Allogeneic hematopoietic cell transplantation is an effective treatment for patients with Richter syndrome: A systematic review and meta-analysis

Treatment of Richter's Transformation with Novel Therapies

PURPOSE OF REVIEW

This review presents recently published clinical trial data and ongoing investigations regarding the treatment of Richter's transformation (RT).

RECENT FINDINGS

Recently, numerous approaches have been investigated for the treatment of RT including: traditional chemoimmunotherapy regimens combined with targeted agents such as BTKi and BCL2i; immunotherapy combined with targeted agents; non-covalent BTKis; bispecific T cell engagers; and CART therapy. In addition, various novel targeted agents are currently being studied for the treatment of RT in phase 1 and 2 clinical trials. Standard of care treatment with chemoimmunotherapy for RT has limited efficacy in achieving durable remissions. Here, we review recent data on the use of combination treatments and targeted agents in RT. Although some progress has been made in the investigation to optimize treatment of RT, further study is needed to evaluate long term outcomes of recently published trials and test efficacy of upcoming novel agents.

Richter's transformation: Transforming the clinical landscape

Richter transformation (RT) represents an aggressive histological transformation from chronic lymphocytic leukaemia, most often to a large B cell lymphoma. It is characterised by chemo-resistance and subsequent short survival. Drug development has struggled over recent years in light of the aggressive kinetics of the disease, lack of pivotal registrational trials and relative rarity of the phenomenon. In this review we will highlight the diagnostic and therapeutic challenges of managing patients with RT as well as taking a look to the future therapeutic landscape. Highly active therapies developed across B cell malignancies are starting to impact this field, with T-cell activation therapies (CAR-T, bispecific antibodies), antibody-drug conjugates, and novel small molecule inhibitor combinations (e.g. BTKi-BCL2i) being actively studied. We will highlight the data supporting these developments and look to the studies to come to provide hope for patients suffering from this devastating disease.

From genetics to therapy: Unraveling the complexities of Richter transformation in chronic lymphocytic leukemia

Richter transformation (RT) refers to the progression of chronic lymphocytic leukemia, the most prevalent leukemia among adults, into a highly aggressive lymphoproliferative disorder, primarily a diffuse large B-cell lymphoma. This is a severe complication that continues to be a therapeutic challenge and remains an unmet medical need. Over the last five years, significant advances have occurred in uncovering the biological processes leading to the RT, refining criteria for properly diagnose RT from other entities, and exploring new therapeutic options beyond the ineffective chemotherapy. This review summarizes current knowledge in RT, including recent advances in the understanding of the pathogenesis of RT, in the classification of RT, and in the development of novel therapeutic strategies for this grave complication.

Accelerated Chronic Lymphocytic Leukemia and Richter Transformation in the Era of Novel Agents

BACKGROUND

Tremendous developments in the field of chronic lymphocytic leukemia (CLL) in recent years have led to a revolutionary change in the treatment approach, which today is based on targeted treatments with a good response and optimal prognosis. Nevertheless, CLL can present or progress to "accelerated CLL" (A-CLL) or to "Richter transformation" (RT) and these two entities have a more aggressive course and are still characterized by challenges in the fields of diagnosis and therapy. In the current review, we summarized the latest knowledge in terms of diagnostic approaches to A-CLL, available treatments and clinical trials, for both A-CLL and RT which still pose an unmet need and require additional basic and clinical investigations.

SUMMARY

A-CLL is a rare and underdiagnosed entity that probably stands in the "gray zone" between CLL and RT, generally holding an intermediate prognosis. Its diagnosis is mainly based on histological findings including expanded proliferation centers, increased mitotic activity, and/or high Ki-67 index. Due to its rarity, its treatment approach has still not been defined, but it seems that novel agents, especially Bruton tyrosine kinase inhibitors (BTKi), are effective. As for RT, the standard therapy still consists of chemo-immunotherapy followed by stem-cell transplantation for fit responders with a dismal prognosis. New approaches are recently adopted including B-cell inhibition via novel agents (BTKi, venetoclax), T-cell engagers (checkpoint inhibitors, bispecific antibodies [BiTe] or the chimeric antigen receptor [CAR] technology), antibody-drug conjugates, or drug combinations. Although both CAR-T and BiTe seem promising, especially when combined with BTKi, evidence is still insufficient, and patients should generally be recruited in clinical trials.

