Failure of ALL recognition by CAR T cells: a review of CD 19-negative relapses after anti-CD 19 CAR-T treatment in B-ALL

How I Investigate Measurable Residual Disease in B-Cell Precursor Acute Lymphoblastic Leukemia After Therapy With Bi-Specific Monoclonal Antibodies and 19CAR-T Cells

INTRODUCTION

Measurable residual disease (MRD) in B-cell precursor acute lymphoblastic leukemia (BCP-ALL) following anti-CD19 targeted therapies requires specific strategies to identify residual blast cells due to loss or reduced CD19 expression that makes it inconsistent as a primitive marker for B-cell gating.

OBJECTIVE

Due to the increased access of BCP-ALL patients to therapies with CD3/CD19 bispecific T-cell engagers (BiTe) and CD19-targeted chimeric antigen receptor T-Cell (CAR-T), it is essential that flow cytometry laboratories are prepared to evaluate therapeutic responses.

MATERIAL AND METHODS

Here, validated strategies for MRD detection in the context of anti-CD19 therapies are described, accessible to flow cytometry laboratories according to their different facilities. The paper includes an 8-color flow cytometry (FC) strategy for BCP-ALL MRD based on alternative gating without the use of additional markers (Euroflow protocol), as well as other strategies using alternative markers to CD19, comprising 2 protocols using 8 colors, one using 10 colors and another 14 colors/15 markers.

CONCLUSION

Different strategies are needed to detect MRD without using CD19 for B-cell population gating after CD19-targeted therapies. However, it is essential that validated protocols are used according to the available resources to ensure reliable results for clinical decision-making.

Theranostics in Hematological Malignancies: Cutting-Edge Advances in Diagnosis and Targeted Therapy

Hematologic malignancies, including leukemia, lymphoma, and multiple myeloma, continue to challenge clinicians with complex treatment regimens that often involve significant side effects and limited success, especially in advanced stages. Recent advancements in nuclear medicine have introduced theranostic strategies that merge diagnostic imaging with targeted therapeutic approaches, offering the potential for more precise and personalized treatment. A key area of progress lies in the development of alpha-emitting radiopharmaceuticals, such as 225Ac, 211At, or 212Pb, which can deliver potent radiation directly to tumor cells, sparing healthy tissue and minimizing collateral damage. In parallel with these therapeutic advancements, molecular imaging using radiolabeled agents enables better disease monitoring, assessment of treatment efficacy, and personalized management of patients with hematologic malignancies. The integration of diagnostic imaging with radiotherapy allows for a more tailored approach, where treatment can be adjusted based on real-time information about tumor progression and response. This review examines the recent strides made in both the development of radiopharmaceuticals and their applications in molecular imaging, with a focus on the potential to improve precision, reduce toxicity, and optimize patient outcomes. The synergy between targeted therapy and molecular imaging represents a transformative shift in the management of hematologic malignancies. As these technologies evolve, they are poised to redefine treatment paradigms, offering new hope for patients and potentially improving survival rates with more effective and less toxic treatment options.

Minimal residual disease assessment following CD19-targeted therapy in B-cell precursor acute lymphoblastic leukemia using standardized 12-color flow cytometry: A EuroFlow study

Detection of minimal/measurable residual disease (MRD) is a critical prognostic marker in B-cell precursor acute lymphoblastic leukemia (BCP-ALL). The EuroFlow Consortium previously developed an 8-color flow cytometric MRD protocol, effective for >98% of BCP-ALL patients treated with chemotherapy. This study aimed to enhance MRD detection, particularly for patients treated with CD19-targeted therapies, by expanding the EuroFlow protocol to a 12-color panel. This new panel incorporates additional B-cell markers and exclusion T/NK-cell markers (CD3 and CD7). Through an evaluation of 237 diagnostic BCP-ALL samples, CD22, CD24, and HLA-DR were selected as additional B-cell gating markers. Two 12-color tubes were technically optimized and clinically validated across 101 patient follow-up samples, demonstrating excellent concordance with molecular MRD levels (R 2 = 0.88). The 12-color BCP-ALL MRD tubes were compatible with the previously developed 8-color automated gating and identification (AGI) tool and demonstrated good reproducibility. Our findings indicate that the 12-color panel performs comparably to the 8-color BCP-ALL MRD panel, including both CD19-positive and CD19-negative cases. However, it offers an improved definition of the B-cell lineage, particularly for expert-guided manual data analysis, and provides additional information on the expression of the targetable marker CD22.

