Expression of PD-1, PD-L1, and PD-L2 in posttransplant lymphoproliferative disorder after solid organ transplantation

Genetic and immunological features of immune deficiency and dysregulation-associated lymphoproliferations and lymphomas as a basis for classification

Immune deficiency and dysregulation-associated lymphoproliferative disorders and lymphomas (IDD-LPDs) encompass a heterogeneous clinical and pathological spectrum of disorders that range from indolent lymphoproliferations to aggressive lymphomas. They arise in a variety of clinical settings and are associated with oncogenic viruses such as the Epstein-Barr virus (EBV) and Kaposi sarcoma-associated herpesvirus/human herpes virus (KSHV/HHV8) in some, but not all, cases. The recognition of IDD-LPDs as distinct from LPDs in immune competent patients is essential to tailor clinical management options for affected patients. The 5th edition of the World Health Organisation classification has introduced an integrated classification of IDD-LPDs with the goal of standardising diagnoses among different settings to enhance clinical decision support. In parallel, new knowledge in the field, particularly surrounding the role of oncogenic viruses and the tumour microenvironment, has led to clearer understanding of the complex pathogenesis of IDD-LPDs and how these features can be precisely harnessed for therapeutic purposes. In this perspective, we highlight the need for multidisciplinary decision-making to augment patient care as well as key areas where evolving concepts offer challenges and opportunities for clinical management, research and future iterations of the classification.

The IPTA Nashville consensus conference on post-transplant lymphoproliferative disorders after solid organ transplantation in children: IV-consensus guidelines for the management of post-transplant lymphoproliferative disorders in children and adolescents

The International Pediatric Transplant Association convened an expert consensus conference to assess current evidence and develop recommendations for various aspects of care relating to post-transplant lymphoproliferative disorders (PTLD) after pediatric solid organ transplantation. This report addresses the outcomes of deliberations by the PTLD Management Working Group. A strong recommendation was made for reduction in immunosuppression as the first step in management. Similarly, strong recommendations were made for the use of the anti-CD20 monoclonal antibody (rituximab) as was the case for chemotherapy in selected scenarios. In some scenarios, there is uncoupling of the strength of the recommendations from the available evidence in situations where such evidence is lacking but collective clinical experiences drive decision-making. Of note, there are no large, randomized phase III trials of any treatment for PTLD in the pediatric age group. Current gaps and future research priorities are highlighted.

Persistence of lung structural and functional alterations at one year post-COVID-19 is associated with increased serum PD-L2 levels and altered CD4/CD8 ratio

BACKGROUND

Persistent respiratory symptoms and lung abnormalities post-COVID-19 are public health problems. This study evaluated biomarkers to stratify high-risk patients to the development or persistence of post-COVID-19 interstitial lung disease.

METHODS

One hundred eighteen patients discharged with residual lung abnormalities compatible with interstitial lung disease (COVID-ILD patients) after a severe COVID-19 were followed for 1 year (post-COVID-ILD patients). Physical examination, pulmonary function tests, and chest high-resolution computed tomography (HRCT) were performed. Soluble forms (s) of PD-L1, PD-L2, TIM-3, and GAL-9 were evaluated in serum and cell culture supernatant, as well as T-cells subsets and the transmembrane expression of PD-L1 and PD-L2 on the cell surface.

RESULTS

Eighty percent of the post-COVID-ILD patients normalized their lung function at 1-year follow-up, 8% presented COVID-independent ILD, and 12% still showed functional and HRCT alterations. PD-L2 levels were heterogeneous during acute COVID-19 (aCOVID); patients who increased (at least 30%) their sPD-L2 levels at 1 year post-COVID-19 and exhibited altered CD4/CD8 ratio showed persistence of chest tomographic and functional alterations. By contrast, patients who decreased sPD-L2 displayed a complete lung recovery. sPD-L1, sTIM-3, and sGAL-9 increased significantly during aCOVID and decreased in all patients after 1-year follow-up.

CONCLUSION

Increased sPD-L2 and an altered CD4/CD8 ratio after 12 months of aCOVID are associated with the persistence of lung lesions, suggesting that they may contribute to lung damage post-COVID-19.