KEY MESSAGES

The field of CLL has been a subject of major advances in recent years, but A-CLL and RT remain topics of "unmet need" and require further studies to identify the best diagnostic approach and a more effective treatment.

Cellular Therapies in Chronic Lymphocytic Leukemia and Richter’s Transformation: Recent Developments in Chimeric Antigen Receptor T-Cells, Natural Killer Cells, and Allogeneic Stem Cell Transplant

Cellular therapies can be viewed as both the newest and oldest techniques for treating chronic lymphocytic leukemia (CLL) and Richter’s transformation (RT). On one hand, allogeneic hematopoietic stem cell transplantation (alloHSCT) has been available for decades, though its use is diminishing with the increasing availability of effective novel targeted agents, especially in CLL. Among newer techniques, chimeric antigen receptor T-cells (CAR-T) have demonstrated astounding efficacy in several hematologic malignancies, leading to FDA approval and use in clinical practice. However, though CLL is the earliest disease type for which CAR-T were studied, development has been slower and has yet to lead to regulatory approval. Owing partially to its rarity but also due to the aggressive behavior of RT, CAR-T in RT have only been minimally explored. Here, we will focus on the applications of cellular therapies in CLL and RT, specifically reviewing more recent data related to alloHSCT in the novel-agent era and CAR-T cell development in CLL/RT, focusing on safety and efficacy successes and limitations. We will review strategies to improve upon CAR-T efficacy and discuss ongoing trials utilizing CAR-T in CLL/RT, as well as emerging technologies, such as allogeneic CAR-T and natural killer CAR (CAR NK) cells.

The role of allogeneic hematopoietic cell transplantation for chronic lymphocytic leukemia: A review

Although the use of allogeneic hematopoietic cell transplantation (HCT) for chronic lymphocytic leukemia (CLL) has declined with the development of novel targeted agents, it continues to play an important role for eligible patients with high-risk or heavily pretreated CLL who lack other treatment options. CLL is susceptible to a potent graft-versus-leukemia (GVL) effect which produces long-lasting remissions in 30-50% of transplanted patients. While allogeneic HCT is associated with significant risks of graft-versus-host disease (GVHD), infection, and non-relapse mortality (NRM), improvements in patient and donor selection, reduced intensity conditioning (RIC), GVHD prophylaxis, and supportive care have rendered this an increasingly safe and effective procedure in the current era. In this review, we discuss recent advances in allogeneic HCT for CLL, with a focus on the optimal evidence-based strategies to maximize benefit and minimize toxicity of this potentially curative cellular therapy.

A systematic review evaluating the efficacy of autologous hematopoietic transplantation for diffuse large B cell lymphoma-type Richter syndrome

Background

Chronic lymphocytic leukemia (CLL) can transform into fast growing lymphoma for diffuse large B-cell lymphoma (DLBCL) called Richter's syndrome (RS), which is commonly related to an existence of large B-cells with equal or larger size than macrophage nuclei or more than twice those of normal lymphocyte. We conducted a systematic review of the existing literature to assess the clinical efficacy of auto-HCT for patients with RS.

Methods

We searched 4 main databases; EMBASE, Google Scholar, Scopus, PubMed and Web of Science and was done on December 26, 2021. All analyses in this study were performed by Stata software and this review was reported in accordance with PRISMA 2020.

Results

Data was extracted from 4 articles; the total number of patients was reported to be 110. Based on the meta-analysis findings, pooled overall survival rate was 56.36% (95%CI= (46.98-65.31). In figure 2, the forest plot of combined results is shown.

