Bispecific antibodies and autologous chimeric antigen receptor T cell therapies for treatment of hematological malignancies

Abstract

In recent years, the therapeutic landscape for hematological malignancies has markedly advanced, particularly since the inaugural approval of autologous chimeric antigen receptor T cell (CAR-T) therapy in 2017 for relapsed/refractory acute lymphoblastic leukemia (ALL). Autologous CAR-T therapy involves the genetic modification of a patient’s T cells to specifically identify and attack cancer cells, while bispecific antibodies (BsAbs) function by binding to both cancer cells and immune cells simultaneously, thereby triggering an immune response against the tumor. The subsequent approval of various CAR-T therapies and BsAbs have revolutionized the treatment of multiple hematological malignancies, highlighting high response rates and a subset of patients achieving prolonged disease control. This review explores the mechanisms underlying autologous CAR-T therapies and BsAbs, focusing on their clinical application in multiple myeloma, ALL, and non-Hodgkin lymphoma. We provide comprehensive insights into their individual efficacy, limitations concerning broad application, and the potential of combination therapies. These upcoming strategies aim to propel the field forward, paving the way for safer and more effective therapeutic interventions in hematological malignancies.

Graphical abstract

Suzuki and colleagues review the use of autologous chimeric antigen T cell therapy and bispecific antibodies for hematological malignancies. The review explores their mechanisms and clinical applications, offering insights into future combination therapies for enhanced efficacy and safety.

Introduction

Bispecific antibodies (BsAbs), engineered to bind two antigens, facilitate targeted cytotoxicity by acting as mediators between immune and tumor cells. Conversely, chimeric antigen receptor T cells (CAR-T cells), genetically modified T lymphocytes expressing synthetic receptors, recognize and eliminate cancer cells directly. Both BsAbs and CAR T cells activate the immune system against cancer, with BsAbs bridging immune and tumor cells, while CAR-T cells engage and eliminate tumor cells through engineered receptors.

The therapeutic landscape of CAR-T therapy and BsAbs for the treatment of various hematological malignancies has markedly advanced, particularly since the inaugural approval of CAR-T therapy in 2017 for relapsed/refractory (R/R) acute lymphoblastic leukemia (ALL).¹ Currently multiple autologous CAR-T therapies and BsAbs are approved to treat patients with hematological malignancies (Table 1).

Table 1.

FDA-approved CAR-T cell therapy and bispecific antibodies in hematological malignancies

Product	Year approved	Costimulatory domain/vector delivery	Targeted antigen	Indication
CAR-T cell therapy
Brexucabtagene autoleucel	2020	CD28/retrovirus	CD19	to treat adult patients with R/R MCLa
	2021			to treat adult patients with R/R B cell precursor ALL
Tisagenlecleucel	2017	4-IBB(CD137)/lentivirus	CD19	to treat patients up to age 25 years with B cell precursor ALL that is refractory or in second or later relapse
	2018			to treat adult patients with R/R LBCL after two or more lines of systemic therapy including DLBCL NOS, high-grade B cell lymphoma and DLBCL arising from FL
	2022			to treat adult patients with R/R FL after two or more lines of systemic therapya
Lisocabtagene maraleucel	2021	4-IBB(CD137)/lentivirus	CD19	to treat adult patients with R/R LBCL after two or more lines of systemic therapy, including DLBCL NOS (including DLBCL arising from indolent lymphoma), high-grade B cell lymphoma, PMLBCL, and FL grade 3B
	2022			to treat adult patients with LBCL who have refractory disease to first-line chemoimmunotherapy or relapse within 12 months of first line chemoimmunotherapy; or refractory disease to first-line chemoimmunotherapy or relapse after first-line chemoimmunotherapy and are not eligible for HSCT due to comorbidities or age
Axicabtagene ciloleucel	2017	CD28/retrovirus	CD19	To treat adult patients with R/R LBCL after two or more lines of systemic therapy, including DLBCL NOS, PMLBCL, high-grade B cell lymphoma, and DLBCL arising from FL
	2021			to treat adult patients with R/R FL after two or more lines of systemic therapya
	2022			to treat adult patients with LBCL that is refractory to first-line chemoimmunotherapy or relapses within 12 months of first-line chemoimmunotherapy
Idecabtagene vicleucel	2021	4-IBB(CD137)/lentivirus	BCMA	to treat adult patients with R/R MM after four or more prior lines of therapy, including a PI, an IMiD, and an anti-CD38 monoclonal antibody
Ciltacabtagene autoleucel	2022	4-IBB(CD137)/lentivirus	BCMA	to treat adult patients with R/R MM after four or more prior lines of therapy, including a PI, an IMiD, and an anti-CD38 monoclonal antibody
Bispecific antibodies
Blinatumomab	2014	N/A	CD19	to treat patients with Philadelphia chromosome-negative R/R B cell precursor ALL
	2017			to treat patients with relapsed or refractory B cell precursor ALL in adults and children including both Philadelphia chromosome-negative and -positive disease
	2018			to treat adult and pediatric patients with B cell precursor ALL in first or second complete remission with MRD greater than or equal to 0.1%
Teclistamab-cqyv	2022	N/A	BCMA	to treat adult patients with R/R MM who have received at least four prior lines of therapy, including a PI, an IMiD, and an anti-CD38 monoclonal antibodya
Mosunetuzumab axgb	2022	N/A	CD20	to treat adult patients with R/R FL after two or more lines of systemic therapya
Epcoritamab-bysp	2023	N/A	CD20	to treat R/R DLBCL not otherwise specified, including DLBCL arising from indolent lymphoma, and high-grade B cell lymphoma after two or more lines of systemic therapya
Glofitamab-gxbm	2023	N/A	CD20	to treat R/R DLBCL, NOS, or LBCL arising from FL, after two or more lines of systemic therapya
Talquetamab-tgvs	2023	N/A	GPRC5D	to treat or adults with R/R MM who have received at least four prior lines of therapy, including a PI, an IMiD, and an anti-CD38 monoclonal antibodya
Elranatamab-bcmm	2023	N/A	BCMA	to treat adults with R/R MM who have received at least four prior lines of therapy, including a PI, an IMiD, and an anti-CD38 monoclonal antibodya

BCMA, B cell maturation antigen; GPRC5D, G protein-coupled receptor class C group 5 member D; R/R, relapsed or refractory; MCL, mantle cell lymphoma; ALL, acute lymphoblastic leukemia; LBCL, large B cell lymphoma; DLBCL, diffuse large B cell lymphoma; NOS, not otherwise specified; FL, follicular lymphoma, PMLBCL, primary mediastinal large B cell lymphoma; HSCT, hematopoietic stem cell transplantation; MM, multiple myeloma; PI, proteasome inhibitor; IMiD, immunomodulatory drug; MRD, minimal residual disease; N/A, not applicable.

