Fundamental Biological Features of Spaceflight: Advancing the Field to Enable Deep-Space Exploration.

Research on astronaut health and model organisms have revealed six features of spaceflight biology that guide our current understanding of fundamental molecular changes that occur during space travel. The features include oxidative stress, DNA damage, mitochondrial dysregulation, epigenetic changes (including gene regulation), telomere length alterations, and microbiome shifts. Here we review the known hazards of human spaceflight, how spaceflight affects living systems through these six fundamental features, and the associated health risks of space exploration. We also discuss the essential issues related to the health and safety of astronauts involved in future missions, especially planned long-duration and Martian missions.

Single-cell RNA sequencing reveals a signature of sexual commitment in malaria parasites.

Pathogens have to balance transmission with persistence. For Plasmodium falciparum, the most widespread and virulent malaria parasite, persistence within its human host requires continuous asexual replication within red blood cells, while its mosquito-borne transmission depends on intra-erythrocytic differentiation into non-replicating sexual stages called gametocytes. Commitment to either fate is determined during the preceding cell cycle that begins with invasion by a single, asexually committed merozoite and ends, 48 hours later, with a schizont releasing newly formed merozoites, all committed to either continued asexual replication or differentiation into gametocytes. Sexual commitment requires the transcriptional activation of ap2-g (PF3D7_1222600), the master regulator of sexual development, from an epigenetically silenced state during asexual replication. AP2-G expression during this 'commitment cycle' prepares gene expression in nascent merozoites to initiate sexual development through a hitherto unknown mechanism. To maintain a persistent infection, the expression of ap2-g is limited to a sub-population of parasites (1-30%, depending on genetic background and growth conditions). As sexually committed schizonts comprise only a sub-population and are morphologically indistinguishable from their asexually committed counterparts, defining their characteristic gene expression has been difficult using traditional, bulk transcriptome profiling. Here we use highly parallel, single-cell RNA sequencing of malaria cultures undergoing sexual commitment to determine the transcriptional changes induced by AP2-G within this sub-population. By analysing more than 18,000 single parasite transcriptomes from a conditional AP2-G knockdown line and NF54 wild-type parasites at multiple stages of development, we show that sexually committed, AP2-G+ mature schizonts specifically upregulate additional regulators of gene expression, including other AP2 transcription factors, histone-modifying enzymes, and regulators of nucleosome positioning. These epigenetic regulators may act to facilitate the expression and/or repression of genes that are necessary for the initiation of gametocyte development in the subsequent cell cycle.

Matrix stiffening promotes a tumor vasculature phenotype.

Tumor microvasculature tends to be malformed, more permeable, and more tortuous than vessels in healthy tissue, effects that have been largely attributed to up-regulated VEGF expression. However, tumor tissue tends to stiffen during solid tumor progression, and tissue stiffness is known to alter cell behaviors including proliferation, migration, and cell-cell adhesion, which are all requisite for angiogenesis. Using in vitro, in vivo, and ex ovo models, we investigated the effects of matrix stiffness on vessel growth and integrity during angiogenesis. Our data indicate that angiogenic outgrowth, invasion, and neovessel branching increase with matrix cross-linking. These effects are caused by increased matrix stiffness independent of matrix density, because increased matrix density results in decreased angiogenesis. Notably, matrix stiffness up-regulates matrix metalloproteinase (MMP) activity, and inhibiting MMPs significantly reduces angiogenic outgrowth in stiffer cross-linked gels. To investigate the functional significance of altered endothelial cell behavior in response to matrix stiffness, we measured endothelial cell barrier function on substrates mimicking the stiffness of healthy and tumor tissue. Our data indicate that barrier function is impaired and the localization of vascular endothelial cadherin is altered as function of matrix stiffness. These results demonstrate that matrix stiffness, separately from matrix density, can alter vascular growth and integrity, mimicking the changes that exist in tumor vasculature. These data suggest that therapeutically targeting tumor stiffness or the endothelial cell response to tumor stiffening may help restore vessel structure, minimize metastasis, and aid in drug delivery.

