High-parametric evaluation of human invariant natural killer T cells to delineate heterogeneity in allo- and autoimmunity.

Human invariant natural killer T (iNKT) cells are a rare innate-like lymphocyte population that recognizes glycolipids presented on CD1d. Studies in mice have shown that these cells are heterogeneous and are capable of enacting diverse functions, and the composition of iNKT cell subsets can alter disease outcomes. In contrast, far less is known about how heterogeneity in human iNKT cells relates to disease. To address this, we used a high-dimensional, data-driven approach to devise a framework for parsing human iNKT heterogeneity. Our data revealed novel and previously described iNKT cell phenotypes with distinct functions. In particular, we found 2 phenotypes of interest: (1) a population with T helper 1 function that was increased with iNKT activation characterized by HLA-II+CD161- expression, and (2) a population with enhanced cytotoxic function characterized by CD4-CD94+ expression. These populations correlate with acute graft-versus-host disease after allogeneic hematopoietic stem cell transplantation and with new onset type 1 diabetes, respectively. Our study identifies human iNKT cell phenotypes associated with human disease that could aid in the development of biomarkers or therapeutics targeting iNKT cells.

Analysis of the Whole CDR3 T Cell Receptor Repertoire after Hematopoietic Stem Cell Transplantation in 2 Clinical Cohorts.

A major cause of morbidity and mortality for patients who undergo hematologic stem cell transplantation (HSCT) is acute graft-versus-host disease (aGVHD), a mostly T cell-mediated disease. Examination of the T cell receptor (TCR) repertoire of HSCT recipients and the use of next-generation nucleotide sequencing have raised the question of whether features of TCR repertoire reconstitution might reproducibly associate with aGVHD. We hypothesized that the peripheral blood TCR repertoire of patients with steroid-nonresponsive aGVHD would be less diverse. We also hypothesized that patients with GVHD who shared HLA might also share common clones at the time of GVHD diagnosis, thereby potentially providing potential clinical indicators for treatment stratification. We further hypothesized that HSCT recipients with the same HLA mismatch might share a more similar TCR repertoire based on a potentially shared focus of alloreactive responses. We studied 2 separate patient cohorts and 2 separate platforms for measuring TCR repertoire. The first cohort of patients was from a multicenter Phase III randomized double-blinded clinical trial of patients who developed aGVHD (NCT01002742). The second cohort comprised samples from biobanks from 2 transplantation centers and the Center for International Blood and Marrow Transplant Research of patients who underwent mismatched HSCT. There were no statistically significant differences in the TCR diversity of steroid responders and nonresponders among patients with aGVHD on the day of diagnosis. Most clones in the repertoire were unique to each patient, but a small number of clones were found to be both exclusive to and shared among aGVHD nonresponders. We were also able to show a strong correlation between the presence of Vß20 and Vß29 and steroid responsiveness. Using the Bhattacharya coefficient, those patients who shared the same HLA mismatch were shown to be no more similar to one another than to those who had a completely different mismatch. Using 2 separate clinical cohorts and 2 separate platforms for analyzing the TCR repertoire, we have shown that the sampled human TCR repertoire is largely unique to each patient but contains glimmers of common clones of subsets of clones based on responsiveness to steroids in aGVHD on the day of diagnosis. These studies are informative for future strategies to assess for reproducible TCR responses in human alloreactivity and possible markers of GVHD responsiveness to therapy.

A novel antibody-cell conjugation method to enhance and characterize cytokine-induced killer cells.

