Abstract: Abstract 459 Background: While cord blood transplantation is a known risk factor for Human Herpesvirus-6 (HHV-6) reactivation, recent studies have yielded inconsistent results in regard to the level of viremia which is associated with a high risk of HHV-6 encephalitis. Moreover, the association with graft failure or transplant-related mortality is controversial. Methods: We conducted a retrospective analysis of 125 patients who underwent double-unit cord blood transplantation (DCBT) for the treatment of hematologic malignancies from 2/2006-3/2012 who were monitored for HHV-6 reactivation to examine the incidence and severity of HHV-6 viremia, the incidence of encephalitis, and the association with DCBT outcome. HHV-6 viremia was measured by quantitive PCR of HHV-6 DNA from plasma (lower limit of detection 100 DNA copies/ml). Results: Of the 125 patients (median age 42, range 1–69), 93 (74%) received myeloablative conditioning and 32 (26%) received a non-myeloablative regimen followed by 4–6/6 HLA-A, B antigen, DRB1 allele matched DCBT for the treatment of AML (N = 43, 34%), ALL (N = 24, 19%), MDS/CML/other leukemia (N = 12, 10%), or lymphoma/CLL (N = 46, 37%). No patient received anti-thymocyte globulin (ATG). Of 125 monitored patients, 117 (94%) reactivated HHV-6 to a median peak of 7,600 (range 100–160,000) copies/ml at a median onset of 20 days (range 10–59) post-DCBT. The median time to peak viremia was 23 days (range 12–62) with a median viremia duration of 10 days (range 1–60 days). Fifty-one patients (41% of total, 44% of viremic patients) developed HHV-6 〉 10,000 copies/ml (median peak viremia 31,200 copies/ml at 20 days, range 12–57). Only 6 patients (5% of total, 5% of viremic patients) developed HHV-6 〉 100,000 copies/ml (median peak 130,000 copies/ml at 19 days, range 14–29). HHV-6 encephalitis occurred in 2 patients (1.6%, peak viremias 13,000 and 118,000, respectively). One patient died from encephalitis and the other had a complete recovery following therapy. Four additional viremic patients had HHV-6 isolated from bronchoalveolar lavage but did not meet criteria for HHV-6 pneumonia. Using a high level viremia definition of 〉 10,000 copies/ml from days 14–60 (a level reportedly associated with end-organ disease and decreased survival, Dulery, BBMT 2011), viremia was not associated with diagnosis or conditioning regimen. Engrafting unit-recipient HLA-match and TNC, CD34+ and CD3+ cell dose were not associated with high level viremia. Treating viremia as a time-dependent covariate in Cox regression analysis, no association was found between viremia and neutrophil or platelet engraftment. Specifically, there were two graft failures in patients with no or low level viremia and two in patients with high level viremia. There was also no association between viremia and CMV reactivation, day 100 grade II-IV aGVHD, day 100 TRM, relapse or overall survival. A second analysis was performed to examine effects of high level viremia defined as a level 〉 25,000 copies/ml (N = 31 patients, the highest peak viremia quartile during days 14–60) and no associations with DCBT outcomes were detected. Conclusions: In our DCBT population, nearly all patients have reactivated HHV-6. However, the incidence of end-organ disease is relatively low. We postulate the difference between our findings and other studies reporting higher rates of HHV-6 encephalitis in DCBT recipients could be due to our exclusion of ATG from the conditioning regimen. At this time our understanding of the significance of HHV-6 after CBT is incomplete. We are currently evaluating anti-viral treatment responses, and ultimately a prospective trial is needed to better define the causality between HHV-6 viremia and transplantation outcomes, and to investigate the risk-benefits of pre-emptive therapy. Disclosures: No relevant conflicts of interest to declare.

Abstract: Introduction: Unrelated donor CB transplantation (CBT) is effective therapy for patients (pts) with high-risk hematologic malignancies without suitable adult donors. CBT, however, can be complicated by CMV infection in seropositive recipients with viremia rates as high as 100%. Moreover, CMV infection is associated with increased transplant-related mortality (TRM) in some reports. Therefore, our center is investigating: 1) the efficacy of pre-transplant ganciclovir (GAN) prophylaxis, 2) the efficacy of early pre-emptive therapy based on frequent serial qPCR monitoring, & 3) anti-viral therapy toxicities. The aim of this strategy is to rapidly eradicate viremia & thereby prevent disease without prohibitive toxicity. Methods: Eligible pts were adult CMV seropositive 1st allograft CB recipients transplanted 3/2013-2/2016. Pts received Cy 50/Flu 150/Thio 5-10/TBI 400 cGy myeloablative conditioning + CSA/MMF (no ATG). GAN prophylaxis (5 mg/kg IV daily) was given days -7 to -2. Viremia was evaluated by qPCR (lower detection limit 137 copies/ml) twice weekly from day +14 or earlier if indicated. Treatment for viremia was usually initiated at 1st or 2nd qPCR positivity. Foscarnet (FOS), GAN or valganciclovir (VALGAN) dosing (maintenance vs induction) was selected based on viremia level & assessment of severe infection vs toxicity risk. CMV disease was treated with induction dosing. CMV response was defined as 3 consecutive negative qPCR & no evidence of disease. Results: 42 CBT recipients [median 51 years (range 23-66), 33 acute leukemias, 6 MDS/MPD, 3 lymphomas] received double unit grafts [median donor-recipient HLA-allele match 5/8 (range 2-7/8) & infused CD34+ cell dose 1.3 (range 0.2-3.2) x 105/kg/unit]. 