Conclusion

Despite the use of common treatment regimens such as chemo immunotherapy and the availability of novel therapies including B-cell receptor inhibitors and rituximab-cyclophosphamide-hydroxydaunorubicin-Oncovin-prednisone (CHOP-R) regimen, the status of disease progression and recovery in RS cases is still not strong enough.

SOHO State of the Art Updates and Next Questions | Management of Most Difficult Cases of Chronic Lymphocytic Leukemia: Relapse After Both BTK and BCL2 Inhibition and Richter Transformation

The introduction of targeted therapies in chronic lymphocytic leukemia (CLL) has ushered in a new era in which patients achieve better control of their disease, survive longer, and experience fewer toxicities than before. Despite this progress, a subgroup of patients with CLL will develop resistance to both Bruton tyrosine kinase (BTK) and B-cell lymphoma 2 inhibitors. In addition, a subgroup of CLL cases will transform into aggressive lymphoma - called Richter transformation - either before or during targeted therapy. These two subgroups of patients have a poor prognosis, and available therapies lead to long-term remission in only a minority of patients. In this paper, two cases are presented that are reflective of these difficult scenarios. In the first case, a patient with CLL, complex karyotype, del 17p, and a mutation in TP53 experiences progression after ibrutinib, venetoclax, bendamustine, rituximab, and idelalisib. In the second case, a patient with CLL and del 17p develops a Richter transformation to diffuse large B-cell lymphoma after treatment with obinutuzumab, chlorambucil, ibrutinib, venetoclax, and idelalisib. The aggressive lymphoma is refractory to chemoimmunotherapy, and she expires. The literature pertaining to these two scenarios is reviewed, including the role of available targeted therapies, chemoimmunotherapy, and hematopoietic cell transplantation. Emerging novel therapies, including reversible BTK inhibitors and CAR T cell therapy, are discussed.

Cellular Therapy in High-Risk Relapsed/Refractory Chronic Lymphocytic Leukemia and Richter Syndrome

Despite the development of highly effective, targeted inhibitors of B-cell proliferation and anti-apoptotic pathways in chronic lymphocytic leukemia (CLL), these treatments are not curative, and many patients will develop either intolerance or resistance to these treatments. Transformation of CLL to high-grade lymphoma—the so-called Richter syndrome (RS)—remains a highly chemoimmunotherapy-resistant disease, with the transformation occurring following targeted inhibitors for CLL treatment being particularly adverse. In light of this, cellular therapy in the form of allogenic stem cell transplantation and chimeric antigen receptor T-cell therapy continues to be explored in these entities. We reviewed the current literature assessing these treatment modalities in both high-risk CLL and RS. We also discussed their current limitations and place in treatment algorithms.

Biology and Treatment of Richter Transformation

Richter transformation (RT), defined as the development of an aggressive lymphoma on a background of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), represents a clinical unmet need because of its dismal prognosis. An increasing body of knowledge in the field of RT is arising from the recent development of preclinical models depicting the biology underlying this aggressive disease. Consistently, new therapeutic strategies based on a genetic rationale are exploring actionable pathogenic pathways to improve the outcome of patients in this setting. In this review, we summarize the current understandings on RT biology and the available treatment options.

Richter's Transformation

PURPOSE OF REVIEW

Richter's transformation (RT) occurs when chronic (CLL) transforms into an aggressive lymphoma. Despite improvements in the treatment of CLL, prognosis for RT remains poor. Here, we review current literature of RT, with a focus on novel treatment options.

RECENT FINDINGS

Efforts are underway to improve outcomes for patients with RT. While small molecule inhibitors have limited efficacy as monotherapy, recent developments combining them with chemo-immunotherapy show promise. Studies exploring the use of cellular therapies including chimeric antigen receptor T-cells and bispecific antibodies are ongoing. The current treatment paradigm for RT is to enroll these patients on a clinical trial when available, together with consultation for a consolidative allogeneic stem cell transplant. Trials investigating novel combinations and cellular therapy are ongoing. Determining predictive variables of transformation is imperative to design studies that allow for early identification and intervention for patients with RT.

