Journal of Cancer Immunology
ISSN: 2689-968X

Review Article - Journal of Cancer Immunology (2020) Volume 2, Issue 4

Immunotherapy in Pediatric Acute Lymphoblastic Leukemia

Julie M. Asare1,2, Cara A. Rabik1,2, Stacy Cooper1,2, Patrick A. Brown1,2*

1The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Department of Oncology, Johns Hopkins University School of Medicine, Baltimore, MD, USA

2Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, MD, USA

*Corresponding Author:
Patrick Brown
E-mail:pbrown2@jhmi.edu

Received date: September 13, 2020; Accepted date: October 02, 2020

Citation: Asare JM, Rabik CA, Cooper S, Brown PA. Immunotherapy in Pediatric Acute Lymphoblastic Leukemia. J Cancer Immunol. 2020; 2(4): 159-184.

Copyright: © 2020 Asare JM, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


Abstract

Leukemia is the most common childhood malignancy and cause of pediatric cancer death. Significant advances in the cure rates of B-cell acute lymphoblastic leukemia (B-ALL) and T-cell acute lymphoblastic leukemia (T-ALL) have been achieved; however, patients with refractory or relapsed B-ALL or T-ALL continue to have poor outcomes. Immunotherapy is a revolutionary treatment aimed to improve survival and reduce the toxicity of chemotherapy by harnessing the patient’s own immune system to target cancer cells. Several immunotherapies have been developed including monoclonal antibodies, antibody drug conjugates, Bispecific T-cell engagers (BiTEs), and chimeric antigen receptor T-cell (CAR-T) therapy. Immunotherapy has been shown to have efficacy in relapsed acute leukemia; however, antigen escape relapse remains a challenge and the duration of effect is unknown. Nevertheless, immunotherapy holds the potential to significantly improve outcomes in relapsed pediatric acute B-ALL and T-ALL and is actively being studied in upfront therapy.


Keywords

B-ALL, T-ALL, Immunotherapy, Monoclonal Antibodies, Antibody-drug Conjugates Bispecific T-Cell Engager (BiTE), Chimeric Antigen Receptor (CAR) T-Cells


Abbreviations

ASMT: American Society for Transplantation and Cellular Therapy; B-ALL: B-cell Acute Lymphoblastic Leukemia; BiTE: Bispecific T-cell Engagers; CAR-T: Chimeric Antigen Receptor T-cell; COG: Children’s Oncology Group; CR: Complete Remission; CRh: Complete Remission with partial hematologic recovery; CRS: Cytokine Release Syndrome; FDA: U.S. Food and Drug Administration; HSCT: Hematopoietic Stem Cell Transplant; InO: Inotuzumab Ozogamicin; NK: Natural Killer; MRD: Minimal Residual Disease; OS: Overall Survival; OR: Odds Ratio; PFS: Progression-free Survival; scFv: Single-chain variable fragment; SOC: Standard of Care; SOS: Sinusoidal Obstructive Syndrome; T-All: T-cell acute lymphoblastic leukemia; TCR: T-cell Receptor; VHR: Very High-risk


Introduction

Leukemia is the most common childhood malignancy and is the most common cause of cancer death before the age of 20 [1]. Pediatric leukemia can be subdivided into acute versus chronic and lymphoid versus myeloid leukemia. Acute lymphoid leukemia (ALL) can be further divided into B-cell precursor ALL (B-ALL) and T-cell ALL (T-ALL). The focus of this paper will be pediatric B-ALL and T-ALL.

B-ALL

Approximately 85% of ALL cases are B-ALL [2]. Cure rates for B-ALL significantly rose over the past five decades from 10% to 90% [1-3] due to multi-agent chemotherapy regiments, CNS prophylaxis and better risk stratification [3]. Despite these successes, about 2% of patients are refractory to chemotherapy and another 10% to 15% of patients will relapse [4]. Treatment for these patients remains a therapeutic challenge. Event free survival for patients with relapsed or refractory ranges from 13% to 40% [4-7]. Attempts to intensify chemotherapy in high risk patients resulted in excessive toxicity [8,9].

T-ALL

T-ALL accounts for approximately 15% of pediatric ALL cases [1,10]; and historically these patients have inferior outcomes to patients with B-ALL with event-free and overall survival around 70% and 80% respectively [11-13]. Survival has improved with intensification of therapy and T-cell focused regimens, such as the addition of nelarabine to treatment paradigms [14]. However, survival after relapse is about 30% due to a lack of effective salvage therapies [15].

Immunotherapy

Immunotherapy is a revolutionary treatment aimed to improve survival and reduce the toxicity of chemotherapy by harnessing the patient’s own immune system to target cancer cells. Several different approaches have been developed. Antibody therapy utilizes antigens present on the surface of leukemia cell to aid in the immune system’s attack of the cancer cell. Therapies include monoclonal antibodies, antibody drug conjugates and Bispecific T-cell engagers (BiTES). Adaptive therapies manipulate patient’s cytolytic immune cells to recognize tumor cells and elicit an anti-tumor response. These therapies include chimeric antigen receptor T-cell (CAR-T) therapy. This review will focus on immunotherapeutic options approved and under investigation for pediatric ALL. Common targets are highlighted in Tables 1 and 2.

TargetDrug
CD10CD10 CAR-T
CD19Antibody-drug conjugates
•SAR3419
•SGN-CD19A
•SGN-CD19B
BiTE•Blinatumomab
CAR-T
•CD19 CAR-T
•CARCIK-CD19
CD20Antibody
•Rituximab
•Ofatumumab
BiTE: Preclinical
CAR-T
•CD20 CAR-T
•CD20/CD19 CAR-T
CD22Antibody
•Epratuzumab
•Moxetumomab pasudotox
Antibody-drug conjugates
•Inotuzumab Ozogamicin
CAR-T
•CD22 CAR-T
•CD19/CD22 CAR-T

Table 1: B-ALL Targets.

TargetDrug
CD1aCAR-T (Preclinical)
CD3CD3 NK CART-T (Preclinical)
CD4CD4 CAR-T
CD5CAR-T
CD7CAR-T
UCART7 (Preclinical)
TruUcar GC027 (Preclinical)
CD38Daratumab Isatuximab Mogalizumab
CD52Alemtuzumab
CD194Mogamulizumab CD194/30 CAR-T
Interleukin-2receptor alphaBasiliximab (Preclinical)
Interleukin-7 receptor alphaPreclinical
TALLA-1Preclinical
Hedgehog interacting proteinsPreclinical
Human telomerase reverse transcriptasePreclinical

Table 2: T-ALL targets.