BACKGROUND: Cytokine-induced killer (CIK) cells are an ex vivo-expanded cellular therapy product with potent anti-tumor activity in a subset of patients with solid and hematologic malignancies. We hypothesize that directing CIK cells to a specific tumor antigen will enhance CIK cell anti-tumor cytotoxicity. METHODS: We present a newly developed method for affixing antibodies directly to cell surface proteins. First, we evaluated the anti-tumor potential of CIK cells after affixing tumor-antigen targeting monoclonal antibodies. Second, we evaluated whether this antibody-conjugation method can profile the surface proteome of CIK cells. RESULTS: We demonstrated that affixing rituximab or daratumumab to CIK cells enhances cytotoxic killing of multiple lymphoma cell lines in vitro. These 'armed' CIK cells exhibited enhanced intracellular signaling after engaging tumor targets. Cell surface proteome profiling suggested mechanisms by which antibody-armed CIK cells concurrently activated multiple surface proteins, leading to enhanced cytolytic activity. Our surface proteome analysis indicated that CIK cells display enhanced protein signatures indicative of immune responses, cellular activation and leukocyte migration. CONCLUSIONS: Here, we characterize the cell surface proteome of CIK cells using a novel methodology that can be rapidly applied to other cell types. Our study also demonstrates that without genetic modification CIK cells can be rapidly armed with monoclonal antibodies, which endows them with high specificity to kill tumor targets.

Donor-Derived Cytokine-Induced Killer Cell Infusion as Consolidation after Nonmyeloablative Allogeneic Transplantation for Myeloid Neoplasms.

Non-myeloablative conditioning, such as with total lymphoid irradiation and antithymocyte globulin (TLI-ATG), has allowed allogeneic hematopoietic cell transplantation (allo-HCT) with curative potential for older patients and those with comorbid medical conditions with myeloid neoplasms. However, early achievement of full donor chimerism (FDC) and relapse remain challenging. Cytokine-induced killer (CIK) cells have been shown to have antitumor cytotoxicity. Infusion of donor-derived CIK cells has been studied for hematologic malignancies relapsed after allo-HCT but has not been evaluated as post-transplant consolidation. In this phase II study, we prospectively studied whether a one-time infusion of 1 × 108/kg CD3+ donor-derived CIK cells administered between day +21 and day +35 after TLI-ATG conditioning could improve achievement of FDC by day +90 and 2-year clinical outcomes in patients with myeloid neoplasms. CIK cells, containing predominantly CD3+CD8+NKG2D+ cells along with significantly expanded CD3+CD56+ cells, were infused in 31 of 44 patients. Study outcomes were compared to outcomes of a retrospective historical cohort of 100 patients. We found that this one-time CIK infusion did not increase the rate of FDC by day +90. On an intention-to-treat analysis, 2-year non-relapse mortality (6.8%; 95% confidence interval [CI], 0-14.5%), event-free survival (27.3%; 95% CI, 16.8-44.2%), and overall survival (50.6%; 95% CI, 37.5-68.2%) were similar to the values seen in the historical cohort. The cumulative incidence of grade II-IV acute graft-versus-host disease at 1-year was 25.1% (95% CI, 12-38.2%). On univariate analysis, the presence of monosomal or complex karyotype was adversely associated with relapse-free survival and overall survival. Given the favorable safety profile of CIK cell infusion, strategies such as repeat dosing or genetic modification merit exploration. This trial was registered at ClinicalTrials.gov (NCT01392989).

Third-party CD4+ invariant natural killer T cells protect from murine GVHD lethality.

Graft-versus-host disease (GVHD) is driven by extensive activation and proliferation of alloreactive donor T cells causing significant morbidity and mortality following allogeneic hematopoietic cell transplantation (HCT). Invariant natural killer T (iNKT) cells are a potent immunoregulatory T-cell subset in both humans and mice. Here, we explored the role of adoptively transferred third-party CD4(+) iNKT cells for protection from lethal GVHD in a murine model of allogeneic HCT across major histocompatibility barriers. We found that low numbers of CD4(+) iNKT cells from third-party mice resulted in a significant survival benefit with retained graft-versus-tumor effects. In vivo expansion of alloreactive T cells was diminished while displaying a T helper cell 2-biased phenotype. Notably, CD4(+) iNKT cells from third-party mice were as protective as CD4(+) iNKT cells from donor mice although third-party CD4(+) iNKT cells were rejected early after allogeneic HCT. Adoptive transfer of third-party CD4(+) iNKT cells resulted in a robust expansion of donor CD4(+)CD25(+)FoxP3(+) regulatory T cells (Tregs) that were required for protection from lethal GVHD. However, in vivo depletion of myeloid-derived suppressor cells abrogated both Treg expansion and protection from lethal GVHD. Despite the fact that iNKT cells are a rare cell population, the almost unlimited third-party availability and feasibility of in vitro expansion provide the basis for clinical translation.

