Post-Transplantation Cyclophosphamide Uniquely Restrains Alloreactive CD4+ T-Cell Proliferation and Differentiation After Murine MHC-Haploidentical Hematopoietic Cell Transplantation

Treatment-Responsive Acute Graft-versus-Host Disease after Post-Transplantation Cyclophosphamide-Based Prophylaxis: Incidence and Clinical Outcomes

Post-transplantation cyclophosphamide (PTCy) following hematopoietic cell transplantation (HCT) has emerged as standard of care for graft-versus-host disease (GVHD) prevention in adult patients without increasing malignant relapse. We previously defined acute GVHD (aGVHD) treatment response categories as corticosteroid-sensitive (SS), -dependent (SD), or -resistant (SR) based on response to first-line corticosteroids and reported their clinical outcomes following non-PTCy-based prophylaxis. More than one-third of patients developed aGVHD necessitating systemic therapy. Cases were predominantly SR, with a 14% overall incidence of SR aGVHD. The incidence and clinical outcomes of these 3 distinct aGVHD treatment response groups following PTCy-based prophylaxis have not been well described. The objective of this retrospective single-institution cohort study was to assess the incidence and clinical outcomes of SS, SD, and SR aGVHD following HCT with PTCy-based prophylaxis using a prophylactic regimen of PTCy, tacrolimus, and mycophenolate mofetil (MMF). We included 196 consecutive adult and pediatric patients undergoing allogeneic HCT for malignant and non-malignant disorders at the University of Minnesota between 2017 and 2021. Patients received PTCy on days +3 and +4 plus tacrolimus and MMF prophylaxis. Bone marrow and peripheral blood stem cell graft sources and related and unrelated donors were included. Recipients received myeloablative or reduced-intensity conditioning regimens. Of the 196 allografts, 54 (28%) developed aGVHD before day +180, with a median time to onset of 50 days (interquartile range, 34 to 71 days). Of those, 32 patients (16% overall) developed maximum grade II-III aGVHD necessitating systemic corticosteroids, with the following response: 13 SS (41%), 10 SD (31%), and 9 SR (28%). The overall incidence of SR aGVHD was 4.6%. Only 12 patients (6%) developed maximum grade III aGVHD, and none had grade IV aGVHD. The 2-year overall survival analyzed from 80 days after initiation of systemic treatment was similar in the SS and SD groups (77 and 75%, respectively), comparable to those without aGVHD (81%), and was lowest in the SR group (20%), with GVHD the primary cause of death. Nonrelapse mortality was highest in the SR group. MN high-risk and higher GVHD grade at onset were risk factors for developing SR aGVHD. Overall, we report a low incidence (16%) of aGVHD requiring systemic corticosteroids with PTCy-based prophylaxis. aGVHD cases were predominantly SS aGVHD, with lower incidences of SD and SR aGVHD. Our findings suggest that PTCy-based prophylaxis reduces the rate of treatment-resistant aGVHD. Patients with SR aGVHD had the worst clinical outcomes and poorest survival. Those with SS and SD aGVHD had similar clinical outcomes, both better than seen with SR aGVHD.

Early CAR- CD4+ T-lymphocytes recovery following CAR-T cell infusion: A worse outcome in diffuse large B cell lymphoma

CAR- CD4+ T cell lymphopenia is an emerging issue following CAR-T cell therapy. We analyzed the determinants of CD4+ T cell recovery and a possible association with survival in 31 consecutive patients treated with commercial CAR-T for diffuse large B-cell (DLBCL) or mantle cell lymphoma. Circulating immune subpopulations were characterized through multiparametric-flow cytometry. Six-month cumulative incidence of CAR- CD4+ T cell recovery (≥200 cells/μL) was 0.43 (95% confidence interval [CI]: 0.28-0.65). Among possible determinants of CD4+ T cell recovery, we recognized infusion of a 4-1BB product (tisagenlecleucel, TSA) in comparison with a CD28 (axicabtagene/brexucabtagene, AXI/BRX) (hazard ratio [HR] [95% CI]: 5.79 [1.16-24.12] p = 0.016). Higher CD4+ T cell counts resulted with TSA at month-1, -2 and -3. Moderate-to-severe infections were registered with prolonged CD4+ T cell lymphopenia. Early, month-1 CD4+ T cell recovery was associated with a worse outcome in the DLBCL cohort, upheld in a multivariate regression model for overall survival (HR: 4.46 [95% CI: 1.12-17.71], p = 0.03). We conclude that a faster CAR- CD4+ T cell recovery is associated with TSA as compared to AXI/BRX. Month-1 CAR- CD4+ T cell subset recovery could represent a "red flag" for CAR-T cell therapy failure in DLBCL patients.