Phase I trial of plerixafor combined with decitabine in newly diagnosed older patients with acute myeloid leukemia.

Acute myeloid leukemia carries a dismal prognosis in older patients. The objective of this study was to investigate the safety and efficacy of decitabine combined with the CXCR4 antagonist plerixafor in newly diagnosed older patients with acute myeloid leukemia and to evaluate the effects of plerixafor on leukemia stem cells. Patients were treated with monthly cycles of decitabine 20 mg/m2 days 1-10 and escalating doses of plerixafor (320-810 mcg/kg) days 1-5. Sixty-nine patients were treated, with an overall response rate of 43%. Adverse karyotype did not predict response (P=0.31). Prior hypomethylating agent treatment was the strongest independent predictor of adverse overall survival (hazard ratio 3.1; 95%CI: 1.3-7.3; P=0.008) and response (14% in previously treated patients, 46% in treatment naïve; P=0.002). As expected, the most common toxicities were myelosuppression and infection. Plerixafor induced mobilization of leukemia stem and progenitor cells, but did not cause clinically significant hyperleukocytosis. Reduction in leukemia stem cells appeared to correlate with duration of response. Plerixafor can be safely added to decitabine in poor-prognosis, elderly acute myeloid leukemia patients. The maximum tolerated dose of the combination was 810 mcg/kg. While mobilization of leukemia stem cells was observed in some patients, the clinical benefit of adding plerixafor was uncertain. This trial was registered at clinicaltrials.gov identifier: 01352650.

The effect of initial molecular profile on response to recombinant interferon-α (rIFNα) treatment in early myelofibrosis.

BACKGROUND: Although recombinant interferon-α (rIFNα) effectively treats patients with early myelofibrosis, the effect of driver and high molecular risk (HMR) mutations has not been considered. In this phase 2 study, for the first time, the authors correlate response to rIFNα treatment with driver and HMR mutations. METHODS: Patients were diagnosed using World Health Organization or International Working Group for Myeloproliferative Neoplasms Research and Treatment criteria. Only patients who had low or intermediate-1 Dynamic International Prognostic Scoring System scores with ≥15% hematopoietic bone marrow foci were included. History, symptom assessment, physical examination, and blood and bone marrow studies were performed. Genomic DNA was extracted from frozen cells, and next-generation targeted sequencing of 45 genes was performed. Either rIFNα-2b (0.5 million units subcutaneously 3 times weekly) or pegylated rIFNα-2a (45 µg weekly) with escalation was initiated. All patients were followed at the authors' institution, and regular bone marrow biopsies were encouraged. International Working Group for Myeloproliferative Neoplasms Research and Treatment and European LeukemiaNet treatment response criteria were used. RESULTS: Of 30 patients (16 women and 14 men; median age, 58 years), 22 were classified as low risk, and 8 were classified as intermediate-1 risk. Two patients achieved complete remission, 9 achieved partial remission, 4 had clinical improvement, 7 had stable disease; 3 had progressive disease, 1 relapsed, and 4 died. There were 22 patients with JAK mutations, 6 with CALR mutations, and 2 with MPL mutations. Seventy-three percent of patients improved or remained stable with acceptable toxicity, including 37% who achieved complete or partial remission. There was no correlation between treatment response and baseline driver mutations or Dynamic International Prognostic Scoring System scores. Of 8 poor responders, 3 had ASXL1 or SRSF2 mutations. CONCLUSIONS: Early treatment with rIFNα in patients without HMR mutations may prevent the development of marked splenomegaly, anemia, and florid myelofibrosis. Molecular profiling at the time of diagnosis may predict prognosis and treatment response. Cancer 2017;123:2680-87. © 2017 American Cancer Society.

Oligomonocytic chronic myelomonocytic leukemia (chronic myelomonocytic leukemia without absolute monocytosis) displays a similar clinicopathologic and mutational profile to classical chronic myelomonocytic leukemia.

