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Introduction The advent of venetoclax (VEN) based chemotherapy has revolutionized the treatment of elderly acute myeloid leukemia (AML), with improvement in remission rates from historical 10%-20% to 60%-70%. However, remission duration is short-lived in patients (pts) with high-risk AML with consequent dismal outcome. As our knowledge of genomic landscape of AML expands and more immunotherapies become available, exploration of the immune tumor microenvironment (TME) of AML may allow identification of subsets of pts that may benefit from immune based therapy. We conducted an investigator initiated prospective study to evaluate TME of pts receiving VEN plus hypomethylating agent (HMA; azacitidine or decitabine) combination. We hypothesize that these pts will cluster into immune-infiltrated vs. immune-depleted sub-types by high-definition immune cell profiling. Methods In 26 newly diagnosed AML pts, who were planned to receive VEN plus HMA therapy, we isolated bone marrow (BM) and peripheral blood (PB) derived mononuclear cells (MC) by density gradient centrifugation and cryopreserved. We performed CyTOF (cytometry time-of-flight) analysis to study their immune signatures. Thawed cells were labeled with metal-conjugated antibodies that bind CD33, CD196, CD19, CD127, CD11b, CD4, IgD, CD11c, CD14, CD56, CD123, TCRgd, CD185/CXCR5, CD45RA, CD27, CD28, CD66b, CD183 (CXCR3), CD161, CD45RO, CD197 (CCR7), CD8a, CD25, CD3, CD20, CD38, HLA-DR, CD194 (CCR4), CD57, CD16 and CD45. We performed a Rphenograph clustering on 25 paired BMMC and PBMC samples (one patient only had PBMC) to create 35 unique clusters for each ( Figure 1). Then we broke down the distribution of cluster by two different groupings: pts with TP53 mutation (m) and those who achieve complete remission. Statistical significance of clusters calculated using t-test. We performed Pearson correlation test on the paired BMMC and PBMC samples to assess correlation between BMMC and PBMC samples. Results Baseline characteristics The median age of the pts was 74 years (range, 53-88), and 17 (65%) pts were male. Ten (37%) pts had secondary AML, and 12 (46%) pts had ELN adverse risk disease (n=6; TP53m). There was no significant difference in median age (p= >0.99), proportion of pts with secondary AML (p= 0.64), acute myelomonocytic leukemia (p= 0.14) white blood cell count (WBC) ≥ 100 (10 9/L) (p= >0.99), and frequency of commonly occurring co-mutations ( ASXL1 [p=0.35]), FLT3 ITD [p=0.54], splicing [p=0.29], IDH1/2 [p=0.28], DNMT3A [p=0.29], NPM1 [p=0.29], TET2 [p=0.35]) in TP53m and TP53 wild-type group. Response 12/20 (60%) evaluable pts achieved complete remission with or without count recovery (CR/CRi). There was no significant difference in median age (p= 0.06), proportion of pts with secondary AML (p= 0.16), therapy related AML (p= 0.60) WBC ≥ 100 (10 9/L) (p= 0.40), and frequency of commonly occurring mutations ( TP53 [p=0.60], ASXL1 [p > 0.99]), FLT3 ITD [p=0.54], splicing [p > 0.99], IDH1/2 [p=0.60], DNMT3A [p=>0.99], NPM1 [p=0.61], TET2 [p >0.99]) in CR/CRi and no-CR/CRi group. CyTOF analysis and Rphenograph clustering on 25 paired BMMC and PBMC samples We found significant clustering with high expression of B-cell activated (cluster 2; p= 0.005), NK cell rich (cluster 1; p= 0.005, cluster 35; p= 0.0009), CD8 T-cells (cluster 31; p= 0.01) and CD4 effector cells (cluster 17; p= 0.005) phenotype among TP53m AML ( Table 1). Among pts who achieved CR/CRi, significant clustering with low expression of B-cell activated (cluster 29; p= 0.01), CD8 cytotoxic (cluster 14; p= 0.01) CD4 activated (cluster 21; p= 0.03) phenotypes observed. Correlation between BMMC and PBMC clustering Among clusters which showed significance for a particular phenotype, we performed Pearson correlation (R 2) and observed strong correlation between BMMC and PBMC samples clustering in cluster 1 (R 2 = 0.99), cluster 2 (R 2 = 0.95), cluster 17 (R 2 = 0.96), cluster 21 (R 2 = 0.99) and cluster 29 (R 2 = 0.93). Conclusion In this single institutional study using CyTOF analysis we have identified novel clustering with immune- infiltrated phenotype among pts with TP53m AML and conversely immune-depleted phenotype among AML pts who responded to VEN plus HMA. Moreover, we found strong correlation in CyTOF analysis conducted from BMMC and PBMC samples. Future studies with larger sample size needed to validate our findings.

