Donor cell leukemia arising from clonal hematopoiesis after bone marrow transplantation

International Society for Cell & Gene Therapy Stem Cell Engineering Committee report on the current state of hematopoietic stem and progenitor cell-based genomic therapies and the challenges faced

Genetic manipulation of hematopoietic stem cells (HSCs) is being developed as a therapeutic strategy for several inherited disorders. This field is rapidly evolving with several novel tools and techniques being employed to achieve desired genetic changes. While commercial products are now available for sickle cell disease, transfusion-dependent β-thalassemia, metachromatic leukodystrophy and adrenoleukodystrophy, several challenges remain in patient selection, HSC mobilization and collection, genetic manipulation of stem cells, conditioning, hematologic recovery and post-transplant complications, financial issues, equity of access and institutional and global preparedness. In this report, we explore the current state of development of these therapies and provide a comprehensive assessment of the challenges these therapies face as well as potential solutions.

Clonal hematopoiesis of indeterminate potential: the root cause of, and fertile ground for, hematological malignancies

Clonal hematopoiesis (CH) of indeterminate potential (CHIP), characterized by propagation of blood cell clones carrying somatic mutations in specific driver genes, is increasingly recognized as a critical factor in the development of hematological malignancies. This phenomenon, which often emerges with age, underscores the complex interplay between genetic predisposition and environmental influences in cancer initiation and progression. Recent years have witnessed significant advances in our understanding of the link between CHIP and hematological diseases. In this review, we provide a comprehensive overview of the features of CHIP and explore its role in promoting tumorigenesis and influencing treatment outcomes for blood cancers. Finally, we summarize current available tools for risk stratification and discuss management strategies for patients with CHIP.

Recipient clonal hematopoiesis in allogeneic bone marrow transplantation for lymphoid malignancies

ABSTRACT

Allogeneic blood and marrow transplantation (alloBMT) is increasingly being used in older patients with blood cancer. Aging is associated with an increasing incidence of clonal hematopoiesis (CH). Although the effects of donor CH on alloBMT has been reported, the impact of recipient CH on alloBMT outcomes is unknown. In this retrospective study, alloBMT recipients age 60 and older with lymphoid malignancies were included. Among 97 consecutive patients who received alloBMT between 2017 and 2022, CH was detected in 60 (62%; 95% confidence interval [CI], 51-72). CH was found in 45% (95% CI, 28-64) of patients aged 60 to 64, 64% (95% CI, 44-81) of patients aged 65% to 69%, and 73% (95% CI, 59-87) in those above 70. Pretransplant CH was associated with worse survival after alloBMT: 3-year overall survival (OS) was 78% (95% CI, 65-94) for patients without CH vs 47% (95% CI, 35-63) for those with CH, (unadjusted HR, 3.1; [95% CI, 1.4-6.8; P < .001]). Nonrelapse mortality (NRM) was higher in patients with CH; cumulative incidence of NRM at 1-year was 11% (95% CI, 1-22) vs 35% (95% CI, 23-48), (HR, 3.4; [95% CI, 1.4-8.5], P = .009]). Among CH patients, worse OS and NRM was associated with CH burden and number of mutations. Recipient CH had no effect on relapse. In conclusion, older patients with CH experience worse outcomes after alloBMT, almost exclusively attributable to increased NRM. CH is a strong, independent predictor of outcomes. Novel strategies to ameliorate the adverse impacts of patient CH on transplant outcomes are being evaluated.

Donor-Derived Malignancy and Transplantation Morbidity: Risks of Patient and Donor Genetics in Allogeneic Hematopoietic Stem Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains a key treatment option for hematologic malignancies (HMs), although it carries significant risks. Up to 30% of patients relapse after allo-HSCT, of which up to 2% to 5% are donor-derived malignancies (DDMs). DDMs can arise from a germline genetic predisposition allele or clonal hematopoiesis (CH) in the donor. Increasingly, genetic testing reveals that patient and donor genetic factors contribute to the development of DDM and other allo-HSCT complications. Deleterious germline variants in CEBPA, DDX41, GATA2, and RUNX1 predispose to inferior allo-HSCT outcomes. DDM has been linked to donor-acquired somatic CH variants in DNMT3A, ASXL1, JAK2, and IDH2, often with additional new variants. We do not yet have evidence to standardize donor genetic sequencing prior to allo-HSCT. The presence of hereditary HM disorders should be considered in patients with myeloid malignancies and their related donors, and screening of unrelated donors should include family and personal history of cytopenia and HMs. Excellent multidisciplinary care is critical to ensure efficient timelines for screening and necessary discussions among medical oncologists, genetic counselors, recipients, and potential donors. After allo-HSCT, HM relapse monitoring with genetic testing effectively results in genetic sequencing of the donor, as the transplanted hematopoietic system is donor-derived, which presents ethical challenges for disclosure to patients and donors. We encourage consideration of the recent National Marrow Donor Program policy that allows donors to opt-in for notification about detection of their genetic variants after allo-HSCT, with appropriate genetic counseling when feasible. We look forward to prospective investigation of the impact of germline and acquired somatic genetic variants on hematopoietic stem cell mobilization/engraftment, graft-versus-host disease, and DDM to facilitate improved outcomes through knowledge of genetic risk.

Clonal hematopoiesis in the setting of hematopoietic cell transplantation

Clonal hematopoiesis (CH) in autologous transplant recipients and allogeneic transplant donors has genetic features and clinical associations that are distinct from each other and from non-cancer populations. CH in the setting of autologous transplant is enriched for mutations in DNA damage response pathway genes and is associated with adverse outcomes, including an increased risk of therapy-related myeloid neoplasm and inferior overall survival. Studies of CH in allogeneic transplant donors have yielded conflicting results but have generally shown evidence of potentiated alloimmunity in recipients, with some studies showing an association with favorable recipient outcomes.

Causes and consequences of clonal hematopoiesis

ABSTRACT

Clonal hematopoiesis (CH) is described as the outsized contribution of expanded clones of hematopoietic stem and progenitor cells (HSPCs) to blood cell production. The prevalence of CH increases dramatically with age. CH can be caused by somatic mutations in individual genes or by gains and/or losses of larger chromosomal segments. CH is a premalignant state; the somatic mutations detected in CH are the initiating mutations for hematologic malignancies, and CH is a strong predictor of the development of blood cancers. Moreover, CH is associated with nonmalignant disorders and increased overall mortality. The somatic mutations that drive clonal expansion of HSPCs can alter the function of terminally differentiated blood cells, including the release of elevated levels of inflammatory cytokines. These cytokines may then contribute to a broad range of inflammatory disorders that increase in prevalence with age. Specific somatic mutations in the peripheral blood in coordination with blood count parameters can powerfully predict the development of hematologic malignancies and overall mortality in CH. In this review, we summarize the current understanding of CH nosology and origins. We provide an overview of available tools for risk stratification and discuss management strategies for patients with CH presenting to hematology clinics.

