A key treatment for patients with multiple myeloma is high-dose melphalan followed by autologous stem cell transplant (ASCT). It can provide a deep response with long-term remission. However, some patients progress quickly, and it is not clear why. In this study, we performed single-cell RNA and T-cell receptor sequencing of the immune microenvironment of 40 patients before and after ASCT to determine if differences in the immune composition could define those who would progress. Clear differences in cell populations were identified in progressors, including increased T-cell infiltration, decreased T-cell receptor diversity, and decreased frequency of monocytes and CD56bright NK cells. We identified cell interactions that predicted progression, including increased frequency of CD8+ exhausted T cells and stromal cells and decreased frequency of CD56bright NK cells and plasmacytoid dendritic cells. We propose and validate a model of progression that can also be determined by flow cytometry. Together, these data highlight the importance of the immune microenvironment in understanding responses to ASCT.

Background. There is a growing population of solid organ transplant (SOT) survivors who subsequently require a hematopoietic cell transplant (HCT), although there are limited data on survival, risk factors for SOT graft loss, and death in this cohort. Methods. This retrospective Center for International Blood and Marrow Transplant Research study included recipients of SOT followed by HCT between 1989 and 2017. HCT data were merged with organ transplant data from the Organ Procurement and Transplantation Network. Results. Eighty-three patients with an SOT underwent an HCT. Organs transplanted included heart/lung (thoracic, n = 15), kidney (n = 42), and liver (n = 26); 24 patients (29%) received a living donor graft and 59 (71%) a deceased graft. Forty-one patients (49.4%) received an allogeneic HCT and 42 (50.6%) an autologous HCT. Three-year overall survival (OS) from HCT in the entire cohort was 38.6%. There were no significant differences in OS by SOT type, although 3-y OS appeared lowest in the kidney SOT group at 29.9%, compared with liver SOT at 40.6% and thoracic SOT at 58.2%. The incidence of SOT graft failure 3 y post-HCT was 59.1%. There were no significant differences in SOT graft failure by organ type: 3-y failure probability 67.2% for kidney, 56.5% for liver, and 46.2% for thoracic. Shared risk factors for death and graft failure included HCT indication (leukemia, lymphoma, and nonmalignant diseases), HCT type (allogeneic), and SOT type (kidney). Conclusions. Although some SOT recipients may benefit from HCT, the incidence of SOT graft failure was high and OS was poor, particularly after allogeneic HCT.

Patients who undergo human leukocyte antigen-matched unrelated donor (MUD) allogeneic hematopoietic stem cell transplantation (HSCT) with myeloablative conditioning for hematologic malignancies often develop acute graft-versus-host disease (GVHD) despite standard calcineurin inhibitor-based prophylaxis in combination with methotrexate. This trial evaluated a novel human CD24 fusion protein (CD24Fc/MK-7110) that selectively targets and mitigates inflammation due to damage-associated molecular patterns underlying acute GVHD while preserving protective immunity after myeloablative conditioning. This phase 2a, multicenter study evaluated the pharmacokinetics, safety, and efficacy of CD24Fc in combination with tacrolimus and methotrexate in preventing acute GVHD in adults undergoing MUD HSCT for hematologic malignancies. A doubleblind, placebo-controlled, dose-escalation phase to identify a recommended dose was followed by an open-label expansion phase with matched controls to further evaluate the efficacy and safety of CD24Fc in preventing acute GVHD. A multidose regimen of CD24Fc produced sustained drug exposure with similar safety outcomes when compared with single-dose regimens. Grade 3 to 4 acute GVHD-free survival at day 180 was 96.2% (95% confidence interval [CI], 75.7-99.4) in the CD24Fc expansion cohort (CD24Fc multidose), compared with 73.6% (95% CI, 63.2-81.4) in matched controls (hazard ratio, 0.1 [95% CI, 0.0-0.6]; log-rank test, P = .03). No participants in the CD24Fc escalation or expansion phases experienced dose-limiting toxicities (DLTs). The multidose regimen of CD24Fc was well tolerated with no DLTs and was associated with high rates of severe acute GVHD-free survival after myeloablative MUD HSCT. This trial was registered at ClinicalTrials.gov as #NCT02663622.