^aAccelerated approval (continued approval for this indication may be contingent upon verification and description of clinical benefit in a confirmatory trial).

In this review, we explore the mechanisms, shared targets, and advantages of BsAbs and autologous CAR-T therapy in multiple myeloma (MM), ALL, and non-Hodgkin lymphoma (NHL). We discuss resistance mechanisms, side effects, combination trials, future improvements, evolving approvals, treatment sequencing, dosing nuances, and the potential for global accessibility, considering the elimination of chemotherapy.

Biology of BsAbs and CAR-T cell therapy

T-Lymphocytes are key immune components in surveilling and controlling the growth of tumors and pre-malignant cells, and when their activity is hindered, tumors may develop. Immunotherapy strategies aim to enhance the patient’s own immune response against cancer cells, addressing the common challenge of tumors silencing anti-cancer immune responses.^2,3 CAR-T therapy involves the modification of T cells to express a CAR designed for a specific tumor-associated antigen. The introduction of CAR-T cells enhances the immune response against tumors. The CAR, a hybrid of several separate protein components, represents an engineered receptor for antigens that redirects the specificity and function of T lymphocytes and/or other immune cells. It comprises an extracellular domain with antigen specificity, a hinge region for flexibility, a transmembrane domain, and an intracellular domain with co-stimulatory and stimulatory elements mimicking T cell receptor (TCR) signals during activation.

The CAR extracellular domain typically contains a single-chain variable fragment from a monoclonal antibody linked through a flexible linker for antigen specificity. The hinge region, derived from CD4 or IgGs, connects to the transmembrane domain, ensuring flexibility. The intracellular domain has a co-stimulatory element such as CD28, 4-1BB, ICOS, or OX40, mimicking the TCR’s costimulatory signal, and a component of the TCR activation complex such as CD3ζ concludes the activation process.^4,5,6,7 CAR-T cells, once infused into the patient, specifically identify cancer cells, become activated and destroy their malignant targets. Notably, this recognition is not dependent on interaction with the major histocompatibility complex (MHC), providing a significant broader range of target cells, unrestricted by expression particular MHC polymorphisms (Figure 1).

Figure 1.

Mechanism of action of CAR-T and BsAbs

BsAbs serve a comparable purpose by featuring dual binding sites, allowing them to target either two epitopes on the same antigen or two distinct antigens.^8,9,10,11 In the case of BsAbs, one arm binds to the tumor-associated antigen, while the other concurrently binds CD3 on CD4+ helper T cells and CD8+ cytotoxic T cells. This dual binding initiates the formation of an immunological synapse, activating T cells without requiring T cell recognition of the MHC/antigen complex on tumor cells.⁸ The activated T cells subsequently release perforin and granzyme, inducing T cell-dependent apoptosis in tumor cells (Figure 1). Although CAR-T therapies and BsAbs have overlapping approved indications, they represent distinct treatment modalities with several differences (Table 2).

Table 2.

Differences between CAR-T cell therapy and bispecific antibodies in hematological malignancies

Variable	CAR-T	Bispecific antibodies
Duration of manufacturing	variable, usually weeks	off the shelf, readily available
Duration of treatment	single dose	variable, usually until progression or months
Need for LD chemotherapy	requires LD chemotherapy	no LD chemotherapy
Treatment setting	inpatient (usually)	variable, outpatient (usually) with some requiring inpatient step-up dosing
Route of administration	intravenous	subcutaneous or intravenous
Need for step-up dosing	no step-up dosing	step-up dosing usually required
Logistics	more complex	less complex (usually)
Risk for CRS	higher (usually)	lower (usually)
Infrastructure	requires dedicated centers (cell therapy units)	requires access to a close-by hospital with specific training to identify adverse events (no need for cell therapy unit)
Real world experience	more experience	less experience

LD, lymphodepleting chemotherapy; CRS, cytokine release syndrome.

The ease of CAR-T cell manufacturing is improving. At the time of initial approval of idecabtagene vicleucel (ide-cel) in MM, a real-world outcome for patients wait-listed for commercial CAR-T therapy showed that a quarter of the wait-listed patients died while waiting for the therapy.¹² Traditionally, CAR-T cell manufacturing takes several weeks, requiring collection, transportation, activation, viral transduction, ex vivo expansion, and 14-day release testing for sterility, etc. Technological advances may lead to fully functional CAR T cells within 24 h of culturing peripheral blood-derived T cells, eliminating the need for ex vivo expansion, and sterility testing may now be abbreviated.¹³ These are important advances, not just for patient accessibility but also because lengthy ex vivo cultivation and expansion of T cells can decrease persistence and efficacy of CAR-T cells post-transfer. Recent work indicates that CAR-T cells made within 3 days have improved proliferation and anti-leukemic effects compared with those cultured for 5 or 9 days.^14,15

Mechanisms of resistance in BsAbs and CAR-T cell therapy

Resistance to CAR-T cell therapy encompasses three main categories: CAR-T cell dysfunction, tumor-intrinsic resistance, and the immunosuppressive tumor microenvironment.¹⁶ CAR-T cell exhaustion involves a gradual loss of function, caused by persistent antigen stimulation or tonic CAR signaling, leading to reduced cytotoxicity.^17,18 In addition, immunosuppressive cells and factors within the tumor microenvironment contribute to CAR-T cell exhaustion by inhibiting T cell activity and promoting the expression of inhibitory receptors.^19,20 Tumor-intrinsic mechanisms include antigen-negative tumor cells, antigen mutations, or alternative splicing hindering CAR recognition.^21,22,23 Inhibitory ligands expressed by tumors, defects in apoptotic machinery, lineage switch, and deficiencies in engaging CAR co-accessory molecules are other intrinsic barriers to CAR-T cell efficacy.^16,24,25 Moreover, environmental barriers, such as impaired tumor vasculature, fibrotic extracellular matrix, and competition for nutrients, hinder CAR-T cell infiltration and functionality within tumors.¹⁶

