CONFLICT of INTEREST
All authors declare that they have no conflict of interest.
DATA AVAILABILITY
STATEMENT
The data that support the findings of this study are available from the
corresponding author upon reasonable request.
CLINICAL TRIAL REGISTRATION NO:
ChiCTR2000038532
Text word count: 1051 words
The number of figures: 1
The number of supplemental tables: 3
Abstract words: 104 words
To the Editor:
Mixed phenotype acute leukemia (MPAL) is a relatively rare and
heterogeneous group of diseases, which account for 2-5% of
leukemia.1 These cases are partitioned according to
the lineage mix they display, i.e, as B/myeloid, T/myeloid, and rare
types including triple lineage or B/T co-expression.2MPAL is at higher risk of induction failure with a poor prognosis and an
event-free survival (EFS) rate of less than 50% in children for the
reason that mixed-phenotype leukemic stem cells are chemo-resistant
owing to slow cell replication.3, 4 So far, no optimal
treatment regimens have been established for these patients. Despite
CD19 chimeric antigen cell receptor (CAR T) therapy has demonstrated
remarkable efficacy for B-cell malignancies,5, 6clinical benefit varies among different disease types. A previous study
reported that B-ALL patients had a higher response rate (93%) than CLL
patients (62%),7 which indicates that even if CD19
expression is at a comparable level, the response sensitivity might be
quite different. Nowadays, there is still no specific report on CAR
T-cell therapy for refractory/relapsed (r/r) MPAL patients. Due to above
considerations, we are interested to know whether CD19 CAR T cells can
eradicate MPAL leukemia blasts and whether MAPL patients can benefit
from CD19 CAR T cell therapy. Consequently, we carried out a study and
reported the safety and efficacy of CD19 CAR T therapy for r/r MPAL
patients (ChiCTR2000038532).
5 patients diagnosed as MPAL in 2019 were enrolled in this study. One
patient was primary refractory disease and the other four patients had a
second relapse. Patient 2, patient 3 and patient 5 displayed B/Myeloid
bi-phenotype, patient 1 had a triple lineage (T/B/Myeloid) phenotype,
whereas patient 4 had a T/Myeloid phenotype with CD19 aberrantly
expression. In addition, patient 2 had the extramedullary disease (EMDs)
with multiple sites, and patient 1 once previously underwent allogeneic
hematopoietic stem cell transplantation (allo-HSCT). All patients had no
central nervous system leukemia (CNSL) and all of them had bright CD19
expression on malignant B cells as examined by FCM. Detailed patient
characteristics are summarized in Table S1.
Chemotherapy regimen before CAR cell infusion were listed in Table S1.
Between May and September in 2019, all the patients underwent
fludarabine (30
mg/m2 per day) and cyclophosphamide (250
mg/m2 per day) lymphodepleting chemotherapy for 3
consecutive days as described before.8 Subsequently,
the patients received CAR T cells targeting CD19. The transduction
efficiencies ranged from 12 to 67.5%. The dose was
3◊105/kg of body weight. Dynamic CAR T expansion in
peripheral blood (PB) was monitored at certain time intervals. All the
patients underwent bone marrow
(BM) biopsy examination and radiology studies on the day
30th following the cell infusion to determine the
response and remission status.
As shown in Figure 1A, CAR T cells showed an obvious expansion in 4 of 5
patients and peaked around day 10 or 11 in PB after infusion. With the
expansion of CAR T cells, patient 1, patient 2 and patient 3 obtained
FCM-MRD-negative CR on day 30 after infusion judged by flow cytometry.
Wright-Giemsa staining also suggested that leukemia blasts disappeared
in bone marrow on day 30 after infusion in patient 2 (Figure 1C)
Repeated PET/CT showed no evidence of abnormal FDG uptake compared to
initial scans in patient 2 (Figure 1B), suggesting his multiple EMD
lesions were also eradicated after CAR-T cell infusion. Notably, CAR T
cells in patient 4 couldn’t successfully expanded, which might be
associated with her T cell’s malignancies. She developed a serious
pleural effusion on day 25 after CAR T infusion. MRD-FCM analysis showed
that 94.09% of the nucleated cells in pleural effusion and 86.52% of
the nucleated cells in the peripheral blood (PB) were
CD7+CD19- cells, which were almost
malignant T lymphocytes, suggesting CAR T cells couldn’t control
leukemia progression. With the increase of the leukemia blasts burden,
ascities, pericardiac effusion, pulmonary infection and septicemia also
appeared one after another. Finally, this patient died on day 27 after
CAR T infusion. Interestingly, although patient 5 had a remarkable
expansion of CAR T cells, the leukemia blasts were non-responsive to the
infusion. The reasons were unclear at this point.
As results, CR rate of 60% (3/5) was achieved among these 5 patients.
Although the CR rate was seemingly lower than the previously reported CR
rate in r/r B-ALL (≥90%) patients, it is still significant for the r/r
MPAL patients, especially when there is no other optimal treatment
available.
Meanwhile, we observed mild adverse events associated with associated
with CD19 CAR T therapy. As shown in Figure 1D, with the expansion of
CAR T cells, plasma IL10 and IFNγ both elevated, which was consistent
with our previous findings.9 Due to the mild cytokine
release, patient 2 and patient 5 had grade 1 CRS manifested by fever,
dizziness and slight fatigue, which was well managed with supportive
care and dexamethasone. Neurotoxicity was not observed in any of these
patients (Table S2). Serum CRP in patient 2 increased to 29.91 mg/L on
day 9 after CAR T infusion, and G and GM experiments were positive,
which all suggested fungi infection might have occurred. Accordingly,
Lynaiamine and Bispycin B were given for anti-infection.
No other adverse events were
observed during the treatment.
Once achieved CR,patient 1, patient 2 and patient 3
were proceed to allo-HSCT on day
46, 59 and 53 after infusion, respectively (Table S3). Although the
blasts were not completely eradicated, patient 5 still received
allo-HSCT on day 48 after infusion. The 2-year Fellow-up data showed
that patient 1 and patient 2 both remained CR till August 2021. Notably,
although Patient 5 couldn’t achieve CR after CD19 CAR T therapy, she
achieved CR through all-HSCT and remained CR till the last follow-up.
Unfortunately, patient 3 died of serious infection shock 5 months after
allo-HSCT.
In summary, this study showed that despite the CR rate is lower compared
with those B-ALL patients, the majority of refractory/relapsed MPAL
patients with CD19 expression still can benefit from CD19 CAR T cell
therapy. In addition, these patients maintain a better leukemia free
survival (LFS) after bridging to HSCT following CAR T treatment, which
raised a new therapeutic strategy to these r/r MPAL patients. It should
also be noted that only a small number of patients were enrolled in this
study, more cases and further studies are needed to verify these
findings.