Expression of the immune checkpoint molecules PD‑L1 and PD‑1 in EBV‑associated lymphoproliferative disorders: A meta‑analysis

Epstein-Barr virus (EBV) has been implicated in the development of a wide range of lymphoproliferative disorders. In this process, the role of programmed cell death 1 (PD-1)/programmed cell death ligand 1 (PD-L1) has remained to be clarified. A meta-analysis of 20 studies was performed and risk ratios (RRs) with 95% confidence intervals (CIs) were used to evaluate the association between PD-L1/PD-1 expression and the status of EBV infection. The results showed that the expression level of PD-L1 in tumor cells was significantly higher in EBV+ cases with a pooled RR of 2.26 (95% CI, 1.63-3.14; P<0.01), particularly in subtypes of diffuse large B-cell lymphoma (DLBCL) and classical Hodgkin lymphoma. Similarly, EBV infection increased the expression of PD-L1 in immune cells with a pooled RR of 2.20 (95% CI, 1.55-3.12; P<0.01). In subtypes of DLBCL and post-transplant lymphoproliferative disorder, the expression of PD-L1 in immune cells is increased in EBV+ cases. Regarding the expression level of PD-1 in tumor-infiltrating lymphocytes (TILs), no significance was found between EBV infection and PD-1 expression, with a pooled RR of 1.10 (95% CI, 0.81-1.48; P>0.05). The present meta-analysis demonstrated that in EBV-associated lymphoproliferative disorders, EBV infection was associated with the expression level of PD-L1 in tumor cells and immune cells but was not associated with the expression of PD-1 in TILs.

Programmed cell death ligand 1 expression associated with subtypes of post-transplant lymphoproliferative disorder among pediatric kidney transplant recipients

BACKGROUND

Programmed cell death ligand 1 (PD-L1) expression on tumor cells engages the PD-1 receptor on T cells, inhibiting anti-tumor responses. PD-L1 has been detected in cases of post-transplant lymphoproliferative disorder (PTLD) but reports are limited. Here we examine PD-L1 expression and evaluate for clinical correlations.

METHODS

Twenty-one cases of PTLD were identified among pediatric kidney transplant recipients at our institution from February 1996 to April 2017. Using paraffin-embedded tissue biopsies, we examined 21 primary tumors for expression using PD-L1 monoclonal antibody performed with PAX5 as a double stain. We scored expression of PD-L1 on lesional B-cells as a percentage of positive cells. Clinical course and outcome were obtained from retrospective chart review.

RESULTS

Applying revised 2017 WHO PTLD classification showed five non-destructive, nine polymorphic, and seven monomorphic cases. Average PD-L1 expression based upon PTLD subtype was: non-destructive 11%, polymorphic 43%, and monomorphic 73% (p = .01). Two patients transferred shortly after diagnosis, five received chemotherapy, and three died from PTLD. Among the fatalities, all showed monomorphic PTLD and 90% of lesional B-cells expressed PD-L1.

CONCLUSION

In this case series, significant differences in PD-L1 expression were seen among different subtypes, and monomorphic PTLD demonstrated the highest expression. Study of a larger cohort is needed, and if the correlation of PD-L1 expression and PTLD subtype is confirmed, this may highlight the potential utility of checkpoint inhibitor therapy in cases of severe or refractory disease among kidney transplant recipient in whom the risk of allograft loss is acceptable given the option of chronic dialysis.

PD-L1 and PD-1 expression in pediatric post-transplant Burkitt lymphoma and other monomorphic post-transplant lymphoproliferative disorders

BACKGROUND

Post-transplant lymphoproliferative disorders (PTLD) develop as a consequence of immune suppression. Programmed death protein 1 (PD-1), a regulator of host immune activation, binds to programmed death-ligand 1 (PD-L1) to suppress the T-cell immune response. PD-1/PD-L1 pathway may play a role in PTLD. The objective was to describe intratumoral expression of PD-L1 and PD-1 in pediatric monomorphic PTLD, and assess if density of these cells is associated with progression-free survival (PFS) and overall survival (OS).

PROCEDURE

Clinical variables and outcome data were collected on B-cell monomorphic PTLD treated in Toronto, Canada between 2000 and 2017. Diagnostic area from tumor tissue was identified to count CD3-positive or PD-1-positive cells and CD3-negative lymphoma B cells or PD-L1-positive cells. CD3+ , PD-1+ , and PD-L1+ cell densities were compared between cases of PTLD. OS and PFS were analyzed.