98% of pts engrafted (1 graft failure unrelated to CMV) & 86% (26 gr. II, 7 gr. III, 3 gr. IV) had gr. II-IV aGVHD by day 100 (median onset 29 days, range 19-35). Of the 42 pts, 35 reactivated CMV in the first 100 days [median viremia onset 33 days (range 5-74) & median viral load at 1st detection 〈 137 copies/mL (range 〈 137-245)] for a day 100 cumulative incidence of 83% (95%CI 67-92). Of 31 pts with both CMV & aGVHD, 15 developed viremia prior to & 16 after aGVHD onset. The median time from CMV detection to therapy initiation was 3 days (range 0-39). Treatment dosing, viremia vs disease & responses are shown (Figure). Induction dosing was given to one third of pts (n = 11). These pts started therapy later in their transplant course & predominantly received VALGAN. By day 100, just over half cleared viremia but none developed disease. Two-thirds of pts (n = 24) were started on maintenance dosing. They required therapy earlier post-CBT & most received FOS. 10 of these pts cleared viremia by day 100 although GI CMV disease developed in 1 pt after early therapy cessation. This pt was then successfully treated. Notably, half of the maintenance pts required escalation to induction due to persistent viremia in 10 or development of CMV pneumonia in 2 pts. The 2 pneumonia pts developed disease 26 & 12 days post-therapy initiation, respectively, & their peak viremias were 1,330 & 613 IU/ml, respectively. Both pts died of CMV & constituted 2/4 TRM deaths by day 100 in the study (other deaths were 1 DAH & 1 grade IV aGVHD). We then examined therapy toxicity in the first 100 days (Table). 4 pts received only FOS, 10 only GAN/ VALGAN, & 21 had courses of each. Therapy switches were due to toxicity, inadequate response, or convenience of oral VALGAN & therapy duration was highly variable according to infection severity, concurrent GVHD therapy, speed of viremia clearance & tolerance of drug toxicities. One-third of FOS pts & over half of GAN/ VALGAN pts had clinically significant toxicities. Conclusion: CMV infection is very frequent in adult seropositive CBT recipients & pre-CBT GAN is not effective prophylaxis. Early intensive monitoring permits early pre-emptive therapy which is effective in most pts. While maintenance dosing is effective in some, the development of lethal CMV pneumonia in 2 maintenance pts suggests dose escalation may be appropriate if rapid viremia eradication is not achieved. However, FOS/GAN/VALGAN toxicities are also significant. Ultimately, the optimal drug dosing to enhance efficacy but mitigate toxicity, how to predict pts at greatest risk of disease, appropriate therapy duration, & how to predict recurrence risk are not known. Improved CMV prophylaxis & therapy for allograft recipients including CBT pts are needed. Disclosures No relevant conflicts of interest to declare.

Abstract: Intestinal diversity is predictive of mortality in allo-HSCT.

Abstract: Introduction: We have previously reported that clinically relevant, dramatic reductions occur in intestinal bacterial diversity during allogeneic hematopoietic stem cell transplant (allo-HSCT). These are likely attributable to antibiotic exposure, nutritional alterations, and intestinal mucosa injury from high-dose chemotherapy. Patients undergoing autologous hematopoietic stem cell transplantation (AHCT) also receive antibiotics and experience nutritional alterations due to mucositis and other gastrointestinal toxicities. We hypothesized that the pattern of dysbiosis seen in AHCT patients would reflect the changes in allo-HSCT patients. Here, we present a novel analysis of microbiota diversity in AHCT patients from two independent institutions. Methods: We retrospectively identified a cohort of 365 patients (median age 60 years) who underwent AHCT for treatment of hematologic malignancy between May 2009 to February 2018 at two large-volume transplant centers in the US. The population was diverse in terms of histology, conditioning regimens and remission status prior to transplant, with 179 (49%) patients diagnosed with multiple myeloma, 153 (42%) patients diagnosed with lymphoma, and 33 (9%) patients with other diseases. Stool samples from the selected patients were collected approximately weekly during inpatient hospitalization. Sequencing of the V4-V5 region of the bacterial 16S rRNA genes from all samples was performed on the Illumina platform at a central site. Microbial diversity was measured by the Simpson reciprocal a-diversity index (S). We defined the pre-AHCT period as days -10 to 0, and computed median values for patients with multiple samples within that period. We additionally defined monodomination of the microbiota as a single operational taxonomic unit comprising 〉 30% of bacterial abundance. For comparison, we sequenced samples from 17 healthy volunteers and used a public dataset of sequences from 313 healthy volunteers from the NIH Human Microbiome Project (HMP). Median pre-transplant microbial diversity in the healthy patient and AHCT groups was compared by a pairwise Wilcox test to a retrospective cohort of allo-HSCT patients. Results: We evaluated 857 samples from 365 adult patients undergoing AHCT, with 