Safety and Anti-Tumor Activity of CD5 CAR T-Cells in Patients with Relapsed/Refractory T-Cell Malignancies

Introduction:

We describe a Phase I dose escalation study (NCT03081910) of autologous CD5-directed chimeric antigen receptor T cell (CD5 CAR T) therapy for relapsed or refractory (r/r) T-cell leukemia and lymphoma. Establishing a CAR T cell platform to target neoplasms of T-cell origin has been hindered by the shared expression of most targetable antigens on both malignant and normal T lymphocytes, which can promote CAR T cell fratricide. CD5 is one such pan-T cell surface marker present in ~85% of T-cell malignancies. We developed a second-generation CD5-specific CAR with CD28 costimulatory endodomain that produces minimal and transient fratricide when expressed in T cells. We designed this study to evaluate the safety and feasibility of treating patients with r/r T-cell malignancies with these CD5 CAR T cells as a bridge to allogeneic hematopoietic stem cell transplant (HSCT). Secondary objectives of our study included evaluating the antitumor response, in vivo expansion, persistence of CD5 CAR T cells, as well as their impact on normal T-cell numbers and function.

Patients and methods:

CD5 CAR T cells were generated from autologous PBMCs using gammaretroviral transduction and cryopreserved. We detected no residual malignant cells in the CD5 CAR T cell products by flow cytometry. To date, we have treated a total of 9 patients (8 adults and 1 adolescent; age 16-71 years [median 62 yrs]) with CD5+ r/r T-acute lymphoblastic leukemia (T-ALL; n=4) or T-non-Hodgkin's lymphoma (T-NHL; n=5) on dose levels 1 and 2. All patients were transplant-eligible with an identified allogeneic HSCT donor, yet unable to proceed due to residual disease. All patients had been heavily pretreated, with a median of 5 (range 2 -18) prior lines of therapy. Two patients had previously failed allogeneic HSCT. Patients received cytoreductive chemotherapy with cyclophosphamide and fludarabine followed by a single dose of CD5 CAR T cells. We evaluated adverse events, clinical responses, and in vivo expansion and persistence pre and post-infusion.

Results:

Three patients received CD5 CAR T cells on dose level 1 (1x10⁷ CAR T cells/m²) and 6 on dose level 2 (5x10⁷ CAR T cells/m²). In all patients treated, CAR T cells reached peak expansion in peripheral blood (PB) 1-4 weeks following infusion, followed by a gradual contraction in most patients (Figure 1). CD5 CAR T cells were present in lymph node and marrow biopsies in patients with T-NHL and T-ALL, respectively, and were also detected in a CSF sample in 1 T-ALL patient. After cytoreduction and CAR T cell infusion, we observed decreased PB CD3+ cell numbers but this ablation was never complete. Cytokine release syndrome (CRS) occurred in 3/9 patients (all at dose level 2). Grade 1 CRS was observed in 2 patients. One patient experienced Grade 2 CRS and Grade 2 neurotoxicity, which resolved after administration of tocilizumab and supportive care, respectively. Two patients had prolonged cytopenias at 6 weeks, 1 of whom had viral reactivation (CMV and BK virus) requiring antiviral therapy.

On disease re-evaluation 4-8 weeks post-CD5 CAR T cell infusion, 4 of 9 evaluable patients obtained an objective response (1 of 3 on DL1 and 3 of 6 on DL2). Complete responses (CR) were achieved in 3 patients, one with angioimmunoblastic T cell lymphoma (AITL), one with peripheral T cell lymphoma (PTCL), and one with T-ALL. Two of these patients did not wish or were unable to proceed to planned HSCT and relapsed with their underlying CD5+ malignancy at 6 weeks and 7 months post-infusion. The remaining patient is currently undergoing work-up for HSCT (Figure 2). An additional patient with extensive AITL was classified as a mixed response (Figure 3) due to the appearance of a new PET-avid lesion. This patient received a second infusion of CD5-CAR T cells, proceeded to HSCT, and remains in CR at 125 days post-transplant.

Conclusions:

These results demonstrate that CD5 CAR T cells are safe and can induce clinical responses in heavily treated patients with r/r CD5+ T-ALL and T-NHL without inducing complete T-cell aplasia. Importantly, elimination of malignant T cells by CD5 CAR T cells may allow previously ineligible patients to proceed to HSCT.

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