CD4+ invariant natural killer T cells protect from murine GVHD lethality through expansion of donor CD4+CD25+FoxP3+ regulatory T cells.

Dysregulated donor T cells lead to destruction of host tissues resulting in graft-versus-host disease (GVHD) after allogeneic hematopoietic cell transplantation (HCT). We investigated the impact of highly purified (>95%) donor CD4(+) invariant natural killer T (iNKT) cells on GVHD in a murine model of allogeneic HCT. We found that low doses of adoptively transferred donor CD4(+) iNKT cells protect from GVHD morbidity and mortality through an expansion of donor CD4(+)CD25(+)FoxP3(+) regulatory T cells (Tregs). These Tregs express high levels of the Ikaros transcription factor Helios and expand from the Treg pool of the donor graft. Furthermore, CD4(+) iNKT cells preserve T-cell-mediated graft-versus-tumor effects. Our studies reveal new aspects of the cellular interplay between iNKT cells and Tregs in the context of tolerance induction after allogeneic HCT and set the stage for clinical translation.

A distinct evolution of the T-cell repertoire categorizes treatment refractory gastrointestinal acute graft-versus-host disease.

Steroid refractory gastrointestinal (GI) acute graft-versus-host disease (aGVHD) is a major cause of mortality in hematopoietic stem cell transplantation (HCT) without immune markers to establish a diagnosis or guide therapy. We found that T-cell receptor ß (TCRß) complementarity-determining region 3 repertoire sequencing reveals patterns that could eventually serve as a disease biomarker of T-cell alloreactivity in aGVHD. We identified T-cell clones in GI biopsies in a heterogeneous group of 15 allogeneic HCT patients with GI aGVHD symptoms. Seven steroid-refractory aGVHD patients showed a more conserved TCRß clonal structure between different biopsy sites in the GI tract than 8 primary therapy-responsive patients. Tracking GI clones identified longitudinally at endoscopy in the blood also revealed an increased clonal expansion in patients with steroid-refractory disease. Immune repertoire sequencing-based methods could enable a novel personalized way to guide diagnosis and therapy in diseases where T-cell activity is a major determinant.

Single-center randomized trial of T-reg graft alone vs T-reg graft plus tacrolimus for the prevention of acute GVHD.

ABSTRACT: Allogeneic hematopoietic cell transplantation (HCT) is a curative therapy for hematological malignancies for which graft-versus-host disease (GVHD) remains a major complication. The use of donor T-regulatory cells (Tregs) to prevent GVHD appears promising, including in our previous evaluation of an engineered graft product (T-reg graft) consisting of the timed, sequential infusion of CD34+ hematopoietic stem cells and high-purity Tregs followed by conventional T cells. However, whether immunosuppressive prophylaxis can be removed from this protocol remains unclear. We report the results of the first stage of an open-label single-center phase 2 study (NCT01660607) investigating T-reg graft in myeloablative HCT of HLA-matched and 9/10-matched recipients. Twenty-four patients were randomized to receive T-reg graft alone (n = 12) or T-reg graft plus single-agent GVHD prophylaxis (n = 12) to determine whether T-reg graft alone was noninferior in preventing acute GVHD. All patients developed full-donor myeloid chimerism. Patients with T-reg graft alone vs with prophylaxis had incidences of grade 3 to 4 acute GVHD of 58% vs 8% (P = .005) and grade 3 to 4 of 17% vs 0% (P = .149), respectively. The incidence of moderate-to-severe chronic GVHD was 28% in the T-reg graft alone arm vs 0% with prophylaxis (P = .056). Among patients with T-reg graft and prophylaxis, CD4+ T-cell-to-Treg ratios were reduced after transplantation, gene expression profiles showed reduced CD4+ proliferation, and the achievement of full-donor T-cell chimerism was delayed. This study indicates that T-reg graft with single-agent tacrolimus is preferred over T-reg graft alone for the prevention of acute GVHD. This trial was registered at www.clinicaltrials.gov as #NCT01660607.

CD39 delineates chimeric antigen receptor regulatory T cell subsets with distinct cytotoxic & regulatory functions against human islets.