Anti-CD19 antibody cotreatment enhances serial killing activity of anti-CD19 CAR-T/-NK cells and reduces trogocytosis

ABSTRACT

Anti-CD19 chimeric antigen receptor (CAR)-engineered T and natural killer (NK) cell therapies have revolutionized the treatment of B-cell malignancies, but challenges including CD19 antigen loss greatly hinder their full therapeutic potential. Here, we revealed that cotreatment with anti-CD19 monoclonal antibody enhances antitumor activity of anti-CD19 CAR-T and -NK cells. Even though the treated antibody interferes with CD19 antigen binding of CAR, it significantly induces rapid detachment of anti-CD19 CAR effector cells from target cells, facilitating improved serial killing. This reduced interaction between CAR effector cells and target cells also leads to the alleviation of CAR-mediated trogocytosis. Interestingly, cotreatment with anti-CD19 antibody reveals time-dependent effects on the antitumor activity of anti-CD19 CAR-T cells, characterized by a reduction in early T cell activation followed by sustained high activity during prolonged exposure to target cells. This temporal modulation ultimately results in enhanced antitumor potency in vivo. These findings underscore the improved therapeutic efficacy achieved by combining anti-CD19 antibody with anti-CD19 CAR-T or -NK cells against B-cell malignancies.

A Switch Protein Adapter for Anti-LILRB4 CAR-T Cells

Chimeric antigen receptor-T cell (CAR-T) immunotherapy has shown remarkable results for the treatment of certain hematologic malignancies. A redirection strategy that utilizes clinically relevant CAR-T cells in combination with adapter proteins may be an effective strategy to target other hematologic and solid cancers. We established a fusion antibody-based strategy with flexibility to target multiple tumor types in combination with a novel anti-leukocyte immunoglobulin-like receptor-B 4 (LILRB4) CAR-T cell. Specifically, we engineered switch protein (SwP) adapters containing the LILRB4 extracellular domain fused to either an anti-CD19 or anti-CD20 single-chain variable fragment (scFv). These SwPs were sufficient to stimulate anti-LILRB4 CAR-T cells against SwP-tagged LILRB4-CD19+ and LILRB4-CD20+ cancers in vitro and in vivo. This strategy may allow CAR-T cells to be redirected against a variety of tumor antigens and cancer types and become a valuable approach to expand the impact of cellular immunotherapy.

Innovative approaches in stem cell therapy: revolutionizing cancer treatment and advancing neurobiology - a comprehensive review

Stem cell therapy represents a transformative frontier in medical science, offering promising avenues for revolutionizing cancer treatment and advancing our understanding of neurobiology. This review explores innovative approaches in stem cell therapy that have the potential to reshape clinical practices and therapeutic outcomes in cancer and neurodegenerative diseases. In this dynamic and intriguing realm of cancer research, recent years witnessed a surge in attention toward understanding the intricate role of mesenchymal stem cells (MSCs). These cells, capable of either suppressing or promoting tumors across diverse experimental models, have been a focal point in the exploration of exosome-based therapies. Exosomes released by MSCs have played a pivotal role, in unraveling the nuances of paracrine signaling and its profound impact on cancer development. Recent studies have revealed the complex nature of MSC-derived exosomes, showcasing both protumor and antitumor effects. Despite their multifaceted involvement in tumor growth, these exosomes show significant promise in influencing both tumor development and chemosensitivity, acting as a pivotal factor that increases stem cells' potential for medicinal use. Endogenous MSCs, primarily originating from the bone marrow, exhibited a unique migratory response to damaged tissue sites. The genetic modification of stem cells, including MSCs, opened avenues for the precise delivery of therapeutic payloads in the milieu around the tumor (TME). Stem cell therapy offers groundbreaking potential for treating neurodegenerative and autoimmune disorders by regenerating damaged tissues and modulating immune responses. This approach aims to restore lost function and promote healing through targeted cellular interventions. In this review, we explored the molecular complexities of cancer and the potential for breakthroughs in personalized and targeted therapies. This analysis offers hope for transformative advancements in both cancer treatment and neurodegenerative disorders, highlighting the promise of precision medicine in addressing these challenging conditions.