Monoclonal Antibodies/Antibody-drug Conjugates

Antibody therapy is engineered to attack specific antigens on tumor cells. Monoclonal antibodies stimulate antibody-dependent cytotoxicity; whereas, drug-antibody conjugates deliver a cytotoxic drug to the tumor cell when it binds and is phagocytosed by the target cell. In pediatric leukemia, both monoclonal antibody and antibody-drug conjugates have shown promise.

Inotuzumab ozogamicin (InO)

Mechanism of action: CD22 is expressed on 80% to 90% of B-ALL cells. Inotuzumab ozogamicin (InO) is a humanized anti-CD22 monoclonal antibody conjugated to the cytotoxic drug, calicheamicin [16]. Calichaemicin is cleaved and binds to minor DNA grooves causing doublestranded DNA breaks and apoptosis of the leukemia cell [16]. Clinical trials of InO in B-ALL are highlighted in Table 3.

 

Adult and pediatric CD22+ R/R B-ALL Phase II Single centerN=491.8mg/m2/cycle every 3-4 weeksCR/CRh: 28
(57%)
MRD negative: 19 (39%)
Median OS: 5.1 mo (95%CI; 3.8–6.4)
N=22[79] NCT01134575
Adult R/R CD22+, Ph+/- B-ALL Phase III

Randomized (SOC
chemotherapy vs. Inotuzumab ozogamicin)
N=326
Ino n=164
SOC n=162
1.8mg/m2/cycle Days 1, 8, 21CR/CRh: (73.8% vs.
35%), p<0.001 |

MRD negative: 78.4% (95%
CI; 68.4-86.5]
vs. 28.1% (95%
CI; 13.7-46.7), p<0.001

DOR: 4.6 mo
(95% CI; 3.9-
5.4) vs. 3.1 mo
(95% CI; 1.4-
4.9, p = 0.03

Median PFS: 5.0 mo (95%
CI; 3.9-5.8) vs.
1.7 mo (95%
CI; 0.34-
0.60); HR,
0.45 (97.5%
CI; 0.34-0.61), p<0.001)

Median OS:
7.7 mo vs. 6.2 mo (95%CI, 4.7-8.3)

2-year OS: 22.8% vs.
10.0% (HR
0.75; 97.5CI,
0.57-0.99), p=0.0105
Patients who proceed to transplant and developed SOS
InO-18/79 (22.8%)
SOC-3/35 (8.6%)
[17] NCT01564784
INO-VATE
Pediatric R/R CD22+ B-ALL Phase IIN=51.3mg/m2 every 3 weeks (n=3)

Increased to 1.8mg/m2 every 3 weeks (n=1 of the 3)

Then weekly 0.8mg/m2 on Day 1 followed by 0.5mg/m2 on Days 8 & 15
CR: 1 (20%)

CRh: 2 (40%)

No response: 2
(40%)

[18]
Pediatric R/R. CD22+ 
ALL compas- sionate use 
Retrospective analysisN=51 3 not evaluable for responseCycle one: three doses: 0.8mg/ m2 on week
1 followed by 0.5mg/m2 on weeks 2 and 3

One patient with MRD-only disease received 0.5mg/ m2/dose
for all three doses.

In second and subsequent cycles, assuming CR/CRh during cycle 1, patients received 0.5mg/m2/dose on days 1, 8, and
15.
CR/CRh: 67%

CR: 15 (39%)

CRh: 13 (25%)

MRD negative: 20 (71%)

No response: 8
(16%)

12-month EFS 23.4±7.5%

12-month OS 36.3±9.3%

[19]
Pediatric and AYA CD22+ 
B ALL in 2nd  relapse, refractory 
to two prior regimens, relapse after HSCT, or 1st relapse with DS 
Phase II Single armN=48
CR/CRh:
28 (58.3%)
(95%CI, 43.2-
72.4)

CR: 19 (40%)

CRh: 9 (19%)

MRD negative: 17 (65%)

Progressive disease: 8
(16.7%)
4 (30.7%)[20] NCT02981628
AALL1621

Table 3: Inotuzumab ozogamicin studies.


Adult experience with InO: U.S. Food and Drug Administration (FDA) approval of InO for relapsed/ refractory CD22 positive ALL was based on the INOVATE trial. The study showed a superiority of InO compared to standard of care (SOC) chemotherapy with improved complete remission (CR)/remission with partial hematologic recovery (CRh) rates, 73.8% vs. 35% and progression-free survival (PFS) 5.0 months vs. 1.7 months. More patients proceed to transplant in the InO arm (48% vs. 22%, p<0.0001) [17]. At the two-year follow-up, overall survival (OS) rates were superior with InO 22.8% and 10.0% [17].

Pediatric experience with InO: Of five pediatric patients with relapsed CD22 positive B-ALL treated with InO as part of an adult phase 2 trial, three had a CR/CRh [18]. A retrospective analysis of compassionate use of InO in fifty-one pediatric patients with relapsed/refractory B-ALL showed a 12-month EFS and OS of 23% and 36% respectively [19]. Twenty-one patients underwent a hematopoietic stem cell transplant (HSCT) after achieving CR [19]. In the Children’s Oncology Group (COG) trial AALL1621 (NCT02981628) of InO in heavily pre-treated relapsed/refractory, CD22 positive B-ALL patients, 58.3% had a CR/CRh, with 65.4% of those having a minimal residual disease (MRD) response [20].

Ongoing Trials with InO in pediatrics: There are several ongoing pediatric trials investigating the timing and indications for InO. InO is being studied in upfront therapy, relapsed/refractory MRD positive ALL with chemotherapy, and as consolidation post-transplant (Table 4).