316 patients from Memorial Sloan Kettering Cancer Center (MSKCC) and 49 patients from Duke University Medical Center (DUMC). Median pre-transplant diversity in AHCT patients from both centers was significantly lower than in normal controls (Fig 1A) (HMP vs MSKCC AHCT, S=12.05 vs. 9.19, p 〈 0.005; HMP vs DUMC AHCT, S=12.05 vs 6.91, p 〈 0.005) and reduced in both AHCT patients and allo-HSCT patients (MSKCC AHCT vs MSKCC allo-HSCT, S = 12.05 vs 8.74, p=0.53). In samples taken from days -10 to +30 after transplant, diversity decreased comparably after AHCT and allo-HSCT across both centers, while AHCT patients demonstrated a more rapid recovery at day +30 compared to allo-HSCT patients (Fig 1B). Finally, monodominance was observed in the samples (Fig 1C), with Streptococcus as the most common genus. The cumulative incidence of intestinal domination by any organism was 〉 50% by day 0 and was 〉 75% by day +14. Conclusion: Microbial diversity is reduced prior to transplant in both AHCT and allo-HSCT patients. Loss of diversity after AHCT occurs across centers and the degree of injury is comparable to the dysbiosis in allo-HSCT patients. Preliminary analysis suggests that lower diversity may correlate with worse progression-free survival (PFS) in myeloma patients in our diverse AHCT cohort. Given the known associations of alterations in microbiota composition with toxicities and overall survival in allo-HSCT patients, further evaluation of microbiota injury and its associations with toxicities, PFS, and overall survival (OS) in AHCT patients is warranted. Figure 1: A: The median Simpson reciprocal a-diversity index (S) of pre-transplant (days -10 to 0) samples of AHCT and allo-HSCT patients from two centers, as well as two cohorts of healthy volunteers, was plotted and a pairwise Wilcox test was performed, with p-values as indicated. B: (S) was plotted against time relative to allo-HSCT (on L) and AHCT (on R), for samples collected from day -10 to day +30. Larger values indicate greater diversity. C: Microbiota composition and changes in bacterial monodominance after transplant (days -14 to +28); the most common genus post-transplant is Streptococcus. Figure 1. Figure 1. Disclosures Peled: Seres Therapeutics: Research Funding. Sauter:Juno Therapeutics: Consultancy, Research Funding; Sanofi-Genzyme: Consultancy, Research Funding; Spectrum Pharmaceuticals: Consultancy; Novartis: Consultancy; Precision Biosciences: Consultancy; Kite: Consultancy. Shah:Amgen: Research Funding; Janssen: Research Funding. Perales:Novartis: Other: Personal fees; Incyte: Membership on an entity's Board of Directors or advisory committees, Other: Personal fees and Clinical trial support; Merck: Other: Personal fees; Takeda: Other: Personal fees; Abbvie: Other: Personal fees. Jenq:Ziopharm Oncology: Consultancy; Seres Therapeutics, Inc.: Membership on an entity's Board of Directors or advisory committees; MicrobiomeDx: Consultancy; Seres Therapeutics, Inc.: Patents & Royalties.

Abstract: Background: While autologous stem cell transplantation (ASCT) can be curative for patients (pts) with relapsed or refractory diffuse large B-cell lymphoma (DLBCL), relapse remains common. With the emergence of novel effective therapies, it is even more important to identify pts at high risk of treatment failure who may not benefit from ASCT, and pts with impending post-ASCT relapse who may be candidates for pre-emptive interventions. We assembled cohorts of DLBCL pts who underwent ASCT and had apheresis stem cell (ASC) samples or serially collected post-ASCT peripheral blood mononuclear cell (PBMC) and plasma samples. We hypothesized that circulating tumor DNA (ctDNA) identified using immunoglobulin-based next generation sequencing (IgNGS) in ASC or PB samples could predict relapse. Methods: Samples from 3 cohorts were analyzed. Pts in cohort 1 (C1) underwent ASCT at Dana-Farber Cancer Institute (DFCI) from 2003-2013 (Herrera, ASH 2015). Archival tumor tissue and ASC samples were retrospectively collected for analysis. Pts in cohort 2 (C2) were prospectively enrolled on a banking protocol at DFCI and underwent ASCT from 2014-2016. Pts in cohort 3 (C3) underwent ASCT from 2015-2016 and participated in a multicenter phase II trial of post-ASCT pembrolizumab maintenance (PM) (Frigault, Blood Adv 2020). Pts in C2/C3 had tumor tissue and serially collected post-ASCT PBMC and plasma samples as mandated by protocol, and a subset had available pre-ASCT PB or ASC samples. Because PM did not demonstrate a clear benefit in the trial, all cohorts were analyzed together. IgNGS (Adaptive Biotechnologies; Seattle, WA) was performed, as previously described (Armand, BJH 2013). In all cases, ctDNA testing was not performed in real-time or used to drive clinical decisions. Results: 152 pts were enrolled. Among 141 pts with sufficient DNA for testing, a clonotype was identified in 112 (78%) with a higher detection rate in more recent cohorts - C2 (93%) and C3 (90%) vs C1 (67%). Among 97 pts with an available ASC sample, 23 (24%) were ctDNA-positive (pos). With a median follow-up among survivors of 69 months (m) (range 13-185), the 5-year (y) progression-free survival (PFS) for ASC ctDNA-pos and ASC ctDNA-negative (neg) pts were 13% (95% CI 3-30%) and 52% (95% CI 40-63%), respectively (HR 2.8, p & lt;0.001), while the 5y cumulative incidences of relapse were 83% (95% CI 66-99%) and 39% (95% CI 27-50%), respectively (HR 3.1, p & lt;0.001). The sensitivity and specificity of ASC ctDNA for progression or death were 36% and 95%, respectively. ASC ctDNA (HR 2.5, p=0.002) was the only significant predictor of PFS in a multivariable model that included pre-ASCT positron emission tomography (PET), lines of therapy, age, and primary refractory status. Inferior overall survival was observed for ASC ctDNA-pos pts (HR 2.1 p=0.037). In an exploratory analysis, we examined 14 pts with an available pre-ASCT plasma sample. 