Resistance to BsAb blinatumomab appears linked to reduced T cell activity, likely due to heightened immune checkpoints and changes in the CD19 target antigen. Studies indicate that non-responder patients display elevated levels of Tim-3, TIGIT, and specific ligands such as galectin-9, PD-L2, and CD155 on tumor cells. Moreover, increased regulatory T cell frequencies hinder T cell proliferation, leading to decreased anti-leukemic cytotoxicity. The upregulation of immune checkpoints such as PD-L1/PD-1 contributes to T cell exhaustion, potentially contributing to blinatumomab resistance.^26,27,28,29

The mechanisms of resistance to BsAbs targeting BCMA and GPRC5D involve several factors influencing their efficacy.³⁰ High disease burden and soluble BCMA (sBCMA) levels contribute to lower responses, creating a "sink effect" that diminishes free antibody availability.^31,32 Strategies to counteract this effect include using antibodies with higher BCMA affinity to the full-length BCMA rather than sBCMA and adjusting treatment concentrations.³⁰ Gamma-secretases, cleave the BCMA transmembrane domain and thereby increase concentration of free antigen; inhibiting these enzymes increases the concentration of BCMA molecules on MM cells, reducing the sBCMA sink effect and boosting the effectiveness of anti-BCMA BsAbs.³³ Pre-existing T cell fitness significantly affects response; non-responders often have exhausted T cells, suggesting the importance of T cell baseline status.³⁴ Antigenic escape, particularly BCMA or GPRC5D loss mutations, is a common acquired resistance mechanism.^{35,36,37,38,39} Some mutations abrogate BsAbs binding to antigens, leading to relapse.³⁶ In patients progressing on BCMA BsAbs teclistamab and elranatamab, a cluster of mutations was identified within the BCMA extracellular domain, specifically between amino acids 27 (arginine) and 34 (proline), along with the monoallelic loss of TNFRSF17 (chromosome 16p). Trial designs exploring multi-antigen targeting or sequential therapies aim to minimize clonal escape and improve treatment efficacy, offering promising strategies for overcoming resistance.⁴⁰

Approved BsAbs and autologous CAR-T cell therapies

MM

In MM, two CAR-T therapies (ide-cel and ciltacabtagene autoleucel [cilta-cel]) and three BsAbs (teclistamab-cqyv, talquetamab-tgvs, and elranatamab-bcmm) are currently approved by the US Food and Drug Administration (FDA) for use in R/R MM after four lines of therapy including an immunomodulatory drug, a proteasome inhibitor and an anti-CD38 antibody (Figure 2). It is approved by the European Medicines Agency after at least three lines of therapy including an immunomodulatory drug, a proteasome inhibitor, and an anti-CD38 antibody. Both ide-cel and cilta-cel were recently approved by FDA for earlier use in R/R MM after two and one lines of therapy, respectively. All those agents target BCMA apart from talquetamab, which targets GPRC5D. Efficacy data from the initial trials that supported the use of those agents in MM are summarized in Table 3.

Figure 2.

Approved targets in various hematological malignancies

Table 3.

Clinical data on approved T cell redirecting therapy

Product	Clinical trial(s)	Trial phase	n	Median age (years)	LOT n (range)	DOR months	Time to first response months (range)	PFS (months)	OS (months)	Follow-up (months)
Multiple myeloma
Idecabtagene vicleucel	KarMMa-1	II	128	61	6 (3–16)	10.7	1 (0.5–8.8)	8.8	19.4	13.3
	KarMMa-3	III	254	63	3 (2–4)	14.8	2.9 (0.5–13)	13.3	N/A	18.6
Ciltacabtagene autoleucel	CARTITUDE-1	Ib/II	97	61	6 (3–18)	N/A	1 (0.9–10.7)	NR 27-month PFS: 55%	NR 27-month OS: 70%	27.7
	CARTITUDE-4	III	208	62	2 (1–3)	NR 12-month DOR: 85%	2.1 (0.9–11.1)	NR 12-month PFS: 76%	NR 12-month OS: 84%	15.9
Teclistamab-cqyv	MajesTEC-1	I/II	165	64	5 (2–14)	18.4	1.2 (0.2–5.5)	11.3	18.3	14.1
Elranatamab-bcmm	MagnetisMM-3	II	123	68	5 (2–22)	NR 12-month DOR: 75%	1.2 (0.9–7.4)	NR 12-month PFS: 57%	NR 15-month OS: 57%	14.7
Talquetamab-tgvs	MonumenTAL-1	I/II	232	64–65	6 (2–20)	7.8–10.2	0.9 (0.2–3.8)–1.2 (0.3–6.8)	7.5–11.9 months	N/A	4.2–11.7
Acute lymphoblastic leukemia
Tisagenlecleucel	ELIANA	II	75	11	3 (1–8)	NR	N/A	NR 12-month PFS: 50%	12-month OS: 76%	13.1
Brexucabtagene autoleucel	ZUMA-3	II	55	40	2 (2–3)	12.8	N/A	11.6	18.2	16.4
Blinatumomab	NCT01466179	II	189	39	1	N/A	N/A	5.9	6.1	9.8
	TOWER	III	271	37	2	7.3	N/A	6-month PFS: 31%	7.7	11.7
	ALCANTARA	II	45	55	2	N/A	N/A	6.7	7.1	8.8
Non-Hodgkin lymphoma
Tisagenlecleucel	JULIET	II	93	56	2 (1–8)	NR 12-month DOR: 79%	N/A	NR 12-month PFS: 65%	12	14
	ELARA	II	97	57	4 (2–13)	NR 9-month DOR: 87%	N/A	NR 12-month PFS: 67%	NR	16.6
Axicabtagene ciloleucel	ZUMA-1	II	101	58	3 (1–10)	8.1	1 (0.8–6)	5.8	NR 18-month OS: 52%	15.4
	ZUMA-5	II	153	61	3 (2–4)	NR	1	NR 18-month PFS: 66%	NR 18-month OS: 87%	17.5
	ZUMA-7	III	180	58	1	N/A	N/A	14.7	NR 24-month OS: 61%	24.9
Brexucabtagene autoleucel	ZUMA-2	II	74	65	3 (1–5)	NR	1	NR 1 2-month PFS: 61%	NR 12-month OS: 83%	12.3
Lisocabtagene maraleucel	TRANSCEND	I	269	63	3 (2–4)	NR 12-month DOR: 55%	1	6.8	21.1	18.8
	TRANSFORM	III	92	60	1	NR 12-month DOR: 62%	N/A	14.8	NR 12-month OS: 79%	6.2
Mosunetuzumab axgb	NCT02500407	II	90	60	3 (2–4)	22.8	1.4	17.9	NR 18-month OS: 90%	18.3
Epcoritamab-bysp	EPCORE NHL-1	I/II	157	64	3 (2–11)	12	1.4	4.4	NR	10.7
Glofitamab-gxbm	NCT03075696	II	155	66	3 (2–7)	18.4	1.4	4.9	11.5	12.6