[The mechanisms and salvage treatment strategies underlying positive relapse following CD19 CAR-T cell therapy in B-acute lymphoblastic leukemia]

Approximately 50% of patients suffering from relapsed/refractory B-acute lymphoblastic leukemia (R/R B-ALL), experience relapse within one year, with around 60% of these relapses being antigen-positive, despite the transformative impact of chimeric antigen receptor (CAR) T cell therapy. The mechanisms underlying relapse are primarily associated with tumor heterogeneity, CAR-T cell dysfunction, subopimal in vivo expansion and persistence, and an inhibitory immune microenvironment. This review aims to investigate salvage strategies designed to enhance outcomes for patients undergoing relapse or disease progression following the CAR-T cell therapy. These strategies include a second CAR-T cell infusion that targets either the same antigen or an alternative target, the administration of immune checkpoint inhibitors, and the utilization of novel targeted therapies including monoclonal antibodies, antibody-conjugated drugs and small molecule compounds aimed at mitigating CD19-positive relapse or overcoming CAR-T cell resistance. Nevertheless, achieving improved long-term survival for these patients continues be challenging.

Exploring the potential of the convergence between extracellular vesicles and CAR technology as a novel immunotherapy approach

Cancer therapy is a dynamically evolving field, witnessing the emergence of innovative approaches that offer a promising outlook for patients grappling with persistent disease. Within the realm of therapeutic exploration, chimeric antigen receptor (CAR) T cells as well as CAR NK cells, have surfaced as novel approaches, each possessing unique attributes and transformative potential. Immune cells engineered to express CARs recognizing tumour-specific antigens, have shown remarkable promise in treating terminal cancers by combining the precision of antibody specificity with the potent cytotoxic function of T cells. However, their application in solid tumours is still in its nascent stages, presenting unique major challenges. On the same note, CAR NK cells offer a distinct immunotherapeutic approach, utilizing CARs on NK cells, providing advantages in safety, manufacturing simplicity, and a broader scope for cancer treatment. Extracellular vesicles (EVs) have emerged as promising therapeutic agents due to their ability to carry crucial biomarkers and biologically active molecules, serving as vital messengers in the intercellular communication network. In the context of cancer, the therapeutic potential of EVs lies in delivering tumour-suppressing proteins, nucleic acid components, or targeting drugs with precision, thereby redefining the paradigm of precision medicine. The fusion of CAR technology with the capabilities of EVs has given rise to a new therapeutic frontier. CAR T EVs and CAR NK EVs, leveraging the power of EVs, have the potential to alleviate challenges associated with live-cell therapies. EVs are suggested to reduce the side effects linked to CAR T cell therapy and hold the potential to revolutionize the penetrance in solid tumours. EVs act as carriers of pro-apoptotic molecules and RNA components, enhancing immune responses and thereby expanding their therapeutic potential. In this review article, we navigate dynamic landscapes, with our objective being to evaluate comparative efficacy, safety profiles, manufacturing complexities, and clinical applicability.

CAR-T cell combination therapies in hematologic malignancies

Chimeric antigen receptor-T cell therapy, a groundbreaking cancer treatment, has achieved remarkable success against hematologic malignancies. However, CAR-T monotherapy faces challenges in certain cases, including treatment tolerance and relapse rates. To overcome these challenges, researchers are investigating combining CAR-T cells with other treatments to enhance therapeutic efficacy. Therefore, this review aims to investigate the progress of research in combining CAR-T cells for hematologic malignancies. It covers the basic principles and clinical applications of CAR-T cell therapy, detailing combinations with chemotherapy, immune checkpoint inhibitors, targeted drugs, radiotherapy, hematopoietic stem cell transplantation, and other treatments. These combinations synergistically enhance the antitumor effects of CAR-T cells and comprehensively target tumors through different mechanisms, improving patient response and survival rates.

Clinicopathologic features of relapsed CD19(-) B-ALL in CD19-targeted immunotherapy: Biological insights into relapse and LILRB1 as a novel B-cell marker for CD19(-) B lymphoblasts

INTRODUCTION

The mechanism of relapsed CD19(-) B-ALL after anti-CD19 immunotherapy (Kymriah [CART-19] and blinatumomab) is under active investigation. Our study aims to assess LILRB1 as a novel B-cell marker for detecting CD19(-) B-lymphoblasts and to analyze the clinicopathologic/genetic features of such disease to provide biological insight into relapse.