2/14 were ctDNA-pos (14%) and both pts relapsed (HR for PFS 9.4, p=0.03). Among 13 pts with both pre-ASCT PB and ASC samples (drawn a median of 19 days apart [range 11-47]), results were concordant in 12/13 pts (92%). 56 pts had a median of 3 (range 1-8) post-ASCT plasma samples available for analysis. Within this cohort, 25 pts relapsed and 2 pts died in remission. 21 pts (38%) had detectable ctDNA in a median of 2 post-ASCT samples (range 1-5); among them, 18 (86%) relapsed with a median lead time from first ctDNA detection to relapse of 52 days (range 0-518). Among the 3 ctDNA-pos pts who did not relapse, 2 had detectable ctDNA at a single time point and subsequently became ctDNA-neg, and 1 developed acute myeloid leukemia and underwent allogeneic transplantation. Among 20 pts who relapsed and had ≥1 plasma sample available within 100 days of relapse, 18 (90%) had detectable ctDNA. PBMC testing had inferior performance characteristics (Table). Conclusions: Identification of ctDNA using IgNGS within an ASC sample is a powerful predictor of post-ASCT relapse and provides (at least in this cohort) a better way to predict relapse than pre-ASCT PET. Detection of ctDNA in pre-ASCT plasma also appears to be predictive of relapse. In ctDNA-pos pts, given the dismal PFS, strong consideration could be given to alternative treatment strategies, e.g. CAR-T cell therapy. Furthermore, detection of ctDNA in post-ASCT plasma samples is closely associated with impending relapse, which provides an attractive platform for pre-emptive therapeutic intervention. Figure Disclosures Brown: Dynamo Therapeutics: Consultancy; Morphosys: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other; Octapharma: Consultancy; Pfizer: Consultancy; Acerta: Consultancy; Sun: Research Funding; Genentech: Consultancy; Rigel Pharmaceuticals: Consultancy; Eli Lilly and Company: Consultancy; Juno/Celgene: Consultancy; Invectys: Membership on an entity's Board of Directors or advisory committees, Other: DSMC; Gilead: Consultancy, Research Funding; Astra-Zeneca: Consultancy; Janssen: Honoraria; Sunesis: Consultancy; Novartis: Consultancy; Loxo: Consultancy, Research Funding; Nextcea: Consultancy; MEI Pharma: Consultancy; Kite: Consultancy; Pharmacyclics: Consultancy; AbbVie: Consultancy; Catapult: Consultancy; BeiGene: Consultancy; Verastem: Consultancy, Research Funding; TG Therapeutics: Consultancy. Crombie:AbbVie: Research Funding; Bayer: Research Funding. Davids:Gilead Sciences: Consultancy; Zentalis: Consultancy; Sunesis: Consultancy; Syros Pharmaceuticals: Consultancy; Research to Practice: Honoraria; Merck: Consultancy; Bristol Myers Squibb: Research Funding; Janssen: Consultancy; Genentech: Consultancy, Research Funding; Eli Lilly: Consultancy; Celgene: Consultancy; AstraZeneca: Consultancy, Research Funding; BeiGene: Consultancy; Ascentage Pharma: Consultancy, Research Funding; Adaptive Biotechnologies: Consultancy; AbbVie: Consultancy; Novartis: Consultancy, Research Funding; Verastem: Consultancy, Research Funding; MEI Pharma: Consultancy, Research Funding; Surface Oncology: Research Funding; Pharmacyclics: Consultancy, Research Funding; TG Therapeutics: Consultancy, Research Funding. Fisher:Kyowa Kirin: Membership on an entity's Board of Directors or advisory committees. Jacobsen:Merck, Pharmacyclics, F. Hoffmann-LaRoche, Novartis: Research Funding; Takeda: Honoraria; Acerta, AstraZeneca, Merck: Consultancy. LaCasce:BMS: Consultancy; Research to Practice: Speakers Bureau; UptoDate: Patents & Royalties. Dahi:Kite: Consultancy. Nieto:Secura Bio: Other: Grant Support; Novartis: Other: Grant Support; Affimed: Consultancy, Other: Grant Support; Astra Zeneca: Other: Grant Support. Chen:Incyte Corporation: Consultancy; Takeda: Consultancy; Magenta: Consultancy; Kiadis: Consultancy; Actinium: Other: Data and Safety Monitoring Board Member; Equillium: Other: Data and Safety Monitoring Board Member; AbbVie: Other: Data and Safety Monitoring Board Member. Herrera:Pharmacyclics: Research Funding; Bristol Myers Squibb: Consultancy, Other: Travel, Accomodations, Expenses, Research Funding; Karyopharm: Consultancy; Merck: Consultancy, Research Funding; Genentech, Inc./F. Hoffmann-La Roche Ltd: Consultancy, Research Funding; Gilead Sciences: Consultancy, Research Funding; Seattle Genetics: Consultancy, Research Funding; Immune Design: Research Funding; AstraZeneca: Research Funding. Armand:IGM: Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria, Research Funding; Affimed: Consultancy, Research Funding; ADC Therapeutics: Consultancy; Celgene: Consultancy; Pfizer: Consultancy; Infinity: Consultancy; Otsuka: Research Funding; Genentech: Research Funding; Roche: Research Funding; Tensha: Research Funding; Merck: Consultancy, Honoraria, Research Funding; Adaptive: Consultancy, Research Funding; Sigma Tau: Research Funding.

