'Off-the-shelf' allogeneic CAR T cells: development and challenges.

Autologous chimeric antigen receptor (CAR) T cells have changed the therapeutic landscape in haematological malignancies. Nevertheless, the use of allogeneic CAR T cells from donors has many potential advantages over autologous approaches, such as the immediate availability of cryopreserved batches for patient treatment, possible standardization of the CAR-T cell product, time for multiple cell modifications, redosing or combination of CAR T cells directed against different targets, and decreased cost using an industrialized process. However, allogeneic CAR T cells may cause life-threatening graft-versus-host disease and may be rapidly eliminated by the host immune system. The development of next-generation allogeneic CAR T cells to address these issues is an active area of research. In this Review, we analyse the different sources of T cells for optimal allogeneic CAR-T cell therapy and describe the different technological approaches, mainly based on gene editing, to produce allogeneic CAR T cells with limited potential for graft-versus-host disease. These improved allogeneic CAR-T cell products will pave the way for further breakthroughs in the treatment of cancer.

Correction to: Grading of cytokine release syndrome associated with the CAR T cell therapy tisagenlecleucel.

The original article contains several small errors. The errors & concurrent corrections are listed below [1].

Generation of a multi-antigen-directed immune response for durable control of acute lymphoblastic leukemia.

This corrects the article DOI: 10.1038/leu.2017.290.

Improved anti-leukemia activities of adoptively transferred T cells expressing bispecific T-cell engager in mice.

Despite the impressive clinical efficacy of T cells engineered to express chimeric antigen receptors (CAR-Ts), the current applications of CAR-T cell therapy are limited by major treatment-related toxicity. Thus, safer yet effective alternative approaches must be developed. In this study, we compared CD19 bispecific T-cell engager (BiTE)-transferred T cells that had been transfected by RNA electroporation with CD19 CAR RNA-transferred T cells both in vitro and in an aggressive Nalm6 leukemia mouse model. BiTEs were secreted from the transferred T cells and enabled both the transferred and bystander T cells to specifically recognize CD19(+) cell lines, with increased tumor killing ability, prolonged functional persistence, increased cytokine production and potent proliferation compared with the CAR-T cells. More interestingly, in comparison with CD3/CD28 bead-stimulated T cells, T cells that were expanded by a rapid T-cell expansion protocol (REP) showed enhanced anti-tumor activities for both CAR and BiTE RNA-electroporated T cells both in vitro and in a Nalm6 mouse model (P<0.01). Furthermore, the REP T cells with BiTE RNAs showed greater efficacy in the Nalm6 leukemia model compared with REP T cells with CAR RNA (P<0.05) and resulted in complete leukemia remission.

Toxicities of busulfan/melphalan versus carboplatin/etoposide/melphalan for high-dose chemotherapy with stem cell rescue for high-risk neuroblastoma.

The optimal autologous stem cell rescue (HDC-SCR) regimen for children with high-risk neuroblastoma (HR-NBL) is not defined. Carboplatin/etoposide/melphalan (CEM) is the current US standard; however, European data suggest busulfan/melphalan (Bu/Mel) may have less toxicity. Published data regarding toxicities associated with CEM and Bu/Mel are limited. We conducted a single-institution retrospective cohort study of children with HR-NBL who received CEM or Bu/Mel preparative regimens. Toxicity data were analyzed using χ(2) or Fisher's exact, Wilcoxon two-sample or log-rank tests. Sinusoidal obstruction syndrome (SOS) was observed in 7/44 CEM (15.9%) and 5/21 (24%) Bu/Mel patients (P=0.50). Median time to SOS was longer following Bu/Mel than CEM (20 versus 9 days, P=0.02). Pulmonary hypertension (PHTN) was observed in ~20% of children after Bu/Mel and none after CEM (P=0.01). CEM patients had more nephrotoxicity (P=0.001), packed red blood cell (P=0.02) and platelet transfusions (P=0.008), and days on maximum pain support (P=0.0007). Time to engraftment, length of stay, documented infection rates and HDC-SCR-related mortality were similar. Nephrotoxicity and resource utilization associated with cytopenias and mucositis were greater after CEM. Pulmonary toxicities were more severe after Bu/Mel, and increased vigilance for PHTN may be warranted, particularly in children with hypoxemia out of proportion to respiratory distress.