StudyAimDesignAgeStatus
NCT03959085 AALL1732InO added to post-induction chemotherapy in HR B-ALLPhase III Randomized Multicenter1 y.o. to 24 y.o.Recruiting
NCT03150693InO with frontline chemotherapy with young adults with newly diagnosed CD22 + B-ALLPhase III Randomized Multicenter18 y.o. to 39 y.oRecruiting
NCT04307576Addition of InO in chemotherapy for newly diagnosed B-ALL (IR/HR)Phase III Randomized1 y.o. to 45 y.o.Not yet recruiting
NCT03739814InO and Blinatumomab in newly diagnosed, or R/R CD22+ B-ALLPhase II Multicenter≥ 18 y.o.Suspended-Request for amendment
NCT03962465InO with augmented BFM Re-induction for AYA pa- tients with R/R B-ALLPhase I
Single Center-U. Virginia
18 y.o. to 55 y.o.Recruiting
NCT03991884InO with chemotherapy in R/R CD22+  B-ALL (Ph+/-)Phase I
Single Center- U. Washington
≥ 18 y.o.Recruiting
NCT01925131S1312InO with chemotherapy in R/R CD22+ B-ALLPhase I≥ 18 y.o.Recruiting
NCT03677596Study of a lower dose of InO in R/R, transplant eligible
B-ALL at risk of liver disease and plan for HSCT
Phase IV Randomized Multicenter18 y.o. to 75 y.o.Recruiting
NCT03851081InO and Vincristine sulfate liposome in R/R CD22+
B-ALL
Phase ib/II Single Center- Roswell Park Cancer Institute≥ 18 y.o.Not yet recruiting
NCT02311998Bosutinib with InO in R/R Ph+ B-ALLPhase I/II
Single Center-MD Anderson
≥ 18 y.o.
NCT03856216InO in CD22+ R/R B-ALL in patients who are not eligible for a myeloablative HSCT but eligible for a RIC HCSTPhase II
Single Center-MD Anderson
18 y.o. to 70 y.o.Recruiting
NCT03610438 ALL2418InO in B-ALL who have MRD+ disease after at least 3 months of any therapy
Ph+/-
Phase IIa Exploratory Multicenter≥ 18 y.o.Not yet recruiting
NCT03913559InO for children with MRD+, CD22+ ALL with <5% blasts in BMPhase II MulticenterUp to 21 y.o.Recruiting
NCT03441061InO in MRD+ B-ALLPhase II
Single Center- MD Anderson
≥ 18 y.o.Recruiting
NCT03104491InO post-transplant in ALL who have a high risk of relapsePhase I/II Multicenter16 y.o to 75 y.o.Recruiting
NCT03564678Levocarnitine and Vitamin B Complex in treating InO and PEG-Asparaginase hyperbilirubinemia in ALLPhase II
Single Center-MD Anderson
12 y.o and olderRecruiting

*Table is not comprehensive, please see clinicaltrials.gov for additional ongoing trials

Table 4: Ongoing trials with Inotuzumab ozogamicin in pediatric and AYA patients.

Sinusoidal obstructive syndrome (SOS): Sinusoidal obstructive syndrome (SOS) was seen more commonly in patients who are treated with InO than salvage chemotherapy, a serious concern in patients whom subsequent transplant is a consideration. In INOVATE trial, rates of SOS were 14.0% (5% fatal) in the InO arm vs. 2.1% in the SOC chemotherapy arm [17]. Risk factors for SOS included conditioning with dual alkylators, hyperbilirubinemia before HSCT, and prior HSCT (OR 6.02; p=0.032) [17]. In the pediatric experience, 4 of the 13 patients (30.7%) who went on to HSCT developed grade 3 SOS in AALL1621 study [20] at 11 of the 21 (52%) patients in compassionate use study [19]. Strategies to prevent SOS include avoiding dual alkylating agents and/or thiotepa and hepatoxic agents, prophylactic ursodiol, proceeding to HCT after two cycles of InO, and close monitoring for SOS [21]. Ongoing trials include Levocarnitine and Vitamin B to reduce hyperbilirubinemia with InO treatment (NCT03564678), lowering the dose of InO pre-transplant (NCT03677596) and reduced intensity transplant (NCT03856216).

Daratumumab

Mechanism of action: CD38 is a type II transmembrane glycoprotein on the surface of thymocytes, activated T-cells and terminally differentiated B cells, with low level expression on other normal lymphoid and myeloid cells [22]. CD38 expression has been seen on T-ALL blasts and remains stable after treatment with chemotherapy [22]. Daratumumab is a human monoclonal antibody directed against CD38 [22]. It is FDA approved for multiple myeloma both as monotherapy and in combination [23,24]. Preclinical data has shown efficacy of Daratumumab in T-ALL models [22,25], and case series have shown efficacy as salvage therapy in relapsed T-ALL [26,27]. There are ongoing clinical trials of Daratumumab in pediatric T-ALL and B-ALL in combination with cytotoxic chemotherapy (NCT03384654). Other monoclonal antibodies being tested in T-ALL are listed in Table 2.

BiTEs

Bispecific T-cell-Engaging (BiTE) antibodies are antibodybased molecules that bind to distinct surface markers on T-cells and tumor cells to form the immunological synapse [28,29]. BiTEs bind the invariant signaling component of the T-cell receptor (TCR), CD3, and a surface target antigen on tumor cells, resulting in T-cell activation, expansion and tumor cell lysis [28,29]. BiTEs are independent of T-cell receptor specificity and do not require MHC presentation of the antigen; thus, bypassing T-cell regulation [29]. Unlike CARTs, BiTEs do not require manufacturing and infusion of T-cells [29].

Blinatumomab

Mechanism of action: CD19 is expressed on approximately 90% of B-ALL cells [30]. Blinatumomab is a BiTE that binds to CD19 on leukemic cells and CD3- subunit of the TCR on T-cells [29]. Clinical trials of Blinatumomab for B-ALL are highlighted in Table 5.

Patients
Phase
N
Dosing
Response
Group/study
 
 
 
 
 
 
Adults with Ph- R/R B- ALL 
 
 
 
 
 
Multicenter, single -arm, open-label, phase II,
 
 
 
 
 
189
(185- received blina)
 
Continuous infusion over 4 wks of a 6 wk cycle
 
Two cycles for induction and 3 for consolidation
 
Cycle 1 initial dose 9μ/day  for 7 days then 28μ/day for the
remaining 3 wks.
 
Subsequent
cycles 28μ/day
CR or CRh 81 (43%) (95%CI;
36-50)
CR 63 (33%)
CRh 18 (10%)
MRD negative: 60
(82%)
 
Median RFS (MRD responders vs. non- responders) 6.9
mo (95% CI, 5.5-
10.1) vs 2.3 (95% CI 1.2-NE)
Median OS: (MRD responders vs. non-responders
11.5 mo (95% CI, 8.5-NE) vs. 6.7 mo (95% CI 2.0-NE)
 
 
 
 
 
[31]
MT103-211 (NCT01466179)
 
 
Ph- R/R ALL 
Blinatumomab vs standard 
of care (SOC) chemotherapy 
- 
 
Phase III, randomized, open-label, multi- center trial comparing
Blinatumomab with conventional chemotherapy (2:1 ratio)
 
 
405 pts
-271 in the blina arm
-134 in the SOC
Intent-to treat
Blina 9μ/day
days 1-7 and 28
μ/day days 8-28
(induction)
Cycles 2-5  days 1-28 in a 42 day cycles (consolidation)
Cycles 6-9 in
84 day cycles (maintenance)
 
CR : 91 (34%)
(95%CI, 28-40) vs
21 (16%) (95%CI,
10-23; p<0.001)
CRh: 24 (44%) vs.
6 (25%)  (p<0.001
MRD negative: 76% vs. 48%
(95%CI, 9-47)
 
 
 
[32, 36] TOWER (NCT02013167)
 
 
 
 
 
 
 
 
Ph- or + R/R Pediatric 
<18 (2 to 17) 
>25% BM blasts 
 
 
 
 
 
 
 
 
 
Phase I/II open label, multicenter
 
 
 
 
 
 
 
40 pts- phase I 44 phase II
70
recommended dosage
phase I (n =
26) or phase II (n = 44)
 
 
 
 
 
 
Phase I: dosages of 5, 15, and 30 μ/m2/d and a stepwise dosage of 15/30 μg/ m2/d (15 μ/ m2/d for the first 7 days and 30 μ/m2/d thereafter).
 