RESULTS

We identified 25 cases of B-cell monomorphic PTLD; majority Burkitt lymphoma (32%) and diffuse large B-cell lymphoma (56%). All cases had CD3+ cells infiltrating the tumor, and median percentage of CD3+ cells was 14% (interquartile range: 6.2%-25%). Twelve cases (48%) had PD-1+ cell infiltrating (range: 1%-83%) and 13 cases (52%) had no PD-1+ cells infiltrating. Sixteen cases (64%) had PD-L1+ cells present; however, there was no PD-L1 expression on any Burkitt lymphoma tissue. When comparing PD-1 and PD-L1 expression, there was no difference in OS or PFS.

CONCLUSION

Intratumoral presence of PD-1+ and PD-L1+ cells varied in pediatric patients with monomorphic PTLD; however, no relationship to OS and PFS was identified.

Post-transplant lymphoproliferative disease in children, adolescents, and young adults

Post-transplant lymphoproliferative disease (PTLD) remains a major complication of transplantation. PTLD is a rare entity and very heterogenous making consensus on diagnosis and treatment very challenging. The majority are Epstein-Barr virus (EBV) driven, CD20+ B-cell proliferations. PTLD does occur following hematopoietic stem cell transplant (HSCT), but due to the relative short risk period and efficacy of pre-emptive therapy, PTLD following HSCT will not be discussed in this review. This review will focus on the epidemiology, role of EBV, clinical presentation, diagnosis and evaluation and the current and emerging treatment strategies for pediatric PTLD following solid organ transplantation.

Post-transplant lymphoproliferative disorder: Update on treatment and novel therapies

Post-transplant lymphoproliferative disorder (PTLD) is rare and heterogeneous lymphoid proliferations that occur as a result of immunosuppression following solid organ transplant (SOT) and haematopoietic stem cell transplant (HSCT) with the majority being driven by EBV. Although some histologies are similar to lymphoid neoplasms seen in immunocompetent patients, treatment of PTLD may be different due to difference in pathobiology and higher risk of treatment complications. The most common treatment approach in SOT PTLD after failing immunosuppression reduction (RIS) takes into consideration a risk-stratified sequential algorithm with rituximab +/- chemotherapy based on phase 2 studies. In HSCT PTLD, RIS alone and chemotherapy are usually ineffective making rituximab +/- RIS as the gold standard of frontline treatment. In this review, we give an update on the treatment of PTLD beyond RIS. We highlight the most recent studies that attempted to incorporate more aggressive chemotherapy regimens and novel treatments into the traditional risk-stratified sequential approach. We also discuss the role of EBV-cytotoxic T lymphocytes in treatment of EBV-driven PTLD. Other novel agents with potential role in PTLD will be discussed in addition to the challenges that could arise with chimeric antigen receptor T-cell therapy and immune checkpoint inhibitors in this population.

Diagnosis and management of post-transplant lymphoproliferative disease following solid organ transplantation in children, adolescents, and young adults

Post-transplant Lymphoproliferative Disease (PTLD) remains a major complication of solid organ transplantation (SOT) in pediatric patients. The majority are Epstein-Barr Virus (EBV) driven CD20⁺ B-cell proliferations responsive to reduction to immunosuppression and anti-CD20 directed immunotherapy. This review focusses on the epidemiology, role of EBV, clinical presentation, current treatment strategies, adoptive immunotherapy and future research in EBV + PTLD in pediatric patients.

