The CRISPR-Cas System and Clinical Applications of CRISPR-Based Gene Editing in Hematology with a Focus on Inherited Germline Predisposition to Hematologic Malignancies.

Clustered regularly interspaced short palindromic repeats (CRISPR)-based gene editing has begun to transform the treatment landscape of genetic diseases. The history of the discovery of CRISPR/CRISPR-associated (Cas) proteins/single-guide RNA (sgRNA)-based gene editing since the first report of repetitive sequences of unknown significance in 1987 is fascinating, highly instructive, and inspiring for future advances in medicine. The recent approval of CRISPR-Cas9-based gene therapy to treat patients with severe sickle cell anemia and transfusion-dependent ß-thalassemia has renewed hope for treating other hematologic diseases, including patients with a germline predisposition to hematologic malignancies, who would benefit greatly from the development of CRISPR-inspired gene therapies. The purpose of this paper is three-fold: first, a chronological description of the history of CRISPR-Cas9-sgRNA-based gene editing; second, a brief description of the current state of clinical research in hematologic diseases, including selected applications in treating hematologic diseases with CRISPR-based gene therapy, preceded by a brief description of the current tools being used in clinical genome editing; and third, a presentation of the current progress in gene therapies in inherited hematologic diseases and bone marrow failure syndromes, to hopefully stimulate efforts towards developing these therapies for patients with inherited bone marrow failure syndromes and other inherited conditions with a germline predisposition to hematologic malignancies.

Classification of acute myeloid leukemia by the revised fourth edition World Health Organization criteria: a retrospective single-institution study with appraisal of the new entities of acute myeloid leukemia with gene mutations in NPM1 and biallelic CEBPA.

The 2016/2017 World Health Organization (WHO2016/2017) classification for acute myeloid leukemia (AML) includes new entities with gene mutations in NPM1 (AML-NPM1mut) and biallelic CEBPA (AML-biCEBPAmut). To retrospectively identify and study these new molecularly defined WHO2016/2017entities, we reviewed clinicopathologic data and pretherapy archived pathologic materials at diagnosis for 143 consecutive AML cases (55.2% male, median age 62 [range 18-89] years) and classified all cases by the 2008 WHO (WHO2008) and revised WHO2016/2017 criteria. By WHO2008, cases included 21 (15%) with recurrent genetic abnormalities (52.3% male, median age 54 [range 18-82] years), 54 (38%) with myelodysplasia-related changes (57.4% male, median age 65 [range 32-84] years), 3 (2%) therapy related (100% male, median age 66 [range 32-84] years), and 65 (45%) not otherwise specified (52.3% male, median age 61 [range 19-89] years). Twenty-two (15.4%) cases (21 AML, not otherwise specified; 1 AML with myelodysplasia-related changes by WHO2008) reclassified by WHO2016/2017 as AML-NPM1mut showed female predominance (54.5%), and median (range) values were as follows: age 60.5 (23-84) years, hemoglobin 8.6 (5.6-12.9) g/dL, total leucocytes 30.1 (2.58-241.84) × 109/L, monocytes 1.65 (0-49.34) × 109/L, neutrophils 1.96 (0-29.79) × 109/L, platelets 55 (11-320) × 109/L, blasts (peripheral blood 41% [2%-98%], bone marrow 66% [17%-97%]), with myeloblastsCD34neg (17 [77%]/21), cytogeneticsnormal (20 [91%]/22), FLT3-ITDpos (9 [41%]/22), FLT3-ITDnegFLT3-TKDpos (5 [23%]/22), FLT3-ITDnegFLT3-TKDneg (8 [36%]/22), and extramedullary involvement (6 [27%]/22), including 1 novel cutaneous presentation. Notably, presenting features among AML-NPM1mut included those of anemia (22 [100%]) and thrombocytopenia (20 [91%]/22). This is also the first report of 4 [18%]/22 AML-NPM1mut (including 3 [75%]/4 nonsmokers) with a family history of leukemia and one 74-year-old with familial AML-biCEBPAmut. This study validates the application of the WHO2016/2017 classification criteria by retrospectively identifying AML-NPM1mut and AML-biCEBPAmut cases using single-gene molecular analyses. Additional studies are needed to characterize the complete spectrum of WHO2016/2017-defined AML-biCEBPAmut and for familial AML including AML-NPM1mut.

