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CD22 (Siglec 2) is a receptor predominantly restricted to B cells. It was initially characterized over 30 years ago and named \"CD22\" in 1984 at the 2nd International workshop in Boston (1). Several excellent reviews have detailed CD22 functions, CD22-regulated signaling pathways and B cell subsets regulated by CD22 or Siglec G (2-4). This review is an attempt to highlight recent and possibly forgotten findings. We also describe the role of CD22 in autoimmunity and the great potential for CD22-based immunotherapeutics for the treatment of autoimmune diseases such as systemic lupus erythematosus (SLE).

Background Despite the impressive complete remission (CR) induced by CD19 CAR-T cell therapy in B-ALL, the high rate of complete responses is sometimes limited by the emergence of CD19-negative leukemia. Bispecific CAR-modified T cells targeting both CD19 and CD22 may overcome the limitation of CD19-negative relapse. Methods We here report the design of a bispecific CAR simultaneous targeting of CD19 and CD22. We performed a phase 1 trial of bispecific CAR T cell therapy in patients with relapsed/refractory precursor B-ALL at a dose that ranged from 1.7 × 10 6 to 3 × 10 6 CAR T cells per kilogram of body weight. Results We demonstrate bispecific CD19/CD22 CAR T cells could trigger robust cytolytic activity against target cells. MRD-negative CR was achieved in 6 out of 6 enrolled patients. Autologous CD19/CD22 CAR T cells proliferated in vivo and were detected in the blood, bone marrow, and cerebrospinal fluid. No neurotoxicity occurred in any of the 6 patients treated. Of note, one patient had a relapse with blast cells that no longer expressed CD19 and exhibited diminished CD22 site density approximately 5 months after treatment. Conclusion In brief, autologous CD19/CD22 CAR T cell therapy is feasible and safe and mediates potent anti-leukemic activity in patients with relapsed/refractory B-ALL. Furthermore, the emergence of target antigen loss and expression downregulation highlights the critical need to anticipate antigen escape. Our study demonstrates the reliability of bispecific CD19/CD22 CAR T cell therapy in inducing remission in adult patients with relapsed/refractory B-ALL. Trial registration ClinicalTrials.gov identifier: NCT03185494 .

Despite impressive progress, more than 50% of patients treated with CD19-targeting chimeric antigen receptor T cells (CAR19) experience progressive disease. Ten of 16 patients with large B cell lymphoma (LBCL) with progressive disease after CAR19 treatment had absent or low CD19. Lower surface CD19 density pretreatment was associated with progressive disease. To prevent relapse with CD19 − or CD19 lo disease, we tested a bispecific CAR targeting CD19 and/or CD22 (CD19-22.BB.z-CAR) in a phase I clinical trial ( NCT03233854 ) of adults with relapsed/refractory B cell acute lymphoblastic leukemia (B-ALL) and LBCL. The primary end points were manufacturing feasibility and safety with a secondary efficacy end point. Primary end points were met; 97% of products met protocol-specified dose and no dose-limiting toxicities occurred during dose escalation. In B-ALL ( n  = 17), 100% of patients responded with 88% minimal residual disease-negative complete remission (CR); in LBCL ( n  = 21), 62% of patients responded with 29% CR. Relapses were CD19 −/lo in 50% (5 out of 10) of patients with B-ALL and 29% (4 out of 14) of patients with LBCL but were not associated with CD22 −/lo disease. CD19/22-CAR products demonstrated reduced cytokine production when stimulated with CD22 versus CD19. Our results further implicate antigen loss as a major cause of CAR T cell resistance, highlight the challenge of engineering multi-specific CAR T cells with equivalent potency across targets and identify cytokine production as an important quality indicator for CAR T cell potency. Bispecific CAR T cells targeting CD19 and CD22 exhibit clinical activity and low toxicity in patients with large B cell lymphoma and B cell acute lymphoblastic leukemia, with relapses associated with loss of CD19 but not CD22.

New therapies are needed for patients with Hodgkin or non-Hodgkin lymphomas that are resistant to standard therapies. Indeed, unresponsiveness to standard chemotherapy and relapse after autologous stem-cell transplantation are indicators of an especially poor prognosis. Chimeric antigen receptor (CAR) T cells are emerging as a novel treatment modality for these patients. Clinical trial data have demonstrated the potent activity of anti-CD19 CAR T cells against multiple subtypes of B-cell lymphoma, including diffuse large-B-cell lymphoma (DLBCL), follicular lymphoma, mantle-cell lymphoma, and marginal-zone lymphoma. Importantly, anti-CD19 CAR T cells have impressive activity against chemotherapy-refractory lymphoma, inducing durable complete remissions lasting >2 years in some patients with refractory DLBCL. CAR-T-cell therapies are, however, associated with potentially fatal toxicities, including cytokine-release syndrome and neurological toxicities. CAR T cells with novel target antigens, including CD20, CD22, and κ-light chain for B-cell lymphomas, and CD30 for Hodgkin and T-cell lymphomas, are currently being investigated in clinical trials. Centrally manufactured CAR T cells are also being tested in industry-sponsored multicentre clinical trials, and will probably soon become a standard therapy. Herein, we review the clinical efficacy and toxicity of CAR-T-cell therapies for lymphoma, and discuss their limitations and future directions with regard to toxicity management, CAR designs and CAR-T-cell phenotypes, conditioning regimens, and combination therapies.