"Oncocytoid Renal Cell Carcinomas After Neuroblastoma" Represent TSC -mutated Eosinophilic Solid and Cystic Renal Cell Carcinomas : Association With Prior Childhood Malignancy and Multifocality With Therapeutic Implications

The concept of oncocytoid renal cell carcinoma in patients who have survived neuroblastoma as a distinct biologic entity has been controversial since its original description in 1999. This is in part because similar oncocytoid renal cell carcinomas have been described in association with other pediatric cancers, and also because other renal cell carcinoma subtypes (such as MiT family translocation renal cell carcinoma) have been described in children who have survived neuroblastoma. We identified an index case of a child who survived medulloblastoma and developed multifocal bilateral oncocytoid renal cell carcinomas with morphology and immunophenotype compatible with eosinophilic solid and cystic renal cell carcinoma (ESC RCC) and demonstrated that both neoplasms harbored distinctive mutations in the TSC1/TSC2 genes. Remarkably, the child's remaining bilateral multifocal renal neoplasms completely responded to MTOR inhibitor therapy without need for further surgery. To confirm our hypothesis that oncocytoid renal cell carcinomas after childhood cancer represent ESC RCC, we obtained formalin-fixed paraffin-embedded tissue blocks from 2 previously published cases of oncocytoid renal cell carcinoma after neuroblastoma, confirmed that the morphology and immunophenotype was consistent with ESC RCC, and demonstrated that both cases harbored somatic TSC gene mutations. Both expressed markers previously associated with neoplasms harboring TSC gene mutations, glycoprotein nonmetastatic B, and cathepsin K. Of note, one of these patients had 2 ESC RCC which harbored distinctive TSC2 mutations, while the background kidney of the other patient had multiple small cysts lined by similar oncocytoid cells which showed loss of TSC2 protein. We then reviewed 3 of 4 cases from the original 1999 report of oncocytoid renal cell carcinomas after neuroblastoma, found that all 3 demonstrated morphology (including basophilic cytoplasmic stippling) that is characteristic of ESC RCC, showed that all 3 overexpressed glycoprotein nonmetastatic B, and showed that both cases with adequate material demonstrated loss of TSC2 protein and expressed cytokeratin 20 and cathepsin K by immunohistochemistry. In summary, "oncocytoid renal cell carcinomas after neuroblastoma" represent ESC RCC which are often multifocal in patients who have survived childhood cancer, likely representing an incompletely characterized tumor predisposition syndrome. MTOR-targeted therapy represents an effective therapeutic option for such patients to preserve functional nephrons.

Hypothesis: can transfer of primary neoplasm-derived extracellular vesicles and mitochondria contribute to the development of donor cell-derived hematologic neoplasms after allogeneic hematopoietic cell transplantation?

Allogeneic hematopoietic cell transplantation (allo-HCT) is an essential treatment option for various neoplastic and non-neoplastic hematologic diseases. Although its efficacy is modest, a significant proportion of patients experience relapse, graft-versus-host disease, infection or impaired hematopoiesis. Among these, the most frequent cause of post-transplant mortality is relapse, whereas the development of de novo hematologic neoplasms from donor cells after allo-HCT occurs on some occasion as a rare complication. The mechanisms involved in the pathogenesis of the de novo hematologic neoplasms from donor cells are complex, and a multifactorial process contributes to the development of this complication. Recently, extracellular vesicles, particularly exosomes, and mitochondria have been shown to play crucial roles in intercellular communication through the transfer of specific constituents, such as deoxyribonucleic acids, ribonucleic acids, lipids, metabolites and cytosolic and cell-surface proteins. Here, I discuss the potential causative roles of these subcellular components in the development of de novo hematologic neoplasms from donor cells after allo-HCT, in addition to other etiologies.

Donor-derived acute myeloid leukemia in solid organ transplantation

We report the transmission of acute myeloid leukemia (AML) undetected at donation from a deceased organ donor to two kidneys and one liver recipients. We reviewed the medical records, and performed molecular analyses and whole exome sequencing (WES) to ascertain AML donor origin and its molecular evolution. The liver recipient was diagnosed 11 months after transplantation and died from complications 2 months later. The two kidney recipients (R1 and R2) were diagnosed 19 and 20 months after transplantation and both received treatment for leukemia. R1 died of complications 11 months after diagnosis, while R2 went into complete remission for 44 months, before relapsing. R2 died 10 months later of complications from allogenic bone marrow transplantation. Microsatellite analysis demonstrated donor chimerism in circulating cells from both kidney recipients. Targeted molecular analyses and medical records revealed NPM1 mutation present in the donor and recipients, while FLT3 was mutated only in R1. These findings were confirmed by WES, which revealed additional founder and clonal mutations, and HLA genomic loss in R2. In conclusion, we report the first in-depth genomic analysis of AML transmission following solid organ transplantation, revealing distinct clonal evolution, and providing a potential molecular explanation for tumor escape.

Clonal Hematopoiesis: Role in Hematologic and Non-Hematologic Malignancies

Hematopoietic stem cells (HSCs) ensure the coordinated and balanced production of all hematopoietic cell types throughout life. Aging is associated with a gradual decline of the self-renewal and regenerative potential of HSCs and with the development of clonal hematopoiesis. Clonal hematopoiesis of indeterminate potential (CHIP) defines the clonal expansion of genetically variant hematopoietic cells bearing one or more gene mutations and/or structural variants (such as copy number alterations). CHIP increases exponentially with age and is associated with cancers, including hematologic neoplasia, cardiovascular and other diseases. The presence of CHIP consistently increases the risk of hematologic malignancy, particularly in individuals who have CHIP in association with peripheral blood cytopenia.

Clonal hematopoiesis in men living with HIV and association with subclinical atherosclerosis

OBJECTIVES

People with HIV (PWH) are at increased risk for premature cardiovascular disease (CVD). Clonal hematopoiesis is a common age-related condition that may be associated with increased CVD risk. The goal of this study was to determine the prevalence of clonal hematopoiesis and its association with chronic inflammation and CVD in PWH.

DESIGN

Cross-sectional study utilizing archived specimens and data from 118 men (86 PWH and 32 HIV-uninfected) from the Baltimore-Washington DC center of the Multicenter AIDS Cohort Study (MACS) who had had coronary computed tomography angiography (CTA) and measurement of 34 serologic inflammatory biomarkers.

METHODS

Clonal hematopoiesis was assessed on peripheral blood mononuclear cells utilizing targeted error-corrected next generation sequencing (NGS) focused on 92 genes frequently mutated in hematologic malignancies. Clinical and laboratory data were obtained from the MACS database.

RESULTS

Clonal hematopoiesis with a variant allele frequency (VAF) greater than 1% was significantly more common in PWH [20/86 (23.3%)] than in HIV-uninfected men [2/32 (6.3%)] ( P  = 0.035). PWH with clonal hematopoiesis (VAF > 1%) were more likely to have coronary artery stenosis of at least 50% than those without clonal hematopoiesis [6/20 (30%) vs. 6/64 (9%); P  = 0.021]. Presence of clonal hematopoiesis was not significantly associated with serological inflammatory markers, except for significantly lower serum leptin levels; this was not significant after adjustment for abdominal or thigh subcutaneous fat area.

CONCLUSION

Clonal hematopoiesis was more common in PWH and among PWH was associated with the extent of coronary artery disease. Larger studies are needed to further examine the biological and clinical consequences of clonal hematopoiesis in PWH.

Xanthomatous Giant Cell Renal Cell Carcinoma: Another Morphologic Form of TSC-associated Renal Cell Carcinoma

Over the past decade, several distinct novel renal epithelial neoplasms driven by underlying tuberous sclerosis comples (TSC)/mammalian target of rapamycin (MTOR) pathway mutations have been described. We report herein two distinctive TSC2-mutated renal cell carcinomas which do not fit any previously described entity. The two renal carcinomas occurred in young patients (ages 10 and 31 y), and were characterized by highly permeative growth within the kidney with metastases to perirenal lymph nodes. The neoplastic cells were predominantly large, multinucleated giant cells having variably eosinophilic to xanthomatous cytoplasm with basophilic stippling and frequent vacuolization. While the discohesive nature of the neoplastic cells, xanthomatous cytoplasm, immunoreactivity for histiocytic markers and minimal immunoreactivity for conventional epithelial markers raised the possibility of a histiocytic neoplasm, multifocal immunoreactivity for cytokeratin 20 helped establish their epithelial nature. Despite the aggressive growth pattern of these neoplasms and lymph node metastases, mitotic figures were rare and Ki-67 indices were low (<1%). One patient with follow-up shows no evidence of disease seven years after nephrectomy with no adjuvant therapy. Next-generation sequencing demonstrated TSC2 mutations in each case. By immunohistochemistry, downstream markers of mTOR pathway activation S6K1, 4EBP1, and glycoprotein nonmetastatic melanoma protein B were all highly expressed in these neoplasms, suggesting mTOR pathway activation as the neoplastic driver. While the cytokeratin 20 immunoreactivity and focal basophilic cytoplasmic stippling suggest a relationship to eosinophilic solid and cystic renal cell carcinoma, and cytoplasmic vacuolization suggests a relationship to eosinophilic vacuolated tumor, these neoplasms appear to be distinctive given their permeative growth patterns and predominant xanthomatous giant cell morphology. Addition of cytokeratin 20 to a panel of epithelial markers helps avoid misdiagnosis in such cases.