Post-Transplant Lymphoproliferative Disease (PTLD) after Allogeneic Hematopoietic Stem Cell Transplantation: Biology and Treatment Options

Post-transplant lymphoproliferative disease (PTLD) is a serious complication occurring as a consequence of immunosuppression in the setting of allogeneic hematopoietic stem cell transplantation (alloHSCT) or solid organ transplantation (SOT). The majority of PTLD arises from B-cells, and Epstein-Barr virus (EBV) infection is present in 60-80% of the cases, revealing the central role played by the latent infection in the pathogenesis of the disease. Therefore, EBV serological status is considered the most important risk factor associated with PTLDs, together with the depth of T-cell immunosuppression pre- and post-transplant. However, despite the advances in pathogenesis understanding and the introduction of novel treatment options, PTLD arising after alloHSCT remains a particularly challenging disease, and there is a need for consensus on how to treat rituximab-refractory cases. This review aims to explore the pathogenesis, risk factors, and treatment options of PTLD in the alloHSCT setting, finally focusing on adoptive immunotherapy options, namely EBV-specific cytotoxic T-lymphocytes (EBV-CTL) and chimeric antigen receptor T-cells (CAR T).

Epstein-Barr virus-associated posttransplant lymphoproliferative disorders: new insights in pathogenesis, classification and treatment

PURPOSE OF REVIEW

Posttransplant lymphoproliferative disorder (PTLD) is a serious complication following transplantation from an allogeneic donor. Epstein-Barr Virus (EBV) is involved in a substantial number of cases. In this review, we aim to summarize recent knowledge on pathogenesis, classification and treatment of EBV + PTLD.

RECENT FINDINGS

New insights in the complex oncogenic properties of EBV antigens noncoding Ribonucleic acids (RNAs), especially EBV MicroRNA (miRNAs), have increased our knowledge of the pathogenesis of EBV + PTLD. In addition the potential influence of EBV on the tumor microenvironment is becoming clearer, paving the way for new types of immunotherapy. Currently PTLD is classified according to the World Health Organization classification together with other lymphoproliferative disorders, based on the specific immunosuppression. However, a new framework integrating all types of lymphoproliferative disorders in all different settings of immune deficiency and dysregulation is needed. Although treatment of EBV + and EBV - PTLD was largely similar in the past, EBV-directed therapies are currently increasingly used.

SUMMARY

The use of EBV-directed therapies and new agents, based on better understanding of pathogenesis and classification of PTLD, will change the treatment landscape of EBV + PTLD in the next era.

Enhanced PD-L1 Expression in LMP1-positive Cells of Epstein-Barr Virus-associated Malignant Lymphomas and Lymphoproliferative Disorders: A Single-cell Resolution Analysis With Multiplex Fluorescence Immunohistochemistry and In Situ Hybridization

Epstein-Barr virus (EBV) is associated with various types of human malignancies and with programmed death ligand (PD-L) 1 expression in neoplastic cells. However, in EBV-associated malignant lymphomas and lymphoproliferative disorders (LPDs), there is limited information regarding PD-L1 expression profiles among different histologic types and patterns of EBV latency. First, we investigated PD-L1 and EBV latent gene expression using conventional immunohistochemistry and in situ hybridization in 42 EBV-associated malignant lymphomas and LPDs. Classic Hodgkin lymphoma showed the highest PD-L1 expression with diffuse expression in all cases, followed by diffuse large B-cell lymphoma/Burkitt lymphoma, LPDs, and extranodal NK/T-cell lymphoma. EBV latency at the case level was not associated with PD-L1 expression. We further evaluated the expression of PD-L1 and EBV latent genes in tumor cells at single-cell resolution using multiplex fluorescence imaging. This analysis revealed that positivity rates of latent membrane protein (LMP) 1 in tumor cells were 1.0% to 89.5% (mean 35.4%) in latency type II/III cases, and LMP1+ cells showed more frequent PD-L1 expression than LMP1- cells (P<0.0001, paired t test). In contrast, no association was observed between EBV nuclear antigen 2 and PD-L1 expression. Notably, tumor cells exhibiting Hodgkin/Reed-Sternberg cell-like morphology co-expressed PD-L1 and LMP1 more often than those that do not. Our observations suggested that LMP1 upregulates PD-L1 expression and is a potential biomarker for predicting the efficacy of immune checkpoint inhibitors. In addition, the heterogeneous expression of PD-L1 and EBV latent genes may produce diverse tumor cells with different oncogenic and immune-evasive properties, leading to resistance to targeted therapies.