The Value of T-Cell Receptor γ (TRG) Clonality Evaluation by Next-Generation Sequencing in Clinical Hematolymphoid Tissues.

OBJECTIVES: To evaluate feasibility of assessing T-cell receptor γ (TRG) clonality by next-generation sequencing (NGS) in hematolymphoid tissues. METHODS: We evaluated TRG clonality using NGS and polymerase chain reaction (PCR) assays in blood, bone marrow, and formalin-fixed, paraffin-embedded tissues in 41 archived cases, including 21 benign cases with no history of any lymphoproliferative disorders (LPDs), 16 LPDs (nine mature T-cell neoplasms, seven mature B-cell neoplasms and immune dysregulation-associated LPDs), and four atypical LPDs from 22 females and 19 males with a median age of 58 (range, 9-87) years. RESULTS: (1) NGS analyzed TRG sequence and peak ratios, and it had a greater sensitivity than PCR. (2) NGS identified small clones, including biallelic or monoallelic, and minimum clonal percentages (range, ~2.4% to ~69%) within all T cells. (3) We provide our strategy and criteria for evaluating NGS results. (4) We describe every case, with definitive evaluation of TRG clonality in 100% cases by NGS. CONCLUSIONS: TRG clonality evaluation by NGS provides greater clinical utility than PCR.

Acute myeloid leukemia in the era of precision medicine: recent advances in diagnostic classification and risk stratification.

Acute myeloid leukemia (AML) is a genetically heterogeneous myeloid malignancy that occurs more commonly in adults, and has an increasing incidence, most likely due to increasing age. Precise diagnostic classification of AML requires clinical and pathologic information, the latter including morphologic, immunophenotypic, cytogenetic and molecular genetic analysis. Risk stratification in AML requires cytogenetics evaluation as the most important predictor, with genetic mutations providing additional necessary information. AML with normal cytogenetics comprises about 40%-50% of all AML, and has been intensively investigated. The currently used 2008 World Health Organization classification of hematopoietic neoplasms has been proposed to be updated in 2016, also to include an update on the classification of AML, due to the continuously increasing application of genomic techniques that have led to major advances in our knowledge of the pathogenesis of AML. The purpose of this review is to describe some of these recent major advances in the diagnostic classification and risk stratification of AML.

An infant with MLH3 variants, FOXG1-duplication and multiple, benign cranial and spinal tumors: A clinical exome sequencing study.

A 4-month-old male infant presented with severe developmental delay, cerebellar, brainstem, and cutaneous hemangiomas, bilateral tumors (vestibular, hypoglossal, cervical, and lumbar spinal), and few café-au-lait macules. Cerebellar and lumbar tumor biopsies revealed venous telangiectasia and intraneural perineuroma, respectively. Sequencing NF1, NF2, and RASA1 (blood), and NF2 and SMARCB1 (lumbar biopsy) was negative for pathogenic mutations. Clinical exome sequencing (CES), requested for tumor syndrome diagnosis, revealed two heterozygous missense variants, c.359T>C;p.Phe120Ser and c.3344G>A;p.Arg1115Gln, in MLH3 (NM_001040108.1), a DNA mismatch repair (MMR) gene, Polyphen-predicted as probably damaging, and benign, respectively. Sanger sequencing confirmed both variants in the proband, and their absence in the mother; biological father unavailable. Both biopsied tissues were negative for microsatellite instability, and expressed MLH1, MSH2, PMS2, MSH6, and MLH3 immunohistochemically. Chromosomal microarray showed a 133 kb segment copy number duplication of 14q12 region encompassing FOXG1, possibly explaining the developmental delay, but not the tumors. The presence of MLH3 variants with multiple benign neural and vascular tumors was intriguing for their possible role in the pathogenesis of these neoplasms, which were suspicious for, but not diagnostic of, constitutional MMR deficiency. However, functional assays of non-neoplastic patient-derived cells showed intact base-base MMR function. Also, no previous FOXG1-aberrant patient was reported with tumors. We now report a 3-year-old FOXG1-duplicated patient with a yet undescribed tumor syndrome with clinical features of neurofibromatosis types I and II, where several validation studies could not ascertain the significance of CES findings; further studies may elucidate precise mechanisms and diagnosis for clinical management, including tumor surveillance.

