Supplementary Figure S2. BTN2A1 is broadly expressed in normal and tumor cells.

Supplementary Figure S8. Segmentation of live cells using Refractive Index (RI).

Supplementary Figure S10. The caspase-3-specific inhibitor zDEVD-FMK inhibits the cleavage of GSDME.

Supplementary Figure S6. Anti-BTN2A1 107G3B5 increases Vɣ9Vδ2 T cell effectors functions against hematological cell lines.

Supplementary Figure S5. Cytotoxicity assays of 4 cancer cell lines (PC3, KARPAS, 697 and SUP-T1) and primary ALL blasts (n=4) using Annexin and 7-AAD labelling.

Supplementary Figure S4. Anti-BTN2A1 107G3B5 mAb characterization.

Supplementary Figure S9. Anti-BTN2A1 sensitizes Vɣ9Vδ2 T cell cytotoxicity against PC3 cell line.

Visualization of Vγ9Vδ2 T cells (E) and SUP-T1 (T) coculture using a label-free method within 20 hours. Ratio T/E = 1/2. Cells treated with 107G3B5 antibody (10ug/ml).

Supplementary Figure S7. 107G3B5 primes Vγ9Vδ2T cells by mechanisms that are dependent on BTN3A and BTN2Abut independent of the pAg-binding B30.2 intracellular domain.

Supplementary Figure 12. The caspase-3-specific inhibitor zDEVD-FMK inhibits the cleavage of GSDME.

Supplementary figure S11. Anti-BTN2A1 107G3B5 induces a colocalization of BTN3A1 and BTN2A1.

Supplementary Raw Data Excel File S1

Butyrophilins (BTNs) are emerging as novel druggable immune targets in oncology, promoting the activation of gamma delta (γδ) T cells against cancer cells. Therapies targeting BTN3A or BTN2A1 are under development, but their regulation is poorly understood. Here, we report that lymphocytes' BTN2A1 expression increases with CD3/CD28 stimulation, mediated by trogocytosis in the presence of activated myeloid cells. For instance, BTN2A1 can be acquired by the BTN2A1-knockout (BTN2A1KO) B cell line through trogocytosis when cultured with monocytes. In addition, cytotoxicity assays determine that BTN2A1-acquired normal or tumor cells exhibit higher sensitivity to Vγ9Vδ2 T cell lysis. Finally, we show that trogocytosis-mediated acquisition of BTN2A1 by circulating lymphocytes involves activated monocytes and is correlated with endometrial cancer stage in a cohort of 87 patients. This study provides new insights about the regulation and functions of BTN2A1 but also highlights the potential impact of trogocytosis in regulating the expression of immune checkpoints in normal and pathological conditions.

Abstract Vγ9Vδ2 T cells are potent but elusive cytotoxic effectors. Butyrophilin subfamily 2 member A1 (BTN2A1) is a surface protein that has recently been shown to bind the Vγ9 chain of the γδ T-cell receptor, but its precise role in modulating Vγ9Vδ2 T-cell functions remains unknown. Here, we show that 107G3B5, a monoclonal BTN2A1 agonist antibody, was able to significantly enhance Vγ9Vδ2 T-cell functions against hematologic or solid cell lines and against primary cells from patients with adult acute lymphoblastic leukemia. New computer vision strategies applied to holotomographic microscopy videos showed that 107G3B5 enhanced the interaction between Vγ9Vδ2 T cells and target cells in a quantitative and qualitative manner. In addition, we found that Vγ9Vδ2 T cells activated by 107G3B5 induced caspase 3/7 activation in tumor cells, thereby triggering tumor cell death by pyroptosis. Together, these data demonstrate that targeting BTN2A1 with 107G3B5 enhances the Vγ9Vδ2 T-cell antitumor response by triggering pyroptosis-induced immunogenic cell death. These new pyroptosis-based therapies have great potential to stimulate the immune system to fight cancer, especially “cold” tumors. See related Spotlight by Kabelit, p. 1662

194 Background: Despite the recent progress in cancer management, metastatic prostate cancer remains incurable. In the context of immunotherapy failure, we need to identify new immune biomarkers, to improve patient therapy, and explore their potential as therapeutic target. To this end, we screened the prognostic value of soluble immune checkpoints in the plasma of metastatic prostate cancer patients at diagnosis, and depicted their role in anti-tumor activities. Methods: Patients with hormone naive metastatic prostate cancer were prospectively included in the NK-Prostate study (NCT02963155). Blood collection was performed before treatment and patients were followed for 5 years. We determined by ELISA assay plasma levels the soluble form of PD-L1, Pan-BTN3A, BTN3A1, BTN2A1 and BTLA. Large extracellular vesicles (MVs) were pelleted at 10 000g by sequential ultracentrifugation. Results: 66 patients were included in the NK-Prostate with a median follow-up of 42.6 months. Only plasma levels of BTN2A1 were associated with overall survival > 50 months. Patients with enriched sBTN2A1 (soluble form of BTN2A1) presented poorer overall survival (HR for death 2.91 95%CI 1.33 – 6.33, p=0.0072) and progression-free survival than low-level patients (HR for progression 2.73 95%CI 1.48 – 5.05, p=0.0012). Prostate cancer cell line produced sBTN2A1, with 40% associated with extracellular vesicles. High level of BTN2A1+ microvesicles (MVs) were identified by spectral cytometry in patient’ plasma but not in healthy volunteer plasma, and deep phenotyping revealed that B cell-derived BTN2A1+ MVs were associated with shorter overall survival (HR 4.22 95%CI 1.68 – 10.57, p=0.0021). To evaluate the impact of BTN2A1+ MVs on γδ T cells, we generated BTN2A1 KO MVs, BTN2A1 overexpressed MVs, and BTN2A1 mutant overexpressed MVs (that do not interact with γδ TCR). We demonstrated that BTN2A1 overexpressed MVs could specifically interact with γδ T cell; and impaired their proliferation and cytotoxicity against prostate cancer cell lines (LNCaP, DU145 and PC3). Conclusions: Our study shows the negative impact of B cell derived BTN2A1+ MVs in hormone naïve metastatic prostate cancer. Plasma MVs phenotyping is an easy-to-perform test, accessible for all patients. Our results highlight the role of γδ T cell in the anti-tumor immunity in prostate cancer, making them an interesting target for immunotherapy in this pathology. Clinical trial information: NCT02963155 .

