Disappearance of CD21-positive follicular dendritic cells preceding the transformation of follicular lymphoma: immunohistological study of the transformation using CD21, p53, Ki-67, and P-glycoprotein

Follicular Lymphoma Microenvironment: An Intricate Network Ready for Therapeutic Intervention

Follicular Lymphoma (FL), the most common indolent non-Hodgkin's B cell lymphoma, is a paradigm of the immune microenvironment's contribution to disease onset, progression, and heterogeneity. Over the last few years, state-of-the-art technologies, including whole-exome sequencing, single-cell RNA sequencing, and mass cytometry, have precisely dissected the specific cellular phenotypes present in the FL microenvironment network and their role in the disease. In this already complex picture, the presence of recurring mutations, including KMT2D, CREBBP, EZH2, and TNFRSF14, have a prominent contributory role, with some of them finely tuning this exquisite dependence of FL on its microenvironment. This precise characterization of the enemy (FL) and its allies (microenvironment) has paved the way for the development of novel therapies aimed at dismantling this contact network, weakening tumor cell support, and reactivating the host's immune response against the tumor. In this review, we will describe the main microenvironment actors, together with the current and future therapeutic approaches targeting them.

The Biological Basis of Histologic Transformation

Histologic transformation of follicular lymphoma remains the leading cause of follicular lymphoma-related mortality in the rituximab era. Both the diverse timing of transformation and heterogeneity in associated genomic events suggest that histologic transformation may itself comprise distinct disease entities. Successive indolent and transformation episodes occur by divergent clonal evolution from an inferred common progenitor cell, representing a potential therapeutic target. Existing biological knowledge largely pre-dates anti-CD20 therapy, and further prospective validation is essential. Inclusion of transformation cases in clinical trials incorporating biomarker discovery, and an integrated understanding of the genetic and microenvironmental factors underpinning transformation, may unearth renewed clinical opportunities.

Can histologic transformation of follicular lymphoma be predicted and prevented?

Transformation to aggressive lymphoma is a critical event in the clinical course of follicular lymphoma (FL) patients. Yet, it is a challenge to reliably predict transformation at the time of diagnosis. Understanding the risk of transformation would be useful for guiding and monitoring patients, as well as for evaluating novel treatment strategies that could potentially prevent transformation. Herein, we review the contribution of clinical, pathological, and genetic risk factors to transformation. Patients with multiple clinical high-risk factors are at elevated risk of transformation but we are currently lacking a prognostic index that would specifically address transformation rather than disease progression or overall survival. From the biological standpoint, multiple studies have correlated individual biomarkers with transformation. However, accurate prediction of this event is currently hampered by our limited knowledge of the evolutionary pathways leading to transformation, as well as the scarcity of comprehensive, large-scale studies that assess both the genomic landscape of alterations within tumor cells and the composition of the microenvironment. Liquid biopsies hold great promise for achieving precision medicine. Indeed, mutations detected within circulating tumor DNA may be a better reflection of the inherent intratumoral heterogeneity than the biopsy of a single site. Last, we will assess whether evidence exists in the literature that transformation might be prevented altogether, based on the choice of therapy for FL.

Analysis of dendritic cell subpopulations in follicular lymphoma with respect to the tumor immune microenvironment

The immune cell composition of the follicular lymphoma (FL) tumor microenvironment is increasingly recognized as an important determinant for clinical outcome. Here, we explored frequency and distribution of dendritic cell (DC) subtypes in relation to regulatory T cells (Treg) by immunohistochemistry in lymph node biopsies from patients with de novo FL. We found that neoplastic follicles contained lower DC and higher Treg frequencies than hyperplastic follicles in control lymph nodes. Treg numbers particularly correlated with the subset of conventional CD11c(+ )DCs. Additionally, both a high intra- to interfollicular ratio of CD11c(+ )DCs and increased intrafollicular Treg frequencies were associated with decreased overall survival. This suggests that functional interactions between these cells may be relevant for FL progression/recurrence. The presence of CD11c(+ )DCs in the tumor microenvironment may assist tumor infiltration by Tregs, thus contributing to the suppression of an otherwise beneficial T-cell-dominated FL microenvironment.