Exuberant cortical thymocyte proliferation mimicking T-lymphoblastic lymphoma within recurrent large inguinal lymph node masses of localized Castleman disease.

We report a 13-year-old adolescent girl, the youngest thus far, with "an indolent T-lymphoblastic" proliferation (~10%) that uniquely presented within recurrent, large inguinal lymph node masses in a predominating (90%) background of Castleman disease. These nodal masses were resected thrice; the patient is well 5 years after diagnosis without further treatment. Histologically, the features of Castleman disease, hyaline vascular type, were present. Importantly, the interfollicular T-lymphoblastic component occurred as multiple clusters and islands of variable shapes and sizes composed of small "lymphoblasts" indistinguishable from normal cortical thymocytes but without thymic epithelial cells. Immunohistochemically, these lymphoblasts were consistent with the intermediate stage of T-cell differentiation (TdT(+)CD34(-)CD99(+)CD1a(+)CD2(+)CD3(+)CD4(+)CD8(+)CD5(+)CD7(+)CD10(+) [subset]), with 80% Ki-67. Molecularly, the T cells were nonclonal. Our case provides evidence for the benign nature of this highly unusual and poorly understood entity; because the current terminology can be readily misinterpreted as an indolent lymphoblastic lymphoma, we suggest a new term accurately reflecting this entity.

Clinical Next Generation Sequencing for Precision Medicine in Cancer.

Rapid adoption of next generation sequencing (NGS) in genomic medicine has been driven by low cost, high throughput sequencing and rapid advances in our understanding of the genetic bases of human diseases. Today, the NGS method has dominated sequencing space in genomic research, and quickly entered clinical practice. Because unique features of NGS perfectly meet the clinical reality (need to do more with less), the NGS technology is becoming a driving force to realize the dream of precision medicine. This article describes the strengths of NGS, NGS panels used in precision medicine, current applications of NGS in cytology, and its challenges and future directions for routine clinical use.

Intranodular clusters of activated cells with T follicular helper phenotype in nodular lymphocyte predominant Hodgkin lymphoma: a pilot study of 32 cases from Finland.

In nodular lymphocyte predominant Hodgkin lymphoma (NLPHL), little is known about the presence of intranodular clusters of cytologically activated lymphoid cells producing a moth-eaten pattern histologically. This pilot study of 32 NLPHL cases from Finland ascertained (1) the frequency of the intranodular clusters of activated lymphoid cells, (2) the immunophenotype of the activated cells, (3) the size and immunophenotype of the rosetting cells, and (4) the clinical significance of the activated cells. Histologically, intranodular clusters of activated cells produced a moth-eaten pattern in 100% (32 cases; subtle in 62.5%, overt in 37.5%). In immunostains, activated cells in subtle clusters (20 cases) were very difficult to identify. Twelve cases had overt clusters of activated cells, which were positive with CD3, CD4, PD1, CXCL13 (T follicular helper [T(FH)] phenotype), but rarely with Ki-67 and BCL2. Most activated rosetting cells had the same immunophenotype as the nonrosetting cells, except for CXCL13. Clinical presentation for all 32 Finnish patients was distinctive: 97% men, 97% with peripheral lymphadenopathy and 35.5% with stage III/IV disease. Only 22% relapsed; 97% were in remission. There was no significant clinical difference between cases with overt and subtle clusters. Intranodular activated TFH cells in NLPHL appeared to be nonproliferating and not long-living, and they were not associated with any adverse clinical outcome. Although most activated cells were TFH cells, it seemed that they were unable to increase the number of malignant cells. The pathogenetic role of the intranodular activated TFH and the small T cells in NLPHL needs further investigation.