Chronic myelomonocytic leukemia is characterized by persistent absolute monocytosis (≥1 × 109/l) in the peripheral blood and dysplasia in ≥1 lineages. In the absence of dysplasia, an acquired clonal genetic abnormality is required or causes for reactive monocytosis have to be excluded. Oligomonocytic chronic myelomonocytic leukemia showing increased monocytes but no absolute monocytosis in the peripheral blood occurs occasionally. These cases are likely classified as myelodysplastic syndrome or myelodysplastic/myeloproliferative neoplasm, unclassifiable. A subset eventually develop overt chronic myelomonocytic leukemia. Better characterization of oligomonocytic chronic myelomonocytic leukemia is essential since the distinction between chronic myelomonocytic leukemia and myelodysplastic syndrome is clinically relevant. We identified 44 cases of oligomonocytic chronic myelomonocytic leukemia (≥10% peripheral blood monocytes with absolute monocyte count of 0.5-1 × 109/l) and 28 consecutive chronic myelomonocytic leukemia controls. Clinicopathologic features were compared and mutation analysis was performed. Oligomonocytic chronic myelomonocytic leukemia patients were significantly younger (median age of 65 vs 72). They had lower WBC and absolute neutrophil count, while the monocyte percentage, hemoglobin and platelet counts were similar in the two groups. The myeloid to erythroid ratio was predominantly decreased or normal, compared with the characteristic increase in chronic myelomonocytic leukemia (P=0.006). 38% of patients progressed to overt chronic myelomonocytic leukemia (median: 12 months). The overall percentage of mutations was significantly lower in oligomonocytic chronic myelomonocytic leukemia. However, the most frequent mutations in both groups were the 'signature' chronic myelomonocytic leukemia mutations in ASXL1, TET2 and SRSF2. Mutations in CBL were found exclusively in overt chronic myelomonocytic leukemia. In conclusion, we demonstrate clinical and genetic similarities between overt chronic myelomonocytic leukemia and oligomonocytic chronic myelomonocytic leukemia. The findings suggest that at least a subset of oligomonocytic chronic myelomonocytic leukemia represents early phase 'dysplastic type' chronic myelomonocytic leukemia.

Genome and clonal hematopoiesis stability contrasts with immune, cfDNA, mitochondrial, and telomere length changes during short duration spaceflight.

Background: The Inspiration4 (I4) mission, the first all-civilian orbital flight mission, investigated the physiological effects of short-duration spaceflight through a multi-omic approach. Despite advances, there remains much to learn about human adaptation to spaceflight's unique challenges, including microgravity, immune system perturbations, and radiation exposure. Methods: To provide a detailed genetics analysis of the mission, we collected dried blood spots pre-, during, and post-flight for DNA extraction. Telomere length was measured by quantitative PCR, while whole genome and cfDNA sequencing provided insight into genomic stability and immune adaptations. A robust bioinformatic pipeline was used for data analysis, including variant calling to assess mutational burden. Result: Telomere elongation occurred during spaceflight and shortened after return to Earth. Cell-free DNA analysis revealed increased immune cell signatures post-flight. No significant clonal hematopoiesis of indeterminate potential (CHIP) or whole-genome instability was observed. The long-term gene expression changes across immune cells suggested cellular adaptations to the space environment persisting months post-flight. Conclusion: Our findings provide valuable insights into the physiological consequences of short-duration spaceflight, with telomere dynamics and immune cell gene expression adapting to spaceflight and persisting after return to Earth. CHIP sequencing data will serve as a reference point for studying the early development of CHIP in astronauts, an understudied phenomenon as previous studies have focused on career astronauts. This study will serve as a reference point for future commercial and non-commercial spaceflight, low Earth orbit (LEO) missions, and deep-space exploration.

Matrix stiffness enhances cancer-macrophage interactions and M2-like macrophage accumulation in the breast tumor microenvironment.