The utility of IgM, CD21, HGAL and LMO2 in the diagnosis of pediatric follicular lymphoma

Pediatric follicular lymphoma (pFL) is a rare neoplasm with features differing from follicular lymphoma arising in adults. Here, we describe a rare case of pFL that showed morphologic features partially overlapping with progressive transformation of germinal centers and reactive follicular hyperplasia. As typical of pFL, neoplastic B cells within follicles did not express B-cell leukemia/lymphoma 2 (BCL2). However, this case showed additional distinctive abnormal findings, which contributed to the diagnosis: (1) diffuse and uniform staining of immunoglobulin M (IgM) on cells within and outside of follicles, (2) abnormally dim expression of CD21 on follicular dendritic cells, and (3) expression of human germinal center-associated lymphoma (HGAL) and LIM domain only 2 (LMO2) on B cells in interfollicular and follicular areas. This case demonstrates the utility of these abnormal features, which can be seen in adult- or usual-type follicular lymphoma, in the diagnosis of pFL. Further studies are necessary to evaluate the significance of these findings in other cases of pFL.

Expression of multidrug resistance 1 gene in B-cell lymphomas: association with follicular dendritic cells

AIMS

  Multidrug resistance (MDR) in B-cell lymphomas still constitutes a major obstacle to the effectiveness of chemotherapy even in the anti-CD20 antibody therapy era. The aim of this study was to investigate the expression of MDR-associated molecules in reactive lymphadenopathy (RL), follicular lymphoma (FL), and diffuse large B-cell lymphoma (DLBCL).

METHODS AND RESULTS

  The expression of mRNA for ABC-transporter family genes was determined by real-time RT-PCR in lymph nodes from RL, FL, and DLBCL cases. MDR1 exhibited significantly stronger expression in RL, FL, and DLBCL than Raji B-cell lymphoma cells. RL and FL showed significantly higher expression than DLBCL. Immunohistochemically, MDR1 positive cells were localized in the germinal centers of RL and center of the nodular lesions of FL showing associations with CD21 positive follicular dendritic cells (FDCs). Raji cells were co-cultured with FDC sarcoma-derived cells and the expression of MDR1 and drug resistance were analyzed. The co-culture of Raji cells with FDCs induced strong expression of MDR1 and introduced resistance to doxorubicin-induced apoptosis.

CONCLUSIONS

  These results suggest that FDCs induce MDR1 expression in reactive as well as neoplastic B-cells. Inhibition of the interaction of FDCs with B-cells may provide a novel strategy for treating the chemotherapy resistant fraction.

Transformation of follicular lymphoma

Histological transformation of follicular lymphoma (FL) to a more aggressive non-Hodgkin's lymphomas is a pivotal event in the natural history of FL and is associated with poor outcome. While commonly observed in clinical practice and despite multiple studies designed to address its pathogenesis, the biology of this process represents an enigma. In this chapter we present a state of the art review summarizing the definition of histologic transformation, its incidence, pathogenesis, clinical manifestations, treatment and outcome. Furthermore, we specifically emphasize gaps in our knowledge that should be addressed in future studies.

Novel therapeutic agents for B-cell lymphoma: developing rational combinations

Several novel targeted therapies have recently emerged as active in the treatment of non-Hodgkin lymphoma, including small molecules that inhibit critical signaling pathways, promote apoptotic mechanisms, or modulate the tumor microenvironment. Other new agents target novel cell surface receptors or promote DNA damage. Although most of these drugs have single-agent activity, none have sufficient activity to be used alone. This article reviews the utility and potential role of these new agents in the treatment of non-Hodgkin lymphoma with a specific focus on data that highlight how these agents may be incorporated into current standard treatment approaches.

