Significance: Natural brain adaptations often involve changes in synaptic strength. The artificial manipulations can help investigate the role of synaptic strength in a specific brain circuit not only in various physiological phenomena like correlated neuronal firing and oscillations but also in behaviors. High-and low-frequency stimulation at presynaptic sites has been used widely to induce long-term potentiation (LTP) and depression. This approach is effective in many brain areas but not in the basolateral amygdala (BLA) because the robust local GABAergic tone inside BLA restricts synaptic plasticity. Aim: We aimed at identifying the subclass of GABAergic neurons that gate LTP in the BLA afferents from the dorsomedial prefrontal cortex (dmPFC). Approach: Chemogenetic or optogenetic suppression of specific GABAergic neurons in BLA was combined with high-frequency stimulation of the BLA afferents as a method for LTP induction. Results: Chemogenetic suppression of somatostatin-positive interneurons (Sst-INs) enabled the ex vivo LTP by high-frequency stimulation of the afferent but the suppression of parvalbuminpositive interneurons (PV-INs) did not. Moreover, optogenetic suppression of Sst-INs with Arch also enabled LTP of the dmPFC-BLA synapses, both ex vivo and in vivo. Conclusions: These findings reveal that Sst-INs but not PV-INs gate LTP in the dmPFC-BLA pathway and provide a method for artificial synaptic facilitation in BLA.

Clinical trials of novel salvage therapies have encouraging outcomes for relapsed/refractory transplant‐eligible classic Hodgkin lymphoma (R/R cHL) but comparison with conventional chemotherapy is lacking. Herein, we report the final analysis of a multicenter retrospective cohort of R/R cHL assessing outcomes by type of salvage therapy before autologous stem cell transplant (ASCT). R/R cHL patients who underwent ASCT at 14 institutions across the United States were included. Outcomes were compared among patients receiving conventional chemotherapy, brentuximab vedotin (BV) + chemotherapy, BV alone, and a checkpoint inhibitor (CPI)‐based regimens before ASCT. Study endpoints included event‐free survival (EFS), progression‐free survival (PFS), and overall survival (OS). All endpoints are defined from relapse. Of 936 patients, 728 received conventional chemotherapy, 73 received BV + chemotherapy, 70 received BV alone, and 65 received CPI‐based regimens prior to ASCT. When adjusted for time to relapse, pre‐ASCT response and use of BV maintenance, patients receiving CPI‐based regimens had superior 2‐year EFS compared to conventional chemotherapy, BV + chemotherapy, and BV alone (79.7, 49.6, 62.3, and 36.9%, respectively, p < .0001). Among 649 patients transplanted after 1 line of salvage therapy, CPI‐based regimens were associated with superior 2‐year PFS compared to conventional chemotherapy (98% vs. 68.8%, hazard ratio: 0.1, 95% confidence interval: 0.03–0.5, p < .0001). OS did not differ by pre‐ASCT salvage regimen. In this large multicenter retrospective study, CPI‐based regimens improved EFS and PFS compared to other salvage regimens independent of pre‐ASCT response. These data support earlier sequencing of CPI‐based regimens in R/R cHL in the pre‐ASCT setting.

Introduction: Clinical trials of novel salvage therapies (ST) have encouraging outcomes for relapsed/refractory classic Hodgkin lymphoma (R/R cHL) after autologous stem cell transplant (ASCT); yet studies comparing novel ST with conventional salvage chemotherapy are lacking. In a single center cohort, we demonstrated that bendamustine/brentuximab (BBV) had higher overall response rates (ORR) and complete response (CR) rates in ASCT-eligible R/R cHL (Desai et al JCO, 2021). Herein we report comparative outcomes of novel and conventional ST in R/R cHL who undergo ASCT, in a large multicenter retrospective cohort. Methods: Consecutive R/R cHL pts who underwent ASCT at 12 institutions across United States were included. Demographics and clinical variables at relapse including age, sex, B symptoms, stage, bulky disease (BD, single mass &gt; 6 cm) extra nodal disease (END), primary refractory disease (PRD) and early relapse (ER, within 1 year) were recorded by electronic health records review. Study objectives were ORR, CR to first ST, post-ASCT PFS and OS by final ST. Time to event endpoints were defined from date of ASCT. Results: From 12 participating institutions, 853 pts of R/R cHL who underwent ASCT were eligible for this study. Median age was 33 (14-72) years, 457 (54%) were male, 446 (52%) had BD, 257 (30%) had advanced stage, 271 (32%) had END, 369 (43%) had B symptoms, 142 (17%) had PRD and 307 (36%) had ER. All 853 received at least 1 ST, 245 received 2 ST, 71 received 3 ST and 26 received 4 ST. Seven groups of ST were identified: 1. Conventional platinum-based chemotherapy (PBC) group including ICE, DHAP and ESHAP 2. BBV 3. Brentuximab Vedotin and nivolumab (BV/Nivo) 4. BV alone (BV) 5. gemcitabine-based chemotherapy (Gem) 6. checkpoint inhibitors (CPI) and 7. other miscellaneous agents (Misc). 