Fry et al . report the first results from a human trial of a CD22-directed chimeric antigen receptor (CAR) T cell therapy providing evidence of efficacy in the treatment of pre–B cell acute lymphoblastic leukemia that is immunotherapy-naive or resistant to CD19-directed CAR T cells. Chimeric antigen receptor (CAR) T cells targeting CD19 mediate potent effects in relapsed and/or refractory pre–B cell acute lymphoblastic leukemia (B-ALL), but antigen loss is a frequent cause of resistance to CD19-targeted immunotherapy. CD22 is also expressed in most cases of B-ALL and is usually retained following CD19 loss. We report results from a phase 1 trial testing a new CD22-targeted CAR (CD22-CAR) in 21 children and adults, including 17 who were previously treated with CD19-directed immunotherapy. Dose-dependent antileukemic activity was observed, with complete remission obtained in 73% (11/15) of patients receiving ≥1 × 10 6 CD22-CAR T cells per kg body weight, including 5 of 5 patients with CD19 dim or CD19 − B-ALL. Median remission duration was 6 months. Relapses were associated with diminished CD22 site density that likely permitted CD22 + cell escape from killing by CD22-CAR T cells. These results are the first to establish the clinical activity of a CD22-CAR in B-ALL, including leukemia resistant to anti-CD19 immunotherapy, demonstrating potency against B-ALL comparable to that of CD19-CAR at biologically active doses. Our results also highlight the critical role played by antigen density in regulating CAR function.

Treatment with CD19 or CD22-targeted chimeric antigen receptor-engineered T (CD19/CD22 CAR-T) cells achieve complete responses in 60–90% of adults and children with refractory or relapsed (R/R) acute lymphoblastic leukemia (ALL). This led to the approval of tisagenlecleucel (Kymriah) by the FDA and several European regulatory agencies in ALL patients up to 25 years of age. Although CAR T-cell therapy is likely to transform the ALL therapeutic landscape, its development and wide dissemination have been impacted by the occurrence of significant toxicities; namely, cytokine release syndrome (CRS) and Immune effector cell-Associated Neurotoxicity Syndrome (ICANS) have been reported at higher rates in ALL patients compared to other B cell malignancies, particularly in the adult population. Here, we review recent data suggesting a significant proportion of ALL patients are at risk of developing severe, sometimes life-threatening, CRS, and ICANS after CD19 and CD22 CAR T-cell therapy. After describing the key clinical and laboratory features of severe CRS and ICANS, we explore the disease and treatment-related factors that may predict the severity of these toxicities. Last, we review strategies under investigation in the prophylactic and therapeutic settings to improve the safety of CAR T-cells for ALL.

Chimeric antigen receptor (CAR) T cells targeting CD19 or CD22 have shown remarkable activity in B cell acute lymphoblastic leukemia (B-ALL). The major cause of treatment failure is antigen downregulation or loss. Dual antigen targeting could potentially prevent this, but the clinical safety and efficacy of CAR T cells targeting both CD19 and CD22 remain unclear. We conducted a phase 1 trial in pediatric and young adult patients with relapsed or refractory B-ALL ( n  = 15) to test AUTO3, autologous transduced T cells expressing both anti-CD19 and anti-CD22 CARs (AMELIA trial, EUDRA CT 2016-004680-39). The primary endpoints were the incidence of grade 3–5 toxicity in the dose-limiting toxicity period and the frequency of dose-limiting toxicities. Secondary endpoints included the rate of morphological remission (complete response or complete response with incomplete bone marrow recovery) with minimal residual disease-negative response, as well as the frequency and severity of adverse events, expansion and persistence of AUTO3, duration of B cell aplasia, and overall and event-free survival. The study endpoints were met. AUTO3 showed a favorable safety profile, with no dose-limiting toxicities or cases of AUTO3-related severe cytokine release syndrome or neurotoxicity reported. At 1 month after treatment the remission rate (that is, complete response or complete response with incomplete bone marrow recovery) was 86% (13 of 15 patients). The 1 year overall and event-free survival rates were 60% and 32%, respectively. Relapses were probably due to limited long-term AUTO3 persistence. Strategies to improve CAR T cell persistence are needed to fully realize the potential of dual targeting CAR T cell therapy in B-ALL. Bicistronic CAR T cells targeting CD19 and CD22 exhibit clinical activity and low toxicity in pediatric and young adult patients with B cell acute lymphoblastic leukemia, with relapses associated with limited CAR T cell persistence.