LOT, lines of therapy; DOR, duration of response; PFS, progression-free survival; OS, overall survival; NR, not reached; N/A, not available.

CAR T cell therapies

Cilta-cel demonstrated a high overall response rate (ORR) of 97% and stringent complete response (sCR) in 67% of patients after 12 months, with improved sCR rates (83%) at 28 months.^41,42 Median progression-free survival (PFS) and overall survival (OS) were not reached at 28 months, with rates of 55% and 70%, respectively.⁴² With a median follow-up of 33 months, the median duration of response (DOR) was 34 months, PFS reached 35 months, and the estimated survival at 36 months was 63%.⁴³

Ide-cel’s ORR was 73% with sCR of 26% and median PFS was 8.8 months.⁴⁴ The median DOR was found to be 11 months among responders. For patients who achieved sCR, the median DOR was higher at 19 months.⁴⁵ It is important to note that only 86% of patients enrolled to receive cilta-cel and 91% of patients enrolled to receive ide-cel received the CAR-T product. Bridging therapy between both studies differed as well as manufacturing failure (defined as receiving a product that missed release specification or due to insufficient data to confirm product release specifications), which was higher for cilta-cel when compared with ide-cel (18% vs. 2%).

Two randomized controlled trials comparing ide-cel and cilta-cel vs. standard of care regimens in earlier disease setting showed superior efficacy.^46,47 In KarMMa-3, ide-cel exhibited significantly longer median PFS (13.3 months) than the standard regimen (4.4 months) after a median follow-up of 18.6 months. The ide-cel group also demonstrated higher ORR (71% vs. 42%), with CR in 39%, compared with 5% in the standard-regimen group.⁴⁶ In more recent update, OS was not different between both groups.⁴⁸ This may challenge the assumption that the use of CAR-T as an earlier line of therapy will result in better outcomes since the improvement in PFS was not associated with OS benefit. The FDA Oncologic Drugs Advisory Committee met to review the results of OS and subsequently approved the use of ide-cel for earlier lines of R/R MM.⁴⁹

In CARTITUDE-4, the cilta-cel group had not reached the median PFS, while it was 11.8 months in the standard-care group after a median follow-up of 15.9 months. Cilta-cel also demonstrated higher ORR (85% vs. 67%), and CR or better (73% vs. 22%) compared with standard care.⁴⁷

It is important to note that in CARTITUDE-4, only 21% of enrolled patients were refractory to daratumumab compared with 95% in KarMMa-3, which necessitates careful cross-trial comparison of efficacy results. Moreover, median time from first apheresis to infusion was longer in the cilta-cel arm (79 [range: 34–117] vs. 49 [range: 45–246] days).

In real-world use, the use of ide-cel showed comparable efficacy with a KarMMa-1 trial with PFS of 8.5 months and median OS of 12.5 months.^50,51 For cilta-cel, efficacy results from real-world use seem to be lower with 12-month PFS and OS of 67% and 79%, respectively.⁵²

BsAbs

Both teclistamab and elranatamab target BCMA and are administered once a week. Two-thirds of patients achieved a response, and their overall efficacy is generally comparable.^53,54 Elranatamab enrolled older patients with a median age of 68 vs. 64 when compared with teclistamab and was associated with higher PFS (NR vs. 11.3 months) with 15-month PFS of elranatamab of 51%. In real-world use of teclistamab, earlier reports showed high ORR and activity in difficult-to-treat patients who will not be candidates for clinical trial enrollment.^55,56

Talquetamab is a first-in-class BsAb that targets GPRC5D, allowing for dosing every other week. Two-thirds of patients achieved a response, and the median DOR ranged from 7.8 to 10.2 months based on the studied dose.⁵⁷ It is crucial to highlight that all patients in this initial trial had not received prior therapy with BCMA-based therapy.

Acute lymphoblastic leukemia

In ALL, two CAR-T therapies (tisagenlecleucel and brexucabtagene autoleucel [brexu-cel]) and one bsAb (blinatumomab) are currently approved to use for various indications (Table 1). Efficacy data from the initial trials that supported the use of those agents in ALL is summarized in Table 3.