Abstract: Background: Patients with diffuse large B cell lymphoma (DLBCL) who do not achieve a complete response (CR) following CD19-targeted Chimeric Antigen Receptor T cell (CAR T) therapy are less likely to obtain durable benefit. Greater tumor burden pre-CAR T has been shown to predict lower CR rate and shorter survival. Recently, patterns of failure studies have identified baseline lesion characteristics including size, SUV, and extranodal location as associated with increased risk of post-CAR T failure. It is not yet known how bridging radiotherapy (BRT) prior to CAR T can alter subsequent patterns of failure. Methods: We reviewed DLBCL patients treated from 2017 to 2021 with BRT for any intent in the period from 30d pre-leukapheresis to CAR T infusion. Comprehensive BRT fields were defined as no avidity above liver mean outside of the BRT field. Bulky disease was defined as a max diameter of ≥7.5cm in any dimension. PET response was evaluated by Lugano criteria. Pattern of failure analysis was performed to identify failure sites as pre-existing (present pre-CAR T) vs. new and as in-field, marginal, or distant with respect to BRT. Marginal was defined as failure outside of the area receiving prescription dose but within 1cm of BRT field edge. One patient with a cutaneous target was excluded from size-based analyses. Significance was assessed by Fisher's exact test or T-test. Results: Thirty-five patients were identified with a median age of 66. Most were advanced stage (74%) at BRT with a median of 3 prior lines of systemic therapy. Twelve (35%) had bulky disease at any site pre-BRT (median max diameter 5.9 cm; range 1.1 - 24) with highest overall SUV median 19.8 (range 3.4 - 47); 83% (n=29) had ≥1 extranodal site (bone: n=13; CNS: n=4). Most common BRT sites were head/neck (n=10), pelvis (n=6), and extremity (n=5). BRT targeted the largest lesion in 85% (median 5.8 cm; 32% bulky) and the site of highest SUV in 81% (median 18.7); 49% (n=17) of targets were extranodal. BRT fields were comprehensive in 39%; median radiation treatment volume was 751cc (range 18 - 5856). Twenty-four patients (63%) received ≥30 Gy (median 30 Gy; range 20 - 54). Systemic therapy was given during the bridging period to 31% (n=11). Patients received axicabtagene (n=20), tisagenlecleucel (n=11), lisocabtagene (n=3), or experimental CAR T (n=1). On PET after BRT and pre-infusion (median 12d from BRT), 85% (n=23) had achieved partial response (PR) or better in-field (CR: n=7) though 63% had kinetically active disease with out-of-field progression (PD) and 19% (n=5) had marginal PD. Despite short interval restaging, there was a significant reduction in patients with bulky disease after BRT both within the irradiated field (p=0.007) and at any site (p=0.01). (Fig 1a) A median 81% SUV reduction in the irradiated site was noted with a significant decrease in max SUV in both the irradiated (p & lt;0.001) and any (p=0.03) site. Following CAR T, 82% (n=26) achieved in-field CR and 68% (n=21) overall CR. With median post CAR T follow up of 11.5 mo (range 1.5 - 40), 20 patients (57%) ultimately failed at any site. Most failures (18/20) involved sites distant to the BRT field, however the predominant failure pattern remained within lesions that were present prior to CAR T (16/20). (Fig 1b) Eight patients failed in-field and 8 patients failed marginally; the majority (7/8 in both cases) also experienced distant failure. Comprehensive BRT was not significantly associated with decreased risk of pre-existing site failure. In the subset of patients with a bulky lesion irradiated (n=11; median lesion size 11cm), 73% (n=8) achieved a CR in-field post CAR T and of those 8, only one progressed in-field at 22 mo post CAR T. Conclusion: BRT significantly reduced the number of patients with bulky disease at any site at time of CAR T and significantly reduced the overall highest lesional SUV. Marginal failure rates of 19% and 23% at interim scan post-BRT and after CAR T, respectively in conjunction with the pattern of post CAR T failure predominantly in pre-existing sites, may suggest a need for more generous fields when a BRT approach is used in this population with rapidly proliferating disease. Further work and larger sample sizes are needed to evaluate the impact of dose on local control in bulky lesions as well as to investigate whether comprehensive BRT affects outcomes or patterns of failure. Figure 1 Figure 1. Disclosures Palomba: Juno: Patents & Royalties; Notch: Honoraria, Other: Stock; Novartis: Consultancy; Kite: Consultancy; PCYC: Consultancy; Wolters Kluwer: Patents & Royalties; Seres: Honoraria, Other: Stock, Patents & Royalties, Research Funding; Magenta: Honoraria; Ceramedix: Honoraria; WindMIL: Honoraria; Nektar: Honoraria; Rheos: Honoraria; Priothera: Honoraria; BeiGene: Consultancy; Lygenesis: Honoraria; Pluto: Honoraria. Shouval: Medexus: Consultancy. Batlevi: Kite Pharma: Consultancy; Viatris: Current holder of individual stocks in a privately-held company; Dava Oncology: Honoraria; TG Therapeutics: Consultancy; ADC Therapeutics: Consultancy; Regeneron: Current holder of individual stocks in a privately-held company; TouchIME: Honoraria; Juno/Celgene: Consultancy; Medscape: Honoraria; BMS: Current holder of individual stocks in a privately-held company; Seattle Genetics: Consultancy; Life Sciences: Consultancy; Pfizer: Current holder of individual stocks in a privately-held company; Karyopharm: Consultancy; Moderna: Current holder of individual stocks in a privately-held company; Memorial Sloan Kettering Cancer Center: Current Employment; Bayer: Research Funding; GLG Pharma: Consultancy; Xynomic: Research Funding; Roche/Genentech: Research Funding; Novartis: Research Funding; Epizyme: Research Funding; Janssen: Research Funding; Autolus: Research Funding. Brentjens: Gracell Biotechnologies, Inc: Consultancy, Ended employment in the past 24 months; BMS: Consultancy, Patents & Royalties, Research Funding; sanofi: Patents & Royalties; Caribou: Patents & Royalties. Dahi: Kite / Gilead: Membership on an entity's Board of Directors or advisory committees. Giralt: JAZZ: Membership on an entity's Board of Directors or advisory committees; AMGEN: Membership on an entity's Board of Directors or advisory committees; JENSENN: Membership on an entity's Board of Directors or advisory committees; PFIZER: Membership on an entity's Board of Directors or advisory committees; GSK: Membership on an entity's Board of Directors or advisory committees; SANOFI: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees; CELGENE: Membership on an entity's Board of Directors or advisory committees; Actinnum: Membership on an entity's Board of Directors or advisory committees. Park: BMS: Consultancy; Kite Pharma: Consultancy; Innate Pharma: Consultancy; Novartis: Consultancy; Minerva: Consultancy; Servier: Consultancy; Kura Oncology: Consultancy; PrecisionBio: Consultancy; Amgen: Consultancy; Intellia: Consultancy; Artiva: Consultancy; Curocel: Consultancy; Autolus: Consultancy; Affyimmune: Consultancy. Scordo: Angiocrine Bioscience: Consultancy, Research Funding; Kite - A Gilead Company: Membership on an entity's Board of Directors or advisory committees; i3 Health: Other: Speaker; Omeros Corporation: Consultancy; McKinsey & Company: Consultancy. Sauter: Bristol-Myers Squibb: Research Funding; GSK: Consultancy; Gamida Cell: Consultancy; Precision Biosciences: Consultancy; Kite/Gilead: Consultancy; Celgene: Consultancy, Research Funding; Genmab: Consultancy; Novartis: Consultancy; Spectrum Pharmaceuticals: Consultancy; Juno Therapeutics: Consultancy, Research Funding; Sanofi-Genzyme: Consultancy, Research Funding. Shah: Amgen: Research Funding; Janssen Pharmaceutica: Research Funding. Perales: Merck: Honoraria; Bristol-Myers Squibb: Honoraria; Celgene: Honoraria; Cidara: Honoraria; Miltenyi Biotec: Honoraria, Other; Kite/Gilead: Honoraria, Other; Equilium: Honoraria; Incyte: Honoraria, Other; Medigene: Honoraria; Karyopharm: Honoraria; Takeda: Honoraria; Servier: Honoraria; NexImmune: Honoraria; Novartis: Honoraria, Other; Nektar Therapeutics: Honoraria, Other; Sellas Life Sciences: Honoraria; Omeros: Honoraria; MorphoSys: Honoraria.

Abstract: Background: Guidelines recommend reimmunization starting 12 months after autologous hematopoietic stem cell transplant (AHCT). However, lymphoma patients routinely receive rituximab, an anti-CD20 monoclonal antibody that depletes CD20+ B-cells and may impair response to vaccination. We have shown that rituximab use may prevent on time vaccination in patients who undergo an allogeneic stem cell transplant (BBMT 2018 S427-S428). We therefore aimed to evaluate the impact of rituximab on responses to revaccination after AHCT and included patients with B-cell Non-Hodgkin Lymphoma (B-NHL) and T-cell NHL (T-NHL) and Hodgkin Lymphoma (HL), with the latter two groups not routinely receiving rituximab. Methods: Lymphoma patients who underwent AHCT between 2012 - 2016 were identified from the institutional database and included if they had completed the primary series and had pre- and post-vaccination titers to evaluate for response. Patients were divided by histology (B-NHL vs T-NHL and HL), and chart reviewed confirmed if they had received pre- or post- AHCT rituximab. Vaccine responses were determined by comparison of pre- and post- vaccination titers. Patients were classified as responders, non-responders, immune by pre-vaccination titer, and not evaluable due to missing data (had not received vaccine or had missed pre- or post-vaccination titers) by previously described criteria (Palazzo BBMT 2017). Descriptive statistics were used to summarize results, and the Fishers exact test was used for comparisons. Results: Of the 161 patients who met our inclusion criteria, 104 (65%) received rituximab pre-AHCT with 20% of these receiving additional rituximab post-HCT. Of the 57 patients who did not receive pre-AHCT rituximab, 2% received post-AHCT rituximab. The median age of the whole group was 53 years (range, 19-73), with patients not receiving rituximab being younger (median age 43 years (range 19-71) vs 58 years (21-73), p 〈 0.001). While 57% of the total population was male, there was a statistically significant difference based on rituximab use (42% of those not receiving rituximab vs 65.5% of those receiving rituximab, p=0.005). The no rituximab group comprised of 67% HL and 33% NHL, while the rituximab receiving group was 83% NHL. The most common conditioning regimen was BEAM (77%, carmustine, etoposide, cytarabine, and melphalan) with 12% receiving TBC (thiotepa, busulfan, and cyclophosphamide). Time to vaccination from AHCT was not different with a median of 12.4 months (range 9.1-21.8) in the no rituximab group compared to 12.6 months (range 11.3 - 45.7) in the rituximab exposed patients (p=0.08). The median time between last pre-AHCT rituximab and first vaccination was 14.1 months (range 12 - 