Allogeneic Hematopoietic Cell Transplantation in Advanced Systemic Mastocytosis: A retrospective analysis of the DRST and GREM registries

We identified 71 patients with AdvSM (aggressive SM [ASM], SM with an associated hematologic neoplasm [SM-AHN, e.g., acute myeloid leukemia, SM-AML], mast cell leukemia [MCL]) in two national registries (DRST/GREM) who received an allogeneic hematopoietic cell transplantation (alloHCT) performed in Germany from 1999-2021. Median overall survival (OS) of ASM/SM-AHN (n = 30, 45%), SM-AML (n = 28, 39%) and MCL ± AHN (n = 13, 19%) was 9.0, 3.3 and 0.9 years (P = 0.007). Improved median OS was associated with response of SM (17/41, 41%; HR 0.4 [0.2-0.9], P = 0.035) and/or of AHN (26/43, 60%, HR 0.3 [0.1-0.7], P = 0.004) prior to alloHCT. Adverse predictors for OS included absence of KIT D816V (10/61, 16%, HR 2.9 [1.2-6.5], P < 0.001) and a complex karyotype (9/60, 15%, HR 4.2 [1.8-10.0], P = 0.016). HLA-match, conditioning type or transplantation at centers reporting above-average alloHCTs (≥7) had no impact on OS. Taking into account competing events at years 1, 3 and 5, relapse-related mortality and non-relapse mortality rate were 15%/23%, 20%/30% and 23%/35%, respectively. Irrespective of subtype, subsequent treatment response was achieved in 13/30 (43%) patients and was highest on midostaurin/avapritinib (7/9, 78%). We conclude that outcome of alloHCT in AdvSM is more affected by disease phenotype and treatment response prior to transplant than by transplant characteristics.

A Validated Risk Stratification That Incorporates MAGIC Biomarkers Predicts Long-Term Outcomes in Pediatric Patients with Acute GVHD

Acute graft versus host disease (GVHD) is a common and serious complication of allogeneic hematopoietic cell transplantation (HCT) in children but overall clinical grade at onset only modestly predicts response to treatment and survival outcomes. Two tools to assess risk at initiation of treatment were recently developed. The Minnesota risk system stratifies children for risk of nonrelapse mortality (NRM) according to the pattern of GVHD target organ severity. The Mount Sinai Acute GVHD International Consortium (MAGIC) algorithm of 2 serum biomarkers (ST2 and REG3α) predicts NRM in adult patients but has not been validated in a pediatric population. We aimed to develop and validate a system that stratifies children at the onset of GVHD for risk of 6-month NRM. We determined the MAGIC algorithm probabilities (MAPs) and Minnesota risk for a multicenter cohort of 315 pediatric patients who developed GVHD requiring treatment with systemic corticosteroids. MAPs created 3 risk groups with distinct outcomes at the start of treatment and were more accurate than Minnesota risk stratification for prediction of NRM (area under the receiver operating curve (AUC), .79 versus .62, P = .001). A novel model that combined Minnesota risk and biomarker scores created from a training cohort was more accurate than either biomarkers or clinical systems in a validation cohort (AUC .87) and stratified patients into 2 groups with highly different 6-month NRM (5% versus 38%, P < .001). In summary, we validated the MAP as a prognostic biomarker in pediatric patients with GVHD, and a novel risk stratification that combines Minnesota risk and biomarker risk performed best. Biomarker-based risk stratification can be used in clinical trials to develop more tailored approaches for children who require treatment for GVHD.

CD45-Directed CAR-T Cells with CD45 Knockout Efficiently Kill Myeloid Leukemia and Lymphoma Cells In Vitro Even after Extended Culture

BACKGROUND

CAR-T cell therapy has shown impressive results and is now part of standard-of-care treatment of B-lineage malignancies, whereas the treatment of myeloid diseases has been limited by the lack of suitable targets. CD45 is expressed on almost all types of blood cells including myeloid leukemia cells, but not on non-hematopoietic tissue, making it a potential target for CAR-directed therapy. Because of its high expression on T and NK cells, fratricide is expected to hinder CD45CAR-mediated therapy. Due to its important roles in effector cell activation, signal transduction and cytotoxicity, CD45 knockout aimed at preventing fratricide in T and NK cells has been expected to lead to considerable functional impairment.

METHODS

CD45 knockout was established on T and NK cell lines using CRISPR/Cas9-RNPs and electroporation, and the successful protocol was transferred to primary T cells. A combined protocol was developed enabling CD45 knockout and retroviral transduction with a third-generation CAR targeting CD45 or CD19. The functionality of CD45ko effector cells, CD45ko/CD45CAR-T and CD45ko/CD19CAR-T cells was studied using proliferation as well as short- and long-term cytotoxicity assays.