The role of intratumor heterogeneity is becoming increasingly apparent in part due to expansion in single cell technologies. Clinically, tumor heterogeneity poses several obstacles to effective cancer therapy dealing with biomarker variability and treatment responses. Matrix stiffening is known to occur during tumor progression and contribute to pathogenesis in several cancer hallmarks, including tumor angiogenesis and metastasis. However, the effects of matrix stiffening on intratumor heterogeneity have not been thoroughly studied. In this study, we applied single-cell RNA sequencing to investigate the differences in the transcriptional landscapes between stiff and compliant MMTV-PyMT mouse mammary tumors. We found similar compositions of cancer and stromal subpopulations in compliant and stiff tumors but differential intercellular communication and a significantly higher concentration of tumor-promoting, M2-like macrophages in the stiffer tumor microenvironments. Interestingly, we found that cancer cells seeded on stiffer substrates recruited more macrophages. Furthermore, elevated matrix stiffness increased Colony Stimulating Factor 1 (CSF-1) expression in breast cancer cells and reduction of CSF-1 expression on stiffer substrates reduced macrophage recruitment. Thus, our results demonstrate that tissue phenotypes were conserved between stiff and compliant tumors but matrix stiffening altered cell-cell interactions which may be responsible for shifting the phenotypic balance of macrophages residing in the tumor microenvironment towards a pro-tumor progression M2 phenotype. STATEMENT OF SIGNIFICANCE: Cells within tumors are highly heterogeneous, posing challenges with treatment and recurrence. While increased tissue stiffness can promote several hallmarks of cancer, its effects on tumor heterogeneity are unclear. We used single-cell RNA sequencing to investigate the differences in the transcriptional landscapes between stiff and compliant MMTV-PyMT mouse mammary tumors. We found similar compositions of cancer and stromal subpopulations in compliant and stiff tumors but differential intercellular communication and a significantly higher concentration of tumor-promoting, M2-like macrophages in the stiffer tumor microenvironments. Using a biomaterial-based platform, we found that cancer cells seeded on stiffer substrates recruited more macrophages, supporting our in vivo findings. Together, our results demonstrate a key role of matrix stiffness in affecting cell-cell communication and macrophage recruitment.

Paired bone marrow and peripheral blood samples demonstrate lack of widespread dissemination of some CH clones.

Clonal hematopoiesis (CH) represents clonal expansion of mutated hematopoietic stem cells detectable in the peripheral blood or bone marrow through next generation sequencing. The current prevailing model posits that CH mutations detected in the peripheral blood mirror bone marrow mutations with clones widely disseminated across hematopoietic compartments. We sought to test the hypothesis that all clones are disseminated throughout hematopoietic tissues by comparing CH in hip vs peripheral blood specimens collected at the time of hip replacement surgery. Here, we show that patients with osteoarthritis have a high prevalence of CH, which involve genes encoding epigenetic modifiers and DNA damage repair pathway proteins. Importantly, we illustrate that CH, including clones with variant allele frequencies >10%, can be confined to specific bone marrow spaces and may be eliminated through surgical excision. Future work will define whether clones with somatic mutations in particular genes or clonal fractions of certain sizes are either more likely to be localized or are slower to disseminate into the peripheral blood and other bony sites.

Chemical genomic screening reveals synergism between parthenolide and inhibitors of the PI-3 kinase and mTOR pathways.

We have previously shown that the plant-derived compound parthenolide (PTL) can impair the survival and leukemogenic activity of primary human acute myeloid leukemia (AML) stem cells. However, despite the activity of this agent, PTL also induces cellular protective responses that likely function to reduce its overall cytotoxicity. Thus, we sought to identify pharmacologic agents that enhance the antileukemic potential of PTL. Toward this goal, we used the gene expression signature of PTL to identify compounds that inhibit cytoprotective responses by performing chemical genomic screening of the Connectivity Map database. This screen identified compounds acting along the phosphatidylinositol 3-kinase and mammalian target of rapamycin pathways. Compared with single agent treatment, exposure of AML cells to the combination of PTL and phosphatidylinositol 3-kinase/mammalian target of rapamycin inhibitors significantly decreased viability of AML cells and reduced tumor burden in vitro and in murine xenotransplantation models. Taken together, our data show that rational drug combinations can be identified using chemical genomic screening strategies and that inhibition of cytoprotective functions can enhance the eradication of primary human AML cells.