79.8 months). Most patients received the completed series for each vaccine (84% Haemophilus influenzae, 99% pneumococcus, 96% polio, 66% tetanus, 76% diphtheria, 91% pertussis, 78% Hepatitis A, and 84% Hepatitis B), but vaccine responses varied by vaccine type with 48% responding to Haemophilus influenzae, 45% pneumococcus, 32% tetanus, 34% diphtheria, 52% pertussis, 31% Hepatitis A, and 37% Hepatitis B (Figure 1). Response to polio vaccine could not be calculated as 53% retained immunity and the rest of the patients were non-evaluable possibly due to a change in assay. No patients retained immunity to pneumococcus or diphtheria on the pre-vaccine titers. Univariate analyses were performed for pertussis, diphtheria, Hepatitis A, Hepatitis B and Pneumococcal vaccines evaluating the association with age, gender, disease type, and rituximab exposure. More females than males responded to B. pertussis (90% vs 78%, p=0.045). Hepatitis A and Hepatitis B response was associated with a younger age (50.7 years vs 59.6 years, p=0.037 and 54.2 years vs 62.4 years, p=0.007, respectively), and disease type was associated with pneumococcal response (62% HL vs 39% NHL, p=0.022). Patients who did not receive rituximab were more likely to respond to pneumococcus and Hepatitis B (63% vs 35%, p=0.001, and 82% vs 56%, p=0.026, respectively, Figure 2). Conclusions: Response to reimmunization with inactivated vaccines in lymphoma patients after AHCT is similar to previously reported populations, but prior rituximab exposure appears to impact response. Disclosures Matasar: Seattle Genetics: Honoraria. Moskowitz:Merck & Co: Consultancy, Research Funding; Genentech: Consultancy, Research Funding; Pharmacyclics: Research Funding; Seattle Genetics: Consultancy, Research Funding; Celgene: Consultancy. Sauter:Juno Therapeutics: Consultancy, Research Funding; Sanofi-Genzyme: Consultancy, Research Funding; Spectrum Pharmaceuticals: Consultancy; Novartis: Consultancy; Precision Biosciences: Consultancy; Kite: Consultancy. Shah:Amgen: Research Funding; Janssen: Research Funding. Perales:Abbvie: Other: Personal fees; Incyte: Membership on an entity's Board of Directors or advisory committees, Other: Personal fees and Clinical trial support; Takeda: Other: Personal fees; Merck: Other: Personal fees; Novartis: Other: Personal fees.

Abstract: Background: Classical Hodgkin lymphoma (cHL) displays near-universal genetic deregulation of PD-1 ligand expression, and relapsed/refractory (R/R) cHL is uniquely sensitive to PD-1 blockade. However, such treatment for patients (pts) who relapse after or are ineligible for autologous stem cell transplantation (ASCT) appears to be rarely, if ever, curative. Deploying PD-1 blockade early after ASCT could leverage the remodeling immune landscape and minimal residual disease state to increase the cure rate of ASCT. We therefore conducted a phase 2 multi-center single-arm study of the anti-PD-1 monoclonal antibody pembrolizumab (pembro) in pts with chemosensitive R/R cHL after ASCT. Another arm of this study enrolled pts with R/R DLBCL and will be presented separately. Methods: Adult pts with R/R cHL who had received 2-3 lines of prior therapy and ASCT and who were chemosensitive prior to ASCT were enrolled on this study. In addition to meeting standard eligibility criteria for pembro treatment, pts had to have recovered from ASCT toxicities and begin study treatment within 60 days of stem cell infusion (goal within 21 days). They received pembro 200mg IV every 3 weeks for 8 cycles. PET-CT scans were obtained at post-ASCT baseline, after 3 and 7 cycles, then at 12 and 18 months post-ASCT. The primary endpoint was the progression-free survival rate (PFS) at 18 months after ASCT, assessed using International Harmonization Project 2007 criteria. Results: 31 pts were enrolled and 1 withdrew consent before starting treatment. Among the 30 eligible patients, median age was 33 (20-69). 26 pts (87%) were high-risk by virtue of primary refractory disease (57%), relapse within 12 months (17%), extranodal disease at relapse (27%) or absence of metabolic CR at ASCT (10%). At study baseline post-ASCT, 97% were in CR. 24 pts (80%) completed 8 cycles of pembro per protocol. 6 pts (20%) stopped pembro early for pt choice (n=2, including 1 pt with gr2 pneumonitis) or toxicity (n=4, including 2 pts with gr3 hepatitis, 1 with g3 pneumonitis, 1 with g2 diplopia). 9 pts (30%) experienced a total of 28 gr3 or higher adverse events (AEs). The most common gr4 AE was neutropenia (10%). 3 patients (10%) experienced 7 gr3-4 AEs at least probably related to pembro (gr3 diarrhea and gr3 eosinophilic colitis in 1 pt, gr3 leukopenia and gr4 neutropenia in 1 pt, gr3 leukopenia and gr3 ALT and AST elevation in 1 pt). 11 pts (37%) experienced at least one immune-related AE of gr2 or higher severity: pneumonitis (n=2 gr2, n=1 gr3), thyroid dysfunction (n=1 gr2), transaminitis (n=2 gr3), colitis/diarrhea (n=1 gr2, n=2 gr3), rash (n=2 gr2), pulmonary hemorrhage (n=1 gr3), arthritis (n=1 gr2), and increased creatinine (n=1 gr2). There was no treatment-related death. Among the 30 eligible pts, 2 were lost to follow-up after their 12m assessments (both in CR). 27 pts (90%) were evaluable for the primary endpoint (the last pt is still in follow-up and results will be updated for the meeting). 