METHODS

Six patients (3 males/3 females, median age of 14 years) with relapsed CD19(-) B-ALL were analyzed for cytogenetic/genetic profile and immunophenotype.

RESULTS

CD19(-) B-ALL emerged after an interval of 5.8 months following anti-CD19 therapy. Five of six patients had B-cell aplasia, indicative of a persistent effect of CART or blinatumomab at relapse. Importantly, LILRB1 was variably expressed on CD19(-) and CD19(+) B lymphoblasts, strong on CD34(+) lymphoblasts and dim/partial on CD34(-) lymphoblasts. Three of six patients with paired B-ALL samples (pre- and post-anti-CD19 therapy) carried complex and different cytogenetic abnormalities, either as completely different or sharing a subset of cytogenetic abnormalities.

CONCLUSION

LILRB1 can be used as a novel B-cell marker to identify CD19(-) B lymphoblasts. The emergence of CD19(-) B-ALL appears to be associated with complex cytogenetic evolutions. The mechanism of CD19(-) B-ALL relapse under anti-CD19 immune pressure remains to be explored by comprehensive molecular studies.

Unraveling resistance mechanisms in anti-CD19 chimeric antigen receptor-T therapy for B-ALL: a novel in vitro model and insights into target antigen dynamics

BACKGROUND

Cellular immunotherapy, represented by the chimeric antigen receptor T cell (CAR-T), has exhibited high response rates, durable remission, and safety in vitro and in clinical trials. Unfortunately, anti-CD19 CAR-T (CART-19) treatment alone is prone to relapse and has a particularly poor prognosis in relapsed/refractory (r/r) B-ALL patients. To date, addressing or reducing relapse remains one of the research priorities to achieve broad clinical application.

METHODS

We manufactured second generation CART-19 cells and validated their efficacy and safety in vitro and in vivo. Through co-culture of Nalm-6 cells with short-term cultured CART-19 cells, CD19-negative Nalm-6 cells were detected by flow cytometry, and further investigation of the relapsed cells and their resistance mechanisms was evaluated in vitro.

RESULTS

In this study, we demonstrated that CART-19 cells had enhanced and specific antileukemic activities, and the survival of B-ALL mouse models after CART-19 treatment was significantly prolonged. We then shortened the culture time and applied the serum-free culture to expand CAR-T cells, followed by co-culturing CART-19 cells with Nalm-6 cells. Surprisingly, we observed the proliferation of CD19-negative Nalm-6 cells around 28 days. Identification of potential resistance mechanisms showed that the relapsed cells express truncated CD19 proteins with decreased levels and, more importantly, CAR expression was detected on the relapsed cell surface, which may ultimately keep them antigen-negative. Furthermore, it was validated that CART-22 and tandem CART-22/19 cells could effectively kill the relapsed cells, but neither could completely eradicate them.

CONCLUSIONS

We successfully generated CART-19 cells and obtained a CD19-negative refractory relapsed B-ALL cell line, providing new insights into the underlying mechanisms of resistance and a new in vitro model for the treatment of r/r B-ALL patients with low antigen density.

Expanding the role of CAR T-cell therapy: From B-cell hematological malignancies to autoimmune rheumatic diseases

Chimeric antigen receptor (CAR) T-cell therapy is a form of immunotherapy where the lymphocytes, mostly T-cells, are redirected to specifically recognize and eliminate a target antigen by coupling them with CARs. The binding of CAR and target cell surface antigens leads to vigorous T cell activation and robust anti-tumor immune responses. Areas of implication of CAR T-cell therapies include mainly hematological malignancies (i.e., advanced B-cell cancers); however, recent studies have proven the unprecedented success of the new immunotherapy also in autoimmune rheumatic diseases. We aim to review the recent advances in CAR T-cell therapies in rheumatology but also to address the limitations of their use in the real clinical practice based on the data on their efficacy and safety.