Allogeneic TCRαß deficient CAR T-cells targeting CD123 in acute myeloid leukemia.

Acute myeloid leukemia (AML) is a disease with high incidence of relapse that is originated and maintained from leukemia stem cells (LSCs). Hematopoietic stem cells can be distinguished from LSCs by an array of cell surface antigens such as CD123, thus a candidate to eliminate LSCs using a variety of approaches, including CAR T cells. Here, we evaluate the potential of allogeneic gene-edited CAR T cells targeting CD123 to eliminate LSCs (UCART123). UCART123 cells are TCRαßneg T cells generated from healthy donors using TALEN® gene-editing technology, decreasing the likelihood of graft vs host disease. As safety feature, cells express RQR8 to allow elimination with Rituximab. UCART123 effectively eliminates AML cells in vitro and in vivo with significant benefits in overall survival of AML-patient derived xenograft mice. Furthermore, UCART123 preferentially target AML over normal cells with modest toxicity to normal hematopoietic stem/progenitor cells. Together these results suggest that UCART123 represents an off-the shelf therapeutic approach for AML.

Mutant PPM1D- and TP53-Driven Hematopoiesis Populates the Hematopoietic Compartment in Response to Peptide Receptor Radionuclide Therapy.

PURPOSE: Hematologic toxic effects of peptide receptor radionuclide therapy (PRRT) can be permanent. Patients with underlying clonal hematopoiesis (CH) may be more inclined to develop hematologic toxicity after PRRT. However, this association remains understudied. MATERIALS AND METHODS: We evaluated pre- and post-PRRT blood samples of patients with neuroendocrine tumors. After initial screening, 13 cases of interest were selected. Serial blood samples were obtained on 4 of 13 patients. Genomic DNA was analyzed using a 100-gene panel. A variant allele frequency cutoff of 1% was used to call CH. RESULT: Sixty-two percent of patients had CH at baseline. Persistent cytopenias were noted in 64% (7 of 11) of the patients. Serial sample analysis demonstrated that PRRT exposure resulted in clonal expansion of mutant DNA damage response genes (TP53, CHEK2, and PPM1D) and accompanying cytopenias in 75% (3 of 4) of the patients. One patient who had a normal baseline hemogram and developed persistent cytopenias after PRRT exposure showed expansion of mutant PPM1D (variant allele frequency increased to 20% after exposure from < 1% at baseline). In the other two patients, expansion of mutant TP53, CHEK2, and PPM1D clones was also noted along with cytopenia development. CONCLUSION: The shifts in hematopoietic clonal dynamics in our study were accompanied by emergence and persistence of cytopenias. These cytopenias likely represent premalignant state, as PPM1D-, CHEK2-, and TP53-mutant clones by themselves carry a high risk for transformation to therapy-related myeloid neoplasms. Future studies should consider CH screening and longitudinal monitoring as a key risk mitigation strategy for patients with neuroendocrine tumors receiving PRRT.

Patient-Derived Bone Marrow Spheroids Reveal Leukemia-Initiating Cells Supported by Mesenchymal Hypoxic Niches in Pediatric B-ALL.