RESULTS

As expected, the introduction of a CD45-CAR into T cells resulted in potent fratricide that can be avoided by CD45 knockout. Unexpectedly, the latter had no negative impact on T- and NK-cell proliferation in vitro. Moreover, CD45ko/CD45CAR-T cells showed potent cytotoxicity against CD45-expressing AML and lymphoma cell lines in short-term and long-term co-culture assays. A pronounced cytotoxicity of CD45ko/CD45CAR-T cells was maintained even after four weeks of culture. In a further setup, we confirmed the conserved functionality of CD45ko cells using a CD19-CAR. Again, the proliferation and cytotoxicity of CD45ko/CD19CAR-T cells showed no differences from those of their CD45-positive counterparts in vitro.

CONCLUSIONS

We report the efficient production of highly and durably active CD45ko/CAR-T cells. CD45 knockout did not impair the functionality of CAR-T cells in vitro, irrespective of the target antigen. If their activity can be confirmed in vivo, CD45ko/CD45CAR-T cells might, for example, be useful as part of conditioning regimens prior to stem cell transplantation.

Data-driven grading of acute graft-versus-host disease

Despite advances in allogeneic hematopoietic cell transplantation, acute graft-versus-host disease (aGVHD) remains its leading complication, yet with heterogeneous outcomes. Here, we analyzed aGVHD phenotypes and clinical classifications in depth in large, multicenter cohorts involving 3019 patients and addressed prevailing gaps by developing data-driven models. We compared, tested and verified these along with all conventional classifications in independent cohorts and found that data-driven grading outperformed conventional grading in Akaike information criterion and concordance index metrics. Data-driven classifications refined aGVHD assessment with up to 12 severity grades, which were associated with distinct nonrelapse mortality (NRM) and confirmed the key role of intestinal aGVHD. We developed an online calculator for physicians to implement principal component-derived grading (PC1). These results provide substantial insight into the evaluation of aGVHD phenotypes and multiorgan involvement, which relegates the exclusive reporting of overall aGVHD severity grades in transplant registries and clinical trials. Data-driven aGVHD grading provides an expandable platform to refine classification and transplant risk assessment.

Molecular monitoring of T-cell kinetics and migration in severe neurotoxicity after real-world CD19-specific chimeric antigen receptor T cell therapy

CD19-specific chimeric antigen receptor (CD19-CAR) T-cell therapies mediate durable responses in late-stage B-cell malignancies, but can be complicated by a potentially severe immune effector cell-associated neurotoxicity syndrome (ICANS). Despite broad efforts, the precise mechanisms of ICANS are not entirely known, and resistance to current ICANSdirected therapies (especially corticosteroids) has been observed. Recent data suggest that inflammatory cytokines and/or targeting of cerebral CD19-expressing pericytes can disrupt the blood-brain barrier and facilitate influx of immune cells, including CAR T cells. However, specific tools for CD19-CAR T-cell analysis within often minute samples of cerebrospinal fluid (CSF) are not broadly available. Here, we applied our recently developed digital polymerase chain reaction assays to monitor CD19-CAR T-cell kinetics in CSF and blood in real-world patients with neurotoxicity. Consistently, we observed a CAR T-cell enrichment within CSF in ICANS patients with further progressive accumulation despite intense corticosteroid- containing immuno-chemotherapies in a subset of patients with prolonged and therapy-resistant grade 3-4 neurotoxicity. We used next-generation T-cell receptor-b sequencing to assess the repertoire of treatment-refractory cells. Longitudinal analysis revealed a profound skewing of the T-cell receptor repertoire, which at least partly reflected selective expansion of infused T-cell clones. Interestingly, a major fraction of eventually dominating hyperexpanded T-cell clones were of non-CAR T-cell derivation. These findings hint to a role of therapy-refractory T-cell clones in severe ICANS development and prompt future systematic research to determine if CAR T cells may serve as 'door openers' and to further characterize both CAR-positive and non-CAR T cells to interrogate the transcriptional signature of these possibly pathologic T cells.

Digital PCR Assays for Precise Quantification of CD19-CAR-T Cells after Treatment with Axicabtagene Ciloleucel

Treatment with axicabtagene ciloleucel (Axi-cel) CD19-CAR-T (chimeric antigen receptor T) cells has been approved for refractory/relapsed diffuse large B cell lymphoma (DLBCL) and primary mediastinal large B cell lymphoma (PMBCL). Because treatment success as well as side effects might depend on CAR-T cell expansion in vivo, we aimed at developing digital PCR (dPCR) assays for detection and quantification of CAR-T cells. To this end, we cloned and sequenced the complete cDNA of the CAR construct. We designed different combinations of primers and dual-labeled hydrolysis probes located in various CAR regions. Three combinations were successfully tested on CAR-positive and -negative cells in duplex reactions with a reference gene (REF) to concomitantly assess cell numbers. All assays demonstrated excellent specificity and reproducibility with neglectable inter-assay variations. For all three assays, almost perfect correlation between the two dPCRs (Axi-cel versus REF) was observed, and the limit of detection was one single CAR-transduced cell corresponding to a sensitivity of 0.01% for 100 ng genomic DNA. After cross-validation, we used one assay to monitor Axi-cel CAR-T numbers in patients. CAR-T expansion and contraction followed the expected kinetics with median peak value of 11.2 Axi-cel CAR-T cells/μL at 11.3 days (median). Clinically, we observed only two partial responses (PRs) in the five patients with CAR-T cell peak numbers below median, whereas four of the five patients with comparatively good expansion showed clinical responses (two complete responses [CRs] and two PRs) on day 30. In conclusion, we established a novel dPCR assay for the sensitive detection of transgenic CAR-T cells, which should be very useful in the context of Axi-cel treatment.