Klonale Hämatopoese – Verbindungsglied kardiovaskulärer und hämatologischer Erkrankungen

Klonale Hämatopoese ist ein prämaligner Zustand der Blutzellen, der insbesondere in der älteren Bevölkerung sehr häufig ist. Er geht nicht nur mit einem erhöhten Risiko für hämatologische Erkrankungen einher, sondern ist insbesondere aufgrund des vermehrten Vorkommens von kardiovaskulären Erkrankungen klinisch hochrelevant. Auch im Kontext allogener hämatopoetischer Stammzelltransplantationen spielt klonale Hämatopoese eine zunehmend wichtige Rolle.

Targeted molecular profiling of salivary duct carcinoma with rhabdoid features highlights parallels to other apocrine and discohesive neoplasms: which phenotype should drive classification?

BACKGROUND

Salivary duct carcinoma with rhabdoid features (SDC-RF) is a recently-described salivary gland tumor that bears striking histologic similarity to lobular carcinoma of the breast. While this tumor has an apocrine phenotype that supports classification as a variant of SDC, it infrequently arises in association with conventional SDC. Furthermore, discohesive architecture can be seen in non-apocrine salivary carcinomas, raising the possibility that discohesive growth should define a separate entity. In this study, we aimed to perform comprehensive molecular profiling of SDC-RF to better understand its pathogenesis and classification.

METHODS

We documented the clinicopathologic features of 9 cases of SDC-RF and performed immunostains including AR, GCDFP, and e-cadherin on all cases. We also performed targeted next generation sequencing (NGS) panels on 7 cases that had sufficient tissue available.

RESULTS

The SDC-RF represented 8 men and 1 woman with a median age of 67 years (range 63-83 years) and included 6 parotid, 2 buccal, and 1 submandibular primary. All tumors were uniformly composed of discohesive cells with abundant eosinophilic cytoplasm; signet-ring cell features were seen in 2 cases. All tumors were also positive for AR (100%) and GCDFP (100%), and 7 tumors (78%) displayed lost or abnormal e-cadherin. NGS highlighted concomitant PIK3CA and HRAS mutations in 4 tumors, with additional cases harboring TP53, PTEN, and AKT1 mutations. Furthermore, CDH1 alterations were seen in 6 cases, including a novel CDH1::CORO7 fusion. Among 5 patients with follow-up available, 3 (60%) developed local recurrence and widespread distant metastasis and died of disease at a median 20 months (range 10-48 months).

CONCLUSIONS

Overall, our findings confirm frequent CDH1 mutations and e-cadherin inactivation in SDC-RF, similar to discohesive tumors from other sites. We also highlight an apocrine molecular profile similar to conventional SDC. However, occasional AKT1 mutation and signet-ring features suggest SDC-RF may also be related to mucinous adenocarcinoma. As more salivary tumors with discohesive growth are identified, it may become clearer whether SDC-RF should remain in the SDC family or be recognized as a separate entity.

Clonal Hematopoiesis and the Risk of Hematologic Malignancies after Curative Therapies for Sickle Cell Disease

Sickle cell disease (SCD) is associated with severe morbidity and early mortality. Two large population studies found an increased risk for leukemia in individuals with SCD. Notably, while the relative risk of leukemia development is high, the absolute risk is low in individuals with SCD who do not receive cell-based therapies. However, the risk of leukemia in SCD is high after graft rejection and with gene therapy. Clonal hematopoiesis (CH) is a well-recognized premalignant condition in the general population and in patients after high-dose myelotoxic therapies. Recent studies suggest that CH may be more common in SCD than in the general population, outside the cell-based therapy setting. Here, we review risk factors for CH and progression to leukemia in SCD. We surmise why patients with SCD are at an increased risk for CH and why leukemia incidence is unexpectedly high after graft rejection and gene therapy for SCD. Currently, we are unable to reliably assess genetic risk factors for leukemia development after curative therapies for SCD. Given our current knowledge, we recommend counseling patients about leukemia risk and discussing the importance of an individualized benefit/risk assessment that incorporates leukemia risk in patients undergoing curative therapies for SCD.

Post-Transplantation Cyclophosphamide-Based Graft- versus-Host Disease Prophylaxis with Nonmyeloablative Conditioning for Blood or Marrow Transplantation for Myelofibrosis

We describe outcomes after post-transplantation cyclophosphamide and nonmyeloablative conditioning-based allogeneic blood or marrow transplantation for myelofibrosis using matched or mismatched related or unrelated donors. The conditioning regimen consisted of fludarabine, cyclophosphamide, and total body irradiation. Forty-two patients were included, with a median age of 63 years, of whom 19% had Dynamic International Prognostic Scoring System (DIPSS)-plus intermediate-1 risk, 60% had intermediate-2 risk, and 21% had high-risk disease, and 60% had at least 1 high-risk somatic mutation. More than 90% of patients engrafted neutrophils, at a median of 19.5 days, and 7% experienced graft failure. At 1 year and 3 years, respectively, overall survival was 65% and 60%, relapse-free survival was 65% and 31%, relapse was 5% and 40%, and nonrelapse mortality was 30% and 30%. Acute graft-versus-host disease grade 3-4 was seen in 17% of patients at 1 year, and chronic graft-versus-host disease requiring systemic therapy in occurred in 12% patients. Spleen size ≥17 cm or prior splenectomy was associated with inferior relapse-free survival (hazard ratio [HR], 3.50; 95% confidence interval [CI], 1.18 to 10.37; P = .02) and higher relapse rate (subdistribution HR [SDHR] not calculable; P = .01). Age >60 years (SDHR, 0.26; 95% CI, 0.08 to 0.80, P = .02) and receipt of peripheral blood grafts (SDHR, 0.34; 95% CI, 0.11 to 0.99; P = .05) were associated with a lower risk of relapse. In our limited sample, the presence of a high-risk mutation was not statistically significantly associated with an inferior outcome, although ASXL1 was suggestive of inferior survival (SDHR, 2.36; 95% CI, 0.85 to 6.6; P = .09). Overall, this approach shows outcomes comparable those of to previously reported approaches and underscores the importance of spleen size in the evaluation of transplantation candidates.

Donor Clonal Hematopoiesis and Recipient Outcomes After Transplantation

PURPOSE

Clonal hematopoiesis (CH) can be transmitted from a donor to a recipient during allogeneic hematopoietic cell transplantation. Exclusion of candidate donors with CH is controversial since its impact on recipient outcomes and graft alloimmune function is uncertain.

PATIENTS AND METHODS

We performed targeted error-corrected sequencing on samples from 1,727 donors age 40 years or older and assessed the effect of donor CH on recipient clinical outcomes. We measured long-term engraftment of 102 donor clones and cytokine levels in 256 recipients at 3 and 12 months after transplant.

