Complement-mediated thrombotic microangiopathy can be difficult to recognize when it presents in the setting of an apparent clinical trigger, such as pregnancy, severe hypertension, or kidney transplantation. These conditions can each cause endothelial injury directly, but may also unmask complement dysregulation in susceptible individuals. In these situations, the critical question is not whether a trigger exists but whether it fully explains the syndrome and whether urgent complement blockade is warranted to prevent irreversible kidney injury. In this How I Treat article, we use three real-world cases to illustrate how we approach this decision in practice. We emphasize the bedside features that most influence our threshold to treat, including the pattern and severity of kidney injury, tempo of disease progression, and lack of improvement with supportive or trigger-directed care. We also address the interpretation of complement genetic findings, pregnancy- and transplant-specific risk stratification, and individualization of treatment duration. Functional assays can support mechanistic assessment in selected cases but remain an adjunct to the diagnosis and should not drive management decisions.

Although first-line immunotherapy achieves remission in most patients with follicular lymphoma (FL), improved biomarkers and therapeutic strategies are required to identify and manage those who relapse. We investigated the immune microenvironment at diagnosis in uniformly treated FL patients with extended follow-up (>11 years), comparing relapsed and relapse-free cases. Transcriptomic profiling revealed enrichment of inflammatory response pathways in relapsed patients, including cytokine overexpression and upregulation of CD70, a molecule implicated in immune activation and inflammation. Multiplex immunofluorescence confirmed CD70 overexpression at diagnosis in tumor cells as well as in CD8⁺ and CD4⁺ T follicular helper (TFH) cells, correlating with inferior progression-free survival. Functional studies demonstrated that CD70⁺ tumor cells were more proliferative and induced CD70 expression in T cells, suggesting a feed-forward loop sustaining immune activation. To target these cells and enhance current CAR-T approaches, we engineered dual CD19-CD70 chimeric antigen receptor (CAR) T cells by co-transducing the CD19-CAR-T ARI-0001 with a CD27-based anti-CD70 CAR. Dual CAR-T cells exhibited enhanced in vitro cytotoxicity against patient-derived spheroids of FL, diffuse large B-cell lymphoma, and mantle cell lymphoma. In FL xenograft models, dual CAR-T treatment achieved superior disease control compared to monotargeted CAR-T cells, inducing complete tumor clearance in spleen and bone marrow. Collectively, these findings provide strong preclinical rationale for the clinical development of CD19-CD70 dual CAR-T therapy to improve outcomes in high-risk FL and potentially other B-cell non-Hodgkin lymphomas.

Graft-versus-host disease (GVHD) remains a major barrier to the success of allogeneic hematopoietic stem cell transplantation (HSCT). In preclinical models, dysregulation of IL-6 in the peri-transplant period promotes GVHD via STAT3-dependent T cell differentiation and monocyte activation but the nature of immunological effects invoked in patients remains unclear. To advance our understanding of IL-6 signaling in humans during HSCT, we performed single-cell RNA sequencing on circulating CD14+ monocytes and CD4+ T cells from patient samples within a clinical trial of IL-6R inhibition (tocilizumab (TCZ) or placebo) on a backbone of calcineurin inhibition (CNI) and short-course methotrexate. We studied patients who did not develop acute GVHD and included a placebo-treated group analyzed prior to the development of acute GVHD. IL-6R inhibition promoted Type-I IFN-associated transcriptional programs in both CD4+ T cells and CD14+ monocytes. Surprisingly, IL-6R-inhibition with TCZ profoundly enhanced cytolytic CD4+ T cell differentiation. In experimental HSCT and chimeric antigen receptor T cell systems, genetic deletion of IL-6 signaling in donor T cells enhanced the expansion of cytolytic Eomes+ CD4+ regulatory T cell subsets whilst attenuating Th1 and Th17 differentiation. Consistent with the promotion of this cytolytic CD4+ phenotype, anti-tumor effects were improved in the absence of IL-6 signaling. In summary, these data demonstrate that IL-6R inhibition during cell therapy imprints Type-I IFN programs and cytolytic CD4+ T cell differentiation, including the Eomes+ fraction associated with favorable immunotherapy outcomes.

The kinetics of neutrophil development in human bone marrow remain largely unclear, despite the large implications for the mechanisms underlying host defense and inflammatory responses. Here, in situ DNA labeling was used to follow human neutrophil precursor maturation in bone marrow and blood. Human bone marrow samples were obtained by aspiration from healthy volunteers after short-term (6 hrs) labeling of dividing cells via oral intake of glucose containing the stable isotope deuterium. Mature and precursor populations were isolated at different times by fluorescence-activated cell sorting, and the deuterium incorporation in DNA was measured by GC/MS. Promyelocytes quickly incorporated deuterium in their DNA, whereas in mature neutrophils deuterium was only found from 6 days after intake. The enrichment curves of myelocytes, metamyelocytes, banded, and mature neutrophils mirrored that of the promyelocytes, shifted in time. This pattern indicated that neutrophil development in the bone marrow is well described with a linear conveyor belt model, i.e. following the "first-in/first-out" principle. In contrast to the current dogma, myelocytes did not divide, placing them in the postmitotic pool. Furthermore, the deuterium enrichment curves suggested that mature neutrophils constantly exchange between the bone marrow, blood, and tissue. Our unique labeling data of all stages of the neutrophil life cycle allowed us to estimate the lifespan of the mature neutrophil, deriving a value of at least 6 days. This study provides new insights into neutrophil development kinetics, informing the design and application of therapeutic strategies targeting granulopoiesis and the recruitment of mature neutrophils.