Recommended dosage of 5/15 μ/m2/d
 
Of the 70 pts that received the recommended dosage:
CR: 27 (39%)
(95% CI, 27-51%)
MRD negative: 14/27 (52%) (95%
CI, 32-71)
Median RFS: 4.4
mo (95% CI, 2.3-
7.6) (for patients who achieved CR_
Median OS: 7.5
mo (95%CI, 4.0-
11.8)
6 mo estimated EFS (1st relapse): 40.8% (95%CI,
30.1-50.) vs.
25.9% (95%CI;
15.3-37.8)
HR 0.7 (95% CI,
0.47-1.03; p=0.11)
6 mo estimated EFS (2nd or later relapse): 24.0%
(95% CI, 17.4-
31.3%); 1.6% (95%
CI, 0.1-7.5%):
HR 0.49 (95%
CI, 0.29-0.57; p<0.001)
 
 
 
 
 
 
 
 
[37]
MT103-205 (NCT01471782) AALL1121
 
R/R Ph+ B ALL, 
previously treated with at least one 2nd generation TKI or intolerant to 2nd generation TKI and refractory to imatinib 
 
>5% bone marrow blasts 
 
 
 
Phase II, multicenter, single arm trial of blina
 
 
 
 
45 patients
9 μ/day days 1-7
and 28 μ/day
days 8-28 for
cycle 1.
28 μ/day days
1-28 subsequent cycles
 
IF CR achieved could receive up to 3 cycles of consolidation unless a HSCT was scheduled
CR/CRh; 16 (36%)
(95% CI, 22- 51)
CR: 14 (31%) (95%
CI, 18-47)
CRh: 1 (4%) (95%
CI, 1-15)
MRD-negative: 14
(88%) (95% CI,
62-98)
Median OS: 7.1 mo (95% CI, 5.6-NE)
Median RFS: 6.7
mo (95% CI, 4.4- NE)
 
 
 
[33]
ALCANTARA (NCT02000427)
(Martinelli, JCO, 2017)
 
 
 
 
 
Adult R/R B- ALL in 
ftrst or later hematologic CR but MRD positive 
 
 
 
 
 
Multicenter, open label, single arm trial
 
 
 
 
116
113 evaluable patients
Excluded no central MRD assay results or a test sensitivity that did not reach 10−4
 
 
 
 
 
15 μ/m2/day for
28 days followed by 2-2wk tx free period
Up to 4 cycles
 
CR:48/110
(remained in CR
MRD negative: 88/113 (78%)
(95% CI, 69-85)
 
Median OS: 36.5mo (95% CI,
19.1-NE)
 
Median RFS (MRD responders vs nonresponsers): (23.6 vs 5.7
months; p=0.002)
Median OS (MRD responders vs nonresponsers): (38.9 vs 12.5
months; p=0.002
 
 
 
 
 
[35] BLAST
MT103-203 NCT01207388
 
 
Pediatric and AYA R/R B-ALL after re-induction 
chemotherapy 
 
 
Multicenter, randomized phase III trial
 
208 HR/IR
patients were randomized
Chemotherapy arm- Blocks
2 and 3 of UKALLR3
Blinatumomab
 
 
Two cycles at 15 μ/m2/day for 28 day
 
2-year DFS: 59.3
± 5.4% vs. 41.0 ±
6.2% (p=0.05)
2-year OS: 79.4
± 4.5% vs. 59.2 ±
6.0% (p=0.005)
 
 
[38] NCT02101853
AALL1331
 
 
Pts with B-ALL 0 to 21 y.o 
who were transplanted with CR but MRD + 
 
 
 
Retrospective analysis, multicenter
 
 
 
N=15
10/15 CR1 with EOC+
 
Singe 12 day
course 15μ/m2/d
 
2 had course shortened to go to HCT (18 and 20 days of blina)
 
1 received 2 cycles of blina
 
 
MRD negative: 14/15 (93%)
1-yr post HCT relapse incidence 27.8%
1-yr OS: 93.2%
 
 
 
[80]

Table 5: Blinatumomab studies.

Role in relapsed/refractory B-ALL: In 2014, the FDA granted accelerated approval of blinatumomab for adult Philadelphia chromosome negative (Ph-) relapsed/ refractory B-ALL based on a single-arm study of 189 adults that showed efficacy and manageable toxicity [31]. Eightyone patients (43%) had a CR/CRh within two cycles of blinatumomab [31]. Median overall survival was 6.1 months [31]. This was superior to historical controls who received SOC, salvage chemotherapy [31]. Efficacy was confirmed in the TOWER trial, a multicentered, randomized, phase III trial comparing blinatumomab to chemotherapy in adult relapsed/refractory Ph- ALL [32]. CR was achieved in 91 patients (34%) in the blinatumomab arm compared to 21 patients (16%) in the SOC arm. The median overall survival was significantly longer for the blinatumomab arm (7.7 months versus (4.0 months) in the SOC arm [32].

Role in Philadelphia chromosome-positive (Ph+) ALL: The approval of blinatumomab was extend to Ph+ relapsed/refractory B-ALL based on the ALCANTARA trial showing a 36% CR/CRh, with 88% complete MRD response in patients with relapsed/refractory Ph+ ALL, previously treated with TKI treatment [33]. Blinatumomab as consolidation to treatment with TKI has also been studied in a multicenter phase II trial of Ph+ ALL, patients were treated with dasatinib, followed by post-induction consolidation with blinatumomab. At the end of two cycles of blinatumomab 19/35 (54%) had a molecular response that further increased after subsequent cycles [34]. Twelvemonth OS and DFS are 96.2% and 91.6% respectively [34]. There are several ongoing studies examining the efficacy of TKIs with blinatumomab (Table 6).