Identification of the V600D mutation in Exon 15 of the BRAF oncogene in congenital, benign langerhans cell histiocytosis.

Langerhans cell histiocytosis (LCH) is a well-known but rare disease that may occur at any age with markedly variable clinical features: self-regressive, localized, multiorgan, aggressive, or fatal outcome. Congenital LCH is rare and often clinically benign. While LCH is characterized by a clonal proliferation of Langerhans cells, its etiology is unknown. Although BRAF V600E mutations were recently identified as a recurrent genetic alteration in LCH cases, the clinical significance of this mutation within the heterogeneous spectrum of LCH is also currently unknown. We studied a cutaneous, benign form of congenital LCH that occurred in a newborn male, without recurrence for 8 years. Histopathologically, the skin lesion excised after birth showed the typical cytologic and immunophenotypic features of LCH. Sequencing analysis of Exon 15 of the BRAF gene revealed the V600D mutation, with an allelic abundance of 25-30%, corresponding to the LCH cells being hemizygous for the mutant allele. BRAF V600E-specific polymerase chain reaction was negative. Our report is the first to identify the rare, variant BRAF V600D mutation in LCH, and provides support for constitutively activated BRAF oncogene-induced cell senescence as a mechanism of regression in congenital, benign LCH. Further, our clinicopathologic findings provide proof for the first time that the V600D mutation can also occur in the absence of ultraviolet light, and can occur in a clinically benign proliferation, similar to the V600E mutation. Additional clinicopathologic studies in larger numbers of LCH patients may be valuable to ascertain the pathophysiologic role of BRAF mutations in LCH.

Extranodal NK/T-cell lymphoma, nasal type, arising in association with saline breast implant: expanding the spectrum of breast implant-associated lymphomas.

Extranodal NK/T-cell lymphoma, nasal type, is a rare type of non-Hodgkin lymphoma that is most common in Asia and is driven by Epstein-Barr virus infection. These tumors usually arise in the nasal region; in rare cases they can involve extranasal sites, most often skin, with involvement of the breast being rare. Lymphomas arising adjacent to breast implants are rare, and most cases reported to date have been anaplastic lymphoma kinase (ALK)-negative anaplastic large cell lymphoma. Here we report a 41-year-old white woman with bilateral saline breast implants placed for cosmetic reasons who almost 9 years later developed painful swelling at the right-breast implant site. Excisional biopsy revealed lymphoma composed of monomorphic large cells associated with necrosis and angioinvasion. Immunohistochemical analysis showed an aberrant, NK/T-cell immunophenotype with the lymphoma cells being CD2+, CD3+, CD56+, partial CD30+, granzyme B, TIA-1+, CD4+, CD5+, CD7+, and CD8+. In situ hybridization analysis showed Epstein-Barr virus-encoded RNA within the neoplastic cells. Polymerase chain reaction analysis showed monoclonal T-cell receptor-γ chain gene rearrangement. These findings support the diagnosis of extranodal NK/T-cell lymphoma, nasal type. On the basis of our review of the literature, this case is unique. In addition, we believe this case is important to report, because it expands the spectrum of T-cell lymphomas that can be associated with breast implants and may be a forerunner of additional cases to follow.

Good clinical response in a rare aggressive hematopoietic neoplasm: plasmacytoid dendritic cell leukemia with no cutaneous lesions responding to 4 donor lymphocyte infusions following transplant.

Blastic Plasmacytoid Dendritic Cell Neoplasm (BPDCN) is a rare and aggressive malignancy that usually presents with diffuse cutaneous lesions. While a favorable response to therapy occurs in a majority of cases, a sustained long-term response is uncommon. Most patients subsequently relapse within a year. In the following report, we present the case of a 41-year-old woman who has not displayed many of the clinical features traditionally associated with BPDCN. The patient received sporadic chemotherapy treatment over the course of 2 years, before undergoing an allogeneic stem cell transplant. Although she ultimately relapsed following her transplant, her disease has repeatedly returned into remission after donor lymphocyte infusion (DLI). Currently, the patient is in remission following her fourth DLI. We believe that allogeneic transplantation should be considered as front-line therapy for the treatment of this rare malignancy.

