Burkitt lymphoma (BL) is the most common tumor of non-Hodgkin’s lymphoma (NHL) in children and teenagers, accounting for approximately 40% (1). Due to good support with high-intensity chemotherapy regimens combined with rituximab, BL can be a truly curable pediatric cancer and is associated with improved outcomes, with survival rates higher than 90% (2). Nevertheless, the prognosis for pediatric patients with relapsed/refractory (r/r) BL remains poor, with an average overall survival rate of less than 30% (3), so improving the curative effect of therapy for these children should be the focus of future research. In recent years, chimeric antigen receptor T cell (CAR-T) therapy has developed rapidly in pediatric acute lymphoblastic leukemia and achieved excellent efficacy (4, 5). In addition, clinical trials have shown that CAR-T has clear efficacy for B-lineage lymphoma (6), including BL in children (7–9).

However, autologous CAR-T therapy might not be effective in BL patients because of T-cell dysfunction, and the biological characteristics of autologous T cells are also negatively impacted by the previous lines of treatment like chemotherapy (10). In the cases in which the production of a CAR-T cell product from autologous T cells has failed, allogeneic CAR-T can be attempted if there is a good HLA-matched donor.

Here, we report the first refractory BL case successfully treated with allogeneic anti-CD20 and anti-CD22 CAR-T therapy, which resulted in sustained complete remission (CR) and manageable cytokine release syndrome (CRS) and successfully bridged to conditioning-free peripheral blood stem cell transplantation (PBSCT).

Autologous CAR-T cell therapy can persist for a longer time and have better tumor-killing activity compared with allogeneic CAR-T because of the absence of the allogeneic reaction (11). Autologous CAR-T therapy has been extensively used in the treatment of hematological cancers, especially in B-lymphoid tumors (12). However, the successful manufacturing of CAR-T depends on the activity of autoimmune cells. Patients who repeatedly receive high-intense chemotherapy always fail to generate CAR-T cells (10). The ability to use cells from healthy donors, referred to as allogeneic CAR-T cells, could potentially address these issues. Although the difficulty of CAR-T cell preparation can be reduced, allogeneic approaches are associated with two major issues. First, the administered allogeneic T cells may cause life-threatening GVHD (13). Second, these allogeneic T cells may be rapidly eliminated by the host immune system, limiting their antitumor activity. Some strategies have been reported for administering allogeneic CAR-T cells, such as the use of virus-specific memory T cells, non-αβ T cells, gene editing with TCR deletion in αβ T cells, donor-derived allogeneic T cells in stem cell transplant recipients, or induced pluripotent stem cells (iPSCs) as a source of allogeneic CAR-T cells (14, 15).

Based on clinical experience, the ability of allogeneic CAR-T cells to eliminate tumor cells is dependent upon the initial expansion, duration of persistence, absence of GVHD, and the ability of the host immune system to reject these cells. It is possible to use T cells without processing as allogeneic CAR-T therapy if there have been well-matched donors. Therefore, we found a suitable donor and tried allogeneic CAR-T cell therapy. The child was in a state of severe immunodepression after several intense immunosuppressive treatments, which made the allogeneic CAR-T continue to be active in his body for more than 2 months ( Figure 2C ), and he achieved CR without acute GVHD. These results indicate that CAR-T cells derived from unedited lymphocytes from well-matched donors could be safe and have a long-term and effective killing effect on BL.