Allogeneic hematopoietic cell transplantation (HCT) improves outcomes for patients with AML harboring an internal tandem duplication mutation of

6555 Background: TBI/Cy is a commonly used conditioning regimen prior to allogeneic stem cell transplant (SCT). Chemotherapy only regimens, mostly containing busulfan, have been shown to be effective and less toxic in patients with myeloid malignancies. Here, we present the largest reported experience with a non-busulfan myeloablative chemotherapy regimen of TT/Cy in myeloid malignancy patients undergoing allogeneic SCT and compare outcomes with TBI/Cy. Methods: Patients with myeloid malignancies receiving allogeneic SCT at Indiana University from 2007-2020 were included. TT/Cy consisted of TT 15 mg/kg and Cy 120 mg/kg. TBI/Cy consisted of 13.2 Gy in 8 fractions and Cy 3600 mg/m2. The primary endpoint was overall survival (OS). Secondary endpoints included relapse-free survival (RFS), engraftment, and toxicities within the first 100 days. Median follow up for surviving patients is 2,046 (range 816-5,572) days. Results: 225 patients with AML (n=160), CML (n=45), and MDS (n=30) of median age 44 (range 19-59 years) received conditioning with TT/Cy (n=159) or TBI/Cy (n=66). Baseline characteristics were similar. For TT/Cy patients, the median OS was not reached, and 4-year OS was 57.2% (95% confidence interval [CI], 49.2-65.2%), which was significantly better than with TBI/Cy, with median OS 373 days and 4-year OS 33.9% (95% CI, 22.3-45.5%; p<.001). Similarly, for TT/Cy patients, the median RFS was not reached and 4-year RFS was 59.2% (95% CI, 52-67.2%), significantly better than median RFS of 341 days and 4-year RFS 35.2% (95% CI, 23.7-46.9%; p<.001) for recipients of TBI/Cy. On multivariable analysis adjusting for age, sex, diagnosis, disease risk, comorbidity index (HCI), and degree of stem cell source, TT/Cy had significantly lower risk of death (HR 0.44, 95% CI, 0.30-0.65; p<.001) together with female sex (p=.03) and lower HCI (p=.046). As shown in the Table summarizing secondary endpoints, TBI/Cy was associated with significantly higher rates of mucositis, sinusoidal obstruction syndrome (SOS), TPN usage, multiorgan failure, and length of stay of primary admission. Conclusions: TT/Cy is an efficacious regimen for patients with myeloid malignancies undergoing myeloablative allogeneic SCT with less toxicity and improved RFS and OS compared with TBI/Cy. TT/Cy should be compared to other non-TBI containing busulfan-based regimens. [Table: see text]

6556 Background: Total body irradiation (TBI)-based preparative regimens have been standard for patients with ALL undergoing allogeneic stem cell transplant (SCT). It is unclear if chemotherapy-only regimens are equally efficacious. Here, we present the largest reported experience with myeloablative TT/Cy in patients with ALL undergoing allogeneic SCT and compare outcomes with TBI-based regimens. Methods: Patients with ALL receiving myeloablative allogeneic SCT at Indiana University from 2007-2020 were included. TT/Cy consisted of TT 15 mg/kg and Cy 120 mg/kg. TBI/Cy consisted of 13.2 Gy in 8 fractions and Cy 3600 mg/m2 or etoposide 60 mg/kg. The primary endpoint was overall survival (OS). Secondary endpoints included relapse-free survival (RFS), engraftment, and toxicities within the first 100 days. Median follow up for surviving patients is 2,532 (range 599-4,762) days. Results: 80 patients with ALL of median age 40 (range 22-59 years) received conditioning with TT/Cy (n=25) versus TBI/Cy or TBI/etoposide (n=55). Baseline characteristics were similar. For patients receiving TT/Cy, the median OS was not reached, and the 4-year OS was 54.5% (95% confidence interval [CI], 34.3-74.7%), compared with a median OS of 1,491 days and a 4-year OS of 50.9% (95% CI, 37.8-64.2%) for those receiving TBI-based conditioning (p=.75). Similarly, for TT/Cy patients, the median RFS was 847 days and 4-year RFS was 43.2% (95% CI, 23.4-63%), not significantly different from median RFS of 1491 days and 4-year RFS 50.2% (95% CI 36.9-63.5; p=.232) for recipients of TBI regimens. On multivariable analysis, only a higher disease risk index was associated with significantly worse OS (p<.001), while conditioning regimen was not predictive of OS. Similarly, there was no significant difference in RFS between TT/Cy and TBI-based regimens on either univariable or multivariable analysis. Secondary endpoints are summarized in the table. As shown, TT/Cy was associated with significantly lower incidence of mucositis, TPN usage, bacterial infection, sinusoidal obstruction syndrome (SOS), and longer length of stay of primary transplant admission. Conclusions: While there was no significant difference in OS or RFS for patients receiving either TT/Cy or TBI-based conditioning, TBI was associated with greater toxicity. Our data suggests that TT/Cy is an acceptable alternative to TBI-based conditioning for ALL patients undergoing myeloablative allogeneic SCT. [Table: see text]