Extra copies of chromosome 2 are a recurring aberration in ALK-negative lymphomas with anaplastic morphology.

The purpose of this study was to evaluate fluorescence in situ hybridization abnormalities of the 2p23 anaplastic lymphoma kinase (ALK) gene loci in lymphomas with anaplastic morphology. We studied 24 anaplastic large cell lymphomas (ALCL) classified by World Health Organization criteria [17 primary nodal/systemic (10 ALK+, 7 ALK-), seven primary cutaneous], and 17 additional non-Hodgkin's lymphomas [one ALK+ B-lineage lymphoma, 14 ALK- diffuse large B-cell lymphomas (seven anaplastic variants, five nonanaplastic, two secondary CD30+), two follicular lymphomas]. ALK- lymphomas with anaplastic morphology showed extra nonrearranged anaplastic lymphoma kinase gene loci (P=0.004) due to trisomy 2 irrespective of the following factors: B or T/null phenotype (P=0.315), diagnostic categories of systemic or cutaneous ALCL or the above-mentioned B-cell lymphomas (P=0.131), and CD30 positivity by immunohistochemistry (P=1.000). Trisomy 2 was absent in all ALK+ lymphomas (P=0.009), which showed rearranged ALK gene loci (P<0.001). Whether trisomy 2 is a primary or secondary event that leads to ALK- lymphomas cannot be determined from this study. Its presence in secondary B-cell lymphomas suggests that trisomy 2 may be a secondary cytogenetic aberration in lymphomas in general. Further investigation of this finding is necessary to further our understanding of the heterogeneous group of ALK- lymphomas.

Precursor B lymphoblastic leukemia with surface light chain immunoglobulin restriction: a report of 15 patients.

We describe 15 patients (9 children) with precursor B-cell (pB) acute lymphoblastic leukemia (ALL) with surface immunoglobulin (sIg) light chain restriction revealed by flow cytometric immunophenotyping (FCI). The same sIg+ immunophenotype was present at diagnosis and in 3 relapses in 1 patient. In 15 patients, blasts were CD19+ CD10+ (bright coexpression) in 14, CD34+ in 12, surface kappa+ in 12, surface lambda+ in 3; in 8 of 8, terminal deoxyribonucleotidyl transferase (TdT)+; and in 4, surface IgD+ in 2 and surface IgM+ in 1. The 3 CD34- cases included 1 TdT+ case, 1 with t(1;19)(q23;p13), and 1 infant with 70% marrow blasts. One adult had CD10- CD19+ CD20- CD22+ CD34+ TdT+ sIg+ blasts with t(2;11)(p21;q23). Blasts were L1 or L2 in all cases (French-American-British classification). Karyotypic analysis in 12 of 12 analyzable cases was negative for 8q24 (myc) translocation. Karyotypic abnormalities, confirmed by fluorescence in situ hybridization in 6 cases, included hyperdiploidy, t(1;19)(q23;p13), t(12;21)(p13;q22), t(9;22)(q34;q11), t(2;11)(p21;q23), and trisomy 12. The sIg light chain restriction in pB ALL might be present in neoplasms arising from the early, intermediate, and late stages of precursor B-cell maturation; sIg light chain restriction revealed by FCI does not necessarily indicate a mature B-cell phenotype, further emphasizing the importance of a multidisciplinary approach to diagnosing B-lymphoid neoplasms.

Histopathologic features of splenic small B-cell lymphomas. A study of 42 cases with a definitive diagnosis by the World Health Organization classification.