Introduction: Chimeric antigen receptor T-cell therapy (CAR-T) has revolutionized the treatment of non-Hodgkin lymphoma (NHL). Despite having an increased risk of NHL, patients with pre-existing autoimmune disease (AID) were excluded from pivotal CAR-T trials due to concerns that CAR-T may exacerbate AID. As a result, there are limited data on the safety and efficacy of CAR-T for NHL in patients with AID. Interestingly, there is also growing evidence that CAR-T can be therapeutically effective for AID, such as in the treatment of systemic lupus erythematosus (SLE). As CAR-T utilization for NHL increases, it is essential to characterize the safety and efficacy of this potentially curative therapy in patients with AID. This study aimed to evaluate the impact of AID on outcomes in patients treated with commercial CD19-targeted CAR-T for NHL. Methods: Following Institutional Review Board approval, we conducted a retrospective analysis of all patients who were treated with commercial CD19-targeted CAR-T for NHL and had a pre-existing AID across the Mayo Clinic Enterprise (Arizona, Florida, and Minnesota) between January 2018 and May 2023. Variables collected included age, gender, NHL type, AID type, and CAR-T product. Efficacy outcomes, including response rates at 6 and 12 months after CAR-T, were collected. Toxicities, including cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS), were collected and analyzed. Our chart review for AID included SLE, sarcoidosis, ulcerative colitis, celiac disease, pernicious anemia, Crohn's disease, psoriasis, Sjogren's syndrome, hypothyroidism (Hashimoto's disease), hyperthyroidism (Graves' disease), rheumatoid arthritis (RA), vasculitis, scleroderma, and mixed connective tissue disease (MCTD). Results: A total of 235 patients who received commercial CD19-targeted CAR-T for NHL across the Mayo Clinic Enterprise were identified (Table 1). Of these 235 patients, 27 had a pre-existing AID and 208 did not. The median age was 66 years (range 39-81) for patients with AID and 59 years (range 18-88) for patients without AID. Over half of the patients were male (59% of patients with AID and 51% of patients without AID). The most common NHL type was diffuse large B cell lymphoma (41% of patients with AID and 56% of patients without AID). Most patients received axicabtagene ciloleucel (85% of patients with AID and 84% of patients without AID). The most common AID was hypothyroidism (81%, n=22), although other conditions were also identified, including RA (11%, n=3), SLE (4%, n=1), pulmonary sarcoidosis (4%, n=1), psoriasis (4%, n=1), and MCTD (4%, n=1). Two patients had more than one AID. Median follow-up was 18 months (range 1-36) for patients with AID and 14 months (range 2-49) for patients without AID. Six months after CAR-T, the complete response (CR) rate was 77.2% and 45.1% in patients with AID and without AID, respectively (p=0.0042). Twelve months after CAR-T, the CR rate was 50% and 31.4% in patients with AID and without AID, respectively (p=0.0801). CRS of any grade occurred in 78% and 88% of patients with and without AID, respectively. ICANS of any grade occurred in 41% and 54% of patients with and without AID, respectively. Conclusion: AID did not appear to adversely impact the safety or efficacy of CAR-T for NHL. Limitations of our study include the small number of patients with AID and the fact that the most common AID was hypothyroidism. Larger studies are warranted to confirm these findings. Additional data are needed to characterize the impact of CAR-T for NHL on AID outcomes and to describe the effect of disease-modifying antirheumatic drugs on NHL outcomes after CAR-T.