Novel Approaches for the Treatment of Patients with Richter's Syndrome

In the last 10–15 years, the way to treat cancers has dramatically changed towards precision medicine approaches. These treatment options are mainly based on selective targeting against signaling pathways critical for or detrimentally activated in cancer cells in cancer cells, as well as exploiting molecules that are specifically expressed on neoplastic cells, also known as tumor-associated antigens. These considerations hold true also in the hematological field where a plethora of novel targeted agents have reached patients’ bedside, significantly improving clinical responses. Chronic lymphocytic leukemia (CLL) is an example of how targeted therapies, such as BTK, PI3K, or Bcl-2 inhibitors as well as anti-CD20 antibodies, have improved patients’ management, even when adopted as frontline treatment. However, these advancements do not apply to Richter’s syndrome (RS), the transformation of CLL into a very aggressive and fatal lymphoma, occurring in 2–10% of patients. RS is usually a fast-growing lymphoma of the diffuse large B cell or the Hodgkin’s variant, with a dismal prognosis. Despite advancements in depicting and understanding the genetic background of RS and its pathogenesis, no significant clinical results have been registered. In the last couple of years, several studies have started to investigate the impact of novel drugs or drug combinations and some of them have opened for clinical trials, currently in phase I or II, whose results will be soon available. This review will present an overview of current and most recent therapeutic options in RS, discussing also how results coming from xenograft models may help in designing and identifying novel treatment opportunities to overcome the lack of effective therapies.

Richter Transformation in Chronic Lymphocytic Leukemia: Update in the Era of Novel Agents

Richter transformation (RT) is a poorly understood complication of chronic lymphocytic leukemia (CLL) with a dismal prognosis. It is associated with a switch in histopathology and biology, generally with a transformation of the original CLL clone to diffuse large B-cell lymphoma (DLBCL) or less frequently to Hodgkin's variant of Richter transformation (HVRT). It occurs in 2-10% of CLL patients, with an incidence rate of 0.5-1% per year, and may develop in treatment-naïve patients, although it is more common following therapy. In recent years, there has been a deeper understanding of the molecular pathogenesis of RT that involves the inactivation of the TP53 tumor suppressor gene in 50-60% of cases and the activation of aberrations of NOTCH1 and MYC pathways in about 30% of cases. Compared to the preceding CLL, 80% of cases with DLBCL-RT and 30% of HVRT harbor the same IGHV-D-J rearrangements, indicating a clonal evolution of the disease, while the remaining cases represent de novo lymphomas that are clonally unrelated. Despite advances in understanding the molecular variations and the pathogenesis of the disease, there is still no significant improvement in patient outcomes. However, if no clinical trials were designed for patients with RT in the past, now there many studies for these patients that incorporate new drugs and novel combinations that are being explored. In this review, we summarize the new information accumulated on RT with special emphasis on results involving the novel therapy tested for this entity, which represents an unmet clinical need.

Autologous and allogeneic hematopoietic cell transplantation for diffuse large B-cell lymphoma-type Richter syndrome