We studied 42 cases of splenic small B-cell lymphoma (SBL) (21 women, 21 men; aged 32-82 years; median, 65 years) with a definitive diagnosis by the World Health Organization classification: chronic lymphocytic leukemia (CLL), 8; mantle cell lymphoma (MCL), 9; follicular lymphoma (FL), 12; marginal zone lymphoma, 13 (splenic [SMZL], 12; extranodal [EMZL], 1). Splenectomy was performed for diagnosis or therapy; splenic weights were 0.2 to 3.8 kg (median, 1.4 kg). In general, splenic SBLs showed white pulp (WP) expansion; morphologic features of the nodules recapitulated the corresponding lymph node histopathologic features. "Marginal zones" were observed commonly in SMZL and FL, may be present in MCL involving the spleen, and may be seen in hilar lymph nodes (HLNs) in SBLs other than SMZL. FL may simulate SMZL and can be distinguished by the presence of neoplastic follicles and HLN morphologic features. Extracellular hyaline deposits (EH) are common in FL and SMZL. MCL typically shows WP expansion by a monotonous small lymphocytic infiltrate, without diffuse red pulp (RP) infiltration or EH; leukemic MCL may show RP infiltration. Splenic morphologic features in CLL vary in WP or RP dominance; marginal zones usually are not observed in CLL.

Peripheral T-cell lymphoma mimicking marginal zone B-cell lymphoma.

Peripheral T-cell lymphoma (PTCL) may assume a variety of histologic and cytologic appearances. We describe eight cases of PTCL morphologically simulating marginal zone B-cell lymphoma. We reviewed PTCL cases diagnosed in our institution between 1990 and 2000 and selected eight cases for study based on the following criteria: small-cell morphology with abundant, clear cytoplasm and either marginal zone involvement by the neoplastic infiltrate in lymph node biopsies or lymphoepithelial lesions in extranodal biopsies. Histologic features and ancillary studies were reviewed. Patients included six women and two men with a median age of 53 years (range, 35 to 74 years). Six patients were diagnosed with primary nodal PTCL, and two presented with primary extranodal disease. The original diagnosis was PTCL in only four cases; three cases were diagnosed as atypical lymphoid infiltrate, and one case as benign lymphoepithelial lesion. Lymph node biopsies revealed partial effacement of the architecture with residual follicles surrounded by the neoplastic small cells. Extranodal sites included hard palate, tongue, tonsil, and submandibular glands; all but one case demonstrated lymphoepithelial lesions. Monoclonality was demonstrated in six of eight cases (rearrangement of T-cell receptor gene), and three of eight had an aberrant T-cell population by flow cytometry. The differential diagnosis of atypical lymphoid infiltrates with morphologic features of marginal zone B-cell lymphoma should include PTCL. This uncommon morphological mimicry should be recognized, because PTCL is an aggressive disease regardless of morphology and should be treated accordingly.

Follicular hodgkin lymphoma: a histopathologic study.

Follicular Hodgkin lymphoma (FHL) is a form of classic Hodgkin lymphoma with morphologic similarity to nodular lymphocyte predominant Hodgkin lymphoma (NLPHL). We present the clinicopathologic features of 13 FHL cases and compare their morphologic features with 40 cases of NLPHL. Seven males and 6 females had FHL in the lymph nodes of the neck (6 patients), axilla (3 patients), groin (2 patients), and mediastinum (1 patient) and in the nasopharynx (1 patient). All FHLs had follicles with small, eccentric germinal centers (GCs) and expanded mantle zones containing classic Reed-Sternberg (RS) cells; reactive GCs also were seen in 6 of 13 cases. The RS cells were CD30+, fascin+ in 13 cases; CD15+ in 11 cases; CD20+ in 4 cases; CD79alpha+CD20- in 1 case; and negative for epithelial membrane antigen in 12 cases; they were surrounded by CD3epsilon+ and CD57+ rosettes in 13 and 2 cases, respectively. Morphologically, FHL may closely simulate NLPHL, and, thus, immunohistochemical analysis is essential to confirm the diagnosis. Clues helpful in diagnosing FHL include the presence offollicles with GCs, classic RS cells, and a relative absence of histiocytes.