In the TRANSCEND FL primary analysis, lisocabtagene maraleucel (liso-cel) showed high response rates and favorable safety in patients with relapsed/refractory (R/R) follicular lymphoma (FL). Longer follow-up is needed to assess remission durability and long-term or late-onset toxicities. Here, we report 3-year follow-up results (median [range] on-study follow-up, 41.5 months [0.3‒54.0]) in patients with third-line or later (3L+) FL. Patients had R/R FL after ≥2 prior lines of combination systemic therapy, including an anti-CD20 antibody and an alkylator. A total of 107 patients received liso-cel and 103 were efficacy evaluable, with overall and complete response rates (95% CI) per independent review committee of 97% (92‒99) and 94% (88‒98), respectively. Medians were not reached for all time-to-event outcomes; estimated 36-month (95% CI) rates for duration of response, progression-free survival, time free from next treatment, and overall survival were 70% (60‒78), 68% (58‒76), 75% (70‒80), and 86% (78‒92), respectively. Response rates and 36-month time-to-event rates were consistent in high-risk subgroups, including patients with disease progression within 24 months of starting first-line immunochemotherapy, bulky disease, or double-refractory status. Longitudinal safety analyses showed decreasing grade ≥3 cytopenias and hypogammaglobulinemia (immunoglobulin G <500 mg/dL), with use of supportive care (transfusions, growth factors, intravenous immunoglobulin) mostly limited to the 3 months after infusion, and consistently low incidences of grade ≥3 infections in short- and long-term periods. At 3-year follow-up, a single liso-cel infusion delivered durable efficacy and high survival, including in high-risk subgroups, alongside a favorable long-term safety profile in patients with 3L+ FL. Clinicaltrials.gov: NCT04245839.

Hematopoietic stem cells (HSCs) depend upon paracrine signals from bone marrow endothelial cells (BM ECs) and perivascular stromal cells for their maintenance and regeneration. Chemotherapy and total body irradiation (TBI) utilized in the curative treatment of cancer cause profound damage to the BM vascular niche, which impedes hematopoietic reconstitution. The mechanisms controlling regeneration of the HSC vascular niche are not well understood. We discovered that conditional deletion of R spondin 2 (Rspo2) from BM endothelial cells (ECs) impaired HSC regeneration in mice following total body irradiation (TBI), in association with decreased HSC survival. Mice lacking EC - Rspo2 expression demonstrated delayed regeneration of the BM vascular niche following TBI and Rspo2 - deficient BM ECs displayed defective angiogenesis. Conversely, systemic administration of R spondin 2 caused early restoration of the BM sinusoidal vascular niche in irradiated mice and augmented BM EC angiogenesis. Concordantly, R spondin 2 - treated mice displayed accelerated regeneration of the HSC pool. These studies suggest that BM ECs regulate the regeneration of the BM sinusoidal vascular niche via secretion of R spondin 2.

The phase 3 SYMPATICO study included an open-label cohort to evaluate the efficacy and safety of first-line ibrutinib plus venetoclax in patients with non-blastoid mantle cell lymphoma (MCL) ≥65 years (n=65), or ≥18 years with a TP53 mutation (TP53m) (n=11). Eligible patients received oral ibrutinib 560 mg once daily and venetoclax (5-week ramp-up to 400 mg once daily) for 2 years, then single-agent ibrutinib 560 mg until disease progression or unacceptable toxicity. In total, 78 patients were enrolled. With median time on study of 40.5 months (range, 0.6+ to 46.9), the complete response (CR) rate was 69% (95% CI, 58-79), and the overall response rate was 95% (95% CI, 87-99). The median duration of response was 37.1 months (95% CI, 30.3-not estimable [NE]). Median progression-free survival (mPFS) was 40.2 months (95% CI, 29.4-NE); median overall survival (OS) was not reached (3-year OS rate, 79% [95% CI, 68-86]). In patients ≥65 years, CR rates were 76% (no TP53m) and 44% (with TP53m), mPFS was 40.2 and 22.0 months, and 3-year OS was 85% and 66%, respectively. In adult patients <65 years (with TP53m), the CR rate was 73%, mPFS was 15.4 months, and 3-year OS was 73%. The most common treatment-emergent adverse events were diarrhea (49%), fatigue (37%), neutropenia (35%), and COVID-19 (32%). First-line ibrutinib plus venetoclax showed promising efficacy, with high CR rates and durable remissions, in patients with previously untreated non-blastoid MCL and may be an option for patients ≥65 years or patients of any age with TP53m. NCT03112174.