Human regulatory T cells (Treg) suppress other immune cells. Their dysfunction contributes to the pathophysiology of autoimmune diseases, including type 1 diabetes (T1D). Infusion of Tregs is being clinically evaluated as a novel way to prevent or treat T1D. Genetic modification of Tregs, most notably through the introduction of a chimeric antigen receptor (CAR) targeting Tregs to pancreatic islets, may improve their efficacy. We evaluated CAR targeting of human Tregs to monocytes, a human ß cell line and human islet ß cells in vitro. Targeting of HLA-A2-CAR (A2-CAR) bulk Tregs to HLA-A2+ cells resulted in dichotomous cytotoxic killing of human monocytes and islet ß cells. In exploring subsets and mechanisms that may explain this pattern, we found that CD39 expression segregated CAR Treg cytotoxicity. CAR Tregs from individuals with more CD39low/- Tregs and from individuals with genetic polymorphism associated with lower CD39 expression (rs10748643) had more cytotoxicity. Isolated CD39- CAR Tregs had elevated granzyme B expression and cytotoxicity compared to the CD39+ CAR Treg subset. Genetic overexpression of CD39 in CD39low CAR Tregs reduced their cytotoxicity. Importantly, ß cells upregulated protein surface expression of PD-L1 and PD-L2 in response to A2-CAR Tregs. Blockade of PD-L1/PD-L2 increased ß cell death in A2-CAR Treg co-cultures suggesting that the PD-1/PD-L1 pathway is important in protecting islet ß cells in the setting of CAR immunotherapy. In summary, introduction of CAR can enhance biological differences in subsets of Tregs. CD39+ Tregs represent a safer choice for CAR Treg therapies targeting tissues for tolerance induction.

Bendamustine is a safe and effective lymphodepletion agent for axicabtagene ciloleucel in patients with refractory or relapsed large B-cell lymphoma.

BACKGROUND: Fludarabine in combination with cyclophosphamide (FC) is the standard lymphodepletion regimen for CAR T-cell therapy (CAR T). A national fludarabine shortage in 2022 necessitated the exploration of alternative regimens with many centers employing single-agent bendamustine as lymphodepletion despite a lack of clinical safety and efficacy data. To fill this gap in the literature, we evaluated the safety, efficacy, and expansion kinetics of bendamustine as lymphodepletion prior to axicabtagene ciloleucel (axi-cel) therapy. METHODS: 84 consecutive patients with relapsed or refractory large B-cell lymphoma treated with axi-cel and managed with a uniform toxicity management plan at Stanford University were studied. 27 patients received alternative lymphodepletion with bendamustine while 57 received FC. RESULTS: Best complete response rates were similar (73.7% for FC and 74% for bendamustine, p=0.28) and there was no significant difference in 12-month progression-free survival or overall survival estimates (p=0.17 and p=0.62, respectively). The frequency of high-grade cytokine release syndrome and immune effector cell-associated neurotoxicity syndrome was similar in both the cohorts. Bendamustine cohort experienced lower proportions of hematological toxicities and antibiotic use for neutropenic fever. Immune reconstitution, as measured by quantitative assessment of cellular immunity, was better in bendamustine cohort as compared with FC cohort. CAR T expansion as measured by peak expansion and area under the curve for expansion was comparable between cohorts. CONCLUSIONS: Bendamustine is a safe and effective alternative lymphodepletion conditioning for axi-cel with lower early hematological toxicity and favorable immune reconstitution.

Regulatory T cells use heparanase to access IL-2 bound to extracellular matrix in inflamed tissue.

Although FOXP3+ regulatory T cells (Treg) depend on IL-2 produced by other cells for their survival and function, the levels of IL-2 in inflamed tissue are low, making it unclear how Treg access this critical resource. Here, we show that Treg use heparanase (HPSE) to access IL-2 sequestered by heparan sulfate (HS) within the extracellular matrix (ECM) of inflamed central nervous system tissue. HPSE expression distinguishes human and murine Treg from conventional T cells and is regulated by the availability of IL-2. HPSE-/- Treg have impaired stability and function in vivo, including in the experimental autoimmune encephalomyelitis (EAE) mouse model of multiple sclerosis. Conversely, endowing monoclonal antibody-directed chimeric antigen receptor (mAbCAR) Treg with HPSE enhances their ability to access HS-sequestered IL-2 and their ability to suppress neuroinflammation in vivo. Together, these data identify a role for HPSE and the ECM in immune tolerance, providing new avenues for improving Treg-based therapy of autoimmunity.