The Evolving Landscape of Flowcytometric Minimal Residual Disease Monitoring in B-Cell Precursor Acute Lymphoblastic Leukemia

Detection of minimal residual disease (MRD) is a major independent prognostic marker in the clinical management of pediatric and adult B-cell precursor Acute Lymphoblastic Leukemia (BCP-ALL), and risk stratification nowadays heavily relies on MRD diagnostics. MRD can be detected using flow cytometry based on aberrant expression of markers (antigens) during malignant B-cell maturation. Recent advances highlight the significance of novel markers (e.g., CD58, CD81, CD304, CD73, CD66c, and CD123), improving MRD identification. Second and next-generation flow cytometry, such as the EuroFlow consortium's eight-color protocol, can achieve sensitivities down to 10-5 (comparable with the PCR-based method) if sufficient cells are acquired. The introduction of targeted therapies (especially those targeting CD19, such as blinatumomab or CAR-T19) introduces several challenges for flow cytometric MRD analysis, such as the occurrence of CD19-negative relapses. Therefore, innovative flow cytometry panels, including alternative B-cell markers (e.g., CD22 and CD24), have been designed. (Semi-)automated MRD assessment, employing machine learning algorithms and clustering tools, shows promise but does not yet allow robust and sensitive automated analysis of MRD. Future directions involve integrating artificial intelligence, further automation, and exploring multicolor spectral flow cytometry to standardize MRD assessment and enhance diagnostic and prognostic robustness of MRD diagnostics in BCP-ALL.

Histiocytic sarcoma following CAR T-cell therapy: a case report

BACKGROUND

Development of secondary tumor after CART treatment is not well investigated. We report a pediatric B-cell acute lymphoblastic leukemia (B-ALL) patient who developed histiocytic sarcoma shortly after CART therapy.

CASE REPORT

A 9-year-old boy diagnosed with relapsed B-ALL presenting the KRAS A146T mutation received autologous mouse-derived CD19 and CD22 chimeric antigen receptor T-cell therapy at our center (Chinese Clinical Trial Registry: ChiCTR2000032211). Thirty days post-CART therapy, the bone marrow showed complete remission. At 85 days post-CART therapy, the boy presented with fever and chills. An abdominal CT scan showed massive hepatomegaly with multiple low-density lesions in the liver. At 130 days post-CART therapy, a bone marrow smear showed abnormal proliferation of macrophages, some of which exhibited phagocytosis. On day 136 post-CART therapy, laparoscopic liver biopsy was performed, revealing multiple yellow-white lesions on the surface of the liver. Microscopically, multifocal lesions were observed, predominantly composed of cells with abundant cytoplasm. Immunohistochemical staining indicated histiocytic origin. Based on the immunohistochemical results, histiocytic sarcoma was diagnosed. The same cytogenetic markers were identified in histiocytic sarcoma.

CONCLUSION

Our case illustrates a rare complication after CART therapy. The diagnosis and treatment of histiocytic sarcoma pose many challenges.

Enhanced potency of immunotherapy against B-cell precursor acute lymphoblastic leukemia by combination of an Fc-engineered CD19 antibody and CD47 blockade

CD19-directed immunotherapy has become a cornerstone in the therapy of B-cell precursor acute lymphoblastic leukemia (BCP-ALL). CD19-directed cellular and antibody-based therapeutics have entered therapy of primary and relapsed disease and contributed to improved outcomes in relapsed disease and lower therapy toxicity. However, efficacy remains limited in many cases due to a lack of therapy response, short remission phases, or antigen escape. Here, BCP-ALL cell lines, patient-derived xenograft (PDX) samples, human macrophages, and an in vivo transplantation model in NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ (NSG) mice were used to examine the therapeutic potency of a CD19 antibody Fc-engineered for improved effector cell recruitment (CD19-DE) and antibody-dependent cellular phagocytosis (ADCP), in combination with a novel modified CD47 antibody (Hu5F9-IgG2σ). For the in vivo model, only samples refractory to CD19-DE monotherapy were chosen. Hu5F9-IgG2σ enhanced ADCP by CD19-DE in various BCP-ALL cell line models with varying CD19 surface expression and cytogenetic backgrounds, two of which contained the KMT2A-AFF1 fusion. Also, the antibody combination was efficient in inducing ADCP by human macrophages in pediatric PDX samples with and adult samples with and without KMT2A-rearrangement in vitro. In a randomized phase 2-like PDX trial using seven KMT2A-rearranged BCP-ALL samples in NSG mice, the CD19/CD47 antibody combination proved highly efficient. Our findings support that the efficacy of Fc-engineered CD19 antibodies may be substantially enhanced by a combination with CD47 blockade. This suggests that the combination may be a promising therapy option for BCP-ALL, especially in relapsed patients and/or patients refractory to CD19-directed therapy.