EBV+ lymphoproliferative diseases: opportunities for leveraging EBV as a therapeutic target

Epstein-Barr virus (EBV) is a ubiquitous human tumor virus, which contributes to the development of lymphoproliferative disease, most notably in patients with impaired immunity. EBV-associated lymphoproliferation is characterized by expression of latent EBV proteins and ranges in severity from a relatively benign proliferative response to aggressive malignant lymphomas. The presence of EBV can also serve as a unique target for directed therapies for the treatment of EBV lymphoproliferative diseases, including T cell-based immune therapies. In this review, we describe the EBV-associated lymphoproliferative diseases and particularly focus on the therapies that target EBV.

Epstein-Barr virus-associated post-transplant lymphoproliferative disorders: beyond chemotherapy treatment

Post-transplant lymphoproliferative disorder (PTLD) is a rare but life-threatening complication of both allogeneic solid organ (SOT) and hematopoietic cell transplantation (HCT). The histology of PTLD ranges from benign polyclonal lymphoproliferation to a lesion indistinguishable from classic monoclonal lymphoma. Most commonly, PTLDs are Epstein-Barr virus (EBV) positive and result from loss of immune surveillance over EBV. Treatment for PTLD differs from the treatment for typical non-Hodgkin lymphoma because prognostic factors are different, resistance to treatment is unique, and there are specific concerns for organ toxicity. While recipients of HCT have a limited time during which they are at risk for this complication, recipients of SOT have a lifelong requirement for immunosuppression, so approaches that limit compromising or help restore immune surveillance are of high interest. Furthermore, while EBV-positive and EBV-negative PTLDs are not intrinsically resistant to chemotherapy, the poor tolerance of chemotherapy in the post-transplant setting makes it essential to minimize potential treatment-related toxicities and explore alternative treatment algorithms. Therefore, reduced-toxicity approaches such as single-agent CD20 monoclonal antibodies or bortezomib, reduced dosing of standard chemotherapeutic agents, and non-chemotherapy-based approaches such as cytotoxic T cells have all been explored. Here, we review the chemotherapy and non-chemotherapy treatment landscape for PTLD.

Natural Killer Cells in Post-Transplant Lymphoproliferative Disorders

Post-transplant lymphoproliferative disorders (PTLDs) are life-threatening complications arising after solid organ or hematopoietic stem cell transplantations. Although the majority of these lymphoproliferations are of B cell origin, and are frequently associated with primary Epstein-Barr virus (EBV) infection or reactivation in the post-transplant period, rare cases of T cell and natural killer (NK) cell-originated PTLDs have also been described. A general assumption is that PTLDs result from the impairment of anti-viral and anti-tumoral immunosurveillance due to the long-term use of immunosuppressants in transplant recipients. T cell impairment is known to play a critical role in the immune-pathogenesis of post-transplant EBV-linked complications, while the role of NK cells has been less investigated, and is probably different between EBV-positive and EBV-negative PTLDs. As a part of the innate immune response, NK cells are critical for protecting hosts during the early response to virus-induced tumors. The complexity of their function is modulated by a myriad of activating and inhibitory receptors expressed on cell surfaces. This review outlines our current understanding of NK cells in the pathogenesis of PTLD, and discusses their potential implications for current PTLD therapies and novel NK cell-based therapies for the containment of these disorders.

Posttransplant Lymphoproliferative Disorder Following Kidney Transplantation: A Review

Posttransplant lymphoproliferative disorder (PTLD) is one of the most feared complications following kidney transplantation. Over a 10-year period, the risk of PTLD in kidney transplant recipients (KTRs) is 12-fold higher than in a matched nontransplanted population. Given the number of kidney transplants performed, KTRs who experience PTLD outnumber other organ transplant recipients who experience PTLD. Epstein-Barr virus infection is one of the most important risk factors for PTLD, even though 40% of PTLD cases in contemporary series are not Epstein-Barr virus-associated. The overall level of immunosuppression seems to be the most important driver of the increased occurrence of PTLD in solid organ transplant recipients. Reduction in immunosuppression is commonly accepted to prevent and treat PTLD. Although the cornerstone of PTLD treatment had been chemotherapy (typically cyclophosphamide-doxorubicin-vincristinr-prednisone), the availability of rituximab has changed the treatment landscape in the past 2 decades. The outcome of PTLD in KTRs has clearly improved as a result of the introduction of more uniform treatment protocols, improved supportive care, and increased awareness and use of positron emission tomography combined with computed tomography in staging and response monitoring. In this review, we will focus on the most recent data on epidemiology, presentation, risk factors, and management of PTLD in KTRs.