Richter syndrome (RS) represents a transformation from chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) to aggressive lymphoma, most commonly diffuse large B-cell lymphoma (DLBCL), which is associated with a dismal prognosis. Patients with DLBCL-RS have poor outcomes with DLBCL-directed therapy; thus, consolidation with hematopoietic cell transplantation (HCT) has been used, with durable remissions observed. Studies reporting HCT outcomes in patients with DLBCL-RS have been small, have not evaluated the prognostic impact of cytogenetic risk factors, and were conducted prior to the era of novel targeted therapy of CLL/SLL. We performed a Center for International Blood and Transplant Research registry study evaluating outcomes after autologous HCT (auto-HCT; n = 53) and allogeneic HCT (allo-HCT; n = 118) in patients with DLBCL-RS treated in the modern era. More auto-HCT recipients were in complete response (CR) at HCT relative to allo-HCT recipients (66% vs 34%), whereas a higher proportion of allo-HCT recipients had 17p deletion (33% vs 7%) and had previously received novel agents (39% vs 10%). In the auto-HCT cohort, the 3-year relapse incidence, progression-free survival (PFS), and overall survival (OS) were 37%, 48%, and 57%, respectively. Among allo-HCT recipients, the 3-year relapse incidence, PFS, and OS were 30%, 43%, and 52%, respectively. In the allo-HCT cohort, deeper response at HCT was associated with outcomes (3-year PFS/OS, 66%/77% CR vs 43%/57% partial response vs 5%/15% resistant; P < .0001 for both), whereas cytogenetic abnormalities and prior novel therapy did not impact outcomes. In our study, HCT resulted in durable remissions in therapy-sensitive patients with DLBCL-RS treated in the era of targeted CLL/SLL therapy, including patients with high-risk features.

Systematic Reviews in Hematopoietic Cell Transplantation and Cellular Therapy: Considerations and Guidance from the American Society for Transplantation and Cellular Therapy, European Society for Blood and Marrow Transplantation, and Center for International Blood and Marrow Transplant Research Late Effects and Quality of Life Working Committee

Systematic reviews apply rigorous methodologies to address a prespecified, clearly formulated clinical research question. The conclusion that results is often cited to more robustly inform decision making by clinicians, third-party payers, and managed care organizations about the clinical question of interest. Although systematic reviews provide a rigorous standard, they may be infeasible when the task is to create general disease-focused guidelines comprising multiple clinical practice questions versus a single major clinical practice question. Collaborating transplantation and cellular therapy society committees also recognize that the quantity and or quality of reference sources may be insufficient for a meaningful systematic review. As the conduct of systematic reviews has evolved over time in terms of grading systems, reporting requirements, and use of technology, here we provide current guidance on methodologies, resources for reviewers, and approaches to overcome challenges in conducting systematic reviews in transplantation and cellular therapy.

Systematic reviews in hematopoietic cell transplantation and cellular therapy: considerations and guidance from the American Society for Transplantation and Cellular Therapy, European Society for Blood and Marrow Transplantation, and the Center for International Blood and Marrow Transplant Research late effects and quality of life working committee

Systematic reviews apply rigorous methodologies to address a pre-specified, clearly formulated clinical research question. The conclusion that results is often cited to more robustly inform decision-making by clinicians, third-party payers and managed care organizations about the clinical question of interest. While systematic reviews provide a rigorous standard, they may be unfeasible when the task is to create general disease-focused guidelines comprised of multiple clinical practice questions versus a single major clinical practice question. Collaborating transplantation and cellular therapy societal committees also recognize that the quantity and or quality of reference sources may be insufficient for a meaningful systematic review. As the conduct of systematic reviews has evolved over time in terms of grading systems, reporting requirements and use of technology, here we provide current guidance in methodologies, resources for reviewers, and approaches to overcome challenges in conducting systematic reviews in transplantation and cellular therapy.

Richter Syndrome

PURPOSE OF REVIEW

Richter syndrome (RS) is an uncommon but aggressive evolution of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL). RS is an unmet clinical need in the field of CLL. Recent advances in understanding the biology of this condition provide the rationale for testing new therapeutic concepts in order to improve the outcome of patients developing RS, which is so far poor. In this review, we summarize disease characteristics and available therapeutic options for RS.

RECENT FINDINGS

Current regimens with novel agents in monotherapy have shown little impact on survival. Nevertheless, the better reported outcome for RS has been achieved with the combination of chemo-immunotherapy with a novel agent, confirming the synergistic effect of the approaches. Still, the frailty of this population may impose a less toxic management leaving most patients with no reasonable therapeutic option. Treatment options for RS need to be further expanded. Preclinical models in current development may allow to explore actionable pathways and identify new drug targeted combinations.