FOXP3+ regulatory T cells use heparanase to access IL-2 bound to ECM in inflamed tissues.

FOXP3+ regulatory T cells (Treg) depend on exogenous IL-2 for their survival and function, but circulating levels of IL-2 are low, making it unclear how Treg access this critical resource in vivo. Here, we show that Treg use heparanase (HPSE) to access IL-2 sequestered by heparan sulfate (HS) within the extracellular matrix (ECM) of inflamed central nervous system tissue. HPSE expression distinguishes human and murine Treg from conventional T cells and is regulated by the availability of IL-2. HPSE-/- Treg have impaired stability and function in vivo, including the experimental autoimmune encephalomyelitis (EAE) mouse model of multiple sclerosis. Conversely, endowing Treg with HPSE enhances their ability to access HS-sequestered IL-2 and their tolerogenic function in vivo. Together, these data identify novel roles for HPSE and the ECM in immune tolerance, providing new avenues for improving Treg-based therapy of autoimmunity.

Apoptotic cells activate NKT cells through T cell Ig-like mucin-like-1 resulting in airway hyperreactivity.

T cell Ig-like mucin-like-1 (TIM-1) is an important asthma susceptibility gene, but the immunological mechanisms by which TIM-1 functions remain uncertain. TIM-1 is also a receptor for phosphatidylserine (PtdSer), an important marker of cells undergoing programmed cell death, or apoptosis. We now demonstrate that NKT cells constitutively express TIM-1 and become activated by apoptotic cells expressing PtdSer. TIM-1 recognition of PtdSer induced NKT cell activation, proliferation, and cytokine production. Moreover, the induction of apoptosis in airway epithelial cells activated pulmonary NKT cells and unexpectedly resulted in airway hyperreactivity, a cardinal feature of asthma, in an NKT cell-dependent and TIM-1-dependent fashion. These results suggest that TIM-1 serves as a pattern recognition receptor on NKT cells that senses PtdSer on apoptotic cells as a damage-associated molecular pattern. Furthermore, these results provide evidence for a novel innate pathway that results in airway hyperreactivity and may help to explain how TIM-1 and NKT cells regulate asthma.

Allogeneic Hematopoietic Cell Transplantation for Adult Acute Lymphoblastic Leukemia in the Modern Era.

Allogeneic hematopoietic cell transplantation (HCT) remains an important treatment for adults with acute lymphoblastic leukemia (ALL). We hypothesized that advances in ALL and transplantation have resulted in improved HCT outcomes in recent years. In this study, we evaluated the characteristics and outcomes of adult ALL patients undergoing allogeneic HCT over the last decade. Patients with ALL aged 18 years and older who underwent allogeneic HCT at Stanford University between 2008 and 2019 were included in this study. Patients were divided into 2 eras based on year of HCT: 2008 to 2013 (earlier era) and 2014 to 2019 (later era). A total of 285 patients were included: 119 patients underwent HCT in the earlier era and 166 in the later era. Patients who underwent transplantation in the later era were more likely to be Hispanic (38% versus 21%) and to have an HCT-comorbidity index ≥3 (31% versus 18%). Donor source for HCT also differed with an increase in the use of HLA-mismatched donor sources (38% versus 24%), notably umbilical cord blood in the later era (16% versus 0%). Patients in the later era were less likely to undergo transplantation with active disease (4% versus 16%); pre-HCT rates of measurable residual disease were similar across the eras (38% versus 40%). In unadjusted analyses, overall survival (OS) improved across eras, with 2-year estimates for the later and earlier eras of 73% (95% confidence interval [CI], 66%-80%) versus 55% (95% CI, 46%-64%), respectively. Multivariable analysis confirmed the association between later era and OS (hazard ratio = 0.52, 95% CI, 0.34-0.78). Finally, among patients relapsing after HCT (25% in later era and 33% in earlier era), the use of novel immunotherapies increased in the later era (44% versus 3%), as did the median OS after post-HCT relapse (16 months versus 8 months, P< .001). OS after HCT for adult ALL has improved in recent years. This is due, in part, to a significant improvement in the ability to effectively salvage adults with ALL relapsing after HCT.