Study
Aim
Design
Age
Status
NCT02101853 AALL1331
Blinatumomab compared to SOC chemotherapy in pediatric and AYA patients as a bridge
to transplant in relapsed ALL after re-induction with block 1 of UKALLR3/mitoxantrone arm
Phase III trial Multicenter Randomized
1 y.o. to 30 y.o.
Active, not recruiting
HR/IR arm closed early due to trend to superiority
NCT02393859 
Blinatumomab vs. SOC in pediatric patient with
Ph-, HR, first relapsed B-ALL
Phase III Multicenter Randomized
>28 days
to <18 y.o.
Active, not recruit- ing
NCT03914625 AALL1731 
Blinatumomab in combination with chemotherapy in newly diagnosed SR B-ALL
Role of immunotherapy in patients with Down Syndrome and B-ALL
Phase III Randomized Multicenter
1 y.o. to 21 y.o.
Recruiting
NCT03117751 
St. Jude Total Therapy XVII 
Blinatumomab for Newly diagnosed SR ALL
Blinatumomab for patients with HR ALL (and MRD of 0.01 to 1% at the end of induction)
Phase II/III Randomized Multicenter
1 y.o. to 18 y.o.
Recruiting
NCT03643276 
AIEOP-BFM ALL 2017 
Incorporating Blinatumomab with standard chemotherapy regimens in newly diagnosed HR/IR B-ALL
Phase III Randomized Multicenter[ed]
<18 y.o.
Recruiting
NCT02877303 
Blinatumomab and chemotherapy (Hyper-CVAD) in newly diagnosed B-ALL
Phase II
Single center-MD Anderson
14 y.o and older
Recruiting
NCT03367299 
Chemotherapy and blinatumomab in newly diagnosed Ph- ALL
Phase II Multicenter
18 y.o. to
65 y.o
Recruiting
NCT03541083 HOVON146ALL 
Blinatumomab in the prephase and consolidation in newly diagnoses B-ALL
Phase II Multicenter
18 y.o. to
70 y.o.
Recruiting
NCT02807883
Blinatumomab maintenance following allo HSCT in
Ph+ BALL
Phase II
Single center-MD Anderson
1-70 y.o.
Recruiting
NCT03114865
Blinatumomab in B-ALL post allo HSCT as remission maintenance
Phase I
Single Center- SKCC
≥18 y.o.
Recruiting
NCT04044560 (OZM-097) 
Blinatumomab for MRD in Pre-B ALL following stem cell transplant
Phase II Single arm Open label Multicenter
1 y.o and older
Active, not yet recruiting
NCT03982992 DLI-TARGET 
Allogeneic donor lymphocyte infusions combined with Blinatumomab in B-ALL who have mixed chimerism (MC) or are MRD after allo HSCT and are refractory to at least one
MRD-or MC targeted therapy (i.e blinatumomab, DLI, TKI, etc)
Phase II Single center- Klinikum der Universität München
≥18 y.o.
Recruiting
NCT02790515 NCT03849651 
Blinatumomab in naïve T-cell depleted haploidentical donor HCT for R/R ALL
Phase II
Single center-St. Jude
Up to 21 y.o.
Recruiting
NCT02879695 
Blinatumomab and Nivolumab with or without ipilimumab in patients with poor risk relapsed or refractory CD19+ precursor B-ALL
Phase I Multicenter
16 y.o. and older
Recruiting
NCT03605589
Pembrolizumab Blinatumomab in pediatric and AYA R/R ALL
Phase I Pilot
Single Center- Cincinnati Children’s Hospital
1 y.o. to 40 y.o.
Recruiting
NCT03512405
Pembrolizumab and blinatumomab in R/R ALL
Phase I/II
Single center-City of Hope Medical Center
≥18 y.o.
Recruiting
NCT03160079
Pembrolizumab and Blinatumomab in R/R B-ALL with high marrow lymphoblasts (>50% blasts)
Phase i/II Multicenter
≥18 y.o.
Recruiting
NCT02744768 
Dasatinib and Blinatumomab in newly diagnosed Ph+ ALL
Phase II Multicenter
≥18 y.o.
Recruiting
NCT03318770 GIMEMA 2116 
Dasatinib and blinatumomab following chemotherapy in Ph+ ALL
Observational Case-Control Prospective
≥18 y.o.
Not yet recruiting
NCT04329325 
Blinatumomab and TKI (Dasatinib) in patients with Ph+ ALL
Phase II Single
Group-MSKCC
≥18 y.o.
Recruiting
NCT02997761 
Ibrutinib and Blinatumomab in R/R B-ALL
Phase II Single group- University of
California Davis
≥18 y.o.
Recruiting
NCT03263572 
Blinatumomab, Methotrexate, cytarabine and ponatinib in Ph+ R/R ALL
Phase II
Single center-MD Anderson
≥18 y.o.
Recruiting
NCT03147612 
Low-intensity chemotherapy, ponatinib and blinatumomab in newly diagnosed and R/R Ph+ ALL
Phase II
Single center- MD Anderson
≥18 y.o.
Recruiting
NCT03628053 OBERON 
Tisagenlecleucel vs Blinatumomab or Inotuzumab for patients with R/R B-ALL
Phase III Randomized Multicenter
≥18 y.o.
Not yet recruiting
NCT03739814
Inotuzumab ozogamicin and blinatumomab in patients with newly diagnosed or R/R  CD22+ B-ALL
Phase II Multicenter
≥18 y.o.
Suspended-Request for amendment

*Table is not comprehensive, please see clinicaltrials.gov for additional ongoing trials.

Table 6: Ongoing trials with Blinatumomab in pediatric and AYA patients.

Role in MRD positive disease: In 2018 the FDA granted approval for blinatumomab for the treatment of adults and children with B-ALL in a morphological first or second CR with MRD [35]. Eighty-eight of 113 patients (78%) achieved a complete MRD response after one cycle of blinatumomab [35]. Patients who achieved a complete MRD response had a prolonged OS (38.9 vs 12.5 months; p=0.002) and RFS (23.6 vs 5.7 months; p=0.002) [35].

Role in first vs. later relapse: Blinatumomab appears to be a more effective salvage therapy in first versus second or later relapse. In the TOWER study, blinatumomab’s effect on overall survival was greater for first salvage therapy (HR 0.59; p=0.016) than second or greater salvage therapy (HR 0.72; p=0.055) [36]. Similarly, in the BLAST MRD trial, patients who had previously relapsed had inferior RFS and OS compared with those treated in first remission (HR 2.02 for CR2 vs CR1 relapse and HR 3.34 for CR3 vs. CR1 relapse, -p=0.001), suggesting the importance of MRD clearance early in the treatment course [35].