Introduction: NGS is increasingly being utilized to identify pathogenic somatic and targetable variants in patients with newly diagnosed AML and MDS. Patients with high-risk disease are typically recommended to undergo allo-HCT as consolidation, upon achieving morphological complete remission (CR). But, despite achieving hematologic CR, patients often have detectable somatic variants pre allo-HCT that predict for increased risk of disease relapse. Longitudinal monitoring of somatic variants via NGS at diagnosis, pre-allo-HCT and post allo-HCT can assist in prognostication and identify patients that remain at high risk of relapse despite allo-HCT. Methods: Patients with AML or MDS who underwent a first allo-HCT and completed NGS testing at day +100 between years 2016 to 2021 were identified from the transplant registry of Mayo Clinic in Florida. The primary aim of the study was to evaluate the prognostic impact of detectable variants via NGS at day +100 days post allo-HCT on the following outcomes: 1) overall survival (OS), 2) relapse, 3) progression-free survival (PFS), and 4) non-relapse mortality (NRM). Disease risk was assessed based on European Leukemia Network (ELN) 2022 risk classification for AML and Revised International Prognostic Scoring System (R-IPPS) for MDS. Baseline variables were compared between patients with and without mutation at day +100 days post allo-HCT using Wilcoxon rank sum test for continuous variables and Fisher's exact test for categorical variables. Kaplan-Meier (KM) method was used to estimate freedom from events at different time points and draw corresponding survival curves. Results: 105 patients who underwent allo-HCT for AML and MDS and completed NGS testing at day +100 were included in the study population. Median age of the study population was 63 years (22-74) and 58% were of the male gender. Median HCT comorbidity score (HCT-CI) and KPS Karnofsky performance score (KPS) were 3 (0-8) and 90 (60-100), respectively. Matched unrelated donor (50%) and peripheral blood stem cells (98%) were the most common donor and graft source, respectively. Median number of lines of therapy pre allo-HCT was 1(0-6) and 52 (50%) patients had detectable variants after completion of chemotherapy and prior to allo-HCT. Seventeen (16%) had detectable variants via NGS on day +100. Eleven (65%) of these 17 had variants pre-allo-HCT and amongst the 88 patients with no variants post allo-HCT, 41 (47%) had detectable variants pre allo-HCT. There was no significant difference in baseline characteristics between patients with detectable variants at day+100 versus those who did not except for a higher KPS in patients with no variants at Day +100 of 90 (60-100) vs. 80 (60-100) (p=0.003). At a median follow up of 1.4 years (0.1-5.5), presence of a variant at day +100 was associated with inferior 4-year OS (32% vs. 69%, p<0.001) and higher relapse risk (64% vs. 23%, p<0.001). In univariate models, a lower KPS and presence of variants post allo-HCT were significantly associated with inferior OS, high relapse risk and worse PFS. Presence of variants pre allo-HCT was associated with an inferior PFS but did not impact OS or relapse risk. In multivariate models, KPS remained significant for OS, PFS and NRM; presence of variants at day +100 post allo-HCT approached significance for OS (p=0.06) and PFS (p=0.08) and was significant for relapse risk (p=0.002) (Table1) (Figure 1). Data regarding longitudinal evolution of variants and impact of individual variants on long term outcomes will be included at the time of presentation. Conclusion: These results indicate that presence of detectable somatic variants at day +100 is associated with poor long-term outcomes and predicts for high risk of disease relapse. Longitudinal monitoring of somatic variants via NGS should be consistently incorporated in the management of patients with high-risk AML and MDS undergoing allo-HCT. Patients with detectable somatic variants post allo-HCT should be considered for additional intervention to mitigate relapse risk.