CAR-T cell therapies

In the ELIANA trial, tisagenlecleucel demonstrated a 12-month PFS of 50% and a 12-month OS of 76%, with a median follow-up of 13 months.⁵⁸ In the ZUMA-3 trial, brexu-cel showed a 12-month PFS of 13% and a 12-month OS of 16%, with a median follow-up of 18 months.⁵⁹ In the updated analysis of the ELIANA trial, the overall remission rate was 82%, and 59% of responders remained relapse-free at 12 months. With a median follow-up of 39 months, the median event-free survival (EFS) was 24 months, and OS was not reached. At 3 years, the estimated RFS was 52%. Patients also reported sustained improvements in quality of life up to 36 months after infusion.⁶⁰ The 3-year follow-up of ZUMA-3 demonstrated an overall CR/CRh rate of 71% and a median OS of 26 months in all treated patients. Subgroup analyses showed benefit in patients regardless of age, number of prior therapies, prior exposure to blinatumomab, or subsequent allogeneic hematopoietic stem cell transplantation (HSCT) status.⁶¹ A meta-analysis included 38 reports with 2,134 patients treated with CAR-T therapy for R/R ALL. Results indicate a median OS of 36 months, EFS of 13 months, and an ORR of 76%.⁶²

BsAbs

Blinatumomab, initially studied in adults with Philadelphia-chromosome-negative R/R ALL, demonstrated a primary objective of achieving CR or CR with partial hematological recovery (CRh) within the first two cycles in 43% of patients.⁶³ The median OS duration was 6.1 months, with 12% experiencing fatal adverse events, mainly infection.

Blinatumomab approval was extended to include R/R ALL regardless of Philadelphia chromosome status. Approval was based on TOWER and ALCANTARA trials. TOWER, a phase III clinical trial comparing blinatumomab to standard chemotherapy, showed improved OS (median 7.7 vs. 4 months) and higher CR rates (34% vs. 16%).⁶⁴ ALCANTARA, a single-arm trial in Philadelphia-positive R/R ALL, demonstrated a 31% CR rate.⁶⁵ These results led to FDA approval expansion for both Ph-positive and Ph-negative R/R ALL.⁶⁶

BLAST was a study of adults with minimal residual disease (MRD)-positive ALL in hematologic remission, in which blinatumomab treatment resulted in a complete MRD response in 78% of patients.⁶⁷ Achieving a complete MRD response was significantly associated with improved OS. In the landmark assessments, individuals achieving a complete MRD response demonstrated extended relapse-free survival (RFS) (24 vs. 6 months) and OS (39 vs. 13 months) compared with those who did not respond to MRD.

In real-world use, blinatumomab showed a response rate of 65%, with a median RFS of 32 months and OS of 13 months.⁶⁸ Outcomes were better for patients who achieved MRD-negative response.⁶⁹

NHL

Several CAR-T cell therapies have received approvals for the treatment of NHL (Table 1). Efficacy data from the initial trials that supported the use of those agents in NHL is summarized in Table 3.

CAR-T cell therapies

Tisagenlecleucel, evaluated in the JULIET trial in patients with large B cell lymphoma (LBCL), demonstrated an ORR of 56%, with a 2-year DOR reaching 79%.⁷⁰ An updated 40- month follow-up showed ORR of 53%, with 39% of patients achieving a CR.⁷¹ The OS was 11 months. Patients who achieved a CR at 3 or 6 months, or as their best overall response, did not reach the median OS. In addition, the ELARA trial, which enrolled patients with follicular lymphoma (FL), reported a 57% ORR and a notable 9-month DOR of 87%.⁷² The extended follow-up of 29 months, showed that median PFS, DOR, and OS were not reached. Estimated 24-month rates for PFS, DOR, and OS were 57%, 66%, and 88%, respectively.⁷³

Axicabtagene ciloleucel (axi-cel) use resulted in an 82% ORR and a 54% CR rate. After a median follow-up of 15.4 months, 42% of patients maintained a response, with a 40% continued CR rate. The OS rate at 18 months was 52%.⁷⁴ In ZUMA-7, a phase III trial studying axi-cel as second-line therapy for LBCL, axi-cel showed a median EFS of 8 months compared with 2 months in the standard-care group, with 24-month EFS rates of 41% and 16%, respectively. Axi-cel treatment resulted in a response rate of 83%, including a CR in 65%, compared with 50% response and 32% CR in the standard-care group.⁷⁵ The interim analysis estimated a 2-year OS of 61% with axi-cel and 52% with standard care. In the 5-year follow-up of the ZUMA-1 trial, the median OS was 26 months, and the estimated 5-year OS rate was 43%.⁷⁶

In an updated ZUMA-7 analysis, median OS was not reached in the axi-cel group, while it was 31 months in the standard-care group, with estimated 4-year OS rates of 55% and 46%, respectively.⁷⁷

Brexu-cel, assessed in the ZUMA-2 trial for patients with mantle cell lymphoma, achieved a 65% ORR. The 12-month PFS was reported at 61% and the therapy exhibited an 83% OS rate.⁷⁸ The 3-year follow-up showed ORR of 91%, with 68% achieving CRs. Median DOR, PFS, and OS were 28, 26, and 47 months, respectively.⁷⁹

Lisocabtagene maraleucel (liso-cel), investigated in the TRANSCEND trial in patients with LBCL, demonstrated a 63% ORR, accompanied by a 12-month DOR of 55%.⁸⁰ At 2-year follow-up update, the median DOR was 23 months, median PFS was 7 months, and median OS was 27 months.⁸¹ The TRANSFORM trial, which showed superiority to HSCT in patients with LBCL who experience primary refractoriness or relapse within 12 months, reported a 60% ORR, with a 12-month DOR of 62% and a promising 79% OS rate in initial interim analysis.⁸² The primary analysis with an 18-month median follow-up showed that liso-cel significantly improved EFS, CR rate, and PFS compared with HSCT.⁸³

Earlier use of CAR-T therapies in NHL are ongoing (NCT05605899 and NCT05371093).