Chimeric antigen receptor (CAR) T-cells targeting CD19 demonstrate remarkable efficacy in treating B-lineage acute lymphoblastic leukemia (BL-ALL), yet up to 39% of treated patients relapse with CD19(−) disease. We report that CD19(−) escape is associated with downregulation, but preservation, of targetable expression of CD20 and CD22. Accordingly, we reasoned that broadening the spectrum of CD19CAR T-cells to include both CD20 and CD22 would enable them to target CD19(−) escape BL-ALL while preserving their upfront efficacy. We created a CD19/20/22-targeting CAR T-cell by coexpressing individual CAR molecules on a single T-cell using one tricistronic transgene. CD19/20/22CAR T-cells killed CD19(−) blasts from patients who relapsed after CD19CAR T-cell therapy and CRISPR/Cas9 CD19 knockout primary BL-ALL both in vitro and in an animal model, while CD19CAR T-cells were ineffective. At the subcellular level, CD19/20/22CAR T-cells formed dense immune synapses with target cells that mediated effective cytolytic complex formation, were efficient serial killers in single-cell tracking studies, and were as efficacious as CD19CAR T-cells against primary CD19(+) disease. In conclusion, independent of CD19 expression, CD19/20/22CAR T-cells could be used as salvage or front-line CAR therapy for patients with recalcitrant disease.

Despite worldwide promising clinical outcome of CD19 CAR-T therapy, relapse after this therapy is associated with poor prognosis and has become an urgent problem to be solved. We conducted a CD22 CAR T-cell therapy in 34 relapsed or refractory (r/r) B-ALL pediatric and adult patients who failed from previous CD19 CAR T-cell therapy. Complete remission (CR) or CR with incomplete count recovery (CRi) was achieved in 24 of 30 patients (80%) that could be evaluated on day 30 after infusion, which accounted for 70.5% of all 34 enrolled patients. Most patients only experienced mild cytokine-release syndrome and neurotoxicity. Seven CR patients received no further treatment, and 3 of them remained in remission at 6, 6.6, and 14 months after infusion. Eleven CR patients were promptly bridged to transplantation, and 8 of them remained in remission at 4.6 to 13.3 months after transplantation, resulted in 1-year leukemia-free survival rate of 71.6% (95% CI, 44.2–99.0). CD22 antigen loss or mutation was not observed to be associated with relapsed patients. Our study demonstrated that our CD22 CAR T-cells was highly effective in inducing remission in r/r B-ALL patients, and also provided a precious window for subsequent transplantation to achieve durable remission.

While CD19-directed chimeric antigen receptor (CAR) T cells can induce remission in patients with B cell acute lymphoblastic leukemia (ALL), a large subset relapse with CD19 − disease. Like CD19, CD22 is broadly expressed by B-lineage cells and thus serves as an alternative immunotherapy target in ALL. Here we present the composite outcomes of two pilot clinical trials ( NCT02588456 and NCT02650414 ) of T cells bearing a 4-1BB-based, CD22-targeting CAR in patients with relapsed or refractory ALL. The primary end point of these studies was to assess safety, and the secondary end point was antileukemic efficacy. We observed unexpectedly low response rates, prompting us to perform detailed interrogation of the responsible CAR biology. We found that shortening of the amino acid linker connecting the variable heavy and light chains of the CAR antigen-binding domain drove receptor homodimerization and antigen-independent signaling. In contrast to CD28-based CARs, autonomously signaling 4-1BB-based CARs demonstrated enhanced immune synapse formation, activation of pro-inflammatory genes and superior effector function. We validated this association between autonomous signaling and enhanced function in several CAR constructs and, on the basis of these observations, designed a new short-linker CD22 single-chain variable fragment for clinical evaluation. Our findings both suggest that tonic 4-1BB-based signaling is beneficial to CAR function and demonstrate the utility of bedside-to-bench-to-bedside translation in the design and implementation of CAR T cell therapies. A bedside-to-bench analysis identifies single-chain variable fragment linker length as an important component of chimeric antigen receptor (CAR) structure and suggests that, in contrast to CD28-based CAR T cells, tonic signaling can be beneficial for 4-1BB-based CAR T cell function.