Optimizing CAR-T cell therapy in adults with B-cell acute lymphoblastic leukemia

Chimeric antigen receptor T-cell (CAR-T) therapy has demonstrated unprecedented success in the treatment of various hematologic malignancies including relapsed or refractory (R/R) B-cell acute lymphoblastic leukemia (B-ALL). Currently, there are two FDA-approved CD19-directed CAR-T cell products for the treatment of adults with R/R B-ALL. Despite high remission rates following CD19 CAR-T cell therapy in R/R B-ALL, remission durability remains limited in most adult patients, with relapse observed frequently in the absence of additional consolidation therapy. Furthermore, the burden of CAR-T cell toxicity remains significant in adults with R/R B-ALL and further limits the wide utilization of this effective therapy. In this review, we discuss patient and disease factors that are linked to CAR-T cell therapy outcomes in R/R B-ALL and strategies to optimize durability of response to reduce relapse and mitigate toxicity in the adult population. We additionally discuss future approaches being explored to maximize the benefit of CAR-T in adults with B-ALL.

The Biological Significance of Trogocytosis

Trogocytosis is the intercellular transfer of membrane and membrane-associated proteins between cells. Trogocytosis is an underappreciated phenomenon that has historically routinely been dismissed as an artefact. With a greater understanding of the process and the implications it has on biological systems, trogocytosis has the potential to become a paradigm changer. The presence on a cell of molecules they don't endogenously express can alter the biological activity of the cell and could also lead to the acquisition of new functions. To better appreciate this phenomenon, it is important to understand how these intercellular membrane exchanges influence the function and activity of the donor and the recipient cells. In this chapter, we will examine how the molecules acquired by trogocytosis influence the biology of a variety of systems including mammalian fertilization, treatment of hemolytic disease of the newborn, viral and parasitic infections, cancer immunotherapy, and immune modulation.

Trogocytosis of CAR molecule regulates CAR-T cell dysfunction and tumor antigen escape

Chimeric antigen receptor (CAR) T-cell therapy has demonstrated clinical response in treating both hematologic malignancies and solid tumors. Although instances of rapid tumor remissions have been observed in animal models and clinical trials, tumor relapses occur with multiple therapeutic resistance mechanisms. Furthermore, while the mechanisms underlying the long-term therapeutic resistance are well-known, short-term adaptation remains less understood. However, more views shed light on short-term adaptation and hold that it provides an opportunity window for long-term resistance. In this study, we explore a previously unreported mechanism in which tumor cells employ trogocytosis to acquire CAR molecules from CAR-T cells, a reversal of previously documented processes. This mechanism results in the depletion of CAR molecules and subsequent CAR-T cell dysfunction, also leading to short-term antigen loss and antigen masking. Such type of intercellular communication is independent of CAR downstream signaling, CAR-T cell condition, target antigen, and tumor cell type. However, it is mainly dependent on antigen density and CAR sensitivity, and is associated with tumor cell cholesterol metabolism. Partial mitigation of this trogocytosis-induced CAR molecule transfer can be achieved by adaptively administering CAR-T cells with antigen density-individualized CAR sensitivities. Together, our study reveals a dynamic process of CAR molecule transfer and refining the framework of clinical CAR-T therapy for solid tumors.

Updates on lymphoblastic leukemia/lymphoma classification and minimal/measurable residual disease analysis

Lymphoblastic leukemia/lymphoma (ALL/LBL), especially certain subtypes, continues to confer morbidity and mortality despite significant therapeutic advances. The pathologic classification of ALL/LBL, especially that of B-ALL, has recently substantially expanded with the identification of several distinct and prognostically important genetic drivers. These discoveries are reflected in both current classification systems, the World Health Organization (WHO) 5th edition and the new International Consensus Classification (ICC). In this article, novel subtypes of B-ALL are reviewed, including DUX4, MEF2D and ZNF384-rearranged B-ALL; the rare pediatric entity B-ALL with TLF3::HLF, now added to the classifications, is discussed; updates to the category of B-ALL with BCR::ABL1-like features (Ph-like B-ALL) are summarized; and emerging genetic subtypes of T-ALL are presented. The second half of the article details current approaches to minimal/measurable residual disease (MRD) detection in B-ALL and T-ALL and presents anticipated challenges to current approaches in the burgeoning era of antigen-directed immunotherapy.