CONCLUSIONS BCMA-directed CAR T-cell therapy is only available at certain academic centers in the Midwest and requires several weeks for manufacturing, leading to a bottleneck of patients who need therapy for relapsed/refractory multiple myeloma (R/R MM). Teclistamab is an off-the-shelf BCMA-directed bispecific T-cell engager (BiTE) that could help alleviate this bottleneck. The MajesTEC-1 trial was a phase I/II study of teclistamab in patients with R/R MM. Even in patients with triple class-exposed disease, teclistamab showed deep and durable responses. However, clinical trials generally enroll fitter patients, especially when compared to the typical MM patient at the late stages of their disease. We sought to describe the real-world treatment outcomes of patients with R/R MM who received teclistamab at Indiana University (IU). This study was conducted retrospectively at a single center. Patients who received teclistamab between October 25 th, 2022, and July 1 st, 2023, were included. Patients were hospitalized during step-up dosing. The teclistamab dosing and schedule were per standard of care. Response was assessed after each cycle based on the IMWG Uniform Response Criteria. CRS and ICANS were graded per Lee 2020, while other side effects were evaluated using CTCAE 5.0. Demographic information, response, and adverse events were reported descriptively, and survival outcomes were estimated using Kaplan-Meier analysis with Prism GraphPad 10.0. The baseline clinical characteristics are summarized in Table 1. Compared to MajesTEC-1, patients treated in this study were older and more heavily pretreated with a higher baseline burden of disease. Many exhibited organ dysfunction and poor performance status, and 20 of 33 patients were previously exposed to BCMA-directed therapy (BDT). The median follow-up duration was 17.6 weeks. The overall response rate (ORR) was 45.5%, including one-third of patients who achieved a very good partial response (VGPR) or better. When stratified by prior exposure to BDT, ORR was 35% in previously exposed patients and was 61.5% in naïve patients. Thirteen patients died during follow-up (9 from disease progression, 3 from infection, and 1 unexplained sudden cardiac death). Median overall survival in the entire cohort was 17.7 weeks. As shown in the Kaplan-Meier analysis in Figure 2, the median OS was not reached for patients who achieved a response, while patients who did not respond had a median OS of 16.7 weeks (p=.05). CRS was observed in 12 patients (36%), with one grade 3 event requiring tocilizumab, dexamethasone, and ICU transfer for hypoxemic respiratory failure - this patient ultimately died from a hospital-acquired infection. ICANS was observed in 5 patients (15.2%), with one grade 3 event - this patient became unresponsive, requiring intubation and mechanical ventilation. Sixteen of 33 patients had an infectious complication (48.5%), while 3 patients died of a treatment-related infection (Pseudomonas pneumonia, hospital-acquired pneumonia, and sepsis from a urinary source). Grade 3 or 4 neutropenia occurred in 12.1%. In a real-world cohort of heavily pretreated myeloma patients, including those with poor organ function, poor performance status, and prior exposure to BCMA-directed therapy, overall response to teclistamab was lower than previously observed in the MajesTEC-1 study. Achieving a PR or better led to a significantly improved OS, while survival among non-responders was poor. Receipt of prior BCMA-directed therapy led to a lower response rate. The incidence of CRS in the current study was lower than that seen in MajesTEC-1, while the rate of neurotoxicity was similar. High grade CRS and ICANS were infrequent but led to poor patient outcomes in our cohort. Despite a low rate of grade 3 or 4 neutropenia, there was a high rate of infection, even with use of prophylactic IVIG for hypogammaglobulinemia. There were 3 infection-related fatalities. This highlights the severely immunocompromised state of the patient population and the need for early recognition and improved strategies for infection prevention. The early use of BCMA BiTEs may improve access and tolerability. However, there is still a need for better understanding of resistance mechanisms.