RNAseq analysis identifies involvement of EBNA2 in PD-L1 induction during Epstein-Barr virus infection of primary B cells

Epstein-Barr virus (EBV) is a causative agent of infectious mononucleosis and several types of malignancy. RNAseq of peripheral blood primary B cell samples infected with wild-type EBV revealed that expression of programmed cell death ligand-1 (PD-L1) is markedly induced by infection. This induction of PD-L1 was alleviated by knockout of the EBNA2 gene, but knockout of LMP1 had little effect. ChIPseq, ChIA-PET, and reporter assays further confirmed that EBNA2-binding sites in the promoter region and at 130 kb downstream of the PD-L1 gene played important roles in PD-L1 induction. Our results indicate that EBV mainly utilizes the EBNA2 gene for induction of PD-L1 and to evade host immunity on infection of primary B cells. Furthermore, pathway analysis revealed that genes involved in the cell cycle, metabolic processes, membrane morphogenesis, and vesicle regulation were induced by EBNA2, and that EBNA2 suppressed genes related to immune signaling.

Clinical features and treatment strategies for post-transplant and iatrogenic immunodeficiency-associated lymphoproliferative disorders

A specific category termed immunodeficiency-associated lymphoproliferative disorders (LPD) exists in the 2016 revised WHO classification concerning lymphoid neoplasms. This category is defined by etiology and includes LPD developing in association with organ transplantation or immunosuppressive/immunomodulatory agents including methotrexate. The functional mechanism is chiefly explained by the autonomous proliferation of Epstein-Barr virus (EBV)-infected lymphocytes induced by host-immune suppression. This category ranges from reactive lymphocyte hyperplasia to monomorphic lymphoma. Its clinical behavior varies depending on host immunity and pathological features; pathological confirmation by biopsy is thus important for deciding treatment strategies. Owing to the spontaneous regression observed in some patients, uniform chemotherapy is not recommended. The main initial treatment options include the reduction in immunosuppressive drugs, immunotherapy with the anti-CD20 antibody rituximab, chemotherapy, or a combination of these. Other novel treatments such as adoptive immunotherapy with EBV-specific cytotoxic T cells, could be an alternative for relapsed/refractory diseases in clinical trials.

Comparative analysis of post-transplant lymphoproliferative disorders after solid organ and hematopoietic stem cell transplantation reveals differences in the tumor microenvironment

Post-transplant lymphoproliferative disorders (PTLD) occur after solid organ transplantation (SOT) or hematopoietic stem cell transplantation (HCT) and are frequently associated with Epstein-Barr virus (EBV). Because of the complex immune setup in PTLD patients, the tumor microenvironment (TME) is of particular interest to understand PTLD pathogenesis and elucidate predictive factors and possible treatment options. We present a comparative study of clinicopathological features of 48 PTLD after HCT (n = 26) or SOT (n = 22), including non-destructive (n = 6), polymorphic (n = 23), and monomorphic (n = 18) PTLD and classic Hodgkin lymphoma (n = 1). EBV was positive in 35 cases (73%). A detailed examination of the TME with image analysis-based quantification in 22 cases revealed an inflammatory TME despite underlying immunosuppression and significant differences in its density and composition depending on type of transplant, PTLD subtypes, and EBV status. Tumor-associated macrophages (TAMs) expressing CD163 (p = 0.0022) and Mannose (p = 0.0016) were enriched in PTLD after HCT. Double stains also showed differences in macrophage polarization, with more frequent M1 polarization after HCT (p = 0.0321). Higher counts for TAMs (CD163 (p = 0.0008) and cMaf (p = 0.0035)) as well as in the T cell compartment (Granzyme B (p = 0.0028), CD8 (p = 0.01), and for PD-L1 (p = 0.0305)) were observed depending on EBV status. In conclusion, despite the presence of immunosuppression, PTLD predominantly contains an inflammatory TME characterized by mostly M1-polarized macrophages and cytotoxic T cells. Status post HCT, EBV positivity, and polymorphic subtype are associated with an actively inflamed TME, indicating a specific response of the immune system. Further studies need to elucidate prognostic significance and potential therapeutic implications of the TME in PTLD.