UVB induced reactivation leads to HSV1 in the corneas of virtually all latently infected mice and requires STING to develop corneal disease

Reactivation of latent herpes simplex type 1 results in virus returning to the cornea leading to recurrent herpetic stromal keratitis (rHSK). We compare two competing models to reactivate viruses from latency, UV-B irradiation and cyclophosphamide (CP). Results revealed that while both result in corneal recrudescence, only UV-B irradiation results in rHSK. To better understand the dynamics of reactivation, we analyzed corneas for both the presence of infectious viruses and the dynamics of exposure to multiple reactivations using UV-B. We noted that multiple reactivations result in progressively worse corneal disease. We also noted that expression of IFNα and STING, surragate markers for the presence of virus, are induced by the presence of reactivated virus. Studies to determine the importance of STING to the development of HSK revealed that in the absence of STING, mice do not develop significant HSK and the magnitude of the infiltrate of CD45+ cells in these corneas is significantly reduced. The resulting paucity of CD45+CD11b+GR-1+F4/80-neutrophils, and to a lesser extent CD45+CD11b+GR-1-F4/80+ macrophages in B6-STING KO mice following reactivation is likely the underlying cause for lack of rHSK as has been noted by ourselves and others. These results underscore the critical importance of STING's role in developing rHSK.

The best GVHD prophylaxis: Or at least progress towards finding it

Options for GVHD prophylaxis after allogeneic hematopoietic cell transplantation can best be chosen by understanding the pathophysiology of GVHD. Interventions to limit T cell activation, expansion and subsequent tissue injury can each be utilized in designing successful GVHD prevention strategies Depleting, tolerizing or blunting T cells or host antigen presenting cells (APCs), blocking co-stimulation or more broadly suppressing inflammation have all been used. Interventions which spare regulatory T cells (Tregs) may prevent GVHD and facilitate controlled allo-responses and not compromise subsequent relapse risks. Graft manipulations and pharmacologic interventions each have potential to limit the morbidity of GVHD while permitting the immunocompetence to prevent infection or relapse.

Has the shortage of fludarabine altered the current paradigm of lymphodepletion in favor of bendamustine?

The most common lymphodepletion regimen used prior to infusion of chimeric antigen receptor-T cells (CAR-T) is cyclophosphamide (CY) in combination with fludarabine (Flu) (CY-FLU). While cyclophosphamide (CY) possesses lymphotoxic effects, it concurrently preserves regulatory T cell activity, potentially affecting the efficacy of CAR-T cells. Moreover, the use of fludarabine (FLU) has been linked to neurotoxicity, which could complicate the early detection of immune effector cell-associated neurotoxicity syndrome (ICANS) observed in CAR-T cell therapy. Given the ongoing shortage of FLU, alternative lymphodepleting agents have become necessary. To date, only a limited number of studies have directly compared different lymphodepleting regimens, and most of these comparisons have been retrospective in nature. Herein, we review the current literature on lymphodepletion preceding CAR-T cell therapies for lymphoid hematologic malignancies, with a specific focus on the use of bendamustine (BEN). Recent evidence suggests that administering BEN before CAR-T cell infusion yields comparable efficacy, possibly with a more favorable toxicity profile when compared to CY-FLU. This warrants further investigation through randomized prospective studies.