1st ST was as follows: 553 had PBC; 69 had BBV; 48 had BV/Nivo; 65 had BV; 49 had Gem; 4 had CPI and 63 had Misc. There was no significant difference in the baseline characteristics by type of 1 st ST (data not shown). BBV had significantly higher ORR (92% vs 79%, p&lt;0.001) and CR rate (80% vs 49%, p &lt;0.001) compared to PBC. BV/Nivo had significantly higher CR rate (67% vs 49%, p &lt;0.001) and a trend towards higher ORR (86% vs 79%, p = 0.1) compared to PBC. BV had significantly lower ORR (62% vs 79%, p &lt;0.001) and CR rate (34% vs 49%, p &lt;0.001) compared to PBC. There was no difference in ORR and CR rate of PBC, Gem, CPI and Misc agents. Final ST prior to ASCT was PBC in 451, BBV in 76, BV/Nivo in 48, BV in 87, CPI in 24, Gem in 90 and Misc in 64. Table 1 lists K-M estimates of 2-year survival probabilities for different Final ST groups. Median follow up was 3 (range 0.1-13) years. BV/Nivo group had significantly higher proportion of patients with PRD and BD than PBC, no other differences in baseline characteristics were identified amongst ST groups (data not shown). BV/Nivo (HR: 0.1 (CI 95:0.02-0.4), p&lt;0.01) and CPI (HR: 0.12 (CI 95:0.03-0.5), p&lt;0.01) had significantly higher PFS than PBC. There was no significant difference in PFS between other ST groups (Figure 1a). Type of ST was not significantly associated with difference in OS (Figure 1b). 536 pts underwent ASCT in CR, 273 underwent ASCT in partial response (PR) and 31 underwent ASCT with progressive disease (PD). Pre-ASCT PR (HR 1.6 (CI 95:1.3-2.6), p&lt;0.001) and PD (HR: 4.1 (CI 95: 2.5-6.8), p&lt;0.001) predicted significantly lower PFS compared to CR (Figure 2a). OS was also significantly lower in pts with pre-ASCT PR (HR 1.7 (CI 95: 1.2-1.6), p&lt;0.001) and PD (HR 5.3 (CI 95: 2.8-10), p&lt;0.001) (Figure 2b). Higher number of pre-ASCT ST predicted lower PFS (HR 1.3 (CI 95: 1.1-1.6), p&lt;0.001) and OS (HR 1.5 (CI 95: 1.2-1.8), p&lt;0.001). In pts with pre-ASCT CR, all 36 who had pre-ASCT CR after BV/Nivo were alive and relapse free for follow up of 0.1-5 yrs. BV/Nivo was associated with significantly higher PFS (HR 0.1 (CI 95: 0.01-0.7), p &lt;0.05) but not OS compared to PBC in this subgroup. Increasing number of pre-ASCT ST predicted worse PFS (HR 1.5 (CI 95: 1.2-2.0), p&lt;0.01) and OS (HR 2.2 (CI 95: 1.4-3.4), p&lt;0.001) in this subgroup as well. Conclusions: BV/Nivo has a higher CR rate and better post-ASCT PFS compared to conventional chemotherapy and can lead to durable remissions in pts with pre-ASCT CR. BBV had a higher response rate and similar post-ASCT survival to conventional chemotherapy. BV had lower response rates compared to chemotherapy. Novel ST such as BV/Nivo and BBV may be preferable to conventional chemotherapy in R/R cHL. Figure 1 Figure 1. Disclosures Spinner: Notable Labs: Honoraria. Bachanova: FATE: Membership on an entity's Board of Directors or advisory committees, Research Funding; Incyte: Research Funding; KaryoPharma: Membership on an entity's Board of Directors or advisory committees; Gamida Cell: Membership on an entity's Board of Directors or advisory committees, Research Funding. Dorritie: SITC presentation: Honoraria; Genmab: Research Funding; University of Pittsburgh/UPMC Hillman Cancer Center: Current Employment; Janssen: Research Funding; F. Hoffman-La Roche Ltd: Research Funding; Juno/BMS: Research Funding; Kite, a Gilead Company: Research Funding; OncLive/Institutional Perspectives on Cancer presentation: Honoraria. Arai: Magenta Therapeutics: Research Funding. Maurer: Nanostring: Research Funding; Morphosys: Membership on an entity's Board of Directors or advisory committees, Research Funding; Kite Pharma: Membership on an entity's Board of Directors or advisory committees; Genentech: Research Funding; Celgene: Research Funding; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees. Diefenbach: Genentech, Inc./ F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Research Funding; Seattle Genetics: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Celgene: Research Funding; IMab: Research