Activating the Antitumor Immune Response in Non-Hodgkin Lymphoma Using Immune Checkpoint Inhibitors

Non-Hodgkin lymphomas comprise a heterogenous group of disorders which differ in biology. Although response rates are high in some groups, relapsed disease can be difficult to treat, and newer approaches are needed for this patient population. It is increasingly apparent that the immune system plays a significant role in the propagation and survival of malignant cells. Immune checkpoint blocking agents augment cytotoxic activity of the adaptive and innate immune systems and enhance tumor cell killing. Anti-PD-1 and anti-CTLA-4 antibodies have been tested as both single agents and combination therapy. Although success rates with anti-PD-1 antibodies are high in patients with Hodgkin lymphoma, the results are yet to be replicated in those with non-Hodgkin lymphomas. Some lymphoma histologies, such as primary mediastinal B cell lymphoma (PMBL), central nervous system, and testicular lymphomas and gray zone lymphoma, respond favorably to PD-1 blockade, but the response rates in most lymphoma subtypes are low. Other agents including those targeting the adaptive immune system such as TIM-3, TIGIT, and BTLA and innate immune system such as CD47 and KIR are therefore in trials to test alternative ways to activate the immune system. Patient selection based on tumor biology is likely to be a determining factor in treatment response in patients, and further research exploring optimal patient populations, newer targets, and combination therapy as well as identifying biomarkers is needed.

Immune and Cell Therapy in Non-Hodgkin Lymphoma

The promise of immunotherapy has shone brightly for decades in hematologic malignancies and specifically in non-Hodgkin lymphoma. The last decade has witnessed the emergence of completely novel forms of immunotherapy, including immune checkpoint blockade, bispecific antibodies, and chimeric antigen receptor T cells. These treatments have shown phenomenal, and in some cases possibly curative, successes in various relapsed/refractory lymphomas. This review summarizes the most notable successes and promising findings as well as some of the attendant failures. These treatments will doubtlessly transform the treatment paradigms across many lymphoma subtypes. Yet, only if we can better understand their mechanisms of action, toxicity, and resistance will be able to maximize their therapeutic benefit.

Biological Difference Between Epstein-Barr Virus Positive and Negative Post-transplant Lymphoproliferative Disorders and Their Clinical Impact

Epstein–Barr virus (EBV) infection is correlated with several lymphoproliferative disorders, including Hodgkin disease, Burkitt lymphoma, diffuse large B-cell lymphoma (DLBCL), and post-transplant lymphoproliferative disorder (PTLD). The oncogenic EBV is present in 80% of PTLD. EBV infection influences immune response and has a causative role in the oncogenic transformation of lymphocytes. The development of PTLD is the consequence of an imbalance between immunosurveillance and immunosuppression. Different approaches have been proposed to treat this disorder, including suppression of the EBV viral load, reduction of immune suppression, and malignant clone destruction. In some cases, upfront chemotherapy offers better and durable clinical responses. In this work, we elucidate the clinicopathological and molecular-genetic characteristics of PTLD to clarify the biological differences of EBV(+) and EBV(–) PTLD. Gene expression profiling, next-generation sequencing, and microRNA profiles have recently provided many data that explore PTLD pathogenic mechanisms and identify potential therapeutic targets. This article aims to explore new insights into clinical behavior and pathogenesis of EBV(–)/(+) PTLD with the hope to support future therapeutic studies.

Post-transplant lymphoproliferative disorders, Epstein-Barr virus infection, and disease in solid organ transplantation: Guidelines from the American Society of Transplantation Infectious Diseases Community of Practice

PTLD with the response-dependent sequential use of RIS, rituximab, and cytotoxic chemotherapy is recommended. Evidence gaps requiring future research and alternate treatment strategies including immunotherapy are highlighted.