6 patients (20%) relapsed at a median of 8 months (3-18) from ASCT, and all other evaluable patients were in CR at the 18m timepoint. The KM estimate of 18m PFS for high-risk patients was 78% (95%CI 54-91). The 18m overall survival was 100%. Tumor biopsies from a pt who progressed on study demonstrated an increase in the %age of PD1+ T cells at progression, as well as an increase in the %age of PD-L1+ macrophages and PD-L1+ Reed-Sternberg cells (Figure). Other correlative studies including immune reconstitution and MRD analyses are ongoing. Conclusions: Pembrolizumab administered after ASCT in patients with R/R cHL has a safety profile that appears similar to its use in the R/R setting, although possibly with a higher rate of neutropenia. The 18-month progression-free rate in this high-risk cohort compares favorably with previous published studies, and supports the hypothesis that PD-1 blockade in this setting may increase the efficacy of ASCT. This should be tested in a randomized trial. Figure. Figure. Disclosures Armand: Pfizer: Consultancy; Affimed: Consultancy, Research Funding; Otsuka: Research Funding; Merck: Consultancy, Research Funding; Infinity: Consultancy; Adaptive: Research Funding; Bristol-Myers Squibb: Consultancy, Research Funding; Roche: Research Funding; Tensha: Research Funding. Chen:Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda Pharmaceuticals: Consultancy; Magenta Therapeutics: Consultancy; REGiMMUNE: Consultancy. LaCasce:Humanigen: Consultancy, Honoraria; Research to Practice: Speakers Bureau; Bristol-Myers Squibb: Other: Data safety and monitoring board; Seattle Genetics: Consultancy, Honoraria. Jacobson:Pfizer: Consultancy; Humanigen: Consultancy; Precision Bioscience: Consultancy; Novartis: Consultancy; Kite: Consultancy; Bayer: Consultancy. Jacobsen:Merck: Consultancy; Seattle Genetics: Consultancy. Rodig:Bristol-Meyers-Squibb: Research Funding; KITE Pharma: Research Funding; Affimed Inc.: Research Funding; Merck & Co., Inc.: Research Funding. Shipp:AstraZeneca: Honoraria; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Bayer: Research Funding; Merck: Research Funding. Herrera:BMS: Consultancy, Research Funding; Merck: Consultancy, Research Funding; Genentech: Consultancy, Research Funding; Pharmacyclics: Consultancy, Research Funding; KiTE Pharma: Consultancy, Research Funding; Seattle Genetics: Research Funding; Immune Design: Research Funding; Astra Zeneca: Research Funding.

Abstract: Autologous stem cell transplantation (ASCT) is often used as consolidation for several subtypes of peripheral T-cell lymphoma (PTCL) in first remission. However, many patients relapse after ASCT and have a very poor prognosis. There are no approved treatment options for posttransplantation maintenance or consolidation in PTCL. PD-1 blockade has demonstrated some efficacy for patients with PTCL. We, therefore, conducted a phase 2 multicenter study of the anti–PD-1 monoclonal antibody pembrolizumab after ASCT in patients with PTCL in first remission. Pembrolizumab was administered at 200 mg IV every 3 weeks for up to 8 cycles within 21 days from post-ASCT discharge (and within 60 days of stem cell infusion). The primary end point was progression-free survival (PFS) at 18 months after ASCT. Twenty-one patients were treated in this study and 67% (n = 14) completed 8 cycles of treatment. Among all patients who were evaluable, 13 of 21 were alive and achieved PFS at 18 months after ASCT, meeting the study’s primary end point. The estimated 18-month PFS was 83.6% (95% confidence interval [CI], 68-100), and overall survival 94.4% (95% CI, 84-100). The toxicity profile was consistent with the known toxicity profile of pembrolizumab, with no grade 5 toxicities. In conclusion, PD-1 blockade after ASCT with pembrolizumab is feasible with a favorable safety profile and promising activity, supporting further confirmatory studies. This trial was registered at www.clinicaltrials.gov as #NCT02362997.

Abstract: Autologous stem cell transplantation (ASCT) remains the standard of care for patients with relapsed/refractory (RR) classical Hodgkin lymphoma (cHL) who respond to salvage chemotherapy. However, relapse after ASCT remains a frequent cause of treatment failure, with poor subsequent prognosis. Because cHL is uniquely vulnerable to programmed cell death-1 (PD-1) blockade, PD-1 blockade given as consolidation after ASCT could improve ASCT outcomes. We therefore conducted a multicohort phase 2 study of pembrolizumab in patients with RR cHL after ASCT, hypothesizing that it would improve the progression-free survival (PFS) at 18 months after ASCT (primary end point) from 60% to 80%. Pembrolizumab was administered at 200 mg IV every 3 weeks for up to 8 cycles, starting within 21 days of post-ASCT discharge. Thirty patients were treated on this study. The median age was 33 years, and 90% were high-risk by clinical criteria. Seventy-seven percent completed all 8 cycles. Toxicity was manageable, with 30% of patients experiencing at least 1 grade 3 or higher adverse event (AE), and 40% at least 1 grade 2 or higher immune-related AE. Two patients were lost to follow-up in complete remission at 12 months. The PFS at 18 months for the 28 evaluable patients was 82%, meeting the primary end point. The 18-month overall survival was 100%. In conclusion, pembrolizumab was successfully administered as post-ASCT consolidation in patients with RR cHL, and resulted in a promising PFS in a high-risk patient cohort, supporting the testing of this strategy in a randomized trial. This trial was registered at www.clinicaltrials.gov as #NCT02362997.