Phase II Study of Myeloablative 7-8/8-Matched Allotransplantation with Post-Transplantation Cyclophosphamide, Tacrolimus, and Mycophenolate Mofetil

Graft-versus-host disease (GVHD) is the major toxicity of allogeneic hematopoietic cell transplantation (HCT). We hypothesized that a GVHD prophylaxis regimen of post-transplantation cyclophosphamide (PTCy), tacrolimus (Tac), and mycophenolate mofetil (MMF) would be associated with incidences of acute and chronic GVHD in patients receiving a matched or single antigen mismatched HCT. This Phase II study was conducted at the University of Minnesota using a myeloablative regimen of either total body irradiation (TBI) at a total dose of 1320 cGy, administered in 165-cGy fractions, twice daily from day -4 to day -1, or busulfan (Bu) 3.2 mg/kg daily (cumulative area under the curve, 19,000 to 21,000 μmol/min/L) plus fludarabine (Flu) 40 mg/m2 once daily on days -5 to -2, followed by a GVHD prophylaxis regimen of PTCy 50 mg/kg on days +3 and +4, Tac, and MMF beginning on day +5. The primary endpoint was the cumulative incidence of chronic GVHD necessitating systemic immunosuppression (IST) at 1 year post-transplantation. Between March 2018 and May 2022, we enrolled 125 pediatric and adult patients, with a median follow-up of 813 days. The incidence of chronic GVHD necessitating systemic IST at 1 year was 5.5%. The rate of grade II-IV acute GVHD was 17.1%, and that of grade III-IV acute GVHD was 5.5%. Two-year overall survival was 73.7%, and 2-year graft-versus-host disease-free, relapse-free survival was 52.2%. The 2-year cumulative incidence of nonrelapse mortality was 10.2%, and the rate of relapse was 39.1%. There was no statistically significant difference in survival outcomes between recipients of matched donor transplants versus recipients of 7/8 matched donor transplants. Our data show that myeloablative HCT with PTCy/Tac/MMF results in an extremely low incidence of severe acute and chronic GVHD in well-matched allogeneic HCT.

Graft-versus-host disease: teaching old drugs new tricks at less cost

Graft-versus-host disease (GVHD) remains a major cause of morbidity and mortality after allogeneic stem cell transplantation (SCT). Currently, more patients can receive SCT. This is attributed to the use of reduced intensity regimens and the use of different GVHD prophylaxis that breaks the barrier of human leukocyte antigen, allowing an increase in the donor pool. Once an area with relatively few clinical trial options, there has been an increase in interest in GVHD prophylaxis and treatment, which has led to many US Food and Drug Administration (FDA) approvals. Although there is considerable excitement over novel therapies, many patients may not have access to them due to geographical or other resource constraints. In this review article, we summarize the latest evidence on how we can continue to repurpose drugs for GVHD prophylaxis and treatment. Drugs covered by our review include those that have been FDA approved for other uses for at least 15 years (since 2008); thus, they are likely to have generic equivalents available now or in the near future.

UV-B induced HSV-1 reactivation leads to infectious virus in the corneas of virtually all latently infected mice and requires an intact STING to develop herpetic stromal keratitis

Reactivation of latent herpes simplex type 1 results in virus returning to the cornea leading to recurrent herpetic stromal keratitis (rHSK). We compare two competing models to reactivate viruses from latency, UV-B irradiation and cyclophosphamide. Results revealed that while both result in corneal recrudescence, only UV-B irradiation results in rHSK. To better understand the dynamics of reactivation, we analyzed corneas for both the presence of infectious viruses and the dynamics of exposure to multiple reactivations using UV-B. We noted that multiple reactivations result in progressively worse corneal disease. We also noted that expression of IFNα and STING, surragate markers for the presence of virus, are induced by the presence of reactivated virus. Studies to determine the importance of STING to the development of HSK revealed that in the absence of STING, mice do not develop significant HSK and the magnitude of the infiltrate of CD45 + cells in these corneas is significantly reduced. The resulting paucity of CD45 + CD11b + GR-1 + F4/80-neutrophils, and to a lesser extent CD45 + CD11b + GR-1-F4/80 + macrophages in B6-STING KO mice following reactivation is likely the underlying cause for lack of rHSK as has been noted by ourselves and others. These results underscore the critical importance of STING's role in developing rHSK.