PD-L1 and PD1 expression in post-transplantation lymphoproliferative disease (PTLD) of childhood and adolescence: An inter- and intra-individual descriptive study covering the whole spectrum of PTLD categories

Therapy of children with post-transplantation lymphoproliferative disorder (PTLD) after hematopoietic stem cell (HSCT) and solid organ transplantation (SOT) can be challenging. In this retrospective study, we investigated PD-L1 and PD1 expression in all PTLD categories of childhood and adolescence to see whether checkpoint inhibition with PD-L1/PD1 inhibitors may serve as a therapy option. We included 21 patients aged 19 years or younger (at date of transplant) with PTLD following SOT or HSCT having adequate tumor samples available (n = 29). Using immunohistochemistry, we evaluated PD-L1/PD1 expression on both tumor cells and cells of the microenvironment in all samples. Availability of consecutively matched tumor samples during 6 of 21 patients' disease courses also allowed an intra-individual assessment of PD-L1/PD1 expression. We observed lower PD-L1 and higher PD1 expression in non-destructive lesions, and higher PD-L1 and lower PD1 expression in polymorphic and, in particular, in monomorphic PTLD, mostly diffuse large B-cell lymphomas (DLBCL, n = 10/21). The amount of PD-L1- and PD1-positive cells changed in the opposite way in sequential biopsies of the same individual correlating well with the PTLD category. This is the first comprehensive pediatric study assessing PD-L1 and PD1 expression on tumor cells and in the microenvironment of PTLD including not only monomorphic, but also non-destructive early lesions. PD-L1 expression of the tumor cells inversely correlated with PD1 expression in surrounding tissues, with the highest expression in DLBCL. Since PTLD can be therapeutically challenging, our results indicate a potential efficacy of checkpoint inhibitors if standard immune- and/or chemotherapy fail or are impossible. We therefore recommend routine staining of PD-L1 and PD1 in all PTLD categories.

The Tumor Microenvironment in Post-Transplant Lymphoproliferative Disorders

Post-transplant lymphoproliferative disorders (PTLDs) cover a broad spectrum of lymphoproliferative lesions arising after solid organ or allogeneic hematopoietic stem cell transplantation. The composition and function of the tumor microenvironment (TME), consisting of all non-malignant constituents of a tumor, is greatly impacted in PTLD through a complex interplay between 4 factors: 1) the graft organ causes immune stimulation through chronic antigen presentation; 2) the therapy to prevent organ rejection interferes with the immune system; 3) the oncogenic Epstein-Barr virus (EBV), present in 80% of PTLDs, has a causative role in the oncogenic transformation of lymphocytes and influences immune responses; 4) interaction with the donor-derived immune cells accompanying the graft. These factors make PTLDs an interesting model to look at cancer-microenvironment interactions and current findings can be of interest for other malignancies including solid tumors. Here we will review the current knowledge of the TME composition in PTLD with a focus on the different factors involved in PTLD development.

Epstein Barr Virus Associated B-Cell Lymphomas and Iatrogenic Lymphoproliferative Disorders

Epstein-Barr virus (EBV) is a ubiquitous herpesvirus, affecting up to 90% of the population. EBV was first identified as an oncogenic virus in a Burkitt lymphoma cell line, though subsequently has been found to drive a variety of malignancies, including diffuse large B-cell lymphoma (DLBCL) and other lymphoma subtypes. EBV has a tropism for B-lymphocytes and has the unique ability to exist in a latent state, evading the host immune response. In cases of impaired cell mediated immunity, as in patients with advanced age or iatrogenic immune suppression, the virus is able to proliferate in an unregulated fashion, expressing viral antigens that predispose to transformation. EBV-positive DLBCL not otherwise specified, which has been included as a revised provisional entity in the 2016 WHO classification of lymphoid malignancies, is thought to commonly occur in older patients with immunosenescence. Similarly, it is well-established that iatrogenic immune suppression, occurring in both transplant and non-transplant settings, can predispose to EBV-driven lymphoproliferative disorders. EBV-positive lymphoproliferative disorders are heterogeneous, with variable clinical features and prognoses depending on the context in which they arise. While DLBCL is the most common subtype, other histologic variants, including Burkitt lymphoma, NK/T-cell lymphoma, and Hodgkin lymphoma can occur. Research aimed at understanding the underlying biology and disease prevention strategies in EBV-associated lymphoproliferative diseases are ongoing. Additionally, personalized treatment approaches, such as immunotherapy and adoptive T-cell therapies, have yielded encouraging results, though randomized trials are needed to further define optimal management.