Introduction: Cancer-associated cachexia is associated with poor survival rates in several cancer types. Multiple Myeloma (MM) preferentially occurs in the elderly and is the most common cancer that causes lytic bone metastasis causing bone pain, fractures, mobility limitations, and falls. Cachexia is projected to be common in myeloma but has not been fully studied. Myeloma treatments including corticosteroids, radiation and alkylators cause muscle loss, while novel immunotherapy is tumor-specific but their impact on cachexia is unknown. We characterize the changes in body composition in patients with relapsed/refractory myeloma treated with BCMA bispecific antibody teclistamab and determine the association between body composition with treatement response and overall survival. Methods: 49 MM patients treated with teclistamab between 2000 and 2021 were included. All were with relapsed/refractory disease after > 4 lines of therapy and received an approved dose and schedule of teclistamab. The response assessment was according to IMWG criteria. Body weight, body mass index (BMI), tumor burden, and organ function were assessed at baseline and post-treatment. Standard-of-care abdominopelvic CT or PET/CT scans at baseline and at last known follow up were analyzed with Data Analysis Facilitation Suite (DAFS) software to quantify skeletal muscle (SKM), visceral adipose tissue (VAT), and subcutaneous adipose tissue (SAT). Differences between groups were tested using the χ 2 test or paired t-test. Progression free survival (PFS) and overall survival (OS) from the start of teclistamab to progression and death or last follow-up, respectively, were analyzed by the Kaplan-Meier method. Comparisons were made with the log-rank test. Results: Patient characteristics are detailed in Table 1. Based on the WHO definition, 2% were underweight, 16% were normal weight, 19% were overweight and 13% were obese, at baseline. The baseline mean SKM was 105.6 ± 27.8 (Male 122.0 ± 25.3, female 93.4 ± 23.5). SAT and VAT varied widely. Median SAT was 196.5 (range 48.3-558.6), and median VAT was 136.6 (33.09-448.1). Of 32 patients in the obese group, 16 (50%) patients had SKM that was below the mean SKM of the group. Baseline SAT and VAT, but not SKM were correlated with BMI. Twenty-seven of the 49 patients had paired imaging. The absolute changes in skeletal muscle and adipose tissue compartments are shown in Table 2. A majority of patients had a decline in SKM, SAT and VAT post-treatment: mean SKM decrease was 8.9 cm 2 ( p ≤ 0.01), mean SAT decreased 24.3 cm 2 ( p = 0.02) and mean VAT decreased 27.4 cm 2 ( p = 0.03), while BMI and weight were unchanged. Nineteen of 27 (70%) subjects responded to therapy. The changes in SKM, VAT, and SAT loss did not differ significantly between responders and non-responders. 38.8% of patients (19/49) had died by the end of the follow-up. Median follow-up duration was 2.8 years, overall survival was 1.7 years and PFS was 0.9 years. Baseline SKM, SAT, and VAT did not correlate with PFS or OS, but a decline in SMK significantly correlated with a shorter OS (p=0.04); 7/18 patients with decreased SKM and 2/9 patients with unchanged or increased SKM died. Response correlated strongly with overall survival (p=0.002). Conclusions: Body composition analysis of standard CT images may provide clinically relevant information for patients with advanced myeloma. Sarcopenia was common despite high BMI, and a further decline in skeletal muscle mass correlated with shorter survival, regardless of response to tumor-specific immunotherapy. Anthropometric changes should be validated in larger patient cohorts and included in future clinical trials. Further efforts should focus on the maintenance of muscle and visceral adipose tissue in this patient population.