BsAbs

Three BsAbs are currently approved for use in R/R NHL (Table 3). Mosunetuzumab, glofitamab, epcoritamab, and odronextamab were evaluated in patients with R/R B cell NHL. In the study of mosunetuzumab, patients with aggressive B cell NHL (aNHL) showed a 35% ORR and 19% CR, while those with indolent NHL had a 66% ORR and 48% CR.⁸⁴ Glofitamab demonstrated dose-dependent clinical activity, with a 61% ORR in patients with aNHL and a 70% ORR in those with grade I–IIIA FL.⁸⁵ Epcoritamab showed a 68% ORR and 45% CR in aggressive NHL patients.⁸⁶

Odronextamab exhibited clinical activity in diffuse large B cell lymphoma (DLBCL) and FL, with a 33% ORR and 24% CR in DLBCL and a 78% ORR and 63% CR in FL.⁸⁷ Preliminary data for IgM-2323 and plamotamab also showed objective responses.^88,89

Single-agent BsAbs are being investigated in previously untreated B cell NHL patients, with mosunetuzumab producing a 68% ORR and 42% CR in newly diagnosed DLBCL patients unfit for immunochemotherapy. Studies in patients with newly diagnosed indolent NHL are ongoing.^90,91,92

Adverse events with the use of BsAbs and CAR-T cell therapy

Cytokine release syndrome

Cytokine release syndrome (CRS) is a significant AE of CAR-T therapies and BsAbs, presenting with symptoms such as fever, fatigue, and multiorgan dysfunction. Incidence ranges from 50% to 100%, with severe cases in 13%–48% of patients.^93,94,95 Various strategies, including reduced CAR-T cell doses, aim to mitigate CRS risk, but success is partial.⁹⁶ CRS manifestations result from cytokine release by engaged CAR-T cells and from interactions with other innate and adaptive immune system components. Interleukin-6 (IL-6) is often the dominant cytokine and severity may correlate with cytokine levels and exposure duration.⁹⁷ Different grading systems exist, and advanced supportive care is required for severe or life-threatening CRS.⁹⁴

Tocilizumab, an antibody that blocks the IL-6 receptor, received FDA approval in 2017 for treating severe or life-threatening CRS induced by CAR-T therapy in adults and pediatric patients aged 2 years and older, based on a retrospective analysis of CRS data from patients in clinical trials with tisagenlecleucel and axi-cel.⁹⁸ Considerations for the optimal management of CRS may include prevention, early detection, and addressing refractory CRS with steroids and additional cytokine antagonists.⁹⁹

Clinical trials integrating use of prophylactic tocilizumab may help in reducing the risk of CRS without impacting CAR-T efficacy and/or other AEs.^100,101,102 Such use may be especially practical for BsAbs since this may allow safer use in the community.¹⁰³

Immune effector cell-associated neurotoxicity syndrome

Immune effector cell-associated neurotoxicity syndrome (ICANS) is described as a condition marked by a pathological process affecting the central nervous system after undergoing any immune therapy that activates or involves endogenous or infused T cells and other immune effector cells.¹⁰⁴ The mechanisms underlying ICANS are still not fully understood. Progressive symptoms or signs may encompass aphasia, changes in consciousness, cognitive skill impairment, motor weakness, seizures, and cerebral edema. It is emphasized that ICANS should be considered in the context of any immune effector cell-engaging therapy, extending beyond CAR T cells and including BsAbs.

In the early stages, clinical trials used CTCAE v.4.03 to grade neurotoxicity, but refinement occurred with the CARTOX criteria and the development of the CARTOX-10 screening tool.¹⁰⁵ The American Society for Transplantation and Cellular Therapy consensus grading scheme adapts the CARTOX-10 into the Immune Effector Cell-Associated Encephalopathy (ICE) score for objective grading of overlapping encephalopathy terms in approved CAR-T products.¹⁰⁴ The ICE score, aligned with CTCAE v.5.0, designates any new seizure as grade 3 and any life-threatening seizure as grade 4, simplifying classification for improved clarity.

Hematological toxicities

Cytopenias post-CAR-T therapy can be prolonged well beyond the initial phase provoked by the cytoreductive chemotherapy given prior to CAR-T infusion to enhance engraftment. These prolonged cytopenias significantly increase morbidity and mortality. Persistent thrombocytopenia increases bleeding risks, especially within 30 days, requiring transfusion support and impacting quality of life, while infection risks from neutropenia may be further increased due to prolonged hypogammaglobulinemia after CD19- and BCMA-targeting CAR-T treatments (see infections below). A recent consensus on the grading and management of immune effector cell-associated hematotoxicity (ICAHT) introduced a classification system for grading ICAHT.¹⁰⁶ Prolonged cytopenias was associated with higher-grade (grade III/IV) CRS or ICANS.¹⁰⁷

Bone marrow biopsy is an essential diagnostic tool during prolonged cytopenias to evaluate primary/secondary diseases. Despite limited evidence for benefit, interventions include growth factors, thrombopoietin-receptor agonists, stem cell boosts, transfusions, and infection risk mitigation.¹⁰⁸ Stem cell boosts were needed in up to 25% of BCMA CAR-T patients, potentially influencing future upfront use.¹⁰⁹

Infections

Infection can occur after CAR-T therapies and BsAbs. Table 4 provides a summary of incidence and severity of infections from initial clinical trials supporting FDA approvals.

Table 4.