RESULTS

CH was present in 22.5% of donors, with DNMT3A (14.6%) and TET2 (5.2%) mutations being most common; 85% of donor clones showed long-term engraftment in recipients after transplantation, including clones with a variant allele fraction < 0.01. DNMT3A-CH with a variant allele fraction ≥ 0.01, but not smaller clones, was associated with improved recipient overall (hazard ratio [HR], 0.79; P = .042) and progression-free survival (HR, 0.72; P = .003) after adjustment for significant clinical variables. In patients who received calcineurin-based graft-versus-host disease prophylaxis, donor DNMT3A-CH was associated with reduced relapse (subdistribution HR, 0.59; P = .014), increased chronic graft-versus-host disease (subdistribution HR, 1.36; P = .042), and higher interleukin-12p70 levels in recipients. No recipient of sole DNMT3A or TET2-CH developed donor cell leukemia (DCL). In seven of eight cases, DCL evolved from donor CH with rare TP53 or splicing factor mutations or from donors carrying germline DDX41 mutations.

CONCLUSION

Donor CH is closely associated with clinical outcomes in transplant recipients, with differential impact on graft alloimmune function and potential for leukemic transformation related to mutated gene and somatic clonal abundance. Donor DNMT3A-CH is associated with improved recipient survival because of reduced relapse risk and with an augmented network of inflammatory cytokines in recipients. Risk of DCL in allogeneic hematopoietic cell transplantation is driven by somatic myelodysplastic syndrome-associated mutations or germline predisposition in donors.

Donor Clonal Hematopoiesis and Recipient Outcomes After Transplantation

PURPOSE

Clonal hematopoiesis (CH) can be transmitted from a donor to a recipient during allogeneic hematopoietic cell transplantation. Exclusion of candidate donors with CH is controversial since its impact on recipient outcomes and graft alloimmune function is uncertain.

PATIENTS AND METHODS

We performed targeted error-corrected sequencing on samples from 1,727 donors age 40 years or older and assessed the effect of donor CH on recipient clinical outcomes. We measured long-term engraftment of 102 donor clones and cytokine levels in 256 recipients at 3 and 12 months after transplant.

RESULTS

CH was present in 22.5% of donors, with DNMT3A (14.6%) and TET2 (5.2%) mutations being most common; 85% of donor clones showed long-term engraftment in recipients after transplantation, including clones with a variant allele fraction < 0.01. DNMT3A-CH with a variant allele fraction ≥ 0.01, but not smaller clones, was associated with improved recipient overall (hazard ratio [HR], 0.79; P = .042) and progression-free survival (HR, 0.72; P = .003) after adjustment for significant clinical variables. In patients who received calcineurin-based graft-versus-host disease prophylaxis, donor DNMT3A-CH was associated with reduced relapse (subdistribution HR, 0.59; P = .014), increased chronic graft-versus-host disease (subdistribution HR, 1.36; P = .042), and higher interleukin-12p70 levels in recipients. No recipient of sole DNMT3A or TET2-CH developed donor cell leukemia (DCL). In seven of eight cases, DCL evolved from donor CH with rare TP53 or splicing factor mutations or from donors carrying germline DDX41 mutations.

CONCLUSION

Donor CH is closely associated with clinical outcomes in transplant recipients, with differential impact on graft alloimmune function and potential for leukemic transformation related to mutated gene and somatic clonal abundance. Donor DNMT3A-CH is associated with improved recipient survival because of reduced relapse risk and with an augmented network of inflammatory cytokines in recipients. Risk of DCL in allogeneic hematopoietic cell transplantation is driven by somatic myelodysplastic syndrome-associated mutations or germline predisposition in donors.

CHIP: is clonal hematopoiesis a surrogate for aging and other disease?

Somatic mutations are an unavoidable consequence of aging tissues. Even though most mutations are functionally silent, some may affect genes critical to proper tissue self-renewal and differentiation, resulting in the outgrowth of affected cells, also known as clonal expansion. In hematopoietic tissue such clonal dominance is known as clonal hematopoiesis (CH). Sporadic CH is frequent in aging and affects over 10% of individuals beyond the fifth decade of life. It has been associated with an increased risk of hematologic malignancies and cardiovascular disease. In addition to aging, CH has been observed in other hematologic conditions and confers an adaptation of hematopoietic stem cells (HSCs) to various environmental stressors and cell-intrinsic defects. In the presence of extrinsic stressors such as genotoxic therapies, T-cell-mediated immune attack, or inflammation, somatic mutations may result in augmentation of HSC fitness. Such attuned HSCs can evade the environmental insults and outcompete their unadapted counterparts. Similarly, in inherited bone marrow failures, somatic mutations in HSCs frequently lead to the reversion of inherited defects. This may occur via the direct correction of germline mutations or indirect compensatory mechanisms. Occasionally, such adaptation may involve oncogenes or tumor suppressors, resulting in malignant transformation. In this brief article, we focus on the mechanisms of clonal dominance in various clinical and biological contexts.

Validation of Long Mononucleotide Repeat Markers for Detection of Microsatellite Instability

Mismatch repair deficiency (dMMR) predicts response to immune checkpoint inhibitor therapy in solid tumors. Long mononucleotide repeat (LMR) markers may improve the interpretation of microsatellite instability (MSI) assays. Our cohorts included mismatch repair (MMR) proficient and dMMR colorectal cancer (CRC) samples, MMR proficient and dMMR endometrial cancer (EC) samples, dMMR prostate cancer samples, MSI-high (MSI-H) samples of other cancer types, and MSI-low (MSI-L) samples of various cancer types. MMR status was determined by immunohistochemical staining and/or MSI Analysis System Version 1.2 (V1.2). The sensitivity and specificity of the LMR MSI panel for dMMR detection were both 100% in CRC. The sensitivity values of the MSI V1.2 and LMR MSI panels in EC were 88% and 98%, respectively, and the specificity values were both 100%. The sensitivity of the LMR panel was 75% in dMMR prostate cancer detected by immunohistochemistry. The 22 samples of other cancer types that were previously classified as MSI-H were also classified as MSI-H using the LMR MSI panel. For the 12 samples that were previously classified as MSI-L, 1 sample was classified as microsatellite stable using the LMR MSI panel, 8 as MSI-L, and 3 as MSI-H. The LMR MSI panel showed high concordance to the MSI V1.2 panel in CRC and greater sensitivity in EC. The LMR MSI panel improves dMMR detection in noncolorectal cancers.

DEK-AFF2 Carcinoma of the Sinonasal Region and Skull Base: Detailed Clinicopathologic Characterization of a Distinctive Entity

A novel DEK-AFF2 fusion was recently reported in 4 nonkeratinizing squamous cell carcinomas of the sinonasal region and skull base, including 1 with exceptional response to immunotherapy, but it is not yet clear if this rearrangement defines a unique clinicopathologic category or represents a rare event. This study aims to characterize a larger cohort of carcinomas with DEK-AFF2 fusions to assess whether they truly constitute a distinctive entity. Among 27 sinonasal and skull base nonkeratinizing squamous cell carcinoma that were negative for human papillomavirus and Epstein-Barr virus, RNA sequencing identified DEK-AFF2 fusions in 13 cases (48%). Nine were centered in the nasal cavity, 2 in the middle ear/temporal bone, 1 in the nasopharynx, and 1 in the orbit. These tumors displayed recurrent histologic features including (1) complex endophytic and exophytic, frequently papilloma-like growth, (2) transitional epithelium with eosinophilic to amphophilic cytoplasm, (3) absent or minimal keratinization with occasional compact keratin pearls, (4) monotonous nuclei, and (5) prominent tumor-infiltrating neutrophils or stromal lymphocytes. This appearance not only overlaps with high-grade basaloid sinonasal carcinomas but also with benign papillomas and tumors reported as low-grade papillary Schneiderian carcinoma. However, DEK-AFF2 carcinomas showed frequent local recurrence, cervical lymph node metastases, and distant metastasis with 2 deaths from disease, confirming they are aggressive malignancies despite relatively bland histology. Overall, the distinctive molecular, histologic, and clinical features of DEK-AFF2 carcinomas suggest they represent a unique entity in the sinonasal region. This tumor merits increased pathologic recognition to better understand its prognostic and therapeutic implications.