Down-regulation of CD9 expression and its correlation to tumor progression in B lymphomas

Histological transformation, a pivotal event in the natural history of cancers including lymphomas, is typically associated with more aggressive clinical behavior. L3055, a B lymphoma cell line of germinal center (GC) origin, is dependent on follicular dendritic cells (FDCs) for survival and proliferation, similar to GC-B cells. However, L3055 cells become less FDC-dependent after prolonged culture, which is analogous to transformation in vivo. Comparison of two L3055 subclones (i.e., the FDC-dependent indolent clone 12 and the FDC-independent aggressive clone 33) by DNA microarray revealed that CD9 was the most differentially expressed gene (P = 0.05). L3055-12 expresses high levels of CD9 while L3055-33 does not. Reduced levels or loss of CD9 expression is also observed in other CD9-positive B lymphoma cell lines. The resultant CD9-negative cells grow faster than CD9-positive cells due to their greater resistance to apoptosis. Furthermore, CD9-negative cells are less dependent on FDCs for their survival and growth compared with CD9-positive cells. CD9 down-regulation in B lymphomas appears to be controlled epigenetically, mainly through histone modifications. These findings imply that CD9 is inversely correlated with B lymphoma progression, and CD9 inactivation may play an important role in B lymphoma transformation.

Prognostic Factors in Follicular Lymphoma

Follicular lymphoma (FL) is one of the most common types of non-Hodgkin's lymphoma. It is usually diagnosed at an advanced stage, for which many treatment options exist, however, no curative standard therapy has been identified. The outcome is highly variable with a median survival of approximately 10 years. The life expectancy of patients with FL has been extended with the use of rituximab, a monoclonal antibody targeting the CD20 antigen on FL cells, but there remains a group of patients who fail to respond to chemoimmunotherapy and die early of their disease. Transformation of FL to an aggressive histology is an important event with high morbidity and mortality. The Follicular Lymphoma International Prognostic Index has become the clinically useful prognostic tool, but gives only a rough estimate of expected outcome. There is a need for useful biomarkers for prediction of the disease course of single patients to individualize therapy, especially in the new era of chemoimmunotherapy.

Bone marrow aspirate and biopsy: a pathologist's perspective. II. interpretation of the bone marrow aspirate and biopsy

Bone marrow examination has become increasingly important for the diagnosis and treatment of hematologic and other illnesses. Morphologic evaluation of the bone marrow aspirate and biopsy has recently been supplemented by increasingly sophisticated ancillary assays, including immunocytochemistry, cytogenetic analysis, flow cytometry, and molecular assays. With our rapidly expanding knowledge of the clinical and biologic diversity of leukemia and other hematologic neoplasms, and an increasing variety of therapeutic options, the bone marrow examination has became more critical for therapeutic monitoring and planning optimal therapy. Sensitive molecular techniques, in vitro drug sensitivity testing, and a number of other special assays are available to provide valuable data to assist these endeavors. Fortunately, improvements in bone marrow aspirate and needle technology has made the procurement of adequate specimens more reliable and efficient, while the use of conscious sedation has improved patient comfort. The procurement of bone marrow specimens was reviewed in the first part of this series. This paper specifically addresses the diagnostic interpretation of bone marrow specimens and the use of ancillary techniques.

Application of Immunohistochemistry in the Diagnosis of Non-Hodgkin and Hodgkin Lymphoma

Context.—Beginning with the immunologic classifications of Lukes and Collins and Kiel and culminating in the Revised European-American Lymphoma and World Health Organization classifications, the diagnosis of lymphoid tumors relies heavily on the determination of cell lineage, maturation, and function, based on antigen expression in addition to morphology and clinical features. Technologic advances in immunology, antibody production, genetic analysis, cloning, and the identification of new genes and proteins by microarray and proteomics have provided pathologists with many antibodies to use in routine diagnosis.

