T cells isolated from G-CSF-treated multiple myeloma patients are suitable for the generation of BCMA-directed CAR-T cells

We are extremely grateful to the patients for participating in this study and to the nurses from the Department of Haematology and the Apheresis Unit at Hospital Clínic, particularly Maria Teresa Solano Moliner, for their invaluable work in obtaining patient samples. In addition, we acknowledge the Multiple Myeloma Research Center (Little Rock, AK) for providing the ARP-1 cell line and Amer Najjar for providing the plasmid coding for GFP-ffLuc. Finally, we thank the "la Caixa" Foundation (CP042702), the Spanish Institute of Health Carlos III (projects: PI19/00669 and ICI19/00025 ; co-funded by the European Union), and the AECC (LABAE21971FERN) for providing funding for this study. We are extremely grateful to the patients for participating in this study and to the nurses from the Department of Haematology and the Apheresis Unit at Hospital Clínic, particularly Maria Teresa Solano Moliner, for their invaluable work in obtaining patient samples. In addition, we acknowledge the Multiple Myeloma Research Center (Little Rock, AK) for providing the ARP-1 cell line and Amer Najjar for providing the plasmid coding for GFP-ffLuc. Finally, we thank the "la Caixa" Foundation (CP042702), the Spanish Institute of Health Carlos III (projects: PI19/00669 and ICI19/00025; co-funded by the European Union), and the AECC (LABAE21971FERN) for providing funding for this study. Conceptualization, A.M.B. A.U.-I. and C.F.d.L.; data curation, A.M.B.; formal analysis, A.M.B.; funding acquisition, A.U.-I. and C.F.d.L.; investigation, A.M.B. A.O.-C. M.B.i.C. and D.F.M.; methodology, A.M.B.; project administration, A.M.B. A.U.-I. and C.F.d.L.; resources, M.S.-L. M.L. N.M.-C. J.C. A.U.-I. and C.F.d.L.; supervision, C.F.d.L.; visualization, A.M.B.; writing - original draft, A.M.B.; writing - review & editing, A.M.B. L.G.R.-L. A.U.-I. and C.F.d.L. All authors have reviewed and approved the final version of this manuscript. The authors declare no competing interests. Autologous cell immunotherapy using B cell maturation antigen (BCMA)-targeted chimeric antigen receptor (CAR)-T cells is an effective novel treatment for multiple myeloma (MM). This therapy has only been used for relapsed and refractory patients, at which stage the endogenous T cells used to produce the CAR-T cells are affected by the immunosuppressive nature of advanced MM and/or side effects of previous therapies. An alternative pool of "fitter" T cells is found in leukocytoapheresis products that are routinely collected to obtain hematopoietic progenitor cells for autologous stem cell transplantation (ASCT) early in the treatment of MM. However, to mobilize the progenitor cells, patients are dosed with granulocyte colony-stimulating factor (G-CSF), which is reported to adversely affect T cell proliferation, function, and differentiation. Here, we aimed to first establish whether G-CSF treatment negatively influences T cell phenotype and to ascertain whether previous exposure of T cells to G-CSF is deleterious for anti-BCMA CAR-T cells. We observed that G-CSF had a minimal impact on T cell phenotype when added in vitro or administered to patients. Moreover, we found that CAR-T cell fitness and anti-tumor activity were unaffected when generated from G-CSF-exposed T cells. Overall, we showed that ASCT apheresis products are a suitable source of T cells for anti-BCMA CAR-T cell manufacture.