Role in pediatrics: Efficacy and safety of blinatumomab was shown in the pediatric population in the Study MT103- 205 a phase I/II study, of the 70 patients. Twenty-seven (39%) achieved a CR with 14 (52%) of the responders having a completed MRD response [37]. Duration of response was 4.4 months [37]. There are several pediatric trials studying the role of blinatumomab in relapsed/ refractory B-ALL and as consolidation for transplant (Tables 6 and 7). The COG trial AALL1331 (NCT02101853) is a phase III randomized trial for relapsed B-ALL testing blinatumomab as post-reinduction consolidation, with high risk (HR) and intermediate risk (IR) patients proceeding to HSCT, and low risk (LR) patients receiving maintenance chemotherapy. The HR/IR randomization was terminated early due to evidence of superiority and decrease toxicity of the blinatumomab arm [38]. In these groups blinatumomab arm had an improved 2-year DFS (59.3% vs. 41.0% p=0.05), 2-year OS (79.4% vs. 59.2% p=0.005) and MRD clearance (21% vs. 79% p<0.0001) with fewer and less severe toxicities compared to SOC chemotherapy [38]. Data for the low risk (LR) randomization is pending. There are ongoing studies investigating the role of blinatumomab in upfront therapy including the COG trial AALL1731 (NCT03914625) that is studying the addition of blinatumomab to standard chemotherapy in patients with NCI SR B-ALL at high risk for relapse. Blinatumomab is also being studied in HR/IR newly diagnosed B-ALL in the European Studies AIEOP-BFM ALL 2017 (NCT03643276) and PETHEMABLIN- 01 (NCT03523429). Lastly, blinatumomab is also being studied as maintenance after allogenic HSCT (NCT02807883 & NCT03114865) (Table 6). Combining blinatumomab with other immunotherapies is also being investigated. There is an ongoing adult trial combining treatment with inotuzumab ozogamicin with mini-HCVD with or without blinatumomab in previously untreated acute lymphoblastic leukemia, (NCT01371630). In AYA patients, blinatumomab and inotuzumab ozogamicin are being studied in newly diagnosed and relapsed/refractory CD22+ B-ALL (NCT03739814). The ability of checkpoint inhibitors to further enhance the efficacy of blinatumomab is also actively being studied (NCT03605589, NCT03512405, NCT03160079, NCT02879695).

Patients
Phase
N
Response
Group/study
 
Pediatric and adult R/R ALL 
(CTL119) (4-1BBz CAR) 
 
Phase I/IIa
 
N=30
25 pediatric
5 adult
CR: 27 (90%)
MRD negative: 22/27 (81%)
6-mo EFS: 67% (95% CI, 51-88)
6-mo OS: 78% (95% CI, 65-95)
[60] NCT01626495
NCT01029366
Pediatric and AYA R/R B-ALL 
(CTL119) (4-BBz CAR) 
 
Phase I/II
 
N=45
ITT MRD: (40/45) 89%
12-mo EFS: 50.8% (95% CI, 36.9-69.9)
12-mo OS: 69.5% (95% CI, 55.8-86.5)
[46] NCT02028455
PLAT-02
 
 
Children and AYA CD19+ ALL 
(CTL119) (4-1BBz) 
 
 
Pilot protocol
 
 
 
N=53
CR: 50 (94%)
MRD negative: 45 (90%)
6-mo EFS: 70% (95% CI, 58-85)
6-mo RFS: is 72% (95% CI, 59-87%)
12-mo EFS: 45% (95% CI, 31-66)
12-mo RFS: 44% (95% CI, 30-65)
12-mo OS: 78% (95% CI, 67-91)
 
 
 
[81]
Pediatric and AYA R/R B-ALL 
KTE-C19 (CD28 CAR) 
 
Phase 1
 
N=5
4 treated
 
MRD negative CR: 4
[82] (NCT02625480) ZUMA-4
Pediatric and AYA with R/R B-ALL or NHL 
(TCR zeta and CD28 signaling domain) 
 
 
Phase 1
 
 
N=21
 
CR: 14/21 (66.7%) (95% CI, 43.0–85.4)
MRD negative: 12/20 (60%) (95% CI,
36.1–80.9)
OS: 51.6%
 
[45] NCT01593696
 
 
 
Pediatric and AYA R/R B-ALL CD19+ 
Tisagenlecleucel (CD3-zeta: 4-1BB) 
5% blasts in BM 
 
 
 
 
Phase II Multicenter
 
 
 
N=113
screened N=97 enrolled N=75 infused
RR: 65 (81%) (95% CI, 71-89)
CR: 45 (60%)
CRh: 16 (12%)
MRD negative: 64 (98%)
6-mo RFS: 80% (95% CI, 65-89)
12-mo RFS: 59% (95% CI, 41-73)
18 mo RFS: 66% (95% CI, 52-77)
6-mo EFS: 73% (95% CI; 60-82)
6-mo OS: 90% (95% CI 63-86)
12-mo EFS: 50% (95%CI, 35-64)
12-mo OS: 76% (95% CI, 63-86)
18 mo OS: 70% (95% CI, 58-79)
 
 
 
[43, 47] NCT02435849
ELIANA
 
Adult R/R ALL 
KTE-C19 (CD28 CAR) 
 
 
Phase 1
 
 
N=53
CR: 44/53 (83%) (95% CI, 70-92)
MRD: 32 (67%; 95% CI, 52-80)
Median EFS: 6.1 months (95% CI, 5.0-
11.5)
Median OS: 12.9 months (95% CI, 8.7-
23.4)
 
[44] NCT01044069
 
R/R B-ALL treated with CD22 BBz CAR, 
(4-1BB domain) 
 
Phase I
21 Children and adults
17-previously treated with CD19
 
CR: 12 (57%) CR
MRD negative 9 (75%)
 
[48] NCT02315612
 
R/R B-Cell malignances, sequential infusion of  CD19 and CD22 3rd generation CAR-T 
 
 
Pilot
 
N=89 N=51- ALL
MRD Negative: 96% (95% CI, 86.3-
99.5)
 
Median PFS: 13.6 mo (95% CI, 6.5 to NE)
Median OS: 31.0 mo (95% CI, 10.6-NE)
 
[83] ChiCTR-
OPN-16008526
Pediatric R/R B-ALL 
AUTO3-Bicistronic CD19 and CD22 CAR 
Ox40 co-stim for CD19 CAR 
41BB co-stim for CD22 
 
 
 
Phase I
 
 
N=10
7-Treated
 
CR and MRD: 7/10 1 year follow up:
-3 relapses
-4 patients in ongoing CR/CRh with B-Cell
 
 
[84]
Amelia Study
CD19/CD22 
bispeciftc CAR-T in children and AYA patients with B-ALL 
Lentiviral transduction bivalent CAR 
fmc63 CD19 m971 CD22 
41BB costimulatory endo-domain 
 
 
 
Phase I
 
 
 
N=4
 
 
 
CR: 4/4 (100%)
MRD negative: 3/4 (75%)
 
 
 
[85]
 
CD19 and CD22 
CART cocktail for R/RB-ALL 
 
Phase I
 
N=16
 
CR/CRh: 15/15 (100%)
MRD negative: 14/15 (93.3%)
 
[86]

Table 7: B-cell CART studies.