Objective.—To provide guidance to the practicing pathologist in the appropriate selection of an antibody panel for the diagnosis of lymphoma based on morphology and relevant clinical data and to avoid pitfalls in the interpretation of immunohistochemical data. Attention is given to some of the newer antibodies, particularly against transcription factors, that are diagnostically and prognostically useful.

Data Sources.—The information presented in this article is based on review of the literature using the OVID database (Ovid MEDLINE 1950 to present with daily update) and 20 years of experience in diagnostic hematopathology.

Conclusions.—Immunophenotyping is required for the diagnosis and classification of lymphoid malignancies. Many paraffin-reactive antibodies are available to the pathologist but most are not specific. To avoid diagnostic pitfalls, interpretation of marker studies must be based on a panel and knowledge of a particular antigen's expression in normal, reactive, and neoplastic conditions.

BNIP3 expression in follicular lymphoma

AIMS

To investigate the role of BNIP3, a 19-kDa interacting protein of the Bcl-2 family, alongside Bcl-2 in follicular lymphoma in comparison with reactive lymphoid hyperplasia. The results were compared with those from p53 and caspase-3 (apoptotic markers) and Ki67 (proliferation marker).

METHODS AND RESULTS

Immunohistochemistry using monoclonal antibodies showed BNIP3 to be strongly expressed in most follicular lymphomas but to be weak to negative in all of the reactive cases. There was also an inverse relationship with Bcl-2 expression. There was no correlation of BNIP3 immunoreactivity with proliferation and caspase and p53 were virtually negative in all follicular lymphomas and reactive lymphoid cases.

CONCLUSIONS

BNIP3 is strongly expressed in most follicular lymphomas, especially those that are Bcl-2 negative. BNIP3 may serve as a marker of more aggressive behaviour in follicular lymphoma and be useful diagnostically in the distinction from reactive lymphadenitis.

Gene-expression and immunohistochemical study of specific T-cell subsets and accessory cell types in the transformation and prognosis of follicular lymphoma

PURPOSE

Despite the generally favorable clinical course in follicular lymphoma (FL), a minority of patients have a poor prognosis-with death within 3 years of diagnosis-most often due to transformation to aggressive disease.

PATIENTS AND METHODS

In this study, we analyzed the potential of predicting early transformation on the basis of gene expression and immunologic parameters in FL biopsy samples taken at diagnosis.

RESULTS

At the gene-expression level, FL is a highly uniform disease at the time of diagnosis, precluding the detection of sufficiently validated prognostic gene-expression profiles suitable for a clinical setting. Combinations of differentially expressed genes indicate that immunologic mechanisms play a differential role in the risk of early transformation. Using immunohistochemistry for specific cell populations, the spatial distribution to neoplastic follicles and the activation of CD4-positive T-helper cells (P = .002) and specifically T-helper 1 (P = .004) were shown to be highly discriminatory to predict early transformation. A role for functional modulation of follicular dendritic cells could also be supported (P = .04). Other cell populations, including CD68-positive macrophages and regulatory T cells, were not differentially present.

CONCLUSION

These results support the identification of FL as an immunologically functional disease in which an interaction of the tumor cells and the functional composition of the microenvironment determines the clinical behavior.

Immunohistochemical Patterns of Reactive Microenvironment Are Associated With Clinicobiologic Behavior in Follicular Lymphoma Patients

Purpose

Recent molecular data have suggested that non-neoplastic cells are powerful modulators that may confer a selective advantage or disadvantage on the outcome of follicular lymphoma (FL) patients.

Patients and Methods

The prevalence of the principal inflammatory and immune-infiltrated cells was measured immunohistochemically in the tissue of 211 FL patients, and associations were sought with their traditional clinicobiologic characteristics.