Purpose The predominant pattern of relapse for patients with B-cell non-Hodgkin lymphoma (NHL) who undergo anti-CD19 Chimeric Antigen Receptor T-cell Therapy (CART) involves sites previously involved by NHL. Bridging radiotherapy (BRT) has shown to be an effective bridging treatment with excellent local control rates. Our previous work defined limited/oligometastatic lymphoma as disease involving <5 sites. This study is the first to report on the role of BRT for patients with limited (<5 involved sites) disease prior to CART. Methods Following Institutional Review Board approval, a retrospective review from 2018 to 2023 across 3 Mayo Clinic sites (Arizona, Florida, and Minnesota) was performed and identified 139 patients with relapsed/refractory (r/r) B-cell NHL without bone marrow involvement who received CART and had <5 disease sites prior to leukapheresis. Ann Arbor staging was used to define the number of involved disease sites. An involved disease site included the Ann Arbor anatomical lymph node region(s) harboring the pathological lymph node(s) or any extranodal lesion. Bridging treatment (radiation and/or systemic therapy) was defined as treatment administered between leukapheresis and CART infusion. The primary endpoint was event-free survival (EFS),defined from CART infusion to any disease progression or initiation of post-CART consolidative/salvage therapy. Secondary endpoints included progression -free survival (PFS),defined from CART infusion to any disease progression, and overall survival (OS), defined from CART infusion to death. Results Prior to CART infusion, 44 (32%) patients received BRT and 95 (68%) did not. Bridging systemic therapy was given to 5 (11%) and 34 (36%) patients in the BRT and no BRT groups, respectively (p=0.003). The median number of involved disease sites prior to leukapheresis was 2 (range: 1-4). There was no significant difference in the baseline characteristics prior to CART infusion between the BRT and no BRT groups, except for extranodal involvement that was more common in the BRT group (Table 1). The median equivalent 2 Gy dose was 27 Gy (Interquartile range 23-34), and the most common BRT regimen was 20 Gy in 5 fractions. Among the 44 BRT patients, 34 received radiation to all visible PET-avid disease sites, and 10 received radiation to some but not all disease sites. The median follow-up was 20 months. The rate of grade ≥2 cytokine release syndrome was 41% in both groups (p=0.99). The rate of grade ≥2 immune effector cell-associated neurotoxicity syndrome was 21% and 37% in the BRT and no BRT groups, respectively (p=0.059). There were no observed grade ≥3 BRT-related toxicities. Objective response rate by PET 5 point scale was higher in the BRT group (93% versus 79%; p=0.036). Crude rates of progression were 30% in BRT and 55% in no BRT patients, with 9/13 (69%) and 43/52 (83%) patients relapsing in pre-existing sites of disease present prior to CART infusion in the BRT and no BRT group, respectively. Seven (16%) BRT patients relapsed in the radiation field. The 2-year EFS was 50% in the BRT group and 39% in the no BRT group (p=0.01). The 2-year PFS was 55% in the BRT group and 45% in the no BRT group (p=0.017). The 2-year OS was 55% in the BRT group and 62% in the no BRT group (p=0.7). Intriguingly, patients who received BRT to all visible PET-avid disease sites (n=34) had further improvement in 2-year EFS (67% vs 39%, p=0.003) and 2-year PFS (71% vs 46%, p=0.008) compared to no BRT or patients who received BRT to some but not all visible disease sites (n=105). Nine patients (2 in BRT and 7 in no BRT groups) received consolidative radiotherapy for day 30 residual disease with only one patient subsequently experiencing progression. Twenty-five patients (6 in BRT and 19 in no BRT groups) received salvage/palliative RT for post-CART relapsed disease. Thirty-seven (39%) patients in the no BRT group remained without disease progression and did not receive radiation in the bridging, consolidative or salvage/palliative setting. Conclusion Bridging radiotherapy prior to CART infusion for patients with limited (<5 involved disease sites) r/r NHL appears to improve response rate, EFS, and PFS without causing significant toxicities. Approximately one third of patients who do not receive BRT will require subsequent post-CART radiation, and another third will remain free of radiation and disease progression.