Biomarkers to predict response: Predictive biomarkers of response to blinatumomab are emerging. Patients who have a lower baseline disease burden [31] and day 15 MRD have a better response [39]. In addition, superior response was correlated with greater T-cell expansion of effector memory T-cells [40] and a higher percentage of regulatory T-cells [41]. Identifying additional biomarkers to determine response is actively being studied.


CAR-T Therapy

Chimeric antigen receptors (CARs) are T-cells that are engineered to recognize tumor associated antigens. CARs are composed of T-cell signaling moiety and a tumor specific antigen binding domain, commonly a single-chain variable-fragment monoclonal antibody that is fused to a transmembrane domain [42]. Various generations of CARs have been developed to heighten function based on the knowledge that T-cells require two signals to be activated, T-cell receptor (TCR) engagement and co-stimulation. First generation CARs consisted of T-cell receptor complex domain and antigen recognition domains, only providing signal 1; whereas, second generation CARs were constructed to contain co-stimulatory signaling domains including CD28, 4-1BB (CD137), and OX40 (CD134) [42]. Third generation CARs further enhanced T-cell signaling by containing tandem cytoplasmic signaling from two co-stimulator receptors (CD28-4-1BB or CD28-OX40) [42]. Fourth generation CARs have pro-proliferative T-cell costimulatory ligands (4-1BBL) or proinflammatory cytokines (IL-12) [42]. Advantages of CAR-T therapy include HLA-independent recognition of tumor antigen; allowing T-cells to recognize the antigen as foreign and activity is unaffected by HLA down regulation in tumor cells. In addition, both CD4+ and CD8+ T-cell subsets are transduced, allowing for both helper and cytotoxic activity.

CD19 CAR-T

Commercial approval: There are two FDA approved CD19 directed CAR-T products, tisagenlecleucel (CTL019) and axicabtagene ciloleucel. Both are second generation CAR-T-cells. Tisagenlecleucel uses a 41BB costimulatory domain and is transduced by lentivirus, whereas axicabtagene ciloleucel uses the CD28 costimulatory domain and is produced by retroviral transduction. Tisagenlecleucel is FDA approved for relapsed/refractory B-ALL in pediatric and young adult patients. Axicabtagene ciloleucel is approved for relapsed/refractory B-cell lymphoma in adults and is being studied for the treatment of pediatric B-ALL.

The FDA approval of tisagenlecleucel was based on a pivotal, global multicenter trial of tisagenlecleucel in pediatric relapsed/refractory, CD19+, B-ALL that showed an overall remission rate of 81%, all with MRD response [43]. Six- and 12-month relapse-free survival rates were 80% and 59% respectively [43].

Clinical trials: Trials have shown second generation CD19-CAR-T therapy induced remission in heavily pre-treated patients with multiple relapsed/refractory B-ALL [43-46]. Axicabtagene ciloleucel is currently being studied in pediatric patients with relapsed/refractory B-ALL previously treated with salvage therapy or HSCT (NCT02625480). In adult relapsed/refractory B-ALL, 44 of the 53 patients (83%) had a CR and 32 patients (67%) had a MRD response [44]. In a Phase 1 trial of 21 pediatric patients with relapsed/refractory B-ALL or Non-Hodgkin’s Lymphoma, CR was seen in 66.7% (14 of 21) of patients with a MRD response occurring in 60% of patients [45]. CD19-CAR-T therapy is being studied in newly diagnosed very high-risk (VHR) B-ALL patients in the COG trial AALL1721 (NCT03876769) and St Jude Total Therapy XVII (NCT03117751). In addition, CD19- CAR-T is being studied in combination with checkpoint inhibitors to enhance efficacy for the CAR-Ts and decrease T-cell exhaustion (Table 8).

Study
Aim
Design
Age
Status
NCT03117751
St. Jude Total Therapy XVII
 
19-BBzCART for MRD positive B-ALL or isolated CNS relapse
 
Randomized Single Center
 
1 y.o. to 18 y.o.
 
Recruiting
 
NCT03876769 CASSIOPEIA
Tisagenlecleucel in newly diagnosed HR B-ALL with EOC MRD positive disease
(CTL019)
 
Phase II Multicenter
 
1 y.o. to 25 y.o.
 
Recruiting
NCT02625480
ZUMA-4
KTE-C19 in Pediatric and adolescents with R/R B-ALL
Phase I/II Multicenter
 
Up to 21
 
Recruiting
 
NCT02808442
 
UCART19 in R/R pediatric B-ALL
Phase I Multicenter
 
Upt 17 y.o.
 
Recruiting
 
NCT04154709
CTA101 UCAR-T for R/R CD19+ B-ALL
 
Phase I
 
3 y.o. to 70 y.o.
 
Recruiting
 
NCT03876769
Tisagenlecleucel in HR B-ALL with EOC + disease
Phase II Multicenter
 
1 y.o. to 25 y.o.
 
Recruiting
 
NCT02435849
CTL019 in R/R or relapse <6 mot after allo-HSCT
Phase II Multicenter
 
Up to 25 y.o.
Active not Recruiting
NCT03263208
CD19 CAR-T for R/R CD19 B-ALL
Phase I/II
2 y.o. to 70 y.o.
Unknown
 
NCT02924753
 
CD19 CAR-T in B-ALL
Phase I Single center- China
 
4 y.o. to 70 y.o.
 
Unknown
 
 
 
NCT04276870
CD19 autologous CAR-T Cohort A- hypodiloid Cohort B- t(17; 19)
Cohort C- infants with very high risk KMT2A B-ALL
Cohort D- CNS relapse who did not receive XRT or BMT
CART19 cells transduced with a lentiviral vector to express anti-CD19 scFv:41-BB:TCRζ
 
 
 
Phase II Single Center- UPenn
 
 
 
Up to 29 y.o.
 
 
 
Recruiting
NCT03768310 CARMA
CD19 multivirus-specific CAR-for CD19+ B-ALL of NHL undergoing related allo HSCT
Phase I
Single Center- Baylor
 
1 y.o. to 75 y.o.
 
Not yet recruiting
 
NCT04214886
CD19 CAR-T for R/R B-cell malignancies
(CD19-CD34 CAR transduced T cells)
Phase I
Single Center- Loyola University
 
18 y.o. and older
 
Recruiting
NCT04404660 AUTO1
 
CD19 CAR-T in R/R B-ALL
 
Phase I/II Multicenter
 
18 y.o. and older
 
Recruiting
 
NCT04225676
Efficacy and safety of reinfusion of Tisagenlecleucel in pediatric and AYA patients with B-ALL
 
Phase II
 
Up to 25 y.o.
 
Not yet recruiting
 
NCT04094311
Study of out of specification for release as commercial product for Tisagenlecleucel in pediatric and AYA R/R B-ALL and B-NHL
CTL019
 
Phase III
 
Child, AYA, adult
 
Recruiting
NCT03743246(JCAR017)
 
JCAR017 in R/R B-ALL or B-NHL
 
Phase I/II Multicenter
 
Up to 25 y.o.
 
