Folate receptor beta targeting of tumor-associated macrophages improves lymphoma cell responses to CD19 CAR T cells

Chimeric antigen receptor (CAR) T cell therapies have revolutionized the treatment of patients with relapsed or refractory (R/R) diffuse large B-cell lymphoma (DLBCL). However, approximately half of the patients experience lymphoma progression after CD19 CAR T cell therapy. Immunosuppressive, M2-like tumor-associated macrophages (TAMs) contribute to the immunosuppressive tumor microenvironment (TME) and may facilitate resistance to CAR T cell therapy. Here, we identified folate receptor beta (FRβ) as a specific marker of M2-like TAMs and a predictor of poor survival in multiple independent DLBCL cohorts. Co-culture studies of lymphoma-macrophage spheroids revealed reciprocal interactions between lymphoma cells and M2-like macrophages. Lymphoma cell co-cultures promoted the differentiation of monocytes into M2-like macrophages, while M2-like macrophages fostered lymphoma cell growth and interfered with CD19 CAR T cell-mediated killing of lymphoma cells. We demonstrated that M2‑like macrophages drive CAR T cells toward an exhausted phenotype and validated this finding using data from patients treated with CD19 CAR T cell therapy. Lastly, we generated FRβ-targeting CAR T cells and used them prior to CD19 CAR T cells to successfully improve lymphoma cell killing. Taken together, the results suggest active crosstalk between lymphoma cells and M2-like macrophages, as well as TAM-mediated resistance mechanisms to CD19 CAR T cells, which can be circumvented by FRβ CAR T cells targeting the M2-like TAMs. These results support the use of macrophage-targeting to improve CAR T cell therapy outcomes in DLBCL.