Background: Venetoclax (Ven) in combination with hypomethylating agent (HMA) is the preferred treatment for elderly/unfit patients with newly-diagnosed acute myeloid leukemia (AML). Current prognostication for AML is based on European LeukemiaNet (ELN) genetic risk stratification which has limited applicability in patients treated with Ven-HMA ( Blood, 2022). Accordingly, our primary objective was to determine predictors of treatment response and survival outcomes in treatment-naïve AML patients receiving Ven-HMA. Methods: Our study population was recruited from Mayo Clinic (MN, FL, AZ), after institutional review board approval and based on documentation of newly-diagnosed AML treated with Ven-HMA outside of clinical trials between November 2018 and April 2023. Cytogenetic and molecular studies were performed by conventional karyotype, and next-generation sequencing, respectively. Response was assessed according to the 2022 ELN criteria Results: Patient characteristics A total of 301 newly-diagnosed AML patients (median age 73 years, 66% male, 62% de novo) received a median of 3 cycles (range 1-48) of azacitidine 75 mg/m2 days 1-7 ( n=100) or decitabine 20 mg/m2 days 1-5 ( n=201) with Ven. ELN 2022 cytogenetic risk included favorable (1%, n=4), intermediate (61%, n=184) or adverse (38%, n=113). Mutations involved TP53 in 77/301 (25%), ASXL1 in 54/279 (19%), RUNX1 in 54/296 (18%), NPM1 in 44/299 (15%), DNMT3A in 40/296 (13%), K/NRAS in 41/296 (14%), IDH1 in 20/301 (6%), IDH2 in 30/301 (10%), FLT3-ITD in 25/301 (8%) and DDX41 in 9/247 (4%) of informative cases. Predictors of response Complete remission, with (CR) or without (CRi), count recovery, was documented in 182 (60%) patients, including CR in 36% and measurable residual disease (MRD) negative by flow cytometry in 77% of 105 informative cases that achieved CR/CRi. Median time to CR/CRi was 1.4 months. In univariate analysis, CR/CRi was more likely to occur in the presence of NPM1 mutation, (86% vs. 56%; p < .01), IDH2 mutation, (80% vs. 58%; p = .02), DNMT3A mutation, (78% vs. 57%; p = .01), or DDX41 mutation, (100% vs. 58%; p <.01), and in the absence of adverse karyotype, (71% vs. 42%; p < .01), TP53 mutation, (67% vs. 40%; p <.01), FLT3-ITD mutation, (63% vs. 36%; p = .01), or RUNX1 mutation, (64% vs. 44%; p = .01); in multivariable analysis, adverse karyotype, ( p < .01), FLT3-ITD ( p < .01), RUNX1 ( p < .01), NPM1 ( p = .03), IDH2 ( p = .04), and DDX41, ( p = .01) mutations remained significant. Predictors of survival After a median follow-up of 8.5 months (range 0.5-56), 13.2 months for living patients, 174 (58%) deaths, 73 relapses (40% of those achieving CR/CRi), and 41 (14%; including 35 in CR/CRi) allogeneic hematopoietic stem cell tranplants (AHSCT) were documented. In univariate analysis of pre-treatment variables, thrombocytopenia < 100 x 10 9/l, (HR 1.5, 95% CI 1.03-2.2; p = .03), adverse karyotype, (HR 2.8, 95% CI 2.1-3.8; p < .01) TP53 mutation, (HR 2.5, 95% CI 1.8-3.5; p < .01), or absence of IDH2 mutation, (HR 3.5, 95% CI 1.7-7.6; p < .01) predicted inferior survival. Failure to achieve CR/CRi (HR 4.5, 95% CI 3.3-6.1; p < .01) was also associated with inferior survival and in multivariable analysis, failure to achieve CR/CRi, (HR 3.4, 95% CI 2.5-4.8; p< .01), presence of adverse karyotype, (HR 1.6, 95% CI 1.1-2.6; p = .02), TP53 mutation, (HR 1.6, 95% CI 1.002-2.4; p = .04), and absence of IDH2 mutation (HR 2.2, 95% CI 1.004-4.7; p = .04) were identified as risk factors for survival. Subsequent HR-weighted scoring resulted in three-tiered risk stratification: low (0-1 point; n= 130), intermediate (2-3 points; n= 105), and high (4-5 points; n= 66), with respective median survival (3-year rate) of 28.9 (48%), 9.6 (6%), and 3.1 (0%) months ( p < .01) (Figure). AHSCT had an independent favorable impact on survival (HR 0.3, 95% CI 0.1-0.6; p < .01), most apparent in low ( p =0.04), and intermediate ( p <.01), as opposed to high ( p = .06) risk. Conclusions: In the current single institutional series of Ven-HMA treated newly-diagnosed AML, response to Ven-HMA was the foremost predictor of survival. Additional risk factors for survival included adverse karyotype, presence of TP53 and absence of IDH2 mutations. These observations allowed for a three-tiered genetics-enhanced survival model with CR/CRi as a backbone, and also confirmed survival advantage from AHSCT, regardless of risk category.