Results

Our results confirmed the presence of a large number of T lymphocytes (CD4+and CD8+) and CD57+cells and, at a moderate level, the presence of TIA-1+cytotoxic cells, CD68+macrophages, CD123+plasmacytoid cells, and FOXP3+regulatory T cells among the pool of non-neoplastic cells. In addition to the conventional clinical variables, univariate analysis identified a low level of infiltrated CD8+T lymphocytes as a significantly negative prognostic factor of overall survival. The following significant differences in the abundance of cells of specific and nonspecific immunity were observed in relation to the clinicobiologic features of FL: (1) a reactive microenvironment mainly made up of T lymphocytes and macrophages was significantly associated with a favorable clinical behavior of FL patients; and (2) a reactive microenvironment infiltrated predominantly by CD57+T cells was associated with a significantly higher frequency of adverse clinicobiologic manifestations such as “B” symptoms and bone marrow involvement.

Conclusion

Our results demonstrate the existence of two specific patterns in the reactive microenvironment of FL, an immunosurveillance pattern (T lymphocytes and macrophages) and an immune-escape pattern (CD57+T cells), that were directly associated with the clinicobiologic features of these patients.

Molecular pathogenesis of follicular lymphoma: a cross talk of genetic and immunologic factors

Follicular lymphoma (FL) is the second most frequent type of non-Hodgkin's lymphoma in adults. The disease is characterized by an indolent course with frequent relapses. Ultimately, resistance to chemotherapy or transformation to a more aggressive phase of the disease in the form of diffuse large B-cell lymphoma develops, and patients die as a result of their disease. Median survival is 8 to 10 years. The range is very wide, however, with patients surviving for more than 15 years and 10% to 15% of the patients who run a rapidly fatal course and die within 3 years after diagnosis. The translocation t(14;18) is the basic molecular defect in FL and results in protection from apoptosis by aberrant overexpression of bcl-2 protein. Accumulation of genomic alterations and clonal selection account for subsequent progression and transformation. Recently, the role of the immunologic microenvironment of FL in determining clinical behavior and prognosis has been substantiated. Combined genetic and immunologic data may now support a model for the development of FL as a disease of functional B cells in which specific molecular alterations infer intrinsic growth properties of the tumor cells as well as dictate a specific functional cross talk with the immunologic regulatory network resulting in extrinsic growth support. These insights may lead to improvement of risk stratification, but most importantly will provide tools for developing new targets and strategies for treatment.

Analysis of multiple biomarkers shows that lymphoma-associated macrophage (LAM) content is an independent predictor of survival in follicular lymphoma (FL)

We studied the role of multiple biomarkers in determining outcome in follicular lymphoma (FL), concentrating in particular on the role of benign macrophages. The study group consisted of uniformly staged and treated patients with FL enrolled in a phase 2 trial between 1987 and 1993. All patients were younger than 61 years of age, had advanced-stage FL, and were treated with a multiagent chemotherapy regimen, BP-VACOP (bleomycin, cisplatin, etoposide, doxorubicin, cyclophosphamide, vincristine, and prednisone), followed by involved region radiation. The median follow-up of living patients was 12.5 years, and the median survival was 16.3 years. The International Prognostic Index (IPI) was predictive of overall survival (OS) (P = .003). Biopsy specimens from all cases were stained with an anti-CD68 antibody. Of the 99 evaluable patients with FL, 87 had less than 15 CD68+ macrophages/high-power field (hpf) (median, 7; range, 1-14) and 12 had more than 15 CD68+ macrophages/hpf (median, 20; range, 16-25) with a median OS of 16.3 vs 5.0 years, respectively (P < .001). A multivariate Cox model that included the IPI score, the histologic grade, and the lymphoma-associated macrophage (LAM) score, showed IPI and LAM to be independent predictors of OS (P = .009 and P = .004, respectively). The LAM content of FL predicts survival, and these data support a prominent role for nonneoplastic immune cells in the biology of FL. (Blood. 2005;106:2169-2174)

Autopsy case of CD4/CD8 cutaneous T-cell lymphoma presenting disseminated pagetoid reticulosis with aggressive granulomatous invasion to the lungs and pancreas

Pagetoid reticulosis is a rare cutaneous T-cell lymphoma with striking epidermotropism similar to that present in Paget's disease. There are two forms of pagetoid reticulosis: localized and disseminated. Reported herein is an autopsy case of disseminated pagetoid reticulosis with CD4(-)/CD8(-) phenotype T cells and massive invasion of the lungs and pancreas. The abnormal cells in the epidermis expressed a protein derived from a rearranged T-cell receptor beta gene, and this feature was used to confirm the monoclonality of these cells by polymerase chain reaction. At present, the World Health Organization (WHO) classification system considers pagetoid reticulosis to be an indolent form of primary cutaneous T-cell lymphoma and a variant of mycosis fungoides/Sezary syndrome with prominent epidermotropism. Some differences have been observed between pagetoid reticulosis and mycosis fungoides in terms of clinical course, tumor cell phenotype, and genetic findings; and these differences are highlighted in the present case. The relation between disseminated pagetoid reticulosis, CD4(-)/CD8(-) cutaneous T-cell lymphoma, and gammadelta T-cell lymphoma, including whether pagetoid reticulosis is a variant of mycosis fungoides, remains unclear.

Biology and Management of Histologic Transformation of Indolent Lymphoma

The evolution of indolent lymphomas to aggressive histologies, known as histologic transformation (HT), is a frequent occurrence for all subtypes of low grade B cell lymphoproliferative disorders. The risk of developing HT is approximately 3% per year for patients with indolent lymphoma. Clinically these present with a rapid change in the behavior of the disease, with evidence of a highly proliferative malignancy with a propensity to involve extranodal sites. The prognosis of patients following transformation is generally poor, with median survival of about 12 months. Recent studies suggest that the development of HT is very complex with the acquisition of multiple cytogenetic abnormalities in the low-grade lymphoma cells prior to HT. To date, there are no biologic or genetic parameters predictive of the development of HT. A myriad of genetic lesions have been identified in HT, and provide insight into its pathogenesis. These include genes regulating proliferation (C-MYC and C-MYC-regulated genes); control of the cell cycle (CDKN2a and CDKN2B); and programmed cell death (TP53, C-MYC, and BCL2). Gene expression profiling has been applied to the study of HT and has increased our understanding of the transformation process. There has been limited progress in the treatment of patients with HT. Conventional chemotherapy is generally of limited benefit, although a subset of patients are long-term survivors following high-dose therapy and autologous stem cell transplantation. The use of radioimmunotherapy and new agents targeting specific lesions or aberrant pathways may impact on the management of these aggressive diseases.

Efficacy of rituximab plus chemotherapy in follicular lymphoma depends on Ki-67 expression

Rituximab is widely used for the treatment of B-cell non-Hodgkin's lymphoma (NHL), and encouraging results have been obtained. However, some CD20-positive NHL show minimal response to rituximab, indicating that the treatment effect depends on the presence or absence of an unidentified factor. We analyzed the relationship between the effect of rituximab plus chemotherapy and expression of Ki-67, p53 and bcl-2 and several clinical variables in cases of B-NHL, particularly follicular lymphoma (FL) and diffuse large B-cell lymphoma (DLBCL). Forty-four patients were included in the present study, and the overall treatment response rate was 68%. Twelve of 30 patients (40%) achieved a complete response, five (16%) reached an unconfirmed complete response and 13 (43%) achieved a partial response. A high serum lactate dehydrogenase level and International Prognostic Index of high or high intermediate risk were associated with a decreased response in the case of FL. Immunohistochemical assays were performed in 18 FL patients (55%) and 15 DLBCL patients (45%). Significant correlation was found between an inferior response to treatment and high Ki-67 expression in the cases of FL (P = 0.006). p53 and bcl-2 expression did not correlate significantly with the response rate. The cell cycle appears to be an important factor in the efficacy of rituximab treatment. Ki-67 expression might be a predictor of efficacy of rituximab plus chemotherapy.