Background TCM are aggressive diseases with poor outcomes. Translating the CAR T-cell therapy success from B-cell diseases to TCM has proven challenging. CD4 is an attractive therapeutic target, owing to its restricted expression on normal tissues. In this first-in-human phase I study, we investigate the autologous third generation CD4-redirected CAR T-cell safety, tolerability, manufacturing feasibility, trafficking and preliminary efficacy in patients with R/R CD4+ TCM who failed standard therapies. Methods The investigational construct is engineered with a single-chain variable fragment (ScFV) and dual co-stimulators (CD28; 4-1BB), fused to CD3zeta and CD8 leader sequence, packaged in lentivirus and transducer into T-cells. Patients received conditioning therapy with fludarabine and cyclophosphamide. CD4CAR product is administered in a 3+3 dose-escalation scheme. Dose-limiting toxicities (DLT) were monitored during the initial 42-days post-treatment. Treatment-emergent adverse events (AE) were graded by CTCAE v5.0 Results Three patients with median age of 63 years (range, 18-68) were enrolled and treated at DL1 (2.0x10^5/kg), including 2 (66%) women and 2 (66%) African-American. Median number of prior therapies was 3 (range, 2-4) (Figure). AEs included grade 3-4 hematologic toxicity in 3 (100%) patients, all present before enrollment. There was no protocol defined DLTs. All grade ≥3 lymphopenia reverted to grade 2 by day 30 and no related infections occurred between CAR infusion and hematopoietic stem cell transplantation (HSCT). Since infusion, the CAR T-cells percentage in peripheral blood had continued to expand. CD4CAR T-cells were detectable in all patients for at least 28 days post-infusion, meeting the primary endpoint, and on D111 in one patient. CD4CAR expansion was reflected on by a decrease in CD4/CD8 ratio and flow cytometry using ScFV Fab2 specific antibodies (Figure). Cytokine response analysis CD4CAR was associated with variable but significant production that seems to correlate with clinical responses (Figure; More data at meeting). No cytokine-mediated organ toxicities were observed. Bone marrow and peripheral blood flow cytometry confirmed complete remission (CR) in 2 patients at day 30 (PTCL and T-ALL). Patient 3 (mycosis fungoides) achieved hematological CR with stable skin lesions. Post-treatment day 30 skin biopsy demonstrated persistent disease with marked loss of CD4. Conclusions CD4CAR T-cell therapy is feasible in patients with R/R CD4+ TCM. 2/3 patients achieved CR and the third achieved hematological CR with stable skin disease. Toxicities were manageable without DLT upon completion of cohort 1. The cytokine response suggests immune activation and tumor recognition by CD4CAR T-cells. Dose escalation will proceed. NCT03829540

The NCCN Guidelines for Hematopoietic Cell Transplantation (HCT) provide an evidence- and consensus-based approach for the use of autologous and allogeneic HCT in the management of malignant diseases in adult patients. HCT is a potentially curative treatment option for patients with certain types of malignancies; however, recurrent malignancy and transplant-related complications often limit the long-term survival of HCT recipients. The purpose of these guidelines is to provide guidance regarding aspects of HCT, including pretransplant recipient evaluation, hematopoietic cell mobilization, and treatment of graft-versus-host disease-a major complication of allogeneic HCT-to enable the patient and clinician to assess management options in the context of an individual patient's condition. These NCCN Guidelines Insights provide a summary of the important recent updates to the NCCN Guidelines for HCT, including the incorporation of a newly developed section on the Principles of Conditioning for HCT.

Acute Myeloid Leukemia (AML) has a median age at diagnosis of 67 years. The most common curative therapy remains an allogeneic hematopoietic stem cell transplantation (HCT), yet it is complicated by treatment-related mortality (TRM) and ongoing morbidity including graft versus host disease (GVHD) that may impact survival, particularly in older patients. We examined the outcomes and predictors of success in 1321 patients aged 60 years and older receiving a HCT for AML in first complete remission (CR1) from 2007-2017 and reported to the CIBMTR. Outcomes were compared in three age cohorts (60–64; 65–69; 70+). With median follow-up of nearly 3 years, patients aged 60–64 had modestly, though significantly better OS, DFS and lower TRM than those either 65–69 or 70+; cohorts with similar outcomes. Three-year OS for the 3 cohorts was 49.4%, 42.3%, and 44.7% respectively (p = 0.026). TRM was higher with increasing age, cord blood as graft source and HCT-CI score of ≥3. Conditioning intensity was not a significant predictor of OS in the 60-69 cohort with 3-year OS of 46% for RIC and 49% for MAC (p = 0.38); MAC was rarely used over age 70. There was no difference in the relapse rate, incidence of Grade III/IV acute GVHD, or moderate-severe chronic GVHD across the age cohorts. After adjusting for other predictors, age had a small effect on OS and TRM. High-risk features including poor cytogenetics and measurable residual disease (MRD) prior to HCT were each significantly associated with relapse and accounted for most of the adverse impact on OS and DFS. Age did not influence the incidence of either acute or chronic GVHD; while graft type and associated GVHD prophylaxis were most important. These data suggest that age alone is not a barrier to successful HCT for AML in CR1 and should not exclude patients from HCT. Efforts should focus on minimizing residual disease and better donor selection.