Real-World Experience of Cryopreserved Allogeneic Hematopoietic Grafts during the COVID-19 Pandemic: A Single-Center Report.

In response to the widespread COVID-19 pandemic, cryopreservation of allogeneic donor apheresis products was implemented to mitigate the challenges of donor availability and product transport. Although logistically beneficial, the impact of cryopreservation on clinical outcomes and graft composition remains unclear. In this study, we compared outcomes and graft composition with cryopreserved versus fresh allografts in the setting of allogeneic hematopoietic cell transplantation (allo-HCT). We retrospectively analyzed the clinical outcomes of 30 consecutive patients who received cryopreserved allografts between March and August 2020 and 60 consecutive patients who received fresh allografts before the COVID-19 pandemic. Primary endpoints were hematopoietic engraftment and graft failure (GF), and secondary outcomes were overall survival (OS), relapse-free survival (RFS) and nonrelapse mortality (NRM). In addition, extended immunophenotype analysis was performed on cryopreserved and prospectively collected fresh apheresis samples. Compared with recipients of fresh allografts, both neutrophil and platelet recovery were delayed in recipients of cryopreserved reduced-intensity conditioning (RIC) allo-HCT, with a median time to engraftment of 24 days versus 18 days (P = .01) for neutrophils and 27 days versus 18 days (P = .069) for platelets. We observed primary GF in 4 of 30 patients in the cryopreserved cohort (13.3%) versus only 1 of 60 patients (1.7 %) in the fresh cohort (P = .03). Cryopreserved RIC allo-HCT was associated with significantly lower median total, myeloid, and T cell donor chimerism at 1 month. OS and RFS were inferior for cryopreserved graft recipients (hazard ratio [HR], 2.16; 95% confidence interval [CI], 1.00 to 4.67) and HR, 1.90; 95% CI, 0.95 to 3.79, respectively. Using an extended immunophenotype analysis, we compared 14 samples from the cryopreserved cohort to 6 prospectively collected fresh apheresis donor samples. These analyses showed both a decrease in total cell viability and a significantly reduced absolute number of natural killer cells (CD3-CD56+) in the cryopreserved apheresis samples. In this single-institution study, we found delayed engraftment and a trend toward clinical inferiority of cryopreserved allografts compared with fresh allografts. Further evaluation of the use of cryopreserved allografts and their impact on clinical and laboratory outcomes is warranted.

Antigen-specific regulatory T cells develop via the ICOS-ICOS-ligand pathway and inhibit allergen-induced airway hyperreactivity.

Asthma is caused by T-helper cell 2 (Th2)-driven immune responses, but the immunological mechanisms that protect against asthma development are poorly understood. T-cell tolerance, induced by respiratory exposure to allergen, can inhibit the development of airway hyperreactivity (AHR), a cardinal feature of asthma, and we show here that regulatory T (T(R)) cells can mediate this protective effect. Mature pulmonary dendritic cells in the bronchial lymph nodes of mice exposed to respiratory allergen induced the development of T(R) cells, in a process that required T-cell costimulation via the inducible costimulator (ICOS-ICOS-ligand pathway. The T(R) cells produced IL-10, and had potent inhibitory activity; when adoptively transferred into sensitized mice, T(R) cells blocked the development of AHR. Both the development and the inhibitory function of regulatory cells were dependent on the presence of IL-10 and on ICOS-ICOS-ligand interactions. These studies demonstrate that T(R) cells and the ICOS-ICOS-ligand signaling pathway are critically involved in respiratory tolerance and in downregulating pulmonary inflammation in asthma.

Use of Backup Stem Cells for Stem Cell Boost and Second Transplant in Patients with Multiple Myeloma Undergoing Autologous Stem Cell Transplantation.