Antiviral treatment causes a unique mutational signature in cancers of transplantation recipients

Genetic instability is a major concern for successful application of stem cells in regenerative medicine. However, the mutational consequences of the most applied stem cell therapy in humans, hematopoietic stem cell transplantation (HSCT), remain unknown. Here we characterized the mutation burden of hematopoietic stem and progenitor cells (HSPCs) of human HSCT recipients and their donors using whole-genome sequencing. We demonstrate that the majority of transplanted HSPCs did not display altered mutation accumulation. However, in some HSCT recipients, we identified multiple HSPCs with an increased mutation burden after transplantation. This increase could be attributed to a unique mutational signature caused by the antiviral drug ganciclovir. Using a machine learning approach, we detected this signature in cancer genomes of individuals who received HSCT or solid organ transplantation earlier in life. Antiviral treatment with nucleoside analogs can cause enhanced mutagenicity in transplant recipients, which may ultimately contribute to therapy-related carcinogenesis.

Diagnostic Challenge and Clinical Dilemma: The Long Reach of Clonal Hematopoiesis

BACKGROUND

Widespread application of massively parallel sequencing has resulted in recognition of clonal hematopoiesis in various clinical settings and on a relatively frequent basis. Somatic mutations occur in individuals with normal blood counts, and increase in frequency with age. The genes affected are the same genes that are commonly mutated in overt myeloid malignancies such as acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). This phenomenon is referred to as clonal hematopoiesis of indeterminate potential (CHIP).

CONTENT

In this review, we explore the diagnostic and clinical implications of clonal hematopoiesis. In addition to CHIP, clonal hematopoiesis may be seen in patients with cytopenia who do not otherwise meet criteria for hematologic malignancy, a condition referred to as clonal cytopenia of undetermined significance (CCUS). Distinguishing CHIP and CCUS from overt myeloid neoplasm is a challenge to diagnosticians due to the overlapping mutational landscape observed in these conditions. We describe helpful laboratory and clinical features in making this distinction. CHIP confers a risk of progression to overt hematologic malignancy similar to other premalignant states. CHIP is also associated with a proinflammatory state with multisystem implications and increased mortality risk due to cardiovascular events. The current approach to follow up and management of patients with clonal hematopoiesis is described.

SUMMARY

Nuanced understanding of clonal hematopoiesis is essential for diagnosis and clinical management of patients with hematologic conditions. Further data are needed to more accurately predict the natural history and guide management of these patients with respect to both malignant progression as well as nonhematologic sequelae.

Leukemia after gene therapy for sickle cell disease: insertional mutagenesis, busulfan, both or neither

Recently, encouraging data provided long-awaited hope for gene therapy as a cure for sickle cell disease (SCD). Nevertheless, the suspension of the bluebird bio gene therapy trial (ClinicalTrials.gov: NCT02140554) after participants developed acute myeloid leukemia/myelodysplastic syndrome (AML/MDS) is concerning. Potential possibilities for these cases include busulfan, insertional mutagenesis, both or neither. Busulfan was considered the cause in the first reported case, as the transgene was not present in the AML/MDS. However, busulfan is unlikely to have contributed to the most recent case. The transgene was present in the patient's malignant cells, indicating they were infused after busulfan treatment. Several lines of evidence suggest an alternative explanation for events in the bluebird bio trial, including that SCD population studies show an increased relative, but a low absolute, risk of AML/MDS. We propose a new hypothesis: after gene therapy for SCD, the stress of switching from homeostatic to regenerative hematopoiesis by transplanted cells drives clonal expansion and leukemogenic transformation of pre-existing premalignant clones, eventually resulting in AML/MDS. Evidence validating our hypothesis will support pre-screening individuals with SCD for pre-leukemic progenitors before gene therapy. Until a viable, safe strategy has been implemented to resume gene therapy in adults with severe SCD, reasonable alternative curative therapy should be considered for children and adults with severe SCD. Currently, open multi-center clinical trials are incorporating nonmyeloablative conditioning, related haploidentical donors, and post-transplantation cyclophosphamide. Preliminary results from these trials appear promising and NIH-sponsored trials are ongoing in pediatric and adult individuals with SCD using this platform.

Clonal Hematopoiesis of Indeterminate Potential as a Novel Risk Factor for Donor-Derived Leukemia

Hematopoietic stem cell transplantation (HSCT) is a critical treatment modality for many hematological and non-hematological diseases that is being extended to treat older individuals. However, recent studies show that clonal hematopoiesis of indeterminate potential (CHIP), a common, asymptomatic condition characterized by the expansion of age-acquired somatic mutations in blood cell lineages, may be a risk factor for the development of donor-derived leukemia (DDL), unexplained cytopenias, and chronic graft-versus-host disease. CHIP may contribute to the pathogenesis of these significant transplant complications via various cell-autonomous and non-cell-autonomous mechanisms, and the clinical presentation of DDL may be broader than anticipated. A more comprehensive understanding of the contributions of CHIP to DDL may have important implications for the screening of donors and will improve the safety of HSCT. The objective of this review is to discuss studies linking DDL and CHIP and to explore potential mechanisms by which CHIP may contribute to DDL.

Gender-related differences in the outcomes and genomic landscape of patients with myelodysplastic syndrome/myeloproliferative neoplasm overlap syndromes

Myelodysplastic syndrome/myeloproliferative neoplasm (MDS/MPN) overlap syndromes show a male predominance and men with MDS/MPN have worse outcomes, but it is unknown if the mutational burden differs between genders. We reviewed 167 patients with MDS/MPN and found that men had worse overall survival [hazard ratio (HR) 2·09, 95% confidence interval (CI) 1·16-3·75; P = 0·013] independent of subtype, Revised International Prognostic Scoring System score and age at diagnosis. We analysed the genomic data of a subset of 100 patients. Men had 0·88 more somatic mutations on average (95% CI 0·20-1·56, P = 0·011) independent of subtype, sample source and blast percentage. More somatic mutations was associated with a higher incidence of transformation to acute myeloid leukaemia (subdistribution HR 1·30, 95% CI 1·01-1·70; P = 0·046). Men had 0·70 more mutations in high-risk genes [additional sex combs like-1 (ASXL1), enhancer of zeste homolog 2 (EZH2), Runt-related transcription factor 1 (RUNX1), SET binding protein 1 (SETBP1), NRAS proto-oncogene, GTPase (NRAS), stromal antigen 2 (STAG2)] on average (95% CI 0·11-1·29, P = 0·021), and 13-times higher odds of harbouring an EZH2 mutation (95% CI 1·64-102·94, P = 0·015). The presence of an EZH2 mutation was associated with worse survival among men (HR 2·98, 95% CI 1·1-8·0; P = 0·031). Our present findings suggest that the worse outcomes in men with MDS/MPN are associated with a higher number of somatic mutations, especially in high-risk genes. These results warrant validation in larger cohorts and investigation of the underlying mechanisms.

Stem cell donors should not be screened for clonal hematopoiesis

This article has a companion Point by DeZern and Gondek.

Stem cell donors should be screened for CHIP

This article has a companion Counterpoint by Gibson and Lindsley.

