A Report on Lineage Switch at Relapse of CD19 CAR-T Therapy for Philadelphia Chromosome-Positive B-Precursor Acute Lymphoblastic Leukemia
This study presents a unique case of Philadelphia chromosome-positive B-acute lymphoblastic leukemia (Ph+ B-ALL) that underwent a lineage switch to acute myeloid leukemia (AML) following CD19 chimeric antigen receptor (CAR)-modified T (CAR-T) cell therapy. The case highlights a rare but significant phenomenon in the context of CAR-T therapy, which has profound implications for understanding treatment resistance and disease biology.
The patient, a 46-year-old woman, was admitted to the hospital on January 24, 2014, with a 1-month history of chest pain. Initial laboratory examinations revealed a white blood cell count of 12.01 x 10^9/L, hemoglobin of 92 g/L, and platelet count of 47 x 10^9/L. Bone marrow (BM) smears showed a massive infiltrate of blast cells (95.2%), and flow cytometry (FCM) indicated that blast cells accounted for 66.3% of the sample. These blast cells were positive for CD34, CD10, CD19, CD20, CD22, CD38, and human leukocyte antigen DR (HLA-DR). Karyotype analysis revealed no mitotic phase, but fluorescence in situ hybridization (FISH) demonstrated a positive Philadelphia chromosome (BCR-ABL fusion gene). Quantitative real-time polymerase chain reaction (qRT-PCR) detected a positive BCR-ABL p190 transcript (184.1%), leading to a diagnosis of Ph+ B-ALL.
The patient was treated with standard B-ALL induction chemotherapy, including rituximab, vincristine, daunorubicin, cyclophosphamide, and prednisone, combined with oral dasatinib (100 mg/day) starting on January 27, 2014. After the first chemotherapy cycle, BM aspiration indicated complete remission (CR), and the BCR-ABL fusion gene was negative. Consolidation therapy with cyclophosphamide, cytarabine, and 6-mercaptopurine was initiated on March 20, 2014, followed by six cycles of consolidation therapy between April and November 2014. Maintenance therapy with oral methotrexate (7.5 mg/week) and 6-mercaptopurine (25 mg/day) was then administered.
Unfortunately, on March 21, 2016, BM and FCM suggested a relapse of ALL, and CD19-directed CAR-T therapy was introduced. The patient was treated with rituximab, cyclophosphamide, vincristine, and prednisone to reduce tumor burden. BM showed CR on April 7, 2016. Lymphodepleting chemotherapy with the FC regimen (fludarabine 37 mg, days 1–3; cyclophosphamide 370 mg, days 1–3) was started on April 8, 2016. A total of 3 x 10^6 engineered CD19-directed CAR-T cells were administered on April 13, 2016. The patient experienced a low fever, which resolved with anti-infection treatment, and she was discharged half a month later. BM examinations over the next three years showed no relapse.
In May 2019, the patient presented with fatigue. BM aspirate indicated 88% myeloid progenitors. Karyotype analysis revealed a normal karyotype, and qRT-PCR detected a negative BCR-ABL transcript. FCM demonstrated that abnormal myeloblasts expressed CD34, CD13, CD33, CD38, CD117, CD15, and HLA-DR. Next-generation sequencing showed a FLT3-ITD mutation (p.F590delinsLELGSSDNEYF; variant allele fraction 21.99%) and a paired box gene 5 (PAX5) single nucleotide polymorphism (SNP) (p.T264I; variant allele fraction 99.94%). The patient was diagnosed with secondary AML.
From May 22, 2019, the patient was treated with decitabine in combination with low-dose cytarabine, aclarubicin, and granulocyte colony-stimulating factor (DCAG) as induction chemotherapy. Subsequent four cycles of DCAG consolidation therapy were performed in July, August, October, and November 2019. BM examination showed sustained CR, and FCM indicated no minimal residual disease. Neither the FLT3-ITD mutation nor the PAX5 SNP was detected by next-generation sequencing in November 2019. The patient remains in follow-up.
Lineage switch after CAR-T cell infusion is a rare but documented phenomenon. According to the literature, lineage switch has been described in four cases of B-ALL, including three patients with mixed lineage leukemia (MLL) rearrangement and one pediatric patient with TCF3-ZNF384 fusion. Lineage switch was also reported in murine models bearing E2A-PBX1 leukemia. The characteristics of historically reported cases, including the present case, are summarized in Table 1. It was found that phenotype transformation often occurs in childhood leukemia with MLL rearrangement. The five patients (literature reported and ours) developed lineage switch at 1, 1, 36, 16, and 36 months after CAR-T therapy, respectively. All three patients with MLL rearrangement had severe or mild cytokine release syndrome with high serum concentrations of IL-6 and other cytokines after CAR-T infusion. Regarding the management strategy after lineage transformation, three cases were treated with AML induction regimen, among which one received hematopoietic stem-cell transplantation and one with unclear treatment. However, the prognosis of the reported cases was extremely poor, and they died shortly after conversion. After transforming into AML, our patient achieved CR in one course of DCAG regimen chemotherapy treatment. The gene mutation disappeared after four courses of chemotherapy, and the patient is still in CR.
Lineage switch is a special type of post-CAR relapse, and several possible mechanisms have been proposed to explain this phenomenon after CD19-directed treatment. However, the exact mechanism remains unclear. Using murine models, Jacoby et al. supported that lineage switch depends on the genetic oncogenic driver. It was indicated that the absence of CD19 antigen epitope alone cannot drive the lineage conversion, whereas the deletion of PAX5 (important B-cell regulatory transcription factors) is associated with the myeloid lineage switch of B-ALL. One of its crucial functions is to repress FLT3 (a potential regulator of hematopoietic stem cells) transcription in B-cell progenitors. Besides, PAX5 can up-regulate B-cell-related genes, which is necessary for B-cell commitment and can inhibit myeloid cell proliferation by preventing the response of B cells to myeloid growth factors. In addition, Maeda et al. found that CD19+ B cells and more primitive B-lymphoid progenitors were more likely to be lost with the increase of IL-6 level. IL-6 can promote uncommitted progenitor cells to express Id1 transcription factor, which can inhibit lymphocyte proliferation and improve BM hematopoiesis. All three patients in Table 1 with MLL rearrangement presented with severe or mild cytokine release syndrome showed high serum concentrations of IL-6 and other cytokines after CAR-T cells infusion, further suggesting that cytokines may play a vital role in lineage switch. Our case described here was special in that FLT3-ITD mutation and PAX5 SNP during transformation was detected, which may be one of the reasons for her transformation.
In the present case, the interval between exposure to multidrug chemotherapy including cyclophosphamide and AML relapse was 5 years and 4 months. Thus, the possibility cannot be ruled out that AML was secondary to chemotherapy drugs. Exogenous factors, such as chemotherapy, or endogenous factors, such as acquired chromosome abnormalities, can change the differentiation process of leukemic cells, resulting in phenotypic transformation during relapse. On the one hand, chemotherapy seems to eliminate the evident leukemia clones at diagnosis, resulting in the amplification of subclones for different phenotypes. On the other hand, drug-induced changes in the original clone may amplify or inhibit the differentiation process, thus, the phenotypic switch is possible.
In conclusion, lineage switch after CD19-directed therapy is a specific mechanism of CAR resistance, with leukemic cells switching from one cell line to another after complete phenotypic alteration, and usually concerns patients with MLL rearrangement. Although there are some hypotheses, the clear mechanism of lineage transformation is still unknown. Further studies are required to design optimal treatment and elucidate the mechanism of lineage switch.
doi.org/10.1097/CM9.0000000000000962
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