Due to the high tumor burden before CAR-T, the child developed severe CRS (Grade IV) with increased cytokines, persistent high fever, and decreased blood pressure. Although the tumor was gradually cleared after allogeneic CAR-T therapy, there were some side effects that may have been caused by CRS, such as pancytopenia and transfusion dependence. The result was consistent with our own experience and literature reports. Compared with leukemia patients, lymphoma patients with severe CRS after CAR-T tend to have longer pancytopenia and a more difficult recovery. Kai Rejeski (16) reported 12 cases of lymphoma in Europe with bone marrow failure after CAR-T who received autologous or allogeneic CD34 cell infusion, and granulocyte reconstitution was achieved in 92% of the patients, platelet reconstitution in 70%, and long-term survival was achieved in nearly half. Recently, the same author also put forward the concept of Immune Effector Cell Associated Hemato-Toxicity (ICAHT) following CAR-T therapy. The management of ICAHT can broadly be separated into an initial phase which aims to mitigate the risk of infections and/other complications, as well as a later phase that is initiated in case of persistent and/or therapy-refractory cytopenias (17). The possibility cannot be completely ruled out that bone marrow failure is caused by GVHD because of the T cell engraftment. For the severe bone marrow failure, the child received HSCT from the same donor 55 days after allogeneic CAR-T. Unlike traditional transplantation, the patient had severe bone marrow failure before transplantation, and nearly all the T cells in the patient after allogeneic CAR-T were from the donor, so we directly infused the donor cells without any conditioning. The neutrophil recovered 2 weeks after transplantation. If unedited allogeneic CAR-T therapy is selected, we need to be very vigilant and prepared for possible bone marrow failure. These results suggest that it is necessary to preserve lymphoma patients’ own stem cells or prepare for allogeneic hematopoietic stem cell transplantation before allogeneic CAR-T.

Graft-versus-host disease (GVHD) is a pathological process caused by the recognition and attack of donor T cells on host target organs (18). GVHD is the most common complication after allogeneic hematopoietic stem cell transplantation. With the application of allogeneic CAR-T technology, GVHD produced by allogeneic CAR-T has been a concern. In patients with relapse after allogeneic hematopoietic stem cell transplantation, donor-derived allogeneic CAR-T has been shown to have similar effects as autologous CAR-T in a progressively reestablished donor immune state (19), whereas clinical studies of allogeneic CAR-T from novel donors without in vitro editing are rare. In this case, due to severe immunosuppression after multiple rounds of chemotherapy and CAR-T, allogeneic CAR-T cell infusion rapidly expanded in vivo and maintained 99.16% of the donor T cells for a long period of time, which provided an immunotolerant environment for the engraftment of donor hematopoietic stem cells without conditioning. It has been reported that the risk of GVHD will be reduced if the host is in a state of high immune deficiency due to long-term seriously low immunity (20). In addition, some researchers have explored the mechanism by which allogeneic CD19 CAR-T cells mediate anti-lymphoma activity without significantly increasing the incidence of GVHD (21), and found that allogeneic CD19 CAR-T cells expressing CD28 costimulatory molecules undergo enhanced stimulation, leading to gradual loss of effector function and proliferation potential. Thus, the occurrence of GVHD was significantly reduced. The survival time of normal allogeneic CAR-T cells in vivo is about 1 month. Since CAR-T cells express CAR and TCR receptors, they are more likely to be activated and thus suffer from activation-induced cell death failure and apoptosis earlier, and are not likely to produce GVHD (20). Pan et al. (22) also reported that GVHD after allogeneic CAR-T from new donors was mild and very easy to control, which seemed to suggest the feasibility of allogeneic CAR-T prepared from T cells without editing treatment. Now, our experience with more than 20 haplo-identical donor CAR-T cases also suggests that there is little obvious acute GVHD (aGVHD) post unedited allogeneic CAR-T therapy (data not reported). Unfortunately, when the CAR-T cells in the child’s body were at a very low level ( Figure 2C ) and he did not experience CRS caused by CAR-T cells for a long time, it was most likely due to the early cessation of immunosuppressive therapy to control the severe infection and the lack of timely intervention when GVHD occurred; chronic GVHD developed and the patient to date still needs immunosuppressive therapy (IST) even with long-term complete remission. This suggests that close monitoring of GVHD is important.

Our patient was the first case with refractory/relapse BL who achieved complete remission after unedited allogeneic CAR-T cell treatment and bridged to condition-free HSCT successfully. We can conclude that HLA-matched allogeneic CAR-T therapy could be an innovative, effective, and safe treatment for those who fail to utilize their own cells. Close follow-up and GVHD monitoring are important.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving humans were approved by Shanghai children’s medical center. The studies were conducted in accordance with the local legislation and institutional requirements. Written informed consent for participation in this study was provided by the participants’ legal guardians/next of kin. Written informed consent was obtained from the minor(s)’ legal guardian/next of kin for the publication of any potentially identifiable images or data included in this article.

XY, JQ, and XH performed research and draft the manuscript; CJL, JZ, and JW performed the experiments and participated in the writing of the paper; CYL, XQ analyzed the results; BL, JC designed the research and approved the final manuscript.