Engrafted Donor-Derived Clonal Hematopoiesis after Allogenic Hematopoietic Cell Transplantation is Associated with Chronic Graft-versus-Host Disease Requiring Immunosuppressive Therapy, but no Adverse Impact on Overall Survival or Relapse

Clonal hematopoiesis of indeterminate potential (CHIP) is an age-associated condition defined by the presence of a somatic mutation in a leukemia-associated gene in individuals who otherwise have no evidence of a hematologic malignancy. In the allogeneic hematopoietic cell transplantation (HCT) setting, clonal hematopoiesis (CH) mutations present in donor stem cells can be transferred to recipients at the time of HCT. Given that the consequences of donor-derived CH in HCT recipients are not entirely clear, we sought to investigate clinical outcomes in patients with engrafted donor-derived CH using a matched cohort analysis of both related and unrelated donors. Of 209 patients with next-generation sequencing performed before and after HCT, donor-derived CH mutations were detected in 15 (5.2%). DNMT3A was the most commonly mutated gene (9 of 15; 60%); mutations in SF3B1, CSF3R, STAT3, CBLB, TET2, and ASXL1 were also identified. Donor-derived CH was not associated with delayed neutrophil or platelet engraftment, and there was no impact on conversion to full donor chimerism. No patients with donor-derived CH experienced relapse, in contrast to 15.6% (7 of 45) in the matched control cohort without CH (P = .176). Donor-derived CH was not associated with worse overall survival; however, patients with donor-derived CH were more likely to develop chronic graft-versus-host disease (GVHD) necessitating systemic immunosuppressive therapy (IST) (P = .045) and less likely to discontinue IST (P = .03) compared with controls without donor-derived CH. We conclude that donor-derived CH does not have an adverse impact on relapse, survival, or engraftment outcomes but may potentiate a graft-versus-leukemia effect, as reflected by increased chronic GVHD necessitating IST.

Design, implementation and clinical utility of next generation sequencing in myeloid malignancies: acute myeloid leukaemia and myelodysplastic syndrome

Next generation sequencing (NGS) based technology has contributed enormously to our understanding of the biology of myeloid malignancies including acute myeloid leukaemia (AML) and myelodysplastic syndrome (MDS). Assessment of clinically important mutations by NGS is a powerful tool to define diagnosis, determine prognostic risk, monitor measurable residual disease and uncover predictive mutational markers/therapeutic targets, and is now a routine component in the workup and monitoring of haematological disorders. There are many technical challenges in the design, implementation, analysis and reporting of NGS based results, and expert interpretation is essential. It is vital to distinguish relevant somatic disease associated mutations from those that are known polymorphisms, rare germline variants and clonal haematopoiesis of indeterminate potential (CHIP) associated variants. This review highlights and addresses the technical and biological challenges that should be considered before the implementation of NGS based testing in diagnostic laboratories and seeks to outline the essential and expanding role NGS plays in myeloid malignancies. Broad aspects of NGS panel design and reporting including inherent technological, biological and economic considerations are covered, following which the utility of NGS based testing in AML and MDS are discussed. In current practice, patient care is now strongly shaped by the results of NGS assessment and is considered a vital piece of the puzzle for clinicians as they manage these complex haematological disorders.

Establishment and characterization of HXWMF-1: the first mouse fibroblastic tumor cell line derived from leukemia-associated fibroblasts

Background

Chemo-resistance is still a major obstacle in leukemia treatment. Accumulating evidence indicates that cancer-associated fibroblasts (CAFs), the most abundant stromal cells in tumor microenvironment (TME), play a crucial role in cancer progression and response to chemotherapy. To Figure out the role of leukemia-associated fibroblasts (LAFs) in relapsed/refractory leukemia, we constructed the first leukemia-associated fibroblastic tumor cell line, HXWMF-1.

Methods

A cell culture technique was used to establish the leukemia-associated fibroblastic tumor cell line. Molecular and cellular biological techniques including flow cytometry, MTT assay, western blotting, and short tandem repeat (STR) analysis were used to characterize the cell line. Nude mice were used for xenograft studies.

Results

We established a LAFs derived tumor cell line HXWMF-1, originated from the subcutaneous xenografts of HXEX-ALL1, a cell line originated from a patient with acute lymphoblastic leukemia (ALL) at the second relapse. The HXWMF-1 cell line was authenticated as a tumor cell line and being derived from CAFs based on morphologic, immunophenotypic, cytogenetic and STR analyses and tumorigenicity test in nude mice. To clarify the reliability of the method, we got the LAFs derived tumor cells from three different tumor mass of HXEX-ALL1 xenografts.

Conclusions

To our knowledge, HXWMF-1 is the first fibroblastic tumor cell line derived from LAFs or CAFs. In addition, the cell line provided firm evidence for that leukemia cells may induce LAFs/CAFs malignant transformation, which may help to develop brand new theory and therapeutic strategies for patients with relapsed /refractory ALL.

Clonal haematopoiesis of emerging significance

Clonal haematopoiesis (CH) is a ubiquitous feature of aging and provides mechanistic insight into the inextricable relationship between chronic inflammation and age-related diseases. Although CH confers a cumulative risk of subsequent haematological malignancy, particularly myeloid neoplasms, that risk is heavily mutation- and context-specific. Individuals with mutations in DNA damage response pathway genes receiving select cytotoxic therapies for solid tumours are among the highest risk groups for subsequent development of myeloid neoplasms. Multiple lines of evidence suggest that TET2-mutated macrophages causally contribute to cardiometabolic disease through the generation of proinflammatory cytokines. It is speculated that such CH-related inflammation is a shared driver of several other chronic diseases. Whether we can intervene in individuals with CH to diminish the risk of subsequent haematological malignancy or non-haematological disease remains to be seen. However, precision anti-cytokine therapies are a rational starting point to break the feedforward loop between clonal myeloid expansion, inflammation, and end-organ damage.

The clinical implications of clonal hematopoiesis in hematopoietic cell transplantation

Clonal hematopoiesis (CH) describes somatic mutations in hematopoietic stem and progenitor cells resulting in clonal expansion in individuals with no overt hematologic disease. Since CH increases in an age-related manner, understanding its role in hematopoietic cell transplantation (HCT) has become increasingly relevant to an aging transplant population. Multiple factors distinguish post-transplant hematopoiesis from unperturbed, steady-state hematopoiesis, including the influence of immunosuppressants, cytotoxic reagents, and marked proliferative stress, all of which may enhance or diminish the opportunity for clonal expansion. We reviewed the available clinical evidence on the consequences of CH at time of transplant in patients undergoing autologous HCT, and the impact of donor and recipient CH on allogeneic HCT outcomes. In the absence of evidence-based guidelines, we share our suggestions for managing donors and recipients found to have CH. Large-scale studies are needed to guide an evidence-based, uniform approach for the management of CH in the setting of HCT.

Salivary Mucinous Adenocarcinoma Is a Histologically Diverse Single Entity With Recurrent AKT1 E17K Mutations: Clinicopathologic and Molecular Characterization With Proposal for a Unified Classification

Mucin-producing salivary adenocarcinomas were historically divided into separate colloid carcinoma, papillary cystadenocarcinoma, and signet ring cell carcinoma diagnoses based on histologic pattern, but have recently been grouped together in the adenocarcinoma not otherwise specified category. It is currently unclear if these tumors represent 1 or more distinct entities and how they are related to well-circumscribed papillary mucinous lesions with recurrent AKT1 E17K mutations that were recently described as salivary intraductal papillary mucinous neoplasm. Here, we sought to evaluate the clinicopathologic and molecular features of salivary mucinous adenocarcinomas to clarify their classification. We identified 17 invasive mucin-producing salivary adenocarcinomas, 10 with a single histologic pattern, and 7 with mixed patterns. While most tumors demonstrated papillary growth (n=15), it was frequently intermixed with colloid (n=6) and signet ring (n=3) architecture with obvious transitions between patterns. All were cytokeratin 7 positive (100%) and cytokeratin 20 negative (0%). Next-generation sequencing performed on a subset demonstrated recurrent AKT1 E17K mutations in 8 cases (100%) and TP53 alterations in 7 cases (88%). Of 12 cases with clinical follow-up (median: 17 mo), 4 developed cervical lymph node metastases, all of which had colloid or signet ring components. Overall, overlapping histologic and immunohistochemical features coupled with recurrent AKT1 E17K mutations across patterns suggests that mucin-producing salivary adenocarcinomas represent a histologically diverse single entity that is closely related to tumors described as salivary intraductal papillary mucinous neoplasm. We propose a unified mucinous adenocarcinoma category subdivided into papillary, colloid, signet ring, and mixed subtypes to facilitate better recognition and classification of these tumors.

