Modulation of Target Antigen Density Improves CAR T-cell Functionality and Persistence

Abstract

Purpose: Chimeric antigen receptor T-cell (CART) therapy targeting CD22 induces remission in 70% of patients with relapsed/refractory acute lymphoblastic leukemia (ALL). However, the majority of post-CD22 CART remissions are short and associated with reduction in CD22 expression. We evaluate the implications of low antigen density on the activity of CD22 CART and propose mechanisms to overcome antigen escape. Experimental Design: Using ALL cell lines with variable CD22 expression, we evaluate the cytokine profile, cytotoxicity, and in vivo CART functionality in the setting of low CD22 expression. We develop a high-affinity CD22 chimeric antigen receptor (CAR) as an approach to improve CAR sensitivity. We also assess Bryostatin1, a therapeutically relevant agent, to upregulate CD22 and improve CAR functionality. Results: We demonstrate that low CD22 expression negatively impacts in vitro and in vivo CD22 CART functionality and impairs in vivo CART persistence. Moreover, low antigen expression on leukemic cells increases na€ ve phenotype of persisting CART. Increasing CAR affinity does not improve response to low-antigen leukemia. Bryostatin1 upregulates CD22 on leukemia and lymphoma cell lines for 1 week following single-dose exposure, and improves CART functionality and in vivo persistence. While Bryostatin1 attenuates IFNg production by CART, overall in vitro and in vivo CART cytotoxicity is not adversely affected. Finally, administration of Bryostain1 with CD22 CAR results in longer duration of in vivo response. Conclusions: We demonstrate that target antigen modulation is a promising strategy to improve CD22 CAR efficacy and remission durability in patients with leukemia and lymphoma. See related commentary by Guedan and Delgado, p. 5188

Results from an international phase 2 study of the anti‐CD22 immunotoxin moxetumomab pasudotox in relapsed or refractory childhood B‐lineage acute lymphoblastic leukemia

“…Possibilities include combination with azacytidine, which may improve its antitumor effect, 27 or with bryostatin1, which might increase the efficacy of moxetumomab pasudotox by upregulation of CD22 expression. 28 In conclusion, while the risk-benefit profile did not support progressing to phase 3 evaluation, these data demonstrate that moxetumomab pasudotox is an agent with some activity against precursor B-ALL. Given the FDA approval of this agent in adults with HCL and an emerging population of patients in need of effective CD22-targeted therapies, further study of this agent to optimize response rates and tolerability in precursor B-ALL could be considered.…”

“…Combining moxetumomab pasudotox with other agents to potentially enhance activity is another strategy. Possibilities include combination with azacytidine, which may improve its antitumor effect, or with bryostatin1, which might increase the efficacy of moxetumomab pasudotox by upregulation of CD22 expression …”

Immunobiology of chimeric antigen receptor T cells and novel designs

“…This principle has also been seen in TCRs targeting low site density pMHC; where increased TCR affinity allowed for enhanced responses against low antigen as long as affinity was low enough to allow for fast off‐rates and serial triggering, In contrast, a study of multiple affinity‐modified variants of a CD123 CAR demonstrated that neither increasing or decreasing the affinity of the CAR significantly altered the killing of target cells . Similarly, T cells engineered to express a high‐affinity variant of the CD22 CAR did not demonstrate improved efficacy against B‐ALL with low CD22 expression when compared to the standard affinity CD22 CAR . Given the mixed results of the effect of affinity on the antigen sensitivity of CAR T cells, it is possible that the role of affinity may differ from CAR to CAR or from antigen to antigen and that the optimal affinity for each CAR may need to be empirically established.…”

“…77 Furthermore, the PKC-modulating drug, Bryostatin 1, was shown to upregulate CD22 expression on B-ALL and improve the cytokine production, cytotoxicity, and in vivo durability of CD22 CAR T cells. 78 Such observations not only offer strategies for improving CAR T cell efficacy, but also illustrate the importance of antigen sensitivity to the success of CAR T cell therapy.…”

“…97 Similarly, T cells engineered to express a high-affinity variant of the CD22 CAR did not demonstrate improved efficacy against B-ALL with low CD22 expression when compared to the standard affinity CD22 CAR. 78 Given the mixed results of the effect of affinity on the antigen sensitivity of CAR T cells, it is possible that the role of affinity may differ from CAR to CAR or from antigen to antigen and that the optimal affinity for each CAR may need to be empirically established.…”