CAR-T therapy has demonstrated a dramatic effect on r/r B-ALL patient with a high CR rate from 62–95.92%(3–10, 25). To overcome the drawback of single target CAR-T cells therapy, researchers combined CD19 and CD22 dual targets for a prolonged efficacy and low incidence of CD19− relapse(14, 15). In our study, we performed the tandem CD19/CD22 CAR-T cells in a large cohort to show its potent therapeutic benefit, and the moderate side effects for r/r B-ALL patients.
Tandem CD19/CD22 CAR-T cells have achieved robust remission for high-risk subtypes in our trials. CR rate is 100% and 40/47 (85.1%) patients got MRD−CR. Another unpublished study in our group demonstrated that tandem CAR-T cells obtains superior CR rate than single CD19 and sequential CD19/CD22 CAR-T cells therapy. In fact, the majority of anticipants in the trial accepted multi-line therapies previously, and were characterized by extremely high tumor burden, unfavorable genetic or molecular aberrations. For 21 refractory patients, they achieved CR1 owing to CAR-T therapy, which provide the opportunity for the next transplantation. The tandem dual targets CAR-T efficacy for high-risk B-ALL patients is still not clear. TP53 gene aberrations have been reported to be associated with worse survival. A cohort of 33 TP53 patients treated with CD19 CAR-T therapy show a lower CR rate than patients without mutation(26). In our center, 6 TP53 positive patients got MRD−CR which shows the great killing capability of dual targets CAR-T. Pre-transplant MRD negativity after CAR-T therapy could greatly improve the LFS and OS in patients with r/r B-ALL(27), which was also confirmed in our multivariable analysis related to LFS. As a result, we analyzed the factors associated with MRD−CR and found out Ph-like ALL patients would suffer a more dismal outcome. Consistent with recent reports, Ph-like ALL is a poor-risk subtype of B-ALL due to the high possibility of induction failure and dismal outcome(28). We treated 6 Ph-like ALL patients with CD19/CD22 CAR-T, all of them were resistant to TKIs and conventional chemotherapy. Though a half of them were MRD positive after CAR-T therapy, 4 of 6 patients have kept MRD−CR post bridging HSCT until now.
Dual targets CAR-T cells therapy have the potential to target an alternative antigen, besides CD19, so that it can mediate similarly potent antineoplastic effects and triumph over antigen loss(14). But the need for tandem CAR-T cells in clinical use were not clear so far. As such, we herein for the first time summarized the clinical trials of CD19 CAR-T cell therapy in a large cohort in Supplementary Table 2 and compared two different approaches. Our dual targets product demonstrated better CR rate and lower CD19− relapse rate than that in the majority CD19 CAR-T trials. In our cohort, we observed an unfortunate relapse in 12 patients after CAR-T therapy. The limitation of CAR-T persistence may account for the antigen positive relapse. Two of 12 patients were CD19−, and both of them have undertaken multiple lines therapy previously. We also concluded the recent clinical trials of CD19/CD22 CAR-T cell therapy (Supplementary Table 3). Although the sequential and cocktail CAR targeting of dual antigens resulted in clinical benefit, a high relapse rate was observed. Wang et al(18) reported the CD19/CD22 cocktail CAR-T cells therapy for 49 r/r B-ALL patients, 24 patients thereafter suffered a relapse, with one patient CD19−CD22dim relapse. Simultaneous multi-specific targeting may be a more effective approach to enhance the durability of CAR induced remission in B-ALL. Recent published reports detailing bispecific CAR-T therapy were in a relatively small sample size(20, 21, 29–31). One out of 6 patients, treated with tandem CD19/CD22 CAR-T cells, was found the recurrence of CD19− and CD22dim blasts in a published study(21). As described before, mechanisms leading to loss of CD19 expression varies a lot, such as trogocytosis(15), lineage switch(32, 33), alternative splicing(34) and acquired mutations(35). For these patients who relapsed, CD20 or CD38 may be in consideration for next induction therapy. CD38 CAR-T cells have been performed in 3 relapsed ALL patients in the cohort, which shown high effectiveness. We proposed that the multi-targets immunotherapy may diminish the likelihood of tumor escape and more mechanisms underlying are need to explore.
Bridging allo-HSCT after tandem CD19/CD22 CAR-T cells therapy is an efficient and relatively safe way that prolongs LFS and reduces the relapse risk. An increasing number of clinical trials have compared the outcomes of patients with and without consolidative allo-HSCT after CD19 CAR-T therapy. A recent meta-analysis identified 19 clinical trials with 690 patients, and found that bridging HSCT was beneficial for OS, the relapse rate, and LFS(36). The application of allo-HSCT is mature in the area of hematological therapy, and there are no considerable technical obstacles at most transplantation centers. However, the role of consolidative HSCT in dual targets CAR-T therapy is still not clear. Here, we found that patients bridging allo-HSCT after CAR-T therapy, experienced more survival advantage than patients without allo-HSCT. Also, the risk of leukemia recurrence was found to be lower in our research. The timing of transplantation should be considered. A longer bridging time may deteriorate the long-term outcome for the limit persistence of CAR-T cells(37). The majority of patients in our study undertaken the consolidative allo-HSCT in 3 months post CAR-T cells infusion, without another chemotherapy during the window period.
For patients relapsed after allo-HSCT, the role of second transplantation is explicit. One patient in our study, with BCR/ABL positive and T315I mutation, achieved molecular CR through CD19/CD22 CAR-T therapy when he relapsed after first allo-HSCT. Five months post CAR-T, he accepted the second unrelated donor transplantation and died in next 5 month of abdominal hemorrhage. The team of Beijing Boren Hospital reported 21 relapsed patients with CD19 and CD22 sequential CAR-T cells infusion. Fourteen cases remained in CR without more treatment and one patient withdrew to undergo a second transplantation21. A second allo-HSCT is associated with multiple factors, such as regimen intensity, the donor selection and GVHD prophylaxis(38). In brief, researchers have to optimize the second transplantation strategy. More studies are needed to determine whether relapsed patients with an allo-HSCT history can benefit from second allo-HSCT after CAR-T therapy.
Taken together, our results indicate that tandem CD19/CD22 CAR-T cells, with a trend toward reduce the CD19− relapse rate, are safety and highly effective in inducing CR for high-risk B-ALL patients. The consolidative allo-HSCT can provide long-term durable disease control in these patients.