Activation of Receptor Tyrosine Kinases Mediates Acquired Resistance to MEK Inhibition in Malignant Peripheral Nerve Sheath Tumors

Malignant peripheral nerve sheath tumors often arise in patients with neurofibromatosis type 1 and are among the most treatment-refractory types of sarcoma. Overall survival in patients with relapsed disease remains poor, and thus novel therapeutic approaches are needed. NF1 is essential for negative regulation of RAS activity and is altered in about 90% of malignant peripheral nerve sheath tumors (MPNST). A complex interplay of upstream signaling and parallel RAS-driven pathways characterizes NF1-driven tumorigenesis, and inhibiting more than one RAS effector pathway is therefore necessary. To devise potential combination therapeutic strategies, we identified actionable alterations in signaling that underlie adaptive and acquired resistance to MEK inhibitor (MEKi). Using a series of proteomic, biochemical, and genetic approaches in an in vitro model of MEKi resistance provided a rationale for combination therapies. HGF/MET signaling was elevated in the MEKi-resistant model. HGF overexpression conferred resistance to MEKi in parental cells. Depletion of HGF or MET restored sensitivity of MEKi-resistant cells to MEKi. Finally, a combination of MEK and MET inhibition demonstrated activity in models of MPNST and may therefore be effective in patients with MPNST harboring genetic alterations in NF1. SIGNIFICANCE: This study demonstrates that MEKi plus MET inhibitor may delay or prevent a novel mechanism of acquired MEKi resistance, with clinical implications for MPNST patients harboring NF1 alterations.

Case Report: Late Onset of Myelodysplastic Syndrome From Donor Progenitor Cells After Allogeneic Stem Cell Transplantation. Which Lessons Can We Draw From the Reported Case?

Background

Myelodysplastic syndromes and acute leukemias after allogeneic stem cell transplantation (allo-SCT) are mainly caused by recurrence of the primitive leukemic clones. More rarely, they originate from donor hematopoietic stem cells, developing the so-called donor cell leukemia (DCL) or myelodysplastic syndromes (DC-MDSs). DCL and DC-MDS can be considered as an in vivo model of leukemogenesis, and even if the pathogenetic mechanisms remain speculative, a genetic predisposition of donor progenitor cells, an altered host microenvironment, and the impairment of immune surveillance are considered the main causes.

Case Presentation

We report a case of DC-MDS diagnosed 5 years after an allo-SCT from a matched related donor (patient’s sister) in a patient with Philadelphia chromosome-positive B-cell acute lymphoblastic leukemia (Ph+ B-ALL). The sex-mismatch allowed us to identify the donor cell origin. At the onset, the DC-MDS was characterized by chromosome seven monosomy and NRAS, RUNX1, and BCOR mutations. Because of a familiar history of colorectal neoplasia and the variant allele frequency (VAF) of NRAS mutation at the onset, this mutation was searched on germline DNA in both the donor and the recipient, but the result was negative. Moreover, after transplant (+4 months), the patient developed severe and long-lasting chronic graft-versus-host disease (cGVHD), requiring multiple lines of treatments. Because of the severe immunosuppression, recurrent infections occurred and, lately, the patient died due to septic shock.

Conclusion

This case report highlights the need, whenever possible, to evaluate the donor origin of the posttransplant myelodysplasia and acute leukemias. The potential key role of the impaired immune surveillance and of long-lasting immunosuppression appears to be emerging in the development of this case of DC-MDS. Finally, this case reminds the importance to investigate the familiar genetic predisposition in donors with a familiar history of neoplasia.

Aging and leukemic evolution of hematopoietic stem cells under various stress conditions

Hematopoietic stem cells (HSCs) have self-renewal capacity and differentiation potential into all lineages of blood cells throughout the lifetime of an organism. The function of HSCs gradually changes during aging. To date, various stress factors influencing HSC aging have been identified. The increased production of reactive oxygen species and DNA damage responses are causatively attributed to HSC aging. The increased apolarity is a prominent feature of aged HSCs, whereas it is less obvious in young HSCs. The bone marrow (BM) microenvironment niche is a crucial factor for HSC aging. Mesenchymal stem cells show skewed differentiation during aging, which leads to decreased bone formation and increased adipogenesis. The accumulation of adipocytes confers negative effects on hematopoiesis. Loss of sympathetic nerve fibers or adrenoreceptor β3 signaling induces premature HSC and niche aging. Epigenetic regulators such as polycomb group proteins and the sirtuin family of proteins act to prevent premature aging. Targeting these factors, several rejuvenation strategies for aged HSCs have been employed in mice. However, we still do not know whether these strategies can be extrapolated to human HSCs. Aging is frequently accompanied by the development of clonal hematopoiesis, which is called age-related clonal hematopoiesis (ARCH) or clonal hematopoiesis of indeterminate potential (CHIP). Most ARCH/CHIP mutations occur in genes encoding epigenetic regulators including DNMT3A, TET2, and ASXL1, which suggests the relevance of epigenetic drift during the aging process. ARCH/CHIP is a strong risk factor for subsequent hematologic cancer. Notably, it also has an impact on the development of non-malignant disorders such as coronary heart disease. Further studies are warranted to decipher the complete picture of molecular crosstalk that regulates HSC aging.

Recurrent DICER1 Hotspot Mutations in Malignant Thyroid Gland Teratomas: Molecular Characterization and Proposal for a Separate Classification

Thyroid gland teratomas are rare tumors that span a wide clinicopathologic spectrum. Although benign and immature teratomas arise in infants and young children and generally have good outcomes, malignant teratomas affect adults and follow an aggressive course. This divergent behavior raises the possibility that benign/immature and malignant teratomas are separate entities rather than different grades of a single tumor. However, the histogenesis and molecular underpinnings of thyroid gland teratomas are poorly understood regardless of grade. In this study, we performed next-generation sequencing on 8 thyroid gland teratomas, including 4 malignant, 3 benign, and 1 immature. We identified DICER1 hotspot mutations in all 4 malignant cases (100%) but not in any benign/immature cases (0%). No clinically significant mutations in other genes were found in either group. We also performed immunohistochemistry to characterize the primitive components of malignant teratomas. Not only did all cases consistently contain immature neural elements (synaptophysin and INSM1 positive), but also spindled cells with rhabdomyoblastic differentiation (desmin and myogenin positive) and bland epithelial proliferations of thyroid follicular origin (TTF-1 and PAX8 positive). Although DICER1 mutations have previously been implicated in multinodular hyperplasia and well-differentiated thyroid carcinomas, these findings demonstrate the first recurrent role for DICER1 in primitive thyroid tumors. The combined neural, rhabdomyoblastic, and homologous epithelial elements highlighted in this series of malignant thyroid gland teratomas parallel the components of DICER1-mutated tumors in other organs. Overall, these molecular findings further expand the differences between benign/immature teratomas and malignant teratomas, supporting the classification of these tumors as separate entities.