Prognostic factors for donor lymphocyte infusions following non-myeloablative allogeneic stem cell transplantation in multiple myeloma

In this retrospective study, we evaluated donor lymphocyte infusions given for relapsed (n=48) or persistent (n=15) myeloma following non-myeloablative allogeneic stem cell transplantation (Allo-SCT). Twenty-four of 63 patients (38.1%) responded: 12 patients (19.0%) with a partial response (PR) and 12 patients (19.0%) with a complete response (CR). Overall survival after donor lymphocyte infusions (DLI) was 23.6 months (1.0-50.7+). Median overall survival for non-responding patients was 23.6 months and has not been reached for the patients responding to DLI. In responders, progression-free survival after DLI was 27.8 months (1.2-46.2+). Patients with a PR had a median progression-free survival of 7.0 months, whereas patients with a CR to DLI had a median progression-free survival of 27.8 months. Major toxicities were acute graft-versus-host disease (GVHD) (38.1%) and chronic GVHD (42.9%). Seven patients (11.1%) died from treatment-related mortality. The only significant prognostic factors for response to DLI were the occurrence of acute and chronic GVHD. There was a trend towards significance for time between transplantation and DLI, and response. Donor lymphocyte infusion following non-myeloablative Allo-SCT is a valuable strategy for relapsed or persistent disease.

Antithymocyte globulin induces complement-dependent cell lysis and caspase-dependent apoptosis in myeloma cells

OBJECTIVE

Allogeneic stem cell transplantation is a potentially curative therapy for patients with multiple myeloma. Polyclonal antithymocyte globulins (ATG) or monoclonal anti-CD52 (Alemtuzumab) are included in conditioning regimens to enhance engraftment and reduce risk of severe graft-vs-host disease. Because both agents have been reported to induce depletion of B cells, we sought to investigate their cytotoxic activity on myeloma cells.

MATERIALS AND METHODS

Complement-mediated and complement-independent activity of ATG-Fresenius and Alemtuzumab was investigated on four myeloma cell lines (RPMI-8226, U266, KMS-12-BM, and EJM) and bone marrow samples from six myeloma patients. Cytotoxicity was determined by staining with annexin V-fluorescein isothiocyanate and 7-amino-actinomycin D followed by flow cytometry.

RESULTS

ATG at a concentration of 500 microg mL(-1) induced up to 100% and 85% complement-dependent killing of myeloma cell lines and primary myeloma samples respectively. In the absence of complement ATG still could induce up to 50% and 80% apoptosis in myeloma cell lines and primary myeloma samples, respectively. Preincubation of myeloma cells with a general caspase inhibitor abrogated ATG-induced complement-independent cell death. Alemtuzumab-mediated myeloma cytotoxicity was only observed in KMS-12-BM cells, and in none of the patient samples.

CONCLUSION

ATG induces marked cytotoxic activity both in myeloma cell lines and in primary myeloma samples. Further elucidation of antibodies and antigens involved may pave the way for antibody-based myeloma therapy.

T lymphocytes as targets of gene transfer with Moloney-type retroviral vectors

Peripheral T lymphocytes are a target of choice for many gene therapeutic strategies. Retrovirus-mediated transduction allows genomic integration and long-term expression of transgenes in target cells. Over many years, low transduction efficiency into primary T lymphocytes has limited clinical application of existing protocols. Recently, gene transfer rates > 50% have been achieved facilitating clinical studies. More attention is thus being focused on the ability of gene-modified cells to carry out innate as well as conferred functions in vivo and the influence of culture conditions, retroviral vector and host response thereon.

Retroviral transduction of T lymphocytes for suicide gene therapy in allogeneic stem cell transplantation

Transplantation of suicide gene modified allogeneic T lymphocytes is an approach to prevent T cell mediated GVHD while preserving the 'graft-versus-leukemia' (GVL) effect of an allograft. A prerequisite for such a therapy is the efficient transduction of T cells with suitable vectors. Since existing techniques allow only insufficient transduction of T cells, the development of more efficient gene transfer protocols into these cells is of great importance. We present here a protocol for the highly efficient transduction of human primary T cells at high densities (1 x 10(6) cells/ml) by retroviral infection. The presented protocol allowed us to obtain transduction rates of more than 70% of CD3+ cells after two cycles of infection. It is based on the use of FBS-free media for both the production of retrovirus-containing supernatant, as well as the cultivation of the primary T cells. Since the protocol presented here works just as efficiently under large scale conditions, it may easily be adapted to clinical needs and 'good manufacturing practice' (GMP) standards.