Introduction Atrial fibrillation/flutter (Afib) contributes independently to the hematopoietic cell transplant comorbidity index (HCTCI) and is a known complication of allogeneic hematopoietic transplantation (AlloHCT) which has been linked to inferior outcomes, particularly in older patients. An electrocardiogram (ECG)-based artificial intelligence (AI) algorithm to predict Afib and cardiac contractile dysfunction risk has been validated (Lancet 394:861, 2019). We hypothesized that assessment of pre-transplant Afib risk using the AI algorithm may predict future development of Afib and help identify patients at higher risk for this complication. Methods 191 consecutive MDS patients undergoing AlloHCT with curative intent using myeloablative (28.3%) or reduced intensity conditioning (62.3%) in the Mayo Clinic Comprehensive Cancer Center (Rochester, Jacksonville, Phoenix) between November 2015 and January 2022 were included in this retrospective analysis. Primary outcome was Afib within 100 days and 365 days of transplantation, and we also assessed the outcomes of Death and Relapse. Revised IPSS (IPSS-R) and HCTCI scores were included for all patients. Elevated Afib risk score using the AI algorithm was calculated from pre-transplant ECG, performed during vital organ testing at AlloHCT clearance. In addition to left ventricular (LV) ejection fraction (EF) we evaluated detailed echocardiographic (Echo) parameters including LV volume and mass indices, left atrial volume index (LAVI), maximum trans mitral flow velocities during LV filling (E velocity) and during the diastolic phase due to atrial contraction (A velocity), the velocity of the annulus away from the apex during the protodiastolic phase (e' velocity), E/A and E/e' ratios, the presence of valvular disease, and right ventricular systolic pressure (RVSP). We performed an analysis using a Cox proportional hazards regression models (adjusting for age and sex) to evaluate associations with Afib risk, Relapse, and Overall Survival. Results The median age was 64 years (18-75), 58.6% were male, 6.9% non-white race, and 3.7% Hispanic/Latino ethnicity. Most patients had an HCTCI score of 0-3 (76.3%). GVHD prophylaxis was predominantly with calcineurin inhibitor-based regimes plus/minus methotrexate or mycophenolate mofetil (83.8%). 5.2% of patients had a history of Afib before transplant. Non-relapse mortality was 7.9% at 100 days, and 18.3% at 365 days. N=25 patients (13.1%) developed Afib within 100 days, and n=28 (14.7%) within 1-year after AlloHCT. On multivariable analysis, Age [Hazard Ratio (HR) 2.83, 95% Confidence Interval (CI) 1.36-5.89, p=0.0055] and Echo parameters [including LAVI (HR 2.10, CI 1.23-3.58, p=0.0067), E velocity (HR 3.28, CI 1.29-8.80, p=0.013), E/A ratio (HR 3.74, CI 1.75-7.97, p=0.0006), E/e ' ratio (HR 1.81, CI 1.07-3.07, p=0.026) and RVSP (HR 1.68, CI 1.04-2.70, p=0.032)] were significantly associated with Afib risk; elevated AI risk score was significant in the univariate model (HR 2.74, CI 1.15-6.53, p=0.023) but was borderline in the multivariate model (HR 2.34, CI 0.98-5.60, p=0.056) ( Table 1). Based on previous observations we evaluated the association of AI and Echo parameters with Relapse and Death after AlloHCT ( Table 1). Age (HR 1.32, CI 1.01-1.71, p=0.041) and IPSS-R (HR 1.20, CI 1.08-1.33, p=0.0009) were significantly associated with Death after AlloHCT, while HCTCI (HR 1.10, CI 1.00-1.22, p=0.052) and higher LV EF (HR 0.63, CI 0.38-1.06, p=0.084) were borderline. For Relapse, only IPSS-R (HR 1.52, CI 1.31-1.75, p=1.22E-08) was significant, while increase Echo E velocity was of borderline significance (HR 0.45, CI 0.20-1.02, p=0.057). Conclusions Afib is a common post-AlloHCT complication and is more frequent with increasing Age. Echo parameters (specifically E/A ratio) predict significantly higher Afib risk, while the baseline ECG AI algorithm was of borderline significance. The selection of patients with lower HCTCI scores, and the low background prevalence of Afib in this cohort (i.e., selection of patients with lower baseline cardiac morbidity) are possible explanations for non-significance of the AI algorithm. As anticipated Age and IPSS-R are the greatest predictors of Death after AlloHCT, although the suggestion of an association with baseline Echo parameters highlights the importance of identifying those who may benefit from preemptive Cardiology intervention.

