O-10.02 Targeting CSF1R⁺ myelo-monocytic cells enhances CAR-T cell response in B cell lymphoma

<h3>Background</h3> Chimeric antigen receptor (CAR) T cell therapy has revolutionized the treatment of patients suffering from relapsed and/or refractory (r/r) B cell lymphoma. However, around 60% of CAR-T cell-treated patients do not experience long-term remissions. Recent studies indicate that the lymphoma microenvironment (LME) plays a crucial role in both response and resistance to CAR-T cell therapy. To date, targeting the LME in B cell lymphoma patients treated with CAR-T cells has not yet been sufficiently investigated. Here, we aim to elicidate the immunosuppressive capacity of lymphoma-associated myeloid-monocytic (LAMM) cells in the context of CAR-T cell treatment. <h3>Materials and Methods</h3> We applied multi-dimensional analyses to pre- and post-CAR-T cell-treated human lymphoma specimens, including bulk RNA sequencing, single-cell RNA sequencing of and Imaging Mass Cytometry (IMC). To further validate our findings, we applied <i>ex vivo</i> co-culture experiments and tested potential therapeutic targets in combination with murine CD19 CAR-T cells using an immunocompetent, autochthonous DLBCL mouse model. <h3>Results</h3> We identified a prognostically relevant LAMM gene signature in CAR-T cell non-durable responding lymphoma patients, including genes such as <i>CD14, CD68, ITGAM, IL1B</i> and <i>S100A9.</i> Furthermore, a non-durable response was associated with reduced T cell infiltration and increased hypoxia. In particular, our analyses revealed a CSF1R⁺CD14⁺CD68⁺ LAMM cell population linked to poor clinical outcomes in CAR-T cell-treated patients. Of note, in <i>ex vivo</i> co-culture experiments we demonstrated that CSF1R⁺CD14⁺CD68⁺ LAMM cells exhibit immunosuppressive functions and inhibit CAR-T activity. Most strikingly, using a fully autochthonous DLBCL CAR T cell mouse model, we showed that combining CD19 CAR-T cell therapy with CSF1R inhibition promotes a shift towards a T cell-enriched LME, accompanied by follicular architecture restoration and blood vessel normalization in diseased spleens. Finally, the combination of CSF1R inhibition and CD19 CAR-T cell therapy displayed synergistic therapeutic effects, leading to prolonged survival and long-lasting remissions in treated mice. <h3>Conclusions</h3> These data indicate that CSF1R⁺ LAMM cells contribute to CAR-T cell failure in B cell lymphoma. CSF1R inhibition synergistically enhances CD19 CAR-T cell response and restores anti-lymphoma immunity. Based on these findings, we suggest to test the combination of CAR-T cell therapy and CSF1R inhibitors in patients with r/r B cell lymphoma in prospective clinical trials. D. Stahl: None. P. Gödel: None. H. Balke-Want: None. P. Segbers: None. L. Tetenborg: None. R. Gholamipoorfard: None. F. Rose: None. D. Bachurski: None. A.G. Simon: None. R. Flümann: None. T. Riet: None. P. Bröckelmann: None. R.D. Jachimowicz: None. K. Bozek: None. M. Hallek: None. M. Chmielewski: None. H.C. Reinhardt: None. N. Abedpour: None. P. Borchmann: None. R.T. Ullrich: None.