Immunopathogenic mechanisms and modulatory approaches to graft-versus-host disease prevention in acute myeloid leukaemia

Allogeneic haematopoietic stem cell transplantation (HSCT) remains the only potential cure for intermediate to high-risk acute myeloid leukaemia (AML). The therapeutic effect of HSCT is largely dependent on the powerful donor-derived immune response against recipient leukaemia cells, known as graft-versus-leukaemia effect (GvL). However, the donor-derived immune system can also cause acute or chronic damage to normal recipient organs and tissues, in a process known as graft-versus-host disease (GvHD). GvHD is a leading cause of non-relapse mortality in HSCT recipients. There are many similarities and cross talk between the immune pathways of GvL and GvHD. Studies have demonstrated that both processes require the presence of mismatched alloantigens between the donor and recipient, and activation of immune responses centered around donor T-cells, which can be further modulated by various recipient or donor factors. Dissecting GvL from GvHD to achieve more effective GvHD prevention and enhanced GvL has been the holy grail of HSCT research. In this review, we focused on the key factors that contribute to the immune responses of GvL and GvHD, the effect on GvL with different GvHD prophylactic strategies, and the potential impact of various AML relapse prevention therapy or treatments on GvHD.

Phase II Study of Myeloablative 8/8- or 7/8-Matched Allotransplantation with Post-Transplant Cyclophosphamide, Tacrolimus, and Mycophenolate Mofetil: Marked Reduction in GVHD Risk Without Increased Relapse Risk Compared to Historical Cyclosporine/Methotrexate

Introduction

Graft-versus host disease (GVHD) is a major limitation to the success of allogeneic hematopoietic cell transplant (HCT). We hypothesized that the GVHD prophylaxis regimen of post-transplant cyclophosphamide (PTCy), tacrolimus (Tac) and mycophenolate mofetil (MMF) would reduce the incidence of GVHD in patients receiving a matched or single antigen mismatched HCT without an increase in risk of malignant relapse.

Methods

This is a phase II study conducted at the University of Minnesota using a myeloablative regimen of either: (A) total body irradiation (TBI, total dose 1320 cGy, administered in 165 cGy fractions, twice a day from days -4 to -1) or (B) Busulfan 3.2mg/kg daily (cumulative AUC 19,000 - 21,000 μmol/min/L) plus fludarabine 160mg/m2 days -5 to -2, followed by a GVHD prophylaxis regimen of PTCy (50mg/kg days +3 and +4), Tac and MMF (beginning day +5). The primary endpoint is cumulative incidence of chronic GVHD requiring systemic immunosuppression at 1-year post-transplant. We compared results to our previous myeloablative protocol for matched donors utilizing cyclosporine/methotrexate (CSA/MTX) GVHD prophylaxis.

Results

From March 2018 - June 2022, we enrolled and treated 125 pediatric and adult patients with a median follow up of 472 days. Grade II-IV acute GVHD occurred in 16% (95% confidence interval (CI): 9-23%); Grade III-IV acute GVHD was 4% (CI: 0-8%). No patients experienced grade IV GVHD, and there were no deaths due to GVHD before day 100. Only 3 developed chronic GVHD requiring immune suppression, (4%, CI: 0-8%). Two-year overall survival (OS) was 80% (CI: 69-87%), and (graft-versus-host disease-free, relapse-free survival) GRFS 57% (CI: 45-67%), both higher than historical CSA/MTX. The incidence of grade II-IV aGVHD, cGVHD, and NRM were all lower with PTCy/Tac/MMF compared to historical CSA/MTX. One-quarter (25%) experienced relapse (CI: 15-36%) similar to historical CSA/MTX. There was no statistically significant difference in survival outcomes between recipients of matched versus 7/8 donors.

Conclusion

Myeloablative HCT with PTCy/Tac/MMF results in extremely low incidence of severe acute or chronic GVHD, the primary endpoint of this clinical trial. Relapse risk is not increased compared to our historical CSA/MTX cohort.

Partially replacing cyclophosphamide with bendamustine in combination with cyclosporine A improves survival and reduces xenogeneic graft-versus-host-disease

Introduction

The use of allogeneic hematopoietic cell transplantation (allo-HCT) for treating hematological disorders is increasing, but the development of graft-versus-host disease (GvHD) remains a major cause of morbidity and mortality. The use of post-transplant cyclophosphamide (CY) has significantly improved outcomes following allo-HCT, but complications of viral reactivation due to delayed immune reconstitution or relapse remain. Other laboratories are evaluating the potential benefit of lowering the dose of CY given post-transplant, whereas our laboratory has been focusing on whether partially replacing CY with another DNA alkylating agent, bendamustine (BEN) may be advantageous in improving outcomes with allo-HCT.