Purpose: Family may play an important role in Hematopoietic stem cell transplantation (HSCT) recovery; however, little is known about the effect of family functioning on an individual’s health. The purpose of this study was to examine the effect of family cohesion (family functioning) on the trajectory of HSCT recipients’ symptom distress (symptom frequency and symptom bother) before, during, and after HSCT. Methods: Secondary analysis was conducted using data collected from178 individuals who underwent HSCT. Longitudinal parallel-process (LPP) modeling was used to examine how family cohesion and HSCT associated symptoms (symptom frequency and symptom bother) change over time; and how these longitudinal changes relate to each other. Results: The trajectory of family cohesion predicted the trajectories of HSCT associated symptom frequency and bother. HSCT recipients who experienced higher family cohesion at baseline (T1) showed lower symptom frequency (p<.01) as well as symptom bother (p<.01) at T1. This trajectory analysis also showed that HSCT recipients who had improved family cohesion over time reported decrease in symptom frequency (p<.01) as well as bother (p<.01) over time. Conclusion: Findings indicate that higher family cohesion predicts decrease in symptom distress over the HSCT trajectory. Interventions aimed at enhancing family cohesion have the potential to lower HSCT recipients’ symptom distress. Further research is needed to understand the critical role of family cohesion and family functioning and their relationship with HSCT symptom distress prevention, early detection, and risk stratification.

Introduction: Dipeptidyl peptidase-4 (DPP-4; also known as CD26) is a homodimeric type II transmembrane receptor expressed on a variety of cell types and is present in an enzymatically active form in plasma. DPP-4/CD26 is involved in a number of biological processes, including T cell activation. The interaction of DPP-4/CD26 on T cells with its ligand caveolin-1 on antigen-presenting cells (APC) enhances T cell activation, proliferation, and cytokine production and also upregulates CD86 on APC resulting in co-stimulation. We have recently shown that DPP-4 inhibition using the specific inhibitor sitagliptin is associated with remarkably low rates of acute graft-versus-host disease (Farag et al. NEJM 2021, 384:11-19). Herein we describe the in vitro and in vivo effects of DPP-4 inhibition alone and in combination with bortezomib, as a rationale for further studies in GvHD prevention. Methods: One-way mixed lymphocyte reactions (MLR) using PBMC obtained from random donor buffy coats were used to evaluate the effect of the specific DPP-4 inhibitor sitagliptin alone and in combination with bortezomib, on T cell activation and proliferation in vitro. Cytokines in MLR supernatant were assayed using Luminex multiplex assay. MHC-mismatched mouse transplant (BL6 → BALB/c) model using CD26 gene knockout or wild type mice donors were used to investigate the effect of DPP-4 on GvHD in vivo. RNA sequencing (RNA-seq) was used to profile gene expression in CD3 positive cells from 72 hours of MLR groups. Results: Sitagliptin induced a dose-dependent inhibition on T-cell activation and proliferation in 96h MLR using concentrations readily obtainable clinically (400-800 µg/ml) as shown in Fig.1, as well as reduction in the production of Th1 cytokines, IFN-γ, TNF-α and IL-1β, Th2 cytokine, IL-10, and Th17 cytokines, IL-17A and IL-17F in MLR supernatants. Compared with wild-type (CD26+/+) counterparts, mice receiving CD26-/- BM and splenic T cells developed significantly less acute GvHD as measured by mortality and clinical score. In our transplant model, recipients of WT BL6 BM + CD3+ cells developed focal and mild liver and skin pathogenic but moderate gastrointestinal toxicity, which included crypt loss in the colon and villous blunting, crypt loss in the small intestine. CD26-/- BL6 BM + CD3+ cells reduced the intestinal injury, which showed normal colon and small intestine structure. The Histopathological scores of GvHD between recipients of WT BL6 BM + CD3+ cells and that of CD26-/- BL6 BM + CD3+ cells were 2.67±0.67 vs 0.58±0.12 (p<0.05) in colon, 2.67±0.76 vs 0.88±0.18 (p<0.05) in small intestine, and 0.73 ±0.06 vs 0.65±0.64 (p>0.05) in liver. Also, recipient mice transplanted with BL6 CD26-/- BM and spleen cells showed significantly improved survival compared to those receiving wild type (CD26+/+) cells. The combination of sitagliptin (400 µg/ml or 500 µg/ml) and bortezomib (4.5 nM) showed synergistic inhibition on T-cell proliferation (Fig. 2) and reduction on IFN-γ, IL-10, IL-17A and IL-17F production in MLR. Bulk sequencing of RNA from CD3+ cells obtained after 72-hour MLR showed a significant change in the JAK-STAT signaling pathway, including downregulation of STAT1, IL7R,PIK3R1, IL6ST, IL6R, SOS1 and PIAS1 genes with sitagliptin alone (400 µg/ml). The combination of sitagliptin (400 µg/ml) and bortezomib (4.5 nM) reduced expression in genes associated with DNA replication (including MCM2, MCM3, MCM4, MCM5, MCM6, MCM7, DNA2, PCNA, LIG1, and other genes), cell cycle (including CDC6, CDC7, CDC20, CDC25A, CDC45, CDK1, CDK2 and other genes), and Th17 cell differentiation (including IL17F, IL21, IL21R, and IL23R genes). Conclusions: Our studies show that the specific DPP-4 inhibitor sitagliptin results in a dose dependent reduction in T cell activation and proliferation in MLR, and that DPP-4 elimination using CD26 gene knockout donor cells is associated with protection from GvHD in mouse transplant. The findings are consistent with our recently published clinical trial demonstrating low incidence of acute GVHD with high dose sitagliptin in combination with standard prophylaxis of tacrolimus and sirolimus. Furthermore, we demonstrate in vitro synergy of sitagliptin with bortezomib in inhibiting T cell activation and proliferation. Our data provides rationale for further clinical testing of sitagliptin for acute GvHD prevention, including in combination with bortezomib. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

TPS3156 Background: Hematopoietic stem cell transplantation (HSCT) is used with curative intent for AML and MDS-EB. MGTA-117 is a novel Ab-drug conjugate (ADC) in development for conditioning prior to HSCT. MGTA-117 selectively targets CD117 (c-Kit) with a human monoclonal Ab to CD117 conjugated to an amanitin payload that depletes CD117-expressing cells by inhibiting RNA polymerase II. Human hematopoietic stem cells and AML tumor cells express high levels of CD117, and MGTA-117 potently depletes these target cells, with an IC50 of <10pM in vitro. MGTA-117 has demonstrated in vitro and in vivo stability, confirming its characterization as a highly potent and selective agent. In a primate GLP toxicology study, MGTA-117 maximally depleted bone marrow stem cells at a dose not associated with evidence of toxicity in other tissues. Dose-dependent reduction of peripheral reticulocytes, produced from CD117+ erythroid precursors in the bone marrow, was an early and time sensitive biomarker of bone marrow CD117+ cell depletion. Higher doses were associated with the elevation of transaminases and histopathology that were asymptomatic and transient. Highest Non- Severely Toxic Dose (HNSTD) was used to establish the starting dose in this First-in-Human study. Based upon dose exposure and allometric scaling, it is expected that the clinical exposures after a 0.02 mg/kg dose in the first human cohort will provide an optimal > 100-fold safety margin over exposures observed after the 0.3 mg/kg dose that was the HNSTD in the primate GLP toxicology study. Methods: This phase I/II, multicenter, open-label, dose-escalation study will investigate the safety, tolerability, PK profile, PD activity, and blast depletion activity of MGTA 117 given intravenously as a single dose in adults with R/R AML or MDS-EB. Patients must be 18-75 yrs, have a WHO-defined diagnosis of CD117+ R/R AML or MDS-EB with ≥5% marrow myeloblasts. Patients must have ECOG PS ≤2, and adequate hepatic, renal, and cardiac function. The primary objective is to establish a minimum safe and biologically effective (MSBE) dose of MGTA-117 in R/R AML and MDS-EB patients based on safety and CD117 receptor occupancy (RO) in circulating leukemic blasts after dosing. The observation period for dose limiting toxicities is 21 days. Patients will be followed for changes in reticulocyte, neutrophil, and platelet counts in PB and percent change from baseline in leukemic blasts or stem/progenitor cells in PB and/or BM. CD117 receptor occupancy by MGTA-117 will be measured and MSBE dose will be based on safety and receptor occupancy. The study is designed with the possibility that subjects would proceed to HSCT >28 days after MGTA-117 administration, if eligible per the local transplant practices. Clinical trial information: NCT05223699.