Key safety outcomes on approved T cell redirecting therapy

Product	Clinical trial	Infections (all grades) (%)	Infections (grade ≥ 3) (%)	CRS (all grades) (%)	CRS (grad e ≥3) (%)	ICANS (all grades) (%)	ICANS (grade ≥3 ) (%)	Neurotoxicity (all grades) (%)	Neurotoxicity (grade ≥ 3) (%)	Neutropenia (grade ≥ 3) (%)	Thrombocytopenia (grade ≥ 3) (%)	Anemia (grade ≥ 3) (%)	Tocilizumab use (%)
Multiple myeloma
Idecabtagene vicleucel	KarMMa-1	69	22	84	5	N/A	N/A	18	3	89	52	60	52
	KarMMa-3	58	24	88	5	N/A	N/A	15	3	76	42	51	72
Ciltacabtagene autoleucel	CARTITUDE-1	58	20	95	4	17	2	21	9	95	60	68	69
	CARTITUDE-4	62	27	76	1	5	0	21	3	90	41	36	40
Teclistamab-cqyv	MajesTEC-1	76	45	72	1	3	0	15	1	64	21	37	36
Elranatamab-bcmm	MagnetisMM-3	70	40	58	0	3	0	17	1	49	24	37	23
Talquetamab-tgvs	MonumenTAL-1	34-47	7	77–80	3–5	N/A	N/A	6–8	0–3	26–60	11–23	23–33	54–65
Acute lymphoblastic leukemia
Tisagenlecleucel	ELIANA	43	24	77	46	N/A	N/A	40	13	9	9	N/A	48
Brexucabtagene autoleucel	ZUMA-3	N/A	25	89	24	N/A	N/A	60	25	27	30	49	80
Blinatumomab	NCT01466179	N/A	N/A Grade V: 9	NA/	2	N/A	N/A	52	13	16	8	14	N/A
	TOWER	N/A	34	14	5	N/A	N/A	N/A	9	38	N/A	N/A	N/A
	ALCANTARA	N/A	N/A	7	0	N/A	N/A	47	7	7	27	18	N/A
Non-Hodgkin lymphoma
Tisagenlecleucel	JULIET	34	20	58	22	N/A	N/A	21	12	33	28	39	14
	ELARA	19	5	49	0	4	1	37	3	32	9	13	34
Axicabtagene ciloleucel	ZUMA-1	26	16	93	13	N/A	N/A	64	28	78	38	43	43
	ZUMA-5	53	18	82	7	N/A	N/A	59	19	33	15	25	50
	ZUMA-7	41	14	92	6	N/A	N/A	60	21	69	15	30	65
Brexucabtagene autoleucel	ZUMA-2	56	32	91	15	N/A	N/A	63	31	85	51	50	59
Lisocabtagene maraleucel	TRANSCEND	N/A	12	42	2	N/A	N/A	30	10	60	27	37	20
	TRANSFORM	N/A	15	49	1	N/A	N/A	7	4	80	49	49	23
Mosunetuzumab axgb	NCT02500407	20	14	44	2	3	0	3	0	26	4	N/A	18
Epcoritamab-bysp	EPCORE NHL-1	45	15	50	3	6	1	N/A	N/A	15	6	10	N/A
Glofitamab-gxbm	NCT03075696	38	15	63	4	8	3	7	3	27	7	7	32

LOT, lines of therapy; DOR, duration of response; PFS, progression-free survival; OS, overall survival; NR, not reached; N/A, not available.

Patients with MM are at generally higher risk of infection.¹¹⁰ Infections may be particularly high in MM patients who receive BCMA targeting therapies, especially BsAbs. Pooled analysis of BsAbs in MM showed that BCMA-targeting BsAbs are associated with higher incidence of infection when compared with GPRC5D BsAbs.¹¹¹ The higher risk of infection associated with BCMA BsAbs was also shown in real-world use.¹¹² The use of CAR-T targeting BCMA was also associated with infections, some of which occurred after 100 days of CAR-T infusion.¹¹³

The risk of infections after CD-19 CAR-T therapy is well described. In prospective registration clinical trials, the frequency of infections in patients receiving CD19 CAR T cells ranges from approximately one-fifth to over half. Similarly, retrospective cohort analyses show infection incidence in this patient group spanning from around one-fifth to two-thirds.¹¹⁴

It is important to consider mitigation strategies including the use of prophylactic antimicrobials and intravenous immunoglobulin to decrease the risk of infections, especially with the use of BsAbs.^{115,116,117,118,119}

Long-term safety concerns

The US FDA has reported cases of T cell malignancies, including CAR-positive lymphoma, in patients receiving BCMA- or CD19-directed CAR-T cell therapies, underscoring the importance of long-term monitoring.¹²⁰ While the FDA acknowledges potential risks, it emphasizes the overall benefits and, despite 20 reported cases, specialized cell therapy centers are encouraged to continue offering CAR-T products, guided by the latest safety information. CAR-T therapy administrators should actively participate in FDA-recommended long-term follow-up, promptly reporting subsequent malignancies and emphasizing lifelong monitoring for new cases based on ongoing research.¹²¹

Cilta-cel use in CARTITUDE-1 resulted in 10% of patients developing secondary myeloid malignancies, a notably higher risk compared with ide-cel and other CD19-targeting CAR-T therapies. While awaiting more granularity of safety data, the risk of secondary myeloid malignancies associated with the use of cilta-cel may result in more use of ide-cel by some centers. This elevated risk warrants further investigation, especially considering the long-term follow-up of MM patients treated with multi-agent chemotherapy and tandem HSCT showing lower risk.¹²²

BCMA.CAR-T cell treatment for MM may be associated with a rare hypokinetic movement disorder resembling Parkinsonism, as observed in patients from the CARTITUDE-1 study for cilta-cel.¹²³ Reports also highlight a similar movement disorder with ide-cel, and concerns about a potential causal link between circulating CAR-T cells and parkinsonian symptoms. Even though some cases showed full reversibility in other patient symptoms, such as limb rigidity and tremor, they were not fully reversible, raising uncertainties about permanence of the disability.^124,125 Late onset of Parkinsonism warrants caution, and further investigations are needed for monitoring unusual toxicities, emphasizing timely expert clinical assessment.

Emerging CAR-T- and BsAb-based therapies

Ongoing trials explore additional agents in combination with BsAbs and maintenance therapy post-CAR-T, emphasizing the need to balance expected efficacy gains with potential increased toxicity risks. Most combination trials are being done with blinatumomab given that it was the first bsAb to be approved.¹²⁶ Insufficient T cell activation, often due to barriers such as T cell exhaustion or the immunosuppressive tumor microenvironment, can lead to therapy escape. Addition of agents such as checkpoint inhibitors presents a logical approach, and early trials studying such combinations have promising efficacy.^127,128

Combination of blinatumomab with chemotherapy and inotuzomab-ozogamicin (a CD22-specific antibody-drug conjugate) has demonstrated median OS of 13.4 months and a 3-year OS rate of 33% in patients with R/R ALL.¹²⁹ Blinatumomab consolidation after use of chemotherapy and inotuzomab-ozogamicin was also shown to result in better OS.¹³⁰

In the ECOG-ACRIN E1910 trial, 488 patients underwent standard induction chemotherapy for Philadelphia-negative ALL. Those achieving a CR/CRh were then assigned to consolidation chemotherapy alone or with blinatumomab. In MRD-negative patients, the addition of blinatumomab significantly improved OS, with a median not reached vs. 71 months with chemotherapy alone.¹³¹

The combination of dasatinib and blinatumomab for Philadelphia-positive ALL was investigated in 63 patients (median age: 54), with 98% achieved CR. After dasatinib induction therapy, 29% had a molecular response at day 85, increasing to 60% after two cycles of blinatumomab. At 18 months follow-up, OS was 95%, and disease-free survival was 88%. ABL1 mutations detected during induction therapy were cleared by blinatumomab.¹³² The use of other tyrosine kinase inhibitors in combination with blinatumomab as chemotherapy-sparing regimens is being explored by various clinical trials with early promising results.^126,133

One area of major interest is high-risk disease in which responses to both BsAbs and CAR-T are fewer and shorter. For example, in MM, the combination of both teclistamab and talquetamab is being explored in the REDIRECT-1 trial with early results in R/R MM showing excellent responses in difficult-to-treat patients with extramedullary disease.⁴⁰

BsAbs and CAR-T therapies are being explored in earlier disease settings. The ZUMA-12 study evaluated axi-cel as a first-line treatment for high-risk LBCL, demonstrating a 78% CR rate and 89% objective response rate in efficacy-evaluable patients. Axi-cel exhibited prolonged DOR, EFS, and PFS.¹³⁴ With a median follow-up exceeding 40 months, axi-cel continued to exhibit an excellent rate of sustained responses without any additional safety concerns.¹³⁵ A study comparing high-dose chemotherapy with HSCT to CAR-T therapy for newly diagnosed MM is planned (NCT05257083). In the TRIMM-2 study, the combination of talquetamab and daratumumab showed a high ORR of 78% but was associated with side effects such as dysgeusia (75%), skin exfoliation (45%), and grade III/IV infections (22%). The median PFS was 19.4 months, and the 12-month PFS and OS rates were 76% and 93%, respectively.¹³⁶

Combination therapies using BsAbs are also being explored in NHL in relapsed as well as newly diagnosed patients.⁹² Glofitamab and epcoritamab were integrated into standard-of-care platinum-based chemoimmunotherapy platforms for R/R aNHL with promising clinical results.^137,138 Both mosunetuzumab and glofitamab were combined with polatuzumab vedotin in R/R DLBCL, showing high response rates.^139,140 Studies also explored combining BsAb with immunomodulatory agents, with mosunetuzumab and epcoritamab combined with lenalidomide showing remarkable preliminary activity in R/R FL.^141,142,143

In newly diagnosed DLBCL, phase 1/2 studies combining mosunetuzumab or glofitamab with standard chemotherapy produced encouraging efficacy signals.¹⁴⁴ The addition of BsAb to chemotherapy in trials did not interfere significantly with chemotherapy delivery, and the toxicity profile largely mirrored that of its components, with no significant impact on the rate or severity of CRS.⁹²

Sequencing

The sequencing of CAR-T therapies and BsAbs presents an area of uncertainty. Given CAR-T therapies' precedence in approval for MM and NHL, current evidence suggests initiating treatment with CAR-T therapy followed by BsAbs upon targeting the same antigen during relapse. In ALL, CAR-T therapy post-blinatumomab failure is supported by clinical trial data. In ZUMA-3, where 45% received prior blinatumomab, this subset exhibited a 60% CR rate.⁶⁶ Conversely, BCMA.CAR-T post-BCMA BsAb failure in MM showed a low response rate in CARTITUDE-2. The anti-BCMA BsAb-exposed group had a shorter DOR (8.2 months) and PFS (5.3 months), with only 57% achieving a response.¹⁴⁵ The limited number of patients and the varied nature of prior anti-BCMA therapies preclude definitive conclusions. Within cohort C of the MajesTEC-1 study, 38 patients, previously exposed to anti-BCMA treatments, including CAR-T therapy, received teclistamab, demonstrating a 40% ORR.¹⁴⁶ Notably, responses were rapid, deepening over time, and the median DOR was not reached.

In NHL, data support efficacy of BsAbs after failure of CAR-T therapy with recent retrospective data, suggesting that prior exposure to BsAb treatment targeting different antigens does not have a negative impact on survival outcomes after CAR T cell therapy.^147,148 Prospective trials directly comparing these strategies, such as NCT04889716, will play a vital role in treatment decision-making, especially with risk stratification to identify optimal sequencing paradigms for CAR-T and BsAbs therapies.

Future directions

The earlier use of CAR-T therapy faces constraints related to manufacturing and accessibility, including institutional limitations and high costs. Institution-based point of care produced autologous CD19-directed CAR T cell therapy showed promising results with a production efficiency of 99% and a short vein-to-vein turnover time (10 days), avoiding bridging therapy in most patients, and may result in better accessibility and lower costs.^149,150,151

TRUKS (T cells redirected for antigen-unrestricted cytokine-initiated killing) in CAR-T cell therapy involves engineering T cells with a transgenic cytokine to modulate the immune environment within the tumor. Known as “4th generation” CAR-T cells, TRUKS enhance local cytokine production, addressing limitations of conventional CAR-T cells and inducing a comprehensive antitumor response in preclinical studies.^152,153

Multispecific antibodies, especially trispecifics, show promise in advancing cancer therapy by targeting two tumor-associated antigens simultaneously.^154,155 Trispecific antibodies, engaging CD3 and co-stimulatory/co-inhibitory molecules, aim to enhance cancer cell selectivity, reduce immune escape, and reverse T cell exhaustion. Exploring fixed-duration treatment and less frequent dosing in future clinical trials will be crucial to determine optimal therapy duration with BsAbs.

The global adoption of CAR-T therapies may face obstacles due to their high cost and limited availability, although the possibility of developing allogeneic CAR platforms of equivalent or superior safety and efficacy may help overcome these obstacles.¹⁵⁶ Meanwhile, combining BsAbs and CAR-T with small-molecule targeted therapies are already showing the potential for lower toxicity and higher efficacy regimens for treating hematological malignancies.¹³²

Conclusions

CAR-T cells and BsAbs have transformed hematological malignancy treatments, offering high response rates and prolonged disease control. This marks a shift toward potentially safer and more effective interventions in hematological malignancies.