B-cell acute lymphoblastic leukemia (B-ALL) results from the expansion of malignant lymphoid precursors within the bone marrow (BM), where hematopoietic niches and microenvironmental signals provide leukemia-initiating cells (LICs) the conditions to survive, proliferate, initiate disease, and relapse. Normal and malignant lymphopoiesis are highly dependent on the BM microenvironment, particularly on CXCL12-abundant Reticular (CAR) cells, which provide a niche for maintenance of primitive cells. During B-ALL, leukemic cells hijack BM niches, creating a proinflammatory milieu incompetent to support normal hematopoiesis but favoring leukemic proliferation. Although the lack of a phenotypic stem cell hierarchy is apparent in B-ALL, LICs are a rare and quiescent population potentially responsible for chemoresistance and relapse. Here, we developed novel patient-derived leukemia spheroids (PDLS), an ex vivo avatar model, from mesenchymal stromal cells (MSCs) and primary B-ALL cells, to mimic specialized niche structures and cell-to-cell intercommunication promoting normal and malignant hematopoiesis in pediatric B-ALL. 3D MSC spheroids can recapitulate CAR niche-like hypoxic structures that produce high levels of CXCL10 and CXCL11. We found that PDLS were preferentially enriched with leukemia cells displaying functional properties of LICs, such as quiescence, low reactive oxygen species, drug resistance, high engraftment in immunodeficient mice, and long-term leukemogenesis. Moreover, the combination of PDLS and patient-derived xenografts confirmed a microenvironment-driven hierarchy in their leukemic potential. Importantly, transcriptional profiles of MSC derived from primary patient samples revealed two unique signatures (1), a CXCL12low inflammatory and leukemia expansion (ILE)-like niche, that likely supports leukemic burden, and (2) a CXCL11hi immune-suppressive and leukemia-initiating cell (SLIC)-like niche, where LICs are likely sustained. Interestingly, the CXCL11+ hypoxic zones were recapitulated within the PDLS that are capable of supporting LIC functions. Taken together, we have implemented a novel PDLS system that enriches and supports leukemia cells with stem cell features driven by CXCL11+ MSCs within hypoxic microenvironments capable of recapitulating key features, such as tumor reemergence after exposure to chemotherapy and tumor initiation. This system represents a unique opportunity for designing ex vivo personalized avatars for B-ALL patients to evaluate their own LIC pathobiology and drug sensitivity in the context of the tumor microenvironment.

Targeting the epichaperome as an effective precision medicine approach in a novel PML-SYK fusion acute myeloid leukemia.

The epichaperome is a new cancer target composed of hyperconnected networks of chaperome members that facilitate cell survival. Cancers with an altered chaperone configuration may be susceptible to epichaperome inhibitors. We developed a flow cytometry-based assay for evaluation and monitoring of epichaperome abundance at the single cell level, with the goal of prospectively identifying patients likely to respond to epichaperome inhibitors, to measure target engagement, and dependency during treatment. As proof of principle, we describe a patient with an unclassified myeloproliferative neoplasm harboring a novel PML-SYK fusion, who progressed to acute myeloid leukemia despite chemotherapy and allogeneic stem cell transplant. The leukemia was identified as having high epichaperome abundance. We obtained compassionate access to an investigational epichaperome inhibitor, PU-H71. After 16 doses, the patient achieved durable complete remission. These encouraging results suggest that further investigation of epichaperome inhibitors in patients with abundant baseline epichaperome levels is warranted.

Discovery of agents that eradicate leukemia stem cells using an in silico screen of public gene expression data.

Increasing evidence indicates that malignant stem cells are important for the pathogenesis of acute myelogenous leukemia (AML) and represent a reservoir of cells that drive the development of AML and relapse. Therefore, new treatment regimens are necessary to prevent relapse and improve therapeutic outcomes. Previous studies have shown that the sesquiterpene lactone, parthenolide (PTL), ablates bulk, progenitor, and stem AML cells while causing no appreciable toxicity to normal hematopoietic cells. Thus, PTL must evoke cellular responses capable of mediating AML selective cell death. Given recent advances in chemical genomics such as gene expression-based high-throughput screening (GE-HTS) and the Connectivity Map, we hypothesized that the gene expression signature resulting from treatment of primary AML with PTL could be used to search for similar signatures in publicly available gene expression profiles deposited into the Gene Expression Omnibus (GEO). We therefore devised a broad in silico screen of the GEO database using the PTL gene expression signature as a template and discovered 2 new agents, celastrol and 4-hydroxy-2-nonenal, that effectively eradicate AML at the bulk, progenitor, and stem cell level. These findings suggest the use of multicenter collections of high-throughput data to facilitate discovery of leukemia drugs and drug targets.

Clonal Hematopoiesis and Premalignant Diseases.