Introduction Relapsed or refractory (r/r) acute myeloid leukemia (AML) has a dismal prognosis. Treatment options are limited and include fludarabine (Flu) and cytarabine (Ara-C), +/- anthracyclines (e.g., FLAG-Ida). Recent progress has been limited to targeted therapies, which benefit only a subset of the population; efforts to develop cellular therapies have not been met with success. NKX101 is an NK cell therapy derived from healthy donors and engineered to express an NKG2D ligand-directed chimeric antigen receptor (CAR) to enhance killing of malignant cells, as well as a membrane bound form of interleukin (IL)-15 to promote persistence and activity. Because Ara-C is known to upregulate NKG2D ligand expression, use of Flu/Ara-C as an alternative to standard Flu/cyclophosphamide (Flu/Cy) for lymphodepletion (LD) was tested for NKX101. Methods Six patients with r/r AML were enrolled in this cohort of NKX101-101, a Phase 1 safety study. All patients had received at least one prior line of therapy, as well as approved targeted therapies for those with underlying genetic mutations. Patients received NKX101 at a dose of 1.5 billion (B) viable CAR+ cells/dose on Days 0, 7, and 14 after LD comprising Flu (30 mg/m2) and Ara-C (2 g/m2) each once daily for five days and 2 days of rest. Efficacy assessments were performed on Day 27 and included bone marrow aspiration and biopsy. Additional treatment cycles of LD and NKX101 were given to some patients to deepen or consolidate responses. Pharmacokinetic (PK) and cytokine sampling were performed throughout the treatment cycle(s). Results At baseline, five out of six patients had poor-risk genetic features, including TP53 mutation; the median bone marrow blast count was 35% (range: 20 - 86%). Patients had received a median of two prior lines of therapy, with all patients having previous venetoclax exposure (Table 1). All patients received at least three doses of NKX101 at 1.5 B cells/dose. There were no cases of cytokine release syndrome (CRS), immune cell associated neurotoxicity syndrome (ICANS), or graft-versus-host disease of any grade in any patients (Table 2). Myelosuppression and infection were the most common higher-grade toxicities. Four out of six patients had CR/CRi, with three out of six achieving CR. Three of these patients had no detectable MRD by flow, and one had 0.18% RUNX1-RUNX1T1 translocation via polymerase chain reaction testing on bone marrow. One subject was taken to consolidative hematopoietic cell transplant (HCT) and remains in CR. Another subject received a consolidative cycle of therapy and remains in CR. A third subject had three cycles of treatment with successive decrease in disease burden and remains in CRi. The fourth subject had CR after one cycle of treatment. PK profiling showed that NKX101 was consistently detected and correlated with infusion days (Figure 1). Cytokine data showed minimal post-infusion elevations above baseline; no association was observed between clinical response and elevation of serum cytokines (including IL-15, IL-6, IFNγ, IL-10, and IL-8). Data on the expression of NKG2D ligands (MICA, MICB, ULBP1, and ULBP3) in subject bone marrow samples were obtained via multiplex immunohistochemistry. This was evaluated as a composite H-score. Responders were split between those with relatively low ligand expression and those with higher ligand expression, suggesting that further factors may contribute to NK cell resistance. Conclusions Alternative LD with Flu/Ara-C followed by NKX101 shows promising early responses including MRD negativity in r/r AML. The toxicity profile of this regimen is manageable and was consistent with underlying AML and exposure to LD, without any events of CRS or ICANS. Expansion of enrollment and longer follow-up are needed. Despite being an allogeneic, non-HLA-matched cell product, NKX101 persisted for up to three weeks in PK testing. Directly comparing the data from patients treated with Flu/Cy with NKX101 versus Flu/Ara-C with NKX101 suggests that Flu/Ara-C can replace the Flu/Cy regimen common to CAR T cell therapy as LD without compromising overall NKX101 exposure.

Background: BMT CTN 1703 was a Phase 3 trial comparing Tac/MTX (n = 217) to post-transplant cyclophosphamide (PT-Cy)/Tac/MMF (n = 214) GVHD prophylaxis after reduced intensity conditioning unrelated donor hematopoietic cell transplant (HCT). PT-Cy significantly improved GVHD-free Relapse-Free Survival (Bolanos-Meade et al NEJM 2023). However overall survival was not significantly different and the # of Grade 2 infections was higher with PT-Cy. To investigate its biologic underpinnings 1703 was linked to a mechanistic study, BMT CTN 1801, which co-enrolled 324 pts (159 CNI/MTX 165 PT-Cy). The resulting dataset enabled an analysis of post-HCT T cell reconstitution at an unprecedented level of detail. Methods: Samples were collected from the HCT infusion and on D+7, 14, 28, 63, 98, 180, 270, 1- and 2-yr. We extracted DNA (2,225 samples) and performed Adaptive Biotech β-strand T Cell Receptor (TCR) Immunosequencing (TCR-Seq). We profiled 44,077 (median) TCRs/sample resulting in 215,155,719 T cells analyzed. We evaluated multiple TCR diversity measures