Background Advances in autologous CD19 CAR T therapies have transformed treatment for B-cell malignancies (BCM). Despite the transformational benefit, many challenges remain for autologous CAR T therapies, including operational, logistical, and cost burdens, plus the need for alternative treatment strategies for patients who are refractory to approved CD19 CAR T therapies. CD22 is a B-cell specific antigen expressed on most BCMs and autoreactive B cells and is a validated target for CD22-directed CAR T products in BCMs.^1–3 Umoja is developing UB-VV400, an off-the-shelf, multidomain fusion (MDF) protein surface engineered lentiviral vector designed to generate CD22-directed CAR T cells in vivo without requiring lymphodepleting chemotherapy. In addition to the CD22-CAR, UB-VV400 delivers a rapamycin-activated cytokine receptor (RACR™) as part of the payload, which is designed to enrich and expand CAR T cells in vivo in the presence of rapamycin. Herein, we describe preclinical evaluations of UB-VV400 ± rapamycin.

Methods UB-VV400 lots were manufactured internally by a transient transfection of suspension 293T cells. The transgene payload includes the RACR system and the CD22-directed CAR with 4-1BB and CD3ζ intracellular signaling domains. In vitro studies with UB-VV400 utilized healthy donor and patient PBMCs. Functional assays were performed by co-culturing UB-VV400-generated CAR T cells with target cell lines. In vivo studies were performed in PBMC-humanized NSG MHC-I/II DKO mice bearing systemic tumor, and analyses were performed using in vivo imaging and flow cytometry.

Results In vitro treatment of PBMCs with UB-VV400 demonstrated MDF surface engineering mediated selective binding and activation of T cells and subsequent transduction of T cells resulting in expression of RACR and anti-CD22 CAR. UB-VV400 generated CAR T cells mediated antigen-specific tumor cell killing and cytokine secretion in response to CD22^hi (Raji) and CD22^lo (Nalm6) cells, but not CD22-negative cells (K562, Raji-CD22^KO). In humanized mouse studies, UB-VV400 generated CAR T cells that mediated anti-tumor activity. Combination treatment with rapamycin further enriched and expanded CAR T cells in vivo and corresponded with complete tumor cell eradication and prolonged animal survival.

Conclusions UB-VV400 demonstrated specific and efficient transduction of T cells, which corresponded with generation of CD22-directed CAR T cells capable of killing both CD 22^hi and CD22^lo tumor cells in vitro and in vivo. Moreover, the RACR system and administration of rapamycin promoted enrichment and expansion of CAR T in vivo resulting in complete tumor clearance. These nonclinical data support planned studies in R/R LBCL post CD19-directed CAR T therapy.

References

1. Fry T, Shah N, Orentas R, et al. CD22-targeted CAR T cells induce remission in B-ALL that is naive or resistant to CD19-targeted CAR immunotherapy. Nat Med. 2018;24:20–28.

2. Pan J, Niu Q, Deng B, et al. CD22 CAR T-cell therapy in refractory or relapsed B acute lymphoblastic leukemia. Leukemia. 2019;33:2854–2866.

3. Tan Y, Cai H, Li C, et al. A novel full-human CD22-CAR T cell therapy with potent activity against CD22low B-ALL. Blood Cancer J. 2021;11:71.