Risk factors and timing of relapse after allogeneic transplantation in pediatric ALL: for whom and when should interventions be tested?

We previously showed that minimal residual disease (MRD) detection pre-hematopoietic cell transplant (HCT) and acute GvHD (aGvHD) independently predicted risk of relapse in pediatric ALL. In this study we further define risk by assessing timing of relapse and the effects of leukemia risk category and post-HCT MRD. By multivariate analysis, pre-HCT MRD <0.1% and aGvHD by day +55 were associated with decreased relapse and improved event-free survival (EFS). Intermediate leukemia risk status predicted decreased relapse, and improved EFS and overall survival (OS). Patients with pre-HCT MRD ⩾0.1% who did not develop aGvHD compared with those with MRD <0.1% who did develop aGvHD had much worse survival (2 years EFS 18% vs 71%; P=0.001, 2 years OS 46 vs 74%; P=0.04). Patients with pre-HCT MRD <0.1% who did not experience aGvHD had higher rates of relapse than those who did develop aGvHD (40% vs 13%; P= 0.008). Post-HCT MRD led to a substantial increase in relapse risk (HR=4.5, P<0.01). Patients at high risk of relapse can be defined after transplant using leukemia risk category, presence of MRD pre or post HCT, and occurrence of aGvHD. An optimal window to initiate intervention to prevent relapse occurs between day +55 and +200 after HCT.

Allogeneic hematopoietic cell transplantation for neuroblastoma: the CIBMTR experience.

Although the role of autologous hematopoietic cell transplantation (auto-HCT) is well established in neuroblastoma (NBL), the role of allogeneic HCT (allo-HCT) is controversial. The Center for International Blood and Marrow Transplant Research conducted a retrospective review of 143 allo-HCT for NBL reported in 1990-2007. Patients were categorized into two different groups: those who had not (Group 1) and had (Group 2) undergone a prior auto-HCT (n=46 and 97, respectively). One-year and five-year OS were 59% and 29% for Group 1 and 50% and 7% for Group 2, respectively. Among donor types, disease-free survival (DFS) and OS were significantly lower for unrelated transplants at 1 and 3 years but not at 5 years post HCT. Patients in CR or very good partial response (VGPR) at transplant had lower relapse rates and better DFS and OS, compared with those not in CR or VGPR. Our analysis indicates that allo-HCT can cure some neuroblastoma patients, with lower relapse rates and improved survival in patients without a history of prior auto-HCT as compared with those patients who had previously undergone auto-HCT. Although the data do not address why either strategy was chosen for patients, allo-HCT after a prior auto-HCT appears to offer minimal benefit. Disease recurrence remains the most common cause of treatment failure.

A pilot study of tandem high-dose chemotherapy with stem cell rescue as consolidation for high-risk neuroblastoma: Children's Oncology Group study ANBL00P1.

Increasing treatment intensity has improved outcomes for children with neuroblastoma. We performed a pilot study in the Children's Oncology Group to assess the feasibility and toxicity of a tandem myeloablative regimen without TBI supported by autologous CD34-selected peripheral blood stem cells. Forty-one patients with high-risk neuroblastoma were enrolled; eight patients did not receive any myeloablative consolidation procedure and seven received only one. Two patients out of 41 (4.9%) experienced transplant-related mortality. CD34 selection was discontinued after subjects were enrolled due to serious viral illness. From the time of study enrollment, the overall 3-year EFS and OS were 44.8 ± 9.6% and 59.2 ± 9.2% (N=41). These results demonstrate that tandem transplantation in the cooperative group setting is feasible and support a randomized comparison of single vs tandem myeloablative consolidation with PBSC support for high-risk neuroblastoma.