Autologous hematopoietic stem cell transplantation (ASCT) is a standard treatment for multiple myeloma (MM). Consensus guidelines recommend collecting sufficient stem cells in case there is a need for stem cell boost for delayed/poor engraftment or for future second ASCT. However, collecting and storing backup stem cells in all patients requires significant resources and cost, and the rates of backup stem cell utilization are not well studied. We sought to examine the utilization of backup stem cells (BSCs) in patients with MM undergoing ASCT. Patients with MM aged ≥18 years old who underwent first ASCT at our institution from January 2010 through December 2015 and collected sufficient stem cells for at least 2 transplants were included in this single-center retrospective study. This timeframe was selected to allow for adequate follow-up. A total of 393 patients were included. The median age was 58 years (range, 25-73). After a median follow-up of 6 years, the median progression-free survival (PFS) of the cohort was 3 years. Sixty-one percent (n = 240) of patients progressed or relapsed. Chemotherapy-based mobilization was used in almost all patients (98%). The median total CD34+ cells collected was 18.2 × 106/kg (range, 3.4-112.4). A median of 5.7 × 106 CD34+ cells/kg (range, 1.8-41.9) was infused during the first ASCT, and a median of 10.1 × 106 CD34+ cells/kg (range, 1.5-104.5) was cryopreserved for future use. Of the patients, 6.9% (n = 27) used backup stem cells, with 2.3% (n = 10) using them for stem cell boost, 4.6% (n = 18) for a second salvage ASCT, including 1 patient for both stem cell boost and second ASCT. Rates of backup stem cell use among patients aged <60, 60-69, and ≥70 years were 7.8%, 5.7%, and 5.9%, respectively. There was a trend toward higher rates of backup stem cell use for second ASCT in patients who were younger, had suboptimal disease control at time of first ASCT, and longer PFS. The median dose of stem cell boost given was 5.6 × 106 CD34+ cells/kg (range, 1.9-20). The median time from stem cell boost to neutrophil, hemoglobin, and platelet engraftment was 4 (range, 2-11), 15 (range, 4-34), and 12 (range, 0-34) days, respectively. Lower CD34+ dose and older age at time of ASCT predicted need for stem cell boost. With new salvage therapies for relapsed MM, the rates of second ASCT are very low. The low rates of use suggest that institutional policies regarding universal BSC collection and long-term storage should be reassessed and individualized. However, need for stem cell boost in 2.3% of patients may present a challenge to that.

Stem Cell Mobilization in Multiple Myeloma: Comparing Safety and Efficacy of Cyclophosphamide +/- Plerixafor versus Granulocyte Colony-Stimulating Factor +/- Plerixafor in the Lenalidomide Era.

Growth factor and chemotherapy-based stem cell mobilization strategies are commonly used to treat patients with multiple myeloma. We retrospectively compared 398 patients mobilized between 2017 and 2020 using either cyclophosphamide (4 g/m2) plus granulocyte colony-stimulating factor (G-CSF) or G-CSF alone, with on demand plerixafor (PXF) in both groups. Although total CD34+ yield was higher after chemomobilization compared with G-CSF +/- PXF (median, 13.6 × 106/kg versus 4.4 × 106/kg; P < .01), achievement of ≥2 × 106 CD34+ cells (95% versus 93.7%; P = .61) and rates of mobilization failure (5% versus 6.3%; P = .61) were similar. Fewer patients required PXF with chemomobilization (12.3% versus 49.5%; P < .01), and apheresis sessions were fewer (median, 1 [range, 1 to 4] versus 2 [range, 1 to 5]). The rate of complications, including neutropenic fever, emergency department visits, and hospitalizations, was higher after chemomobilization (30% versus 7.4%; P < .01). Previous use of ≤6 cycles of lenalidomide did not impair cell yield in either group. The median cost of mobilization was 17.4% lower in the G-CSF +/- PXF group (P = .01). Between group differences in time to engraftment were not clinically significant. Given similar rates of successful mobilization, similar engraftment time, and less toxicity and lower costs compared with chemomobilization, G-CSF with on-demand PXF may be preferable in myeloma patients with adequate disease control and limited lenalidomide exposure.