Recruiting
 
NCT03103971
huJCAR014 for R/R B-Cell ALL and NHL
(CD19CAR-4-1BB-CD3zeta-
EGFRt-expressing CD4+/CD8+
T-lymphocytes)
 
Phase I
Single Center- University of Washington
 
18 y.o. and older
 
Recruiting
 
NCT04264039
 
Anti-CD19 U-CAR-T for B cell hema- tologic malignancies
Early Phase I Single Center- China
 
2 to 70 y.o.
 
Not yet recruiting
 
NCT03389035 CARCIK
 
CARCIK-CD19 in R/R ALL post HSCT
Phase I/II Multicenter- Italy
 
1 y.o. to 75 y.o.
 
Recruiting
 
NCT03666000
 
PBCAR0191 for patients with R/R NHL and R/R B-ALL
 
Phase I/IIa Multicenter
 
18 y.o. and older
 
Recruiting
 
NCT04088890
 
Autologous CD22 CAR-T in R/R B-ALL
Phase I
Single Center- Stanford University
 
18 y.o. and older
 
Recruiting
 
 
NCT03241940
 
CD19/CD22 CAR-T for R/R B-cell malignancies
 
Phase I Single center-
Lucile Packard Children’s Hospital, Stanford
 
 
1 y.o. to 30 y.o.
 
 
Recruiting
 
NCT03289455 AMELIA
 
CD19/22 CART (AUTO3) for R/ALL
 
Phase I/II Multicenter-UK
 
1 y.o. to 24 y.o.
 
Active, not recruiting
 
NCT03448393
 
CD19/CD22 CAR-T in R/R B-ALL
Phase I Single center- NCI
 
3 y.o. to 30 y.o.
 
Recruiting
 
NCT03233854
 
CD19/CD22 CAR-T in R/R B-cell malignancies
Phase I Single center- Stanford University
 
18 y.o. and older
 
Recruiting
 
NCT03330691
 
CD19/CD22 CAR for R/R B-ALL
 
Phase I Single center- Seattle
 
Up to 30 y.o.
 
Recruiting
 
NCT04049383
 
CD20/19 CAR-T for R/R B-ALL
 
Phase I Single center-
Medical College Wisconsin
 
1 y.o. to 39 y.o.
 
Not yet recruiting
 
NCT02906371
 
Optimization of Tocilizumab timing for CD19 CAR-T associated CRS
(CTL019)
 
Pilot study Single Center- CHOP
 
1 y.o. to 24 y.o.
 
Active, not recruiting
 
NCT02445222
 
Long term follow-up of CAR-T.
Patients are followed for 15 years following their last CAR-T infusion
 
Not applicable Multicenter
 
All ages
 
Recruiting

*Table is not comprehensive, please see clinicaltrials.gov for additional ongoing trials.

Table 8: Ongoing CAR-T trials for B-ALL.

Unanswered questions: Several unanswered questions remain including the role of CD19-CAR-T in upfront therapy and if it should be used as monotherapy versus a bridge to HSCT. Historically, patients at high risk of relapse, myeloablative transplant is recommended. In the Park et al. study, subsequent transplant did not influence EFS or OS for the patients who had a MRD response after CD19-CAR-T [44]. In the Eliana study, the 18-month EFS was 66% with a median persistence of CAR-T of 168 days [43,47]. Eight patients underwent allogeneic hematopoietic stem-cell transplantation while in remission [43,47]. Conversely, 29 (45%) patients had an ongoing response without additional treatment, and 19 patients (29%) relapsed without receiving additional therapy [43,47]. An association has been seen between early loss of B-cell aplasia with relapse. In patients with early loss of B-cell aplasia, if there is an available donor and the patient is in good functional status, early transplant is recommended. Long term follow-up is needed to better assess which patient’s CAR-T can be used as monotherapy.

CD22 CAR-T

Studies of CD22 showed a similar anti-leukemic effect and safety profile to CD19-CARs. In a phase I trial of CD22 BB.z CART in heavily pretreated relapsed/refractory patients, 12/21 (57%) of patients had a CR, with nine patients having a MRD response (NCT02315612) [48]. To further potentate the efficacy of CD22, CAR-T Bryostatin 1 has been seen to upregulate CD22 on leukemia cell lines and improve CART function and persistence [49].

Dual targeting CAR-T

Antigen-escape relapse after CD19 directed therapies is a major challenge, thus dual targeting of CD19 and CD22 is being developed. Bi-cistronic CAR-T that express CD19 and CD22 scFv simultaneously on every cell and mono- CARs that express CD19 and CD22 scFv separately have been developed as dual-target CAR-T cells. Phase 1 trials of different dual targeting CAR-T therapies are highlighted in Table 8.

CAR-T for T-ALL

Several challenges have been encountered in the development of CAR-T including disease heterogeneity, T-cell aplasia, fratricide, and increased side effects in T-ALL. There is a large amount of disease heterogeneity in T-ALL due to distinct stages when T-cell differentiation arrest occurs, making identifying a target difficult [50]. Furthermore, targets on T-lymphoblasts are likely to be on normal T-cells leading to a severe immunocompromised state and fratricide of CAR-T. Fratricide of the CAR-T product or the destruction of the CAR-T due to the target being on both the malignant T-cells and on the CAR-T, leads to decreased CAR-T expansion and persistence. CD3 and CD7 CAR-Ts are more prone to fratricide compared to other targets such as CD1a and CD5 [51,52]. Gene editing to decrease expression of the target antigen on the CAR-T is being studied [53,54] in addition to “off-the-shelf” CAR-T without the target antigen [55]. Preclinical efficacy has been shown in NK-CARs [56,57].

Challenges in CAR-T manufacturing

One of the challenges of CAR-T is manufacturing the product. For adequate collection of T-cells, it requires an absolute lymphocyte count ≥ 500 cells/μL or an absolute CD3 count ≥ 150 cells/μL. This is particularly challenging in heavily pre-treated patients due to poor bone marrow in patients with a higher cumulative dose of chemotherapy [58] and in younger patients due to their size. In the phase II study of tisagenlecleucel, eight patients did not receive the CAR-T infusion due to manufacturing related issues and another seven died before infusion [43,47]. Early collection is suggested for high risk patients; and gene-edited, universal CAR-T-cells are in development. Allogeneic CD19-CAR-T-cells successfully treated two infants with B-ALL using non–HLA-matched, universal, CAR19 (UCART19) T-cells manufactured from a healthy female donor [59].

Persistence of CAR

There have been several mechanisms proposed explaining why certain patients do not respond or&

References