Combined Inhibition of SHP2 and MEK Is Effective in Models of NF1-Deficient Malignant Peripheral Nerve Sheath Tumors

Loss of the RAS GTPase-activating protein (RAS-GAP) NF1 drives aberrant activation of RAS/MEK/ERK signaling and other effector pathways in the majority of malignant peripheral nerve sheath tumors (MPNST). These dysregulated pathways represent potential targets for therapeutic intervention. However, studies of novel single agents including MEK inhibitors (MEKi) have demonstrated limited efficacy both preclinically and clinically, with little advancement in overall patient survival. By interrogation of kinome activity through an unbiased screen and targeted evaluation of the signaling response to MEK inhibition, we have identified global activation of upstream receptor tyrosine kinases (RTK) that converges on activation of RAS as a mechanism to limit sensitivity to MEK inhibition. As no direct inhibitors of pan-RAS were available, an inhibitor of the protein tyrosine phosphatase SHP2, a critical mediator of RAS signal transduction downstream of multiple RTK, represented an alternate strategy. The combination of MEKi plus SHP099 was superior to MEKi alone in models of NF1-MPNST, including those with acquired resistance to MEKi. Our findings have immediate translational implications and may inform future clinical trials for patients with MPNST harboring alterations in NF1. SIGNIFICANCE: Combined inhibition of MEK and SHP2 is effective in models of NF1-MPNST, both those naïve to and those resistant to MEKi, as well as in the MPNST precursor lesion plexiform neurofibroma.

Tumor-Based Genetic Testing and Familial Cancer Risk

As genetic testing on somatic tumor tissue becomes a more routine part of personalized cancer treatment, a growing opportunity arises to identify hereditary germline variants within those results. These germline results can affect future cancer screening for both patients and their family members. Finding this germline information can be complicated as a result of differences between somatic and germline testing processes, nomenclature, and outcome goals (e.g., treatment impact). The goal of this review is to highlight differences between somatic and germline testing and outline a potential guide to allow for appropriate clinical interpretation of somatic testing results in order to better facilitate genetic counseling referrals and confirmatory germline testing.

Sex determines the presentation and outcomes in MPN and is related to sex-specific differences in the mutational burden

The factors underlying the variable presentation and clinical course of myeloproliferative neoplasms (MPNs) remain unclear. The aim of this study was to evaluate the independent effect of sex on MPN presentation and outcomes. A total of 815 patients with essential thrombocytosis, polycythemia vera, or primary myelofibrosis were evaluated between 2005 and 2019, and the association of sex with presenting phenotype, JAK2 V617F burden, progression, and survival was examined. Men presented more often with primary myelofibrosis vs essential thrombocytosis (relative risk, 3.2; P < .001) and polycythemia vera (relative risk, 2.1; P < .001), had higher rates of transformation to secondary myelofibrosis (hazard ratio [HR], 1.55; P = .013) and acute myeloid leukemia (HR, 3.67; P < .001), and worse survival (HR, 1.63; P = .001) independent of age, phenotype at diagnosis, and MPN-specific mutation. Men had higher JAK2 V617F allele burdens in their CD34+ cells (P = .001), acquired more somatic mutations (P = .012) apart from the MPN-specific mutations, and had an increased frequency of 1 (odds ratio, 2.35; P = .017) and 2 (odds ratio, 20.20; P = .011) high-risk mutations independent of age, phenotype, and driver mutation. Male sex is an independent predictor of poor outcomes in MPNs. This seems to be due to an increased risk of non-MPN-specific somatic mutations, particularly high-risk mutations, rather than MPN-specific mutation allele frequency. Conversely, disease progression in female subjects is more dependent on JAK2 mutation allele burden than on acquisition of other somatic mutations. Sex should be considered in prognostic models and when evaluating therapeutic strategies in MPNs.

BRAF V600E-mutated metastatic pediatric Wilms tumor with complete response to targeted RAF/MEK inhibition

Wilms tumor (WT) is the most common renal malignancy of childhood and accounts for 6% of all childhood malignancies. With current therapies, the 5-yr overall survival (OS) for children with unilateral favorable histology WT is greater than 85%. The prognosis is worse, however, for the roughly 15% of patients who relapse, with only 50%–80% OS reported in those with recurrence. Herein, we describe the extended and detailed clinical course of a rare case of a child with recurrent, pulmonary metastatic, favorable histology WT harboring a BRAF V600E mutation. The BRAF V600E mutation, commonly found in melanoma and other cancers, and previously undescribed in WT, has recently been reported by our group in a subset of epithelial-predominant WT. This patient, who was included in that series, presented with unilateral, stage 1, favorable histology WT and was treated with standard chemotherapy. Following the completion of therapy, the patient relapsed with pulmonary metastatic disease, that then again recurred despite an initial response to salvage chemotherapy and radiation. Next-generation sequencing (NGS) on the metastatic pulmonary nodule revealed a BRAF V600E mutation. After weighing the therapeutic options, a novel approach with dual BRAF/MEK inhibitor combination therapy was initiated. Complete radiographic response was observed following 4 months of therapy with dabrafenib and trametinib. At 12 months following the start of BRAF/MEK combination treatment, the patient continues with a complete response and has experienced minimal treatment-related side effects. This represents the first case, to our knowledge, of effective treatment with BRAF/MEK molecularly targeted therapy in a pediatric Wilms tumor patient.

Jumping translocations of 1q in donor cell-derived myelodysplastic syndrome after cord blood transplantation: Case report and review of the literature

Donor cell-derived leukemia and myelodysplastic syndrome (DCL) is a rare complication in patients after allogenic stem cell transplantation (SCT). Since 1971, numerous cases of DCL have been reported, but the detailed mechanisms of DCL are still unclear. A patient with jumping translocations (JTs) of 1q in umbilical cord blood donor cell-derived myelodysplastic syndrome (MDS), which likely occurred due to genetic alterations of TET2 and ASXL1 after cord blood transplantation (CBT), was examined in this study. Previously reported DCL cases after CBT that focused on the cytogenetic and molecular characteristics of these patients and patient outcome were reviewed. A total of 30 cases of DCL after CBT were identified between 2005 and 2018. The median time from CBT to the development of DCL was 16 months. The number of patients with DCL who were diagnosed with acute myeloid leukemia (AML) and MDS was 19 and 8, respectively. JTs were frequently observed in 5 of 27 DCL patients who had cytogenetic abnormalities, including our patient. Molecular abnormalities were described in 7 of the cases, and the most frequent abnormality was an NPM1 mutation. Other gene mutations that were usually found in de novo MDS or AML were observed in JT-DCL after CBT. From these results, chromosomal abnormalities such as JTs that occur subsequent to genetic alterations were seemed an important mechanisms underlying DCL onset in patients after CBT. Further molecular analyses regarding the genetic alterations of JTs are required to understand the pathogenesis of umbilical cord blood-derived JT-DCL.

Assessing clonal haematopoiesis: clinical burdens and benefits of diagnosing myelodysplastic syndrome precursor states

Diagnosing, surveilling, and understanding the biological consequences of clonal haematopoiesis poses a clinical challenge for both patients and clinicians. The relationship between peripheral blood cytopenias and myeloid neoplasms-such as myelodysplastic syndrome-is an area of active research, and understanding of clonal haematopoiesis has developed markedly on the basis of findings concerning somatic mutations in genes known to be associated with myelodysplastic syndrome. These findings have raised the conundrum of how to appropriately define and follow myelodysplastic syndrome precursor states, such as clonal haematopoiesis of indeterminate potential (CHIP) and clonal cytopenias of undetermined significance (CCUS). Identifying these conditions could allow earlier diagnosis of myelodysplastic syndrome, modify surveillance for myelodysplastic syndrome, and possibly guide therapies, but this information also comes at a cost to patients that might or might not be justified by our present understanding of clonal haematopoiesis. When faced with a diagnosis of clonal haematopoiesis, some patients and providers might be content to let the events unfold naturally, whereas others may insist on intense follow-up and early interventions. This Viewpoint assesses recent developments in clonal haematopoiesis and the related implications for affected patients and their providers.