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There has been a fast progress in clinical use of antibody-based immunotherapy, given the superior efficacy commonly achieved in clinic and the limited toxicity. However, personalization of treatment remains of major importance, both to achieve better clinical performance for monotherapy and to identify the best combinations on a patient-by-patient basis. Predicting patient's response is complex due to the need to characterize both tumor response and immunologic mechanisms possibly activated by the therapy, including antibody dependent cellular cytotoxicity (ADCC). We present the Inter-Cell Networking Profiling (ICNP), a novel analytical method enabling a comprehensive and precise characterization of the modulatory effect of immunotherapies on immune-tumor cell interactions. ICNP works on the Open Microwell (OMW) microfluidic system which recreates 20,000 unique cell clusters from ex-vivo patient samples and exposes them to anticancer drugs. We validated the ICNP using multiple myeloma (MM) patient samples to characterize the efficacy of Daratumumab, an anti-CD38 antibody (Ab). Bone marrow samples in EDTA were collected from 11 MM patients. 8 samples were processed by Ficoll-Paque, preserving the original composition of effector (E) and target (T) cells, i.e. NK and plasma cells respectively. 3 samples were processed to obtain co-cultures of WBC depleted of plasma cells (which include NK cells) and U-266 MM cell line. NK and plasma cells were stained with anti-CD16/CD56 and anti-CD138 fluorescently-labeled Abs, respectively. Propidium Iodide (PI) was used as death marker. A statistical model was created to project the optimal experimental setup (E:T ratio, cell concentration) to maximize the co-localization of E/T cells in the 20,000 microwells of the OMW platform. After seeding, cells were incubated with Daratumumab 10µg/mL or no drug and analyzed through fluorescence time lapse microscopy for up to 12 hours. ICNP analysis first separates microwells with both E/T cells in close proximity from those not featuring both cell types (Fig 1A). Then, anti-CD38 efficacy is evaluated in microwells with E/T co-localization, thus implementing a miniaturized ADCC assay (Fig 1B). At the same time, spontaneous NK activity is measured in microwells with E/T co-localization and no drug, while direct effect of the drug on target cells can be measured in microwells with T but not E cells. We first validated our statistical model of co-localization in microwells against the actual number of wells with E/T co-localization (correlation R2: 0.79-0.97, n=5). Then, we characterized the immune composition of 8 MM patients samples with the OMW, finding that E/T cell fractions were in the ranges 5-21% (E) and 1-28% (T). Interestingly, according to our statistical model, co-localization occurs in at least 1% of microwells for all the 8 samples, making ICNP applicable with good statistical significance in the OMW system on ex-vivo clinical samples without any pre-enrichment. Finally, ICNP was evaluated on 4 cases (3 obtained by mixing patient's WBC with U-266 MM cell line and 1 complete MM patient sample). We measured the effect of anti-CD38 Ab using i) the standard approach, considering all microwells regardless of the co-presence of E and T; ii) ICNP approach, considering only microwells featuring E/T co-localization. Results show that drug effect is much evident with ICNP in all the 4 cases with an average increase in target cell death of 40%, indicating a higher sensitivity of this approach than the averaged analysis (Fig 1C, right). Importantly, in one case, the standard analysis did not identify significant differences between anti-CD38 treated and control cells, that could instead be observed with ICNP (p ICNP proved to enable a comprehensive profiling of the immune system by evaluating in one test the immune composition and the fitness of immune cells, both native and drug-treated. These results open the opportunity to develop functional precision medicine approaches for predicting patient's response to drugs with immune-mediated mechanisms of action. AB and RR equally contributed Figure 1 Disclosures Bettelli: CellPly.S.r.l.: Employment. Ruggiano:Cellply S.r.l.: Employment. Bocchi:CellPly S.r.l.: Employment. Rocchi:CellPly.S.r.l.: Employment. Faenza:CellPly S.r.l.: Employment. Zamagni:Janssen: Honoraria, Other: Advisory board, Speakers Bureau; Amgen: Honoraria, Other: Advisory board, Speakers Bureau; BMS: Honoraria, Other: Advisory Board, Speakers Bureau; Takeda: Honoraria, Speakers Bureau; Sanofi: Honoraria, Other: Advisory Board, Speakers Bureau; Celgene Corporation: Honoraria, Other: Advisory board, Speakers Bureau. Bettelli:CellPly S.r.l.: Employment. Rambelli:CellPly S.r.l.: Employment. Guadagnuolo:CellPly S.r.l.: Employment. Pecorari:CellPly S.r.l.: Employment. Giulianelli:CellPly S.r.l.: Employment. Pisani:CellPly S.r.l.: Employment. Biscarini:CellPly S.r.l.: Employment. Cavo:amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; bms: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accommodations, Speakers Bureau; sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; novartis: Honoraria; takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accommodations, Speakers Bureau; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Guerrieri:CellPly S.r.l.: Equity Ownership. Bocchi:CellPly S.r.l.: Equity Ownership, Membership on an entity's Board of Directors or advisory committees.