Background: γ9δ2 T cells are emerging as a novel tumor-infiltrating effector cell that harbors strong cytolytic and pro-inflammatory activities, and whose intratumoral presence is associated with a favorable prognosis across solid and liquid cancer patients (Gentles et al., 2015; Tosolini et al., 2017). ICT01, a first-in-class anti-BTN3AmAb activating γ9δ2 T cells, completed Phase 1 testing in relapsed/refractory (r/r) solid tumors as monotherapy and in combination with pembrolizumab, and as monotherapy in r/r AML and lymphoma (EVICTION-NCT04243499). ICT01 activates circulating γ9δ2 T, CD8 T, and NK cells that leads to tumor infiltration and remodeling of the TME (De Gassart et al., 2021; Wermke et al., 2021) without any dose-limiting toxicities and a good safety profile. Encouraging clinical activity was observed in the hematologic cancer cohort with a 30% DCR on the 10 patients evaluable at week 8 or beyond (Garciaz, SITC 2023) supporting further clinical testing of ICT01 in combination with Venetoclax (VEN) and 5-Azacytidine (AZA), considered the standard of care for patients with newly diagnosed AML who are not candidates for intensive chemotherapy. Both ICT01 + γ9δ2 T cells and VEN/AZA induce killing of AML blasts, while VEN/AZA has been shown to enhance T-cell- and NK-cell-mediated cytotoxicity against AML blasts, suggesting that the combination of ICT01 plus VEN/AZA could lead to greater efficacy. We used preclinical models to demonstrate the ability of VEN/AZA to potentiate the anti-leukemic activity of ICT01-activated γ9δ2 T cells to support the clinical evaluation of ICT01 + VEN/AZA in 1L AML patients eligible to receive VEN/AZA. Results: Preclinical in vitro studies showed that ICT01-mediated activation of g9d2 T cells significantly increased survival against VEN toxicity by >50%, as compared to untreated control (p<0.01). Furthermore, killing assays performed by co-culture of AML blasts and HD-PBMC demonstrated that VEN/AZA enhances the blast killing capacity of ICT01-activated g9d2 T cells. These results were confirmed in vivo in NSG mice engrafted with human AML that were adoptively transferred with human g9d2 T cells and treated with VEN (40mg/kg/day OG)/AZA (2mg/kg/day IP), ICT01 (1mg/kg IV) or the combination. In this model the use of ICT01 together with VEN/AZA significantly delayed tumor growth (p<0.001) and significantly prolonged median survival to 42.5 days (vs 28 and 32.5 days for animals receiving ICT01 or VEN/AZA, respectively) (Figure 1). These results led to the design of the recently initiated Phase 2a arm of EVICTION in 1L AML where ICT01 is given at 10 mg or 75 mg IV Q4W on Day 1 of the 28-day approved regimen of VEN/AZA until toxicity or disease progression. Up to 25 patients will be treated at each dose level, following an interim analysis after 10 pts are treated at each dose. Clinical sites in France, Spain and the USA are participating. Biomarkers include multiparametric flow cytometry analysis of g9d2 T cells and other immune cells, and BTN3A expression in peripheral blood and in bone marrow aspirates at baseline and on Day 21-28. Circulating cytokine levels (including IFNγ, TNFa, IL-1ß, IL-2, IL-4, IL-6, IL-8, IL-10, IL-17a and MCP-1) are also assessed with MSD technology. Clinical response is evaluated per AML-specific standards (e.g., Cheson/IWG Criteria), with a target CR rate of >40%. Preliminary safety, biomarker and efficacy data from patients will be presented. Conclusion: Encouraging results obtained in the EVICTION Phase 1 trial and preclinical demonstration of the benefit of using ICT01 plus VEN/AZA allowed the initiation of a Phase 2a expansion cohort to evaluate the clinical benefit of this combination in 1L AML patients.

Supplementary Figure S3 shows the effect of SKI-I on cell death in BRAFi-sensitive and -resistant melanoma cells

Legends to the supplemental figures

Supplementary Figure S2 shows the plasma SL levels in patients responding or not to BRAFi

Supplementary Figure S4 shows that MITF expression is associated to S1PR1 in PLX-treated melanoma cells