longitudinally and before/after cGVHD and infections. Each measure evaluates a specific aspect of TCR diversity, including Simpsons Clonality (focuses on the most expanded clones) Diversity Slope (mid-range clones) Richness (both mid-range and less-expanded clones) and Singletons (the TCR-Seq equivalent of naïve T cells). This analysis was robust to the full range (1000-50,000) of down-sampled TCRs sequenced. Results: We identified major differences in TCR reconstitution in Tac/MTX vs PT-Cy that begin early and persist through 2 yr post-HCT. These resulted in a significantly less diverse TCR repertoire with PT-Cy with substantial implications for its efficacy and toxicity. The most salient differences are: (1) PT-Cy caused significant in-vivo T cell depletion early post-HCT (% T cells/total WBC at D+28: 8.2% (Tac/MTX) vs 2.2% (PT-Cy) p=2.2x10 -23). (2) The remaining donor T cells in PT-Cy undergo substantial clonal expansion ( Fig 1) resulting in significantly constrained TCR diversity measured by Clonality, Slope, Richness, Singletons (not shown) and Singletons/Richness ( Fig 2) which began early (D+14) and persisted for 2 yr. (3) Linked T cell depletion and clonal expansion resulted in a TCR diversity bottleneck after PT-Cy ( Fig 1). Due to the bottleneck, while the fraction of T cells originating from the transplant infusion at =/> 1 yr was similar between arms (18% vs 24%, p=0.7) there were significantly fewer Singleton TCRs in PT-Cy, suggesting a reduction in naïve T cells ( Fig 2), an outcome that has critical consequences for both cGVHD and infection. Thus while cGVHD onset with Tac/MTX was linked to a significant drop in TCR diversity due to singleton clonal expansion (median log-2 fold change in singletons with Tac/MTX = -0.25 p = 0.01) this drop was not observed with PT-Cy (log-2 fold change = -0.05, p = 0.1). Along with the significantly decreased # singletons at all time-points in PT-Cy ( Fig 2) this suggests that while cGVHD after Tac/MTX is linked to substantial naïve T cell expansion, the same is not true with PT-Cy, identifying a novel mechanism for cGVHD control with PT-Cy. The substantially fewer singletons in PT-Cy vs Tac/MTX may also increase the risk of Grade 2+ infections. T cell responses to new infections rely on antigen recognition/effector maturation of naïve (singleton TCR) T cells. After infection, the TCR repertoire became less diverse for both Tac/MTX and PT-Cy (log-2-fold singleton change -0.17 and -1.2 p = 0.0006 and 0.01) indicating that singletons in both cohorts were capable of expanding to pathogens. However the markedly decreased # singletons in PT-Cy at all timepoints was associated with significantly fewer singletons prior to infection (mean 3979 at 5K read-depth for Tac/MTX vs 2820 for PT-Cy p<0.001). This singleton deficit would place PT-Cy patients at higher risk of missing the critical mass of TCRs required to respond effectively to infections, consistent with their increased rate of Gr 2 infections. Conclusions: We performed longitudinal TCR-Seq on >200 million T cells from 324 HCT patients, representing the largest post-HCT TCR-Seq analysis in the history of the field, and enabling novel insights into TCR dynamics. These data identify a previously unappreciated global TCR diversity bottleneck with PT-Cy that simultaneously protects patients from cGVHD and places them at higher risk of infectious complications.

AbstractAnti‐CD19 chimeric antigen receptor T‐cell therapy (CART) has revolutionized the outcomes of relapsed and/or refractory B‐cell non‐Hodgkin lymphoma. However, CART is still limited by its availability, toxicity, and response durability. Not all patients make it to the CART infusion phase due to disease progression. Among those who receive CART, a significant number of patients experience life‐threatening cytokine release syndrome toxicity, and less than half maintain a durable response with the majority relapsing in pre‐existing sites of disease present pre‐CART. Radiation therapy stands as a promising peri‐CART and salvage treatment that can improve the outcomes of these patients. Evidence suggests that bridging radiotherapy prior to CART controls the disease during the manufacturing period, augments response rates and local control, cytoreduces/debulks the disease and decreases the severity of cytokine release syndrome, and may prolong disease‐free intervals and survival especially in patients with bulky disease. Consolidative radiotherapy for residual post‐CART disease alters the pattern of relapse and improves local recurrence‐free and progression‐free survivals. Salvage radiotherapy for relapsed post‐CART disease has favorable survival outcomes when delivered comprehensively for patients with limited relapsed disease and palliates symptoms for patients with diffuse relapsed disease. The biology of the disease during the peri‐CART period is poorly understood, and further studies investigating the optimal timing and dosing of radiation therapy (RT) are needed. In this review, we tackle the most significant challenges of CART, review and propose how RT can help mitigate these challenges, and provide The Mayo Clinic experts' approach on incorporating RT with CART.