Background: Patient stratification to match individual patients with the most effective drug treatment is still a major open challenge in cancer care. For instance, cytarabine is the main drug used for AML treatment but 30% of patients fail to respond to this agent. Laboratory developed tests determining ex-vivo cellular response to cytotoxic anticancer drugs have demonstrated good correlations with clinical response, sometimes surpassing the predictive power of molecular and genetic profiling. Standardizing sample processing to remove operator-dependent biases and maintaining live cells in a functional status that closely resembles in-vivo function are major challenges affecting these tests. Here we present the open microwell (OMW) platform, a microfluidic-based system that integrates the entire process of ex-vivo testing of anticancer drug efficacy and enables drug testing in the clinical setting prior to therapy administration. The concept was validated for the first time on 13 AML patients at Sant'Orsola hospital, Italy, showing the possibility to initiate the analysis readily after sample collection, thus minimizing drifts in cell function that typically start occurring within hours from sampling, and provide results in about 24 hours, with a fully-automated system. Methods: 13 refractory, relapsed or newly diagnosed AML patients were enrolled in the study. 2 ml of fresh bone marrow in EDTA and 1 ml of serum blood were collected from each patient. White blood cells (WBC) were separated from bone marrow by standard Ficoll-Paque, suspended in medium additioned with 2% autologous serum and loaded in microfluidic chips featuring 16 microchannels and 1200 microwells/channel (70 μm diameter), open at the bottom end (Fig. 1A-B). After settling down in microwells, cells were stained with CMAC cell tracker, anti-human-CD34/CD45 fluorescently-labeled antibodies and Propidium Iodide (PI) by injecting the reagents in the microchannels. Cytarabine or combination therapies (FLAI-3, FLAI-5, FLA, MEC-4) were then injected in the microchannels and cells were incubated for 24 hours in the system (Fig. 1C). Four channels were used per therapeutic condition, including reference (ref), high (ref x 10) and low (ref/10) dosages plus a non-treated channel as reaction control. Finally, a custom software was used to detect cells in images, classify AML blasts and analyze cell death (Fig. 1D). Drug efficacy was determined by evaluation of both cell depletion and apoptosis induction. Results: We first validated the OMW platform against gold standard (FacsAria flow cytometer) for the detection of tumor cells and measurement of cell viability and apoptosis. Count of blast frequency was carried out on 5 patient samples using anti-CD34/CD45 staining. Results (Fig. 2B) show a correlation between the gold standard and OMW (n=5, R2=0.99, p Conclusion: The OMW platform was able to count AML blasts and analyze viability and apoptosis showing high concordance with conventional diagnostics represented by flow cytometry. The assay requires 30 μl of bone marrow sample and simple manual pre-processing. Profiling of patient response to specific drugs or combination is provided within 24h. These features make the OMW platform suitable for bedside analysis, to evaluate drug activity on tumor cells within a heterogeneous sample and promptly guide personalized treatment in hematologic malignancies, with a first proof achieved on AML patients. LRo and AF equally contributed. Disclosures Rocchi: CellPly S.r.l.: Employment. Faenza:CellPly S.r.l.: Employment. Rambelli:CellPly S.r.l.: Employment. Guadagnuolo:CellPly S.r.l.: Employment. Pecorari:CellPly S.r.l.: Employment. Giulianelli:CellPly S.r.l.: Employment. Biscarini:CellPly S.r.l.: Employment. Martinelli:Novartis: Speakers Bureau; Roche: Consultancy, Speakers Bureau; Ariad: Consultancy, Speakers Bureau; BMS: Speakers Bureau; Pfizer: Consultancy, Speakers Bureau; Amgen: Consultancy, Speakers Bureau; MSD: Consultancy; Celgene: Consultancy, Speakers Bureau; Genentech: Consultancy. Guerrieri:CellPly S.r.l.: Equity Ownership. Bocchi:CellPly S.r.l.: Equity Ownership, Membership on an entity's Board of Directors or advisory committees.