Clonal hematopoiesis (CH) arises when mutations in the hematopoietic system confer a fitness advantage to specific clones, thereby favoring their disproportionate growth. The presence of CH increases with age and environmental exposures such as cytotoxic chemotherapy or radiotherapy. The most frequent mutations occur in epigenetic regulators, such as DNMT3A, TET2, and ASXL1, leading to dysregulation of tumor suppressor function, pathogen response, and inflammation. These dysregulated processes elevate risk of overall mortality, cardiovascular disease, and eventual hematologic malignancy (HM). CH is likely acting as an initiating event leading to HM when followed by cooperating mutations. However, further evidence suggests that CH exerts a bystander influence through its pro-inflammatory properties. Delineating the mechanisms that lead to the onset and expansion of CH as well as its contribution to risk of HM is crucial to defining a management and intervention strategy. In this review, we discuss the potential causes, consequences, technical considerations, and possible management strategies for CH in the context of HMs and pre-HMs.

Plasma Cell Myeloma Presenting With Amyloid-Laden Crystal-Negative Histiocytosis.

OBJECTIVES: Crystal-storing histiocytosis (CSH) is rare in plasma cell dyscrasias, with only 3 cases reported in the setting of amyloid. No cases of crystal-negative histiocytosis coincident with multiple myeloma and amyloidosis have been reported previously. METHODS: A 58-year-old woman presented with pain due to destructive bone lesions and was found to have plasma cell myeloma (PCM) and marrow amyloid deposition associated with crystal-negative histiocytosis. Differential diagnoses included Langerhans cell histiocytosis, Erdheim-Chester disease, and Rosai Dorfman disease. BRAF mutations were negative, and there was no evidence of paraprotein crystals, arguing against typical CSH. RESULTS: The patient was treated with bortezomib, cyclophosphamide, and dexamethasone, and she subsequently underwent autologous stem cell transplant and ixazomib maintenance. She achieved complete remission with improvement of her symptoms and preserved remission after following up at 60 months. CONCLUSIONS: We describe a case of crystal-negative histiocytosis associated with PCM. CSH is a rare disorder associated with paraprotein-producing conditions in which immunoglobulins aggregate as intracellular crystals in the lysosomes of organ-specific phagocytic macrophages. Light chain tropism in PCM can also lead to the development of amyloid deposition in organs and, in rare cases, is associated with light chain aggregation as intracellular crystals in macrophages.

Clonal Hematopoiesis Before, During, and After Human Spaceflight.

Clonal hematopoiesis (CH) occurs when blood cells harboring an advantageous mutation propagate faster than others. These mutations confer a risk for hematological cancers and cardiovascular disease. Here, we analyze CH in blood samples from a pair of twin astronauts over 4 years in bulk and fractionated cell populations using a targeted CH panel, linked-read whole-genome sequencing, and deep RNA sequencing. We show CH with distinct mutational profiles and increasing allelic fraction that includes a high-risk, TET2 clone in one subject and two DNMT3A mutations on distinct alleles in the other twin. These astronauts exhibit CH almost two decades prior to the mean age at which it is typically detected and show larger shifts in clone size than age-matched controls or radiotherapy patients, based on a longitudinal cohort of 157 cancer patients. As such, longitudinal monitoring of CH may serve as an important metric for overall cancer and cardiovascular risk in astronauts.

Clonal Hematopoiesis and risk of Acute Myeloid Leukemia.

Acute Myeloid Leukemia, the most common form of acute leukemia in adults, is an aggressive hematopoietic stem cell malignancy that is associated with significant morbidity and mortality. Though AML generally presents de novo, risk factors include exposure to chemotherapy and/or radiation, as well as both familial and acquired bone marrow failure syndromes. Clonal Hematopoiesis (CH) refers to an expansion of blood or marrow cells resulting from somatic mutations in leukemia-associated genes detected in individuals without cytopenias or hematological malignancies. While CH is considered part of normal ageing, CH is also significantly associated with cardiovascular disease, solid tumors, and hematological malignancies. In this review, we will discuss evidence linking CH with the development of AML, as well as describe challenges in and strategies for monitoring patients with high risk CH mutations.