Funding; Morphosys: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria, Research Funding; Merck Sharp & Dohme: Consultancy, Honoraria, Research Funding; Perlmutter Cancer Center at NYU Langone Health: Current Employment; AbbVie: Research Funding; IGM Biosciences: Research Funding; Incyte: Research Funding; Trillium: Research Funding; Gilead: Current equity holder in publicly-traded company; MEI: Consultancy, Research Funding. Nowakowski: Kyte Pharma: Consultancy; Ryvu Therapeutics: Consultancy; Selvita: Consultancy; Curis: Consultancy; Karyopharm Therapeutics: Consultancy; Celgene/Bristol Myers Squibb: Consultancy, Research Funding; Roche: Consultancy, Research Funding; Genentech: Consultancy, Research Funding; MorphoSys: Consultancy; Bantham Pharmaceutical: Consultancy; Daiichi Sankyo: Consultancy; Zai Labolatory: Consultancy; Incyte: Consultancy; Kymera Therapeutics: Consultancy; TG Therapeutics: Consultancy; Blueprint Medicines: Consultancy; Nanostrings: Research Funding. Advani: Astellas/Agensys: Research Funding; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; Bayer: Membership on an entity's Board of Directors or advisory committees; Bristol Myer Squibb: Membership on an entity's Board of Directors or advisory committees; Cell Medica: Membership on an entity's Board of Directors or advisory committees; Forty Seven: Membership on an entity's Board of Directors or advisory committees, Research Funding; Genetech Inc.: Membership on an entity's Board of Directors or advisory committees, Research Funding; Gilead: Membership on an entity's Board of Directors or advisory committees; Janssen Pharmaceutical: Research Funding; Juno: Membership on an entity's Board of Directors or advisory committees; Kite Pharma: Membership on an entity's Board of Directors or advisory committees; Kura: Research Funding; Kyowa: Membership on an entity's Board of Directors or advisory committees; Merck: Research Funding; Millenium: Research Funding; Pharmacyclics: Consultancy, Research Funding; Portola Pharmaceuticals: Consultancy; Regeneron: Research Funding; Roche: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees.

7515 Background: Primary refractory disease (PRD) and early relapse (ER) are predictors of poor prognosis in classic Hodgkin lymphoma (cHL). In this multicenter retrospective study, we describe outcomes of PRD and ER in pts with relapsed/refractory (R/R) cHL treated with salvage therapy (ST) and autologous stem cell transplant (ASCT). Methods: Of 14 sites, adult patients with R/R cHL who received ST and underwent ASCT were enrolled. PRD was defined as progression on frontline chemoimmunotherapy or within 6 months of diagnosis. ER was defined as relapse from 6 months-1 yr of diagnosis. Pts who relapsed >1 yr of diagnosis were called late relapses (LR). Study objectives were Overall response rates (ORR), CR rates, PFS, and OS. Results: Of 986 total pts, 160 had PRD, 365 had ER and 461 had LR. Significantly higher number of pts with PRD, but not ER, had bulky disease (41% vs 27%, p<0.01) and B symptoms (53% vs 38%, p<0.001) than LR. Higher proportions of pts with PRD and ER required >1 line of ST (44% vs 30% vs 23%, p<0.001) before ASCT and received BV maintenance (25% vs 24% vs 16%, p<0.05). When adjusted for B symptoms and Bulky disease, PRD and ER had significantly lower ORR (65% vs 76% vs 84%, p<0.001) and CR (37% vs 46% vs 57%, p<0.001) to first ST than LR. Pts with PRD and ER had significantly lower PFS (56.3%, 61.4%, vs 77.6%, p<.0001) and OS (93% vs 89% vs 94%, p=0.01) than LR. In pts with ER, Brentuximab/bendamustine (BBV) and brentuximab vedotin/nivolumab (BV/nivo) had a trend towards higher ORR (92% vs 92% vs 75%) but significantly higher CR (79.2% vs 76% vs 42%, p<0.01) than platinum based chemotherapy (PBC). In pts with PRD, BBV and BV/Nivo had a statistically insignificant trend towards higher ORR and CR than PBC. The table shows 2 yr PFS by type of ST in PRD, ER, LR. There was no difference in PFS by time to relapse in BV/nivo, CPI and miscellaneous agents. BV/Nivo had a significantly higher PFS than PBC in PRD (88% vs 48%, p<0.05) and ER (95% vs 57%, p<0.05). There was no difference in PFS of PBC and other ST in PRD, ER or LR. OS was not significantly associated with type of ST in either group. Conclusions: PRD and ER are associated with lower response to ST and survival after ASCT compared to late relapse. In pts with PRD and ER, BV/Nivo has high ORR and CR and leads to significantly higher PFS comparable to pts with late relapse and may be preferable ST regardless of time to relapse. [Table: see text]