Methods

Here, we utilized a xenogeneic GvHD (xGvHD) model in which immunodeficient NSG mice are infused with human peripheral blood mononuclear cells (PBMCs).

Results

We show that a lower dose of CY (25 mg/kg) given on days +3 and +4 or CY (75 mg/kg) given on only day +3 post-PBMC infusion is not sufficient for improving survival from xGvHD, but can be improved with the addition of BEN (15 mg/kg) on day +4 to day +3 CY (75 mg/kg). CY/BEN treated mice when combined with cyclosporine A (CSA) (10mg/kg daily from days +5 to +18 and thrice weekly thereafter), had improved outcomes over CY/CY +CSA treated mice. Infiltration of GvHD target organs was reduced in both CY/CY and CY/BEN treatment groups versus those receiving no treatment. CY/CY +CSA mice exhibited more severe xGvHD at day 10, marked by decreased serum albumin and increased intestinal permeability. CY/BEN treated mice had reductions in naïve, effector memory and Th17 polarized T cells. RNAseq analysis of splenocytes isolated from CY/CY and CY/BEN treated animals revealed increased gene set enrichment in multiple KEGG pathways related to cell migration, proliferation/differentiation, and inflammatory pathways, among others with CY/BEN treatment.

Conclusion

Together, we illustrate that the use of CY/BEN is safe and shows similar control of xGvHD to CY/CY, but when combined with CSA, survival with CY/BEN is significantly prolonged compared to CY/CY.

Efflux Capacity and Aldehyde Dehydrogenase Both Contribute to CD8+ T-cell Resistance to Posttransplant Cyclophosphamide

CD8⁺ T cells increase drug effluxing and aldehyde dehydrogenase expression in allogeneic reactions, enhancing resistance to cyclophosphamide.

Common γ-chain cytokines and the proliferative state of the cell modulate these resistance pathways.

Mechanisms of T-cell survival after cytotoxic chemotherapy, including posttransplantation cyclophosphamide (PTCy), are not well understood. Here, we explored the impact of PTCy on human CD8⁺ T-cell survival and reconstitution, including what cellular pathways drive PTCy resistance. In major histocompatibility complex (MHC)-mismatched mixed lymphocyte culture (MLC), treatment with mafosfamide, an in vitro active cyclophosphamide analog, preserved a relatively normal distribution of naïve and memory CD8⁺ T cells, whereas the percentages of mucosal-associated invariant T (MAIT) cells and phenotypically stem cell memory (Tscm) T-cell subsets were increased. Activated (CD25⁺) and proliferating CD8⁺ T cells were derived from both naïve and memory subsets and were reduced but still present after mafosfamide. By contrast, cyclosporine-A (CsA) or rapamycin treatment preferentially maintained nonproliferating CD25⁻ naïve cells. Drug efflux capacity and aldehyde dehydrogenase-1A1 expression were increased in CD8⁺ T cells in allogeneic reactions in vitro and in patients, were modulated by common γ-chain cytokines and the proliferative state of the cell, and contributed to CD8⁺ T-cell survival after mafosfamide. The CD8⁺ T-cell composition early after hematopoietic cell transplantation (HCT) in PTCy-treated patients was dominated by CD25⁺ and phenotypically memory, including Tscm and MAIT, cells, consistent with MLC. Yet, MHC-mismatched murine HCT studies revealed that peripherally expanded, phenotypically memory T cells 1 to 3 months after transplant originated largely from naïve-derived rather than memory-derived T cells surviving PTCy, suggesting that initial resistance and subsequent immune reconstitution are distinct. These studies provide insight into the complex immune mechanisms active in CD8⁺ T-cell survival, differentiation, and reconstitution after cyclophosphamide, with relevance for post-HCT immune recovery, chemotherapy use in autologous settings, and adoptive cellular therapies.