Dual Antigen Targeting with Co-Transduced CD19/22 CAR T Cells May Prevent Antigen-Negative Relapse after CAR T Cell Therapy for Relapsed/Refractory ALL

Background: CD19 negative escape is a major cause of relapse after CD19 CAR T cell therapy for relapsed/refractory (r/r) paediatric Acute Lymphoblastic Leukemia (ALL) and dual targeting of CD19/CD22 may overcome this. We have previously shown that AUTO1, a fast off rate autologous CD19 CAR T cell therapy was highly active in ALL with a favorable safety profile and excellent persistence (Ghorashian et al Nat.Med. 2019). Building on these properties, we developed AUTO1/22 an autologous CAR T cell product co-transduced with two different lentiviral vectors encoding our existing CD19 CAR and a novel CD22CAR designed to recognise targets with low antigen density. We have evaluated the safety and biological efficacy of AUTO1/22 in a Phase I study in children/young adults with r/r ALL (NCT02443831). Methods: Patients with r/r B-ALL age < 25 yrs who were ineligible for/relapsed after Tisagenlecleucel were recruited. Following fludarabine/cyclophosphamide lymphodepletion, patients received 1x106 /kg CAR+ T cells. The presence of CAR T cells in the blood/bone marrow (BM) was assessed by flow cytometry + qPCR and BM MRD was assessed by IgH qPCR + flow cytometry. Primary endpoints were incidence of grade 3-5 toxicity and the proportion of patients achieving MRD negative remission. Results: 12 patients have been treated. The median age was 12 years (range 3-21) and patients had a median of 3 prior lines of therapy (range 2-6). Six of 12 patients had relapsed post allogeneic SCT, 6 had received prior Blinatumomab/Inotuzumab and 4 had relapsed after prior Tisagenlecleucel. Prior to lymphodepletion, 4 patients had >5% BM disease by morphology/flow, 5 had detectable BM MRD and 3 were BM MRD negative. Six patients had extramedullary relapse (of which 2 had non-CNS EM disease). Three had detectable CD19 negative disease at enrolment. One of these was completely CD19 negative and in addition had a 5% CD22 negative population. CAR T cell products had a central memory phenotype with predominance of CD19/22CAR double positive cells (median 54.4%) and balanced populations of CD19 and CD22 single positive cells (13.1% and 11.6% respectively). Cytokine release syndrome (CRS) occurred in 11/12 patients (grade 1 n=5, grade 2 n=6) requiring Tocilizumab in 5 cases, but severe (≥ grade 3) CRS was not seen and no patients required ICU admission for CRS. Grade 1-2 ICANS was observed in 5 patients. One patient had delayed grade 4 leucoencephalopathy (MRI/brain biopsy were more indicative of fludarabine toxicity than CAR T related) and has ongoing neurological recovery. Nine patients had grade 3-4 cytopenia persisting beyond/recurring after day 28, requiring a CD34+ stem cell top up in 1 case. Flow cytometry showed significant initial expansion of all 3 CAR +ve populations early post-infusion but CD19/22CAR double positive cells were lost at later time points. Six patients had circulating CAR T cells by qPCR at last follow up and the median duration of B cell aplasia has not been reached. Ten of 12 patients (83%) achieved MRD negative CR/CRi at one month post-infusion and 2 patients did not respond. Importantly 2/3 patients with CD19-ve disease achieved molecular CR demonstrating the efficacy of our CD22CAR. Of the 10 responding patients, 2 have relapsed with CD19+CD22+ disease, one patient with CD19-ve disease pre-infusion has relapsed with CD19partialCD22+ disease and one had emergence of MRD level disease, in all cases associated with loss of CAR T cells. One other patient had early loss of CAR T cells with B cell recovery but ongoing MRD negative CR at 3 months post-infusion and remains in MRD negative CR on maintenance chemotherapy. Overall, at a median follow-up of 8.7 months (range 1-15 months), 6/10 responding patients remain in MRD negative CR at last follow-up. Importantly, antigen-negative relapse has not been observed. Summary/Conclusion: Our data show that dual CD19/22 targeting CAR T cells generated by co-transduction show a favorable safety profile, with robust expansion/persistence and early efficacy in a heavily pre-treated cohort. To date with we have not observed antigen negative relapse. This contrasts to an incidence of 5/6 CD19 negative relapses in the 12 responders treated with single CD19 targeting CAR T cells (AUTO1) in an earlier cohort and suggests dual targeting may be effective in preventing antigen escape. However, longer follow up will be needed to confirm this. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal