protein (GFP) in mature osteoblasts. Utilizing this model, we were able to investigate if hematopoietic derived cells have the potential to give rise to mature osteoblasts. Analyses of this triple transgenic mouse model demonstrated that DsRed and GFP did not co-localize in either normal skeletogenesis, bone regeneration after fracture, or HO. This indicates that in these conditions hematopoietic derived cells do not differentiate into mature osteoblasts. Interestingly, we observed the presence of previously unidentified DsRed positive bone lining cells (red BLCs) which are derived from hematopoietic cells but lack CD45 expression. These red BLCs fail to produce GFP even under in vitro osteogenic conditions. These findings indicate that, even though both osteoblasts and hematopoietic cells are developmentally derived from mesoderm, hematopoietic derived cells do not contribute to osteogenesis in fracture healing or HO.

Promyelocytic Leukemia with No Retinoic Acid Receptor Alpha Abnormality but with RUNX1T1 Insertion to Chromosome 7q: A Classification and Management Dilemma.

A case of acute promyelocytic leukemia (APL) with RUNX1T1 insertion to 7q is described and compared to reported cases of APL with negative retinoic acid receptor alpha (RARA) abnormality. In this report, we describe the case of a 2-year-old boy who presented with bone pain and was found to have pancytopenia. Bone marrow examination showed morphologic and immunophenotypic findings typical of APL, but conventional cytogenetics, fluorescence in situ hybridization (FISH), and real-time polymerase chain reaction (RT-PCR) showed no evidence of RARA rearrangements. The only cytogenetic abnormality found was a small insertion in 7q, and three copies of RUNX1T1. Gene sequencing results became available after initiating therapy but were not informative. We describe the rarity of such cases and discuss how the typical morphologic and immunophenotypic findings of APL, coupled with the definite absence of RARA rearrangement (by FISH and RT-PCR), present a diagnostic and classification dilemma, raising the possibility of an unknown alternative mechanism for the leukemogenesis and maturation arrest seen in other APL variants. The diagnostic challenges and urgent management issues this unusual case raises may justify including it, along with similar cases, in a separate subtype of acute myeloid leukemia (AML) in future classifications.