Background: MGTA-117 is a novel anti-CD117 (c-KIT)-amanitin antibody-drug conjugate (ADC) targeting CD117 that is in development as a single agent for myeloid conditioning prior to hematopoietic stem cell transplantation (HSCT). Preclinical studies show rapid and selective depletion of CD117+ stem cells and progenitor cells in bone marrow at low doses in humanized mice and nonhuman primates, rapid and predictable clearance, and potent antileukemic effects in patient-derived xenograft murine models (Lanieri et al, ASH 2020, #1044). Objectives: To report initial results from Cohort 1 of a phase 1/2 clinical study in which MGTA-117 is administered IV as a single dose in adults with relapsed/refractory (R/R) AML or MDS-EB. Methods: This is a multicenter, open-label study (NCT05223699). Adult participants (pts) are eligible who have a WHO-defined diagnosis of CD117+ R/R AML or MDS-EB with ≥5% bone marrow blasts (or ≥2% peripheral blasts for MDS-EB); an identified human stem cell donor; an ECOG PS ≤2; and adequate hepatic, renal, and cardiac function. The trial uses a 3+3 dose-escalation design, with an initial starting dose of 0.02 mg/kg. Overall objectives are to investigate the safety, tolerability, pharmacokinetics (PK), pharmacodynamics (PD), antileukemia activity, and to establish the minimum safe and biologically effective dose of MGTA-117. The observation period for dose-limiting toxicities (DLTs) is 21 days. Results: Demographics and disease characteristics of enrolled pts are shown in the Table. In Cohort 1 (0.02 mg/kg), 4 pts were dosed; 1 pt withdrew from the study prior to completion of the DLT observation period because of disease progression and was replaced. To date, 2 pts have been dosed in Cohort 2 (0.04 mg/kg). MGTA-117 has been well tolerated to date; no DLTs, treatment-related serious adverse events (AEs), treatment-related deaths, or treatment-related hypersensitivity or anaphylactoid infusion reactions have been observed. One pt had transient related grade 1 elevations in alanine and aspartate aminotransferase levels that resolved without intervention. The remaining treatment-emergent AEs (TEAEs) were consistent with underlying disease and were considered unrelated to MGTA-117. TEAEs occurring at a frequency of >25% irrespective of causality included nausea, vomiting, tachycardia, thrombocytopenia, anemia, and liver enzyme elevation. Maximum concentrations of MGTA-117 in Cohort 1 were reached within 1 hour post-infusion. As expected, the observed half-life was approximately 10 hours or less, and MGTA-117 concentrations were no longer measurable 48 hours after dosing in all pts (n=4). Free amanitin-containing payload was undetectable in all PK blood samples from all pts indicating stability of the ADC linker. MGTA-117 was shown to rapidly and selectively bind CD117+ cells in the blood as measured by a receptor occupancy (RO) assay, with reduction of binding to low levels within 24 hours post-dose. MGTA-117 concentrations in blood consistently mirrored RO levels over time (Figure). There was evidence supporting biologic activity of MGTA-117 in the bone marrow in 2 of 3 evaluable pts at the lowest dose level; an observed reduction in CD117+ erythroid progenitors in the bone marrow of 1 pt and complete remission with hematologic recovery (CR) in a second pt with primary refractory AML failing 2 lines of induction chemotherapy. The pt with CR later proceeded to HSCT with successful engraftment. Cohort 2 enrollment is ongoing, and further data are forthcoming. Conclusions: MGTA-117 has been well tolerated with no unexpected safety concerns. Preliminary data show in vivo stability of the ADC with rapid clearance from blood, robust binding of MGTA-117 on CD117+ cells, and early evidence of single-agent biological activity. The observed PK/PD profile in humans is highly consistent with predictions based on data from studies in preclinical species. The trial continues to advance, and progress is being made toward development of MGTA-117 as a myelodepletive conditioning agent for HSCT in AML/MDS and gene therapy indications. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal